Metasurface structure and mold

Abstract

This metasurface structure comprises a plurality of nanopillars disposed on a support surface of a substrate. In the plurality of nanopillars, the smaller the width or volume, the smaller the height. Each nano-pillar is configured so as to shift the phase of light having a specific wavelength according to a position where the nano-pillar is disposed in the support surface. The mold of the present invention comprises a plurality of nanoholes for transferring the plurality of nanopillars in the metasurface structure to a substrate. In the plurality of nanoholes, the smaller the width or the volume, the shallower the depth.

Description

Metasurface structure and mold

[0001] The present disclosure relates to metasurface structures and molds for forming metasurface structures.

[0002] In recent years, there has been growing interest in metasurfaces with nanopillars smaller than the wavelength of light. One example of a metasurface includes multiple nanopillars (see, for example, Patent Document 1). The nanopillars are formed of a dielectric material that transmits light of a specific wavelength. In a metasurface, the phase or amplitude of light incident on the metasurface, or the polarization state separated by the metasurface, can be controlled by adjusting the material, size, orientation, etc. of the nanopillars.

[0003] Japanese Patent Application Laid-Open No. 2023-37577

[0004] To more precisely control the state of light using metasurfaces, it is necessary to suppress the formation of defective nanopillars in the metasurface manufacturing process. In other words, it is desirable to more precisely control the state of light incident on the metasurface by suppressing the formation of defective nanopillars.

[0005] In one aspect, a metasurface structure is provided, comprising a plurality of nanopillars disposed on a support surface of a substrate, the plurality of nanopillars having smaller widths and smaller heights, each nanopillar configured to shift the phase of light having a particular wavelength depending on the location of the nanopillar within the support surface.

[0006] In another aspect, a mold is provided, the mold comprising a plurality of nanoholes for transferring the nanopillars of the metasurface structure to the substrate, the nanoholes having smaller widths and shallower depths.

[0007] In another aspect, a metasurface structure is provided, comprising a plurality of nanopillars disposed on a support surface of a substrate, each nanopillar having a smaller volume and a smaller height, and each nanopillar configured to shift the phase of light having a specific wavelength depending on where the nanopillar is located within the substrate.

[0008] In another aspect, a mold is provided, the mold comprising a plurality of nanoholes for transferring the nanopillars of the metasurface structure to the substrate, the nanoholes having smaller volumes and shallower depths.

[0009] In another aspect, a metasurface structure is provided, comprising a plurality of nanopillars disposed on a support surface of a substrate, the plurality of nanopillars including 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 configured to shift the phase of light having a particular wavelength depending on the position of the first nanopillar within the support surface.

[0010] In another aspect, a mold is provided, comprising a plurality of nanoholes for transferring the nanopillars of the metasurface structure to the substrate, the plurality of nanoholes including: a plurality of first nanoholes disposed in a third region for transferring the first nanopillars to the substrate; and a plurality of second nanoholes disposed in an annular fourth region surrounding the third region for transferring the second nanopillars to the substrate.

[0011] FIG. 1 is a cross-sectional view of a metalens of the first embodiment. FIG. 2 is a plan view of the metalens of the first embodiment. FIG. 3 is a cross-sectional view of a mold of the first embodiment. FIG. 4 shows formula (1) representing the first phase shift amount. FIG. 5 shows formula (2) representing the second phase shift amount. FIG. 6 shows formula (3) representing the effective refractive index. FIG. 7 is a table showing the evaluation results of Example 1. FIG. 8 is a table showing the evaluation results of Comparative Example 1. FIG. 9 is a graph showing the evaluation results of Example 1 and Comparative Example 1. FIG. 10 is a cross-sectional view of a metalens of the second embodiment. FIG. 11 is a plan view of a metalens of the second embodiment. FIG. 12 is a cross-sectional view of a mold of the second embodiment. FIG. 13 is a cross-sectional view of an SOQ (silicon on quartz) wafer in Example 2 after a positive electron beam resist layer has been formed. FIG. 14 is a cross-sectional view of the positive electron beam resist layer in Example 2 after exposure. FIG. 15 is a cross-sectional view of the metalens of Example 2. FIG. 16 is a cross-sectional view of the metalens of Comparative Example 2.

[0012] Below, first and second embodiments of a metasurface structure and a mold for forming the metasurface structure will be described with reference to the drawings. In the following first and second embodiments, a metalens having a metasurface structure will be described. The metalens has optical transparency, which allows light having a specific wavelength to be transmitted. A metalens with optical transparency controls, for example, the phase, amplitude, polarization, and other states of light passing through the metalens. Note that the metalens may also have optical reflectivity, which allows light having a specific wavelength to be reflected. A metalens with optical reflectivity controls, for example, the phase, amplitude, polarization, and other states of light reflected by the metalens.

[0013] First Embodiment A first embodiment will be described with reference to Figures 1 to 6. As shown in Figure 1, a metalens 10 of the first embodiment includes a substrate 11 and a plurality of nanopillars 12. The substrate 11 and the plurality of nanopillars 12 are optically transparent, allowing light having a specific wavelength to be controlled to pass through. As an example, the metalens 10 has the function of focusing light having the specific wavelength to be controlled onto a single point.

[0014] The substrate 11 is made of, for example, glass or resin, but may also be formed of a plurality of layers combining these. The substrate 11 has a support surface 11S that supports a plurality of nanopillars 12.

[0015] In the metalens 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 metalens 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.

[0016] The nanopillars 12 are formed of a dielectric material having a refractive index greater than 1. The material forming the nanopillars 12 may be a silicon-based material such as single crystal silicon, polycrystalline silicon, or amorphous silicon, an inorganic material such as titanium dioxide, or a resin material such as a polymer material that functions as a dielectric.

[0017] 2, in the metalens 10, a plurality of nanopillars 12 are periodically arranged along a first direction D1 and a second direction D2, which are perpendicular to each other.

[0018] For example, the multiple nanopillars 12 are arranged in a predetermined orientation and at 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 multiple nanopillars 12 are arranged in a square 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 the nanopillars 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.

[0019] 1, each nanopillar 12 has a rectangular parallelepiped shape. The plurality of nanopillars 12 includes two or more nanopillars 12 having different heights H and widths W, with the height H decreasing as the width W decreases. The plurality of nanopillars 12 also includes two or more nanopillars 12 having different heights H and volumes, with the height H decreasing as the volume decreases.

[0020] The width W refers to the dimension of the nanopillar 12 in the first direction D1. The nanopillar 12 also has the same dimension in the second direction D2 as in the first direction D1. That is, the nanopillar 12 is configured so that the width in the second direction D2 is equal to the width W in the first direction D1.

[0021] The width W of the nanopillar 12 is, for example, the average width from the top to the bottom of the nanopillar 12. The width W of the nanopillar 12 is, for example, the average width of the top and bottom of the nanopillar 12. The width W of the nanopillar 12 may be, for example, the maximum width from the top to the bottom of the nanopillar 12. The width W of the nanopillar 12 is approximately equal to or smaller than the specific wavelength of light to be controlled.

[0022] The multiple nanopillars 12 are arranged, for example, in each of the first direction D1 and the second direction D2, so that the height H and width W of each nanopillar 12 change periodically depending on the position at which each nanopillar 12 is positioned within the support surface 11S.

[0023] [Method of Manufacturing Metalens 10] One example of a method of manufacturing the metalens 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. One example of a method of manufacturing the metalens 10 is to form the nanopillars 12 by depositing or lifting off an inorganic material by physical or chemical vapor deposition or atomic layer deposition (ALD) on a pattern formed on the support surface 11S of the substrate 11 using electron beam lithography. One example of a method of manufacturing the metalens 10 is to form the nanopillars 12 by using a mold in which a nanohole pattern, which is the inverse of the nanopillars 12, has been formed by dry etching, electrocasting, or the like, to transfer a resin that functions as a dielectric onto the support surface 11S of the substrate 11, thereby forming the nanopillars 12.

[0024] 3 shows a mold 20 for transferring nanopillars 12 formed from a resin onto a substrate 11. The mold 20 includes a base 21. The base 21 is formed of, 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.

[0025] The mold 20 transfers the resin filled in the nanoholes 22 to the support surface 11S of the substrate 11. As a result, the nanoholes 22 have an inverted shape of the multiple nanopillars 12 included in the metalens 10. That is, the multiple nanoholes 22 include two or more nanoholes 22 that have different widths and depths, and the smaller the width, the shallower the depth from the first surface 21S. Furthermore, the multiple nanoholes 22 include two or more nanoholes 22 that have different volumes and depths, and the smaller the volume, the shallower the depth from the first surface 21S.

[0026] As an example, the nanoholes 22 are formed by dry etching the first surface 21S of the base 21. When dry etching is used as the manufacturing process for the mold 20, the depth of the nanoholes 22 can be changed depending on the width by utilizing the microloading effect. Alternatively, the nanoholes 22 may be formed by electroforming a nanopillar-shaped resist pattern of different heights formed by electron beam lithography. When electron beam lithography is used as the manufacturing process for the mold 20, the height of the resist pattern can be changed depending on the width (pillar width) of the resist pattern by utilizing the difference in development speed due to the exposure dose.

[0027] 4 to 6, the manner in which light is controlled in the metalens 10 will be described. The metalens 10 refracts light incident on each nanopillar 12, thereby focusing light that has passed through the metalens 10 at a single point (focal point). That is, each nanopillar 12 shifts the phase of light having a specific wavelength to be controlled, depending on the position of the nanopillar 12 within the support surface 11S.

[0028] For example, in the metalens 10, the first phase shift amount φ required for each nanopillar 12 is １ is given by equation (1) shown in FIG. 4. In equation (1), f represents the design focal length of the metalens 10. ｄ is the wavelength of light to be controlled. x and y represent the coordinates of each nanopillar 12 when the origin is the point where a perpendicular line drawn from the focal point to the metalens 10 intersects with the metalens 10. For example, x represents the distance from the origin to the nanopillar 12 in the first direction D1. y represents the distance from the origin to the nanopillar 12 in the second direction D2.

[0029] The second phase shift amount φ occurring in each nanopillar 12 ２ is the height H of each nanopillar 12, the effective refractive index n′ of each nanopillar 12, and λ, the wavelength of the light to be controlled. ｄand is given by equation (2) shown in Figure 5. When multiple media with different refractive indices exist within a unit space of a given size, the effective refractive index n' refers to the average value of the refractive index of the unit space, taking into account parameters such as the refractive index and thickness of each medium. 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 contains one nanopillar 12. The multiple media within the unit space refer to air and the nanopillar 12.

[0030] The effective refractive index n′ is given by equation (3) shown in FIG. 6 using the refractive index n of the material forming the nanopillars 12, the width W of each nanopillar 12, and the pitch L at which multiple nanopillars 12 are arranged.

[0031] Therefore, the shape of each nanopillar 12 is set to a second phase shift amount φ in order to focus the light transmitted through each nanopillar 12 at a focal point. ２ is the first phase shift amount φ １ In other words, the second phase shift amount φ in each nanopillar 12 is determined according to the position and material of the nanopillar 12 so as to be equal to ２ is defined so that the plurality of nanopillars 12 collectively function as a focusing lens.

[0032] Specifically, in order to focus light transmitted through the metalens 10 at a focal point in a plurality of nanopillars 12 having a predetermined pitch L and refractive index n, a second phase shift amount φ is determined depending on the position of the nanopillars 12. ２ It is necessary to adjust the angle within the range of 0 degrees to 360 degrees (0 rad to 2π rad).

[0033] For example, in formula (3), the value of W / L, which represents the ratio of the width W of the nanopillars 12 to the pitch L, can be adjusted within the range of 0.2 to 0.8 by changing the width W of the nanopillars 12. In formula (3), the value of n, which represents the refractive index of the material, is determined depending on the material forming the nanopillars 12. Therefore, the second phase shift amount φ expressed by formula (2) ２In order to achieve an adjustment range of 0 degrees or more and 360 degrees or less, it is preferable to make the height H of the nanopillars 12 as large as possible.

[0034] On the other hand, if the aspect ratio (H / W), which represents the ratio of the height H to the width W, of each nanopillar 12 becomes excessively large, stable patterning of the nanopillars 12 becomes difficult in the manufacturing process of the metalens 10. For example, when forming the nanopillars 12 by dry etching or lift-off, a large aspect ratio of the resist pattern can lead to formation defects such as pattern collapse. In the case of a transfer process, the larger the aspect ratio, the more likely it is that the mold 20 will not be filled with resin sufficiently, or the nanopillars 12 will have insufficient strength.

[0035] Therefore, the nanopillars 12 of the first embodiment are configured so that the smaller the volume or width W, the smaller the height H, and vice versa, so that the larger the volume or width W, the larger the height H. This prevents the aspect ratio of each nanopillar 12 from becoming excessively large.

[0036] The aspect ratio (H / W) of each nanopillar 12 is preferably less than 3.5, and more preferably 3.1 or less. By setting the aspect ratio within the above range, the second phase shift amount φ ２ This makes it possible to ensure the adjustment range of the above while suitably suppressing poor formation of the nanopillars 12.

[0037] Additionally, it is preferable that the nanopillars 12 be configured so that the aspect ratio decreases as the height H increases, which makes it easier to manufacture the metalens 10 and the mold 20 for manufacturing the metalens 10.

[0038] Advantages of the First Embodiment (1-1) In the metalens 10, the nanopillars 12 are configured so that the smaller the width W or volume, the smaller the height H. This prevents the aspect ratio of the nanopillars 12 from becoming excessively large, compared to a configuration in which the height H of the nanopillars 12 is constant, for example, while allowing the second phase shift amount φ ２Therefore, since it is possible to suppress the formation defects of the nanopillars 12, it is possible to more accurately control the state of the light incident on the nanopillars 12. Furthermore, with the configuration of the first embodiment, even if the refractive index n is relatively low, the second phase shift amount φ ２ Since the adjustable range of the nanopillars 12 can be secured, the options for the material for forming the nanopillars 12 can be expanded.

[0039] (1-2) The nanopillars 12 of the first embodiment have a rectangular parallelepiped shape. If the nanopillars 12 have a distribution of effective refractive index in the height direction, it may be difficult for light incident on the nanopillars 12 to transmit through them. In this regard, if the nanopillars 12 are rectangular parallelepiped, they have a uniform effective refractive index in the height direction, which prevents the shape of the nanopillars 12 from affecting the transmittance of incident light.

[0040] (1-3) The aspect ratio (H / W) of each nanopillar 12 is set to less than 3.5, preferably 3.1 or less, thereby reducing the second phase shift amount φ ２ This makes it possible to suitably ensure the adjustment range of the nanopillars 12 while suppressing defective formation of the nanopillars 12.

[0041] (1-4) Second phase shift amount φ in each nanopillar 12 ２ are defined so that the plurality of nanopillars 12 collectively function as a lens. This allows, for example, the metalens 10 of the first embodiment to function as a focusing lens that focuses light incident on the plurality of nanopillars 12 to a single point.

[0042] (1-5) The mold 20 includes a plurality of nanoholes 22 with different widths and depths. Using such a mold 20, a plurality of nanopillars 12 with different heights H and widths W can be formed at once. Dry etching is used as a manufacturing process for the mold 20, and processing that increases the depth of the nanoholes 22 according to their width can be easily performed by the microloading effect.

[0043] [Modifications of the First Embodiment] The first embodiment can be modified as follows: The modifications can be combined within the scope of technical compatibility.

[0044] In the first embodiment, a metalens 10 having a metasurface structure was described. That is, a configuration in which multiple nanopillars 12 included in the metasurface structure collectively function as a focusing lens was described as an example. However, without being limited to this, for example, the multiple nanopillars 12 may function as a phase control lens that controls the phase of light for purposes other than focusing (e.g., light dispersion), or as a spectroscopic lens that disperses light by wavelength. Alternatively, the multiple nanopillars 12 may function as a polarization control lens that controls the polarization state of transmitted light by selectively transmitting only specific polarization components or by changing the polarization state of the transmitted light. Furthermore, by providing the multiple nanopillars 12 on a reflector, the multiple nanopillars 12 may function in a form other than a lens, such as reflecting light of a specific wavelength in a desired direction.

[0045] The aspect ratio of each nanopillar 12 is not limited to a range of less than 3.5. For example, nanopillars 12 with an aspect ratio of 3.5 or more may be included as long as this does not interfere with the manufacturing process of the metalens 10. Furthermore, nanopillars 12 with an aspect ratio of 1 or less may be included as long as the adjustment range of the second phase shift amount φ2 can be ensured.

[0046] The shape of the nanopillars 12 is not limited to a rectangular parallelepiped, but may be, for example, a cylindrical shape. When the nanopillars 12 are cylindrical, the diameter of the cylindrical shape corresponds to the width W. Even in this case, the nanopillars 12 have a uniform effective refractive index in the height direction, preventing the shape of the nanopillars 12 from affecting the transmittance of incident light. Furthermore, the shape of the nanopillars 12 may be any shape other than a rectangular parallelepiped or a cylindrical shape. For example, the shape of the nanopillars 12 may be any quadrangular prism, such as a truncated pyramid, or a truncated cone. The shape of the nanoholes 22 can also be similarly modified.

[0047] In the above embodiment, the nanopillars 12 have the same width W in both the first direction D1 and the second direction D2. However, the width in the second direction D2 may be different from the width W in the first direction D1. In this case, it is preferable that at least one of the first aspect ratio, which represents the ratio of the height H to the width W in the first direction D1, and the second aspect ratio, which represents the ratio of the height H to the width in the second direction D2, of each nanopillar 12 is less than 3.5, more preferably 3.1 or less. It is also more preferable that both the first aspect ratio and the second aspect ratio are less than 3.5, more preferably 3.1 or less.

[0048] At least some of the nanopillars 12 may be configured so that the smaller the width W, the lower the height H. For example, the nanopillars 12 may include two nanopillars 12 having approximately the same width W but different heights H. For example, the nanopillars 12 may include a nanopillar 12 having a width W greater than that of a specific nanopillar 12 but a height H less than that of the specific nanopillar 12. Similar modifications are also possible for the nanoholes 22.

[0049] At least some of the nanopillars 12 may be configured so that the height H decreases as the volume decreases. For example, the nanopillars 12 may include two nanopillars 12 having approximately the same volume but different heights H. For example, the nanopillars 12 may include a nanopillar 12 having a volume larger than a specific nanopillar 12 but a height H smaller than that of the specific nanopillar 12. Assume, for example, that the nanopillars 12 include a mixture of rectangular nanopillars 12 having a square shape in top view and cylindrical nanopillars 12, with the volume of the rectangular parallelepiped equal to or larger than the volume of the cylindrical nanopillars. In this case, the radius of the cylindrical shape is considered to be the width W, and 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 nanopillar 12. Similar modifications are also possible for the nanoholes 22.

[0050] The arrangement of the nanopillars 12 in the metalens 10 may be determined as appropriate depending on the application of the metalens 10. Furthermore, the nanopillars 12 are not limited to being arranged in a square pattern in the first direction D1 and the second direction D2, and may be arranged, for example, from an arbitrary point on the substrate 11 as the center, outwardly according to the distance from the center. Furthermore, the pitch L and the orientation of the nanopillars 12 do not have to be constant.

[0051] [Examples and Comparative Examples of First Embodiment] Example 1 of the first embodiment and Comparative Example 1 will be described with reference to Figures 7 to 9. Note that the following examples do not limit the configuration of the present disclosure.

[0052] Example 1: Fabrication of a mold In Example 1, a metalens 10 was fabricated that included nanopillars 12 with different heights H and widths W. First, a mold 20 for transferring the nanopillars 12 to the substrate 11 was fabricated.

[0053] First, an electron beam positive resist material was applied to a silicon wafer having a diameter of 200 mm using a spin coater. The spin coater conditions were a rotation speed of 700 rpm and a rotation time of 120 seconds. This resulted in an electron beam positive resist layer having a thickness of 500 nm being formed on the silicon wafer. The electron beam positive resist material applied to the silicon wafer was then pre-baked using a hot plate to remove residual solvent contained in the electron beam positive resist material. The pre-baking conditions were a heating temperature of 120°C and a heating time of 5 minutes.

[0054] Next, the electron beam positive resist layer on the silicon wafer was exposed to light to write a nanohole pattern on the electron beam positive resist layer. An electron beam lithography system was used for the exposure. During the exposure, an electron beam was irradiated at an acceleration voltage of 100 keV. The exposure dose was 18 μC / cm ２ The nanohole pattern was a square array with a pitch L of 800 nm.

[0055] Next, the exposed portions of the electron beam positive resist layer (hereinafter referred to as "exposed portions") were developed to form a square nanohole pattern. Specifically, the exposed portions were developed for 60 seconds using an alkaline developer (product name: SD-1, manufactured by Tokuyama Corporation), dissolving the exposed portions to form a nanohole pattern. Subsequently, the developer was removed from the electron beam positive resist layer on the silicon wafer by rinsing with ultrapure water, and then the wafer was dried using a spin dryer. The width of the openings of the nanohole pattern formed in the electron beam positive resist layer was set to a range of 140 nm to 700 nm.

[0056] Next, the silicon wafer with the electron beam positive resist layer on which the nanohole pattern was formed was subjected to dry etching to transfer the nanohole pattern onto the silicon wafer. ６ and C ４ F ８ A mixed gas containing the above was used. The etching time was 300 seconds. In dry etching, the depth of the silicon hole can be changed depending on the width by adjusting the amount of etching gas, etc., 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 to 740 nm and the depth of the silicon hole was in the range of 580 nm to 1060 nm.

[0057] 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 (80°C) of sulfuric acid and hydrogen peroxide for 10 minutes, rinsed with ultrapure water, immersed in a mixed solution (room temperature) of ammonia and hydrogen peroxide for 10 minutes, and rinsed with ultrapure water, in that order. Through the above procedures, a silicon mold, which is an example of the mold 20, was obtained.

[0058] Example 1: Fabrication of a Metalens Next, the metalens 10 was fabricated by transferring nanopillars 12 to a substrate 11 using the silicon mold. A 125 mm square glass substrate was used as the substrate 11. First, a UV-curable resin was applied to the support surface 11S of the substrate 11. Then, with the silicon mold pressed against the UV-curable resin, the UV-curable resin was cured by irradiating it with light having a wavelength of 365 nm from the substrate 11 side. The UV-curable resin was then released from the silicon mold, forming nanopillars 12 made of the cured UV-curable resin 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. The UV-curable resin used had a refractive index of 1.99 for light having a wavelength of 850 nm, which was the target of control, after curing.

[0059] Comparative Example 1: Fabrication of Metalens In Comparative Example 1, a metalens 10 was fabricated using the same procedure as in Example 1, except that the depth of the silicon holes was kept constant, i.e., the height H of the nanopillars 12 was kept constant. In Comparative Example 1, 13 patterns of nanopillars 12 (nanopillars B1 to B13) were formed, each having the same height H but different widths W. 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.

[0060] [Evaluation: Dimensional Measurement, Visual Inspection] The metalenses 10 of Example 1 and Comparative Example 1 were cleaved, and images of the nanopillars 12 were obtained using an FE-SEM. The width W and height H of each nanopillar 12 were measured from the obtained images. The measurement results for Example 1 are shown in FIG. 7 . The measurement results for Comparative Example 1 are shown in FIG. 8 . Additionally, the results of the visual inspection of each nanopillar 12 to determine whether it had collapsed are shown in FIGS. 7 and 8 .

[0061] As shown in FIG. 7 , in Example 1, the width W of the nanopillars 12 was within the range of 185.7 nm to 740 nm. The height H of the nanopillars 12 was within the range of 584.9 nm to 1051.3 nm. The aspect ratio (H / W) of the nanopillars 12 was within the range of 1.4 to 3.1. Furthermore, the smaller the width W of the nanopillars 12, the lower the height H of the nanopillars 12. The higher the height H of the nanopillars 12, the smaller the aspect ratio of the nanopillars 12. In Example 1, no collapse of the nanopillars 12 was observed.

[0062] As shown in Figure 8, in Comparative Example 1, the width W of the nanopillars 12 was in the range of 185.7 nm to 740 nm. 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 to 5.7. In Comparative Example 1, collapse was observed in nanopillars 12 with an aspect ratio of 3.5 or greater.

[0063] [Evaluation: Phase Shift Amount] Rigorous Coupled-Wave Analysis (RCWA) was performed on each nanopillar 12 of the metalens 10 in Example 1 and Comparative Example 1 to calculate the phase of transmitted light at a predetermined position. Then, for each of Example 1 and Comparative Example 1, the phase of the nanopillar 12 having the smallest width W was used as a reference, and the phase difference from the reference was calculated as the phase shift amount for each nanopillar 12. Note that in Example 1, nanopillar A1, which has a width W of 185.7 nm, was used as the reference (phase shift amount = 0 degrees). Furthermore, in Comparative Example 1, nanopillar B5, which has the smallest width W of 320 nm among the uncollapsed nanopillars 12, was used as the reference (phase shift amount = 0 degrees).

[0064] 9 , the horizontal axis represents the width W of the nanopillars 12, and the vertical axis represents the phase shift of light transmitted through the nanopillars 12. A curve 101 in the graph 100 represents the phase shift of light transmitted through the nanopillars 12 relative to the width W of the nanopillars 12 in Example 1. A curve 102 in the graph 100 represents the phase shift of light transmitted through the nanopillars 12 relative to the width W of the nanopillars 12 in Comparative Example 1.

[0065] 9 , in Example 1, in which the width W and height H were varied, it was confirmed that the phase shift amount could be adjusted in a range from 0 degrees to 381.9 degrees, based on nanopillar A1, which had a width W of 185.7 nm. On the other hand, in Comparative Example 1, in which only the width W was varied while the height H was kept constant, it was confirmed that the adjustable range of the phase shift amount was limited to a range from 0 degrees to 196.6 degrees, based on nanopillar B5, which had a width W of 320 nm. From the above, it was confirmed that by configuring nanopillars 12 in metalens 10 so that the height H decreases as the width W or volume decreases, the adjustable range of the phase shift amount can be expanded compared to when the height H is constant.

[0066] Second Embodiment A second embodiment will now be described with reference to FIGS. 10 to 12. As shown in FIG. 10, a metalens 30 of the second embodiment includes a substrate 31 and a plurality of nanopillars 32. The plurality of nanopillars 32 is disposed on a support surface 31S of the substrate 31. The substrate 31 and the plurality of nanopillars 32 are optically transparent, allowing light having a specific wavelength to be controlled to pass through. As an example, the metalens 30 has the function of focusing light having the specific wavelength to be controlled onto a single point.

[0067] In the metalens 30, the state of light having a specific wavelength to be controlled is controlled by the nanopillars 32. In other words, the nanosurface structure of the metalens 30 includes a plurality of nanopillars 32. 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.

[0068] The plurality of nanopillars 32 includes a plurality of first nanopillars 33 and a plurality of second nanopillars 34. The plurality of first nanopillars 33 are arranged in the first region 30A. The plurality of second nanopillars 34 are arranged in the second region 30B. The first nanopillars 33 and the second nanopillars 34 are arranged in a square array at a constant pitch L.

[0069] Each first nanopillar 33 shifts the phase of light having a specific wavelength depending on the position of the first nanopillar 33 within the support surface 31S. The first nanopillar 33 has, for example, a rectangular parallelepiped shape. The first nanopillar 33 has, for example, a constant height H1. In the metalens 30 of the second embodiment, the width W1 of the first nanopillar 33 is changed to focus light transmitted through each first nanopillar 33.

[0070] Therefore, the shape of each first nanopillar 33 is set to a second phase shift amount φ in order to focus the light transmitted through each first nanopillar 33 at a focal point. ２ is the first phase shift amount φ １ In other words, the second phase shift amount φ in each first nanopillar 33 is determined according to the position and material of the first nanopillar 33 so as to be equal to ２ is defined so that the plurality of first nanopillars 33 collectively function as a focusing lens.

[0071] The multiple second nanopillars 34 have the same shape. For example, the second nanopillars 34 have a shape in which the width W2 decreases from the substrate 31 side toward the tip. For example, the second nanopillars 34 have a needle-like or cone-like shape that tapers toward the tip. In other words, the cross-sectional area of ​​the second nanopillars 34 in a cross section perpendicular to the height direction changes stepwise or continuously in the height direction. This allows the second nanopillars 34 to have an effective refractive index that changes 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. For 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.

[0072] As shown in Figure 11, the metalens 30 has, as an example, a circular shape in top view. The metalens 30 includes a first region 30A having a circular shape in top view, and a second region 30B surrounding the first region 30A. The second region 30B has an annular shape in 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. Note that in Figure 11, the first region 30A and the second region 30B are indicated by dots of different densities.

[0073] For example, the multiple nanopillars 32 are arranged in a square pattern with a predetermined pitch L along each of the first direction D1 and the second direction D2. The multiple first nanopillars 33 are arranged with a width W that changes periodically in each of the first direction D1 and the second direction D2. Note that the pitch L and the orientation of the nanopillars 32 do not have to be constant.

[0074] For example, the multiple first nanopillars 33 have an arrangement pattern as one repeating unit in which first nanopillars 33 with smaller widths W are arranged from the center P of the metalens 30 toward the periphery in the first direction D1. In the first region 30A, the multiple first nanopillars 33 are arranged such that a large number of repeating units are arranged from the center P of the metalens 30 toward the periphery. For example, the length of one repeating unit in the first direction D1 is 0.1 μm or more and 10 μm or less. Note that the first region 30A is also configured with a similar arrangement pattern in the second direction D2.

[0075] The second region 30B has a radial width W3. The lower limit of the width W3 is, for example, at least 10 μm or more, preferably 100 μm or more. The upper limit of the width W3 is not particularly limited, but is, for example, 1 mm or less, preferably 500 μm or less.

[0076] Note that metalens 30 is not limited to a circular shape in top view and may have any shape. Similarly, the shape of first region 30A is not limited to a circular shape in top view and may have any shape. The shape of second region 30B is not limited to annular shape in top view and may be any shape as long as it is annular and surrounds first region 30A.

[0077] [Method of 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.

[0078] 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.

[0079] The base 41 has 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.

[0080] The plurality of nanoholes 42 includes a plurality of first nanoholes 43 for transferring a plurality of first nanopillars 33 to the substrate 31 and a plurality of second nanoholes 44 for transferring a plurality of second nanopillars 34 to the substrate 31.

[0081] The nanoholes 42 have an inverted shape of the multiple nanopillars 32 included in the metalens 30. That is, the first nanoholes 43 have an inverted shape of the first nanopillars 33. The second nanoholes 44 have an inverted shape of the second nanopillars 34.

[0082] The mold 40 includes a third region 40A and a fourth region 40B. A plurality of first nanoholes 43 are arranged in the third region 40A. A plurality of second nanoholes 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.

[0083] [Function of Second Embodiment] In the manufacturing process of the metalens 30, when forming the nanopillars 32 on the substrate 31, if the pattern density, which refers to the density of the nanopillars 32 around each nanopillar 32 to be formed, becomes small, defects in the formation of the nanopillars 32 are more likely to occur.

[0084] The pattern density refers to the proportion of the area occupied by the nanopillars 32 in a virtual region centered at an arbitrary position within the metalens 30, as viewed from a viewpoint opposite the support surface 31S. The virtual region for which the pattern density is calculated may be rectangular or circular. The virtual region contains multiple nanopillars 32. For example, the virtual region contains one or more repeating units formed by multiple first nanopillars 33. As an example, the virtual region is configured in a circular shape with a radius of 10 μm or more and 100 μm or less.

[0085] For example, the pattern density is calculated from an SEM image captured from a position opposite the support surface 31S. For example, the ratio of the area of ​​the nanopillars 32 included in a virtual region to the total area of ​​the virtual region is calculated from an SEM image captured of the virtual region containing multiple nanopillars 32. When calculating the pattern density, the SEM image may be subjected to image processing such as binarization to distinguish between areas where the nanopillars 32 are arranged and other areas.

[0086] A plurality of first nanopillars 33 having different widths W1 are periodically arranged in the first region 30A of the metalens 30. Therefore, most of the first region 30A has a substantially constant pattern density.

[0087] On the other hand, if the second nanopillars 34 were not formed in the second region 30B, the virtual region for calculating the pattern density would include an area in which the first nanopillars 33 are not formed near the outer edge of the first region 30A. Therefore, if the second nanopillars 34 were not formed in the second region 30B, the pattern density would rapidly decrease as it approached the outer edge of the first region 30A in the metalens 30.

[0088] A sudden change in pattern density near the outer edge of first region 30A can cause processing defects in the manufacturing process of metalens 30. For example, in electron beam lithography, the proximity effect causes the effective exposure dose to decrease in regions with lower pattern density. Therefore, regions with lower pattern density are more likely to experience insufficient exposure dose, leading to pattern formation defects. The proximity effect refers to a phenomenon in which an electron beam is scattered or reflected by the resist surface or substrate 31, resulting in energy diffusion. Note that this phenomenon can occur not only when manufacturing metalens 30 using electron beam lithography, but also when manufacturing mold 40 using electron beam lithography.

[0089] For example, in dry etching, the etching rate increases in regions with lower pattern density due to the microloading effect. Therefore, regions with lower pattern density are more likely to have excessive etching (excavation depth), resulting in pattern formation defects. Furthermore, in a transfer process using a mold 40, for example, formation defects such as poor filling or changes in remaining film thickness due to abrupt changes in pattern density are more likely to occur.

[0090] In this regard, in the metalens 30 of the second embodiment, a second region 30B in which second nanopillars 34 are arranged is provided so as to surround a first region 30A in which first nanopillars 33 for shifting the phase of light having a specific wavelength are arranged. Therefore, the second nanopillars 34 arranged in the second region 30B suppress a sudden change in pattern density near the outer edge of the first region 30A.

[0091] For example, the pattern density of a first virtual region that includes the first nanopillars 33 of the first region 30A but does not include the second nanopillars 34 of the second region 30B is defined as a first pattern density ρ1. The pattern density of a second virtual region that includes the second nanopillars 34 of the second region 30B but does not include the first nanopillars 33 of the first region 30A is defined as a second pattern density ρ2.

[0092] The first virtual region and the second virtual region are circular and have the same radius. This radius is large enough to include at least one repeating unit of the first nanopillar 33 in the first virtual region. Furthermore, this radius is large enough to prevent the second virtual region from extending beyond the second region 30B. As mentioned above, this radius is preferably 10 μm or more and 100 μm or less.

[0093] 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, and 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.

[0094] The ratio of the second pattern density ρ2 to the first pattern density ρ1 (ρ2 / ρ1) is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.8 to 1.2. When ρ2 / ρ1 is within the above range, a sudden change in pattern density near the outer edge of the first region 30A is suitably suppressed.

[0095] When electron beam lithography is used to pattern the nanopillars 32 of the metalens 30, it is preferable that the average exposure dose per nanopillar 32 be approximately equal between the first region 30A and the second region 30B, in order to suitably reduce the influence of the proximity effect. In other words, it is preferable that the first average exposure dose E1 per first nanopillar 33 in the first region 30A be approximately equal to the second average exposure dose E2 per second nanopillar 34 in the second region 30B. This configuration can further reduce the influence of the proximity effect in electron beam lithography when patterning the first nanopillars 33 located near the outer edge of the first region 30A. For example, the ratio of the second average exposure dose E2 to the first average exposure dose E1 (E2 / E1) is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.8 to 1.2.

[0096] Furthermore, when electron beam lithography is used to form the pattern of the nanopillars 32, the exposure dose for forming each nanopillar 32 correlates with the volume of each nanopillar 32. For example, when exposing the patterned portion of the nanopillars 32 in the pattern formation of the nanopillars 32, the exposure dose for forming each nanopillar 32 correlates positively with the volume of each nanopillar 32. For example, when exposing the portion other than the pattern of the nanopillars 32 in the pattern formation of the nanopillars 32, the exposure dose for forming each nanopillar 32 correlates negatively with the volume of each nanopillar 32.

[0097] Therefore, it is preferable that the first average volume V1 per one first nanopillar 33 in the first region 30A and the second average volume V2 per one second nanopillar 34 in the second region 30B are approximately equal to each other. This allows the first average exposure dose E1 in the first region 30A and the second average exposure dose E2 in the second region 30B to be equal to each other when electron beam lithography is used to form the pattern of the nanopillars 32. The ratio of the second average volume V2 to the first average volume V1 (V2 / V1) is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.8 to 1.2.

[0098] The first average volume V1 of the first nanopillars 33 in the first region 30A can be calculated by dividing the sum of the volumes of the first nanopillars 33 in the first region 30A by the total number of the first nanopillars 33 in the first region 30A. The second average volume V2 of the second nanopillars 34 in the second region 30B can be calculated by dividing the sum of the volumes of the second nanopillars 34 in the second region 30B by the total number of the second nanopillars 34 in the second region 30B.

[0099] Similarly, when electron beam lithography is used to pattern the nanoholes 42 in the mold 40, it is preferable that the average exposure dose per nanohole 42 be approximately equal between the third region 40A and the fourth region 40B in order to effectively reduce the influence of the proximity effect. In other words, it is preferable that the third average exposure dose E3 per first nanohole 43 in the third region 40A be approximately equal to the fourth average exposure dose E4 per second nanohole 44 in the fourth region 40B. This configuration further reduces the influence of the proximity effect in electron beam lithography when patterning the first nanoholes 43 at positions corresponding to the first nanopillars 33 located near the outer edge of the first region 30A. For example, the ratio (E4 / E3) of the fourth average exposure dose E4 to the third average exposure dose E3 is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.8 to 1.2.

[0100] Furthermore, when electron beam lithography is used to form the pattern of nanoholes 42, the exposure dose for forming each nanohole 42 correlates with the volume of each nanohole 42. For example, when exposing the pattern portion of the nanoholes 42 in forming the pattern of nanoholes 42, the exposure dose for forming each nanohole 42 correlates positively with the volume of each nanohole 42. For example, when exposing the portion other than the pattern of nanoholes 42 in forming the pattern of nanoholes 42, the exposure dose for forming each nanohole 42 correlates negatively with the volume of each nanohole 42.

[0101] Therefore, it is preferable that the first average volume C1 per one first nanohole 43 in the third region 40A and the second average volume C2 per one second nanohole 44 in the fourth region 40B are approximately equal to each other. This allows the third average exposure dose E3 in the third region 40A and the fourth average exposure dose E4 in the fourth region 40B to be equal to each other when electron beam lithography is used to form the pattern of the nanoholes 42. For example, the ratio (C2 / C1) of the second average volume C2 to the first average volume C1 is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.8 to 1.2.

[0102] The first average volume C1 of the first nanoholes 43 in the third region 40A can be calculated by dividing the sum of the volumes of the first nanoholes 43 in the third region 40A by the total number of the first nanoholes 43 in the third region 40A. The second average volume C2 of the second nanoholes 44 in the fourth region 40B can be calculated by dividing the sum of the volumes of the second nanoholes 44 in the fourth region 40B by the total number of the second nanoholes 44 in the fourth region 40B.

[0103] Advantages 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. The metalens 30 also includes a plurality of second nanopillars 34 arranged in a second region 30B that surrounds the first region 30A in which the plurality of first nanopillars 33 are arranged. With this configuration, the second nanopillars 34 arranged in the second region 30B can suppress defective formation of the first nanopillars 33 that occurs due to a sudden change in pattern density near the outer edge of the first region 30A. This allows for more accurate control of the state of light incident on the plurality of first nanopillars 33. In the example of the second embodiment, the light-collecting efficiency can be improved when light incident on the plurality of first nanopillars 33 is concentrated to a single point.

[0104] (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 set to 0.5 to 2.0, preferably 0.6 to 1.5, and more preferably 0.8 to 1.2. This allows the second nanopillars 34 arranged in the second region 30B to suitably suppress abrupt changes in pattern density near the outer edge of the first region 30A.

[0105] (2-3) Because the effective refractive index of the second nanopillars 34 changes in the height direction, the second nanopillars 34 function as a moth-eye structure that extremely reduces the reflection and refraction of incident light. This prevents light that deviates from the first region 30A from becoming stray light due to reflection or refraction by the second nanopillars 34. Furthermore, the metalens 30 of the second embodiment also contributes to reducing the focal diameter when light incident on multiple first nanopillars 33 is focused to one point.

[0106] (2-4) The first nanopillars 33 have a rectangular parallelepiped shape, similar to the nanopillars 12 of the first embodiment. Therefore, the same advantages as those in (1-2) above can be obtained. (2-5) The second phase shift amount φ in each first nanopillar 33 ２are defined so that the plurality of first nanopillars 33 collectively function as a lens. This allows, for example, the metalens 30 of the second embodiment to function as a focusing lens that focuses light incident on the plurality of first nanopillars 33 to a single point.

[0107] (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 set to 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. This allows the first average exposure dose E1 in the first region 30A and the second average exposure dose E2 in the second region 30B to be approximately equal to each other when electron beam lithography is used to form the pattern of the nanopillars 32. 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.

[0108] (2-7) According to the mold 40 of the second embodiment, in the manufacturing process of the mold 40, it is possible to suppress defective formation of the first nanoholes 43 due to a sudden change in pattern density near the outer edge of the third region 40A. Consequently, it is possible to suppress defective formation of the first nanopillars 33 due to defective formation of the first nanoholes 43, and therefore it is possible to form multiple first nanopillars 33 that can more accurately control the state of incident light. Furthermore, according to the mold 40, it is possible to suppress defective formation, such as defective filling or changes in remaining film thickness, due to a sudden change in pattern density, in the transfer process of transferring multiple nanopillars 32 to the substrate 31.

[0109] (2-8) The ratio (C2 / C1) of the second average volume C2 of the second nanoholes 44 to the first average volume C1 of the first nanoholes 43 is set to 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. This allows the third average exposure dose E3 in the third region 40A and the fourth average exposure dose E4 in the fourth region 40B to be approximately equal to each other when electron beam lithography is used to form the pattern of the nanoholes 42. 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.

[0110] [Modifications of the Second Embodiment] The second embodiment can be modified as follows: The modifications can be combined within the scope of technical compatibility.

[0111] In the second embodiment, a metalens 30 having a metasurface structure was described. That is, a configuration in which the multiple first nanopillars 33 included in the metasurface structure collectively function as a focusing lens was described as an example. This is not limiting, and for example, the multiple nanopillars 12 may function as a phase control lens for purposes other than focusing, a spectroscopic lens, or a polarization control lens. Furthermore, by providing the multiple first nanopillars 33 on a reflector, the multiple first nanopillars 33 may function in a form other than a lens, such as reflecting light having a specific wavelength in any direction.

[0112] The shape of the first nanopillars 33 is not limited to a rectangular parallelepiped, and may be, for example, cylindrical. Even in this case, the first nanopillars 33 have a uniform effective refractive index in the height direction, preventing the shape of the first nanopillars 33 from affecting the transmittance of incident light. Furthermore, the shape of the first nanopillars 33 may be any shape other than a rectangular parallelepiped or a cylindrical shape. For example, the shape of the first nanopillars 33 may be any quadrangular prism, such as a truncated pyramid, or a truncated cone.

[0113] For example, the second nanopillars 34 may have a blazed structure that refracts incident light away from the focal point. The effective refractive index of the second nanopillars 34 may be constant in the height direction. In this case, for example, the shape and arrangement of the second nanopillars 34 may be determined so that the first nanopillars 33 focus incident light to a single point (focal point), while the second nanopillars 34 refract incident light away from the focal point. For example, the second nanopillars 34 may be arranged in an antiphase state, inverting the shape and arrangement of the first nanopillars 33. This configuration can prevent light that deviates from the first region 30A from passing near the focal point as stray light. It also contributes to reducing the focal diameter.

[0114] The second nanopillars 34 are not limited to needle-like structures and may be configured in any shape, such as a rectangular parallelepiped having a width W2 larger than the width W1 of the first nanopillars 33, or a cylindrical shape (in this case, the diameter corresponds to the width W2). This, for example, can effectively suppress formation defects such as pattern collapse in the second nanopillars 34. It can also effectively prevent light incident on the second nanopillars 34 from becoming stray light. Since the second nanopillars 34 are configured so that their W2 is larger than the W1 of the first nanopillars 33, the ratio of the second pattern density ρ2 to the first pattern density ρ1 (ρ2 / 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 equal to or less than 1.5.

[0115] The shape and arrangement of the second nanopillars 34 in the second region 30B are not limited to the above example and may be any shape and arrangement. For example, the shape and arrangement of the second nanopillars 34 may be configured to function as an identifier such as a two-dimensional code. In this case, for example, the shape and arrangement of the second nanopillars 34 arranged in the second region 30B can be used to trace the manufacturing lot and to determine the authenticity of counterfeit products.

[0116] In the metalens 30, the arrangement of the multiple first nanopillars 33 may be determined as appropriate depending on the application of the metalens 30. Furthermore, the multiple first nanopillars 33 are not limited to being arranged in a square pattern in the first direction D1 and the second direction D2, and may be arranged in a radial direction with any point on the substrate 31 as the center, for example.

[0117] The shape and arrangement of the first nanopillars 33 in the first region 30A are not limited to the above example, and any shape and arrangement may be used. For example, the first embodiment and the second embodiment may be combined. That is, in the metalens 30 of the second embodiment, the multiple first nanopillars 33 arranged in the first region 30A may be configured such that the smaller the width W1 and volume, the lower the height H1, 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 in which the nanopillars 12 of the first embodiment are arranged. In the above case, the modified example of the first embodiment and the modified example of the second embodiment may be combined within a range that does not cause technical contradictions.

[0118] Even when electron beam lithography is used to form the pattern of the nanopillars 32 of the metalens 30, the first average exposure dose E1 per one first nanopillar 33 and the second average exposure dose E2 per one second nanopillar 34 may be set to be different from each other. Furthermore, even when electron beam lithography is used to form the pattern of the nanoholes 42 of the mold 40, the third average exposure dose E3 per one first nanohole 43 and the fourth average exposure dose E4 per one second nanohole 44 may be set to be different from each other.

[0119] As long as poor formation of the first nanopillars 33 due to a sudden change in pattern density near the outer edge of the first region 30A can be suppressed, the ratio of the second pattern density ρ2 to the first pattern density ρ1 (ρ2 / ρ1) may be less than 0.5 or greater than 2.0. Furthermore, while the first pattern density ρ1 is defined as the ratio of the area occupied by the first nanopillars 33 within the circular first virtual region, the first virtual region may be any region within the first region 30A. For example, the first pattern density ρ1 may be calculated using the entire first region 30A as the first virtual region. Similarly, the second pattern density ρ2 is defined as the ratio of the area occupied by the second nanopillars 34 within the 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 using the entire second region 30B as the second virtual region.

[0120] [Examples and Comparative Examples of Second Embodiment] Example 2 of the second embodiment and Comparative Example 2 will be described with reference to Figures 13 to 16. Note that the following examples do not limit the configuration of the present disclosure.

[0121] [Example 2: Fabrication of a Metalens] As shown in FIG. 13 , in Example 2, an SOQ wafer 50 was first prepared, which had a 150 nm-thick silicon layer 52 formed on a quartz glass wafer 51 having a diameter of 200 mm. Then, a 400 nm-thick electron beam positive resist layer 53 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 spin coater conditions were a rotation speed of 700 rpm and a rotation time of 120 seconds. The electron beam positive resist layer 53 coated on the SOQ wafer 50 was then pre-baked using a hot plate to remove residual solvent contained in the electron beam positive resist layer 53. The pre-baking conditions were a heating temperature of 180° C. and a heating time of 5 minutes.

[0122] Next, the electron beam positive resist layer 53 was exposed to light to write a pattern of nanopillars 32 corresponding to the first nanopillars 33 in the first region 30A and the second nanopillars 34 in the second region 30B. An electron beam lithography system was used for the exposure. During the exposure, an electron beam was irradiated at an acceleration voltage of 100 keV.

[0123] The first region 30A was circular and had a diameter of 2 mm. Square dots corresponding to the unexposed areas were arranged in a square array with a pitch L of 600 nm within the first region 30A. The width of each square dot was adjusted within a range from 120 nm to 480 nm depending on the position of the first region 30A to achieve a phase profile that focused near-infrared light having a wavelength of 940 nm at a single point in space. The exposure dose of the exposed areas of the first region 30A, corresponding to the areas other than the square dots, was 150 μC / cm. ２ It was decided.

[0124] The ratio of the area of ​​the exposed portion in the first region 30A was 71%. 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. The average exposure dose per unit cell, which is a square with a side having a pitch L, was 106.5 μC / cm ２ It was.

[0125] The second region 30B was annular with a width W3 of 400 μm (see FIG. 11 ). The second region 30B was arranged to surround the first region 30A. A gradation drawing pattern for forming needle-like structures was laid out in a square array in the second region 30B. The gradation exposure pattern had a shape in which squares with different side sizes were overlapped so that their centers of gravity coincided. The sides of the squares in the gradation exposure pattern were 60 nm, 120 nm, 180 nm, 240 nm, 300 nm, 360 nm, 420 nm, 480 nm, 540 nm, and 600 nm, in order from the inside.

[0126] In the gradation drawing pattern, different exposure doses were assigned to the 10 areas divided by the 10 squares. The exposure doses for each area were 15, 30, 45, 60, 75, 90, 105, 120, 135, and 150 μC / cm from the inside, respectively. ２ The average exposure amount per gradation drawing pattern calculated from the area ratio of each area and the exposure amount was 107.25 μC / cm ２ It was.

[0127] 14, the exposed electron beam positive resist layer 53 was then developed. As a result, rectangular parallelepiped first transfer nanopillars 53A were formed in the first region 30A. Furthermore, needle-shaped second transfer nanopillars 53B were formed in the second region 30B. The first transfer nanopillars 53A and second transfer nanopillars 53B were composed of the electron beam positive resist layer 53.

[0128] Specifically, the exposed portions were dissolved by developing the electron beam positive resist layer 53 for 75 seconds using methyl isobutyl ketone. Since the development speed increases with increasing exposure dose, the electron beam positive resist layer 53 remains as needle-shaped second transfer nanopillars 53B in the gradation exposure pattern. Subsequently, the developer was removed from the electron beam positive resist layer 53 on the SOQ wafer 50 by rinsing with ultrapure water, and the wafer was then dried using a spin dryer. The height of the first transfer nanopillars 53A and the height of the second transfer nanopillars 53B fabricated through the above process were approximately 320 nm and 250 nm, respectively.

[0129] 15, next, the SOQ wafer 50 with the electron beam positive resist layer 53 was dry-etched to transfer the shapes of the first transfer nanopillars 53A and the second transfer nanopillars 53B to the silicon layer 52 of the SOQ wafer 50. As a result, rectangular parallelepiped first nanopillars 52A made of the silicon layer 52 were formed in the first region 30A, and needle-shaped second nanopillars 52B made of the silicon layer 52 were formed in the second region 30B.

[0130] The etching gas is SF ６ and C ４ F ８ A mixed gas containing the above was used. The etching time was 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. This allows the shape of the electron beam positive resist layer 53 to be faithfully transferred to the silicon layer 52. The etching time was set based on the etching rate of the silicon layer 52 so that the silicon layer 52 and the electron beam positive resist layer 53 would be removed by 150 nm.

[0131] 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 (80°C) of sulfuric acid and hydrogen peroxide for 10 minutes, rinsed with ultrapure water, immersed in a mixed solution (room temperature) of ammonia and hydrogen peroxide for 10 minutes, and rinsed with ultrapure water, in that order. Through these procedures, a metalens including first nanopillars 52A and second nanopillars 52B was obtained.

[0132] The first pattern density ρ1 of the first nanopillars 52A in the first region 30A was 0.28. The second pattern density ρ2 of the second nanopillars 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).

[0133] Comparative Example 2: Fabrication of a Metalens In Comparative Example 2, when electron beam positive resist layer 53 was exposed, square dots similar to those in Example 2 were written in first region 30A, while no pattern was written in second region 30B. Otherwise, the same procedure as in Example 2 was used to obtain the metalens shown in FIG.

[0134] 16 , the metalens of Comparative Example 2 includes, in the first region 30A, first nanopillars 52A formed of a silicon layer 52. In the second region 30B, the silicon layer 52 remains in the state in which it was deposited.

[0135] [Evaluation: Light-collecting performance evaluation] An infrared laser having 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 produced in Example 2 and Comparative Example 2. The light that passed through the metalens was captured by a CCD (Charge Coupled Devices) camera installed at the focal position and then converted into a light intensity distribution on a plane parallel to the metalens and including the focal point. Here, the light-collecting efficiency is defined as the sum of the light intensity distribution in a region having a radius of 20 μm centered on the focal point divided by the sum of the light intensity distribution in a region having a radius of φ2 mm of the infrared laser. The focusing diameter is defined as the half-width of the light intensity distribution in a region having a radius of 20 μm centered on the focal point.

[0136] The metalens of Example 2 had a light collection efficiency of 52% and a focusing diameter of 4.1 μm. The metalens of Comparative Example 2 had a light collection efficiency of 46% and a focusing diameter of 4.9 μm. Therefore, it was confirmed that by forming second nanopillars 52B in second region 30B surrounding first region 30A in which first nanopillars 52A are arranged, it is possible to increase the light collection efficiency and reduce the focusing diameter.

Claims

1. A metasurface structure comprising a plurality of nanopillars disposed on a support surface of a substrate, the nanopillars having smaller widths and smaller heights, each nanopillar configured to shift the phase of light having a particular wavelength depending on where the nanopillar is located within the support surface.

2. The metasurface structure of claim 1, wherein each nanopillar has a rectangular parallelepiped shape.

3. The metasurface structure of claim 2, wherein each nanopillar has an aspect ratio, which is the ratio of the height to the width, of 3.1 or less.

4. A metasurface structure described in any one of claims 1 to 3, wherein the amount of phase shift of the light at each nanopillar is determined so that the multiple nanopillars collectively function as a lens.

5. A metasurface structure comprising a plurality of nanopillars disposed on a support surface of a substrate, the nanopillars having smaller volumes and smaller heights, each nanopillar configured to shift the phase of light having a particular wavelength depending on where the nanopillar is located within the substrate.

6. A mold comprising a plurality of nanoholes for transferring the plurality of nanopillars in the metasurface structure described in claim 1 to the substrate, wherein the smaller the width of the plurality of nanoholes, the shallower their depth.

7. A mold comprising a plurality of nanoholes for transferring the plurality of nanopillars in the metasurface structure described in claim 5 to the substrate, wherein the smaller the volume of the plurality of nanoholes, the shallower their depth.

8. A metasurface structure comprising a plurality of nanopillars arranged on a support surface of a substrate, the plurality of nanopillars including 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, each first nanopillar configured to shift the phase of light having a particular wavelength depending on the position at which the first nanopillar is located within the support surface.

9. The metasurface structure of claim 8, wherein a first pattern density is the ratio of an area occupied by the first nanopillars per unit area in the first region, and a second pattern density is the ratio of an area occupied by the second nanopillars per unit area in the second region, and the ratio of the second pattern density to the first pattern density is greater than or equal to 0.5 and less than or equal to 2.

0.

10. The metasurface structure described in claim 8 or 9, wherein the second nanopillar is configured so that the effective refractive index changes in the height direction.

11. The metasurface structure of claim 10, wherein the first nanopillar has a rectangular parallelepiped shape.

12. A metasurface structure as described in claim 8 or 9, wherein the amount of phase shift of the light at each first nanopillar is determined so that the multiple first nanopillars collectively function as a lens.

13. A metasurface structure as described in claim 8 or 9, wherein a ratio of a second average volume of the second nanopillars in the second region to a first average volume of the first nanopillars in the first region is greater than or equal to 0.5 and less than or equal to 2.

0.

14. The metasurface structure of claim 8, wherein the width of the second nanopillar is greater than the width of the first nanopillar.

15. A mold comprising a plurality of nanoholes for transferring the plurality of nanopillars in the metasurface structure described in claim 8 to the substrate, the plurality of nanoholes including: a plurality of first nanoholes arranged in a third region 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.

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