Meta-optical element and method for manufacturing meta-optical element

Abstract

This meta-optical element comprises: a support substrate having a first surface; and a pattern layer provided on the first surface and including a plurality of pillars protruding in the thickness direction of the support substrate from the first surface. A pillar height C of the pillars is 2.0 μm or more. When a cross section orthogonal to the height direction of the pillars at a position where the pillar height of the pillars from the first surface is 0.9 C is observed, the distance of an area passing through the center of gravity of the cross section and having the shortest distance in the cross section is defined as a distance A, and when a cross section orthogonal to the height direction of the pillars at a position where the pillar height of the pillars from the first surface is 0.1 C is observed, the distance of an area passing through the center of gravity of the cross section and having the shortest distance in the cross section is defined as a distance B. In this case, an aspect ratio represented by "C / ((A+B) / 2)" is 5.0 or more.

Description

Meta-optical element and method for manufacturing a meta-optical element

[0001] This disclosure relates to a meta-optical element and a method for manufacturing a meta-optical element.

[0002] As a lightweight and thin lens, a planar lens with a metasurface (hereinafter sometimes referred to as a metalens) is considered promising. A metalens exhibits lens function by having a metasurface with a fine periodic structure smaller than the incident wavelength. As a method for forming the fine periodic structure of the metasurface possessed by a meta-optical element including a metalens, a method is known in which fine columnar structures (pillars) are formed using deep ultraviolet (DUV) lithography or electron beam lithography and reactive ion etching (RIE) (see, for example, Patent Document 1 and Non-Patent Document 1).

[0003] Patent Document 1: International Publication No. 2024 / 014272

[0004] Non-patent document 1: Joon-Suh Park et al., "All-Glass, Large Metalens at Visible Wavelength Using Deep-Ultraviolet Projection Lithography" Nano Lett. 2019, 19, 8673-8682.

[0005] For example, in Patent Document 1, the height of the pillar actually obtained was approximately 1.5 μm, and its width was 200 to 350 nm. On the other hand, in Non-Patent Document 1, the height of the pillar was 1.5 μm and 2 μm. However, pillars formed by combining DUV lithography and RIE have a tapered shape in the processed form from the viewpoint of the selectivity ratio of quartz glass, and the processing depth may reach a limit of about 2 μm. Therefore, it may not be possible to obtain a pillar with an ideal shape for the meta-optical element. In addition, in RIE, the mask material is also etched, resulting in side etching. This disclosure has been made in view of the above conventional circumstances, and the first aspect of this disclosure aims to provide a meta-optical element equipped with a pillar with an ideal shape for the meta-optical element. The second aspect of this disclosure aims to provide a method for manufacturing a meta-optical element that can easily obtain a pillar with an ideal shape for the meta-optical element.

[0006] The specific means for achieving the above objectives are as follows: <1> A meta-optical element comprising: a support substrate having a first surface; and a pattern layer provided on the first surface and including a plurality of pillars protruding from the first surface in the thickness direction of the support substrate, wherein the pillar height C of the pillars is 2.0 μm or more, and when a cross section perpendicular to the height direction of the pillars is observed at a position where the pillar height of the pillars is 0.9 C from the first surface, the distance passing through the centroid of the cross section and the shortest distance in the cross section is defined as distance A, and when a cross section perpendicular to the height direction of the pillars is observed at a position where the pillar height of the pillars is 0.1 C from the first surface, the distance passing through the centroid of the cross section and the shortest distance in the cross section is defined as distance B, the aspect ratio expressed as "C / ((A + B) / 2)" is 5.0 or more. <2> The meta-optical element according to <1>, wherein the pillar height C of the pillars is 20.0 μm or less. <3> The meta-optical element according to <1> or <2>, wherein the ratio (A / B) of distance A to distance B is 0.90 to 1.10. <4> The meta-optical element according to any one of <1> to <3>, wherein a fillet is formed at the portion of the pillar that contacts the first surface. <5> The pillar height C is the height of the tallest pillar among the pillars in a 10 mm × 10 mm area when the first surface is tilted 30° and observed with a scanning electron microscope (SEM). Ｈ In this case, the pillar height C for all pillars in the aforementioned region Ｈ A meta-optical element according to any one of items <1> to <4>, wherein the proportion of pillars with a height of less than 90% of the total height is 10% or less. <6> A meta-optical element according to any one of items <1> to <5>, wherein the surface roughness Ra of the tip of the pillar is 2.00 nm or less. <7> When the angle θ calculated from the following formula (1) based on the distance A, the distance B and the pillar height C is referred to as the taper angle of the pillar,

[0007]

[0008] A meta-optical element according to any one of <1> to <6>, wherein the taper angle θ is 0.00° ≤ θ ≤ 2.00°. <8> A meta-optical element according to any one of <1> to <7>, wherein the support substrate is a quartz glass substrate, a crystal substrate, or a sintered substrate of silica particles. <9> A method for manufacturing a meta-optical element according to any one of <1> to <8>, comprising: preparing a workpiece having a first surface, wherein the elements constituting the first surface are elements whose boiling point as a fluoride is 550°C or less; arranging a catalyst material containing an organic compound having polar functional groups in a film thickness of 0.01 to 0.9 μm in locations other than where pillars are formed on the first surface of the workpiece; and exposing the workpiece to a fluorine-containing gas at 80°C or higher. <10> The method for manufacturing a meta-optical element according to <9>, further comprising performing ultraviolet ozone cleaning on the first surface of the workpiece after placing the catalyst material on the first surface of the workpiece and before exposing the workpiece to a fluorine-containing gas. <11> The treatment time for the ultraviolet ozone cleaning is 5 to 240 minutes, and the irradiation dose is 0.1 to 288 J / cm². ２ A method for producing a meta-optical element according to <10>. <12> A method for producing a meta-optical element according to any one of <9> to <11>, wherein the polar functional group comprises at least one selected from the group consisting of a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, a sulfo group, a thiol group, an amide bond, a carbonyl group, a nitro group, a cyano group, an ether bond, and an ester bond.

[0009] According to a first aspect of this disclosure, a meta-optical element can be provided that has a pillar of an ideal shape for the meta-optical element. Furthermore, according to a second aspect of this disclosure, a method for manufacturing a meta-optical element can be provided that allows for easy acquisition of a pillar of an ideal shape for the meta-optical element.

[0010] This is a magnified plan view of a part of the metalens 10. This is a magnified front view of the main part of the metalens 10. This is a diagram showing a cross-section of the pillar 16 perpendicular to the height direction. This is a diagram for explaining the taper angle θ of the pillar 16. This is a schematic diagram showing the etching mechanism assumed on the first surface of the workpiece when the organic compound does not have polar functional groups. This is a schematic diagram showing the reaction mechanism on the first surface of the workpiece when the organic compound has polar functional groups. This is a schematic cross-sectional view showing how the catalyst material is arranged on the workpiece. This is a schematic diagram showing an example of a cross-section of the workpiece 110 after etching. This shows a scanning electron microscope (SEM) image of the first surface of sample 1 observed at a 30° tilt. This shows a magnified SEM image of the pillar of sample 1. This shows a SEM image of the split section of sample 2. This shows a SEM image of the split section of sample 3. This shows a SEM image of the split section of sample 4. This shows a SEM image of the split section of sample 5. This shows a SEM image of the split section of sample 6. This shows a SEM image of the split section of sample 7. The following images are shown: A SEM image of the fractured surface of sample 8; an SEM image of the first surface of sample 9 observed at a 30° angle; a magnified SEM image of the pillar of sample 9; a magnified SEM image of the base of the pillar of sample 3; a SEM image of the fractured surface of sample 10; a SEM image of the fractured surface of sample 11; a SEM image of the fractured surface of sample 12; a planar SEM image of the pillar tip of sample 2; a planar SEM image of the pillar tip of sample 3; and a planar SEM image of the pillar tip of sample 4.

[0011] In this disclosure, numerical ranges indicated using "~" mean a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, the amount of each component means the total amount of multiple substances if there are multiple substances corresponding to each component, unless otherwise specified.

[0012] <Meta-optical element> The meta-optical element of this disclosure comprises a support substrate having a first surface, and a pattern layer provided on the first surface and including a plurality of pillars projecting from the first surface in the thickness direction of the support substrate, wherein the pillar height C of the pillars is 2.0 μm or more, and when a cross section perpendicular to the height direction of the pillars is observed at a position where the pillar height of the pillars is 0.9 C from the first surface, the distance passing through the centroid of the cross section and the shortest distance in the cross section is defined as distance A, and when a cross section perpendicular to the height direction of the pillars is observed at a position where the pillar height of the pillars is 0.1 C from the first surface, the distance passing through the centroid of the cross section and the shortest distance in the cross section is defined as distance B, the aspect ratio expressed as "C / ((A + B) / 2)" is 5.0 or more. The meta-optical element of this disclosure has a pillar height C of 2.0 μm or more, and a pillar aspect ratio of 5.0 or more, and is equipped with pillars of an ideal shape for a meta-optical element.

[0013] The details of the meta-optical elements of this disclosure will be described below with reference to the drawings. In the following description, a meta-lens will be used as an example of a meta-optical element, but the meta-optical elements of this disclosure are not limited to meta-lenses and can be applied to filters, mirrors, splitters, etc. The sizes of the components in each figure are conceptual, and the relative relationships of the sizes of the components are not limited thereto. Also, components having substantially the same function will be given the same reference numeral throughout all drawings, and redundant explanations may be omitted. Furthermore, in the following embodiments, a meta-lens equipped with a cylindrical pillar will be described as an example, but the shape of the pillar is not limited to a cylindrical shape, but may be a polygonal prism such as a triangular prism or a rectangular prism.

[0014] Figure 1 is an enlarged plan view of a part of the metalens 10 according to the first embodiment. Figure 2 is an enlarged front view of the main part of the metalens 10. As shown in Figures 1 and 2, the metalens 10 has a support substrate 14 having a first surface 12. A plurality of pillars 16 are provided on the first surface of the support substrate 14, projecting from the first surface 12 in the thickness direction of the support substrate 14. A pattern layer 18 is formed by the plurality of pillars 16.

[0015] The thickness of the support substrate 14 is not particularly limited and is set appropriately according to the application of the metalens 10. For example, the thickness of the support substrate 14 may be 0.05 to 2 mm.

[0016] The material of the support substrate 14 is not particularly limited, but it is preferable to use a material that has excellent light transmittance from the viewpoint of the light transmittance of the metalens 10. The support substrate 14 may be a quartz glass substrate, a crystal substrate, a sintered silica particle substrate, or SiO ２ Examples include substrates on which SiN (silicon nitride) or SiON (silicon oxynitride) films have been deposited. Among these, from the viewpoint of suitability for manufacturing when applying the metalens manufacturing method described later, a quartz glass substrate such as a synthetic quartz glass substrate, a crystal substrate, or a sintered silica particle substrate is preferred as the support substrate 14. ２When using a substrate on which a film has been deposited, it is acceptable to form pillars by processing only the film deposited on the substrate. In that case, SiO is used on a substrate such as a sintered substrate. ２ These are metal lenses equipped with pillars such as the ones mentioned above.

[0017] The shape of the support substrate 14 when viewed from above is not particularly limited and can be rectangular, circular, etc., and can be set appropriately depending on the application of the metal lens 10. Similarly, the size of the support substrate 14 when viewed from above is not particularly limited and can be set appropriately depending on the application of the metal lens 10. For example, if the support substrate 14 is rectangular, it can be a square or rectangle with sides of 2 to 100 mm.

[0018] The pattern layer 18 is formed by a plurality of pillars 16. The shape of the pattern layer 18 as an aggregate of the plurality of pillars 16 when the metalens 10 is viewed from above is appropriately set according to the application of the metalens 10, and may be circular, rectangular, or the like. The metalens 10 may be provided with one pattern layer 18 as an aggregate of the plurality of pillars 16, or it may be provided with two or more pattern layers 18.

[0019] The height C of the pillar 16 is set to 2.0 μm or more. Because the height C of the pillar 16 is 2.0 μm or more, a phase difference of 2π for the metalens 10 is easily achieved, and as a result, it becomes easier to obtain a metalens with low chromatic aberration and a large numerical aperture (NA). The height C of the pillar 16 is a value that is appropriately set according to the application of the metalens 10, for example, 4.0 μm or more is preferred, and 6.0 μm or more is more preferred. The height C of the pillar 16 may be 20.0 μm or less. A height C of 20.0 μm or less is preferable in terms of mechanical strength and reliability. The height C of the pillar 16 is preferably 15.0 μm or less, and 10.0 μm or less is more preferred. The height C of the pillar 16 may be between 2.0 and 20.0 μm.

[0020] In this disclosure, the height C of each pillar 16 refers to the value obtained by observing the cross-section of the metalens 10 using an electron microscope. The individual heights of the five pillars 16 are determined by the method described above, and the arithmetic mean of the obtained values ​​is taken as the height C of the pillar 16.

[0021] When observing a cross-section of pillar 16 perpendicular to the height direction at a pillar height of 0.9C from the first surface 12, distance A is defined as the distance passing through the centroid of the cross-section and to the shortest distance in the cross-section. When observing a cross-section of pillar 16 perpendicular to the height direction at a pillar height of 0.1C from the first surface 12, distance B is defined as the distance passing through the centroid of the cross-section and to the shortest distance in the cross-section. The aspect ratio expressed as "C / ((A + B) / 2)" is 5.0 or greater. Because the aspect ratio of the pillar is 5.0 or greater, the pillar shape tends to be an ideal shape for a meta-optical element. The aspect ratio is preferably 7.0 or greater, and more preferably 10.0 or greater. The aspect ratio may be 50.0 or less. The aspect ratio is preferably between 5.0 and 50.0.

[0022] The following will explain, based on the drawings, the "position where the pillar height is 0.9C from the first surface 12," the "position where the pillar height is 0.1C from the first surface 12," the "cross-section perpendicular to the height direction of the pillar 16," and the "distance between the centroid of the cross-section and the shortest distance in the cross-section." The positions where the pillar height is 0.9C and 0.1C from the first surface 12 are as shown in the pillar 16 located in the center of Figure 2. Figure 3 shows the cross-section of the pillar 16 perpendicular to the height direction. Figure 3(A) shows an example of a pillar 16 with a circular cross-section, Figure 3(B) shows an example of a pillar 16 with a square cross-section, and Figure 3(C) shows an example of a rectangular cross-section. In Figure 3, the centroid of each shape is represented by the symbol G. Other shapes of the cross-section perpendicular to the height direction of the pillar 16 include multi-cylinder shapes, cross shapes, etc. Multiple shapes may be combined to produce the pillar function. For a pillar 16 with a circular cross-section, the "distance passing through the centroid of the cross-section and the shortest distance in the cross-section" means the diameter of the circle, as shown in Figure 3(A). For a pillar 16 with a square cross-section, the "distance passing through the centroid of the cross-section and the shortest distance in the cross-section" means the length of one side of the square, as shown in Figure 3(B). For a pillar 16 with a rectangular cross-section, the "distance passing through the centroid of the cross-section and the shortest distance in the cross-section" means the length of the shorter side of the rectangle, as shown in Figure 3(C).

[0023] The ratio (A / B) of distance A to distance B for pillar 16 is preferably 0.90 or more, and more preferably 0.95 or more. The ratio (A / B) for pillar 16 is preferably 1.10 or less, and more preferably 1.05 or less. The ratio (A / B) for pillar 16 is preferably between 0.90 and 1.10. If the ratio (A / B) is between 0.90 and 1.10, it becomes possible to form pillars with the dimensions as designed, reducing the need for pillar design that takes into account dimensional errors that may occur in the manufacturing process, and simplifying metalens design. The details of distance A and distance B are as described above. In this disclosure, distance A and distance B for each pillar 16 refer to values ​​obtained by observing the split surface of the metalens 10 using an electron microscope. For five pillars 16, distance A and distance B are determined by the method described above, and the arithmetic mean of the obtained values ​​is taken as distance A and distance B for pillar 16.

[0024] As shown in Figure 2, a fillet 20 may be formed at the point where the pillar 16 contacts the first surface 12 (the base of the pillar 16). Forming a fillet 20 at the base of the pillar 16 makes it easier to maintain the strength of the pillar 16 against stress from the planar direction. As a result, the strength of the metalens 10 tends to improve. Note that in Figure 2, the fillet 20 is shown only at the base of the pillar 16 located on the left side.

[0025] The angle (so-called taper angle) between the side wall of the pillar 16 and the thickness direction of the support substrate 14 is preferably 0.00 to 2.00°, and more preferably 0.00 to 1.00°. The taper angle θ of the pillar 16 will be explained below with reference to Figure 4. In Figure 4, a cylindrical pillar 16 is used as an example, but the shape of the pillar 16 is not limited to a cylindrical shape. For the sake of convenience in explaining the taper angle, the taper angle θ of the pillar 16 shown in Figure 4 is shown in greater emphasis than that of the pillar 16 shown in Figure 2. Figure 4 shows a cross-section of a cylindrical pillar 16 that passes through the centroid of the circle and is perpendicular to the support substrate 14. In Figure 4, arrow L represents the thickness direction of the support substrate 14. In Figure 4, A, B, and C represent the distance A, distance B, and pillar height C, respectively. Based on A, B, and C in Figure 4, the taper angle θ of the pillar 16 is calculated from the following equation (1).

[0026]

[0027] (1) The taper angle θ calculated from the formula serves as an index of the "perpendicularity" of the pillar 16. That is, the smaller the taper angle θ, the more the inclination of the side wall 22 of the pillar 16 with respect to the thickness direction L of the support substrate 14 is suppressed.

[0028] The tip of the pillar 16 is preferably flat because it tends to suppress a decrease in the utilization efficiency of light due to light scattering. When the tip of the pillar 16 is "flat", it means that no dents, protrusions, etc. are observed when observing the tip of the pillar 16 with an electron microscope. From the viewpoint of suppressing a decrease in the utilization efficiency of light due to light scattering, the surface roughness Ra of the tip of the pillar 16 is preferably 2.00 nm or less, more preferably 1.00 nm or less, and even more preferably 0.50 nm or less. The lower limit value of the surface roughness Ra of the tip of the pillar 16 is not particularly limited and may be 0.00 nm. The surface roughness Ra of the tip of the pillar 16 is preferably 0.00 to 2.00 nm. In the present disclosure, the surface roughness Ra of the tip of the pillar refers to a value measured by the following method. Analyze the surface of the meta-optical element (metalens) using an atomic force microscope (AFM). At the time of analysis, first, a 5 μm□ area is set as the analysis range to confirm the location of the pillar surface. Next, move the probe on the pillar surface and measure in a 100 nm□ analysis range to obtain the surface roughness Ra of the meta-optical element. For the analysis apparatus, for example, Cyfer ES of OXFORD INSTRUMENTS may be used. The pillar height C of the pillar 16 is preferably such that the heights of the respective pillars are substantially the same. For example, when the pillar height of the tallest pillar among the pillars in a 10 mm × 10 mm region when observing with a scanning electron microscope (SEM) with the first surface 12 tilted at 30° is taken as the pillar height C Ｈ for all the pillars in the region. ＨIt is preferable that the ratio occupied by pillars with a height less than 90% is 10% or less. By having the pillar height C uniform as in this configuration, a proper phase difference can be generated and it can function well as a meta-lens. For all the pillars in the region, the pillar height C of the tallest pillar Ｈ It is preferable that the ratio occupied by pillars with a height less than 95% is 10% or less, and the pillar height C of the tallest pillar Ｈ It is more preferable that the ratio occupied by pillars with a height less than 95% is 5% or less.

[0029] The material of the pillar 16 is not particularly limited. Examples of the material of the pillar 16 include silicon oxide, silicon nitride, titanium oxide, tantalum oxide, zirconium oxide, hafnium oxide, gallium arsenide, gallium nitride, and niobium oxide. The material of the pillar 16 may be a metal material such as gold (Au), silver (Ag), or copper (Cu). The material of the pillar 16 is preferably a material with excellent light transmissibility from the viewpoint of the light transmissibility of the meta-lens 10, and silicon oxide is more preferable. The material of the pillar 16 may be the same as the material of the support substrate 14. In the case of a meta-lens manufactured by the manufacturing method of the meta-lens of the present disclosure described later, the material of the pillar 16 is made the same as the material of the support substrate 14.

[0030] <Manufacturing method of meta-lens> The meta-lens of the present disclosure may be manufactured by any method. The meta-lens of the present disclosure may be manufactured, for example, using DUV lithography and RIE. Note that pillars formed using DUV lithography and RIE may have problems such as the processed shape being tapered as described above and the problem that the processing depth cannot be increased due to a small selectivity ratio with the mask. Therefore, when manufacturing a meta-lens using DUV lithography and RIE, in order to prevent the occurrence of the above problems, it is preferable to vertically pattern a thick metal film.

[0031] The metalens of this disclosure may be manufactured by a method for manufacturing a metalens of this disclosure, which comprises: preparing a workpiece having a first surface, wherein the elements constituting the first surface are elements whose boiling point when the elements are converted into a fluoride is 550°C or lower (hereinafter sometimes referred to as a preparation step); arranging a catalyst material containing an organic compound having polar functional groups in a film thickness of 0.01 to 0.9 μm in locations on the first surface of the workpiece other than where pillars are formed (hereinafter sometimes referred to as a catalyst arrangement step); and exposing the workpiece to a fluorine-containing gas at 80°C or higher (hereinafter sometimes referred to as an exposure step). The method for manufacturing a metalens of this disclosure will now be described in detail. The method for manufacturing a metalens of this disclosure comprises a preparation step, a catalyst arrangement step, and an exposure step, and may include other steps as necessary.

[0032] (Principle) In the method for manufacturing a metalens described herein, a metalens is manufactured by having a workpiece prepared in a preparation step go through a catalyst placement step and an exposure step. The principle of the method for manufacturing a metalens is described below. The catalyst material contains an organic compound having a polar functional group. Such an organic compound having a polar functional group is thought to play a role in lowering the activation energy of fluoride formation on the surface of the workpiece. In other words, on the first surface of the workpiece, the region where the catalyst material is placed (hereinafter referred to as the "coated region") is selectively etched. Also, since no significant etching reaction occurs in the region where the catalyst material is not placed (hereinafter referred to as the "uncoated region"), pillars are formed in that region.

[0033] The role of this will be explained below using Figures 5 and 6. Figures 5 and 6 schematically show the reaction on the surface of the object to be treated where the catalyst material is placed. In the following explanation, as an example, the object to be treated is SiO ２ Let's assume that the first surface is hydrogen-terminated. We also assume a hydroxyl group as the polar functional group. First, Figure 5 schematically shows the expected etching mechanism on the first surface of the workpiece when the organic compound does not have a polar functional group. The workpiece is SiO ２When hydrogen fluoride (HF) gas is supplied from the environment to the region on the surface where the catalyst material is located, i.e., the "coating region," the HF molecule (a) performs a nucleophilic attack on the Si atom (b), as shown in (i). However, for the Si atom (b) to react with the F atom on the surface of the object being treated, the OH group (c) on the surface must interact with the H atom of the HF molecule (a) to weaken the H-F bond, as shown in (ii). In other words, unless energy is provided to break the H-F bond in the HF molecule (a), the H will not react, as shown in (iii). ２ The Si-F bond (d) accompanied by the elimination of O(g) is unlikely to form. However, in this reaction system, there are no substances that contribute to the decrease in the activation energy of the Si-F bond (d). Therefore, significant etching is suppressed in the coated region. In this system, as in normal mask pattern processing, the etching rate tends to be higher in the areas where the workpiece is in direct contact with HF gas, i.e., in the areas where the catalyst material on the surface is not placed, i.e., the "uncoated region".

[0034] On the other hand, Figure 6 schematically shows the reaction mechanism at the first surface of the treated object when the organic compound has a polar functional group. In this case as well, when HF gas is supplied from the environment to the coated region of the catalyst material, the HF molecule (a) performs a nucleophilic attack on the Si atom (b), as shown in (i). However, in the case of Figure 6, in addition to this, the O atom of the -δ part (e) of the polar functional group interacts with the H of the HF molecule (a). Also, the H atom of the +δ part (f) of the polar functional group interacts with the OH group (c) on the surface. Therefore, as shown in (ii), the H-F bond of the HF molecule (a) is weakened. The Si (b)-OH (c) bond is also weakened. As a result, the activation energy required for the bonding reaction between the Si atom and the F atom is reduced. As a result, as shown in (iii), the O atom of the -δ part (e) of the polar functional group removes an H atom from the HF molecule (a), and the H atom of the +δ part (f) reacts with the OH group on the surface, resulting in H ２ O(g) elimination occurs.

[0035] As a result, the Si atom (b) bonds with the fluorine atom. Finally, according to the following reaction equation (2), SiF４ and H ２ O is formed. SiO ２ +4HF → SiF ４ ↑+ 2H ２ O↑ (2) SiF produced in the reaction ４ and H ２ O is a gas at the processing temperature and is released outside the system. Through the above reaction mechanism, the area directly beneath the coating region of the catalyst material is selectively etched in the object being treated.

[0036] It should be noted that the above reaction is not limited to cases where the polar functional group contains a hydroxyl group. For example, a similar reaction may occur when the polar functional group has at least one of the following: an aldehyde group, a carboxyl group, an amino group, a sulfo group, a thiol group, and an amide bond. Furthermore, Figure 6 illustrates the reaction mechanism using the case where the polar functional group of the organic compound contains a hydrogen atom as an example. However, the polar functional group of an organic compound is not necessarily limited to those containing a hydrogen atom. A similar reaction may occur when the polar functional group does not contain a hydrogen atom and has at least one of the following: a carbonyl group, a nitro group, a cyano group, an ether bond, and an ester bond.

[0037] (Preparation process) In the preparation process, a workpiece is prepared having a first surface, wherein the elements constituting the first surface are elements whose fluoride has a boiling point of 550°C or less. The workpiece undergoes the catalyst placement process and exposure process described later to form the support substrate and pillars of the metalens.

[0038] The object to be treated may be composed of a single component or multiple components. When the object to be treated is composed of a single component, the element constituting the first surface of the object to be treated is an element whose fluoride, when reacted with fluorine (F), has a boiling point of 550°C or lower. Generally, the upper limit temperature at which a catalyst exhibits activity is approximately 550°C, and at temperatures higher than this, polar functional groups may be eliminated, causing the catalytic effect of the catalyst to disappear. By using an element whose fluoride, when reacted with fluorine (F), has a boiling point of 550°C or lower as the element constituting the first surface of the object to be treated, the loss of the catalytic effect can be suppressed. Furthermore, using an element whose fluoride has a boiling point of 550°C or lower is preferable because it allows the use of inexpensive Ni-based alloys such as Inconel in the processing apparatus. For example, the material to be treated may contain at least one element selected from the group consisting of B, C, Si, P, S, Ti, V, Cr, Ge, As, Se, Nb, Mo, Tc, Ru, Rh, Sn, Sb, Te, I, Ta, W, Re, Os, Ir, Pt, and Au. Furthermore, the material to be treated may also contain at least one element selected from the group consisting of H, N, Cl, Br, and O.

[0039] In particular, the element constituting the first surface of the object to be treated is preferably an element whose fluoride, when reacted with fluorine to form a fluoride, has a boiling point of 200°C or lower.

[0040] For example, silicon (Si) is fluoride SiF ４ A workpiece having a boiling point of -86°C and containing silicon as an element constituting the first surface can be suitably used as a workpiece in the method for manufacturing a metalens according to this disclosure.

[0041] Al and Ca are fluorides (AlF) ３ ) and (CaF ２ The boiling point of ) exceeds 550°C. Therefore, Al and Ca cannot be said to be elements whose fluorides have a boiling point of 550°C or lower when they react with fluorine (F).

[0042] The material to be processed is, for example, a quartz glass substrate, a crystal substrate, a sintered silica particle substrate, or SiO２ A substrate on which a film has been formed may also be used. On the other hand, if the object to be treated is composed of a laminate of multiple members, it is preferable that the element constituting the outermost surface (i.e., the "first surface") of the object to be treated is an element whose fluoride has a boiling point of 550°C or less when it reacts with fluorine to form a fluoride. As mentioned above, such an element may be selected from the group consisting of B, C, Si, P, S, Ti, V, Cr, Ge, As, Se, Nb, Mo, Tc, Ru, Rh, Sn, Sb, Te, I, Ta, W, Re, Os, Ir, Pt, and Au. Furthermore, the first surface may also contain at least one element selected from the group consisting of H, N, Cl, Br, and O.

[0043] For example, the object to be processed has one or more films arranged on a substrate, and the outermost film may satisfy the aforementioned characteristics. Alternatively, the entire group of films may satisfy the aforementioned characteristics. Such films may be, for example, SiO ２ Si ３ N ４ The film may have at least one of the following: a film and SiC. Alternatively, the substrate may also have the aforementioned features along with the film. In this case, the substrate may be, for example, a quartz glass substrate, a crystal substrate, or a silicon substrate.

[0044] The size of the object to be processed is not particularly limited; for example, it may be a disc with a diameter of 2.5 to 30 cm. The thickness of the object to be processed is also not particularly limited; for example, it may be 0.05 to 2 mm.

[0045] (Catalyst placement process) In the catalyst placement process, a catalyst material containing an organic compound having polar functional groups is placed to a thickness of 0.01 to 0.9 μm in areas on the first surface of the object to be treated, excluding areas where pillars are formed.

[0046] The catalyst material comprises an organic compound having a polar functional group. The polar functional group may include at least one selected from the group consisting of, for example, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, a sulfo group, a thiol group, an amide bond, a carbonyl group, a nitro group, a cyano group, an ether bond, and an ester bond. Representative examples of such organic compounds include, for example, phenolic resins such as novolac resins, acrylic resins, and methacrylic resins. The catalyst material may consist only of the aforementioned organic compound having a polar functional group, or it may be provided as a mixture with other additives. In the latter case, the catalyst material may include a solvent, a binder, and / or fine particles.

[0047] The method of arranging the catalyst material is not particularly limited. The catalyst material may be arranged on the first surface of the workpiece using, for example, a coating method, a printing method, a spin coating method, or a spray method. If necessary, the catalyst material may be arranged in areas other than where pillars are formed by going through a known exposure and development process. If the catalyst material itself is not very suitable for fine patterning, a film made of a patterning material for microfabrication of the catalyst material may be formed on the catalyst material, and the catalyst material may be processed using the film made of the patterning material as a mask. This makes it possible to form a pattern of a desired shape on a catalyst material that is not very suitable for fine patterning. As for patterning methods for catalyst materials, in addition to methods using resists for EBL (Electron Beam Lithography), nanoimprint lithography, photolithography, and 3D printing can be mentioned. Furthermore, specific methods for processing the catalyst material can be mentioned, such as reactive ion etching and sputtering.

[0048] Figure 7 is a schematic cross-sectional view showing how the catalyst material is arranged on the object to be treated. As shown in Figure 7, the object to be treated 110 has a first surface 112 and a second surface 114. The catalyst material 130 is arranged on a part of the first surface 112 of the object to be treated 110. As shown in Figure 7, the catalyst material 130 is arranged in areas other than the area P where the pillar is formed, and a covered area is formed. The areas other than the covered area are considered uncovered areas (i.e., the area P where the pillar is formed).

[0049] The thickness of the catalyst material is 0.01 to 0.9 μm. From the viewpoint of preventing the catalyst material film from becoming island-like, the thickness of the catalyst material is preferably 0.01 μm or more, and more preferably 0.05 μm or more. Furthermore, from the viewpoint of suppressing the occurrence of wrinkles in the catalyst film due to the high temperature of the exposure process, the thickness of the catalyst material is preferably 0.9 μm or less. Note that a thinner catalyst material can reduce the amount of side etching and is suitable for high-resolution patterning, so it may be 0.1 μm or less. The thickness of the catalyst material may also be 0.1 to 0.8 μm, or 0.05 to 0.5 μm. In this disclosure, the thickness of the catalyst material refers to the value measured by SEM observation of the cut surface of the substrate before the exposure process.

[0050] (Cleaning Step) The manufacturing method of a metalens according to the present disclosure may include, after placing a catalyst material on the first surface of the workpiece and before exposing the workpiece to a fluorine-containing gas (i.e., between the catalyst placement step and the exposure step), performing ultraviolet ozone cleaning on the first surface of the workpiece (hereinafter sometimes referred to as the cleaning step). Ultraviolet ozone cleaning can be carried out in an atmosphere gas containing oxygen. Examples of light sources for ultraviolet ozone cleaning include low-pressure mercury lamps, excimer lamps, high-pressure mercury lamps, etc. The processing time may be 5 to 240 minutes. The irradiation dose may be 0.1 to 288 J / cm². ２ Alternatively, the flatness of the pillar tip can be further improved by performing a cleaning process.

[0051] (Exposure Process) In the exposure process, for example, the workpiece 110 on which the catalyst material 130 is placed is housed in a processing chamber. Subsequently, the processing chamber is heated to a predetermined temperature for etching the workpiece, and a fluorine-containing gas is supplied as a processing gas. This exposes the workpiece 110 to the fluorine-containing gas. The processing gas includes hydrogen fluoride gas or fluorine gas. For example, the processing gas may be adjusted to a predetermined concentration using a carrier gas such as argon gas or nitrogen gas. In this case, the concentration of hydrogen fluoride gas or fluorine gas may be in the range of, for example, 0.1 to 100 vol%. The processing temperature is 80°C or higher. If the processing temperature is below 80°C, proper etching selectivity may not occur between the coated and uncoated areas on the first surface of the workpiece. Therefore, the actual processing temperature varies depending on the elements contained in the workpiece 110 (especially the first surface 112) and the shape of the pillars, but is usually in the range of 200 to 450°C, and preferably in the range of 250 to 400°C. By setting the processing temperature to 450°C or lower, the deterioration of organic compounds contained in the catalyst material 130 can be suppressed.

[0052] As described above, etching the workpiece 110 under these conditions causes the reaction equation (2) to occur in the coated region. The fluoride and water produced by the reaction escape out of the system as gas. As a result, a pattern layer 18 containing multiple pillars 16 is formed in the uncoated region of the first surface 112. The coated region also forms the first surface 12 of the metalens 10. Figure 8 schematically shows an example of a cross-section of the workpiece 110 (metalens 10) after etching.

[0053] (Other steps) In the method for manufacturing a metalens according to the present disclosure, a step to remove the catalyst material 130 may be performed after the exposure step. For example, the catalyst material 130 may be removed by washing the workpiece 110 with an acid solution, an alkaline solution, an organic solvent, a corrosive gas, or plasma. By the above steps, a metalens 10 having a pattern layer 18 containing a plurality of pillars 16 on the first surface 12 can be manufactured.

[0054] Examples of the present disclosure are described below. In the following description, Examples 1-8 and 10-12 are examples, and Example 9 is a comparative example.

[0055] [Example 1] A synthetic quartz glass substrate was prepared as the object to be treated. The elements constituting the surface of the synthetic quartz glass substrate are Si and O, and SiF is a fluoride of Si. ４ The boiling point of is -86°C. Separately, a coating solution containing a catalyst material was prepared. An i-ray resist was used as the catalyst material, and the coating solution was prepared by mixing it with a solvent (ethyl lactate, n-butyl acetate). The i-ray resist used contains a novolac resin represented by the following chemical formula. Therefore, the i-ray resist has a hydroxyl group as a polar functional group.

[0056]

[0057] Next, a coating solution was applied to the first surface of the substrate by spin coating to achieve a dry film thickness of 0.7 μm. Furthermore, exposure and development processes were used to form a pattern of catalyst material on the first surface of the substrate, with holes having a diameter of 500 nm and a distance of 20,000 nm between the centers of each hole (exposure + development). The areas where the catalyst material was applied correspond to the coated areas, and the areas where holes were formed correspond to the uncoated areas.

[0058] A substrate on which a pattern of catalyst material is arranged is exposed to ultraviolet ozone (UV / O). ３ Cleaning was performed. A low-pressure mercury lamp (with main wavelengths of 254 nm and 185 nm) was used for ultraviolet ozone cleaning. The substrate was positioned so that the first surface of the substrate faced the lamp, and the treatment was performed for 15 minutes (irradiation dose: 18 J / cm²). ２ The sample was irradiated with DUV light to remove organic matter adsorbed on the substrate surface. The distance between the substrate and the lamp was 45 mm.

[0059] Next, the substrate on which the catalyst material pattern was arranged was cut to dimensions of approximately 20 mm x 20 mm, and the cut sample was placed in the processing chamber. Gas etching treatment of the sample was then performed in the processing chamber. The processing gas was a mixture of nitrogen gas and hydrogen fluoride gas (HF: 20 vol% / N). ２80 vol%) was used. The processing temperature was 350°C. The processing time was 40 minutes. Table 1 summarizes the "HF gas exposure conditions".

[0060] Next, O ２ Plasma was used to remove the catalyst remaining on the bottom surface of the recesses in the substrate. The processing conditions were: output: 100 W, chamber pressure: 20 Pa, processing time: 15 minutes. Sample 1 of Example 1 was obtained through the above process.

[0061] [Example 2] A coating solution was applied to the first surface of the substrate by spin coating so that the dry film thickness was 0.4 μm. Furthermore, by exposure and development treatment, a pattern of catalyst material having holes with a diameter of 500 nm and a distance between the centers of each hole of 700 nm was placed on the first surface of the substrate. Sample 2 of Example 2 was obtained in the same manner as in Example 1, except that the processing conditions for the processing gas were 250°C for 10 minutes and ultraviolet ozone cleaning was not performed.

[0062] [Example 3-8] Sample 3-8 of Example 3-8 was obtained in the same manner as in Example 2, except that the processing conditions of the processing gas and the presence or absence of ultraviolet ozone washing were as shown in Table 1.

[0063] [Example 9] Sample 9 of Example 9 was obtained in the same manner as in Example 1, except that the coating solution was applied to the first surface of the substrate by spin coating so that the dry film thickness was 1.0 μm.

[0064] [Examples 10-12] Similar to Example 1, a coating solution was placed on the first surface of the substrate so that the dry film thickness was 0.1 μm. Next, an EBL (Electron Beam Lithography) resist was applied thereon, and the EBL resist was processed by exposure and development. After that, the i-line resist, which is a catalyst material, was patterned (etched) using the EBL resist film as a mask (mask + etching). Specifically, in Example 10, a pattern of catalyst material with holes of 80 nm in diameter and a distance between the centers of each hole of 150 nm was formed on the first surface of the substrate; in Example 11, a pattern of catalyst material with holes of 145 nm in diameter and a distance between the centers of each hole of 300 nm was formed on the first surface of the substrate; and in Example 12, a pattern of catalyst material with holes of 220 nm in diameter and a distance between the centers of each hole of 600 nm was formed on the first surface of the substrate. The process following the formation of the catalyst material pattern was carried out in the same manner as in Example 1 to obtain sample 10 of Example 10, sample 11 of Example 11, and sample 12 of Example 12, respectively.

[0065] <Evaluation> The fracture surfaces of each sample were observed using a scanning electron microscope (SEM), and various dimensions were measured. Figures 9-19 show SEM images of samples 1-9, respectively. Figure 9 is an SEM image of the first surface of sample 1 observed at a 30° angle, and Figure 10 is a magnified SEM image of the pillar of sample 1. Figures 11-17 are SEM images of the fracture surfaces of samples 2-8, respectively. Figure 18 is an SEM image of the first surface of sample 9 observed at a 30° angle, and Figure 19 is a magnified SEM image of the pillar of sample 9. Figure 20 is a magnified SEM image of the base of the pillar of sample 3. It can be confirmed that a fillet has been formed at the base of the pillar. Figures 21-23 show SEM images of samples 10-12, respectively. Figures 21-23 are SEM images of the fracture surfaces of samples 10-12, respectively. The manufacturing conditions, various dimensions, and evaluation results for each example are summarized in Table 1.

[0066] -Flatness Evaluation Method- The tips of the pillars for each sample were observed using an electron microscope, and the flatness of the pillar tips was evaluated according to the evaluation criteria below. The evaluation results are shown in Table 1. As an example, planar SEM images of the pillar tips for samples 2-4 are shown in Figure 24-26. -Flatness Evaluation Criteria- A: When there are fewer than 10 reaction spots in the SEM image of the substrate surface B: When there are 10 or more reaction spots in the SEM image of the substrate surface

[0067] - Measurement of surface roughness - The surface roughness of the tips of the pillars in Example 2 and Example 3 was determined using the above method with AFM. The surface roughness of the tip of the pillar in Example 2 was 3.13 nm, and the surface roughness of the tip of the pillar in Example 3 was 0.17 nm. From these results, it can be seen that performing ultraviolet ozone cleaning tends to reduce the surface roughness of the tips of the pillars.

[0068]

[0069] From Table 1, the following can be seen. Samples 1-8 and 10-12 of Examples 1-8 and 10-12, manufactured by the manufacturing method of this disclosure, had pillars with an ideal shape for a meta-optical element. On the other hand, although sample 9 of Example 9, manufactured by a method other than the manufacturing method of this disclosure, had a high aspect ratio of pillars, as is clear from the comparison between the SEM image of sample 1 of Example 1 in Figure 9 and the SEM image of sample 9 of Example 9 in Figure 18, the individual pillar heights were not uniform, and pillars with an ideal shape for a meta-optical element were not formed. In sample 1 of Example 1, the pillar height of the tallest pillar in the 10 mm × 10 mm area is defined as pillar height C. Ｈ In that case, pillar height C Ｈ There were no pillars with a height of less than 90% of the total height. In other words, for all pillars in the aforementioned region, the pillar height C was less than 90%. Ｈ The percentage of pillars with a height of less than 90% was 0%. On the other hand, in Sample 9 of Example 9, the pillar height C was the same for all pillars in the region. Ｈ Pillars that were less than 90% of the total height accounted for more than 10% of the total.

[0070] 10 Metalens 12 First surface 14 Support substrate 16 Pillar 18 Pattern layer

[0071] The disclosure of Japanese Patent Application No. 2024-205803, filed on 26 November 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A meta-optical element comprising: a support substrate having a first surface; and a pattern layer provided on the first surface and including a plurality of pillars protruding from the first surface in the thickness direction of the support substrate, wherein the pillar height C of the pillars is 2.0 μm or more; and when a cross section perpendicular to the height direction of the pillars is observed at a position where the pillar height of the pillars is 0.9 C from the first surface, distance A is the distance passing through the centroid of the cross section and to the shortest distance in the cross section; and when a cross section perpendicular to the height direction of the pillars is observed at a position where the pillar height of the pillars is 0.1 C from the first surface, distance B is the distance passing through the centroid of the cross section and to the shortest distance in the cross section, the aspect ratio expressed as "C / ((A + B) / 2)" is 5.0 or more.

2. The meta-optical element according to claim 1, wherein the pillar height C of the pillar is 20.0 μm or less.

3. The meta-optical element according to claim 1, wherein the ratio of distance A to distance B (A / B) is 0.90 to 1.

10.

4. The meta-optical element according to claim 1 or 2, wherein a fillet is formed at the portion of the pillar that is in contact with the first surface.

5. The pillar height C is defined as the height of the tallest pillar among the pillars in a 10 mm × 10 mm area when the first surface is tilted 30° and observed with a scanning electron microscope (SEM). Ｈ In this case, the pillar height C for all pillars in the aforementioned region Ｈ The meta-optical element according to claim 1 or 2, wherein the proportion of pillars with a height of less than 90% of the total height is 10% or less.

6. The meta-optical element according to claim 1 or 2, wherein the surface roughness Ra of the tip of the pillar is 2.00 nm or less.

7. When the angle θ calculated from the following equation (1) based on the distance A, the distance B, and the pillar height C is referred to as the taper angle of the pillar, The meta-optical element according to claim 1 or 2, wherein the taper angle θ is 0.00° ≤ θ ≤ 2.00°.

8. The meta-optical element according to claim 1 or 2, wherein the support substrate is a quartz glass substrate, a crystal substrate, or a sintered substrate of silica particles.

9. A method for manufacturing a meta-optical element according to claim 1, comprising: preparing a workpiece having a first surface, wherein the elements constituting the first surface are elements whose boiling point when the element is converted into a fluoride is 550°C or lower; arranging a catalyst material containing an organic compound having polar functional groups in a film thickness of 0.01 to 0.9 μm in locations on the first surface of the workpiece other than where pillars are formed; and exposing the workpiece to a fluorine-containing gas at 80°C or higher.

10. The method for manufacturing a meta-optical element according to claim 9, further comprising performing ultraviolet ozone cleaning on the first surface of the workpiece after placing the catalyst material on the first surface of the workpiece and before exposing the workpiece to a fluorine-containing gas.

11. The processing time for the ultraviolet ozone cleaning is 5 to 240 minutes, and the irradiation dose is 0.1 to 288 J / cm². ２ The method for manufacturing a meta-optical element according to claim 10.

12. The method for producing a meta-optical element according to claim 9 or 10, wherein the polar functional group comprises at least one selected from the group consisting of a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, a sulfo group, a thiol group, an amide bond, a carbonyl group, a nitro group, a cyano group, an ether bond, and an ester bond.

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