Mean optical element on curved surface

Abstract

A method comprising: providing a substrate comprising a curved surface; forming a resist layer on the curved surface; patterning the resist layer on the curved surface using imprint lithography to provide a patterned resist layer; removing the residual resist material from the patterned resist layer; forming a first layer on the patterned resist layer by atomic layer deposition; and removing the patterned resist layer to form a patterned first layer on the curved surface.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to optical devices including one or more metastructures. BACKGROUND

[0002] A metasurface refers to a surface having a distribution of small structures (e.g., meta-atoms) arranged to interact with light in a particular way. For example, a metasurface can be a surface having a distributed array of nanostructures. The nanostructures can individually or collectively interact with a light wave. For example, the nanostructures or other meta-atoms can change a local amplitude, a local phase, or both, of an incident light wave. SUMMARY

[0003] In one aspect, the present disclosure describes a method including providing a substrate including a curved surface, forming a resist layer on the curved surface, patterning the resist layer on the curved surface using imprint lithography to provide a patterned resist layer, removing residual resist material from the patterned resist layer, forming a first layer on the patterned resist layer by atomic layer deposition, and removing the patterned resist layer to form a patterned first layer on the curved surface.

[0004] Implementations of the method can include one or more of the following. The patterned first layer on the curved surface includes metastructures. The metastructures include one or more structures formed perpendicular to the curved surface, and a height of each of the one or more metastructures is formed perpendicular to the curved surface. Each of the one or more structures formed perpendicular to the curved surface has a diameter of 30 nanometers to 500 nanometers. The method includes encapsulating the patterned first layer in an encapsulation material.

[0005] Implementations of the method can include one or more of the following. The encapsulation material includes a spin-on glass or a polymer. The method includes removing a portion of the first layer to expose at least a portion of the patterned resist layer. Removing the portion of the first layer to expose at least a portion of the patterned resist layer includes performing an etching of the first layer. The substrate is a substrate that is transparent to visible light, infrared light, near-infrared light, or short-wave infrared light. The patterned resist layer includes physically contacting a mold to the resist layer, where the mold includes a pattern, pressing the mold and the substrate together, curing the resist, and separating the mold from the resist layer to form the patterned resist layer.

[0006] Implementations of the method can include one or more of the following. The mold includes a flexible material. The curved surface includes a convex surface relative to the substrate. The curved surface includes a concave surface relative to the substrate. The curved surface includes a combination of a plurality of convex surfaces relative to the substrate. The curved surface includes a combination of a plurality of concave surfaces relative to the substrate. The curved surface includes a concave surface relative to the substrate and a convex surface relative to the substrate. The resist is a thermally cured resist or a UV cured resist. Removing the residual resist material includes using a dry etching technique. The first layer includes amorphous silicon, niobium oxide, titanium oxide, aluminum oxide, hafnium oxide, silicon oxide, strontium titanate, tantalum oxide, gadolinium oxide, zirconium oxide, gallium oxide, or vanadium oxide.

[0007] In one aspect, the disclosure describes an apparatus including a substrate including a curved surface and one or more metastructures on the curved surface. The apparatus can include one or more metastructures on the curved surface, each metastructure having a diameter of up to 1000 nanometers. The details of one or more implementations of the application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the application will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 Embodiments of a patterned resist on a curved surface formed using photolithography are shown.

[0009] Figures 2A to 2I A method of fabricating an apparatus is shown.

[0010] Figures 3A to 3C Embodiments of a substrate having a curved surface are shown.

[0011] Figures 4A to 4K A method of fabricating an apparatus is shown.

[0012] Like reference numbers in the various drawings indicate like elements. DETAILED DESCRIPTION

[0013] A metasurface includes a surface having meta-atoms (in some cases also referred to as nanostructures) arranged to interact with light in a particular way. For example, a metasurface that can be referred to as a metastructure can be a surface having a distributed array of nanostructures. The nanostructures can individually or collectively interact with a light wave. For example, the nanostructures or other meta-atoms can change a local amplitude, a local phase, or both, of an incident light wave. In some cases, a metasurface can perform optical functions that are traditionally performed by refractive and / or diffractive optical elements. In some cases, the meta-atoms can be arranged in a pattern such that the metasurface functions as an optical element such as, for example, a lens, an array of lenses, a beam splitter, a grating, a grating coupler, a fan-out grating, a diffuser, or other optical element. In other cases, the meta-atoms need not be arranged in a pattern. In some implementations, a metasurface can perform other functions including polarization control, negative refractive index transmission, beam deflection, vortex generation, polarization conversion, optical filtering, and plasmonic optical functions.

[0014] A meta-atom can be a subwavelength nanostructure, which indicates that the structure has a lateral dimension parallel to the surface of the substrate that is smaller than the wavelength of light to be incident on the structure. For example, in some cases, a nanostructure can be in the form of a nanoscale feature having a dimension less than 1 micrometer. By adjusting the geometry of the meta-atom / cell elements formed on the metastructure, optical devices having different properties can be formed.

[0015] The present disclosure describes techniques that facilitate forming metastructures on curved surfaces. When used to form structures on curved surfaces, lithography techniques such as maskless lithography, ultraviolet lithography, deep ultraviolet lithography, and electron beam lithography can have one or more drawbacks. For example, structures formed by such techniques can result in poor contact between a hard lithography mask or reticle and the curved surface of the substrate, or in some cases, the curved surface can interfere with the focus. In some cases, the resolution achievable by those techniques is limited and / or the resulting structures are not aligned normal to the surface of the substrate. Due to these and / or other drawbacks, devices formed using such lithography processes can exhibit poor performance. The techniques described herein encompass methods of forming metastructures on curved surfaces that, in some cases, can provide metastructures having improved contact, surface uniformity, resolution, and / or focus, among other potential advantages. As described in more detail below, metastructures can be formed normal to the curved surface, i.e., the height of each structure extends in a direction parallel to the normal of the curved surface. In some cases, metastructures having diameters of 30 nanometers to 500 nanometers can be formed. In other cases, metastructures having diameters up to 1000 nanometers can be formed.

[0016] Figure 1 Embodiments of patterned resist on a curved surface formed using lithography are shown. As Figure 1As shown, the substrate 102 has a curved surface 106. The substrate 102 can be composed of a support substrate 104 in which the curved surface 106 is formed. The curved surface 106 can correspond to, for example, a lens, such as a microlens. The microlens can be part of a microlens array. In some implementations, the curved surface 106 can correspond to a collimating lens, an imaging lens, a focusing lens, a beam shaper. In other implementations, the curved surface 106 can correspond to an aspheric lens or an asymmetric lens, for example, a lenticular lens. A resist layer 108 in which structures 110 are patterned is disposed on the curved surface 106. While the curved surface 106 is shown as being convex with respect to the substrate 102, the curved surface can be concave with respect to the substrate 102, or can include both convex and concave features. As explained above, lithography techniques such as maskless lithography, ultraviolet lithography, deep ultraviolet lithography, and electron beam lithography can exhibit limitations when used to pattern small structures on a curved surface. For example, as shown, each of the one or more structures 110 formed in the patterned resist 108 is not aligned normal to the curved surface 106. In more detail, as shown, the structure 110A is shaped as a rectangular pillar whose height extends along a direction normal to the curved surface 106. On the other hand, the structures 110B and 110C each have a height that is not aligned with a direction normal to the curved surface 106. When subsequent etching or deposition steps are performed with the resist 108 as a mask, the desired pattern can not be faithfully transferred to the underlying substrate. In the case of an optical element, such limitations can result in the formation of a device that exhibits undesirable properties, for example, poor resolution, poor focus, low efficiency, or excessive stray light, among others. Figure 1 Figure 1

[0017] Figures 2A to 2I Figure 2A ​​​As shown, a substrate 202 with a curved surface 206 is provided. In some implementations, the curved surface 206 is formed in the substrate 202. In these implementations, the curved surface 206 and the substrate are formed of the same material. Alternatively, the substrate 202 may include a support substrate 204 in which the curved surface 206 is formed. In these implementations, the support substrate 204 and the curved surface 206 may be formed of different materials. For example, the support substrate 204 may be formed of silicon, germanium, gallium arsenide, borosilicate glass, fused silica, borosilicate glass, or any other suitable material. The curved surface 206 may be formed of a UV-curable polymer or a thermoplastic. As explained herein, the curved surface 206 may include a convex surface, a concave surface, or a combination of convex and concave surfaces. The curved surface 206 may be formed by nanoimprint lithography (NIL) using, for example, a mold. Depending on the application in which a meta-optical structure is formed on the surface is used, substrate 202 / 204 can be selected to be optically transmissive to radiation of a specific wavelength or wavelength range (e.g., infrared (IR), near-infrared (NIR), short-wave infrared (SWIR), or visible light). For example, substrate 202 and / or support substrate 204 can be formed of borosilicate glass or fused silica, but other materials can be used. In some cases, substrate 202 may include a material that reflects incident light, such as metal or other mirrors.

[0018] Next, as Figure 2B As shown, at least one resist layer 208 is formed on the curved surface 206 of the substrate 202. In some implementations, one or more resist layers may be formed on the curved surface 206. In some cases, the at least one resist layer 208 comprises a nanoimprint resist, which is a UV-curable resist. In other embodiments, the at least one resist layer 208 comprises a thermosetting resist. In some implementations, the resist layer 208 is a high-refractive-index resist, including but not limited to polymethyl methacrylate, polyurethane, or polycarbonate. The resist layer 208 can be applied using different deposition techniques. For example, in some cases, the resist layer 208 is applied by spin coating, spray coating, or injection dispensing.

[0019] like Figure 2CAs shown, the resist layer 208 on the curved surface 206 is patterned using imprint lithography, in some cases, using nano-imprint lithography to pattern the resist layer 208. For example, in some implementations, a mold having a desired pattern is brought into physical contact with the resist layer 208 on the curved surface 206 of the substrate 202. The mold can be formed of a flexible material, such as a UV-curable polymer or a thermoplastic, and can have the ability to stretch and deform and to return to its original shape after deformation. For example, the mold can be formed of a silicone rubber, a polyurethane elastomer, or a natural rubber, or any other suitable elastomeric material. Pressure can be applied to the mold and the resist layer 208 in order to transfer the mold pattern to the resist layer 208. The flexible mold deforms under pressure to allow the mold to conform to the shape of the curved surface 206, thereby ensuring good contact between the mold and the substrate of the surface 206, which results in accurate replication of the desired pattern. Application of the mold to the resist layer 208 can result in the formation of areas of the resist layer 208 that are thinner and other areas of the resist layer 208 that are thicker. The mold can include a pattern that is complementary to the pattern of the meta-structure desired to be formed on the curved surface 206. For example, the mold pattern can include a pattern of repeating structures, such as a one-dimensional line grating or a two-dimensional line grating. The mold pattern can include a square, rectangular, trapezoidal, diamond, star, lozenge, arrowhead, or horseshoe pattern.

[0020] The resist layer 208 is then cured. In some cases, where the resist layer 208 is formed of a UV-curable resist, the mold and the substrate 202 are exposed to UV light for a period of time sufficient to cure the resist. In other cases, where the resist layer 208 is formed of a heat-curable resist, the mold and the substrate 202 are exposed to heat to cure the resist. After the resist is cured, the mold is separated from the substrate 202 to expose the patterned layer of resist 210 on the substrate 202. In some implementations, when a high refractive index nano-imprint resist having a refractive index in the range of 1.6-2.0 is used, the patterned resist 210 on the curved surface 206 can be the final device or can be further processed. For example, the patterned resist 210 can include a distributed array of meta-atoms forming a one- or two-dimensional grating on the curved surface 206. Alternatively or additionally, the patterned resist 210 can include one or more lens elements.

[0021] In contrast to UV lithography or other pattern transfer techniques, the use of imprint lithography on a curved surface with a flexible mold has the advantage that the flexible mold can conform to the curved surface 206, thereby allowing accurate reproduction of the pattern on the curved surface 206. In contrast, when other lithography techniques are used, such as UV exposure of a resist through a mask, the pattern transferred to the resist can be skewed, can be misaligned, and / or can not conform to the substrate surface, which in turn can adversely affect the shape and performance of the device fabricated.

[0022] Next, as shown in Figure 2D residual resist can be removed. The residual resist can include, for example, resist located between structures imprinted in the resist. For example, in Figure 2D , the areas between protrusions 211 formed by imprinting can include residual resist, which should be removed to expose the substrate before the next step in the fabrication. Alternatively, or additionally, the residual resist can include a thin resist layer surrounding the patterned area. The residual resist can be removed using a non-directional or isotropic etching technique, such as a dry etching technique including, for example, a plasma etch. In some implementations, other suitable non-directional etching techniques can be used. In some implementations, when a high refractive index nanoimprint resist having a refractive index range of 1.6-2.0 is used, after removing the residual resist from the patterned resist 210 on the curved surface 206, as shown in Figure 2D , the final device can be or can be further processed.

[0023] As shown in Figure 2E , a first layer 212 is then deposited on the patterned resist 210. In some cases, the first layer 212 can be deposited by atomic layer deposition (ALD). For example, in some cases, the first layer 212 can include an oxide material having a high refractive index. In some cases, the first layer 212 can include titanium dioxide, amorphous silicon, niobium oxide (pentoxide), aluminum oxide, hafnium oxide, silicon oxide, strontium titanate oxide, tantalum oxide, gadolinium oxide, zirconium oxide, gallium oxide, vanadium oxide, and other materials. In some implementations, the first layer 212 can include a metal. Advantages of using ALD to deposit the first layer 212 can include, for example, applying a conformal coating over the three-dimensional structures of the patterned resist layer 210, including high-aspect-ratio geometries, geometries with sharp edges, precise film thickness control, and high-quality films. In particular, in some implementations, using imprint lithography in conjunction with ALD can allow relatively complex geometries to be formed, including, for example, but not limited to, geometries having shapes with cross-sections that are square, rectangular, trapezoidal, rhomboidal, star-shaped, rhomboidal, arrowhead-shaped, horseshoe-shaped, and geometries used in polarization-related devices. In some implementations, the thickness of the deposited material fills the areas between protrusions in the patterned resist layer 210, such that the thickness of the deposited material in those areas is greater than the thickness of adjacent protrusions in the patterned resist layer 210. While in Figure 2EThe diagram shows a single layer of material 212 formed on a patterned resist layer 210, but multiple layers of material can be formed on the patterned resist layer 210. These multiple layers may include the same material or a combination of different materials. For example, in some implementations, the multiple layers may include alternating stacks between a first material and a second material. The first material and the second material may have different refractive indices, for example, alternating between materials having a high refractive index and a low refractive index.

[0024] Next, as Figure 2F As shown, an optional etch-back of the first layer 212 is performed. In some cases, wet or dry etching techniques can be used to etch back a portion of the first layer 212. When the first layer 212 is etched back, material deposited on the surface of the protrusions in the patterned resist layer 210 can be removed to expose portions of the underlying patterned resist layer 210.

[0025] After the optional etchback, as Figure 2G As shown, the patterned resist layer 210 is removed, leaving a patterned first layer 214 on the curved surface. The patterned resist layer 210 can be removed using wet etching techniques employing solvents and / or oxidizing chemicals, or using dry etching techniques such as plasma etching or reactive ion etching. As described herein, the patterned layer 214 formed on the curved surface 206 may include one or more metastructures. For example, metastructures may include nanostructures such as pillars, columns, lines, or other shapes. Due to the conformal nature of imprint lithography and ALD processes during the formation of metastructures, metastructures can be formed such that the height of each structure extends perpendicular to the surface of the curved substrate on which it is located. In some implementations, when the patterned resist 210 is removed, such as... Figure 2G As shown, the resulting structure can be a final device or can be further processed.

[0026] Next, as Figure 2HAs shown, an optional encapsulation material 216 is formed over the patterned layer 214 to encapsulate the one or more metastructures formed on the curved surface 206. In some cases, the encapsulation material 216 is a spin-on glass material or a polymer. In some cases, a polymer can include a photoresist material that is spun on and then cured can be used as an encapsulation material. The encapsulation material 216 can act as a protective layer that can help protect the metastructures from physical, chemical, and / or environmental degradation. In some cases, the thickness of the encapsulation material 216 is at least the thickness of the structures formed in the patterned layer 214. In some cases, the thickness of the encapsulation material 216 is at least twice the wavelength of light for the application in which the metastructure is to be used. In some cases, the encapsulation material 216 can be a material having a refractive index of 1.2-2.1. In some implementations, when forming the encapsulation material 216 over the patterned layer 214, Figure 2H The resulting structure as shown can be a final device or can be further processed.

[0027] In some implementations, as Figure 2I As shown, an optional reflective or anti-reflective coating 218 is formed. The reflective or anti-reflective coating 218 can be formed on the surface of the encapsulation material 216 or, if no encapsulation material is present, on the surface of the one or more metastructures of the patterned layer 214. The coating 218 can be formed using, for example, physical vapor deposition techniques such as thermal evaporation, e-beam evaporation, or sputtering, etc. In some implementations, the coating 218 can be formed using ALD. In some implementations, the coating 218 can be formed on the backside surface of the substrate 202.

[0028] As explained herein, the curved surface 206 is not limited to a surface that is convex relative to the substrate 204. Figures 3A to 3C Embodiments are shown of different types of substrates having curved surfaces. Figure 3A A substrate 302A is depicted having a surface that is both convex and concave relative to the substrate 304A. Figure 3B A substrate 302B is depicted having a surface 306B that is concave relative to the substrate 304B. Figure 3C A substrate 304C is depicted that includes a plurality of lenses arranged in an array. As explained herein, a substrate can be understood to include a support layer in which a curved surface is formed.

[0029] Figures 4A to 4K Manufacturing steps are shown for forming a device that includes one or more metastructures on a curved surface that includes a high refractive index refractive medium layer. Utilizing a high refractive index medium layer provides the advantage of being able to make metastructures with higher transmittance and being able to bend light over a greater range of angles. When used to make optical devices, the high refractive index medium helps improve the performance of the optical device by increasing optical efficiency. Reference is made toFigures 4A to 4K The fabrication process described utilizes a subtractive process to create a pattern on a curved surface. The subtractive process results in the formation of precisely formed, well-defined, and high resolution metastructures.

[0030] As shown in Figure 4A A substrate 402 is provided. The substrate 402 can include a curved surface 406. While shown as being convex with respect to the substrate 402, the curved surface 406 can alternatively be concave, include a combination of convex and concave features. The substrate 402 can include a support layer 404 in which the curved surface 406 is formed. The material of the substrate 402 and / or the support layer 404 can be selected to be optically transmissive with respect to radiation of a particular wavelength or range of wavelengths (e.g., infrared (IR), near infrared (NIR), short wave infrared (SWIR), visible light), depending on the application in which the device will be used.

[0031] As shown in Figure 4A A high refractive index material layer 408 can be disposed on the substrate 402, e.g., on top of the curved surface 406. In some implementations, the high refractive index layer 408 is disposed directly on the substrate surface, e.g., directly on the support layer 404. The high refractive index layer 408 can include a material such as amorphous silicon, titanium dioxide, tantalum pentoxide, niobium oxide (pentoxide), aluminum oxide, hafnium oxide, silicon oxide, strontium titanate, tantalum oxide, gadolinium oxide, zirconium oxide, gallium oxide, vanadium oxide, or silicon nitride. The high refractive index material layer 408 can be formed using different deposition techniques, such as physical vapor deposition (e.g., thermal evaporation or sputtering), electron beam deposition, and the like processes.

[0032] In some implementations, a hard mask layer 410 is disposed over the high refractive index layer 408. The hard mask layer 410 can be used in later processing to transfer a pattern to the underlying high refractive index layer 408. The hard mask layer 410 can include a metal such as, but not limited to, chromium, aluminum, or titanium. In some implementations, the hard mask layer 410 can include tungsten, titanium nitride, silicon nitride, or silicon dioxide. In some implementations, the hard mask layer 410 can be a composite hard mask composed of multiple layers of different materials. The hard mask 410 can be formed using different deposition techniques, such as chemical vapor deposition, atomic layer deposition, physical vapor deposition (e.g., thermal evaporation or sputtering), electron beam deposition, and the like processes.

[0033] Next, as shown in Figure 4BAs shown, at least one resist layer 412 is formed on the hard mask 410. In some cases, the at least one resist layer 412 comprises a nanoimprint resist, which is a UV-curable resist. In other embodiments, the at least one resist layer 412 comprises a thermosetting resist. The resist layer 412 can be applied by different deposition techniques. For example, in some cases, the resist layer 412 is applied by spin coating, spray coating, or injection dispensing.

[0034] like Figure 4C As shown, imprint lithography is used to pattern the resist layer 412 on the curved surface 406. (See above reference.) Figures 2A to 2I For example, a mold with the desired pattern is brought into physical contact with the resist layer 412. The mold may be formed of a flexible material, such as a UV-curable polymer or thermoplastic, and may have the ability to stretch and deform, and to return to its original shape after deformation. For example, the mold may be formed of silicone rubber, polyurethane elastomer, or natural rubber, or any other suitable elastomeric material. Pressure may be applied to the mold and the resist layer 412 to transfer the mold pattern to the resist layer 412. The flexible mold deforms under pressure to allow the mold to conform to the shape of the curved surface 406, thereby ensuring good contact between the mold and the substrate of the surface 406, which results in accurate replication of the desired pattern. Applying the mold to the resist layer 412 may result in the formation of thinner areas and thicker areas of the resist layer 412. The mold may include a pattern complementary to the pattern of the metastructures to be formed on the curved surface 406. For example, the mold pattern may include a pattern of repeating structures, such as a one-dimensional or two-dimensional line grating. The mold pattern may include concentric circles or other patterns, such as squares, rectangles, trapezoids, rhombuses, stars, diamonds, arrows, or horseshoes.

[0035] The resist layer 412 is then cured. In some cases, where the resist layer 412 is formed of a UV-curable resist, the mold and substrate 402 are exposed to UV light for a time sufficient to cure the resist. In other cases, where the resist layer 412 is formed of a heat-curable resist, the mold and substrate 402 are exposed to heat to cure the resist. After the resist has cured, the mold is separated from the substrate 402 to expose a patterned layer of resist 414 on the substrate 402.

[0036] Next, as Figure 4D As shown, any residual resist is removed. Residual resist may include, for example, resist located between structures imprinted in the resist. Non-directional or isotropic etching techniques, such as dry etching techniques including, for example, plasma etching, can be used to remove residual resist. In some implementations, other suitable non-directional etching techniques may be used.

[0037] Removing the residual resist can result in portions 415 of the hard mask 410 being exposed. As shown, the exposed portions of the hard mask 410 are removed. By removing the exposed portions of the hard mask 410, the pattern from the resist layer 412 is transferred to the underlying hard mask layer 410, and then portions of the high refractive index layer 408 are exposed. The portions of the hard mask 410 can be removed using a wet or dry etch process that does not remove or minimally removes the high refractive index layer. Preferably, in some implementations, the exposed portions of the hard mask 410 are removed using an anisotropic etch so that the patterned resist features are not undercut. Figure 4E

[0038] As shown, the remaining portions of the patterned resist layer 414 are removed, leaving a patterned mask layer 416 on the high refractive index layer 408. The patterned resist layer 412 can be removed using a wet or dry etch that does not remove or minimally removes the exposed portions of the underlying high refractive index layer 408. Figure 4F

[0039] As shown, when a thin hard mask 410 is used, the exposed portions of the high refractive index layer 408 are removed, while the portions of the high refractive index layer 408 under the hard mask 410 are protected from removal and remain on the curved surface. In some implementations, the thin hard mask 410 can have a thickness of 5 nanometers to 20 nanometers. The portions of the high refractive index layer 408 can be removed using a directional etch technique, such as reactive ion etching, inductively coupled plasma etching, or deep reactive ion etching. In some implementations, other suitable directional etch techniques can be used. In some cases, a thick hard mask 410 is used, as shown, and the directional etch of the high refractive index material 408 can result in a shadowing effect, where some areas have reduced exposure or are completely shadowed. In some implementations, the thick hard mask 410 can have a thickness of 20 nanometers to 200 nanometers. Figure 4G Figure 4H

[0040] As shown, the remaining portions of the patterned resist layer 414 are removed, leaving a patterned mask layer 416 on the high refractive index layer 408. The patterned resist layer 412 can be removed using a wet or dry etch that does not remove or minimally removes the exposed portions of the underlying high refractive index layer 408. Figure 4I ​​​​As shown, the remaining portion of the hard mask 410 is removed by etching. In some cases, wet etching can be used to remove the hard mask portion 410. In other cases, dry etching can be used to remove the hard mask segment 410. In some implementations, other suitable etching techniques can be used. When the hard mask portion 410 is removed by etching, a patterned layer 414 is formed on the curved surface 406 and may include a plurality of elemental optical structures 416. Each of the plurality of elemental structures 416 has a cross-sectional width of 30 nanometers to 500 nanometers. In some embodiments, when the plurality of elemental structures are formed in a circular or cylindrical shape, the diameter of each structure is 30 nanometers to 500 nanometers. In some implementations, the plurality of elemental structures may have a diameter of up to 1000 nanometers. The patterned layer 414 may be formed with a pattern complementary to the mold used for patterning the resist layer 412. In some implementations, when the hard mask 410 is removed, Figure 4I The resulting structure can be a final device or can be further processed.

[0041] Next, as Figure 4J As shown, an optional encapsulation material 418 is formed over the patterned layer 416 to encapsulate one or more substructures formed on the curved surface 406. In some cases, the encapsulation material 418 is a spin-coated glass material or a polymer. In some cases, the polymer may include a photoresist material that is spin-coated and then cured, and can be used as an encapsulation material. The encapsulation material 418 can serve as a protective layer that helps protect the substructures from physical, chemical, and / or environmental degradation. In some cases, the thickness of the encapsulation material 418 is at least the thickness of the structure formed in the patterned layer 416. In some cases, the thickness of the encapsulation material 418 is at least twice the wavelength of the light used in the application in which the substructures are used. In some cases, the encapsulation material 418 has a refractive index of 1.2-2.1. In some implementations, when the encapsulation material 418 is formed over the patterned layer 416, such as Figure 4J As shown, the resulting structure can be a final device or can be further processed.

[0042] Then, as Figure 4K As shown, an optional reflective or antireflective coating 420 is formed. The reflective or antireflective coating 420 may be formed on the surface of the encapsulation material 418, or, if no encapsulation material is present, on the surface of one or more metastructures of the patterned layer 416. The coating 420 may be formed using, for example, physical vapor deposition techniques, such as thermal evaporation, electron beam evaporation, or sputtering. In some implementations, the coating 420 may be formed using an ALD (Alternating Current Deposition). In some implementations, the coating 420 may be formed on the back surface of the substrate 402.

[0043] A number of implementations of the application have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the application. Accordingly, other implementations are within the scope of the following claims.

Claims

1. A method comprising: providing a substrate comprising a curved surface; forming a resist layer on the curved surface; patterning the resist layer on the curved surface using imprint lithography to provide a patterned resist layer; removing residual resist material from the patterned resist layer; forming a first layer on the patterned resist layer by atomic layer deposition; and removing the patterned resist layer to form a patterned first layer on the curved surface. The patterned first layer on the curved surface comprises meta-structures.

2. The method of claim 1, wherein, The meta-structures comprise one or more structures formed perpendicular to the curved surface, and a height of each of the one or more meta-structures is formed perpendicular to the curved surface.

3. The method of claim 2, wherein, Each of the one or more structures formed perpendicular to the curved surface has a diameter of 30 nanometers to 500 nanometers.

4. The method of claim 3, wherein, 5. The method of claim 1, further comprising: encapsulating the patterned first layer in an encapsulation material. The encapsulation material comprises a spin-on glass or a polymer.

6. The method of claim 5, wherein, 7. The method of claim 1, comprising removing portions of the first layer to expose at least a portion of the patterned resist layer. Removing the portions of the first layer to expose at least a portion of the patterned resist layer comprises performing an etch of the first layer.

8. The method of claim 7, wherein, The substrate is a substrate that is transparent to visible light, infrared light, near infrared light, or short wave infrared light.

9. The method of any of the preceding claims, wherein, Patterning the resist layer comprises:

10. The method of any of the preceding claims, wherein, physically contacting a mold to the resist layer, wherein the mold comprises a pattern; pressing the mold and the substrate together; curing the resist; and separating the mold from the resist layer to form the patterned resist layer. The mold comprises a flexible material.

11. The method of claim 10, wherein, The curved surface comprises a convex surface relative to the substrate.

12. The method of any of the preceding claims, wherein, The curved surface comprises a concave surface relative to the substrate.

13. The method of any one of claims 1 to 9, wherein, The curved surface comprises a combination of multiple convex surfaces relative to the substrate.

14. The method of any one of claims 1 to 9, wherein, The curved surface comprises a combination of multiple concave surfaces relative to the substrate.

15. The method of any one of claims 1 to 9, wherein, The curved surface comprises a concave surface relative to the substrate and a convex surface relative to the substrate.

16. The method of any one of claims 1 to 9, wherein, The resist is a heat-curable resist or a UV-curable resist.

17. The method of claim 1, wherein, Removing the residual resist material comprises using a dry etching technique.

18. The method of claim 1, wherein, The first layer comprises amorphous silicon, niobium oxide, titanium oxide, aluminum oxide, hafnium oxide, silicon oxide, strontium titanate, tantalum oxide, gadolinium oxide, zirconium oxide, gallium oxide, or vanadium oxide.

19. The method of claim 1, wherein, 20. An apparatus comprising: a substrate comprising a curved surface; and one or more meta-structures on the curved surface. The one or more meta-structures on the curved surface have a diameter of up to 1000 nanometers.

21. The apparatus of claim 20, wherein, ​

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