Meta-structure containing meta-atoms with sidewalls inclined outward

Abstract

The present disclosure describes a metastructure optical element (MOE), a method for manufacturing the MOE, and a device incorporating the MOE. The MOE includes meta-atoms having outwardly inclined sidewalls. The meta-atoms can have sidewalls that are substantially perpendicular along an upper section of the meta-atoms and that are outwardly inclined along a lower section of the meta-atoms.

Description

Technical Field

[0001] This disclosure relates to a metastructure optical element (MOE).

Background Art

[0002] Advanced optical elements can include a metasurface that refers to a surface having distributed nanostructures (e.g., meta-atoms) arranged to interact with light in a specific way. For example, a metasurface, which may also be referred to as a metastructure, can be a surface having a distributed arrangement of nanostructures. The nanostructures can interact with light waves individually or collectively. For example, the nanostructures or other meta-atoms can change the local amplitude, local phase, or both of the incident light wave.

[0003] An MOE can include a plurality of meta-atoms. The manufacture of an MOE can sometimes involve etching the meta-atoms in a hierarchy. In some cases, the meta-atoms are present in different groups within the MOE, and the different groups of meta-atoms can have different etching characteristics. An MOE composed of two or more groups having different etching characteristics can be particularly difficult to manufacture using known etching methods.

Summary of the Invention

Means for Solving the Problems

[0004] This disclosure describes an MOE, a method for manufacturing an MOE, and a device incorporating the MOE. The MOE includes meta-atoms having outwardly inclined sidewalls. In particular, the meta-atoms can have sidewalls that are substantially perpendicular along an upper section of the meta-atoms and outwardly inclined along a lower section of the meta-atoms (i.e., the portion of the meta-atoms closer to the surface of the substrate that supports the meta-atoms).

[0005] For example, in one aspect, the present disclosure describes an apparatus including a substrate that supports a plurality of meta-atoms, each having at least one respective outer sidewall. The upper portion of at least one sidewall of each meta-atom is perpendicular to the surface of the substrate that supports the meta-atom. The lower portion of at least one sidewall of each meta-atom is inclined outwardly and the lower portion is adjacent to the interface between the meta-atom and the surface of the substrate.

[0006] Some implementations can include one or more of the following features. For example, in some cases, the lower portion of at least one sidewall of each meta-atom is inclined outwardly or curved outwardly. In some examples, the lower portion of at least one sidewall of each meta-atom is concave. The diameter of each respective one of the meta-atoms at the lower portion can be larger than the diameter of the meta-atom at the upper portion of the meta-atom. In some implementations, the lower portion of at least one sidewall of each meta-atom extends less than 50% of the height of the meta-atom, and in some cases, less than 5 percent of the height of the meta-atom.

[0007] In some implementations, the plurality of meta-atoms includes a first group of meta-atoms each having an upper portion with a first diameter and a second group of meta-atoms each having an upper portion with a second diameter different from the first diameter. In some implementations, the plurality of meta-atoms includes a first group of meta-atoms arranged at a first density and a second group of meta-atoms arranged at a second density different from the first density.

[0008] In some implementations, the substrate is composed of glass or fused silica and / or the meta-atoms are composed of silicon, titanium oxide, zinc oxide, zinc aluminum oxide, or niobium oxide.

[0009] The present disclosure also describes a method that includes providing a structure including a layer of hierarchical material on a substrate, the structure further including a mask on the hierarchical material, the mask defining regions of the hierarchical material in which meta-atoms are formed, each of the respective meta-atoms having at least one sidewall. The method further includes performing an etching process including a first etching stage and a second etching stage. The first etching stage removes a portion of the hierarchical material such that trenches are etched into the hierarchical material to form upper sections of at least one sidewall of each of the meta-atoms, the upper sections being perpendicular to the surface of the substrate. The second etching stage removes a further portion of the hierarchical material to form lower portions of at least one sidewall of each of the meta-atoms, the lower portions being adjacent to an interface between the meta-atoms and the surface of the substrate and sloping outwardly.

[0010] Some implementations can include one or more of the following features. For example, in some cases, each of the first and second etching stages is part of a plasma etching process. In some cases, the first etching stage includes plasma etching having an average flow rate of a passivation gas and an average flow rate of an etchant gas, and the second etching stage includes plasma etching in which at least one of the average flow rate of the passivation gas or the average flow rate of the etchant gas is different from that of the first etching stage. For example, in some cases, in the second etching stage, the average flow rate of the passivation gas is greater than the average flow rate of the passivation gas in the first etching stage. In some cases, in the second etching stage, the average flow rate of the etchant gas is less than the average flow rate of the etchant gas in the first etching stage. In some cases, at least one of the plasma power or the bias to the substrate in the second etching stage is less than that in the first etching stage.

[0011] In some implementations, the first etching stage includes plasma etching and the second stage includes isotropic etching.

[0012] In some implementations, the method further includes removing the mask. In some implementations, outwardly sloped sidewalls can help improve the mechanical stability of some or all of the meta-atoms.

[0013] Other aspects, features, and advantages will become readily apparent from the following detailed description, the accompanying drawings, and the claims.

Brief Description of the Drawings

[0014]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 2

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Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 6C

Figure 6D

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0015] Figures 1A - 1D illustrate examples of some stages of the manufacturing process of one or more metastructure optical elements (MOEs). As shown in Figures 1A - 1D, the metastructure optical assembly can be an intermediate product created during the manufacture of one or more MOEs. The metastructure optical assembly 100 includes a mask 102 disposed on a layer 104. The layer 104 is then disposed on a substrate 108. The metastructure optical assembly 100 can take the form of, for example, a wafer having a large lateral dimension with many MOEs.

[0016] With the mask 102 in place, the layer 104 can be etched to form meta-atoms 116 separated by regions 110 where the layer material has been removed as a result of the etching. A given MOE can include two or more groups 112, 114 of meta-atoms, and these groups may exhibit different etching characteristics from each other, for example, as a result of having different densities. That is, even if the meta-atoms 116 within each of the groups 112, 114 have the same pitch, the diameters of the meta-atoms within the group can be different from each other. For example, the meta-atoms 116 within the first group 112 can have a diameter D1 that is different from (e.g., larger than) the diameter D2 of the meta-atoms 116 within the second group 114 (see Figures 1B and 1C). As a result of the different diameters and thus different densities, the first group 112 of meta-atoms can have a first etching characteristic, and the second group 114 of meta-atoms can have a different second etching characteristic 114.

[0017] Furthermore, as shown in FIG. 1D, as a result of different etching characteristics, some of the meta-atoms 116 within at least one of the groups (e.g., group 114) may be damaged, destroyed, or otherwise impaired during the etching process because the etching rate differs between the two groups 112 and 114. For example, meta-atoms 116 within the second group 114 having a relatively small diameter (D2) and / or a lower density have a higher risk of being damaged by the forces reflected by the substrate during the etching process. The reflected force may, for example, slightly cut off the bottom of the meta-atoms within the second group 114, thereby making the meta-atoms physically unstable as shown in FIG. 1D.

[0018] To reduce the possibility that the meta-atoms become physically unstable, the portion of the meta-atom side closer to the substrate can be slightly inclined outward. That is, as shown in the MOE 200 of FIG. 2, the upper part 218 of each meta-atom 216 has a substantially vertical wall (i.e., a side wall substantially perpendicular to the surface of the substrate 208), but the side wall along the lower part 220 of each meta-atom 216 (i.e., closer to the substrate 208) is inclined outward. For example, in some cases, the side wall along the lower part 220 may taper (e.g., incline) from the vertical side wall such that the diameter of the meta-atom 216 at the interface with the substrate 208 is larger than the diameter of the meta-atom at its upper (free) end 222. In some cases, as shown in FIG. 3, the side wall along the lower part 220 of the meta-atom 216 may be curved (e.g., concave).

[0019] In an exemplary implementation, the upper portion of each meta-atom having a substantially vertical sidewall may represent at least 50% of the height of the meta-atom. Thus, the outwardly inclined portion of the sidewall at the lower portion of the meta-atom generally extends to less than 50% of the height of the meta-atom. In some cases, the outwardly inclined portion of the sidewall extends to 25% or less of the height of the meta-atom, and in some cases 5% or less of the height of the meta-atom. Thus, for a meta-atom having a height of about 500 nm, the outwardly inclined portion of the sidewall can have a height of less than 250 nm, in some cases 125 nm or less, or in some cases 25 nm or less.

[0020] MOE200 can include a few meta-atoms, or dozens, hundreds, thousands, millions, or even hundreds of millions of meta-atoms, depending on the application. MOE200 can include, for example, two or more groups of meta-atoms having meta-atoms of different respective diameters or different respective densities. Thus, in some cases, the sum of the areas (e.g., determined via the meta-atom diameter) of the individual meta-atoms 216 within a particular group 212 divided by the area of the MOE occupied by that particular group can be different from that of another group 214 of meta-atoms 216.

[0021] In some cases, one or more of the meta-atoms 216 in groups 212, 214 have sidewalls that slope outward as described above. In some cases, only a subset of the meta-atoms of a particular MOE can have sidewalls that slope outward. For example, in some cases, meta-atoms having a relatively small diameter and / or lower density (e.g., group 214) can have sidewalls that slope outward as described above, while meta-atoms having a relatively large diameter and / or higher density (e.g., group 212) can have substantially vertical sidewalls that extend from the upper (free) end 222 of the meta-atom to the lower end that contacts the substrate 208. In other cases, meta-atoms having a relatively large diameter and / or higher density (e.g., group 212) can have sidewalls that slope outward as described above, while meta-atoms having a relatively small diameter and / or lower density (e.g., group 214) can have substantially vertical sidewalls that extend from the upper (free) end 222 of the meta-atom to the lower end that contacts the substrate 108.

[0022] The substrate 208 can be composed of, for example, glass or fused silica. The meta-atoms 216 can be composed of, for example, silicon (e.g., polysilicon, amorphous silicon, crystalline silicon, or silicon nitride), titanium oxide, zinc oxide, aluminum zinc oxide, or niobium oxide. The meta-atoms 216 can have, for example, a circular, square, or donut-shaped cross-section. In some implementations, other materials and shapes of the meta-atoms 216 or the substrate 208 can be used.

[0023] MOEs having sidewalls that are substantially perpendicular along the upper part (i.e., near their free ends) and slope outward along the lower part (i.e., adjacent to the interface with the substrate) can be fabricated in various ways. Generally, as shown in FIG. 4, the first stage (402) of etching removes a portion of the layered material such that trenches having substantially perpendicular sidewalls are etched into the layered material to form the upper sections of each respective meta-atom, and the second stage (404) of etching further removes the layered material to form sidewalls that slope outward along the lower sections of each respective meta-atom (i.e., the portion of the meta-atom closer to the surface of the substrate that supports the meta-atom).

[0024] According to some implementations, the meta-atoms are formed using an etching process (e.g., plasma etching) that includes a passivation gas and an etchant gas. The etching process is split into at least two stages, and the ratio of the average flow rate of the passivation gas to the average flow rate of the etchant gas in one stage is different from the ratio in another stage. For example, as shown in FIG. 5, in the first stage (502), plasma etching can include an average flow rate of the passivation gas and an average flow rate of the etchant gas. During a subsequent second stage (504), the average flow rate of the passivation gas can be increased and / or the average flow rate of the etchant gas can be decreased relative to the average flow rate used during the first stage. Exemplary processes are described below in connection with FIGS. 6A - 6C.

[0025] FIG. 6A shows an example of a structure including a mask 202 disposed on a layer 204 of a material in which meta-atoms are formed. The layer 204 may be composed of, for example, polysilicon, amorphous silicon, crystalline silicon, titanium oxide, silicon nitride, zinc oxide, zinc aluminum oxide, or niobium oxide. The mask 202 can be, for example, an organic (e.g., amorphous carbon) or inorganic (e.g., SiN, SiON, TiN) hard mask. In some cases, the mask 202 may be composed of a metal such as chromium, aluminum, or titanium. The layer 204 is disposed on a substrate 208 (e.g., glass or fused silica) and may be deposited on the substrate 208, for example, by chemical vapor deposition. In some cases, the substrate 208 takes the form of a wafer having a large lateral dimension capable of forming many MOEs. For example, some wafers can have a radius exceeding 1 inch to 20 inches and a thickness of only a few hundred microns, but wafers having other dimensions are within the scope of the present disclosure. The mask 202 may be deposited on the layer 204, for example, by sputtering or chemical vapor deposition.

[0026] In the illustrated example, the position of the mask 202 on the layer 204 corresponds to the position of the meta-atoms formed on the substrate 208. In this example, a first portion 232 of the mask material corresponds to the position of a first group of meta-atoms, each having a first relatively large diameter, and the first group of meta-atoms is present at a first relatively high density. A second portion 234 of the mask material corresponds to the position of a group of meta-atoms, each having a second relatively small diameter, and the second group of meta-atoms is present at a first relatively low density.

[0027] In subsequent stages of the process, layer 204 is etched to form meta-atoms. In the illustrated example, layer 204 is etched using plasma etching that includes a passivation gas and an etchant gas. In a first stage of the plasma etching, the ratio of the passivation gas to the etchant gas can be expressed as P:E, but in a subsequent second stage, the ratio is changed by increasing the amount of the passivation gas (i.e., ratio P+x:E), decreasing the amount of the etchant gas (i.e., ratio P:E−y), or both (i.e., ratio P+x:E−y).

[0028] The ratio of the gas in the first stage (P:E) can be selected such that, as shown in FIG. 6B, trenches 210 having substantially vertical sidewalls 218 are etched in layer 204. Due to the different diameters of the meta-atoms formed for each group (and the different densities of each group), the etching ratio can be lower in a first region (e.g., 234) of layer 204 under the first section of mask 202 than in a second region (e.g., 232) of layer 204 under the second section of mask 202. Thus, as a result of the first stage of the etching, the etching depth (H1) in the first region may be smaller than the depth (H2) in the second region.

[0029] The ratio of the gas in the second stage (P+x:E or P:E−y or P+x:E−y) can be selected such that, for example as shown in FIG. 6C, trenches 210 are etched to the surface of substrate 208, taking into account the different etching characteristics of the various sections of the partially etched layer 204. In particular, the etching in the second stage enables the removal of layer material 204 to expose the surface of substrate 208 while avoiding the removal of smaller meta-atoms (i.e., groups of meta-atoms having a lower density). The etching in the second stage can result in at least some of the meta-atoms 216 having outwardly inclined sidewalls 220 as described above.

[0030] Next, the mask 202 can be removed. As shown by FIG. 6D, the resulting structure is a MOE containing meta-atoms 216, at least some of which are substantially perpendicular along the upper section (218) of the meta-atoms and have sidewalls that slope outward along the lower section (220) of the meta-atoms (i.e., the portion of the meta-atoms closer to the surface of the substrate supporting the meta-atoms).

[0031] As a specific example, plasma etching can use a mixed gas of C4F8 as the passivation gas and SF6 as the etchant gas to etch the layer 204 composed of amorphous silicon. In the first stage, a ratio of 50:30 can be used for the amounts of the passivation gas and the etchant gas, but in the second stage, this ratio can be changed to, for example, 50:18. Other ratios may be appropriate for one or both stages. More generally, in the second stage, depending on the implementation, the change in the gas ratio can be obtained by increasing the amount of the passivation gas, decreasing the amount of the etchant gas, or both. In some implementations, other gases can be used for one or both of the passivation gas and the etchant gas. For example, in some implementations, O2 can be used as the passivation gas.

[0032] In some implementations, there may be no passivation gas or no etchant gas in either the first stage or the second stage of the etching process. That is, one stage can contain only the passivation gas (without the etchant gas), and the other stage can contain only the etchant gas (without the passivation gas).

[0033] In some implementations, instead of, or in addition to, increasing the amount of passivation gas in the second stage of plasma etching and / or decreasing the amount of etchant gas in the second stage, the plasma output or the bias to the substrate is reduced in the second stage. That is, the plasma output or the bias to the substrate in the second stage of plasma etching can be made smaller than the value in the first stage of plasma etching. Other factors that can affect the formation of meta-atoms include the temperature of the substrate, the gas flow into the chamber, and the pressure in the chamber. Further, the overall shape of the meta-atoms, their size, and the gap between adjacent meta-atoms can affect the degree of the outward slope of the meta-atom sidewalls.

[0034] In some implementations, as shown in FIG. 7, instead of using plasma etching having two stages where the amount of passivation gas in the second stage is increased relative to the first stage and / or the amount of etchant gas in the second stage is decreased, the etching process includes a first stage (702) using plasma etching and a second stage (704) using isotropic etching. That is, the second stage can use a wet etchant that has a substantially uniform etching rate in all directions, for example, and can provide profile control etching. In some cases, isotropic etching tends to have sidewalls that curve outwardly rather than slope (e.g., concave).

[0035] Although this specification contains many details, these should not be construed as limitations on the scope of the disclosure or of what may be claimed, but rather as descriptions of features specific to particular implementations. The particular features described herein in the context of separate implementations can also be combined. Conversely, the various features described in the context of a single implementation can be implemented separately in multiple implementations or in any suitable partial combination. Various modifications can be made to the foregoing examples. Accordingly, other implementations are within the scope of the claims.

Claims

1. It is a device, The substrate comprises a plurality of metaatoms, each having at least one outer sidewall, The apparatus wherein the upper part of each of the at least one side walls of the metaatom is perpendicular to the surface of the substrate supporting the metaatom, and the lower part of each of the at least one side walls of the metaatom is inclined outward, and the lower part is adjacent to the interface between the metaatom and the surface of the substrate.

2. The apparatus according to claim 1, wherein the lower part of at least one side wall of each of the meta atoms is inclined outward.

3. The apparatus according to claim 1, wherein the lower part of at least one side wall of each of the meta atoms is curved outward.

4. The apparatus according to claim 1, wherein the lower part of each of the at least one side walls of the metaatom is concave.

5. The apparatus according to claim 1, wherein the diameter of each of the metaatoms in the lower part is greater than the diameter of the metaatoms in the upper part of the metaatom.

6. The apparatus according to claim 1, wherein the lower part of at least one side wall of each of the metaatoms extends to less than 50% of the height of the metaatom.

7. The apparatus according to claim 6, wherein the lower part of at least one side wall of each of the metaatoms extends for 5% or less of the height of the metaatom.

8. The apparatus according to claim 1, wherein the plurality of metaatoms include a first group of metaatoms whose upper part has a first diameter and a second group of metaatoms whose upper part has a second diameter different from the first diameter.

9. The apparatus according to claim 1, wherein the plurality of metaatoms include a first group of metaatoms arranged at a first density and a second group of metaatoms arranged at a second density different from the first density.

10. The substrate is made of glass or fused silica. The meta-atom is composed of silicon, titanium dioxide, zinc oxide, aluminum zinc oxide, or niobium oxide. The apparatus according to any one of claims 1 to 9.

11. It is a method, To provide a structure comprising layers of hierarchical material on a substrate, wherein the structure further comprises a mask on the hierarchical material, the mask defining regions of the hierarchical material where metaatoms are formed, and each of the respective metaatoms having at least one sidewall, Etching process, A first etching step of removing a portion of the layered material such that trenches are etched into the layered material to form upper sections of at least one sidewall of each of the metaatoms, wherein the upper sections are perpendicular to the surface of the substrate, A second etching step of removing further portions of the layered material to form the lower part of at least one sidewall of each of the metaatoms, wherein the lower part is adjacent to the interface between the metaatom and the surface of the substrate and is inclined outward, Performing an etching process that includes, Methods that include...

12. The method according to claim 11, wherein each of the first and second etching steps is part of a plasma etching process.

13. The method according to claim 11, wherein the first etching step includes plasma etching having an average flow rate of passivation gas and an average flow rate of etchant gas, and the second etching step includes plasma etching in which at least one of the average flow rate of passivation gas or the average flow rate of etchant gas is different from that of the first etching step.

14. The method according to claim 13, wherein in the second etching step, the average flow rate of the passivation gas is greater than the average flow rate of the passivation gas in the first etching step.

15. The method according to claim 13, wherein in the second etching step, the average flow rate of the etchant gas is less than the average flow rate of the etchant gas in the first etching step.

16. The method according to claim 12, wherein at least one of the plasma output in the second etching step or the bias to the substrate is smaller than that in the first etching step.

17. The method according to claim 11, wherein the first etching step includes plasma etching and the second etching step includes isotropic etching.

18. The method according to claim 11, wherein the metaatoms include a first group of metaatoms, each having a first diameter at its upper end, and a second group of metaatoms, each having a second diameter at its upper end that is different from the first diameter.

19. The method according to claim 11, wherein the metaatoms include a first group of metaatoms arranged at a first density and a second group of metaatoms arranged at a second density different from the first density.

20. The substrate is made of glass or fused silica. The meta-atom is composed of silicon, titanium dioxide, zinc oxide, aluminum zinc oxide, or niobium oxide. The method according to claim 11.

21. The method according to any one of claims 11 to 20, further comprising removing the mask.

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