Superstructures comprising supeatomals having

Abstract

The present disclosure describes a metasurface optical element (MOE), a method for manufacturing the MOE, and an apparatus including the MOE. The MOE includes a superatom having outwardly inclined sidewalls. The superatom may have sidewalls that are substantially vertical along an upper section of the superatom and inclined outwardly along a lower section of the superatom.

Description

Technical Field

[0001] The present disclosure relates to meta-optical elements (MOEs). Background Art

[0002] Advanced optical components may include metasurfaces, which are surfaces with distributed small structures (e.g., meta-atoms) arranged in a specific way to interact with light. For example, a metasurface (also called a metastructure) may be a surface with a distributed array of nanostructures. The nanostructures may interact with light waves individually or collectively. For example, nanostructures or other meta-atoms may change the local amplitude, local phase, or both of an incident light wave.

[0003] A MOE may include multiple superatoms. The fabrication of a MOE sometimes involves etching superatoms into a layer. In some cases, superatoms appear in different groups within the MOE, and different groups of superatoms may have different etching characteristics. It may be particularly difficult to fabricate a MOE configured with two or more groups having different etching characteristics using known etching methods. Summary of the invention

[0004] The present disclosure describes MOEs, methods for making MOEs, and devices containing MOEs. The MOEs include superatoms having outwardly sloping sidewalls. In particular, the superatoms can have sidewalls that are substantially vertical along an upper section of the superatoms and outwardly sloping along a lower section of the superatoms (i.e., a section of the superatoms that is closer to a surface of a substrate supporting the superatoms).

[0005] For example, in one aspect, the present disclosure describes an apparatus comprising a substrate supporting a plurality of meta-atoms, each meta-atom having at least one corresponding outer sidewall. An upper portion of at least one sidewall of each meta-atom is perpendicular to a surface of the substrate supporting the meta-atom. A lower portion of at least one sidewall of each meta-atom is inclined outward, wherein the lower portion is adjacent to an interface between the meta-atom and a surface of the substrate.

[0006] Some embodiments include one or more of the following features. For example, in some cases, a lower portion of at least one sidewall of each superatom slant or bends outward. In some instances, a lower portion of at least one sidewall of each superatom is concave. The diameter of each corresponding superatom in the superatom at the lower portion may be greater than the diameter of the superatom at the upper portion of the superatom. In some embodiments, a lower portion of at least one sidewall of each superatom in the superatom extends less than fifty percent of the height of the superatom, and in some cases, extends no more than five percent of the height of the superatom.

[0007] In some embodiments, the plurality of superatoms includes a first grouping of superatoms and a second grouping of superatoms, the respective upper portions of the first grouping of superatoms having a first diameter, and the respective upper portions of the second grouping of superatoms having a second diameter different from the first diameter. In some embodiments, the plurality of superatoms includes a first grouping of superatoms arranged at a first density and a second grouping of superatoms arranged at a second density different from the first density.

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

[0009] The present disclosure also describes a method, which includes providing a structure including a layer of stratum material on a substrate, wherein the structure also includes a mask on the stratum material, the mask defining partitions of the stratum material for forming super-atoms, each corresponding super-atom having at least one sidewall. The method also includes performing an etching process, the etching process including a first etching phase and a second etching phase. The first etching phase removes a portion of the stratum material so that a groove is etched into the stratum material to form an upper section of at least one sidewall of each super-atom, the upper section being perpendicular to the surface of the substrate. The second etching phase removes a further portion of the stratum material to form a lower portion of at least one sidewall of each super-atom, the lower portion being adjacent to an interface between the super-atom and the surface of the substrate and tilting outward.

[0010] Some embodiments include one or more of the following features. For example, in some cases, each of the first etching phase and the second etching phase is part of a plasma etching process. In some cases, the first etching phase includes a plasma etching having an average flow rate of a passivating gas and an average flow rate of an etchant gas, and the second etching phase includes a plasma etching having an average flow rate of the passivating gas or an average flow rate of the etchant gas that is different from the first etching phase. For example, in some cases, in the second etching phase, the average flow rate of the passivating gas is greater than the average flow rate of the passivating gas during the first etching phase. In some cases, in the second etching phase, the average flow rate of the etchant gas is less than the average flow rate of the etchant gas during the first etching phase. In some instances, at least one of the plasma power or the bias toward the substrate during the second etching phase is less than during the first etching phase.

[0011] In some embodiments, the first etching phase includes plasma etching and the second phase includes isotropic etching.

[0012] In some embodiments, the method further includes removing the mask.

[0013] In some embodiments, outwardly sloped sidewalls can help improve the mechanical stability of some or all of the superatom.

[0014] Other aspects, features, and advantages will become apparent from the following detailed description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figures 1A to 1D Example process steps for fabricating a MOE are depicted.

[0016] Figure 2 is a cross-sectional view of an example superstructure according to the present disclosure.

[0017] Figure 3 is a cross-sectional view of another example superatom according to the present disclosure.

[0018] Figure 4 is a flow chart illustrating an etching process for forming super-atoms according to the present disclosure.

[0019] Figure 5 is a flow chart illustrating a plasma etching process for forming super-atoms according to the present disclosure.

[0020] FIG. 6A to FIG. 6D are cross-sectional views of various stages in a method of making a superstructure according to the present disclosure.

[0021] Figure 7 is a flow chart illustrating another example process for forming super-atoms according to the present disclosure. DETAILED DESCRIPTION

[0022] Figures 1A to 1D An example of several stages of a manufacturing process for one or more meta-optical elements (MOEs) is depicted. Figures 1A to 1D As depicted, a meta-optical assembly can be an intermediate product produced during the fabrication of one or more MOEs. Meta-optical assembly 100 includes a mask 102 disposed on a bottom layer 104. The bottom layer 104 is in turn disposed on a substrate 108. Meta-optical assembly 100 can take the form of, for example, a wafer having a large lateral dimension and having many MOEs.

[0023] With the mask 102 in place, the bottom layer 104 can be etched to form meta-atoms 116 separated by regions 110 where the bottom 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 116 that can exhibit different etching characteristics from one another due to, for example, their different densities. That is, even if the meta-atoms 116 in each grouping 112, 114 have the same spacing, the diameters of the meta-atoms in each grouping can be different from one another. For example, the diameter D1 of the meta-atoms 116 in the first group 112 can be different from (e.g., larger than) the diameter D2 of the meta-atoms 116 in the second group 114 (see FIG. 2 ). Figure 1B and Figure 1C Due to the different diameters and thus the different densities, the first group 112 of meta-atoms may have a first etching characteristic, while the second group 114 of meta-atoms may have a different second etching characteristic.

[0024] Furthermore, if Figure 1D As depicted, due to different etching characteristics, some of the meta-atoms 116 within at least one of the groups (e.g., group 114) may fail, break, or otherwise be damaged during the etching process due to the different etching rates between the two groups 112 and 114. For example, for the meta-atoms 116 in the second group 114 having a relatively smaller diameter (D2) and / or a lower density, there is a greater risk of them being damaged due to energy reflected from the substrate during the etching process. The reflected energy may cause, for example, the bottom of the meta-atoms in the second group 114 to be slightly undercut, thereby causing the meta-atoms to be physically unstable, such as Figure 1D exemplified.

[0025] To reduce the possibility that the meta-atom is physically unstable, the side of the meta-atom close to the substrate can be tilted slightly outward. Figure 2 As shown in the MOE 200 of FIG. 2 , although the upper portion 218 of each superatom 216 has substantially vertical walls (i.e., sidewalls that are substantially perpendicular to the surface of the substrate 208), the sidewalls along the lower portion 220 (i.e., closer to the substrate 208) of each superatom 216 are tilted outward. For example, in some examples, the sidewalls along the lower portion 220 can be tapered (e.g., skewed) away from the vertical sidewalls, such that the diameter of the superatom 216 at the interface with the substrate 208 is greater than the diameter of the superatom at its upper (free) end 222. In some examples, as shown in FIG. Figure 3 As shown, the sidewalls along the lower portion 220 of the meta-atom 216 may be curved (eg, concave).

[0026] In one example embodiment, the upper portion of each superatom having substantially vertical sidewalls may correspond to at least fifty percent of the height of the superatom. Thus, the outwardly sloping portion of the sidewall at the lower portion of the superatom will typically extend by at most less than fifty percent of the height of the superatom. In some instances, the outwardly sloping portion of the sidewall extends by no more than twenty-five percent of the height of the superatom, and in some cases, by no more than five percent of the height of the superatom. Thus, for a superatom having a height of about 500 nm, the outwardly sloping portion of the sidewall may have a height of less than 250 nm, and in some cases, have a height of no more than 125 nm or possibly no more than 25 nm.

[0027] Depending on the application, MOE 200 may include only a few superatoms, or tens, hundreds, thousands, millions, or even hundreds of millions of superatoms. MOE 200 may include two or more groupings of superatoms, for example, having different corresponding diameters or different corresponding densities of superatoms. Thus, in some cases, the sum of the areas (e.g., as determined by the superatom diameters) of the individual superatoms 216 within a particular group 212 divided by the area occupied by the particular grouping of the MOE may be different from the area of ​​another grouping 214 of superatoms 216.

[0028] In some instances, the super-atoms 216 in one or more of the groups 212, 214 have outwardly tilted sidewalls as described above. In some instances, only a subset of super-atoms of a particular MOE may have outwardly tilted sidewalls. For example, in some cases, super-atoms with relatively smaller diameters and / or lower density (e.g., group 214) may have outwardly tilted sidewalls as described above, while super-atoms with relatively larger diameters and / or higher density (e.g., group 212) may have substantially vertical sidewalls extending from the top (free) end 222 of the super-atom to the bottom end contacting the substrate 208. In other cases, super-atoms with relatively larger diameters and / or higher density (e.g., group 212) may have outwardly tilted sidewalls as described above, while super-atoms with relatively smaller diameters and / or lower density (e.g., group 214) may have substantially vertical sidewalls extending from the top (free) end 222 of the super-atom to the bottom end contacting the substrate 208.

[0029] Substrate 208 may be made of, for example, glass or fused silicon dioxide. Superatom 216 may be made of, for example, silicon (e.g., polycrystalline silicon, amorphous silicon, crystalline silicon, or silicon nitride), titanium oxide, zinc oxide, aluminum zinc oxide, or niobium oxide. Superatom 216 may have, for example, a circular, square, or annular cross section. In some embodiments, superatom 216 or substrate 208 may use other materials and shapes.

[0030] An MOE having sidewalls that are substantially vertical along an upper portion (ie, near its free end) and that slope outwardly along a lower portion (ie, adjacent the interface with the substrate) can be fabricated in a variety of ways. Figure 4 As shown, a first stage (402) of etching removes a portion of the underlying material so that a trench having substantially vertical sidewalls is etched into the underlying material to form an upper segment of each respective superatom, and a second stage (404) of etching further removes the underlying material to form outwardly inclined sidewalls along a lower segment of each respective superatom (i.e., a segment of the superatom that is closer to the surface of the substrate supporting the superatom).

[0031] According to some embodiments, the super-atoms are formed using an etching process (e.g., plasma etching) that includes a passivation gas and an etchant gas. The etching process is divided into at least two phases, wherein the ratio of the average flow rate of the passivation gas to the average flow rate of the etchant gas for one phase is different from the ratio during another phase. For example, Figure 5 As shown, in a first phase (502), plasma etching may include an average flow rate of a passivation gas and an average flow rate of an etchant gas. During a subsequent second phase (504), the average flow rate of the passivation gas may be increased and / or the average flow rate of the etchant gas may be decreased relative to the average flow rate used during the first phase. FIG. 6A to FIG. 6C to describe an example process.

[0032] Fig. 6A An example of a structure including a mask 202 is shown, and the mask 202 is disposed on a bottom layer 204 of a material forming a super atom. The bottom layer 204 may be composed of, for example, polycrystalline silicon, amorphous silicon, crystalline silicon, titanium oxide, silicon nitride, zinc oxide, aluminum zinc oxide, or niobium oxide. The mask 202 may be, for example, an organic (e.g., amorphous carbon) or an inorganic (e.g., SiN, SiON, TiN) hard mask. In some examples, the mask 202 may be composed of a metal such as chromium, aluminum, or titanium. The bottom layer 204 is disposed on a substrate 208 (e.g., glass or fused silica) and may be deposited onto the substrate 208 by, for example, chemical vapor deposition. In some examples, the substrate 208 is in the form of a wafer having a larger lateral dimension, and many MOEs may be formed on the wafer. For example, some wafers may have a radius of 1 inch to more than 20 inches and a thickness of only a few hundred microns, but wafers of other sizes are also within the scope of the present disclosure. The mask 202 may be deposited on the bottom layer 204, for example, by sputtering or chemical vapor deposition.

[0033] In the illustrated example, the locations of the mask 202 on the bottom layer 204 correspond to the locations of the superatoms to be formed on the substrate 208. In this example, the first portion 232 of the mask material corresponds to the locations of the first group of superatoms, where each superatom has a (relatively large) first diameter, and the first group of superatoms exists at a (relatively high) first density. The second portion 234 of the mask material corresponds to the locations of the second group of superatoms, where each superatom has a (relatively small) second diameter, and the second group of superatoms exists at a (relatively low) second density.

[0034] During the subsequent processing stage, the bottom layer 204 is etched to form the super-atom. In the illustrated example, the bottom layer 204 is etched using a plasma etch including a passivation gas and an etchant gas. During the first stage of the plasma etching, the ratio of the passivation gas to the etchant gas can be expressed as P:E, and during the subsequent second stage, the ratio is changed by increasing the amount of the passivation gas (i.e., the ratio of P+x:E), or by reducing the amount of the etchant gas (i.e., the ratio of P:Ey), or by doing both at the same time (i.e., the ratio of P+x:Ey).

[0035] The ratio of the gases used in the first stage (P:E) may be selected so that trenches 210 having substantially vertical sidewalls 218 are etched into bottom layer 204, such as Figure 6B As shown. Due to the different diameters of the super-atoms formed for each group (and the different densities for each group), the etching rate of the first sub-area under the first section (e.g., 234) of the bottom layer 204 can be lower than the etching rate of the second sub-area under the second section (e.g., 232) of the mask 202 for the bottom layer 204. Therefore, as a result of the first etching stage, the etching depth (H1) in the first sub-area can be less than the depth (H2) in the second sub-area.

[0036] The ratio of the gases used in the second stage (P+x:E or P:Ey or P+x:Ey) can be selected so that the trench 210 is etched down to the surface of the substrate 208, taking into account the different etching characteristics of the various sections of the partially etched bottom layer 204, as shown in FIG. Figure 6C In particular, etching during the second phase allows for removal of the underlying material 204 to expose the surface of the substrate 208 while avoiding undercutting smaller superatoms (i.e., groups of superatoms with a lower density). Etching during the second phase can cause at least some of the superatoms 216 to have outwardly sloping sidewalls 220 as described above.

[0037] Then, the mask 202 can be removed. Fig.6DAs shown, the resulting structure is a MOE including superatoms 216, wherein at least some of the superatoms have sidewalls that are substantially vertical along an upper section of the superatom (at 218) and that slope outward along a lower section of the superatom (at 220, i.e., a section of the superatom closer to the surface of the substrate supporting the superatom).

[0038] As a specific example, plasma etching can use C 4 F 8 The mixed gas of SF2 is used as the passivation gas, and the etchant gas is SF3. 6 It can be used to etch the bottom layer 204 composed of amorphous silicon. During the first stage, a ratio of 50:30 can be used for the amount of passivation gas and etchant gas, while during the second stage, the ratio can be changed to, for example, 50:18. Other ratios can also be suitable for one stage or both stages. More generally, for the second stage, depending on the embodiment, the ratio change of each gas can be obtained by increasing the amount of passivation gas, reducing the amount of etchant gas, or both. In some embodiments, other gases can also be used for one or both of the passivation gas and the etchant gas. For example, in some embodiments, O 2 Can be used as a passivating gas.

[0039] In some embodiments, there may be no passivation gas or etchant gas in the first or second phase of the etching process. That is, one phase may include only passivation gas (but not etchant gas), while another phase may include only etching gas (but not passivation gas).

[0040] In some embodiments, as an alternative to increasing the amount of passivating gas in the second stage of plasma etching and / or reducing the amount of etchant gas in the second stage, or in addition to increasing the amount of passivating gas in the second stage and / or reducing the amount of etchant gas in the second stage of plasma etching, the plasma power or the bias toward the substrate is reduced in the second stage. That is, the plasma power or the bias toward the substrate during the second stage of plasma etching can be made less than the value during the first stage of plasma etching. Other factors that may affect the formation of superatoms include the temperature of the substrate, the gas flow rate entering the chamber, and the pressure in the chamber. In addition, the overall shape of the superatom and its size and the gaps between adjacent superatoms may affect the degree to which the sidewalls of the superatom tilt outward.

[0041] In some embodiments, Figure 7As shown, as an alternative to using a plasma etch with two stages (wherein the amount of passivation gas in the second stage is increased and / or the amount of etchant gas in the second stage is reduced relative to the first stage), 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, for example, a wet etchant that has a substantially uniform etching rate in all directions and can provide tilt-controlled etching. In some cases, isotropic etching can tend to cause the sidewalls to bow outward (e.g., concave) rather than skew.

[0042] Although this specification contains many details, these details should not be interpreted as limitations on the scope of the present disclosure or possible protection, but should be interpreted as descriptions of features specific to a particular embodiment. Certain features described in this specification in the context of separate embodiments may also be combined in the same embodiment. Conversely, various features described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments. Various modifications may be made to the foregoing examples. Therefore, other embodiments are also within the scope of the claims.

Claims

1. A device comprising: a substrate supporting a plurality of superatoms, each of the superatoms having at least one corresponding outer sidewall, wherein an upper portion of at least one sidewall of each of the superatom is perpendicular to a surface of the substrate supporting the superatom, and wherein a lower portion of the at least one sidewall of each of the superatom is inclined outward, the lower portion being adjacent to an interface between the superatom and the surface of the substrate.

2. The device according to claim 1, wherein: The lower portion of the at least one sidewall of each of the superatom is skewed outward.

3. The device of claim 1, wherein: The lower portion of the at least one sidewall of each of the superatom is bent outwardly.

4. The device of claim 1, wherein: The lower portion of the at least one sidewall of each of the superatom is concave.

5. The device of claim 1, wherein: A diameter of each respective one of the super-atoms at the lower portion is greater than a diameter of the super-atom at the upper portion of the super-atom.

6. The device of claim 1, wherein: The lower portion of the at least one sidewall of each of the superatomes extends less than fifty percent of a height of the superatom.

7. The device of claim 6, wherein: The lower portion of the at least one sidewall of each of the superatomes extends no more than five percent of the height of the superatom.

8. The apparatus according to any one of claims 1 to 7, wherein: The plurality of superatoms include a first group of superatoms and a second group of superatoms, wherein respective upper portions of the first group of superatoms have a first diameter, and respective upper portions of the second group of superatoms have a second diameter different from the first diameter.

9. The device according to any one of claims 1 to 7, wherein: The plurality of superatoms includes a first group of superatoms arranged at a first density and a second group of superatoms arranged at a second density different from the first density.

10. The apparatus according to any one of claims 1 to 9, wherein: The substrate is composed of glass or fused silica, and The superatom is composed of silicon, titanium oxide, zinc oxide, aluminum zinc oxide or niobium oxide.

11. A method comprising: providing a structure including a layer of underlying material on a substrate, the structure further comprising a mask on the underlying material, the mask defining partitions of the underlying material for forming superatoms, each respective superatom having at least one sidewall; as well as Performing an etching process, the etching process comprising: a first etching phase, wherein the first etching phase removes a portion of the underlying material so that a trench is etched into the underlying material to form an upper section of the at least one sidewall of each of the superatom, the upper section being perpendicular to a surface of the substrate; as well as A second etching phase removes a further portion of the underlying material to form a lower portion of the at least one sidewall of each of the superatom, the lower portion being adjacent to an interface between the superatom and the surface of the substrate and tilting outward.

12. The method of claim 11, wherein: Each of the first etch phase and the second etch phase is part of a plasma etch process.

13. The method of claim 11, wherein: The first etching phase includes plasma etching having an average flow rate of a passivation gas and an average flow rate of an etchant gas, and wherein the second etching phase includes plasma etching having at least one of an average flow rate of the passivation gas or an average flow rate of the etchant gas different from that of the first etching phase.

14. The method of claim 13, wherein: In the second etching phase, the average flow rate of the passivation gas is greater than the average flow rate of the passivation gas during the first etching phase.

15. The method of claim 13, wherein: In the second etching phase, the average flow rate of the etchant gas is less than the average flow rate of the etchant gas during the first etching phase.

16. The method according to any one of claims 12 to 15, wherein: At least one of plasma power or a bias toward the substrate during the second etch phase is less than during the first etch phase.

17. The method of claim 11, wherein: The first etching phase comprises a plasma etch and the second phase comprises an isotropic etch.

18. The method according to any one of claims 11 to 17, wherein: The super-atoms include a first group of super-atoms and a second group of super-atoms, respective upper portions of the first group of super-atoms having a first diameter, and respective upper portions of the second group of super-atoms having a second diameter different from the first diameter.

19. The method according to any one of claims 11 to 17, wherein: The superatoms include a first group of superatoms arranged at a first density and a second group of superatoms arranged at a second density different from the first density.

20. The method according to any one of claims 11 to 19, wherein: The substrate is composed of glass or fused silica, and The superatom is composed of silicon, titanium oxide, zinc oxide, aluminum zinc oxide or niobium oxide.

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

Images