Parallel scanning overlay metrology with optical metasurfaces

Abstract

An apparatus may include one or more optical elements configured to direct illumination to a sample and collect sample light from the sample in response to the illumination, where at least one of the one or more optical elements includes one or more metasurfaces, the one or more metasurfaces are configured to manipulate at least one of the illumination or sample light using a sub-wavelength feature, where the sub-wavelength feature is less than at least some wavelengths in the at least one of the illumination or sample light manipulated, and wherein the one or more optical elements provide optical power for at least one of focusing the illumination on the sample or collecting the sample light from the sample.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 457,285, filed on Apr. 5, 2023, by Andrew V. Hill, Jon Madsen, Ido Dolev, Daria Negri, and Yuval Lubashevsky, titled "PARALLEL SCANNING OVERLAY METROLOGY WITH OPTICAL META-SURFACES", under 35 U.S.C. § 119(e), which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure generally relates to optical metrology and, more particularly, to optical metrology using one or more meta-surfaces. Background Art

[0004] Optical measurement systems in semiconductor device fabrication environments typically include an optical head having various optical elements configured to direct light onto a sample and collect light from the sample for measurement. Existing optical heads are formed of bulk optical elements such as bulk reflective, refractive, or diffractive optical elements. However, these existing optical heads typically have an occupied area equal to or greater than that of a typical semiconductor wafer sample, such that only a single optical head can be positioned over the sample. The bulk optical elements within existing optical heads are also relatively expensive and prone to having high variability. As a result, existing optical metrology systems are limited to a single optical head per system and per sample. However, these limitations constrain the achievable throughput and cost of ownership of the optical measurement system. Accordingly, there is a need to develop systems and methods to address the above deficiencies. Summary of the Invention

[0005] In an embodiment, the techniques described herein relate to a device that includes: one or more optical elements configured to direct illumination onto a sample and collect sample light from the sample in response to the illumination, wherein at least one of the one or more optical elements includes one or more meta-surfaces configured to manipulate at least one of the illumination or the sample light using sub-wavelength features, wherein the sub-wavelength features are less than at least some of the wavelengths of at least one of the illumination or the sample light being manipulated, and wherein the one or more optical elements provide optical power for at least one of an operation of focusing the illumination onto the sample or collecting the sample light from the sample.

[0006] In an embodiment, the techniques described herein relate to a device, wherein at least one of the one or more metasurfaces includes a lens.

[0007] In an embodiment, the techniques described herein relate to a device, wherein at least one of the one or more metasurfaces includes a beam splitter.

[0008] In an embodiment, the techniques described herein relate to a device, wherein at least one of the one or more metasurfaces includes one or more beam deflectors.

[0009] In an embodiment, the techniques described herein relate to a device, wherein at least one of the one or more metasurfaces includes an objective lens.

[0010] In an embodiment, the techniques described herein relate to a device, wherein the objective lens is a multi-surface element formed by at least two of the one or more metasurfaces.

[0011] In an embodiment, the techniques described herein relate to a device, wherein the one or more optical elements include one or more bulk optical elements, and at least one of the one or more metasurfaces is formed on a surface of at least one of the one or more bulk optical elements.

[0012] In an embodiment, the techniques described herein relate to a device, wherein the one or more metasurfaces include two or more metasurfaces, and at least one of the one or more bulk optical elements includes at least two of the two or more metasurfaces.

[0013] In an embodiment, the techniques described herein relate to a device, wherein the one or more optical elements include one or more fused optical elements formed by two or more sub-elements, and at least one of the one or more metasurfaces is formed at an interface of two of the two or more sub-elements.

[0014] In an embodiment, the techniques described herein relate to a device, wherein the one or more metasurfaces include two or more metasurfaces, and at least one of the one or more fused optical elements includes at least two of the two or more metasurfaces.

[0015] In an embodiment, the techniques described herein relate to an apparatus, wherein the one or more optical elements include: a first lens formed as at least one of the one or more metasurfaces and configured to collimate the illumination, wherein the illumination is incident on the first lens as a divergent beam; an objective lens formed as at least one of the one or more metasurfaces, wherein the objective lens is configured to direct the illumination to the sample and collect the sample light from the sample; a first grating configured to direct the illumination from the first lens to the objective lens; a second lens formed as at least one of the one or more metasurfaces; and a second grating for receiving the sample light from the objective lens and directing the sample light to the second lens.

[0016] In an embodiment, the techniques described herein relate to an apparatus, wherein the first lens, the objective lens, the first grating, the second lens, and the second grating are integrated in a fused optical element.

[0017] In an embodiment, the techniques described herein relate to an apparatus, wherein the one or more optical elements include: an objective lens formed as one of the one or more metasurfaces, wherein the objective lens is configured to direct the illumination to the sample and collect the sample light from the sample; a first metasurface of the one or more metasurfaces configured to collimate the illumination and direct the illumination to the objective lens, wherein the illumination is incident on the first metasurface as a divergent beam; and a second metasurface of the one or more metasurfaces configured to receive the sample light from the objective lens and focus the sample light.

[0018] In an embodiment, the techniques described herein relate to an apparatus, wherein the second metasurface focuses the light onto a collection field stop.

[0019] In an embodiment, the techniques described herein relate to an apparatus, wherein the objective lens, the first metasurface, and the second metasurface are integrated in a monolithic element.

[0020] In an embodiment, the techniques described herein relate to an apparatus, wherein the one or more optical elements include: an objective lens formed as at least one of the one or more metasurfaces, wherein the objective lens is configured to direct the illumination to the sample and collect the sample light from the sample; a first metasurface of the one or more metasurfaces configured to collimate the illumination, wherein the illumination is incident on a first lens as a divergent beam; a second metasurface; and a beam splitter configured to direct the illumination from the first metasurface to the objective lens and direct the sample light from the objective lens to the second metasurface, wherein the second metasurface focuses the sample light onto a collection field stop.

[0021] In an embodiment, the techniques described herein relate to an apparatus, wherein the second metasurface focuses the light onto a collection field stop diaphragm.

[0022] In an embodiment, the techniques described herein relate to an apparatus, wherein the objective lens, the first metasurface, the second metasurface, and the beam splitter are integrated in a fused optical element.

[0023] In an embodiment, the techniques described herein relate to an apparatus, wherein the fused optical element further includes a surface through which the sample light is guided from the beam splitter to the second metasurface via total internal reflection.

[0024] In an embodiment, the techniques described herein relate to an apparatus, wherein the one or more optical elements include: an objective lens formed as at least one of the one or more metasurfaces, wherein the objective lens is configured to collect the sample light from the sample; and at least one of the one or more metasurfaces configured to direct the illumination to the sample at an angle outside the numerical aperture of the objective lens.

[0025] In an embodiment, the techniques described herein relate to an apparatus, wherein the at least one metasurface of the one or more metasurfaces configured to direct the illumination to the sample at an angle outside the numerical aperture of the objective lens directs two or more beams of the illumination to the sample outside the numerical aperture of the objective lens.

[0026] In an embodiment, the techniques described herein relate to an apparatus, wherein at least some of the sub-wavelength features in at least one particular metasurface of the one or more metasurfaces are arranged as a plurality of islands distributed across the particular metasurface.

[0027] In an embodiment, the techniques described herein relate to an apparatus, wherein at least one of the sub-wavelength features within the islands, the spacing between the islands, or the orientation of the islands varies across the particular metasurface.

[0028] In an embodiment, the techniques described herein relate to an apparatus, wherein the distribution of the sub-wavelength features in at least one particular metasurface of the one or more metasurfaces is uniform across the particular metasurface.

[0029] In an embodiment, the techniques described herein relate to an apparatus, wherein at least some of the sub-wavelength features in at least one of the one or more metasurfaces are formed as blazed features.

[0030] In an embodiment, the techniques described herein relate to an apparatus, wherein at least some of the sub-wavelength features in at least one of the one or more metasurfaces are formed as grating features.

[0031] In an embodiment, the techniques described herein relate to an apparatus, wherein at least some of the sub-wavelength features in at least one of the one or more metasurfaces are formed as stepped features.

[0032] In an embodiment, the techniques described herein relate to an apparatus, wherein the one or more metasurfaces include two or more metasurfaces, and at least two of the two or more metasurfaces are formed as a stacked structure.

[0033] In an embodiment, the techniques described herein relate to an apparatus, wherein at least one of the one or more metasurfaces directs the illumination to the sample at an angle associated with a numerical aperture of at least 0.7.

[0034] In an embodiment, the techniques described herein relate to a metrology system that includes: an illumination source configured to generate illumination; one or more optical subsystems, wherein a respective optical subsystem of the one or more optical subsystems includes one or more optical elements configured to direct the illumination to a sample and collect sample light from the sample in response to the illumination, wherein at least one of the one or more optical elements includes one or more metasurfaces configured to manipulate at least one of the illumination or the sample light using sub-wavelength features that are less than at least some of the wavelengths of at least one of the illumination or the sample light, and wherein the one or more optical elements provide optical power for at least one of an operation of focusing the illumination on the sample or collecting the sample light from the sample; one or more detectors configured to generate detection signals based on the sample light collected by the one or more optical subsystems; and a controller communicatively coupled to the plurality of detectors, wherein the controller includes one or more processors configured to execute program instructions stored in a memory device, and wherein the program instructions are configured to cause the one or more processors to perform a metrology prescription by generating a plurality of metrology measurements of the sample based on the detection signals from the plurality of detectors.

[0035] In an embodiment, the techniques described herein relate to a metrology system, wherein the one or more optical subsystems include two or more optical subsystems.

[0036] In an embodiment, the techniques described herein relate to a metrology system, wherein the distribution of the two or more optical subsystems is arranged to provide parallel measurements of features in one or more fields on the sample.

[0037] In an embodiment, the techniques described herein relate to a metrology system in which the distribution of the two or more optical subsystems is arranged to provide a single optical subsystem among the optical subsystems for at least one of the one or more fields on the sample.

[0038] In an embodiment, the techniques described herein relate to a metrology system in which the distribution of the two or more optical subsystems is arranged to provide at least two optical subsystems among the optical subsystems for at least one of the one or more fields on the sample.

[0039] In an embodiment, the techniques described herein relate to a metrology system in which at least one of the one or more metasurfaces includes a lens.

[0040] In an embodiment, the techniques described herein relate to a metrology system in which at least one of the one or more metasurfaces includes a beam splitter.

[0041] In an embodiment, the techniques described herein relate to a metrology system in which at least one of the one or more metasurfaces includes one or more beam deflectors.

[0042] In an embodiment, the techniques described herein relate to a metrology system in which at least one of the one or more metasurfaces includes an objective lens.

[0043] In an embodiment, the techniques described herein relate to a metrology system in which the objective lens is formed by at least two of the one or more metasurfaces.

[0044] In an embodiment, the techniques described herein relate to a metrology system in which the one or more optical elements include one or more bulk optical elements, and at least one of the one or more metasurfaces is formed on a surface of at least one of the one or more bulk optical elements.

[0045] In an embodiment, the techniques described herein relate to a metrology system in which the one or more metasurfaces include two or more metasurfaces, and at least one of the one or more bulk optical elements includes at least two of the two or more metasurfaces.

[0046] In an embodiment, the techniques described herein relate to a metrology system in which the one or more optical elements include one or more fused optical elements formed by two or more sub-elements, and at least one of the one or more metasurfaces is formed at an interface between two of the two or more sub-elements.

[0047] In an embodiment, the techniques described herein relate to a metrology system, where the one or more metasurfaces include two or more metasurfaces, and where at least one of the one or more fused optical elements includes at least two of the two or more metasurfaces.

[0048] In an embodiment, the techniques described herein relate to a metrology system, where the one or more optical elements include a single monolithic element.

[0049] In an embodiment, the techniques described herein relate to a metrology method that includes: directing illumination to a sample using an optical subsystem that includes one or more optical elements; collecting sample light from the sample in response to the illumination using the optical subsystem, where at least one of the one or more optical elements includes one or more metasurfaces configured to manipulate at least one of the illumination or the sample light using sub-wavelength features that are less than at least some of the wavelengths of at least one of the illumination or the sample light, where the one or more optical elements provide optical power for at least one of an operation of focusing the illumination on the sample or collecting the sample light from the sample; generating a detection signal based on at least a portion of the sample light; and generating one or more metrology measurements of the sample based on the detection signal.

[0050] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily limiting of the claimed invention. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Those skilled in the art will better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0052] Figure 1A Conceptual diagram illustrating an optical measurement system according to one or more embodiments of the present disclosure.

[0053] Figure 1B Conceptual diagram illustrating an optical subsystem according to one or more embodiments of the present disclosure.

[0054] Figure 1C Top view illustrating a first design of a portion of a metasurface according to one or more embodiments of the present disclosure.

[0055] Figure 1D Illustrating according to one or more embodiments of the present disclosure Figure 1C Side view of the design in.

[0056] Figure 1E Top view of a second design of a portion of the metasurface 116 in accordance with one or more embodiments of the present disclosure.

[0057] Figure 1F Diagrammatically illustrates in accordance with one or more embodiments of the present disclosure Figure 1E side view of the design in.

[0058] Figure 2A Conceptual diagram of an optical subsystem in accordance with one or more embodiments of the present disclosure, the optical subsystem being depicted as having bulk optical elements for pupil plane based measurements.

[0059] Figure 2B Diagrammatically illustrates in accordance with one or more embodiments of the present disclosure Figure 2A schematic diagram of an optical subsystem of, the optical subsystem being depicted as having a metasurface formed on a plurality of bulk optical elements.

[0060] Figure 2C Diagrammatically illustrates in accordance with one or more embodiments of the present disclosure Figure 2A schematic diagram of an optical subsystem of, the optical subsystem being depicted as having a metasurface formed on several faces and interfaces of a fused optical element.

[0061] Figure 2D Diagrammatically illustrates in accordance with one or more embodiments of the present disclosure Figure 2A schematic diagram of an optical subsystem of, the optical subsystem being depicted as having a metasurface formed on several faces of a monolithic assembly.

[0062] Figure 2E Diagrammatically illustrates an optical subsystem including an achromatic metasurface in accordance with one or more embodiments of the present disclosure Figure 2A schematic diagram of.

[0063] Figure 3A Conceptual diagram of an optical subsystem in accordance with one or more embodiments of the present disclosure.

[0064] Figure 3B Diagrammatically illustrates in accordance with one or more embodiments of the present disclosure Figure 3A schematic diagram of the optical subsystem 102 of, the optical subsystem being depicted as having a metasurface formed on a fused optical element.

[0065] Figure 4A Conceptual diagram of an optical subsystem in accordance with one or more embodiments of the present disclosure.

[0066] Figure 4B Diagrammatically illustrates in accordance with one or more embodiments of the present disclosure Figure 4ASchematic diagram of an optical subsystem, the optical subsystem being depicted as having a metasurface formed on a fused optical element.

[0067] Figure 5 Conceptual schematic illustration depicting an arrangement of multiple optical subsystems across a sample for parallel measurement in accordance with one or more embodiments of the present disclosure.

[0068] Figure 6 Flowchart illustration, the flowchart illustrating steps performed in a method for providing optical measurement in accordance with one or more embodiments of the present disclosure. Detailed Description

[0069] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to specific embodiments and specific features thereof. The embodiments set forth herein are illustrative and not restrictive. Those skilled in the art will readily appreciate that various changes and modifications in form and detail can be made without departing from the spirit and scope of the present disclosure.

[0070] Embodiments of the present disclosure are directed to systems and methods for providing optical measurements (e.g., metrology measurements, inspection measurements, etc.) using one or more optical elements formed with at least one metasurface. The metasurface can be formed as one or more material layers having a thickness and / or features less than (typically substantially less than) the wavelength of light used in a given application. Such features are referred to herein as sub-wavelength features and can be used to locally manipulate the amplitude, phase, and / or polarization of incident light. In this manner, based on electromagnetic wavefront modulation of light, the metasurface can be formed as a phase modulator, where specific properties depend at least in part on the shape and distribution of the sub-wavelength features. By way of illustration, the sub-wavelength features can provide discrete phase jumps or transitions based on optical resonance effects.

[0071] It is contemplated herein that the metasurface can be designed to perform the functions of many bulk optical elements commonly utilized in the optical head of an optical metrology system, such as but not limited to lenses (e.g., collimating lenses, objective lenses, etc.), beam splitters, beam deflectors, or apertures (e.g., field stop, aperture stop, etc.). Additionally, the metasurface can be designed to combine multiple functions. Thus, it is contemplated herein that an optical head incorporating one or more metasurfaces can provide a compact platform suitable for illuminating a sample and / or collecting light from the sample.

[0072] Some embodiments of the present disclosure are directed to an optical head formed by one or more metasurfaces to manipulate illumination and / or collected light. Some embodiments of the present disclosure are directed to an optical metrology system that includes one or more optical heads formed by one or more metasurfaces. In some embodiments, the optical metrology system includes two or more optical heads to provide parallel characterization of different regions of a sample, where each of the optical heads includes one or more metasurfaces.

[0073] Now referring Figures 1A - 6 , systems and methods for providing optical metrology using metasurfaces are described in more detail in accordance with one or more embodiments of the present disclosure.

[0074] Figure 1A is a conceptual diagram of an optical measurement system 100 in accordance with one or more embodiments of the present disclosure.

[0075] In an embodiment, the optical measurement system 100 includes an optical subsystem 102 to obtain measurement signals from a sample 104 based on any number of measurement prescriptions. Figure 1B is a conceptual diagram of the optical subsystem 102 in accordance with one or more embodiments of the present disclosure. For example, the optical subsystem 102 may direct illumination 106 onto the sample 104 and may further collect light or other radiation emitted from the sample 104 (referred to herein as sample light 108). The optical measurement system 100 may further characterize any part of the optical measurement system 100, such as, but not limited to, a dedicated measurement target (e.g., an overlay target, a metrology target, etc.) or a device feature of interest (e.g., an in-die feature associated with a device being fabricated).

[0076] In an embodiment, the optical measurement system 100 includes a controller 110. The controller 110 may include one or more processors 112 configured to execute program instructions stored (e.g., maintained) in a memory 114 or a memory device. Additionally, the controller 110 may be communicatively coupled to the optical subsystem 102 or any component therein. In this manner, one or more processors 112 of the controller 110 may directly or indirectly execute any of the various process steps described throughout the present disclosure.

[0077] The optical subsystem 102 can include any combination of optical elements suitable for characterizing the sample 104. The optical subsystem 102 can generally operate in an imaging mode or a non-imaging mode. For example, in the imaging mode, individual features on the sample 104 can be resolved within the illuminated spot on the sample (e.g., as part of a bright-field image, a dark-field image, etc.). Using overlay metrology as a non-limiting example, an overlay measurement can be determined based on the relative positions of features associated with different lithography processes. For example, a center of symmetry can be determined for each group of features associated with a particular lithography process such that an overlay measurement can be generated based on the differences between the centers of symmetry of different groups of features. By another example, the optical subsystem 102 can operate as a measurement tool based on scatterometry, where the sample light 108 is analyzed at a pupil plane (e.g., a diffraction plane, a Fourier plane, etc.) to characterize the angular distribution of the sample light 108 generated in response to the incident illumination 106. Continuing with the example of overlay metrology, the overlay target can have periodic features intended to diffract the incident illumination 106 (e.g., diffract into discrete diffraction orders), where an overlay measurement can be generated based on the asymmetry between the diffraction orders (or more generally based on the asymmetry in the pupil plane).

[0078] In addition, the optical measurement system 100 can be configured to generate superposition measurements based on any number of prescriptions (e.g., measurement prescriptions, superposition prescriptions, etc.). The optical measurement system 100 can generally be configured according to a prescription that includes a set of parameters for controlling the illumination 106 directed to the sample 104 and for capturing the sample light 108. It should be appreciated herein that different measurement techniques or applications may require different profiles of the illumination 106 and / or may further utilize different aspects of the sample light 108 for measurement. For example, the prescription can include parameters of the illumination 106 such as, but not limited to, the illumination wavelength, the illumination pupil distribution (e.g., the illumination angles and the associated distribution of illumination intensities at those angles), the incident illumination polarization, the illumination spatial distribution, or the sample height. By way of another example, the prescription can include collection parameters associated with the sample light 108 used for measurement such as, but not limited to, the collection pupil distribution (e.g., the angular light from the sample 104 used for measurement and the desired distribution of the associated filtered intensities at those angles), the collection field stop setting for selecting the portion of the sample of interest, the polarization of the sample light 108 used for measurement, or a wavelength filter for controlling the wavelength (or more generally, the spectrum) of the sample light 108 used for measurement. As another example, the prescription can include parameters associated with the feature design of the sample 104 (e.g., the features of the targets on the sample 104). By way of illustration, the prescription can define various aspects of the features on the sample 104 (e.g., on a dedicated target) such as, but not limited to, the number of features, the size of the features, the periodicity of the features, the spacing between the features, etc. In this way, the sample features and the optical subsystem 102 can be co-designed according to the prescription to provide the desired distribution of the sample light 108 (which can indicate the measurement of interest) on one or more detectors and to provide a series of analysis steps to generate the measurement based on this distribution of the sample light 108.

[0079] In an embodiment, the optical subsystem 102 includes one or more components formed by or otherwise including the metasurface 116, where the metasurface 116 is designed to manipulate the illumination 106 directed to the sample 104 and / or the sample light 108 collected from the sample 104. This metasurface 116 can have any known design suitable for manipulating light (e.g., illumination 106 and / or sample light 108) at least in part based on one or more sub-resolution features. As used herein, the term "sub-resolution feature" refers to a property of the metasurface 116 that has a size sufficiently smaller than the wavelength of the light being manipulated such that the sub-resolution feature can directly modify the amplitude and / or phase of the light. In other words, a typical optical element can manipulate light by the accumulation of different amounts of phase delay in different regions of the element, while the metasurface 116 can manipulate the amplitude and / or phase of light on a sub-wavelength scale using one or more sub-resolution features. Thus, the metasurface 116 can be designed to provide properties similar to traditional bulk optical elements (e.g., light focusing, light refraction, or light diffraction), but in a more compact package. Additionally, the metasurface 116 can be designed to manipulate light in ways that are not possible or practical with traditional bulk optical elements.

[0080] The optical measurement system 100 can include any type of metasurface known in the art. For example, a continuous or discrete sub-resolution feature can be used to form the metasurface 116. As another example, the metasurface 116 can be formed as a periodic, quasi-periodic, or locally periodic distribution of sub-wavelength features. By way of illustration, the metasurface 116 can be formed as, but not limited to: line / space features forming a two-dimensional or three-dimensional grating structure, features having varying heights (e.g., staircase features, stepped features, blazed features, tilted features, etc.), or pillar features having any shape or distribution. Additionally, the periodicity of such features can vary across the surface to provide spatially varying properties on a larger spatial scale (e.g., greater than the wavelength of the light being manipulated). By way of illustration, a metasurface 116 formed as a lens (e.g., a metalens) can include sub-wavelength features designed to adjust the phase of incident light, where the properties of the sub-wavelength features vary across the surface in a manner designed to provide optical power for the operation as a lens.

[0081] Additionally, the metasurface 116 can be a reflective or transmissive element. Further, the optical measurement system 100 can integrate the metasurface 116 with any number of traditional optical components (e.g., refractive components, reflective components, transmissive components, diffractive components, etc.).

[0082] Now referring Figures 1C - 1F , Figures 1C - 1F includes non-limiting examples of sub-wavelength features suitable for forming the metasurface 116.

[0083] Figure 1CTop view of a first design of a portion of a metasurface 116 in accordance with one or more embodiments of the present disclosure. Figure 1D Illustrates a side view of a design in accordance with one or more embodiments of the present disclosure Figure 1C in.

[0084] In some embodiments, the metasurface 116 is formed as a series of islands 140, which are formed as a periodic distribution of sub-wavelength features. For example, Figure 1C and 1D depict a configuration in which the islands 140 include a one-dimensional grating formed by periodic grating features 142. It is contemplated herein that either the grating features 142 or any of the dimensions of the islands 140 as a whole may have dimensions less than the wavelength of the light to be manipulated and may be designed to operate as the metasurface 116. For example, Figure 1C and 1D the grating features 142 in may have a pitch 144, a height 146, a width 148, and a length 150, where one or more of these parameters are less than the wavelength of the light to be manipulated by the metasurface 116. As another example, the various parameters of the islands 140 may be less than but need not be less than the wavelength of the light to be manipulated by the metasurface 116. For example, any combination of the island width 152, the island length 154 (e.g., equivalent to the length 150 of the grating feature 142 in this case), or the pitch 156 of the islands 140 may be less than but need not be less than the wavelength of the light to be manipulated by the metasurface 116.

[0085] Figure 1E and 1F depict another design of a portion of a metasurface 116 in accordance with one or more embodiments of the present disclosure. Figure 1E Top view of a second design of a portion of a metasurface 116 in accordance with one or more embodiments of the present disclosure. Figure 1F Illustrates a side view of a design in accordance with one or more embodiments of the present disclosure Figure 1E in.

[0086] Figure 1E and 1F The second design depicted in includes islands 140 having grating features 142 and additional posts 158, which may or may not be characterized as auxiliary features. Like the grating features 142, one or more properties of the posts 158 (such as but not limited to diameter 160, height 162, pitch 164, or position relative to the grating features 142) may be less than the wavelength of the light to be manipulated by the metasurface 116.

[0087] In some embodiments, one or more properties of the islands 140 may vary across the metasurface 116 to provide spatially varying properties. For example, the spacing 156 between the islands 140 and / or the orientation of the islands 140 may vary across the metasurface 116. As another example, the design of features within the islands 140 may vary across the metasurface 116. For example, at least one of the spacing 144, height 146, width 148, length 150, or number of grating features 142 may vary between the islands 140. In another example, different islands 140 may include different distributions and / or designs of features. As illustrated, the metasurface 116 may have some islands 140 of the first design depicted in Figures 1C - 1D and some islands 140 of the second design depicted in Figures 1E - 1F , where the distribution of the different designs may be uniform across the metasurface 116 or spatially varying across the metasurface 116.

[0088] Generally referring to Figures 1C - 1F , various features of the metasurface 116 may be formed using any material or combination of materials. For example, the grating features 142 and / or the posts 158 may be formed of a high refractive index material such as, but not limited to, TiO2. Additionally, the metasurface 116 may include features formed of multiple materials.

[0089] Contemplated herein Figures 1C - 1F is provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure. For example, the metasurface 116 may have any number or type of features having any design suitable for manipulating light. As another example, Figure 1C and 1E depict grating features 142 and posts 158 formed above a substrate 166. However, this is not a requirement. In some embodiments, the metasurface 116 includes additional material surrounding the grating features 142 and / or the posts 158 to dispose such features within a layer of uniform height, which may be used to integrate this metasurface 116 with additional materials and / or at the interface between different materials. In some embodiments, the metasurface 116 is formed of materials in two or more layers such that the metasurface 116 is a multilayer structure. Additionally, any number of additional layers may be present above or below several features and / or layers forming the metasurface 116.

[0090] In some embodiments, multiple metasurfaces 116 may be fabricated in a stacked configuration. In this case, multiple metasurfaces 116 may be fabricated in an overlapping region in the path of the incident light, with the metasurfaces directly on top of each other or having an intermediate layer between the metasurfaces 116. By way of illustration, the optical response of a particular metasurface 116 may depend on the nature of the incident light, such as but not limited to wavelength or polarization. In this case, different metasurfaces 116 designed for different properties may be stacked to provide the desired performance characteristics for light having these different properties. For example, different metasurfaces 116 designed for different wavelengths may be stacked to provide the desired performance characteristics for multi-wavelength or broadband light. The metasurfaces 116 may further be formed using any fabrication techniques known in the art, such as but not limited to additive manufacturing techniques or subtractive manufacturing techniques.

[0091] The optical measurement system 100 may include one or more metasurfaces 116 that provide any functionality. For example, the optical subsystem 102 of the optical measurement system 100 may include, but is not limited to, one or more metasurfaces 116 formed as lenses (e.g., collimating lenses, objective lenses, etc.), beam splitters, beam deflectors, or apertures (e.g., field stops, aperture stops, etc.). Additionally, in some cases, the metasurfaces 116 may be designed to combine multiple functions.

[0092] In some embodiments, the optical subsystem 102 includes one or more optical heads, where at least one optical head includes at least one metasurface 116 that is arranged to direct the illumination 106 onto the sample 104, capture the sample light 108 from the sample 104, and / or manipulate any combination of the illumination 106 or the sample light 108. Additionally, this optical head may provide a relatively high numerical aperture (e.g., 0.7 or greater) for performing at least one of focusing the illumination 106 onto the sample 104 or collecting the sample light 108. In some cases, the optical head includes an objective lens formed at least in part using one or more metasurfaces 116 that provide optical power for operation as a lens (e.g., a metalens) having a numerical aperture of at least 0.7.

[0093] Referring again to Figure 1B , in accordance with one or more embodiments of the present disclosure, the various components of the optical subsystem 102 are now described in more detail. It is contemplated herein that Figure 1B any component or combination of components depicted in Figure 1B may be formed as one or more metasurfaces 116. Such metasurfaces 116 may be single-layer or multi-layer metasurfaces 116. Additionally, multiple components with or without metasurfaces 116 may be integrated into an integrated component (e.g., a combined component). In this way,

[0094] In one embodiment, the optical subsystem 102 includes an illumination source 118 configured to generate illumination 106 in the form of at least one illumination beam. The illumination from the illumination source 118 may include light of one or more selected wavelengths, including but not limited to ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation. By way of illustration, the wavelength may or may not be in the range of 248 nm to 1600 nm. For example, the optical subsystem 102 may include one or more apertures at the illumination pupil plane to divide the illumination from the illumination source 118 into one or more illumination beams 106 or illumination lobes. In this regard, the optical subsystem 102 may provide dipole illumination, quadrupole illumination, and so on. Additionally, the spatial profile of the illumination beam 106 on the sample 104 may be controlled by a field plane aperture to have any selected spatial profile.

[0095] The illumination source 118 may include any type of illumination source suitable for providing illumination 106. In one embodiment, the illumination source 118 is a laser source. For example, the illumination source 118 may include but not be limited to one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, and so on. In this regard, the illumination source 118 may provide illumination 106 with high coherence (e.g., high spatial coherence and / or temporal coherence). In another embodiment, the illumination source 118 includes a laser sustained plasma (LSP) source. For example, the illumination source 118 may include but not be limited to an LSP lamp, an LSP bulb, or an LSP chamber suitable for accommodating one or more elements that can emit broadband illumination when excited into a plasma state by a laser source. In another embodiment, the illumination source 118 includes a lamp source. For example, the illumination source 118 may include but not be limited to arc lamps, discharge lamps, electrodeless lamps, and so on. In this regard, the illumination source 118 may provide illumination 106 with low coherence (e.g., low spatial coherence and / or temporal coherence).

[0096] The illumination source 118 may provide illumination 106 using free space technology and / or optical fibers. Additionally, the illumination source 118 may be located within the optical head (e.g., the optical subsystem 102) or away from the optical head (e.g., the optical subsystem 102). In this way, the optical head (e.g., the optical subsystem 102) may receive illumination 106 from the illumination source 118 using any combination of free space coupling or optical fibers. Additionally, the illumination 106 may be provided as a diverging beam, a collimated beam, or a beam with any focusing characteristics.

[0097] In some embodiments, the illumination source 118 generates multi-lobe illumination 106 by providing light in two or more optical fibers, where the light output from each optical fiber is an illumination lobe of the illumination beam. In another embodiment, the illumination source 118 generates multi-lobe illumination 106 by diffracting a light source into two or more diffraction orders, where at least some of the diffraction orders of the light source form the illumination lobes of the illumination 106. The efficient generation of multiple illumination lobes by controlled diffraction is generally described in U.S. Patent No. 11,118,903, issued September 14, 2021, which is incorporated herein by reference in its entirety.

[0098] In another embodiment, the optical subsystem 102 directs an illumination beam to the sample 104 via an illumination path 120. The illumination path 120 may include one or more optical elements suitable for modifying and / or conditioning the illumination beam and directing the illumination beam to the sample 104. In one embodiment, the illumination path 120 includes one or more illumination path lenses 122 (e.g., to collimate the illumination beam, relay the pupil, and / or field plane, etc.). In another embodiment, the illumination path 120 includes one or more illumination path optical devices 124 to shape or otherwise control the illumination beam. For example, the illumination path optical devices 124 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0099] In another embodiment, the optical subsystem 102 includes an objective lens 126 to focus the illumination beam onto the sample 104 (e.g., a stacked target having stacked target elements on two or more layers of the sample 104). In another embodiment, the sample 104 is disposed on a sample stage 128, which is suitable for fixing the sample 104 and is further configured to position the sample 104 relative to the illumination beam.

[0100] In another embodiment, the optical subsystem 102 includes one or more detectors 130 configured to capture light or other (e.g., sample light 108) emitted from the sample 104 via a collection path 132. The collection path 132 may include one or more optical elements suitable for modifying and / or conditioning the sample light 108 from the sample 104. In one embodiment, the collection path 132 includes one or more collection path lenses 134 (e.g., to collimate the illumination beam, relay the pupil, and / or field plane, etc.), and the one or more collection path lenses may or may not include the objective lens 126. In another embodiment, the collection path 132 includes one or more collection path optics 136 to shape or otherwise control the sample light 108. For example, the collection path optics 136 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0101] The detector 130 may be located at any selected position within the collection path 132. In one embodiment, the optical subsystem 102 includes a detector 130 located at the field plane (e.g., the plane conjugate to the sample 104) to produce an image of the sample 104. In another embodiment, the optical subsystem 102 includes a detector 130 located at the pupil plane (e.g., the diffraction plane) to produce a pupil image. In this regard, the pupil image may correspond to the angular distribution of light from the sample 104 to the detector 130. For example, diffraction orders associated with the diffraction of the illumination beam from the sample 104 (e.g., superimposed targets on the sample 104) may be imaged or otherwise observed in the pupil plane. In a general sense, the detector 130 may capture any combination of reflected (or transmitted), scattered, or diffracted light from the sample 104.

[0102] The optical subsystem 102 may generally include any number or type of detectors 130 suitable for capturing light indicative of the superposition from the sample 104. In one embodiment, the detector 130 includes one or more detectors 130 suitable for characterizing a static sample. In this regard, the optical subsystem 102 may operate in a static mode in which the sample 104 is static during the measurement. For example, the detector 130 may include a two-dimensional pixel array, such as but not limited to a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) device. In this regard, the detector 130 may produce a two-dimensional image (e.g., a field plane image or a pupil plane image) in a single measurement.

[0103] In one embodiment, detector 130 includes one or more detectors 130 suitable for characterizing a moving sample (e.g., a scanned sample). In this regard, optical subsystem 102 can operate in a scanning mode, in which the sample 104 is scanned relative to the measurement field during measurement. For example, detector 130 can include a 2D pixel array having a capture time and / or refresh rate sufficient to capture one or more images within a selected image tolerance (e.g., image blur, contrast, sharpness, etc.) during scanning. By another example, detector 130 can include a line scan detector to continuously generate an image one row of pixels at a time. By another example, detector 130 can include a time delay integration (TDI) detector.

[0104] In another embodiment, optical subsystem 102 includes a scanning subsystem to scan sample 104 relative to the measurement field during metrology measurements. For example, sample stage 128 can position and orient sample 104 within the focal volume of objective 126. In another embodiment, sample stage 128 includes one or more adjustable stages, such as but not limited to a linear translation stage, a rotational stage, or a tilt / skew stage. In another embodiment, although not shown, the scanning subsystem includes one or more beam scanning optics (e.g., a rotatable mirror, a galvanometer, etc.) to scan the illumination beam relative to sample 104.

[0105] The illumination path 120 and the collection path 132 of optical subsystem 102 can be oriented in a wide range of configurations suitable for illuminating sample 104 with an illumination beam and collecting light emitted from sample 104 in response to the incident illumination beam. For example, as Figure 1B illustrated, optical subsystem 102 can include a beam splitter 138 oriented such that common objective 126 can simultaneously direct the illumination beam to sample 104 and collect light from sample 104. This configuration can be referred to as a through-the-lens (TTL) configuration because illumination 106 is directed to sample 104 through the same objective 126 used to collect sample light 108. By another example, optical subsystem 102 can include an optical element (e.g., illumination path lens 122) to direct illumination 106 to sample 104 and a separate objective 126 to collect sample 104. This configuration can be referred to as an outside-the-lens (OTL) configuration.

[0106] Figures 2 through 4B depict various non-limiting examples of metasurface 116 within optical subsystem 102 in accordance with one or more embodiments of the present disclosure.

[0107] Figures 2A - 2EDepicts the use of a metasurface 116 in a variant of an optical subsystem 102 suitable for coherent point-scanning measurement applications, in accordance with one or more embodiments of the present disclosure.

[0108] Figure 2A Is a conceptual diagram of an optical subsystem 102 in accordance with one or more embodiments of the present disclosure, which is depicted as having bulk optical elements for pupil-plane based measurements. Figure 2A Is Figure 1B A variant of Figure 1B such that all descriptions associated with Figure 2A extend to Figure 2A Specifically, Figure 2A depicts a TTL configuration where coherent illumination 106 is provided by a fiber 202 (e.g., a single-mode fiber), collimated by a collimator 204, and directed to a sample 104 via a beam splitter 138 and an objective 126. The fiber 202 may be associated with an illumination source 118 (e.g., a fiber-based illumination source 118) or may be a delivery fiber. The objective 126 collects sample light 108, which passes through the beam splitter 138 and is transmitted towards one or more detectors 130 located at the pupil plane 206. Figure 2A Further depicts a field stop 208 located in the collection path 132, a field stop 210 located in the illumination path 120, and an aperture 212 (e.g., an aperture stop) located in the illumination path 120.

[0109] Figures 2B - 2E Depicts Figure 2A a variant of a second configuration of the optical subsystem 102 in

[0110] In some embodiments, the optical subsystem 102 includes one or more bulk optical elements, where the surface of such bulk optical element includes a structure forming the metasurface 116. It is contemplated herein that such bulk optical elements may be formed as thin elements, which may be substantially smaller than typical components designed to manipulate light without the metasurface 116.

[0111] Figure 2Bis according to one or more embodiments of the present disclosure Figure 2A schematic diagram of the optical subsystem 102, the optical subsystem is depicted as having a metasurface 116 formed on a plurality of bulk optical elements. In some embodiments, Figure 2B the components in can form an optical head. In Figure 2B the optical subsystem 102 includes a first bulk optical element 214 and a first grating 216, the first bulk optical element having a metasurface 116a formed as a lens (e.g., a collimating lens for collimating the divergent illumination 106), the first grating guiding the collimated illumination 106 to a second bulk optical element 218, the second bulk optical element including a grating beam splitter 220 and a metasurface 116b formed as an objective lens. In this way, the first bulk optical element 214 can be part of the illumination path 120 and can operate as an illumination path lens 122 and illumination path optics 124. The sample light 108 can then be collected by the metasurface 116b formed as an objective lens and guided by the grating beam splitter 220 towards a third bulk optical element 222, the third bulk optical element including a second grating 224 and a metasurface 116c formed as a lens. The metasurface 116c formed as a lens can then focus the sample light 108 towards the detector 130 in the pupil plane 206 through the field stop 208. The third bulk optical element 222 is thus part of the collection path 132 and can operate as a collection path lens 134 and collection path optics 136. In some embodiments, the first bulk optical element 214 and the third bulk optical element 222 can have a similar design (e.g., can be complementary devices).

[0112] In Figure 2B the configuration depicted, the metasurface 116 is fabricated on various surfaces (e.g., faces) of the first bulk optical element 214, the second bulk optical element 218, and the third bulk optical element 222 to manipulate the illumination 106 and / or the sample light 108. Additionally, the optical elements can include any combination of the metasurface 116 or other patterned features (e.g., the first grating 216 and the second grating 224).

[0113] According to one or more embodiments of the present disclosure, Table 1 includes various parameters associated with Figure 2B a non-limiting implementation of. It is contemplated herein that such parameters can be suitable for but not limited to 100 / / operation as a coherent point scanning microscope.

[0114] Table 1

[0115]

[0116]

[0117] In some embodiments, the optical subsystem 102 includes one or more fused optical elements, where one or more metasurfaces 116 are formed on one or more surfaces of the fused optical element and / or on one or more interfaces between subassemblies joined together (e.g., using an optically transparent adhesive or any other suitable joining technique) to form the fused optical element. It is contemplated herein that the fused assembly can be highly compact, mechanically stable, and fix the optical alignment between the constituent metasurfaces 116 and / or other features.

[0118] Figure 2C is of an optical subsystem 102 according to one or more embodiments of the present disclosure Figure 2A schematic diagram, the optical subsystem is depicted as having metasurfaces 116 formed on several faces and interfaces of a fused optical element 226a. Specifically, Figure 2C depicts a fused optical element 226a formed by four sub-elements 228 (individually labeled 228a to 228d). In this configuration, the metasurface 116a formed as a lens and the metasurface 116c formed as a lens are disposed at an interface 230 on any combination of the sub-elements 228a, 228b; the first grating 216 and the second grating 224 are disposed at an interface 232 on any combination of the sub-elements 228b, 228c; the grating beam splitter 220 is disposed at an interface 234 on any combination of the sub-elements 228c, 228d; and the metasurface 116b formed as a lens is disposed at an outer surface 236.

[0119] Figure 2C and thus can be conceptualized, but not limited to Figure 2B a variant in which the first bulk optical element 214 is joined to the third bulk optical element 222 to form a common sub-element 228b (although this is merely illustrative and not required), and in which the sub-element 228c replaces the open space between the bulk optical elements 210, 214, 218. Thus, Figure 2B and 2C can provide substantially the same optical performance, but Figure 2C can provide a more compact package and easier optical alignment. However, Figure 2C is merely illustrative and should not be construed as limiting the scope of the present disclosure.

[0120] Additionally, Figure 2C depicts a configuration in which the sub-element 228a extends to the field plane such that the field stop 208 can be fabricated on the face of the sub-element 228a. However, this is merely illustrative and not required. In some embodiments, the fused optical element 226a does not include the sub-element 228a (e.g., the fused optical element 226a can be formed by the sub-elements 228b to 228d). In this configuration, if desired, a separate field stop 208 can be provided.

[0121] In some embodiments, the metasurface 116 can provide multiple optical functions (e.g., optical power, diffraction, refraction, etc.). In other words, the metasurface 116 can manipulate light in a way that replicates the performance of multiple conventional optical elements that manipulate light via the accumulation of phase delays or other techniques. For example, a single metasurface 116 can include a number of features designed to provide multiple optical functions. As another example, two or more metasurfaces 116 can be fabricated to be stacked (e.g., as a composite metasurface 116) to provide multiple optical functions. It is contemplated herein that using one or more metasurfaces 116 that provide multiple optical functions can further simplify and / or reduce the size of the design of the optical subsystem 102 (or a portion thereof).

[0122] Figure 2D is of one or more embodiments of the present disclosure Figure 2A Schematic diagram of the optical subsystem 102, which is depicted as having metasurfaces 116 formed on several faces of the monolithic assembly 238. In Figure 2D , the monolithic assembly 238 is formed as a single, uniform material element, with metasurfaces 116d to 116e on each surface. For example, a metasurface 116d configured as both a lens and a beam deflector can be formed on a first surface 240 of the monolithic assembly 238, a metasurface 116e configured as both a beam splitter and an objective lens can be formed on a second surface 242, and a metasurface 116f configured as both a lens and a beam deflector can be formed on a different region (or possibly a different surface) of the first surface 240. In this configuration, the metasurface 116d can collimate the illumination 106 and direct this collimated illumination 106 to the metasurface 116e to focus on the sample 104. The metasurface 116e can then collect the sample light 108 and direct this sample light 108 to the metasurface 116f, where the metasurface 116f can operate as a collection path lens 134.

[0123] It is contemplated herein that a monolithic assembly 238 having one or more metasurfaces 116 (e.g., as depicted in Figure 2D ) can more generally provide a robust and highly compact optical head or a portion of the optical subsystem 102.

[0124] Now referring to Figure 2E , Figure 2E is a schematic diagram of an optical subsystem 102 including an achromatic metasurface 116 of one or more embodiments of the present disclosure Figure 2A .

[0125] As previously described herein, a particular design of the metasurface 116 can provide wavelength-sensitive operation. However, multi-wavelength and / or broadband operation can be achieved using a variety of techniques, including but not limited to one or more metasurfaces 116 designed to directly provide multi-wavelength and / or broadband operation. For example, the metasurface 116 (or two or more metasurfaces 116 formed in a stack to form a compound metasurface 116) can be designed as an achromatic lens that can provide wavelength-corrected optical power within at least a selected wavelength range and within a selected tolerance.

[0126] In Figure 2E the optical subsystem 102 includes a fused optical element 226b formed by two sub-elements 228e, 228f. Specifically, Figure 2E the fused optical element 226b in includes a metasurface 116g formed as an achromatic lens and located on the surface 244 to collimate the illumination 106, and a thin-film beam splitter coating disposed on the interface 246 between the sub-elements 228e, 228f and arranged to form a broadband beam splitter. A metasurface 116h formed as an achromatic objective on another surface 248 can receive a portion of the illumination 106 passing through the interface 246, direct this portion of the illumination 106 to the sample 104, collect the sample light 108, and direct this sample light 108 back to the interface 246, where a portion of the sample light 108 can be separated from the illumination 106. As previously described herein, the metasurface 116i formed as an achromatic lens can then operate as the collection path lens 134.

[0127] Figure 2E the fused optical element 226b in further includes an additional surface 250 that provides total internal reflection of the sample light 108 before the metasurface 116i, which can facilitate the desired positioning of the sample light 108 along the collection path 132 toward the detector. However, Figure 2E the particular design of the fused optical element 226b in that includes the surface 250 is illustrative only and should not be construed as limiting the scope of the present disclosure. For example, it is not required to use the surface 250 to redirect the sample light 108. In some embodiments, surfaces that provide TIR reflection can be implemented to direct any combination of the illumination 106 or the sample light 108. In some embodiments, surfaces that provide TIR reflection are not required.

[0128] Now referring to Figures 3A - 3B , Figures 3A - 3B depicts the use of the metasurface 116 in a variant of the optical subsystem 102 suitable for bright-field imaging applications according to one or more embodiments of the present disclosure. Figure 3A is a conceptual diagram of an optical subsystem according to one or more embodiments of the present disclosure. Figure 3A is Figure 1B a variant such that compared toFigure 1B All associated descriptions extend to Figure 3A . Specifically,[[]] Figure 3A depicts a TTL configuration in which incoherent illumination 106 (e.g., multi-wavelength and / or broadband illumination 106) is provided by an optical fiber 302 (e.g., a multi-mode optical fiber), collimated by a collimator 304, and directed to a sample 104 via a beam splitter 138 and an objective lens 126. The optical fiber 302 may be associated with an illumination source 118 (e.g., a fiber-based illumination source 118) or may be a delivery optical fiber. The objective lens 126 collects sample light 108, which passes through the beam splitter 138 and is transmitted towards one or more detectors 130 located at a field plane 306.[[]] Figure 3A The configuration depicted in [] may be suitable for, but is not limited to, incoherent brightfield measurement techniques that utilize a field plane detector 130, non-limiting examples of which are generally described in U.S. Patent Application No. 18 / 422,668, filed on January 25, 2024, which is incorporated herein by reference in its entirety.[[]]

[0129] Figure 3B is of an optical subsystem 102 according to one or more embodiments of the present disclosure Figure 3A and is schematically depicted as having a metasurface 116 formed on a fused optical element 226c. Specifically,[[]] Figure 3B Illustration 308 in [] depicts a detailed view of the fused optical element 226c formed by sub-elements 228g to 228k, where metasurfaces 116j to 116q are formed on the associated surfaces and / or interfaces. For example, a metasurface 116j formed as a lens (e.g., an achromatic lens) may collimate illumination 106 and a metasurface 116k formed as a beam deflector (e.g., a grating deflector) may direct the collimated illumination 106 to a metasurface 116l formed as a beam splitter.[[]] Figure 3B Further depicts a non-limiting configuration of a multi-surface element formed by a plurality of metasurfaces 116. Specifically,[[]] Figure 3B depicts metasurfaces 116m to 116o that form a three-surface metalens (e.g., a three-surface achromatic objective metalens) that may direct illumination 106 to the sample 104 and collect sample light 108. A metasurface 116l formed as a beam splitter may then direct at least a portion of the sample light 108 to a metasurface 116p formed as a beam deflector (e.g., a grating deflector) and then to a metasurface 116q formed as a lens (e.g., an achromatic lens). This metasurface 116q may correspond to a collection path lens 134 and may facilitate imaging the sample 104 onto the detector 130.[[]]

[0130] Now refer to Figures 4A - 4B . Figures 4A - 4BDepicts the use of a metasurface 116 in a variant of an optical subsystem 102 suitable for dark-field imaging applications, in accordance with one or more embodiments of the present disclosure. Figure 4A Is a conceptual diagram of an optical subsystem in accordance with one or more embodiments of the present disclosure. Figure 4A Is Figure 1B A variant of such that all descriptions associated with Figure 1B are extended to Figure 4A . Specifically, Figure 4A depicts an OTL configuration where illumination 106 (e.g., coherent illumination 106) is provided by a fiber optic 402 (e.g., single-mode fiber optic) and is directed to the sample via an illumination path lens 122 outside the numerical aperture (e.g., collection numerical aperture) of an objective 126 as part of a collection path 132. Additionally, multiple illumination beams 106 can be provided through multiple channels 404. Again, the fiber optic 402 can be associated with an illumination source 118 (e.g., a fiber optic-based illumination source 118) or can be a delivery fiber optic. The objective 126 collects sample light 108, and one or more detectors 130 located at a field plane 406 generate one or more dark-field images of the sample 104 based on the collected sample light 108 (e.g., which does not include specular reflections of the illumination 106 that are also outside the collection numerical aperture of the objective 126). Figure 4A The configuration depicted in

[0131] Figure 4B is suitable for, but not limited to, coherent dark-field measurement techniques that utilize a field plane detector 130, non-limiting examples of which are generally described in U.S. Patent No. 11,359,916, filed on June 14, 2022, and U.S. Patent Publication No. 2023 / 0259040, published on August 17, 2023, which patents and patent publications are incorporated herein by reference in their entireties.

[0131] Figure 4B Is an optical subsystem 102 in accordance with one or more embodiments of the present disclosure Figure 4A depicted as having a metasurface 116 formed on a fused optical element 226d. Specifically, Figure 4B Illustration 408 of Figure 4B depicts a fused optical element 226d formed by sub-elements 228l, 228m, where metasurfaces 116r to 116v are formed on associated surfaces and / or interfaces. For example, a metasurface 116r formed as a lens can collimate the illumination 106 and a metasurface 116s formed as a beam deflector (e.g., a grating deflector) can direct the collimated illumination 106 to the sample 104. Additionally, multiple instances of metasurfaces 116r, 116s can provide multiple illumination beams 106. Figure 4B Further depicts metasurfaces 116t to 116v formed as a three-surface superlens (e.g., a three-surface objective superlens) that can collect the sample light 108 as shown.

[0132] in a manner similar to Figures 2A - 2E the examples provided in Figures 3A - 4B depict the use of the metasurface 116 in the optical subsystem 102 (or a portion thereof, such as an optical head), which can achieve robust performance in a highly compact package. However, it should be understood that Figures 3A - 4B this is provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure. For example, the optical subsystem 102 (or a portion thereof) can be formed using any number of metasurfaces 116 on any number of surfaces. As another example, the optical subsystem 102 can be extended to include one or more metasurfaces 116 that provide multiple optical functions (e.g., optical power, diffraction, refraction, etc.). As another example, the optical subsystem 102 can include one or more metasurfaces 116 on any combination of bulk optical elements, fused assemblies, and / or monolithic assemblies. As another example, Figure 3B and 4B the description of the three-surface objective lens in

[0133] Additionally, Figures 2A - 4B the associated configuration and / or associated application fields of the optical subsystem 102 in

[0134] Now referring to Figure 5 , multi-channel optical measurements using multiple optical subsystems 102 incorporating metasurfaces 116 are described in more detail in accordance with one or more embodiments of the present disclosure. In some embodiments, the optical measurement system 100 includes two or more optical subsystems 102, where at least one of the optical subsystems 102 includes one or more metasurfaces 116. As previously described herein, the use of one or more metasurfaces 116 can enable a significant reduction in the physical size of the optical subsystem 102 (or a portion thereof, such as an optical head). Accordingly, multiple optical subsystems 102 (or portions thereof, such as optical heads) can be distributed to provide parallel (and optionally simultaneous) measurements of different portions of the sample 104.

[0135] Figure 5is a conceptual schematic diagram depicting an arrangement of multiple optical subsystems 102 across a sample 104 for parallel measurement in accordance with one or more embodiments of the present disclosure. Large-scale overlay metrology sampling is generally described in U.S. Patent No. 11,899,375, filed on February 13, 2024, which is incorporated herein by reference in its entirety. Specifically, Figure 5 depicts a configuration where a separate optical subsystem 102 is provided for each reticle field 502 associated with a lithography tool (e.g., scanner, stepper, etc.) used to fabricate features on the sample 104. In this way, the separate optical subsystems 102 can be used to provide parallel measurement of features associated with different dies on the sample 104. Additionally, this configuration can utilize a separate detector 130 for each optical subsystem 102, or multiple optical subsystems 102 can share a common detector 130. However, it should be understood that Figure 5 is provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure. Rather, the optical measurement system 100 can include any number of optical subsystems 102, where at least one of the optical subsystems 102 includes one or more metasurfaces 116.

[0136] Figure 6 is a flowchart illustrating steps performed in a method 600 for providing optical measurement in accordance with one or more embodiments of the present disclosure. The embodiments and enabling technologies previously described herein in the context of the optical measurement system 100 should be construed as extending to the method 600. For example, a processor 112 of the controller 110 can execute program instructions that cause the processor 112 to perform the various steps of the method 600 directly or indirectly (e.g., via control signals to additional components). However, it should further be noted that the method 600 is not limited to the architecture of the optical measurement system 100.

[0137] In some embodiments, the method 600 includes step 602 of directing illumination 106 to the sample 104 using an optical subsystem 102 that includes one or more optical elements.

[0138] In some embodiments, the method 600 includes step 604 of collecting sample light 108 from the sample 104 in response to the illumination 106 using the optical subsystem 102, where at least one of the one or more optical elements in the optical subsystem 102 includes one or more metasurfaces 116 to manipulate at least one of the illumination 106 or the sample light 108 using subwavelength features. The subwavelength features can be smaller than at least some of the wavelengths in at least one of the illumination 106 or the sample light 108.

[0139] In some embodiments, method 600 includes step 606 of generating a detection signal based on at least a portion of sample light 108. The detection signal can include any type of signal known in the art, including information indicative of a measurement of sample 104. For example, the detection signal can include, but is not limited to, a field plane image of sample 104 from detector 130 at the field plane, a pupil plane image associated with the distribution of light (e.g., diffracted light) emitted from sample 104, or a time-based signal associated with the pupil plane and / or field plane detector 130 (e.g., a photodiode). In some embodiments, method 600 includes step 608 of generating one or more measurements of sample 104 based on the detection signal. The measurements can include any type of information associated with sample 104. In some embodiments, the measurements include metrology measurements, such as, but not limited to, overlay measurements or critical dimension (CD) measurements. In some embodiments, the measurements include inspection measurements, such as, but not limited to, identifying and / or characterizing defects on sample 104.

[0140] Now referring generally to FIGS. 1 - 6, additional considerations of metasurface 116 within optical measurement system 100 are described in accordance with one or more embodiments of the present disclosure.

[0141] It is contemplated herein that metasurface 116 can provide numerous advantages over conventional optical elements.

[0142] For example, metasurface 116 can enable smaller and / or flatter optical components, which can reduce the size of the optical head (e.g., optical subsystem 102), which in turn enables such optical heads to be more tightly packaged, allowing for multiple parallel measurements to be made on each sample 104. Additionally, metasurface 116 can be integrated into one or more substrates of optical elements (e.g., bulk, fused, or monolithic optical elements) and / or combined (e.g., stacked) as disclosed herein to achieve dense integration and a smaller overall component size.

[0143] As another example, metasurface 116 can enable a relatively short focal length (e.g., when used to form objective lens 126), which can allow for a high numerical aperture (e.g., greater than or equal to 0.7, 0.93, or higher).

[0144] As another example, the fabrication and assembly of the metasurface 116 is relatively low cost. By way of illustration, the metasurface 116 can be fabricated using high-throughput manufacturing processes such as, but not limited to, semiconductor manufacturing processes. As another illustration, optical components fabricated using the metasurface 116 may require fewer mechanical components for mounting, especially when multiple metasurfaces 116 are integrated into a block, fused, or monolithic component as described herein. Further, when multiple metasurfaces 116 are integrated into a block, fused, or monolithic component, such metasurfaces 116 can be aligned during fabrication such that the alignment and / or assembly of the optical subsystem 102 can be easier, faster, and / or may require fewer mechanical components.

[0145] As another example, the metasurface 116 can be fabricated to have a high degree of consistency and / or reliability. For example, semiconductor manufacturing processes used to fabricate the metasurface 116 can be tightly controlled and in some cases more tightly controlled than manufacturing processes for traditional optical components.

[0146] As another example, the metasurface 116 can be combined with traditional optical elements (e.g., refractive, reflective, and diffractive elements or surfaces) within an optical head (e.g., the optical subsystem 102). Additionally, multiple metasurfaces 116 on different surfaces can work together to provide multi-surface elements. By way of illustration, the objective lens 126 can be formed by one or more metasurfaces 116 on any number of surfaces. As another illustration, the objective lens 126 can be formed by a combination of one or more metasurfaces 116 having refractive, reflective, and / or diffractive elements or surfaces. In some embodiments, an objective lens having at least one or more metasurfaces 116 can be designed to operate at finite conjugates to directly produce an image or other distribution on the detector 130 such that no additional collection lens (e.g., the collection path lens 134) is required.

[0147] As another example, the metasurface 116 can be designed to support multiple wavelengths directly or by stacking multiple metasurfaces 116. In this way, a user can select a wavelength or wavelength range for operation. As another example, different optical heads (e.g., different optical subsystems 102) within a single optical measurement system 100 can be designed to support different wavelengths.

[0148] As another example, the metasurface 116 can be used in polarization-sensitive applications. For example, one or more metasurfaces 116 can directly manipulate the polarization of light (e.g., the illumination 106 and / or the sample light 108). By way of illustration, one or more metasurfaces 116 can operate as polarizers, wave plates, or more generally polarization manipulators. In another example, one or more metasurfaces 116 can provide polarization-sensitive operation. In this configuration, the optical subsystem 102 can include a polarizer and / or a polarization manipulator before the polarization-sensitive metasurface 116.

[0149] As another example, the metasurface 116, either alone or in combination with refractive, reflective, and / or diffractive elements or surfaces, can be used to shape the beam profile of light (e.g., illumination 106 and / or sample light 108). In this configuration, such components can operate to replace or supplement an apodizing or truncating component. Additionally, this configuration can conserve light through beam shaping rather than filtering.

[0150] In addition, any component of the optical subsystem 102, including the metasurface 116 or other components, can be tilted or wedged to deflect stray light out of the optical path.

[0151] The subject matter described herein is sometimes illustrated as including different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and in fact, many other architectures can be implemented that achieve the same functionality. In a conceptual sense, any arrangement of components that achieves the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components that are combined herein to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to achieve the desired functionality, and any two components that can be so associated can also be considered to be "couplable" to each other to achieve the desired functionality. Specific examples of couplable include, but are not limited to, components that physically interact and / or physically interact and / or components that can interact wirelessly and / or interact wirelessly and / or components that can interact logically and / or interact logically.

[0152] It is believed that many of the advantages of the present disclosure and its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction, and arrangement of the components without departing from the disclosed subject matter or sacrificing all of its material advantages. The described form is merely illustrative, and the appended claims are intended to embrace and include such changes. Additionally, it should be understood that the invention is defined by the appended claims.

Claims

1. A device, comprising: One or more optical elements configured to direct illumination to a sample and collect sample light from the sample in response to the illumination, wherein at least one of the one or more optical elements includes one or more metasurfaces configured to manipulate at least one of the illumination or the sample light using sub-wavelength features, wherein the sub-wavelength features are less than at least some of the wavelengths in at least one of the illumination or the sample light being manipulated, and wherein the one or more optical elements provide optical power for at least one of the operations of focusing the illumination on the sample or collecting the sample light from the sample.

2. The device according to claim 1, wherein at least one of the one or more metasurfaces includes: A lens.

3. The device according to claim 1, wherein at least one of the one or more metasurfaces includes: A beam splitter.

4. The device according to claim 1, wherein at least one of the one or more metasurfaces includes: One or more beam deflectors.

5. The device according to claim 1, wherein at least one of the one or more metasurfaces includes: An objective lens.

6. The device according to claim 5, wherein the objective lens is a multi-surface element formed by at least two of the one or more metasurfaces.

7. The device according to claim 1, wherein the one or more optical elements include one or more bulk optical elements, and wherein at least one of the one or more metasurfaces is formed on a surface of at least one of the one or more bulk optical elements.

8. The device according to claim 7, wherein the one or more metasurfaces include two or more metasurfaces, and wherein at least one of the one or more bulk optical elements includes at least two of the two or more metasurfaces.

9. The device according to claim 1, wherein the one or more optical elements include one or more fused optical elements formed by two or more sub-elements, and wherein at least one of the one or more metasurfaces is formed at an interface of two of the two or more sub-elements.

10. The device according to claim 9, wherein the one or more metasurfaces include two or more metasurfaces, and wherein at least one of the one or more fused optical elements includes at least two of the two or more metasurfaces.

11. The device according to claim 1, wherein the one or more optical elements include: A first lens formed as at least one of the one or more metasurfaces and configured to collimate the illumination, wherein the illumination is incident on the first lens as a divergent beam; An objective lens formed as at least one of the one or more metasurfaces, wherein the objective lens is configured to direct the illumination to the sample and collect the sample light from the sample; A first grating configured to direct the illumination from the first lens to the objective lens; A second lens formed as at least one of the one or more metasurfaces; And A second grating configured to receive the sample light from the objective lens and direct the sample light to the second lens.

12. The apparatus according to claim 11, wherein the first lens, the objective lens, the first grating, the second lens, and the second grating are integrated in a fused optical element.

13. The apparatus according to claim 1, wherein the one or more optical elements comprise: An objective lens formed as one of the one or more metasurfaces, wherein the objective lens is configured to direct the illumination to the sample and collect the sample light from the sample; A first metasurface of the one or more metasurfaces configured to collimate the illumination and direct the illumination to the objective lens, wherein the illumination is incident on the first metasurface as a divergent beam; And A second metasurface of the one or more metasurfaces configured to receive the sample light from the objective lens and focus the sample light.

14. The apparatus according to claim 13, wherein the second metasurface focuses the sample light onto a collection field stop.

15. The apparatus according to claim 13, wherein the objective lens, the first metasurface, and the second metasurface are integrated in a monolithic element.

16. The apparatus according to claim 1, wherein the one or more optical elements comprise: An objective lens formed as at least one of the one or more metasurfaces, wherein the objective lens is configured to direct the illumination to the sample and collect the sample light from the sample; A first metasurface of the one or more metasurfaces configured to collimate the illumination, wherein the illumination is incident on the first metasurface as a divergent beam; A second metasurface; And A beam splitter configured to direct the illumination from the first metasurface to the objective lens and direct the sample light from the objective lens to the second metasurface, wherein the second metasurface focuses the sample light.

17. The apparatus according to claim 16, wherein the second metasurface focuses the sample light onto a collection field stop.

18. The apparatus according to claim 16, wherein the objective lens, the first metasurface, the second metasurface, and the beam splitter are integrated in a fused optical element.

19. The apparatus according to claim 18, wherein the fused optical element further comprises a surface through which the sample light is directed from the beam splitter to the second metasurface via total internal reflection.

20. The apparatus according to claim 1, wherein the one or more optical elements comprise: An objective lens formed as at least one of the one or more metasurfaces, wherein the objective lens is configured to collect the sample light from the sample; And At least one of the one or more metasurfaces configured to direct the illumination to the sample at an angle outside the numerical aperture of the objective lens.

21. The apparatus according to claim 20, wherein at least one of the one or more metasurfaces configured to direct the illumination to the sample at an angle outside the numerical aperture of the objective lens directs two or more beams of the illumination to the sample outside the numerical aperture of the objective lens.

22. The apparatus according to claim 1, wherein at least some of the sub-wavelength features in at least one particular metasurface of the one or more metasurfaces are arranged as a plurality of islands distributed across the particular metasurface.

23. The apparatus according to claim 22, wherein at least one of the sub-wavelength features within the islands, the spacing between the islands, or the orientation of the islands varies across the particular metasurface.

24. The apparatus according to claim 1, wherein the distribution of the sub-wavelength features in at least one particular metasurface of the one or more metasurfaces is uniform across the particular metasurface.

25. The apparatus according to claim 1, wherein at least some of the sub-wavelength features in at least one of the one or more metasurfaces are formed as blazed features.

26. The apparatus according to claim 1, wherein at least some of the sub-wavelength features in at least one of the one or more metasurfaces are formed as grating features.

27. The apparatus according to claim 1, wherein at least some of the sub-wavelength features in at least one of the one or more metasurfaces are formed as stepped features.

28. The apparatus according to claim 1, wherein the one or more metasurfaces include two or more metasurfaces, and at least two of the two or more metasurfaces are formed as a stacked structure.

29. The apparatus according to claim 1, wherein at least one of the one or more metasurfaces directs the illumination to the sample at an angle associated with a numerical aperture of at least 0.

7.

30. A metrology system, comprising: a light source configured to generate illumination; one or more optical subsystems, wherein a respective optical subsystem of the one or more optical subsystems includes one or more optical elements configured to direct the illumination to a sample and collect sample light from the sample in response to the illumination, wherein at least one of the one or more optical elements includes one or more metasurfaces configured to manipulate at least one of the illumination or the sample light using sub-wavelength features, wherein the sub-wavelength features are less than at least some of the wavelengths in at least one of the illumination or the sample light, and wherein the one or more optical elements provide optical power for at least one of the operations of focusing the illumination on the sample or collecting the sample light from the sample; one or more detectors configured to generate a detection signal based on the sample light collected by the one or more optical subsystems; and A controller communicatively coupled to the one or more detectors, wherein the controller includes one or more processors configured to execute program instructions stored in a memory device, and wherein the program instructions are configured to cause the one or more processors to perform a metrology prescription by generating a plurality of metrology measurements of the sample based on the detection signals from the one or more detectors.

31. The metrology system according to claim 30, wherein the one or more optical subsystems include two or more optical subsystems.

32. The metrology system according to claim 31, wherein the distribution of the two or more optical subsystems is arranged to provide parallel measurements of features in one or more fields on the sample.

33. The metrology system according to claim 32, wherein the distribution of the two or more optical subsystems is arranged to provide a single optical subsystem among the two or more optical subsystems for at least one of the one or more fields on the sample.

34. The metrology system according to claim 32, wherein the distribution of the two or more optical subsystems is arranged to provide at least two optical subsystems among the two or more optical subsystems for at least one of the one or more fields on the sample.

35. The metrology system according to claim 30, wherein at least one of the one or more metasurfaces includes: A lens.

36. The metrology system according to claim 30, wherein at least one of the one or more metasurfaces includes: A beam splitter.

37. The metrology system according to claim 30, wherein at least one of the one or more metasurfaces includes: One or more beam deflectors.

38. The metrology system according to claim 30, wherein at least one of the one or more metasurfaces includes: An objective lens.

39. The metrology system according to claim 38, wherein the objective lens is formed by at least two of the one or more metasurfaces.

40. The metrology system according to claim 30, wherein the one or more optical elements include one or more bulk optical elements, and wherein at least one of the one or more metasurfaces is formed on a surface of at least one of the one or more bulk optical elements.

41. The metrology system according to claim 40, wherein the one or more metasurfaces include two or more metasurfaces, and wherein at least one of the one or more bulk optical elements includes at least two of the two or more metasurfaces.

42. The metrology system according to claim 30, wherein the one or more optical elements include one or more fused optical elements formed by two or more sub-elements, and wherein at least one of the one or more metasurfaces is formed at an interface between two of the two or more sub-elements.

43. The metrology system according to claim 42, wherein the one or more metasurfaces include two or more metasurfaces, and wherein at least one of the one or more fused optical elements includes at least two of the two or more metasurfaces.

44. The metrology system according to claim 30, wherein the one or more optical elements comprise a single monolithic element.

45. A metrology method, comprising: directing illumination to a sample using an optical subsystem comprising one or more optical elements; collecting sample light from the sample in response to the illumination using the optical subsystem, wherein at least one of the one or more optical elements comprises one or more metasurfaces configured to manipulate at least one of the illumination or the sample light using subwavelength features, wherein the subwavelength features are less than at least some of the wavelengths in at least one of the illumination or the sample light, and wherein the one or more optical elements provide optical power for at least one operation of focusing the illumination on the sample or collecting the sample light from the sample; generating a detection signal based on at least a portion of the sample light; and generating one or more metrology measurements of the sample based on the detection signal.

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