Parallel scanning overlay measurement using optical metasurfaces

Abstract

The device comprises one or more optical elements configured to direct illumination 106 onto a sample 104 and to focus sample light 108 from the sample 104 in response to illumination 106, wherein at least one of the one or more optical elements includes one or more metasurfaces 116 configured to manipulate at least one of illumination 106 or sample light 108 using subwavelength features, the subwavelength features being smaller than at least some wavelengths in at least one of the illumination 106 or sample light 108 being manipulated, and the one or more optical elements may provide a refractive force for at least one of focusing illumination 106 onto the sample 104 or focusing sample light 108 from the sample 104.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 457,285, filed on April 5, 2023, entitled "PARALLEL SCANNING OVERLAY METROLOGY WITH OPTICAL META - SURFACES", with inventors Andrew V. Hill, Jon Madsen, Ido Dolev, Daria Negri, and Yuval Lubashevsky, and is incorporated herein by reference in its entirety.

[0002] The present disclosure generally relates to optical metrology, and more particularly to optical metrology using one or more metasurfaces.

Background Art

[0003] Optical measurement systems in semiconductor device manufacturing environments typically include an optical head having various optical elements configured to direct light towards a sample and collect light from the sample for use in measurement. Existing optical heads are formed from bulk optical elements such as bulk reflection, refraction, or diffraction optical elements. However, these existing optical heads typically have a footprint that is larger than a typical semiconductor wafer sample, and thus only a single optical head can be placed on a sample. The bulk optical elements within existing optical heads are also relatively expensive and tend to have a high degree of variability. As a result, existing optical metrology systems are limited to a single optical head per system and per sample.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] However, these limitations impose constraints on the achievable throughput and ownership costs of optical measurement systems. Therefore, there is a need to develop systems and methods to overcome the aforementioned shortcomings. [Means for solving the problem]

[0006] In embodiments, the techniques described herein relate to a device comprising one or more optical elements configured to direct illumination onto a sample and to focus 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 illumination or sample light using subwavelength features, the subwavelength features being smaller than at least some wavelengths in at least one of the illumination or sample light being manipulated, and the one or more optical elements provide refractive power for at least one of focusing illumination onto a sample or focusing sample light from the sample.

[0007] In embodiments, the techniques described herein relate to a device in which at least one of one or more metasurfaces includes a lens.

[0008] In embodiments, the techniques described herein relate to a device in which at least one of one or more metasurfaces includes a beam splitter.

[0009] In embodiments, the techniques described herein relate to a device in which at least one of one or more metasurfaces includes one or more beam deflectors.

[0010] In embodiments, the techniques described herein relate to a device in which at least one of one or more metasurfaces includes an objective lens.

[0011] In embodiments, the techniques described herein relate to a device in which the objective lens is a polyhedral element formed from at least two of one or more metasurfaces.

[0012] In embodiments, the techniques described herein relate to a device in which one or more optical elements comprise one or more bulk optical elements, and at least one of one or more metasurfaces is formed on the surface of at least one of the one or more bulk optical elements.

[0013] In embodiments, the techniques described herein relate to a device in which one or more metasurfaces comprise two or more metasurfaces, and at least one of one or more bulk optical elements comprises at least two of the two or more metasurfaces.

[0014] In embodiments, the techniques described herein relate to a device in which one or more optical elements include one or more fused optical elements formed from two or more sub-elements, and at least one of one or more metasurfaces is formed at the interface of two of the two or more sub-elements.

[0015] In embodiments, the techniques described herein relate to a device in which one or more metasurfaces comprise two or more metasurfaces, and at least one of one or more fused optical elements comprises at least two of the two or more metasurfaces.

[0016] In embodiments, the techniques described herein relate to a device comprising: a first lens formed as at least one of one or more metasurfaces and configured to collimate illumination, such that illumination is incident upon the first lens as a divergent beam; an objective lens formed as at least one of one or more metasurfaces and configured to direct illumination onto a sample and focus sample light from the sample; a first grating configured to direct illumination from the first lens to the objective lens; a second lens formed as at least one of one or more metasurfaces; and a second grating for receiving sample light from the objective lens and directing the sample light to the second lens.

[0017] In embodiments, the techniques described herein relate to a device in which a first lens, an objective lens, a first grating, a second lens, and a second grating are incorporated into a fused optical element.

[0018] In embodiments, the techniques described herein relate to a device comprising: an objective lens formed as one or more metasurfaces, wherein the objective lens is configured to direct illumination onto a sample and focus sample light from the sample; a first metasurface of one or more metasurfaces, configured to collimate illumination and direct the illumination onto the objective lens, wherein the illumination is incident on the first metasurface as a divergent beam; and a second metasurface of one or more metasurfaces, configured to receive sample light from the objective lens and focus the sample light.

[0019] In embodiments, the techniques described herein relate to a device in which a second metasurface focuses light onto a condensing aperture.

[0020] In embodiments, the techniques described herein relate to a device in which an objective lens, a first metasurface, and a second metasurface are incorporated into a monolithic element.

[0021] In an embodiment, the techniques described herein relate to a device that includes an objective lens formed as at least one of one or more metasurfaces, configured to direct illumination toward a sample and collect sample light from the sample; a first metasurface of one or more metasurfaces configured to collimate illumination, wherein the illumination enters the first lens as a diverging beam; a second metasurface; and a beam splitter configured to direct illumination from the first metasurface toward the objective lens and direct sample light from the objective lens toward the second metasurface, wherein the second metasurface focuses the sample light.

[0022] In an embodiment, the techniques described herein relate to a device in which the second metasurface focuses light onto a condenser aperture stop.

[0023] In an embodiment, the techniques described herein relate to a device in which the objective lens, the first metasurface, the second metasurface, and the beam splitter are incorporated into an integrated optical element.

[0024] In an embodiment, the techniques described herein relate to a device in which the integrated optical element further includes a surface for directing sample light from the beam splitter toward the second metasurface by total internal reflection.

[0025] In an embodiment, the techniques described herein relate to a device that includes an objective lens formed as at least one of one or more metasurfaces, configured to collect sample light from a sample; and at least one of one or more metasurfaces configured to direct illumination toward the sample at an angle outside the numerical aperture of the objective lens.

[0026] In embodiments, the techniques described herein relate to a device in which at least one of one or more metasurfaces, configured to direct illumination onto a sample at an angle outside the numerical aperture of the objective lens, directs two or more beams of illumination onto a sample outside the numerical aperture of the objective lens.

[0027] In embodiments, the techniques described herein relate to a device in which at least some of the subwavelength features on at least one particular metasurface among one or more metasurfaces are arranged in islands distributed across the particular metasurface.

[0028] In embodiments, the techniques described herein relate to a device in which at least one of the subwavelength features within an island, the spacing between islands, or the orientation of the islands varies across a particular metasurface.

[0029] In embodiments, the techniques described herein relate to a device in which the distribution of subwavelength features on at least one particular metasurface among one or more metasurfaces is uniform across that particular metasurface.

[0030] In embodiments, the techniques described herein relate to a device in which at least some of the subwavelength features on at least one of one or more metasurfaces are formed as blazed features.

[0031] In embodiments, the techniques described herein relate to a device in which at least some of the subwavelength features on at least one of one or more metasurfaces are formed as lattice features.

[0032] In embodiments, the techniques described herein relate to a device in which at least some of the subwavelength features on at least one of one or more metasurfaces are formed as stepwise features.

[0033] In embodiments, the techniques described herein relate to a device in which one or more metasurfaces comprise two or more metasurfaces, and at least two of the two or more metasurfaces are formed as a stack structure.

[0034] In embodiments, the techniques described herein relate to a device in which at least one of one or more metasurfaces directs illumination onto a sample at an angle associated with an numerical aperture of at least 0.7.

[0035] In embodiments, the technique described herein relates to a measurement system comprising: an illumination source configured to generate illumination; one or more optical subsystems, each of which comprises one or more optical elements configured to direct illumination onto a sample and to focus sample light from the sample in response to the illumination, at least one of which comprises one or more metasurfaces configured to manipulate at least one of illumination or sample light using subwavelength features, the subwavelength features being smaller than at least several wavelengths in at least one of illumination or sample light, and the one or more optical elements providing refractive power for at least one of focusing illumination onto a sample or focusing sample light from the sample; one or more detectors configured to generate detection signals based on the sample light focused by the one or more optical subsystems; and a controller communicatively connected to the plurality of detectors, the controller comprising one or more processors configured to execute program instructions stored in a memory device, the program instructions configured to cause one or more processors to execute a measurement recipe by generating a plurality of measurement values ​​of a sample based on detection signals from the plurality of detectors.

[0036] In embodiments, the techniques described herein relate to a measurement system in which one or more optical subsystems include two or more optical subsystems.

[0037] In embodiments, the techniques described herein relate to a measurement system in which the distribution of two or more optical subsystems is arranged to provide parallel measurements of one or more features in a field of view of a sample.

[0038] In embodiments, the techniques described herein relate to a measurement system in which the distribution of two or more optical subsystems is arranged to provide a single optical subsystem from the two or more optical subsystems to at least one of one or more fields of view in a sample.

[0039] In embodiments, the techniques described herein relate to a measurement system in which the distribution of two or more optical subsystems is arranged to provide at least two of the optical subsystems to at least one of one or more fields of view in a sample.

[0040] In embodiments, the techniques described herein relate to a measurement system in which at least one of one or more metasurfaces includes a lens.

[0041] In embodiments, the techniques described herein relate to a measurement system in which at least one of one or more metasurfaces includes a beam splitter.

[0042] In embodiments, the techniques described herein relate to a measurement system in which at least one of one or more metasurfaces includes one or more beam polarizers.

[0043] In embodiments, the techniques described herein relate to a measurement system in which at least one of one or more metasurfaces includes an objective lens.

[0044] In embodiments, the techniques described herein relate to a measurement system in which the objective lens is formed from at least two of one or more metasurfaces.

[0045] In embodiments, the techniques described herein relate to a measurement system in which one or more optical elements comprise one or more bulk optical elements, and at least one of one or more metasurfaces is formed on the surface of at least one of the bulk optical elements.

[0046] In embodiments, the techniques described herein relate to a measurement system in which one or more metasurfaces comprise two or more metasurfaces, and at least one of one or more bulk optical elements comprises at least two of the two or more metasurfaces.

[0047] In embodiments, the techniques described herein relate to a measurement system in which one or more optical elements include one or more fused optical elements formed from two or more sub-elements, and at least one of one or more metasurfaces is formed at the interface of two of the two or more sub-elements.

[0048] In embodiments, the techniques described herein relate to a measurement system in which one or more metasurfaces comprise two or more metasurfaces, and at least one of one or more fused optical elements comprises at least two of the two or more metasurfaces.

[0049] In embodiments, the techniques described herein relate to a measurement system in which one or more optical elements include a single monolithic element.

[0050] In embodiments, the technique described herein is a measurement method comprising focusing, generating a detection signal based on at least a portion of the sample light, and generating one or more measurement values ​​of the sample based on the detection signal, wherein the technique is to direct illumination onto a sample using an optical subsystem comprising one or more optical elements, and to focus sample light from the sample in response to illumination by 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 illumination or sample light using subwavelength features, the subwavelength features being smaller than at least some wavelengths in at least one of illumination or sample light, and the one or more optical elements provide refractive power for at least one of focusing illumination onto a sample or focusing sample light from the sample.

[0051] It should be understood that both the above summary and the following detailed description are illustrative and descriptive only and do not necessarily limit the claimed invention. The accompanying drawings incorporated herein and constituting part of this specification illustrate embodiments of the invention and, together with the summary, help to illustrate the principles of the invention.

[0052] Many of the advantages of this disclosure can be better understood by those skilled in the art by referring to the accompanying drawings. [Brief explanation of the drawing]

[0053] [Figure 1A] A conceptual diagram illustrating an optical measurement system according to one or more embodiments of this disclosure is shown. [Figure 1B] A conceptual diagram of an optical subsystem according to one or more embodiments of this disclosure is shown. [Figure 1C] The image shows a top view of a first design of a portion of a metasurface according to one or more embodiments of the present disclosure. [Figure 1D] Figure 1C shows a side view of the design according to one or more embodiments of the present disclosure. [Figure 1E]The above shows a top view of a second design of a portion of the metasurface 116 according to one or more embodiments of the present disclosure. [Figure 1F] Figure 1E shows a side view of the design according to one or more embodiments of the present disclosure. [Figure 2A] A conceptual diagram of an optical subsystem having a bulk optical element for pupil-based measurement according to one or more embodiments of the present disclosure is shown. [Figure 2B] Figure 2A shows a schematic diagram of the optical subsystem of one or more embodiments of the present disclosure, which is shown having metasurfaces formed on a plurality of bulk optical elements. [Figure 2C] Figure 2A shows a schematic diagram of the optical subsystem of one or more embodiments of the present disclosure, which is shown having metasurfaces formed on the faces and interfaces of the fused optical element. [Figure 2D] Figure 2A shows a schematic diagram of an optical subsystem according to one or more embodiments of the present disclosure, which is shown having a metasurface formed on the surface of a monolithic component. [Figure 2E] Figure 2A shows a schematic diagram of an optical subsystem, including an achromatic metasurface, according to one or more embodiments of the present disclosure. [Figure 3A] A conceptual diagram of an optical subsystem according to one or more embodiments of the present disclosure is shown. [Figure 3B] Figure 3A shows a schematic diagram of the optical subsystem 102 of the present disclosure, which is shown having a metasurface formed on a fused optical element according to one or more embodiments of the present disclosure. [Figure 4A] A conceptual diagram of an optical subsystem according to one or more embodiments of this disclosure is shown. [Figure 4B] Figure 4A shows a schematic diagram of the optical subsystem of one or more embodiments of the present disclosure, which is shown having a metasurface formed on a fused optical element. [Figure 5] A conceptual diagram is shown illustrating the arrangement of multiple optical subsystems across a sample for parallel measurement according to one or more embodiments of the present disclosure. [Figure 6]A flowchart illustrating the steps taken in a method for providing optical measurements according to one or more of the present disclosures is provided. [Modes for carrying out the invention]

[0054] Next, we will refer in detail to the subject matter disclosed as shown in the accompanying drawings. This disclosure is shown and described in particular with respect to specific embodiments and their particular features. The embodiments described herein are to be considered illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of this disclosure.

[0055] Embodiments of this disclosure relate to systems and methods for providing optical measurements (e.g., measurement, inspection, etc.) using one or more optical elements formed having at least one metasurface. The metasurface can be formed as one or more material layers having a thickness and / or features smaller than (typically substantially smaller than) the wavelength of light used in the intended application. Such features are referred to herein as subwavelength features and can be used to locally manipulate the amplitude, phase, and / or polarization of incident light. Thus, the metasurface can be formed as a phase modulator based on electromagnetic wavefront modulation of light, with certain properties depending at least in part on the shape and distribution of the subwavelength features. Exemplarily, the subwavelength features may provide individual phase jumps or transitions based on optical resonance effects.

[0056] Metasurfaces can be designed to perform the functions of many bulk optical elements typically used in optical heads of optical measurement systems, including but not limited to lenses (e.g., collimation lenses, objective lenses), beam splitters, beam deflectors, or diaphragms (e.g., field diaphragms, aperture diaphragms). Furthermore, metasurfaces can be designed to combine multiple functions. As a result, optical heads containing one or more metasurfaces can provide a compact platform suitable for illuminating a sample and / or focusing light from a sample, as intended herein.

[0057] Some embodiments of the present disclosure relate to optical heads formed from one or more metasurfaces for manipulating light that is illuminated and / or focused. Some embodiments of the present disclosure relate to optical measurement systems comprising one or more optical heads formed from one or more metasurfaces. In some embodiments, the optical measurement system comprises two or more optical heads for providing parallel characterization of various regions of a sample, each optical head comprising one or more metasurfaces.

[0058] Referring here to Figures 1A to 6, a system and method for providing optical measurement using a metasurface, according to one or more embodiments of the present disclosure, will be described in more detail.

[0059] Figure 1A is a conceptual diagram showing an optical measurement system 100 according to one or more embodiments of the present disclosure.

[0060] In embodiments, the optical measurement system 100 includes an optical subsystem 102 for acquiring measurement signals from a sample 104 based on any number of measurement recipes. Figure 1B is a conceptual diagram of the optical subsystem 102 according to one or more embodiments of the present disclosure. For example, the optical subsystem 102 can direct illumination 106 onto the sample 104 and further concentrate light or other radiation (referred to herein as sample light 108) emitted from the sample 104. The optical measurement system 100 can be further characterized by any part of the optical measurement system 100, including, but not limited to, a dedicated measurement target (e.g., an overlay target, a measurement target, etc.) or a device feature of interest (e.g., an in-die feature associated with a manufactured device).

[0061] In embodiments, 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 memory device. Furthermore, the controller 110 may be communicably connected to an optical subsystem 102 or any component within the optical subsystem 102. Thus, one or more processors 112 of the controller 110 can directly or indirectly execute any of the various process steps described throughout this disclosure.

[0062] The optical subsystem 102 may include any combination of optical elements suitable for characterizing the sample 104. The optical subsystem 102 can generally operate in imaging mode or non-imaging mode. For example, in imaging mode, individual features in the sample 104 may be resolvable within an illumination spot in the sample (e.g., as part of a bright-field image, dark-field image, etc.). As a non-limiting example, overlay measurements may be used, where overlay measurements are measured based on the relative positions of features associated with various lithographic processes. For example, a center of symmetry may be determined for each group of features associated with a particular lithographic process, such that overlay measurements can be generated based on the difference between the centers of symmetry of features in various groups. As another example, the optical subsystem 102 can operate as a measurement tool based on scattering measurements, in which the sample light 108 is analyzed at the pupil plane (e.g., diffraction plane, 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 measurement, the overlay target may have periodic features intended to diffract the incident illumination 106 (for example, to individual diffraction orders), and the overlay measurement may be generated based on the asymmetry between diffraction orders (or, more generally, the asymmetry in the pupil plane).

[0063] Furthermore, the optical measurement system 100 can be configured to generate overlay measurements based on any number of recipes (e.g., measurement recipes, overlay recipes, etc.). Typically, the optical measurement system 100 can be configured according to a recipe that includes a set of parameters for controlling the illumination 106 directed at the sample 104 and for capturing the sample light 108. It is understood herein that various measurement techniques or applications may require various profiles of the illumination 106, and / or various aspects of the sample light 108 may be used for measurement. For example, a recipe may include, but is not limited to, the illumination wavelength, illumination pupil distribution (e.g., distribution of illumination angles and the associated intensity of illumination at those angles), polarization of the incident illumination, spatial distribution of illumination, or height of the sample. As another example, a recipe may include, but is not limited to, a focusing pupil distribution (e.g., a desired distribution of angled light from sample 104 used for measurement and the associated filtered intensity at those angles), focusing aperture settings for selecting several portions of the sample of interest, polarization of sample light 108 used for measurement, or wavelength filters for controlling the wavelength (or more generally, spectrum) of sample light 108 used for measurement. As yet another example, a recipe may include parameters associated with the design of the features of sample 104 (e.g., target features in sample 104). For example, a recipe may specify various aspects of features in sample 104 (e.g., in a dedicated target), but is not limited to, the number of features, the size of the features, the periodicity of the features, the pitch between features, etc. Thus, the sample features and the optical subsystem 102 may be jointly designed according to a recipe to provide a desired distribution of sample light 108 in one or more detectors capable of showing measurements of interest, and to provide a series of analytical steps for generating measurements based on this distribution of sample light 108.

[0064] In embodiments, the optical subsystem 102 includes one or more components formed from or otherwise comprising a metasurface 116, the metasurface 116 being designed to manipulate illumination 106 directed at a sample 104 and / or sample light 108 focused from the sample 104. Such a metasurface 116 may have any known design suitable for manipulating light (e.g., illumination 106 and / or sample light 108) at least partially based on one or more sub-resolution features. As used herein, the term sub-resolution feature refers to a feature of the metasurface 116 having dimensions sufficiently smaller than the wavelength of the light being manipulated, such that the sub-resolution feature can directly alter the amplitude and / or phase of the light. In other words, while a typical optical element can manipulate light by the accumulation of varying amounts of phase delay across various regions of the element, the metasurface 116 can manipulate the amplitude and / or phase of light on a sub-wavelength scale using one or more sub-resolution features. As a result, the metasurface 116 can be designed to provide similar properties (e.g., focusing, refraction, or diffraction of light) to conventional bulk optical elements in a more compact package. Furthermore, the metasurface 116 can be designed to manipulate light in ways that are not possible or impractical with conventional bulk optical elements.

[0065] The optical measurement system 100 may include any type of metasurface known in the art. For example, the metasurface 116 may be formed using continuous or discontinuous sub-resolution features. As another example, the metasurface 116 may be formed as a periodic, quasi-periodic, or locally periodic distribution of sub-wavelength features. Exemplarily, the metasurface 116 may be formed as two-dimensional or three-dimensional lattice structures, features with varying heights (e.g., step-like features, stepped features, blazed features, inclined features, etc.), or line / spatial features forming pillar features with any shape or distribution, but are not limited to these. Furthermore, the periodicity of such features may vary across the surface to provide spatially varying properties on a larger spatial scale (e.g., larger than the wavelength of the light being manipulated). Exemplarily, the metasurface 116 formed as a lens (e.g., a metalens) may include sub-wavelength features designed to adjust the phase of incident light, and the properties of the sub-wavelength features vary across the surface, in a sense, to provide refractive power for acting as a lens.

[0066] Furthermore, the metasurface 116 can be a reflective or transmissive element. Additionally, the optical measurement system 100 can integrate the metasurface 116 with any number of conventional optical components (e.g., refractive components, reflective components, transmissive components, diffracting components, etc.).

[0067] Next, referring to Figures 1C to 1F, Figures 1C to 1F include non-limiting examples of subwavelength features suitable for forming the metasurface 116.

[0068] Figure 1C shows a top view of a first design of a portion of the metasurface 116 according to one or more embodiments of the present disclosure. Figure 1D shows a side view of the design in Figure 1C according to one or more embodiments of the present disclosure.

[0069] In some embodiments, the metasurface 116 is formed as a series of islands 140 formed as a periodic distribution of subwavelength features. For example, Figures 1C and 1D show a configuration in which the islands 140 include a one-dimensional grid formed with periodic grid features 142. It is intended herein that the dimensions of the grid features 142 as a whole, or the dimensions of the islands 140, can be smaller than the wavelength of light being manipulated, and can be designed to operate as a metasurface 116. For example, the grid features 142 in Figures 1C and 1D may have a pitch 144, a height 146, a width 148, and a length 150, and one or more of these parameters are smaller than the wavelength of light manipulated by the metasurface 116. As another example, various parameters of the islands 140 can be smaller than the wavelength of light manipulated by the metasurface 116, but are not required. For example, any combination of island width 152, island length 154 (for example, corresponding to the length 150 of lattice feature 142 in this example), or island pitch 156 can be smaller than the wavelength of light manipulated by the metasurface 116, but does not have to be.

[0070] Figures 1E and 1F show alternative designs of a portion of the metasurface 116 according to one or more embodiments of the present disclosure. Figure 1E shows a top view of a second design of a portion of the metasurface 116 according to one or more embodiments of the present disclosure. Figure 1F shows a side view of the design of Figure 1E according to one or more embodiments of the present disclosure.

[0071] The second design shown in Figures 1E and 1F includes an island 140 having a grid feature 142 and further pillars 158 which may, but do not, be characterized as assist features. Similar to the grid feature 142, one or more properties of the pillars 158, such as, but not limited to, a diameter 160, a height 162, a pitch 164, or a position relative to the grid feature 142, can be smaller than the wavelength of light manipulated by the metasurface 116.

[0072] In some embodiments, one or more properties of the island 140 can vary across the metasurface 116 to provide spatially varying properties. For example, the pitch 156 between the islands 140 and / or the orientation of the islands 140 can vary across the metasurface 116. As another example, the design of the features within the islands 140 can vary across the metasurface 116. For example, at least one of the pitch 144, height 146, width 148, length 150, or the number of grid features 142 can vary between the islands 140. In yet another example, the various islands 140 may include various distributions and / or designs of features. Exemplarily, the metasurface 116 may include several islands 140 having a first design shown in Figures 1C to 1D and several islands 140 having a second design shown in Figures 1E to 1F, and the distribution of the various designs can be uniform across the metasurface 116 or spatially varying across the metasurface 116.

[0073] Referring to Figures 1C to 1F as a whole, various features of the metasurface 116 can be formed using any material or combination of materials. For example, the lattice features 142 and / or pillars 158 can be formed from high refractive index materials such as, but not limited to, TiO2. Furthermore, the metasurface 116 may include features formed from multiple materials.

[0074] Figures 1C to 1F are provided for illustrative purposes only and are intended herein not to be construed as limiting the scope of this disclosure. For example, the metasurface 116 may have any number or type of features having any design suitable for manipulating light. As another example, Figures 1C and 1E show a grid feature 142 and pillars 158 formed over a substrate 166. However, this is not a requirement. In some embodiments, the metasurface 116 includes further material surrounding the grid feature 142 and / or pillars 158 so as to provide such features within layers having a uniform height, which may be useful for integrating such metasurface 116 with and / or between various materials at interfaces. In some embodiments, the metasurface 116 is formed from two or more layers of material so that the metasurface 116 is multilayered. Furthermore, any number of further layers may be present above or below the features and / or above or below the layers forming the metasurface 116.

[0075] In some embodiments, multiple metasurfaces 116 can be manufactured in a stacked configuration. In this case, the multiple metasurfaces 116 can be manufactured directly on top of each other or with intermediate layers between them in overlapping regions in the path of incident light. For example, the optical response of a particular metasurface 116 may depend on the properties of the incident light, such as wavelength or polarization, but not limited to these. In this case, various metasurfaces 116 designed for various properties can be stacked to provide desired performance characteristics of light having these various properties. For example, various metasurfaces 116 designed for various wavelengths can be stacked to provide desired performance characteristics of multi-wavelength or broadband light. The metasurfaces 116 can further be formed using any manufacturing technique known in the art, such as additive manufacturing or subtractive manufacturing, but not limited to these.

[0076] The optical measurement system 100 may include one or more metasurfaces 116 that provide any function. 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., collimation lenses, objective lenses, etc.), beam splitters, beam deflectors, or diaphragms (e.g., field diaphragms, aperture diaphragms, etc.). Furthermore, in some cases, the metasurfaces 116 may be designed to combine multiple functions.

[0077] In some embodiments, the optical subsystem 102 includes one or more optical heads, at least one of which includes at least one metasurface 116 arranged to direct illumination 106 onto the sample 104, to capture sample light 108 from the sample 104, and / or to manipulate any combination of illumination 106 or sample light 108. Furthermore, such an optical head can provide a relatively high numerical aperture (e.g., 0.7 or higher) for at least one of focusing illumination 106 onto the sample 104 or focusing sample light 108. In some cases, the optical head includes an objective lens at least partially formed with one or more metasurfaces 116 that provide refractive power for operation as a lens (e.g., a metalens) having a numerical aperture of at least 0.7.

[0078] Referring again to Figure 1B, various components of the optical subsystem 102 according to one or more embodiments of the present disclosure will now be described in more detail. It is intended herein that any component or combination of components shown in Figure 1B may be formed as one or more metasurfaces 116. Such metasurfaces 116 may be single-layer or multi-layer metasurfaces 116. Furthermore, multiple components having or not having metasurfaces 116 may be incorporated into a monolithic component (e.g., a combined component). Thus, the various distinct components shown in Figure 1B are merely illustrative and should not be construed as limiting the scope of the present disclosure.

[0079] In one embodiment, the optical subsystem 102 includes an illumination source 118 configured to produce illumination 106 in the form of at least one illumination beam. Illumination from the illumination source 118 may include, but is not limited to, one or more selected wavelengths of light including ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation. For example, the wavelength may be, but is not limited to, in the range of 248 to 1600 nm. For example, the optical subsystem 102 may include one or more apertures in the illumination pupil plane to split the illumination from the illumination source 118 into one or more beams or illumination lobes of illumination 106. In this regard, the optical subsystem 102 may provide dipole illumination, quadrupole illumination, and the like. Furthermore, the spatial profile of the beam of illumination 106 on the sample 104 may be controlled by a field plane aperture to have any selected spatial profile.

[0080] 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 is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, etc. In this regard, the illumination source 118 can provide illumination 106 having 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 is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements that can emit broadband illumination when excited to 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 is not limited to, an arc lamp, a discharge lamp, an electrodeless lamp, etc. In this regard, the lighting source 118 can provide lighting 106 having low coherence (e.g., low spatial coherence and / or temporal coherence).

[0081] The illumination source 118 can provide illumination 106 using free-space techniques and / or optical fibers. Furthermore, the illumination source 118 may be contained within an optical head (e.g., an optical subsystem 102) or located remotely from the optical head (e.g., an optical subsystem 102). Thus, the optical head (e.g., an optical subsystem 102) can receive illumination 106 from the illumination source 118 using any combination of free-space coupling or optical fibers. Furthermore, the illumination 106 may be provided as a divergent beam, a collimated beam, or a beam with any focal characteristics.

[0082] In some embodiments, the illumination source 118 generates multilobe illumination 106 by supplying light into 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 multilobe illumination 106 by diffracting the light source to two or more diffraction orders, where the illumination lobes of illumination 106 are formed from at least some of the diffraction orders of the light source. 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.

[0083] In another embodiment, the optical subsystem 102 directs the illumination beam to the sample 104 via the illumination path 120. The illumination path 120 may include one or more optical elements suitable for modifying and / or adjusting 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 (for example, to collimate the illumination beam, to relay the pupil plane and / or field plane). In another embodiment, the illumination path 120 includes one or more illumination path optics 124 for shaping or otherwise controlling the illumination beam. For example, the illumination path optics 124 may include, but are not limited to, one or more field diaphragms, one or more pupil diaphragms, 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.).

[0084] In another embodiment, the optical subsystem 102 includes an objective lens 126 for focusing the illumination beam onto the sample 104 (for example, an overlay target having overlay target elements located in two or more layers of the sample 104). In another embodiment, the sample 104 is placed on a sample stage 128 suitable for fixing the sample 104 and further configured to position the sample 104 relative to the illumination beam.

[0085] In another embodiment, the optical subsystem 102 includes one or more detectors 130 configured to capture light or other light (e.g., sample light 108) emitted from the sample 104 through the focusing path 132. The focusing path 132 may include one or more optical elements suitable for modifying and / or adjusting the sample light 108 from the sample 104. In one embodiment, the focusing path 132 includes one or more focusing path lenses 134 (e.g., for collimating the illumination beam, for relaying the pupil plane and / or field plane), which may include, but do not have to include, an objective lens 126. In another embodiment, the focusing path 132 includes one or more focusing path optics 136 for shaping or otherwise controlling the sample light 108. For example, the focusing path optical system 136 may include, but is not limited to, one or more field diaphragms, one or more pupil diaphragms, 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, translationally movable mirrors, scanning mirrors, etc.).

[0086] The detector 130 can be positioned at any selected location within the focusing path 132. In one embodiment, the optical subsystem 102 includes the detector 130 in the field of view (e.g., a plane conjugate to the sample 104) to generate an image of the sample 104. In another embodiment, the optical subsystem 102 includes the detector 130 in the pupil plane (e.g., a diffraction plane) to generate a pupil image. In this regard, the pupil image can correspond to the angular distribution of light from the sample 104. For example, the diffraction order associated with the diffraction of the illumination beam from the sample 104 (e.g., an overlay target in the sample 104) can be imaged in the pupil plane or otherwise observed. In a general sense, the detector 130 can capture any combination of reflected (or transmitted), scattered, or diffracted light from the sample 104.

[0087] The optical subsystem 102 can generally include any number or type of detectors 130 suitable for capturing light from the sample 104 exhibiting an overlay. In one embodiment, the detectors 130 include one or more detectors 130 suitable for characterizing a static sample. In this regard, the optical subsystem 102 can operate in a stationary mode in which the sample 104 is stationary during measurement. For example, the detectors 130 may include, but are not limited to, charge-coupled devices (CCDs) or complementary metal-oxide-semiconductor (CMOS) devices, two-dimensional pixel arrays. In this regard, the detectors 130 can generate a two-dimensional image (e.g., a field-of-view image or pupil-of-view image) in a single measurement.

[0088] In one embodiment, the detector 130 includes one or more detectors 130 suitable for characterizing a moving sample (e.g., a scanning sample). In this regard, the optical subsystem 102 can operate in a scanning mode in which the sample 104 is scanned with respect to the measurement field during measurement. For example, the detector 130 may include a 2D pixel array having sufficient capture time and / or refresh rate to capture one or more images during scanning within selected image tolerances (e.g., image blur, contrast, sharpness, etc.). As another example, the detector 130 may include a line scanning detector for continuously generating images of one line of pixels at a time. As yet another example, the detector 130 may include a time-delayed integral (TDI) detector.

[0089] In another embodiment, the optical subsystem 102 includes a scanning subsystem for scanning the sample 104 with respect to the measurement field during measurement. For example, a sample stage 128 can position and orient the sample 104 within the focal volume of the objective lens 126. In another embodiment, the sample stage 128 includes one or more adjustable stages, such as, but not limited to, a linear translation stage, a rotation stage, or a tip / tilt stage. In another embodiment, not shown, the scanning subsystem includes one or more beam scanning optics (e.g., a rotatable mirror, a galvanometer, etc.) for scanning the illumination beam with respect to the sample 104.

[0090] The illumination path 120 and focusing path 132 of the optical subsystem 102 can be oriented in a wide range of configurations suitable for illuminating the sample 104 with the illumination beam and for focusing the light emitted from the sample 104 in response to the incident illumination beam. For example, as shown in Figure 1B, the optical subsystem 102 may include a beam splitter 138 oriented so that a common objective lens 126 can simultaneously direct the illumination beam towards the sample 104 and focus the light from the sample 104. Such a configuration may be called a through-the-lens (TTL) configuration, since the illumination 106 is directed towards the sample 104 through the same objective lens 126 used to focus the sample light 108. As another example, the optical subsystem 102 may include an optical element (e.g., illumination path lens 122) for directing the illumination 106 towards the sample 104 and a separate objective lens 126 for focusing onto the sample 104. Such a configuration may be called an out-of-lens (OTL) configuration.

[0091] Figures 2 to 4B show various non-limiting examples of the metasurface 116 within the optical subsystem 102 according to one or more embodiments of the present disclosure.

[0092] Figures 2A to 2E show the use of the metasurface 116 in a modified optical subsystem 102 suitable for coherent spot scanning measurement applications, according to one or more embodiments of the present disclosure.

[0093] Figure 2A is a conceptual diagram of an optical subsystem 102 shown having a bulk optical element for pupil-based measurement according to one or more embodiments of the present disclosure. Figure 2A is a modification of Figure 1B, and therefore all descriptions associated with Figure 1B extend to Figure 2A. In particular, Figure 2A shows a TTL configuration in which coherent illumination 106 is provided by an optical fiber 202 (e.g., a single-mode fiber), collimated by a collimator 204, and directed to the sample 104 via a beam splitter 138 and an objective lens 126. The optical fiber 202 may be associated with an illumination source 118 (e.g., a fiber-based illumination source 118) or it may be a delivery fiber. The objective lens 126 focuses the sample light 108, which passes through the beam splitter 138 and is directed to one or more detectors 130 located on the pupil plane 206. Figure 2A further shows the field diaphragm 208 in the focusing path 132, the field diaphragm 210 in the illumination path 120, and the diaphragm 212 (e.g., an aperture diaphragm) in the illumination path 120. The configuration shown in Figure 2A can be, but is not limited to, coherent diffraction-based measurement techniques using the pupil detector 130. Non-limiting examples of coherent diffraction-based measurement techniques are generally described in U.S. Patent No. 11,300,405 issued on 12 April 2022, U.S. Patent Application Publication No. 2023 / 0314319 published on 5 October 2023, U.S. Patent Application Publication No. 2023 / 0314344 published on 5 October 2023, and U.S. Patent No. 11,796,925 issued on 24 October 2023, all of which are incorporated herein by reference in their entirety.

[0094] Figures 2B to 2E show a modified example of the second configuration of the optical subsystem 102 in Figure 2A, which incorporates the metasurface 116.

[0095] In some embodiments, the optical subsystem 102 includes one or more bulk optical elements, the surface of which includes a structure that forms a metasurface 116. It is intended herein that such bulk optical elements may be formed as thin elements that can be substantially smaller than typical components designed to manipulate light without using a metasurface 116.

[0096] Figure 2B is a schematic diagram of the optical subsystem 102 of Figure 2A, shown having metasurfaces 116 formed on a plurality of bulk optical elements according to one or more embodiments of the present disclosure. In some embodiments, the components in Figure 2B can form an optical head. In Figure 2B, the optical subsystem 102 includes a first bulk optical element 214 having a metasurface 116a formed as a lens (e.g., a collimation lens for collimating divergent illumination 106), and a first grating 216 for directing the collimated illumination 106 to a second bulk optical element 218 which includes a grating beam splitter 220 and a metasurface 116b formed as an objective lens. Thus, the first bulk optical element 214 can be part of an illumination path 120 and can operate as an illumination path lens 122 and an illumination path optical system 124. Next, the sample light 108 can be focused by a metasurface 116b formed as an objective lens and directed by a grating beam splitter 220 to a third bulk optical element 222, which includes 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 to the detector 130 at the pupil plane 206 via a field diaphragm 208. Thus, the third bulk optical element 222 can be part of a focusing path 132 and can operate as a focusing path lens 134 and a focusing path optical system 136. In some embodiments, the first bulk optical element 214 and the third bulk optical element 222 can have a similar design (for example, they can be complementary devices).

[0097] In the configuration shown in Figure 2B, the metasurface 116 is fabricated on various surfaces (e.g., planes) 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 sample light 108. Furthermore, the optical elements may include any combination of the metasurface 116 or other patterned features (e.g., the first grating 216 and the second grating 224).

[0098] Table 1 includes various parameters associated with one or more embodiments of the present disclosure, specifically one non-limiting embodiment of Figure 2B. Such parameters may, but are not limited to, those suitable for 100 / / calculations in the case of a coherent spot scanning microscope, as intended herein. [Table 1]

[0099] In some embodiments, the optical subsystem 102 includes one or more fused optical elements, and one or more metasurfaces 116 are formed on one or more surfaces of such fused optical elements and / or on one or more interfaces between subcomponents that are joined together to form such fused optical elements (e.g., by optically transparent bonding or any other bonding technique). It is intended herein that the fused components are very compact, mechanically stable, and capable of fixing the optical alignment between the constituent metasurfaces 116 and / or other features.

[0100] Figure 2C is a schematic diagram of the optical subsystem 102 of Figure 2A, shown with metasurfaces 116 formed on the surfaces and interfaces of the fusion optical element 226a according to one or more embodiments of the present disclosure. In particular, Figure 2C shows a fusion optical element 226a formed from four sub-elements 228 (individually numbered 228a to d). In this configuration, metasurfaces 116a and 116c formed as lenses are provided at the interface 230 in any combination of sub-elements 228a and 228b, a first grating 216 and a second grating 224 are provided at the interface 232 in any combination of sub-elements 228b and 228c, a grating beam splitter 220 is provided at the interface 234 in any combination of sub-elements 228c and 228d, and a metasurface 116b formed as a lens is provided on the outer surface 236.

[0101] Accordingly, Figure 2C can be conceptualized as a modification of Figure 2B in which the first bulk optical element 214 and the third bulk optical element 222 are bonded to a common sub-element 228b (this is merely illustrative and not mandatory), and the sub-element 228c replaces the open space between the bulk optical elements 210, 214, and 218, but is not limited thereto. As a result, Figures 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 this disclosure.

[0102] Furthermore, Figure 2C shows a configuration in which the sub-element 228a extends to the field of view so that the field aperture 208 can be fabricated on the surface of the sub-element 228a. However, this is merely illustrative and not mandatory. In some embodiments, the fused optical element 226a does not include the sub-element 228a (for example, the fused optical element 226a may be formed from sub-elements 228b to d). In this configuration, a separate field aperture 208 may be provided if desired.

[0103] In some embodiments, the metasurface 116 can provide multiple optical functions (e.g., refractive power, diffraction, refraction, etc.). In other words, the metasurface 116 can manipulate light to replicate the performance of multiple conventional optical elements that manipulate light by accumulating phase delays or other techniques. For example, a single metasurface 116 may include features designed to provide multiple optical functions. As another example, two or more metasurfaces 116 may be manufactured in a stack (e.g., as a composite metasurface 116) to provide multiple optical functions. It is intended herein that the use of one or more metasurfaces 116 providing multiple optical functions can further simplify and / or reduce the design of the optical subsystem 102 (or a part thereof).

[0104] Figure 2D is a schematic diagram of the optical subsystem 102 of Figure 2A, shown having metasurfaces 116 formed on the surface of a monolithic component 238 according to one or more embodiments of the present disclosure. In Figure 2D, the monolithic component 238 is formed as a single uniform material element having metasurfaces 116d~e on various surfaces. For example, a metasurface 116d configured as both a lens and a beam deflector may be formed on a first surface 240 of the monolithic component 238, a metasurface 116e configured as both a beam splitter and an objective lens may be formed on a second surface 242, and a metasurface 116f configured as both a lens and a beam deflector may be formed on a different region (or, optionally, a different surface) of the first surface 240. In this configuration, the metasurface 116d can collimate illumination 106 and direct this collimated illumination 106 to a metasurface 116e for focusing onto a sample 104. The metasurface 116e can then focus the sample light 108 and direct this sample light 108 towards the metasurface 116f, which can then act as a focusing path lens 134.

[0105] It is intended herein that a monolithic component 238 having one or more metasurfaces 116 (for example, as shown in Figure 2D) can more generally provide a robust and very compact optical head or portion of an optical subsystem 102.

[0106] Next, referring to Figure 2E, which is a schematic diagram of the optical subsystem 102 of Figure 2A, including an achromatic metasurface 116, according to one or more embodiments of the present disclosure.

[0107] As previously stated herein, certain designs 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, a metasurface 116 (or two or more metasurfaces 116 stacked together as a composite metasurface 116) can be designed as an achromatic lens capable of providing wavelength-corrected refractive power within a selected tolerance over at least a selected wavelength range.

[0108] In Figure 2E, the optical subsystem 102 includes a fused optical element 226b formed from two sub-elements 228e,f. In particular, the fused optical element 226b in Figure 2E includes a metasurface 116g formed as an achromatic lens, along with a thin-film beam splitter coating at the interface 246 between the sub-elements 228e,f arranged to form a broadband beam splitter, and a metasurface 116g positioned on surface 244 to collimate the illumination 106. A metasurface 116h formed as an achromatic objective lens on another surface 248 can receive a portion of the illumination 106 passing through interface 246, direct this portion of the illumination 106 toward the sample 104, focus the sample light 108, and direct this sample light 108 back toward interface 246, so that a portion of the sample light 108 can be separated from the illumination 106. The metasurface 116i formed as an achromatic lens can then operate as a focusing path lens 134 as described herein.

[0109] The fused optical element 226b in Figure 2E further includes a further surface 250 in front of the metasurface 116i that provides total internal reflection of the sample light 108, which can facilitate the desired positioning of the sample light 108 toward the detector along the focusing path 132. However, the specific design of the fused optical element 226b in Figure 2E, including the surface 250, is merely illustrative and should not be construed as limiting the scope of this disclosure. For example, using the surface 250 to redirect the sample light 108 is not a requirement. In some embodiments, the surface providing TIR reflection may be realized to direct any combination of illumination 106 or sample light 108. In some embodiments, the surface providing TIR reflection is not essential.

[0110] Next, referring to Figures 3A and 3B, Figures 3A and 3B illustrate the use of the metasurface 116 in a modified 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 a modified version of Figure 1B, and therefore all the explanations associated with Figure 1B extend to Figure 3A. In particular, Figure 3A shows 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 multimode 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 it may be a delivery fiber. The objective lens 126 focuses the sample light 108, which passes through the beam splitter 138 and is directed to one or more detectors 130 located on the field of view 306. The configuration shown in Figure 3A can be adapted to, but is not limited to, an incoherent bright-field measurement technique using field-of-view detectors 130. Such non-adaptive examples 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.

[0111] Figure 3B is a schematic diagram of the optical subsystem 102 of Figure 3A, shown having metasurfaces 116 formed on a fused optical element 226c according to one or more embodiments of the present disclosure. In particular, inset 308 in Figure 3B shows a detailed view of the fused optical element 226c formed from sub-elements 228g~k, where metasurfaces 116j~q are formed on the associated surfaces and / or interfaces. For example, a metasurface 116j formed as a lens (e.g., an achromatic lens) can collimate the illumination 106, and a metasurface 116k formed as a beam deflector (e.g., a lattice deflector) can direct the collimated illumination 106 to a metasurface 116l formed as a beam splitter. Figure 3B further shows a non-limiting configuration of a polyhedral element formed from a plurality of metasurfaces 116. In particular, Figure 3B shows metasurfaces 116m~o that form a three-sided metalens (e.g., a three-sided achromatic objective metalens), and these metasurfaces 116m~o can direct illumination 106 towards the sample 104 and focus the sample light 108. The metasurface 116l formed as a beam splitter can 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 can correspond to a focusing path lens 134, making it easy to image the sample 104 onto the detector 130.

[0112] Next, referring to Figures 4A and 4B, Figures 4A and 4B illustrate the use of the metasurface 116 in a modified optical subsystem 102 suitable for dark-field imaging applications according to one or more embodiments of the present disclosure. Figure 4A is a conceptual diagram of an optical subsystem according to one or more embodiments of the present disclosure. Figure 4A is a modified version of Figure 1B, and therefore all the explanations associated with Figure 1B extend to Figure 4A. In particular, Figure 4A shows an OTL configuration in which illumination 106 (e.g., coherent illumination 106) is provided by an optical fiber 402 (e.g., single-mode fiber) and directed to a sample via an illumination path lens 122 outside the numerical aperture (e.g., focusing numerical aperture) of the objective lens 126, which is part of the focusing path 132. Furthermore, multiple beams of illumination 106 may be provided through multiple channels 404. In this case as well, the optical fiber 402 may be associated with an illumination source 118 (e.g., fiber-based illumination source 118) or it may be a delivery fiber. The objective lens 126 focuses the sample light 108, and one or more detectors 130 positioned on the field plane 406 generate one or more dark-field images of the sample 104 based on the focused sample light 108 (for example, in this case also not including specular reflections of illumination 106 outside the focusing numerical aperture of the objective lens 126). The configuration shown in Figure 4A can be adapted to, but is not limited to, coherent dark-field measurement techniques using field plane detectors 130, and such non-limiting examples are generally described in U.S. Patent No. 11,359,916 issued on 14 June 2022 and U.S. Patent Application Publication No. 2023 / 0259040 published on 17 August 2023, both of which are incorporated herein by reference in their entirety.

[0113] Figure 4B is a schematic diagram of the optical subsystem 102 of Figure 4A, shown having metasurfaces 116 formed on a fusion optical element 226d according to one or more embodiments of the present disclosure. In particular, inset 408 of Figure 4B shows a fusion optical element 226d formed from sub-elements 228l,m, with metasurfaces 116r~v formed on the associated surfaces and / or interfaces. For example, a metasurface 116r formed as a lens can collimate illumination 106, and a metasurface 116s formed as a beam deflector (e.g., a grating deflector) can direct the collimated illumination 106 towards the sample 104. Furthermore, multiple examples of metasurfaces 116r,s can provide multiple beams of illumination 106. Figure 4B further shows metasurfaces 116t~v formed as triplane metalenses (e.g., triplane objective metalenses), which can focus sample light 108 as shown.

[0114] Similar to the examples provided in Figures 2A–2E, Figures 3A–4B illustrate the use of metasurfaces 116 in an optical subsystem 102 (or a part of the optical subsystem 102, such as an optical head) that can enable robust performance in a very compact package. However, it should be understood that Figures 3A–4B are provided for illustrative purposes only and should not be construed as limiting the scope of this disclosure. For example, the optical subsystem 102 (or a part thereof) may be formed using any number of metasurfaces 116 on any number of surfaces. As another example, the optical subsystem 102 may be extended to include one or more metasurfaces 116 that provide multiple optical functions (e.g., refractive power, diffraction, refraction, etc.). As yet another example, the optical subsystem 102 may include one or more metasurfaces 116 in any combination of bulk optical elements, fused components, and / or monolithic components. As yet another example, the description of the triplane objective metalens in Figures 3B and 4B is for illustrative purposes only. More generally, any number of metasurfaces 116 can be arranged on any number of surfaces to provide the desired optical functionality.

[0115] Furthermore, the relevant configurations of the optical subsystem 102 and / or related application areas in Figures 2A to 4B are also provided for illustrative purposes only and should not be construed as limiting. More generally, the optical measurement system 100 may include an optical subsystem 102 having any design suitable for any type of optical measurement of a sample 104, wherein the optical subsystem 102 includes at least one metasurface 116.

[0116] Next, with reference to Figure 5, multi-channel optical measurements using multiple optical subsystems 102 incorporating metasurfaces 116, according to one or more embodiments of the present disclosure, will be described in more detail. In some embodiments, the optical measurement system 100 includes two or more optical subsystems 102, at least one of which includes one or more metasurfaces 116. As previously stated herein, the use of one or more metasurfaces 116 can enable a substantial reduction in the physical size of the optical subsystems 102 (or parts of the optical subsystems 102, such as optical heads). As a result, multiple optical subsystems 102 (or parts of the optical subsystems 102, such as optical heads) can be distributed to provide parallel (and optionally simultaneous) measurements of various parts of a sample 104.

[0117] Figure 5 is a conceptual schematic diagram showing the arrangement of multiple optical subsystems 102 across a sample 104 for parallel measurement according to one or more embodiments of the present disclosure. Large-scale overlay measurement sampling is generally described in U.S. Patent No. 11,899,375, issued February 13, 2024, which is incorporated herein by reference in its entirety. In particular, Figure 5 shows a configuration in which separate optical subsystems 102 are provided for each reticle field 502 associated with a lithography tool (e.g., scanner, stepper, etc.) used to fabricate features relating to the sample 104. Thus, separate optical subsystems 102 can be used to provide parallel measurement of features associated with various dies in the sample 104. Furthermore, such a configuration may use a separate detector 130 for each optical subsystem 102, or multiple optical subsystems 102 may 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 may include any number of optical subsystems 102, at least one of which includes one or more metasurfaces 116.

[0118] Figure 6 is a flowchart illustrating the steps taken in a method 600 for providing optical measurement according to one or more embodiments of the present disclosure. The embodiments and enabling techniques described herein in the context of the optical measurement system 100 should be interpreted as extending to method 600. For example, the processor 112 of the controller 110 can execute program instructions that cause the processor 112 to perform various steps of method 600 directly or indirectly (e.g., by control signals to further components). However, it should be further noted that method 600 is not limited to the architecture of the optical measurement system 100.

[0119] In some embodiments, the method 600 includes step 602 of directing illumination 106 onto the sample 104 using an optical subsystem 102 which includes one or more optical elements.

[0120] In some embodiments, the method 600 includes a focusing step 604 in which sample light 108 from a sample 104 in response to illumination 106 by an optical subsystem 102, wherein at least one of one or more optical elements in the optical subsystem 102 includes one or more metasurfaces 116 for manipulating at least one of the illumination 106 or the sample light 108 using subwavelength features. The subwavelength features may be smaller than at least some wavelengths in at least one of the illumination 106 or the sample light 108.

[0121] In some embodiments, Method 600 includes step 606 of generating a detection signal based on at least a portion of the sample light 108. The detection signal may include any type of signal known in the art that includes information indicating a measurement of the sample 104. For example, the detection signal may include, but is not limited to, a field-view image of the sample 104 from the detector 130 in the field of view, a pupil image associated with the distribution of light (e.g., diffracted light) emitted from the sample 104, or a time-based signal associated with the pupil and / or the field-view detector 130 (e.g., a photodiode). In some embodiments, Method 600 includes step 608 of generating one or more measurements of the sample 104 based on the detection signal. The measurements may include any type of information associated with the sample 104. In some embodiments, the measurements may include, but are not limited to, measurement measurements such as overlay measurements or limit dimension (CD) measurements. In some embodiments, the measurements may include, but are not limited to, inspection measurements that identify and / or characterize defects in the sample 104.

[0122] Next, with general reference to Figures 1 to 6, further considerations for the metasurface 116 within the optical measurement system 100 according to one or more embodiments of the present disclosure will be described.

[0123] It is intended herein that the metasurface 116 can offer many advantages or provide a conventional optical element.

[0124] For example, the metasurface 116 can enable small and / or flat optical components, which can reduce the size of the optical head (e.g., optical subsystem 102), which in turn allows such optical heads to be more densely packed, enabling multiple parallel measurements per sample 104. Furthermore, the metasurface 116 can be incorporated 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, enabling dense integration and a small overall component size.

[0125] As another example, the metasurface 116 can enable a relatively short focal length (for example, when used to form the objective lens 126), which can enable a high numerical aperture (e.g., 0.7 or greater, 0.93 or greater, or even higher).

[0126] As another example, the metasurface 116 can be manufactured and assembled in a relatively cost-effective manner. For example, the metasurface 116 can be manufactured using efficient mass manufacturing processes, such as, but not limited to, semiconductor manufacturing processes. As yet another example, an optical component manufactured with the metasurface 116 may require fewer mechanical parts for mounting, particularly when multiple metasurfaces 116 are incorporated into a bulk, fused, or monolithic component as described herein. Furthermore, when multiple metasurfaces 116 are incorporated into a bulk, fused, or monolithic component, such metasurfaces 116 can be aligned during manufacturing so that the alignment and / or assembly of the optical subsystem 102 is easier and faster, and / or requires fewer mechanical parts.

[0127] As another example, the metasurface 116 can be manufactured with high consistency and / or reliability. For instance, the semiconductor manufacturing process used to manufacture the metasurface 116 can be tightly controlled, and in some cases, more tightly controlled than the manufacturing processes for conventional optical components.

[0128] As another example, the metasurface 116 can be combined with conventional optical elements (e.g., refractive, reflective, and diffractive elements or surfaces) within an optical head (e.g., optical subsystem 102). Furthermore, multiple metasurfaces 116 on various surfaces can work together to provide a polyhedral element. Exemplarily, the objective lens 126 may be formed from one or more metasurfaces 116 on any number of surfaces. As another example, the objective lens 126 may be formed from a combination of one or more metasurfaces 116 and refractive, reflective, and / or diffractive elements or surfaces. In some embodiments, an objective lens having at least one metasurface 116 may be designed to operate finitely conjugate to directly generate an image or other distribution in the detector 130, so that no further focusing lens (e.g., focusing path lens 134) is required.

[0129] As another example, the metasurface 116 may be designed to support multiple wavelengths, either directly or by stacking multiple metasurfaces 116. Thus, the user can select a wavelength or wavelength range for operation. As yet another example, various optical heads (e.g., various optical subsystems 102) within a single optical measurement system 100 may be designed to support various wavelengths.

[0130] As another example, the metasurface 116 can be used in applications requiring high polarization sensitivity. For example, one or more metasurfaces 116 can directly manipulate the polarization of light (e.g., illumination 106 and / or sample light 108). More commonly, one or more metasurfaces 116 can act as polarizers, waveplates, or polarization manipulators. In another example, one or more metasurfaces 116 can provide high polarization sensitivity. In this configuration, the optical subsystem 102 can include a polarizer and / or polarization manipulator in front of the high polarization sensitivity metasurface 116.

[0131] As another example, the metasurface 116 may be used alone or in combination with a refractive, reflective, and / or diffracting element or surface to shape the beam profile of light (e.g., illumination 106 and / or sample light 108). In this configuration, such elements can operate in place of or in addition to apodization or truncation elements. Furthermore, in such a configuration, the light can be preserved by beam shaping rather than filtering.

[0132] Furthermore, any component of the optical subsystem 102, including the metasurface 116 or other components, may be tilted or wedge-shaped to deflect stray light from the optical path.

[0133] The subject matter described herein may include various components that are contained within or connected to other components. It should be understood that the architectures shown in this manner are merely illustrative, and that many other architectures can indeed be implemented to achieve the same functionality. Conceptually, any arrangement of components to achieve the same function is effectively “associated” in such a way that the desired function is achieved. Therefore, any two components in this specification combined to achieve a particular function can be considered “associated” with each other in such a way that the desired function is achieved, independently of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “joined” with each other to achieve the desired function, and any two components that can be associated in this way can also be considered “joinable” with each other to achieve the desired function. Specific examples of joinable components include, but are not limited to, physically interactable and / or physically interacting components, and / or wirelessly interactable and / or wirelessly interacting components, and / or logically interactable and / or logically interacting components.

[0134] Many of the present disclosure and its associated advantages are to be understood from the above description, and it will be clear that various modifications can be made to the form, structure, and arrangement of the components without departing from the disclosed subject matter or sacrificing all of its important advantages. The forms described are merely descriptive, and the intent of the following claims is to encompass and include such modifications. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims

1. One or more optical elements configured to direct illumination onto a sample and to focus 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 subwavelength features, the subwavelength features being smaller than at least some wavelengths in at least one of the illumination or the sample light being manipulated, and the one or more optical elements provide refractive power for at least one of focusing the illumination onto the sample or focusing the sample light from the sample. A device characterized by comprising:

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

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

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

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

6. A device according to claim 5, wherein the objective lens is a polyhedral element formed from at least two of the one or more metasurfaces.

7. A device according to claim 1, 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 the surface of at least one of the one or more bulk optical elements.

8. A device according to claim 7, 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.

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

10. A device according to claim 9, 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.

11. The device according to claim 1, wherein the one or more optical elements are 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, configured to direct the illumination onto the sample and collect the sample light from the sample, A first grid configured to direct the illumination from the first lens towards the objective lens, A second lens formed as at least one of the one or more metasurfaces, A second grating for receiving the sample light from the objective lens and directing the sample light towards the second lens, A device characterized by comprising:

12. A device according to claim 11, characterized in that the first lens, the objective lens, the first grating, the second lens, and the second grating are incorporated into a fused optical element.

13. The device according to claim 1, wherein the one or more optical elements are An objective lens formed as one of the one or more metasurfaces, configured to direct the illumination towards the sample and to collect the sample light from the sample, A first metasurface among the one or more metasurfaces configured to collimate the illumination and direct the illumination toward the objective lens, wherein the illumination is incident upon the first metasurface as a divergent beam, A second metasurface among the one or more metasurfaces is configured to receive the sample light from the objective lens and focus the sample light, A device characterized by comprising:

14. A device according to claim 13, wherein the second metasurface focuses the sample light onto a condensing aperture.

15. A device according to claim 13, characterized in that the objective lens, the first metasurface, and the second metasurface are incorporated into a monolithic element.

16. The device according to claim 1, wherein the one or more optical elements are An objective lens formed as at least one of the one or more metasurfaces, configured to direct the illumination onto the sample and collect the sample light from the sample, A first metasurface among the one or more metasurfaces configured to collimate the illumination, wherein the illumination is incident on the first metasurface as a divergent beam, The second metasurface and A beam splitter configured to direct the illumination from the first metasurface to the objective lens and the sample light from the objective lens to the second metasurface, wherein the second metasurface includes a beam splitter that focuses the sample light. A device characterized by comprising:

17. A device according to claim 16, wherein the second metasurface focuses the sample light onto a condensing aperture.

18. A device according to claim 16, characterized in that the objective lens, the first metasurface, the second metasurface, and the beam splitter are incorporated into a fused optical element.

19. A device according to claim 18, wherein the fusion optical element further includes a surface for directing the sample light from the beam splitter to the second metasurface by total internal reflection.

20. The device according to claim 1, wherein the one or more optical elements are An objective lens formed as at least one of the one or more metasurfaces, configured to collect the sample light from the sample, At least one of the one or more metasurfaces is configured to direct the illumination onto the sample at an angle outside the numerical aperture of the objective lens, A device characterized by comprising:

21. A device according to claim 20, wherein at least one of the one or more metasurfaces configured to direct the illumination onto the sample at an angle outside the numerical aperture of the objective lens is characterized in that it directs two or more beams of the illumination onto the sample outside the numerical aperture of the objective lens.

22. A device according to claim 1, wherein at least some of the subwavelength features of at least one specific metasurface among the one or more metasurfaces are arranged in islands distributed across the specific metasurface.

23. A device according to claim 22, wherein at least one of the subwavelength features within the island, the spacing between the islands, or the orientation of the islands varies across the particular metasurface.

24. A device according to claim 1, characterized in that the distribution of the subwavelength features in at least one specific metasurface among the one or more metasurfaces is uniform across the specific metasurface.

25. A device according to claim 1, characterized in that at least some of the subwavelength features in at least one of the one or more metasurfaces are formed as blazed features.

26. A device according to claim 1, characterized in that at least some of the subwavelength features in at least one of the one or more metasurfaces are formed as lattice features.

27. A device according to claim 1, wherein at least some of the subwavelength features in at least one of the one or more metasurfaces are formed as stepped features.

28. A device 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 stack structure.

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

7.

30. A lighting source configured to generate light, One or more optical subsystems, each of the one or more optical subsystems comprising one or more optical elements configured to direct illumination onto a sample and to focus 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 subwavelength features, the subwavelength features being smaller than at least some wavelengths in at least one of the illumination or the sample light, and the one or more optical elements providing refractive power for at least one of focusing the illumination onto the sample or focusing the sample light from the sample, One or more detectors configured to generate a detection signal based on the sample light focused by the one or more optical subsystems, A controller communicatively connected to one or more detectors, the controller includes one or more processors configured to execute program instructions stored in a memory device, the program instructions configured to cause the one or more processors to execute a measurement recipe by generating a plurality of measurement values ​​of the sample based on the detection signals from the one or more detectors, A measurement system characterized by comprising the following features.

31. A measurement system according to claim 30, characterized in that the one or more optical subsystems include two or more optical subsystems.

32. A measurement system according to claim 31, characterized in that the distribution of the two or more optical subsystems is arranged to provide parallel measurement of one or more features in a field of view of the sample.

33. A measurement system according to claim 32, characterized in that the distribution of the two or more optical subsystems is arranged to provide a single optical subsystem from the two or more optical subsystems to at least one of the one or more fields of view in the sample.

34. A measurement system according to claim 32, characterized in that the distribution of the two or more optical subsystems is arranged to provide at least two of the two or more optical subsystems to at least one of the one or more fields of view in the sample.

35. A measurement system according to claim 30, characterized in that at least one of the one or more metasurfaces includes a lens.

36. A measurement system according to claim 30, characterized in that at least one of the one or more metasurfaces includes a beam splitter.

37. A measurement system according to claim 30, characterized in that at least one of the one or more metasurfaces includes one or more beam polarizers.

38. A measurement system according to claim 30, characterized in that at least one of the one or more metasurfaces includes an objective lens.

39. A measurement system according to claim 38, wherein the objective lens is formed from at least two of the one or more metasurfaces.

40. A measurement system according to claim 30, 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 the surface of at least one of the one or more bulk optical elements.

41. A measurement system according to claim 40, 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.

42. A measurement system according to claim 30, wherein the one or more optical elements include one or more fused optical elements formed from two or more sub-elements, and at least one of the one or more metasurfaces is formed at the interface of two of the two or more sub-elements.

43. A measurement system according to claim 42, 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.

44. A measurement system according to claim 30, characterized in that the one or more optical elements include a single monolithic element.

45. Directing illumination onto a sample using an optical subsystem containing one or more optical elements, Focusing sample light from the sample in response to illumination by the optical subsystem, 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 subwavelength features, the subwavelength features being smaller than at least some wavelengths in at least one of the illumination or the sample light, and the one or more optical elements provide refractive power for at least one of focusing the illumination onto the sample or focusing the sample light from the sample. A detection signal is generated based on at least a portion of the aforementioned sample light, To generate one or more measured values ​​of the sample based on the detection signal, A measurement method characterized by including

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