Single capture pupil landscape via broadband illumination

Abstract

A method for overlay metrology may include generating a broadband illumination beam and a overlay target directing the broadband illumination beam onto a sample, wherein the overlay target may include cells having periodic features formed as an overlapping grating structure. The method may include generating diffracted light using the periodic feature of the overlay target, wherein the periodic feature may act as a diffraction grating to generate diffracted light by separating the broadband illumination beam into a plurality of wavelengths. The method may include generating a pupil image of a cell of the overlay target, where a light distribution in the pupil plane may include a first order diffraction lobe, where a spectrum of the first order diffraction lobe may be spatially dispersed in the pupil plane. The method may include generating a superposition measurement based on a portion of the pupil image corresponding to a selected wavelength of the spectrum of the first order diffraction lobe.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 63 / 470,737, filed on June 2, 2023, the entirety of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to superposition metrology, and more particularly, to scatterometry superposition metrology. Background Art

[0004] Overlay metrology generally refers to the measurement of the relative alignment of layers on a sample, such as, but not limited to, a semiconductor device. Overlay measurement, or overlay error measurement, generally refers to the measurement of the misalignment of fabricated features on two or more sample layers. In general, proper device function requires proper alignment of fabricated features on multiple sample layers.

[0005] The demand for decreasing feature size and increasing feature density has resulted in a correspondingly increasing demand for accurate and efficient overlay metrology.Metrology systems typically generate metrology data associated with a sample by measuring or otherwise verifying dedicated metrology targets distributed across the sample.

[0006] In typical metrology systems, measurements are performed using monochromatic light. Finding the optimal wavelength requires many time-consuming single-wavelength measurements. A recipe's specific wavelength is chosen so that it lies in the "green zone" of the metrology target's pupil landscape (i.e., where the overlay slope is low and insensitive to wavelength or focus changes). The landscape itself can vary due to process-related reasons, pushing the recipe's intended wavelength out of the "green zone." It would be desirable to provide systems and methods that address the aforementioned drawbacks. Summary of the Invention

[0007] A superposition metrology system according to one or more embodiments of the present disclosure is disclosed. In one embodiment, the superposition metrology system includes an illumination subsystem. In one embodiment, the illumination subsystem includes one or more broadband illumination sources configured to generate one or more broadband illumination beams. In one embodiment, the illumination subsystem includes one or more illumination optics configured to direct the one or more broadband illumination beams toward a superposition target on a sample when implementing a metrology recipe. In one embodiment, the superposition target includes one or more cells having periodic features formed as an overlapping grating structure in accordance with the metrology recipe. In one embodiment, the superposition metrology system includes a light collection subsystem. In one embodiment, the light collection subsystem includes a detector located at a pupil plane. In one embodiment, the detector generates one or more pupil images of the one or more cells of the superposition target based on illumination from the one or more broadband illumination beams. In one embodiment, the light distribution in the pupil plane includes first-order diffraction lobes from the one or more broadband illumination beams in accordance with the metrology recipe, wherein the spectrum of the first-order diffraction lobes is spatially dispersed in the pupil plane. In an embodiment, the light collection subsystem includes one or more light collection optics configured to direct at least the first order diffraction to the detector. In an embodiment, the superposition metrology system includes a controller communicatively coupled to the detector. In an embodiment, the controller, including one or more processors, is configured to execute program instructions causing the one or more processors to receive the one or more pupil images of the one or more cells from the detector and generate a superposition measurement of the sample based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectrum of the first order diffraction lobes.

[0008] A superposition metrology system according to one or more embodiments of the present disclosure is disclosed. In one embodiment, the superposition metrology system includes a controller communicatively coupled to a detector. In one embodiment, the controller, including one or more processors, is configured to execute program instructions to cause the one or more processors to receive one or more pupil images of one or more cells from the detector. In one embodiment, the one or more pupil images are generated using one or more broadband illumination beams from one or more broadband illumination sources. In one embodiment, the controller, including one or more processors, is configured to execute program instructions to cause the one or more processors to generate a superposition measurement of the sample based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectrum of the first-order diffraction lobes.

[0009] A method according to one or more embodiments of the present disclosure is disclosed. In an embodiment, the method includes generating one or more broadband illumination beams with one or more broadband illumination sources. In an embodiment, the method includes directing the generated one or more broadband illumination beams to a superposition target on a sample when implementing a metrology recipe, wherein the superposition target includes one or more cells having periodic features formed into an overlapping grating structure according to the metrology recipe. In an embodiment, the method includes generating diffracted light using the periodic features of the superposition target, wherein the periodic features of the superposition target act as a diffraction grating to generate the diffracted light by separating the broadband illumination beam into a plurality of wavelengths. In an embodiment, the method includes generating one or more pupil images of one or more cells of the superposition target using a detector located at a pupil plane based on illumination using the one or more broadband illumination beams, wherein the light distribution in the pupil plane includes first-order diffraction lobes according to the metrology recipe, wherein the spectrum of the first-order diffraction lobes is spatially dispersed in the pupil plane. In an embodiment, the method includes generating a superposition measurement of the sample based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectrum of the first-order diffraction lobes.

[0010] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Those skilled in the art may better understand the numerous advantages of the present disclosure by referring to the accompanying drawings, in which:

[0012] Figure 1A is a conceptual diagram of a system for performing scatterometry superposition metrology on a superposition target in accordance with one or more embodiments of the present disclosure.

[0013] Figure 1B is a schematic diagram of an overlay metrology tool according to one or more embodiments of the present disclosure.

[0014] Figure 2 is a side view of a superposition target suitable for scatterometry superposition measurements in which cells include stacked grating structures according to one or more embodiments of the present disclosure.

[0015] Figure 3A is a three-dimensional perspective top view of a sample depicting diffraction of a broadband illumination beam according to one or more embodiments of the present disclosure.

[0016] Figure 3Bis a top view of an illuminated pupil image of a superimposed metrology target illuminated with a broadband illumination beam in accordance with one or more embodiments of the present disclosure.

[0017] Figure 3C is a top view of a collection pupil image of a superimposed metrology target illuminated with a broadband illumination beam in accordance with one or more embodiments of the present disclosure.

[0018] Figure 4 is a diagram of a full pupil landscape according to one or more embodiments of the present disclosure.

[0019] Figure 5A is a diagram depicting an overlay according to one or more embodiments of the present disclosure.

[0020] Figure 5B is a diagram depicting an overlay according to one or more embodiments of the present disclosure.

[0021] Figure 5C is a diagram depicting an overlay according to one or more embodiments of the present disclosure.

[0022] Figure 5D is a diagram depicting an overlay according to one or more embodiments of the present disclosure.

[0023] Figure 6 is a flow chart depicting a method for generating overlay measurements using a broadband illumination source in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0024] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments set forth herein are to be considered illustrative rather than restrictive. It will be apparent to those skilled in the art that various changes and modifications in form and details may be made without departing from the spirit and scope of the present disclosure.

[0025] Embodiments of the present disclosure relate to systems and methods for scatterometry superposition metrology based on broadband illumination, in which periodic features on a superposition metrology target act as a diffraction grating to split the broadband illumination beam into multiple different wavelengths.

[0026] For the purposes of this disclosure, the term "overlay" is generally used to describe the relative positions of features on a sample fabricated by two or more lithographic patterning steps, with the term "overlay error" describing the deviation of features from a nominal arrangement. In this context, overlay measurements can be expressed as measurements of relative positions or the overlay errors associated with these relative positions. For example, a multilayer device may include features patterned on multiple sample layers using different lithographic steps for each layer, where the alignment of features between layers must typically be tightly controlled to ensure proper performance of the resulting device. Thus, overlay measurements can characterize the relative positions of features on two or more sample layers. As another example, multiple lithographic steps can be used to fabricate features on a single sample layer. Such techniques, often referred to as double patterning or multi-patterning techniques, can facilitate the fabrication of highly dense features approaching the resolution of the lithographic system. In this context, overlay measurements can characterize the relative positions of features from different lithographic steps on this single layer. It should be understood that throughout this disclosure, examples and descriptions related to specific applications of overlay metrology are provided for illustrative purposes only and should not be construed as limiting the disclosure.

[0027] While in some applications overlay measurements can be performed directly on features of a fabricated device (e.g., device features), overlay measurements are typically performed on a dedicated overlay target that is printed using the same lithography steps as the device features. In this way, features of the overlay target (e.g., target features) can be specifically designed to facilitate overlay measurements. Furthermore, overlays measured at one fabrication step (e.g., after fabricating one or more sample layers) can be used to generate correction terms to precisely align process tools (e.g., lithography tools or the like) used to fabricate additional sample layers in subsequent fabrication steps.

[0028] For the purposes of this disclosure, the term "scatterometry metrology" is used broadly to encompass the terms "scatterometry-based metrology" and "diffraction-based metrology," in which a sample having periodic features on one or more sample layers is illuminated with an illumination beam having a limited angular range, and one or more different diffraction orders are collected for measurement. Furthermore, the term "scanning metrology" is used to describe metrological measurements made when the sample is moved relative to the illumination used for measurement. In general, scanning metrology can be implemented by moving the sample, the illumination, or both.

[0029] It should be recognized herein that many scatterometry overlay metrology techniques typically determine overlay by illuminating an overlay target having grating structures in two layers (e.g., stacked grating structures), where the overlay measurement is based on the asymmetry between positive and negative diffraction orders. For example, various scatterometry techniques are described in: U.S. Patent No. 2021 / 0364279, published on March 11, 2021; U.S. Patent No. 10,824,079, issued on November 3, 2020; U.S. Patent No. 10,197,389, issued on February 9, 2019; and Adel et al., "Diffraction order control in overlay metrology: a reexamination of the roadmap options," Proc. SPIE. 6922, and Metrology, Inspection, and Process Control for Microlithography XXII, 692202. (2008); the entire text of all of the aforementioned documents is incorporated herein by reference.

[0030] As used throughout this disclosure, the term "sample" generally refers to a substrate formed of a semiconductor or non-semiconductor material (e.g., a wafer or the like). For example, the semiconductor or non-semiconductor material may include, but is not limited to, single crystal silicon, gallium arsenide, and indium phosphide. A sample may include one or more layers. For example, such layers may include, but are not limited to, resists, dielectric materials, conductive materials, and semiconducting materials. Many different types of such layers are known in the art, and the term "sample," as used herein, is intended to encompass all types of samples on which such layers may be formed. The one or more layers formed on a sample may be patterned or unpatterned. For example, a sample may include multiple die, each having repeatable patterned features. The formation and processing of such material layers may ultimately result in a finished device. Many different types of devices may be formed on a sample, and the term "sample," as used herein, is intended to encompass a sample on which any type of device known in the art is fabricated. Furthermore, for the purposes of this disclosure, the terms "sample" and "wafer" should be interpreted as interchangeable. Additionally, for the purposes of this disclosure, the terms "patterning device," "mask," and "reticle" should be interpreted as interchangeable.

[0031] Embodiments of the present disclosure relate to providing recipes for configuring overlay metrology tools. Overlay metrology tools can generally be configured according to a recipe that includes a set of parameters for controlling various aspects of overlay measurements, such as, but not limited to, illumination of the sample, collection of light from the sample, or the position of the sample during measurement. In this manner, an overlay metrology tool can be configured to provide selected types of measurements for one or more overlay target designs of interest. For example, a metrology recipe may include illumination parameters, such as, but not limited to, the number of illumination beams, the illumination wavelength, the illumination pupil distribution (e.g., the distribution of illumination angles and the associated illumination intensity at those angles), the polarization of the incident illumination, the bandwidth of the illumination wavelength, or the spatial distribution of the illumination. As another example, a metrology recipe may include collection parameters, such as, but not limited to, the collection pupil distribution (e.g., the desired distribution of angular light from the sample to be measured and the associated filtering intensity at those angles), a collection field stop setting for selecting a portion of the sample of interest, the polarization of the collected light, a wavelength filter, the position of one or more detectors (e.g., photodetectors), or parameters for controlling one or more detectors. As another example, a metrology recipe may include various parameters associated with the sample position during measurement, such as, but not limited to, sample height, sample orientation, whether the sample is static during measurement, or whether the sample is in motion during measurement (as well as associated parameters describing speed, scanning mode, or the like).

[0032] As an illustrative example, diffraction-based superposition metrology techniques can illuminate a superposition target with periodic features with illumination at selected angles of incidence, resulting in the generation of different diffraction orders by the periodic superposition target. Selected diffraction orders can then be collected for determining superposition. Using this approach, the emission angles of the diffraction orders are based on factors such as the periodicity of the metrology target, the wavelength of the illumination, and the illumination angle. Furthermore, different techniques can utilize different combinations of illumination and light collection configurations.

[0033] Embodiments of the present disclosure relate to providing overlay data to one or more process tools. The overlay data from the overlay metrology tool may generally include any output of the overlay metrology tool having sufficient information to determine the overlay (or overlay error) associated with various lithography steps. For example, the overlay data may include (but is not required to include) one or more data sets, one or more images, one or more detector readings, or the like. This overlay data may then be used for various purposes, including but not limited to diagnostic information for the lithography tool or for generating process control correction terms. For example, the overlay data of samples in a batch may be used to generate feedback correction terms for controlling the lithography exposure of subsequent samples in the same batch. In another example, the overlay data of samples in a batch may be used to generate feedforward correction terms for controlling the lithography exposure of the same or similar samples in subsequent lithography steps to account for any deviations in the current exposure.

[0034] Existing scatterometry overlay measurements are performed using monochromatic light. Finding the optimal wavelength when using monochromatic light requires multiple, time-consuming single-wavelength measurements (i.e., pupil landscapes). In such systems, a recipe's specific wavelength is chosen so that it lies within the "green zone" of the target's pupil landscape. However, the landscape itself can vary due to process-related factors, pushing the recipe's intended wavelength out of the green zone.

[0035] For the purposes of this disclosure, the terms "green zone," "stable zone," and variations thereof may be defined as a region where measurements are relatively stable with respect to deviations from process parameters. For example, a "green zone" may be a region where the overlay slope is low and insensitive to wavelength changes or focus changes.

[0036] It is contemplated herein that scatterometry overlay metrology utilizing broadband illumination may provide numerous benefits compared to traditional monochromatic (e.g., single-band) illumination, such as, but not limited to, mitigating the problem of green zone variations (e.g., a set of wavelengths within which overlay measurements may be stable) by using a variety of wavelengths to obtain overlay measurements.

[0037] Furthermore, the disclosed systems and methods allow for rapid (e.g., single-shot) acquisition of full pupil views. In this regard, full pupil views enable local optimization of overlay measurements and tracking of process variations.

[0038] Reference Figures 1A to 6 , describing in more detail systems and methods for scatterometry superposition metrology according to one or more embodiments of the present disclosure.

[0039] Figure 1A is a conceptual diagram of a superposition metrology system 100 for performing scatterometry superposition metrology on a superposition target 106 in accordance with one or more embodiments of the present disclosure.

[0040] In one embodiment, the overlay metrology system 100 includes an overlay metrology tool 102 for acquiring an overlay signal from an overlay target 106 based on any number of overlay recipes. For example, the overlay metrology tool 102 may direct illumination onto the sample 104 and may further collect light or other radiation emitted from the sample 104 to generate an overlay signal suitable for determining an overlay of two or more sample layers. The overlay metrology tool 102 may be any type of overlay metrology tool known in the art suitable for generating an overlay signal suitable for determining an overlay associated with the overlay target 106 on the sample 104. The overlay metrology tool 102 may selectively operate in an illuminated mode or a non-illuminated mode. For example, in the illuminated mode, individual overlay target elements may be distinguishable within an illuminated spot on the sample 104 (e.g., as part of a brightfield image, a darkfield image, or the like). As another example, the overlay metrology tool 102 can operate as a scatterometry-based overlay metrology tool, in which radiation from the sample 104 is analyzed at a pupil plane to characterize the angular distribution of radiation from the sample 104 (e.g., associated with scattering and / or diffraction of radiation by the sample 104).

[0041] Furthermore, the overlay metrology tool 102 may be configurable to generate overlay signals based on any number of recipes defining measurement parameters for obtaining overlay signals suitable for determining overlay of the overlay target 106. For example, a recipe for the overlay metrology tool 102 may include, but is not limited to, illumination wavelength, detection wavelength of light emitted from the sample 104, spot size or shape of the illumination on the sample 104, incident illumination angle, polarization of the incident illumination, polarization of the collected light, position of the incident illumination beam on the overlay target 106, position of the overlay target 104 in the focal volume of the overlay metrology tool 102, or the like.

[0042] Figure 1B is a conceptual diagram illustrating an overlay metrology tool 102 of an overlay metrology system 100 in accordance with one or more embodiments of the present disclosure.

[0043] In one embodiment, the overlay metrology tool 102 includes an illumination subsystem comprising an illumination source 114 configured to generate at least one illumination beam 116 and one or more illumination optics 122. For example, the illumination subsystem may include one or more broadband illumination sources 114 configured to generate one or more broadband illumination beams 116. In this regard, the overlay metrology tool 102 may include one or more apertures at an illumination pupil plane for splitting illumination from the illumination source 114 into one or more illumination beams 116 or illumination lobes. In this regard, the overlay metrology tool 102 may provide dipole illumination, orthogonal illumination, or the like. Furthermore, the spatial distribution of the one or more illumination beams 116 on the sample 104 may be controlled by a field plane stop to have any selected spatial distribution.

[0044] The illumination source 114 may include any type of illumination source suitable for providing at least one broadband illumination beam 116. In an embodiment, the illumination source 114 is a laser source. For example, the illumination source 114 may include a broadband laser source.

[0045] In an embodiment, the overlay metrology tool 102 directs an illumination beam 116 to the sample 104 via an illumination path 118. The illumination path 118 may include one or more optical components suitable for modifying and / or adjusting the illumination beam 116 and directing the illumination beam 116 to the sample 104. In an embodiment, the illumination path 118 includes one or more illumination path lenses 120 (e.g., for collimating the illumination beam 116, for relaying a pupil and / or field plane, or the like). In an embodiment, the illumination path 118 includes one or more illumination path optics 122 for shaping or otherwise controlling the illumination beam 116. For example, the illumination path optics 122 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0046] In an embodiment, the overlay metrology tool 102 includes an objective lens 124 for focusing an illumination beam 116 onto a sample 104 (e.g., an overlay target 106 having overlay target features located on two or more layers of the sample 104). In an embodiment, the sample 104 is disposed on a sample stage 126, which is adapted to secure the sample 104 and is further configured to position the sample 104 relative to the illumination beam 116.

[0047] In an embodiment, the overlay metrology tool 102 includes one or more detectors 128 configured to capture light (e.g., collected light 130) emitted from the sample 104 (e.g., the overlay target 106 on the sample 104) through a collection path 132. The collection path 132 may include one or more optical elements suitable for modifying and / or conditioning the collected light 130 from the sample 104. In an embodiment, the collection path 132 includes one or more collection path lenses 134 (e.g., for collimating the illumination beam 116, for relaying a pupil and / or field plane, or the like), which may, but are not required to, include the objective lens 124. In an embodiment, the collection path 132 includes one or more collection path optics 136 for shaping or otherwise controlling the collected light 130. For example, the collection path optics 136 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0048] The detector 128 may be located at any selected location within the collection light path 132. In embodiments, the overlay metrology tool 102 includes a detector 128 at a field of view plane (e.g., a plane conjugate to the sample 104) for generating an image of the sample 104. In embodiments, the overlay metrology tool 102 includes a detector 128 at a pupil plane (e.g., a diffraction plane) for generating a pupil image. In this regard, the pupil image may correspond to the angular distribution of light from the sample 104 captured by the detector 128. For example, diffraction orders associated with diffraction of the illumination beam 116 from the sample 104 (e.g., a superimposed target on the sample 104) may be imaged or otherwise observed in the pupil plane. In a general sense, the detector 128 may capture any combination of reflected (or transmitted), scattered, or diffracted light from the sample 104.

[0049] The overlay metrology tool 102 may generally include any number or type of detectors 128 suitable for capturing light from the sample 104 indicative of the overlay. In one embodiment, the detectors 128 include one or more detectors 128 suitable for characterizing a static sample. In this regard, the overlay metrology tool 102 may operate in a static mode, wherein the sample 104 is static during measurement. For example, the detectors 128 may include a two-dimensional pixel array, such as, but not limited to, a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) device. In this regard, the detectors 128 may generate a two-dimensional image (e.g., a field plane image or a pupil plan image) in a single measurement.

[0050] In one embodiment, the detector 128 includes one or more detectors 128 adapted to characterize a moving sample 104 (e.g., scanning the sample). In this regard, the overlay metrology tool 102 may operate in a scanning mode, wherein the sample 104 is scanned relative to a measurement field of view during measurement. For example, the detector 128 may include a 2D pixel array having a capture time and / or refresh rate sufficient to capture one or more images within a selected image tolerance (e.g., image blur, contrast, sharpness, or the like) during the scan. As another example, the detector 128 may include a line scan detector for continuously generating images one pixel line at a time. As another example, the detector 128 may include a time delay integration (TDI) detector. The TDI detector can generate continuous images of the sample 104 when the movement of the sample 104 is synchronized with a charge transfer clock signal in the TDI detector. Specifically, the TDI detector acquires charge from exposure on a row of pixels and includes clock pulses to transfer charge between adjacent rows of pixels along the scan direction. When the movement of the sample 104 along the scan direction is synchronized with the charge transfer in the TDI detector, charge accumulates continuously during the scan. This process continues until the charge reaches the final pixel column and is then read out from the detector. In this way, an image of the target is accumulated over a longer timeframe than would be possible with a simple line scan camera. This relatively long acquisition time reduces the photon noise level of the image. Furthermore, the synchronized motion of the image and the charge prevents blurring of the recorded image.

[0051] In one embodiment, the overlay metrology tool 102 includes a scanning subsystem for scanning the sample 104 relative to the measurement field of view during metrology measurements. For example, the sample stage 126 can position and orient the sample 104 within the focal volume of the objective lens 124. In one embodiment, the sample stage 126 includes one or more adjustable stages, such as, but not limited to, a linear translation stage, a rotation stage, or a tilt / tilt stage. In one embodiment, although not shown, the scanning subsystem includes one or more beam scanning optics (e.g., a rotatable mirror, a galvanometer, or the like) for scanning the illumination beam 116 relative to the sample 104.

[0052] The illumination path 118 and the light collection path 132 of the overlay metrology tool 102 may be adapted for various configurations and orientations for illuminating the sample 104 with the illumination beam 116 and collecting light emitted from the sample 104 in response to the incident illumination beam 116. For example, Figure 1B , overlay metrology tool 102 can include beam splitter 138 oriented so that common objective 124 can simultaneously direct illumination beam 116 to sample 104 and collect light from sample 104. As another example, illumination path 118 and collection path 132 can contain non-overlapping optical paths.

[0053] Figure 2is a side view of a superposition target 106 suitable for scatterometry superposition measurements in which a cell 202 includes a stacked grating structure 204 in accordance with one or more embodiments of the present disclosure.

[0054] In one embodiment, the overlay target 106 includes one or more cells 202 having one or more periodic features 206, 208 formed as an overlay grating structure 204 on the sample 104. For example, the one or more cells 202 may include a first periodic feature 206 on a first layer 210 and a second periodic feature 208 on a second layer 212, wherein the first periodic feature 206 and the second periodic feature 208 overlap to form the overlay grating structure 204 on the sample 104.

[0055] In an embodiment, the periodic features of the superimposed target act as a diffraction grating to generate diffracted light by separating a broadband illumination beam into a plurality of wavelengths. For example, the broadband illumination source 114 may generate one or more broadband illumination beams 116 and the one or more illumination optics 122 may direct the one or more broadband illumination beams 116 to the surface of the sample 104. In this regard, the periodic features 206, 208 of the superimposed target 106 on the surface of the sample 104 may separate the one or more broadband illumination beams 116 into a plurality of wavelengths at a plurality of diffraction angles.

[0056] The overlay target 106 may generally be formed from any number of cells 202, and any particular cell 202 may include overlapping grating structures 204 having periodicity along any direction. Furthermore, the overlay target 106 may include multiple cells 202 having grating structures 204 having periodicity along a common direction, with different cells 202 having different periodicity configurations of associated gratings.

[0057] However, it should be understood that Figure 2The overlay target 106 and associated description in FIGURE 1 are provided for illustrative purposes only and should not be construed as limiting. Specifically, the overlay target 106 may include any suitable overlay grating overlay target design. For example, the overlay target 106 may include any number of cells 202 suitable for measurement along two directions. Furthermore, the cells 202 may be distributed in any pattern or arrangement. For example, metrology target designs suitable for scanning metrology are generally described in U.S. Patent No. 11,073,768, issued on July 27, 2021, which is incorporated herein by reference in its entirety. In an embodiment, the overlay target 106 includes one or more cell groupings distributed along a scanning direction (e.g., the direction of motion of the sample 104), wherein the cells 202 within each particular cell grouping are oriented to have periodic features 206 that are periodic along a common direction. For example, a first cell grouping may include one or more cells 202 having periodicity along the X direction, and a second cell grouping may include one or more cells 202 having periodicity along the Y direction. In this manner, all cells 202 within a particular cell grouping can be imaged simultaneously when the sample 104 is scanned with the overlay metrology tool 102. As another example, a diagonal target suitable for performing metrology measurements along orthogonal directions in a single scan is generally described in U.S. Patent Publication No. 2021 / 0364935, published on November 25, 2021, which is incorporated herein by reference in its entirety.

[0058] Generally speaking Figures 3A to 3C , depicting various non-limiting configurations for generating and measuring signals from periodic features 206 in one or more cells 202 of a superposition target 106 in accordance with one or more embodiments of the present disclosure.

[0059] As previously discussed herein, the periodic features 206, 208 on the superposition metrology target 106 can act as diffraction gratings to split the broadband illumination beam 116 into different wavelengths. For example, the sample 104 can be illuminated with one or more illumination beams 116 (e.g., illumination spots 302) where the periodic features 206, 208 produce spatially dispersed diffraction lobes (e.g., 0th order diffraction lobe 304, + / - 1st order diffraction lobes 306, 308) that are also spectrally dispersed.

[0060] In an embodiment, the illumination subsystem illuminates the superimposed target 106 with any number of illumination beams 116 at any angle. For example, the illumination pupil plane may correspond to Figure 1B The pupil plane in the illumination subsystem described in FIG.

[0061] In an embodiment, the one or more detectors 128 may be configured to generate a pupil image of the superimposed target 106 when the superimposed target 106 is illuminated with the broadband illumination beam 116 from the broadband illumination source 114. For example, when the superimposed target 106 is illuminated with broadband illumination, a pupil image of the superimposed target 106 may be generated. For example, the pupil image may include the illumination spot 302 and one or more diffraction lobes (e.g., the 0th order diffraction lobe 304, + / - 1st order diffraction lobes 306, 308), wherein the spectra of the + / - 1st order diffraction lobes 306, 308 may be spatially dispersed in the pupil plane.

[0062] In one embodiment, the one or more illumination optics 122 may be configured to direct the broadband illumination beam 116 toward the overlay target 106 on the sample 104 while implementing a metrology recipe. For example, the overlay target 106 may include one or more cells having periodic features formed into overlapping grating structures (e.g., stacked grating structures) according to the metrology recipe. For example, the periodic features of the overlay target 106 may act as a diffraction grating to generate diffracted light by separating the broadband illumination beam 116 into multiple wavelengths.

[0063] In an embodiment, the one or more detectors 128 are located at a pupil plane.For example, the one or more detectors 128 may be configured to generate a pupil image 300 of the overlay target 106 when the overlay target 106 is illuminated with the broadband illumination beam 116 from the broadband illumination source 114.

[0064] Figure 3A is a three-dimensional perspective top view of a sample depicting diffraction of a broadband illumination beam according to one or more embodiments of the present disclosure. Figure 3B is a top view of the illumination pupil 310 in the illumination pupil plane of the overlay metrology tool 102 in accordance with one or more embodiments of the present disclosure.

[0065] refer to Figure 3A In an embodiment, the one or more broadband illumination sources 114 may include a dipole illumination source that provides illumination beams 116 having opposite azimuth angles in the pupil plane. Figure 3A As shown in , the illumination pupil 310 may include two illumination beams 116 having opposite azimuth angles in the pupil plane.

[0066] refer to Figure 3B In an embodiment, the broadband illumination source 114 may include a rotating quadrupole illumination source 114 that provides tilted illumination beams 116 in two orthogonal directions in the pupil plane. Figure 3B As shown in , the illumination pupil 310 may include four illumination beams 116 along two orthogonal directions in the pupil plane.

[0067] Figure 3C According to one or more embodiments of the present disclosure Figure 3B 1. A top view of a collection pupil image 320 of a superimposed metrology target 106 illuminated by the four broadband illumination beams 116 depicted in FIG. Figure 3C illustrates a non-limiting arrangement of diffraction orders of illumination beam 116 in a collection pupil plane. For example, a collection pupil plane may correspond to Figure 1B In particular, Figure 3C The 0th order diffraction 304, the -1st order grating diffraction 306, and the +1st order grating diffraction 308 are illustrated as being distributed along the periodic direction (e.g., the X direction) of the overlapping grating structure 204 in the collection pupil plane. For example, the -1st order grating diffraction 306 and the +1st order grating diffraction 308 may be associated with the grating diffraction from the first grating layer 208 and the second grating layer 212. In this regard, the spectra of the first order diffraction lobes 306 and 308 may be spatially dispersed in the pupil plane, as shown in FIG. Figure 3A and 3C As shown in .

[0068] As previously discussed herein, the systems and methods of the present disclosure may provide several benefits. For example, the systems and methods of the present disclosure may provide a more robust method for employing existing superposition measurement techniques. For example, the spectra of the first order diffraction lobes 306, 308 may be spatially dispersed in the pupil plane such that a single wavelength superposition measurement may be obtained based on an identified "green zone" corresponding to the first order diffraction lobes 306, 308. As another example, the systems and methods of the present disclosure may allow for the use of multi-wavelength techniques. For example, the spectra of the first order diffraction lobes 306, 308 may be spatially dispersed in the pupil plane such that multiple wavelength regions within the identified "green zone" may be used to obtain superposition measurements, as will be further discussed herein and Figures 5A to 5D As shown in .

[0069] In an embodiment, an overlay measurement of the overlay target 106 may be generated based on selected portions of the pupil image corresponding to selected wavelengths of the spectrum of the first order diffraction lobes 306 , 308 .

[0070] To measure the superposition in the x or y direction, two cells with opposite intentional shifts (±f0) can be used. In each cell, the difference signal (D ± ), as shown and described by Equation 1 below:

[0071] D ± = S +1 (±f0)-S -1 (±f0) (1)

[0072] Among them S +1 is the positive diffraction order signal, S -1 is the negative diffraction order signal, ±f0 is the shift parameter, G=D1-D2 and K=D1+D2.

[0073] The per-pixel superposition (∈) is obtained from Equation 2:

[0074]

[0075] The differential signal (D ± ) is obtained using Equation 1.

[0076] The slope of a straight line (eg, a best fit line) may be proportional to the superposition, as shown and described by Equations 3-4 below:

[0077]

[0078] As considered herein, metrology data associated with multiple elements of a stacking target collected using a scatterometry stacking (SCOL) technique can generally be separated into multiple components, wherein a first component (referred to herein as the K signal) depends on the actual value of the stacking at the location of the stacking target, while a second component (referred to herein as the G signal) does not. Specifically, the G signal depends on the physical properties of the stacking target design and is related to the target's sensitivity to stacking variations. For this reason, this G signal is referred to herein as a sensitivity metric.

[0079] It should be noted that the SCOL measurement at a particular location on the sample requires both a K signal and a G signal. For example, the overlay measurement (OVL) can be calculated using Equation 4 above. However, because the G signal (e.g., the sensitivity metric) does not directly depend on the actual overlay at a particular location of the overlay target, the G signal can be obtained from another source and therefore does not need to be measured at every overlay target. Therefore, when the G signal is obtained from another source, the number of cells required to obtain the overlay measurement of the overlay target can be reduced, which can beneficially reduce measurement time and increase measurement throughput across the sample. Continuing with the description of the first-level SCOL technique, when the G signal is obtained from another source, a single-cell overlay target can be used.

[0080] It is further contemplated herein that sensitivity metrics (e.g., G signals) are correlated with physical properties of the overlay target design. Thus, variations in these sensitivity metrics across samples can be correlated with variations in the physical properties of the overlay target across the wafer, which typically occur on length scales much larger than overlay variations. For example, overlay variations can vary significantly within each lithography exposure field of view, while the physical properties of the overlay target (and therefore the sensitivity metrics) can vary relatively slowly across several fields of view. Thus, a sensitivity metric measured at one location can be correlated with multiple targets within a field of view or potentially between fields of view.

[0081] Although Equations 1-4 relate to first-order scatterometry stacks in which each cell includes a different intentional shift, it should be noted that the systems and methods of the present disclosure are not limited to first-order scatterometry stacks. For example, the systems and methods of the present disclosure can be used with zero-order scatterometry stacks.

[0082] Figure 4 is a diagram depicting a full pupil landscape according to one or more embodiments of the present disclosure.

[0083] In an embodiment, a full and local pupil view 400 may be obtained (e.g. Figure 4 ). For example, a pupil image of each cell may be obtained to generate landscape 400. For example, the broadband pupil data of each pupil image may be sliced along the wavelength direction (eg, various wavelengths of broadband illumination).

[0084] In an embodiment, the landscape 400 may include a “green zone” 402 (or stable region 402 ), where the stable region 402 corresponds to a region where sensitivity to overlay process variations is relatively stable (e.g., a region where overlay measurements are insensitive to overlay process variations). Figure 4 As shown in FIG. 4 , the green area 402 can be shown as a platform (e.g., Figure 4 The plateau on the left side of the graph).

[0085] In an embodiment, landscape 400 may include a resonant region 404 , where resonant region 404 corresponds to a region where sensitivity to process variations is greater.

[0086] Figures 5A to 5D Graphs 500 through 530 depict per-pixel overlays or overlays obtained using multi-wavelength techniques according to one or more embodiments of the present disclosure. Figure 5A Depicted is a graph 500 depicting per-pixel overlay in a pupil, in accordance with one or more embodiments of the present disclosure. Figure 5B Depicts a diagram 510 depicting a diagram having a corresponding Figure 5A KG diagram of the points of the pixels in the longitudinal slice depicted in (whose slope is proportional to the superposition). Figure 5C Depicted is a graph 520 depicting per-pixel overlay in a pupil according to one or more embodiments of the present disclosure. Figure 5D A graph 530 is depicted, which depicts a KG graph (whose slope is proportional to the stacking) generated by slicing and storing pupil data transversely to the wavelength direction according to one or more embodiments of the present disclosure, wherein region 522 is as shown in FIG. Figure 5C As described in .

[0087] In an embodiment, broadband pupil data can be used in a multi-wavelength algorithm to achieve recipe-free ultra-robust measurements. For example, multiple wavelengths within the identified "green zone" 402 can be used to obtain superimposed measurements.

[0088] refer to Figures 5A to 5B In some embodiments, for example, pupil data may be sliced parallel to the wavelength direction to obtain superposition measurements. For example, Figure 5A A graph 500 is depicted that includes a region 502 generated from a grid parallel to the wavelength direction. In an embodiment, multiple wavelengths within region 502 can be used to obtain a superposition measurement. For example, Figure 5B As shown in , the slope of the straight line (best fit line) can be used to determine the overlay measurement according to Equations 3-4 shown and described above.

[0089] refer to Figures 5C to 5D In some embodiments, for example, pupil data may be sliced transversely to the wavelength to obtain superposition measurements. Figure 5C A graph 520 is depicted, which includes regions 522 generated from a grid transverse to the wavelength direction. In embodiments, multiple regions such as 522 (which may be selected to overlap) may be used to obtain superimposed measurements. For example, Figure 5D As shown in , the slope of the straight line (best fit line) can be used to determine the overlay measurement according to Equations 3-4 shown and described above.

[0090] Figure 6 6 is a flow chart depicting a method 600 for performing overlay measurements using a broadband illumination source, in accordance with one or more embodiments of the present disclosure. Applicants note that the embodiments and enabling techniques previously described herein in the context of overlay metrology system 100 should be interpreted as extending to method 600. However, it should be further noted that method 600 is not limited to the architecture of overlay metrology system 100.

[0091] In an embodiment, method 600 includes step 602 of generating one or more broadband illumination beams with one or more broadband illumination sources.

[0092] In an embodiment, method 600 includes step 604 of directing the generated one or more broadband illumination beams to a superimposition target on a sample when implementing a metrology recipe.

[0093] In an embodiment, method 600 includes generating diffracted light using periodic features of the superimposed target 606. For example, the periodic features of the superimposed target may act as a diffraction grating to generate diffracted light by separating a broadband illumination beam into multiple wavelengths.

[0094] In an embodiment, method 600 includes step 608 of receiving a pupil image from one or more detectors located at a pupil plane. For example, the one or more detectors may be configured to generate a pupil image of the superimposed target when the superimposed target is illuminated with one or more broadband illumination beams from one or more broadband illumination sources, wherein the light distribution in the pupil plane includes a zero-order illumination lobe and a first-order diffraction lobe from the illumination from the illumination source according to a metrology recipe, and the spectrum of the first-order diffraction lobe is spatially dispersed in the pupil plane (e.g., Figures 3A to 3C ).

[0095] In an embodiment, method 600 includes a step 610 of generating a superposition measurement of the sample based on a selected portion of the pupil image corresponding to selected wavelengths of the spectrum of the first order diffraction lobes.

[0096] In an embodiment, method 600 includes identifying a region associated with the selected wavelength 612. For example, the identified region may correspond to a stable region, where the stable region corresponds to a region where sensitivity to overlay process variations is stable.

[0097] Referring again to FIG. 1 , additional components of the overlay metrology tool 102 according to one or more embodiments of the present disclosure are described in greater detail.

[0098] In an embodiment, the overlay metrology system 100 includes a controller 108. The controller 108 may include one or more processors 110 and / or a storage medium 112 (eg, memory 112).

[0099] The controller 108 may include one or more processors 110 configured to execute program instructions maintained on a memory medium 112 or memory. In this regard, the one or more processors 110 of the controller 108 may perform any of the various process steps described throughout this disclosure. Furthermore, the controller 108 may be communicatively coupled to the overlay metrology tool 102 or any component thereof.

[0100] The one or more processors 110 of the controller 108 may include any processor or processing element known in the art. For the purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 110 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In embodiments, the one or more processors 110 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute a program configured to operate or operate in conjunction with the overlay metrology system 100, as described throughout this disclosure.

[0101] Furthermore, the various subsystems of the stacking metrology system 100 may include processors or logic elements suitable for implementing at least a portion of the steps described in this disclosure. Therefore, the above description should not be construed as limiting the embodiments of the present disclosure, but rather merely illustrative of them. Furthermore, the steps described throughout this disclosure may be performed by a single controller 108 or, alternatively, by multiple controllers. Furthermore, the controller 108 may include one or more controllers housed in a common housing or multiple housings. In this manner, any controller or combination of controllers may be individually packaged as a module suitable for integration into the stacking metrology system 100.

[0102] The memory medium 112 may comprise any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 110. For example, the memory medium 112 may comprise a non-transitory memory medium. As another example, the memory medium 112 may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical storage devices (e.g., magnetic disks), tape, solid-state drives, and the like. It should be further noted that the memory medium 112 may be housed in a common controller housing with the one or more processors 110. In one embodiment, the memory medium 112 may be located remotely relative to the physical location of the one or more processors 110 and the controller 108. For example, the one or more processors 110 of the controller 108 may access remote storage (e.g., a server) accessible via a network (e.g., the Internet, an intranet, and the like).

[0103] The subject matter described herein sometimes illustrates different components contained within or connected to other components. It should be understood that such depicted architectures are merely illustrative, and in fact, many other architectures that achieve the same functionality can be implemented. In a conceptual sense, any arrangement of components for achieving the same functionality is effectively "associated" so as to achieve the desired functionality. Therefore, regardless of the architecture or intermediate components, any two components combined to achieve a particular functionality herein can be considered to be "associated" with each other so as to achieve the desired functionality. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to achieve the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to achieve the desired functionality. Specific examples of "coupleable" include, but are not limited to, physically interactive and / or physically interactive components and / or wirelessly interactive and / or wirelessly interactive components and / or logically interactive and / or logically interactive components.

[0104] It is believed that the present disclosure and many of its attendant advantages will be appreciated from the foregoing description, and it will be understood that various changes may be made in the form, structure, and arrangement of components without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are merely illustrative, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A superposition metering system comprising: Lighting subsystem, which includes: one or more broadband illumination sources configured to generate one or more broadband illumination beams; and one or more illumination optics configured to direct the one or more broadband illumination beams to a superposition target on a sample while implementing a metrology recipe, wherein the superposition target comprises one or more cells having periodic features formed as an overlying grating structure in accordance with the metrology recipe; A photon collection subsystem comprising: a detector located at a pupil plane, wherein the detector generates one or more pupil images of the one or more elements of the superposition target based on illumination from the one or more broadband illumination beams, wherein the light distribution in the pupil plane includes first-order diffraction lobes from the one or more broadband illumination beams according to the metrology recipe, wherein the spectra of the first-order diffraction lobes are spatially dispersed in the pupil plane; and one or more collecting optics configured to direct at least one order of diffraction to the detector; and a controller communicatively coupled to the detector, the controller comprising one or more processors configured to execute program instructions causing the one or more processors to: receiving the one or more pupil images of the one or more cells from the detector; and A superposition measurement of the sample is generated based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectrum of the first-order diffraction lobes. 2 . The superposition metrology system of claim 1 , wherein the detector generates a first pupil image of a first element of the superposition target and a second pupil image of a second element of the superposition target.

3. The superposition metrology system of claim 1 , wherein generating a superposition measurement of the sample based on the selected portion of the one or more pupil images corresponding to the selected wavelength of the spectrum of the first-order diffraction lobe further comprises: A region associated with the selected wavelength is identified, wherein the identified region corresponds to a stable region, wherein the stable region corresponds to a region where the overlay measurement is insensitive to overlay process variations.

4. The superposition metrology system of claim 1 , wherein the one or more broadband illumination sources comprises a rotating quadrupole illumination source providing tilted illumination beams along two orthogonal directions in the pupil plane.

5. The superimposed metrology system of claim 1 , wherein the one or more processors are further configured to: storing the generated superimposed measurements in a memory when implementing the metering recipe; and One or more process parameters are adjusted based on the stored generated full pupil landscape.

6. The superimposed metrology system of claim 1 , wherein the one or more processors are further configured to: storing the generated superimposed measurements in a memory when implementing the metering recipe; and One or more recipe parameters are adjusted based on the stored generated full pupil landscape.

7. The superimposed metrology system of claim 1 , wherein the one or more processors are further configured to: Slicing the received one or more pupil images; and Additional superimposed measurements of the sample are generated via a multi-wavelength algorithm based on selected portions of the sliced one or more pupil images corresponding to selected wavelengths of the spectrum of first order diffraction lobes.

8. The superposition metrology system of claim 1, wherein the detector comprises a charge coupled device or a complementary metal oxide semiconductor detector.

9. The overlay metrology system of claim 1, wherein the sample comprises a substrate.

10. The overlay metrology system of claim 9, wherein the sample comprises a wafer.

11. A superimposed metering system comprising: A controller communicatively coupled to the detector, the controller comprising one or more processors configured to execute program instructions causing the one or more processors to: receiving from the detector one or more pupil images of one or more cells of a superimposed target, the one or more pupil images being generated using one or more broadband illumination beams from one or more broadband illumination sources; and A superposition measurement of the sample is generated based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectrum of the first order diffraction lobes.

12. The superposition metrology system of claim 11 , wherein generating a superposition measurement of the sample based on the selected portion of the one or more pupil images at the selected wavelength of the spectrum corresponding to a first order diffraction lobe further comprises: A region associated with the selected wavelength is identified, wherein the identified region corresponds to a stable region, wherein the stable region corresponds to a region where the overlay measurement is insensitive to overlay process variations.

13. The superimposed metering system of claim 11, further comprising: Lighting subsystem, which includes: the one or more broadband illumination sources configured to generate the one or more broadband illumination beams; and one or more illumination optics configured to direct the one or more broadband illumination beams to the superposition target on the sample while implementing a metrology recipe, wherein the superposition target includes the one or more cells having periodic features formed as overlapping grating structures according to the metrology recipe, wherein the periodic features of the superposition target act as diffraction gratings to generate diffracted light by separating the one or more broadband illumination beams into a plurality of wavelengths.

14. The superposition metrology system of claim 13, wherein the one or more broadband illumination sources comprise a rotating quadrupole illumination source providing tilted illumination beams in two orthogonal directions in a pupil plane.

15. The superimposed metering system of claim 11, further comprising: A photon collection subsystem comprising: the detector being located at a pupil plane, wherein the detector generates one or more pupil images of the one or more elements of the superposition target based on illumination with the one or more broadband illumination beams, wherein a light distribution in the pupil plane comprises first-order diffraction lobes from the one or more broadband illumination beams according to the metrology recipe, wherein a spectrum of the first-order diffraction lobes is spatially dispersed in the pupil plane; and One or more collecting optics configured to direct at least the first order diffraction lobe to the detector.

16. The superposition metrology system of claim 15, wherein the detector comprises a charge coupled device or a complementary metal oxide semiconductor detector.

17. The overlay metrology system of claim 11, wherein the one or more processors are further configured to: storing the generated superimposed measurements in a memory when implementing the metering recipe; and One or more process parameters are adjusted based on the stored generated full pupil landscape.

18. The overlay metrology system of claim 11 , wherein the one or more processors are further configured to: storing the generated superimposed measurements in a memory when implementing the metering recipe; and One or more recipe parameters are adjusted based on the stored generated full pupil landscape.

19. The overlay metrology system of claim 11 , wherein the one or more processors are further configured to: Slicing the received one or more pupil images; and Additional superimposed measurements of the sample are generated via a multi-wavelength algorithm based on selected portions of the sliced one or more pupil images corresponding to selected wavelengths of the spectrum of first order diffraction lobes.

20. The overlay metrology system of claim 11, wherein the sample comprises a substrate.

21. The overlay metrology system of claim 20, wherein the sample comprises a wafer.

22. A method comprising: generating one or more broadband illumination beams using one or more broadband illumination sources; directing the generated one or more broadband illumination beams toward a superposition target on a sample while implementing a metrology recipe, wherein the superposition target comprises one or more cells having periodic features formed as an overlying grating structure according to the metrology recipe; generating diffracted light using the periodic features of the superimposed target, wherein the periodic features of the superimposed target act as a diffraction grating to generate the diffracted light by separating the broadband illumination beam into a plurality of wavelengths; generating one or more pupil images of one or more cells of the superimposed target using a detector located at a pupil plane based on illumination with the one or more broadband illumination beams, wherein the light distribution in the pupil plane includes first-order diffraction lobes according to the metrology recipe, wherein the spectrum of the first-order diffraction lobes is spatially dispersed in the pupil plane; and A superposition measurement of the sample is generated based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectrum of the first-order diffraction lobes.

Images