Unified eye landscape using broadband illumination

Abstract

A method for overlay measurement may include generating a broadband illumination beam and directing the broadband illumination beam to an overlay target on a sample, the overlay target may include a cell having periodic feature regions formed as an overlapping lattice structure. The method may include generating diffracted light using the periodic feature regions of the overlay target, the periodic feature regions may function as diffraction gratings that generate diffracted light by separating the broadband illumination beam into multiple wavelengths. The method may include generating a pupil image of the cell of the overlay target, the distribution of light on the pupil plane may include primary diffraction regions, and the spectra of the primary diffraction regions may be spatially dispersed on the pupil plane. The method may include generating an overlay measurement based on a portion of the pupil image corresponding to a selected wavelength of the spectrum of the primary diffraction regions.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of U.S. Provisional Application No. 63 / 470,737, filed on June 2, 2023, which is hereby incorporated by reference in its entirety under 35 U.S.C. § 119(e).

[0002] This disclosure generally relates to overlay measurement, and more particularly to scatterometry overlay measurement.

Background Art

[0003] Overlay measurement generally refers to the measurement of the relative overlay of layers on a sample such as a semiconductor device, although not limited thereto. Overlay measurement, or rather the measurement of overlay error, generally refers to the measurement of the displacement of features fabricated on two or more sample layers. As a general concept, for the device to function properly, an appropriate overlay of features fabricated on multiple sample layers is required.

[0004] There is a demand for miniaturization and high integration of features, and accordingly, the need for accurate and efficient overlay measurement is increasing. A measurement system generally generates measurement data associated with a sample through measurement or other inspections of dedicated measurement targets distributed throughout the sample.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0006] [Non-Patent Document 1] Adel, et al., “Diffraction order control in overlay metrology: a review of the roadmap options,” Proc. SPIE. 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 692202. (2008) [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventional measurement systems use monochromatic light for measurements. Finding the optimal wavelength requires repeated, time-consuming single-wavelength measurements. A specific wavelength for a given recipe is selected so that it falls within the "green zone" of the pupil landscape being measured (i.e., where the overlay slope is low and unaffected by wavelength or focal changes). The landscape itself can change due to process-related reasons. This can push a given wavelength in a recipe outside the "green zone." Therefore, there is a need to provide a system and method that overcomes the aforementioned shortcomings. [Means for solving the problem]

[0008] One or more embodiments of an overlay measurement system are disclosed. In an embodiment, the overlay measurement system comprises an illumination subsystem. In an embodiment, the illumination subsystem comprises one or more broadband illumination sources configured to produce one or more broadband illumination beams. In an embodiment, the illumination subsystem comprises one or more illumination optics configured to direct one or more broadband illumination beams to an overlay target on a sample when performing a measurement recipe. In an embodiment, the overlay target according to the measurement recipe comprises one or more cells having periodic feature portions formed as an overlapping lattice structure. In an embodiment, the overlay measurement system comprises a focusing subsystem. In an embodiment, the focusing subsystem comprises a detector positioned on the pupil plane. In an embodiment, the detector generates one or more pupil images of one or more cells of the overlay target based on illumination from one or more broadband illumination beams. In an embodiment, the distribution of light on the pupil plane according to the measurement recipe includes primary diffraction regions from one or more broadband illumination beams, and the spectra of the primary diffraction regions are spatially dispersed on the pupil plane. In an embodiment, the focusing subsystem comprises one or more focusing optics configured to direct at least primary diffractions to the detector. In an embodiment, the overlay measurement system includes a control unit communicatively coupled to the detector. In an embodiment, the control unit includes one or more processing units configured to execute program instructions causing one or more processing units to receive one or more pupil images of one or more cells from the detector and to generate an overlay measurement of the sample based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectrum of the primary diffraction site.

[0009] One or more embodiments of the overlay measurement system of the present disclosure are disclosed. In an embodiment, the overlay measurement system comprises a control unit communicatively coupled to a detector. In an embodiment, the control unit comprises one or more processing units configured to execute program instructions causing one or more pupil images of one or more cells from the detector. In an embodiment, the one or more pupil images are generated using one or more broadband illumination beams from one or more broadband illumination sources. In an embodiment, the control unit comprises one or more processing units configured to execute program instructions causing one or more processing units to generate an overlay measurement of a sample based on selected portions of the one or more pupil images corresponding to selected wavelengths of the spectra of the first diffraction sites.

[0010] Methods according to one or more embodiments of this disclosure are disclosed. In embodiments, the method includes generating one or more broadband illumination beams from one or more broadband illumination sources. In embodiments, the method includes directing the generated one or more broadband illumination beams to an overlay target on a sample when performing a measurement recipe, the overlay target according to the measurement recipe includes one or more cells having periodic feature portions formed as an overlapping grating structure. In embodiments, the method includes generating diffracted light using the periodic feature portions of the overlay target, the periodic feature portions of the overlay target function as a diffraction grating that generates diffracted light by separating the broadband illumination beams into a plurality of wavelengths. In embodiments, the method includes generating one or more pupil images of one or more cells of the overlay target using a detector positioned on the pupil plane based on illumination by one or more broadband illumination beams, the distribution of light on the pupil plane according to the measurement recipe includes primary diffraction regions, and the spectra of the primary diffraction regions are spatially dispersed on the pupil plane. In embodiments, the method includes generating an overlay measurement of a sample based on selected portions of one or more pupil images corresponding to selected wavelengths of the spectra of the primary diffraction regions.

[0011] It should be understood that both the foregoing general description and the following detailed description are by way of illustration and explanation only and are not necessarily limiting of the claimed invention. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention.

Brief Description of the Drawings

[0012] By referring to the following drawings, those skilled in the art can better understand many effects of the present disclosure. [Figure 1A] It is a conceptual diagram of a system for performing scatterometry overlay measurement of an overlay target according to one or more embodiments of the present disclosure. [Figure 1B] It is a schematic diagram of an overlay measurement tool according to one or more embodiments of the present disclosure. [Figure 2] It is a side view of an overlay target suitable for scatterometry overlay measurement in which a cell according to one or more embodiments of the present disclosure has a stacked grating structure. [Figure 3A] It is a three-dimensional top oblique view of a sample representing diffraction of a broadband illumination beam according to one or more embodiments of the present disclosure. [Figure 3B] It is a top view of an illumination pupil image of an overlay measurement target illuminated by a broadband illumination beam according to one or more embodiments of the present disclosure. [Figure 3C] It is a top view of a condenser pupil image of an overlay measurement target illuminated by a broadband illumination beam according to one or more embodiments of the present disclosure. [Figure 4] It is a plot of a full pupil landscape according to one or more embodiments of the present disclosure. [Figure 5A] It is a plot representing an overlay according to one or more embodiments of the present disclosure. [Figure 5B] It is a plot representing an overlay according to one or more embodiments of the present disclosure. [Figure 5C] It is a plot representing an overlay according to one or more embodiments of the present disclosure. [Figure 5D]A plot representing an overlay according to one or more embodiments of the present disclosure. [Figure 6] A flowchart representing a method of generating an overlay measurement using a broadband illumination source according to one or more embodiments of the present disclosure.

Mode for Carrying Out the Invention

[0013] The details of the disclosed subject matter illustrated in the accompanying drawings are described below. The present disclosure is particularly illustrated and described with respect to certain embodiments and specific features thereof. The embodiments described herein are for purposes of illustration and not limitation. It will be apparent to those skilled in the art that various changes and modifications can be made to the form and details without departing from the spirit and scope of the present disclosure.

[0014] Embodiments of the present disclosure relate to systems and methods for scatterometric overlay measurement based on broadband illumination, where periodic features on the overlay measurement target function as diffraction gratings that divide a broadband illumination beam into different wavelengths.

[0015] In this disclosure, the term “overlay” is generally used to describe the relative position of a feature on a sample fabricated by two or more lithography patterning steps, and the term “overlay error” refers to the deviation of the feature from the intended configuration. In this context, overlay measurement may represent either the measurement of relative position or the measurement of overlay error associated with these relative positions. For example, a multilayer element may have feature patterns formed on multiple sample layers using different lithography steps for each layer. Generally, the overlap of feature patterns between layers must be strictly controlled to ensure proper performance of the resulting element. Therefore, overlay measurement can characterize the relative positions of feature patterns on two or more sample layers. In another example, feature patterns on a single sample layer may be fabricated using multiple lithography steps. Such techniques are generally called two-patterning or multiple-patterning techniques and can facilitate the fabrication of highly dense feature patterns close to the resolution of the lithography system. In this context, overlay measurement can characterize the relative positions of feature patterns on this single layer from different lithography steps. The examples in this disclosure relating to specific applications of overlay measurement are provided for illustrative purposes only and should not be construed as limiting this disclosure.

[0016] In some applications, overlay measurements may be performed directly on the feature area of ​​the fabricated element (e.g., the element feature area). However, generally, overlay measurements are performed on a dedicated overlay target printed using the same lithography steps as the element feature area. Thus, the feature area of ​​the overlay target (e.g., the target feature area) may be specifically designed to facilitate overlay measurements. Furthermore, overlays measured in a fabrication step (e.g., after fabricating one or more sample layers) may be used to generate correctors for precisely aligning process tools (e.g., lithography tools) for the fabrication of additional sample layers in subsequent fabrication steps.

[0017] In this disclosure, the term “scatrometry measurement” is used to broadly encompass the terms “scatrometry-based measurement” and “diffraction-based measurement” in which a sample having periodic features on one or more sample layers is illuminated by an illumination beam with a limited angular range, and one or more separate diffraction orders are collected in the measurement. Furthermore, the term “scan measurement” is used to describe a measurement of a measurement produced as the sample moves relative to the illumination used for the measurement. In a general sense, a scan measurement may be performed by moving the sample, the illumination, or both.

[0018] Many scatterometry overlay measurement techniques are generally recognized as determining the overlay by illuminating an overlay object having a lattice structure within two layers (e.g., a grating-over-grating structure), and the overlay measurement is based on the asymmetry between positive and negative diffraction orders. For example, various scatterometry techniques are described in Patent Document 1, published March 11, 2021; Patent Document 2, issued November 3, 2020; Patent Document 3, issued February 9, 2019; and Non-Patent Document 1, all of which are incorporated herein by reference in their entirety.

[0019] As used throughout this disclosure, the term “sample” broadly refers to a substrate formed of a semiconductor or non-semiconductor material (e.g., a wafer). Examples of semiconductor or non-semiconductor materials include, but are not limited to, single-crystal silicon, gallium arsenide, and indium phosphide. A sample may comprise one or more layers. Examples of these layers include, but are not limited to, resists, dielectric materials, conductive materials, and semiconductor materials. Many different types of these layers are known in the art, and as used herein, the term “sample” is intended to encompass samples on which any kind of such layers may be formed. One or more layers formed on a sample may or may not be patterned. For example, a sample may comprise multiple dies, each having repeatable patterned features. The formation and processing of these layers of material may result in a finally completed device. Many different types of devices may be formed on a sample, and as used herein, the term “sample” is intended to encompass samples on which any kind of device known in the art is fabricated. Furthermore, in this disclosure, the terms “sample” and “wafer” should be interpreted as interchangeable. Furthermore, in this disclosure, the terms patterning element, mask, and reticle should be interpreted as interchangeable.

[0020] Embodiments of the present disclosure relate to providing recipes for overlay measurement tools. Overlay measurement tools can generally be configured according to a recipe that includes, in non-limiting examples, a set of parameters that control various aspects of the overlay measurement, such as sample illumination, light focusing from the sample, and the placement of the sample during measurement. Thus, an overlay measurement tool can be configured to provide a selected type of measurement for one or more overlay object designs of interest. For example, a measurement recipe may include, non-limiting illumination parameters such as the number of illumination beams, illumination wavelengths, illumination pupil distribution (e.g., distribution of illumination angles and the corresponding intensity of illumination at these angles), polarization of incident illumination, bandwidth of illumination wavelengths, or spatial distribution of illumination. In another example, a measurement recipe may include, non-limiting focusing parameters such as a focusing pupil distribution (e.g., a desired distribution of angular light from the sample used for measurement and the corresponding filter intensity at these angles), focusing aperture settings for selecting a portion of the sample of interest, polarization of the focused light, wavelength filters, and the position of one or more detectors (e.g., photodetectors), or parameters that control one or more detectors. In yet another example, a measurement recipe could include, without limitation, various parameters associated with the sample position during measurement, such as the sample height, sample orientation, and whether the sample is stationary or moving (according to associated parameters representing velocity, scan pattern, etc.) during measurement.

[0021] As an exemplary example, diffraction-based overlay measurement techniques can generate individual diffraction orders by illuminating an overlay target with periodic features with illumination at a selected incident angle. These selected diffraction orders can then be collected for use in determining the overlay. Using this method, the emission angle of the diffraction order is based on factors such as the periodicity of the target, the wavelength of the illumination, and the angle of illumination. Furthermore, different techniques may employ different combinations of illumination and focusing configurations.

[0022] Embodiments of this disclosure relate to providing overlay data to one or more process tools. Overlay data from an overlay measurement tool generally includes any output of the overlay measurement tool that has sufficient information to determine the overlay (or overlay error) associated with various lithography steps. For example, the overlay data may include, but does not necessarily include, one or more datasets, one or more images, one or more detector readings, etc. This overlay data may be used for various purposes, including, in non-limiting examples, the generation of lithography tool diagnostic information or process control modifiers. For example, overlay data for a sample in a lot may be used to generate a feedback modifier to control the lithography irradiation of subsequent samples in the same lot. In another example, overlay data for a sample in a lot may be used to generate a feedforward modifier to control the lithography irradiation of the same or similar sample in subsequent lithography steps to accommodate any deviations in the current irradiation.

[0023] Existing scatometry overlay measurements are performed using monochromatic light. Finding the optimal wavelength when using monochromatic light requires numerous time-consuming single-wavelength measurements (i.e., of the pupil landscape). In such systems, a specific wavelength for a recipe is selected so that it falls within the "green zone" of the target pupil landscape. However, the landscape itself can vary due to process-related reasons, causing a given wavelength in the recipe to fall outside the green zone.

[0024] In this disclosure, the terms “green zone,” “stable region,” and variations thereof may be defined as regions in which measurements are relatively stable with respect to deviations in process parameters. For example, a “green zone” may be a region with a low overlay slope that is unaffected by wavelength or focal changes.

[0025] Here, scatrometry overlay measurements utilizing broadband illumination can offer several advantages compared to conventional monochromatic (e.g., single-band) illumination, such as mitigating problems in the changing green zone (e.g., a set of wavelengths in which the overlay measurement can be stable) by using various wavelengths to obtain overlay measurements, as an example of a non-limiting approach.

[0026] Furthermore, the system and method of this disclosure enable rapid (e.g., batch) acquisition of the entire pupil landscape. In this sense, the entire pupil landscape may enable localized optimization of overlay measurements and tracking of process variations.

[0027] Here, with reference to Figures 1A to 6, a system and method of scatometry overlay measurement according to one or more embodiments of the present disclosure will be described.

[0028] Figure 1A is a conceptual diagram of an overlay measurement system 100 that performs scattometry overlay measurement of an overlay target 106 according to one or more embodiments of this disclosure.

[0029] In an embodiment, the overlay measurement system 100 includes an overlay measurement tool 102 that acquires an overlay signal from the overlay target 106 based on any number of overlay recipes. For example, the overlay measurement tool 102 can direct illumination onto the sample 104 and can further collect light or other radiation emitted from the sample 104 that generates an overlay signal suitable for determining the overlay of two or more sample layers. The overlay measurement tool 102 may be any type of overlay measurement tool known in a technique suitable for generating an overlay signal suitable for determining the overlay associated with the overlay target 106 on the sample 104. The overlay measurement tool 102 may selectively operate in imaging mode or non-imaging mode. For example, in imaging mode, individual overlay target elements may be resolvable within an illumination spot on the sample 104 (e.g., as part of a bright-field image, dark-field image, etc.). In another example, the overlay measurement tool 102 could operate as a scattometry-based overlay measurement tool, where the radiation from sample 104 is analyzed at the pupil plane to characterize the angular distribution of radiation from sample 104 (e.g., associated with scattering and / or diffraction of radiation by sample 104).

[0030] Furthermore, the overlay measurement tool 102 may be configured to generate an overlay signal based on any number of recipes that define measurement parameters for obtaining an overlay signal suitable for determining the overlay of the overlay target 106. For example, the recipes for the overlay measurement tool 102 may, but are not limited to, the illumination wavelength, the detected wavelength of light emitted from the sample 104, the spot size or shape of the illumination on the sample 104, the angle of the incident illumination, the polarization of the incident illumination, the polarization of the focused light, the position of the beam of the incident illumination on the overlay target 106, and the position of the overlay target 104 in the focal volume of the overlay measurement tool 102.

[0031] Figure 1B is a conceptual diagram showing an overlay measurement tool 102 of an overlay measurement system 100 according to one or more embodiments of the present disclosure.

[0032] In an embodiment, the overlay measurement tool 102 includes an illumination subsystem comprising an illumination source 114 configured to produce at least one illumination beam 116 and one or more illumination optics 122. For example, the illumination subsystem may comprise one or more broadband illumination sources 114 configured to produce one or more broadband illumination beams 116. Thus, the overlay measurement tool 102 may have one or more apertures in the illumination pupil plane for splitting the illumination from the illumination sources 114 into one or more illumination beams 116 or illumination areas. Thus, the overlay measurement tool 102 can provide dipole illumination, orthogonal illumination, etc. Furthermore, the spatial profiles of one or more illumination beams 116 on the sample 104 can be controlled by a field plane aperture to have any selected spatial profile.

[0033] The illumination source 114 may comprise any type of illumination source suitable for providing at least one broadband illumination beam 116. In embodiments, the illumination source 114 is a laser source. For example, the illumination source 114 may comprise a broadband laser source.

[0034] In an embodiment, the overlay measurement tool 102 directs an illumination beam 116 to the sample 104 via an illumination path 118. The illumination path 118 may comprise one or more optical components suitable for correcting and / or adjusting the illumination beam 116 and directing the illumination beam 116 to the sample 104. In an embodiment, the illumination path 118 comprises one or more illumination path lenses 120 (for example, for collimating the illumination beam 116, relaying the pupil and / or field of view). In an embodiment, the illumination path 118 comprises one or more illumination path optics 122 for shaping or otherwise controlling the illumination beam 116. For example, the illumination path optics 122 may comprise, 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., stationary mirrors, translatable mirrors, scanning mirrors, etc.).

[0035] In one embodiment, the overlay measurement tool 102 includes an objective lens 124 that focuses an illumination beam 116 onto a sample 104 (for example, an overlay target 106 having overlay target features arranged on two or more layers of the sample 104). In one embodiment, the sample 104 is placed on a sample stage 126, which is suitable for fixing the sample 104 and is further configured to position the sample 104 relative to the illumination beam 116.

[0036] In an embodiment, the overlay measurement tool 102 comprises one or more detectors 128 configured to capture light (e.g., focused light 130) emitted from a sample 104 (e.g., an overlay target 106 on the sample 104) through a focusing path 132. The focusing path 132 may comprise one or more optical elements suitable for correcting and / or adjusting the focused light 130 from the sample 104. In an embodiment, the focusing path 132 comprises one or more focusing path lenses 134 (e.g., for collimating the illumination beam 116, for relaying the pupil and / or field of view), and may also comprise an objective lens 124, although this is not necessarily required. In an embodiment, the focusing path 132 comprises one or more focusing path optics 136 for shaping or otherwise controlling the focused light 130. For example, the focusing path optical system 136 may, in no particular way, include 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., stationary mirrors, translatable mirrors, scanning mirrors, etc.).

[0037] The detector 128 can be positioned at any selected location within the light-gathering path 132. In an embodiment, the overlay measurement tool 102 includes a detector 128 at the field of view plane (e.g., a plane conjugate to the sample 104) for generating an image of the sample 104. In an embodiment, the overlay measurement tool 102 includes a detector 128 at the pupil plane (e.g., a diffraction plane) for generating a pupil image. Thus, the pupil image may correspond to the angular distribution of light from the sample 104 captured by the detector 128. For example, the diffraction order corresponding to the diffraction of the illumination beam 116 from the sample 104 (e.g., the overlay target on the sample 104) may be imaged or otherwise observed at the pupil plane. Generally speaking, the detector 128 may capture any combination of reflected (or transmitted), scattered, or diffracted light from the sample 104.

[0038] The overlay measurement tool 102 may generally comprise any number or type of detectors 128 suitable for capturing light from the sample 104 exhibiting the overlay. In embodiments, the detectors 128 comprise one or more detectors 128 suitable for characterizing a stationary sample. Thus, the overlay measurement tool 102 may operate in a stationary mode in which the sample 104 is stationary during measurement. For example, the detectors 128 may comprise, in non-limiting examples, two-dimensional pixel arrays such as charge-coupled devices (CCDs) or complementary metal-oxide-semiconductor (CMOS) elements. Thus, the detectors 128 may generate a two-dimensional image (e.g., a field-of-view image or pupil-of-view image) in a single measurement.

[0039] In an embodiment, the detector 128 comprises one or more detectors 128 suitable for characterizing a moving sample 104 (e.g., a scanned sample). Thus, the overlay measurement tool 102 can operate in a scan mode in which the sample 104 is scanned relative to the measurement field during measurement. For example, the detector 128 may comprise a 2D pixel array having sufficient acquisition time and / or refresh rate to capture one or more images during scans within selected image tolerances (e.g., image blur, contrast, sharpness, etc.). In another example, the detector 128 may comprise a line scan detector that continuously generates an image of one row of pixels at a time. In yet another example, the detector 128 may comprise a Time-Delay Integration (TDI) detector. A TDI detector can generate a continuous image of the sample 104 when the movement of the sample 104 is synchronized with a charge transfer clock signal in the TDI detector. In particular, the TDI detector includes a clock pulse to acquire charge from illumination to a row of pixels and to transfer the charge between adjacent rows of pixels along the scan direction. When the movement of sample 104 along the scanning direction is synchronized with the charge transfer in the TDI detector, charge continuously accumulates during the scan. This process continues until the charge reaches the last row of pixels and is subsequently read out from the detector. In this way, an image of the object is accumulated over a longer period than would be possible with a simple line-scan camera. This relatively long acquisition time reduces photon noise in the image. Furthermore, the synchronized movement of the image and charge prevents blurring of the recorded image.

[0040] In an embodiment, the overlay measurement tool 102 includes a scanning subsystem that scans the sample 104 against the measurement field during measurement. For example, the sample stage 126 can position and align the sample 104 within the focal volume of the objective lens 124. In an embodiment, the sample stage 126 includes, as a non-limiting example, one or more adjustable stages such as a linear translation stage, a rotation stage, or a tip / tilt stage. In an embodiment, although not shown, the scanning subsystem includes one or more beam-scanning optical systems (e.g., a rotatable mirror, a galvanometer, etc.) that scan the illumination beam 116 against the sample 104.

[0041] The illumination path 118 and focusing path 132 of the overlay measurement tool 102 can be directed to various configurations suitable for illuminating the sample 104 with the illumination beam 116 and focusing the light emitted from the sample 104 in response to the incident illumination beam 116. For example, as shown in Figure 1B, the overlay measurement tool 102 may include a beam splitter 138 directed so that a common objective lens 124 can simultaneously direct the illumination beam 116 towards the sample 104 and focus the light from the sample 104. In another example, the illumination path 118 and focusing path 132 may include non-overlapping optical paths.

[0042] Figure 2 is a side view of an overlay target 106 suitable for scatrometry overlay measurement, in which cells 202 comprising a superimposed grid structure 204 are found in one or more embodiments of the present disclosure.

[0043] In the embodiment, the overlay target 106 comprises one or more cells 202 having one or more periodic feature portions 206, 208 formed as an overlapping lattice structure 204 on the sample 104. For example, one or more cells 202 comprises a first periodic feature portion 206 on a first layer 210 and a second periodic feature portion 208 on a second layer 212, where the first periodic feature portion 206 overlaps with the second periodic feature portion 208 to form an overlapping lattice structure 204 on the sample 104.

[0044] In this embodiment, the periodic feature portion of the overlay object functions as a diffraction grating that generates diffracted light by separating a broadband illumination beam into multiple wavelengths. For example, a broadband illumination source 114 may generate one or more broadband illumination beams 116, and one or more illumination optics 122 may direct one or more broadband illumination beams 116 to the surface of the sample 104. Thus, the periodic feature portions 206, 208 of the overlay object 106 on the surface of the sample 104 may separate one or more broadband illumination beams 116 into multiple wavelengths with multiple diffraction angles.

[0045] The overlay object 106 can generally be formed from any number of cells 202, and any particular cell 202 may have a superimposed grid structure 204 with periods along any direction. For example, the overlay object 106 may include a plurality of cells 202 having a grid structure 204 with a period along a common direction, where different cells 202 have different configurations of the periods of their corresponding grids.

[0046] However, it should be understood that the overlay object 106 and related description in Figure 2 are provided for illustrative purposes only and should not be construed as limiting. Rather, the overlay object 106 may include any suitable design of a superimposed grid overlay object. For example, the overlay object 106 may comprise any number of cells 202 suitable for measurements along two directions. Furthermore, the cells 202 may be distributed in any pattern or configuration. For example, a design of a measurement object suitable for scan measurements is generally described in Patent Document 4, published on July 27, 2021, which is incorporated herein by reference in its entirety. In embodiments, the overlay object 106 comprises one or more groups of cells distributed along a scan direction (e.g., the direction of movement of the sample 104), and the cells 202 within each particular group of cells are oriented to have periodic feature portions 206 that are periodic along a common direction. For example, a first group of cells may comprise one or more cells 202 having a periodicity along the X direction, and a second group of cells may comprise one or more cells 202 having a periodicity along the Y direction. Thus, all cells 202 within a particular cell group can be imaged simultaneously while the sample 104 is being scanned with the overlay measurement tool 102. In another example, for diagonally positioned objects suitable for measurement in orthogonal directions in a single scan, generally, the entirety of which is described in Patent Document 5, published on November 25, 2021, which is incorporated herein by reference.

[0047] Generally with reference to Figures 3A to 3C, various non-limiting configurations for generating and measuring signals from periodic feature portions 206 in one or more cells 202 of the overlay target 106, according to one or more embodiments of the present disclosure.

[0048] As described above, the periodic feature regions 206 and 208 on the overlay measurement target 106 can function as diffraction gratings that split the broadband illumination beam 116 into different wavelengths. For example, sample 104 may be illuminated by one or more illumination beams 116 (e.g., illumination spot 302). Here, the periodic feature regions 206 and 208 generate spatially dispersed diffraction regions that are also spectrally dispersed (e.g., zero-order diffraction region 304, ±1st-order diffraction regions 306 and 308).

[0049] In this embodiment, the illumination subsystem illuminates the overlay target 106 with any number of illumination beams 116 at any angle. For example, the illumination pupil plane may correspond to the pupil plane in the illumination subsystem as shown in Figure 1B.

[0050] In an embodiment, one or more detectors 128 may be configured to generate a pupil image of the overlay object 106 when the overlay object 106 is illuminated by a broadband illumination beam 116 from a broadband illumination source 114. For example, the pupil image of the overlay object 106 may be generated when the overlay object 106 is illuminated by broadband illumination. For example, the pupil image may include an illumination spot 302 and one or more diffraction regions (e.g., a zero-order diffraction region 304, ±1st-order diffraction regions 306, 308), and the spectra of ±1st-order diffraction regions 306, 308 may be spatially dispersed on the pupil plane.

[0051] In embodiments, one or more illumination optics 122 may be configured to direct a broadband illumination beam 116 to an overlay target 106 on the sample 104 when performing a measurement recipe. For example, the overlay target 106 according to the measurement recipe may include one or more overlapping cells (e.g., a superimposed grating structure) having periodic feature portions formed as an overlapping grating structure. For example, the periodic feature portions 106 of the overlay target may function as a diffraction grating that generates diffracted light by separating the broadband illumination beam 116 into multiple wavelengths.

[0052] In the embodiment, one or more detectors 128 are positioned on the pupil plane. For example, one or more detectors 128 may be configured to generate a pupil image 300 of the overlay object 106 when the overlay object 106 is illuminated by a broadband illumination beam 116 from a broadband illumination source 114.

[0053] Figure 3A is a three-dimensional top perspective view of a sample representing the 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 on the illumination pupil surface of an overlay measurement tool 102 according to one or more embodiments of the present disclosure.

[0054] Referring to Figure 3A, in the embodiment, one or more broadband illumination sources 114 may comprise a dipole illumination source that provides illumination beams 116 having opposing azimuthal angles in the pupil plane. For example, as shown in Figure 3A, the illumination pupil 310 may comprise two illumination beams 116 having opposing azimuthal angles in the pupil plane.

[0055] Referring to Figure 3B, in an embodiment, the broadband illumination source 114 may comprise a rotating quadrupole illumination source 114 that provides oblique illumination beams 116 along two orthogonal directions in the pupil plane. For example, as shown in Figure 3B, the illumination pupil 310 may comprise four illumination beams 116 along two orthogonal directions in the pupil plane.

[0056] Figure 3C is a top view of a focused pupil image 320 of an overlay measurement target 106 illuminated by four broadband illumination beams 116 shown in Figure 3B, according to one or more embodiments of the present disclosure. In particular, Figure 3C shows a non-limiting configuration of the diffraction order of the illumination beams 116 at the focused pupil plane. For example, in a focusing subsystem as shown in Figure 1B, the focused pupil plane may correspond to the pupil plane. In particular, Figure 3C shows zero-order diffraction 304, -1st-order lattice diffraction 306, and +1st-order lattice diffraction 308 distributed along the periodic direction of the overlapping lattice structure 204 (e.g., in this case, the X direction) at the focused pupil plane. For example, the -1st-order lattice diffraction 306 and +1st-order lattice diffraction 308 may correspond to lattice diffraction from the first layer lattice 208 and the second layer lattice 212. Thus, the spectra of the first-order diffraction regions 306, 308 may be spatially dispersed at the pupil plane, as shown in Figures 3A and 3C.

[0057] As described above, the systems and methods of this disclosure may offer several advantages. For example, the systems and methods of this disclosure may provide a more robust way to employ existing overlay measurement techniques. For instance, the spectra of primary diffraction sites 306 and 308 may be spatially dispersed in the pupil plane so that a single wavelength overlay measurement can be obtained based on identified “green zones” corresponding to primary diffraction sites 306 and 308. In another example, the systems and methods of this disclosure may enable the use of multi-wavelength techniques. For example, the spectra of primary diffraction sites 306 and 308 may be spatially dispersed in the pupil plane so that an overlay measurement can be obtained using multiple wavelength regions within identified “green zones,” as further described herein and illustrated in Figures 5A to 5D.

[0058] In this embodiment, the overlay measurement of the overlay target 106 may be generated based on a selected portion of the pupil image corresponding to a selected wavelength of the spectrum of the primary diffraction sites 306, 308.

[0059] To measure the overlay in the x or y direction, two cells with opposing intentional shifts (±f0) may be used. In each cell, the difference signal (D± The result is calculated as shown in Equation 1 below.

number

[0060] In the formula, S +1 S is the positive first diffraction order signal. -1 is the negative first diffraction order signal, ±f0 are the offset parameters, G=D1-D2, and K=D1+D2.

[0061] The overlay (∈) for each pixel can be obtained from Equation 2.

number

[0062] In the formula, the difference signal (D ± The value for ) can be obtained using Equation 1.

[0063] The slope of a straight line (for example, a best-fit line) can be proportional to the overlay, as shown in equations 3 and 4 below.

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number

[0064] In this specification, measurement data collected using the Scatrometry Overlay (SCOL) technique associated with multiple cells to be overlaid can generally be separated into several components, with a first set of components (referred to herein as the K signal) depending on the actual value of the overlay at the location of the overlay, while a second set of components (referred to herein as the G signal) is considered independent. Rather, the G signal depends on the physical properties of the design of the overlay and is related to the sensitivity of the overlay to overlay variations. For this reason, the G signal refers to the sensitivity criterion in this specification.

[0065] Note that both the K signal and the G signal are required for SCOL measurement at a specific location on the sample. For example, overlay measurement (OVL) can be calculated using equation 4 above. However, since the G signal (e.g., the sensitivity criterion) does not directly depend on the actual overlay at a specific location on the overlay target, the G signal can be obtained from another source and therefore does not need to be measured for each overlay target. As a result, the number of cells required for overlay measurement can be reduced if the G signal is obtained from another source, which has the effect of reducing the number of measurements and increasing the overall measurement throughput of the sample. Furthermore, as an example of primary SCOL technique, a single-cell overlay target can be used when the G signal is obtained from another source.

[0066] Furthermore, in this specification, the sensitivity criterion (e.g., G signal) is considered to be related to the physical attributes of the design being overlaid. Consequently, variations in these sensitivity criteria across the entire sample may be related to variations in the physical attributes of the overlaid across the entire wafer, which generally occur over a considerably longer period than variations in the overlay. For example, overlay variations can vary significantly within each lithography field, while the physical attributes of the overlay (and therefore the sensitivity criterion) vary relatively slowly across multiple fields. Thus, a sensitivity criterion measured at a given location may be related to multiple objects within or potentially between fields.

[0067] Equations 1-4 relate to first-order scatterometry overlays, where each cell has a different intentional shift; however, the systems and methods of this disclosure are not limited to first-order scatterometry overlays. For example, the systems and methods of this disclosure may be used for zero-order scatterometry overlays.

[0068] Figure 4 is a plot showing a full pupil landscape according to one or more embodiments of the present disclosure.

[0069] In an embodiment, a total, local pupil landscape 400 (as illustrated in Figure 4) can be acquired. For example, the pupil image of each cell can be acquired to generate the landscape 400. For example, broadband pupil data of each pupil image can be sliced ​​along the wavelength direction (e.g., various wavelengths of broadband illumination).

[0070] In the embodiment, the landscape 400 may include a “green zone” 402 (or stability region 402), the stability region 402 corresponding to a region where sensitivity to overlay processing variations is stable (e.g., a region where overlay measurements are not sensitive to overlay processing variations). For example, as shown in Figure 4, the green zone 402 may be shown as a plateau (e.g., the plateau on the left side of the graph in Figure 4).

[0071] In this embodiment, the landscape 400 may include a resonance region 404, the resonance region 404 being a region with high sensitivity to process fluctuations.

[0072] Figures 5A to 5D are plots 500 to 530 of pixel-by-pixel overlays or overlays acquired using multi-wavelength techniques according to one or more embodiments of the present disclosure. Figure 5A shows plot 500 representing the pixel-by-pixel overlay of the pupil according to one or more embodiments of the present disclosure. Figure 5B shows plot 510 representing a KG plot (with a slope proportional to the overlay) having points corresponding to pixels in the longitudinal slice shown in Figure 5A, according to one or more embodiments of the present disclosure. Figure 5C shows plot 520 representing the pixel-by-pixel overlay of the pupil according to one or more embodiments of the present disclosure. Figure 5D shows plot 530 representing a KG plot (with a slope proportional to the overlay) generated by slicing and binning pupil data across the wavelength direction (region 522 is shown in Figure 5C), according to one or more embodiments of the present disclosure.

[0073] In embodiments, broadband pupil data can be used in multi-wavelength algorithms that enable recipe-free, particularly robust measurements. For example, overlay measurements can be sought using multiple wavelengths within an identified "green zone" 402.

[0074] Referring to Figures 5A and 5B, in some embodiments, for example, pupil data may be sliced ​​parallel to the wavelength direction to obtain an overlay measurement. For example, Figure 5A shows a plot 500 including a region 502 generated from bins parallel to the wavelength direction. In embodiments, multiple wavelengths within region 502 may be used to obtain an overlay measurement. For example, as shown in Figure 5B, the overlay measurement may be determined using the slope of a straight line (e.g., a best-fit line) according to equations 3, 4 above.

[0075] Referring to Figures 5C and 5D, in some embodiments, the pupil data may be sliced ​​across the wavelength direction to obtain an overlay measurement. For example, Figure 5C shows a plot 520 containing a region 522 generated from bins crossing the wavelength direction. In embodiments, multiple regions such as 522 (selected to overlap) may be used to obtain an overlay measurement. For example, as illustrated in Figure 5D, the overlay measurement may be determined using the slope of a straight line (e.g., a best-fit line) according to equations 3, 4 above.

[0076] Figure 6 is a flowchart illustrating a method 600 for performing overlay measurements using a broadband illumination source according to one or more embodiments of the present disclosure. The applicant notes that the enabling techniques described herein in the context of embodiments and the overlay measurement system 100 should be interpreted to extend to method 600, however, method 600 is not limited to the architecture of the overlay measurement system 100.

[0077] In an embodiment, method 600 includes step 602 of generating one or more broadband illumination beams using one or more broadband illumination sources.

[0078] In an embodiment, method 600 includes step 604 of directing one or more generated broadband illumination beams onto an overlay target on the sample when performing a measurement recipe.

[0079] In embodiments, method 600 includes step 606 of generating diffracted light using a periodic feature to be overlaid. For example, the periodic feature to be overlaid may function as a diffraction grating that generates diffracted light by separating a broadband illumination beam into multiple wavelengths.

[0080] In an embodiment, method 600 includes step 608 of receiving pupil images from one or more detectors positioned on the pupil plane. For example, one or more detectors may be configured to generate pupil images of an overlay object when the overlay object is illuminated by one or more broadband illumination beams from one or more broadband illumination sources, and the distribution of light on the pupil plane according to the measurement recipe includes zero-order illumination regions and primary-order diffraction regions from the illumination sources, and the spectra of the primary-order diffraction regions are spatially dispersed on the pupil plane (as shown in Figures 3A to 3C).

[0081] In an embodiment, method 600 includes step 610 of generating an overlay measurement of a sample based on a selected portion of the pupil image corresponding to a selected wavelength of the spectrum of the first diffraction site.

[0082] In an embodiment, method 600 includes step 612 of identifying a region associated with a selected wavelength. For example, the identified region may correspond to a stability region, which corresponds to a stability region of the sensitivity of overlay processing variations.

[0083] Referring again to Figure 1A, additional components of the overlay measurement tool 102 according to one or more embodiments of this disclosure will be described in more detail.

[0084] In one embodiment, the overlay measurement system 100 includes a control unit 108. The control unit 108 may include one or more processing units 110 and / or memory media 112 (e.g., memory 112).

[0085] The control unit 108 may comprise one or more processing units 110 configured to execute program instructions stored in the memory medium 112 or in memory. In this sense, one or more processing units 110 of the control unit 108 may perform any of the process steps described in this disclosure. Furthermore, the control unit 108 may be communicatively coupled to the overlay instrumentation tool 102 or any component thereof.

[0086] One or more processing units 110 of the control unit 108 may comprise any processing unit or processing element known in the art. In this disclosure, the terms “processing unit” or “processing element” may be broadly defined to encompass any element having one or more processing or logic elements (e.g., one or more microprocessing units, one or more Application Specific Integrated Circuit (ASIC) units, one or more Field Programmable Gate Arrays (FPGAs), or one or more Digital Signal Processors (DSPs)). In this sense, one or more processing units 110 may comprise any element configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In embodiments, one or more processing units 110 may be implemented as a desktop computer, mainframe computer system, workstation, image computer, parallel processing unit, networked computer, or any other computer system configured to execute a program configured to operate the overlay measurement system 100 or to operate in conjunction with it, as described throughout this disclosure.

[0087] Furthermore, different subsystems of the overlay measurement system 100 may comprise processing units or logic elements suitable for performing at least some of the steps disclosed herein. Therefore, the foregoing description should not be understood as limiting the embodiments of the disclosure, but is merely illustrative. Furthermore, the steps described throughout this disclosure may be performed by a single control unit 108 or by multiple control units. Furthermore, the control unit 108 may comprise one or more control units housed in a common housing or multiple housings. Thus, any control unit or combination of control units may be separately packaged as modules suitable for integration as the overlay measurement system 100.

[0088] The memory medium 112 may include any storage medium known in the art that is suitable for storing program instructions executable by one or more corresponding processing units 110. For example, the memory medium 112 may include a non-temporary memory medium. In another example, the memory medium 112 may, without limitation, be read-only memory (ROM), random access memory (RAM), magnetic or optical memory elements (e.g., disks), magnetic tape, solid-state drives, etc. Furthermore, the memory medium 112 may be housed in a common control unit housing comprising one or more processing units 110. In embodiments, the memory medium 112 may be located remotely from the physical locations of one or more processing units 110 and the control unit 108. For example, one or more processing units 110 of the control unit 108 may access remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.).

[0089] The subject matter described herein may also illustrate different components that are included in or connected to other components. The structures thus shown are for illustrative purposes only, and it will be understood that in practice, numerous other structures are implementable to achieve the same functionality. Conceptually, any configuration of components to achieve the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components in this specification combined to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality, regardless of the components that constitute or interpose them. Similarly, any two such associated components can also be considered “connected” or “combined” with each other to achieve the desired functionality, and any two components that can be thus associated can also be considered “combinable” with each other to achieve the desired functionality. Specific examples of combinability include, non-limitingly, components that are physically interactable and / or interacting physically, and / or interacting wirelessly and / or interacting wirelessly, and / or interacting logically and / or interacting logically.

[0090] The present disclosure and many of its associated effects are to be understood from the above description, and it is obvious that various modifications can be made to the form, structure, and configuration of the components without departing from the disclosed subject matter and without impairing the effects of the materials. The described forms are for illustrative purposes only, and it is intended that the following claims encompass and include such modifications. Furthermore, it is understood that the present invention is defined by the appended claims.

Claims

1. It is an overlay measurement system, A lighting subsystem, One or more broadband illumination sources configured to generate one or more broadband illumination beams, When performing a measurement recipe, one or more illumination optical systems are configured to direct one or more broadband illumination beams towards an overlay target on a sample, wherein the overlay target according to the measurement recipe includes one or more cells having periodic feature portions formed as an overlapping lattice structure, and the illumination optical system comprises one or more illumination optical systems. A lighting subsystem comprising, A light-gathering subsystem, A detector positioned on the pupil plane, wherein the detector generates one or more pupil images of the one or more cells to be overlaid based on illumination from the one or more broadband illumination beams, and the light distribution on the pupil plane according to the measurement recipe includes primary diffraction regions from the one or more broadband illumination beams, and the spectra of the primary diffraction regions are spatially dispersed on the pupil plane; One or more focusing optical systems configured to direct at least the first-order diffraction toward the detector, A light-gathering subsystem equipped with, A control unit is communicatively coupled to the detector, the control unit comprising one or more processing units configured to execute program instructions, the program instructions are transmitted to the one or more processing units, The detector receives one or more pupil images of one or more cells. To generate an overlay measurement of the sample based on selected portions of one or more pupil images corresponding to selected wavelengths of the spectrum of the primary diffraction region, Control unit and An overlay measurement system equipped with the following features.

2. The overlay measurement system according to claim 1, wherein the detector generates a first pupil image of the first cell to be overlaid and a second pupil image of the second cell to be overlaid.

3. To generate an overlay 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 primary diffraction region, The overlay measurement system according to claim 1, further comprising identifying a region associated with the selected wavelength, wherein the identified region corresponds to a stability region, and the stability region corresponds to a region insensitive to variations in the overlay measurement.

4. The overlay measurement system according to claim 1, wherein the one or more broadband illumination sources include a rotating quadrupole illumination source that provides oblique illumination beams along two orthogonal directions on the pupil plane.

5. The one or more processing units described above are: When carrying out the aforementioned measurement recipe, the generated overlay measurement is stored in memory. The overlay measurement system according to claim 1, further configured to adjust one or more process parameters based on the stored generated whole pupil landscape.

6. The one or more processing units described above are: When carrying out the aforementioned measurement recipe, the generated overlay measurement is stored in memory. The overlay measurement system according to claim 1, further configured to adjust one or more recipe parameters based on the stored generated whole pupil landscape.

7. The one or more processing units described above are: The received pupil images are sliced, The overlay measurement system according to claim 1, further configured to generate additional overlay measurements of the sample based on selected portions of one or more sliced ​​pupil images corresponding to selected wavelengths of the spectrum of the primary diffraction region via a multi-wavelength algorithm.

8. The overlay measurement system according to claim 1, wherein the detector comprises a charge-coupled element or a complementary metal-oxide-semiconductor detector.

9. The sample is the overlay measurement system according to claim 1, comprising a substrate.

10. The overlay measurement system according to claim 9, wherein the sample comprises a wafer.

11. It is an overlay measurement system, The detector comprises a control unit that is communicatively coupled to the detector, the control unit comprises one or more processing units configured to execute program instructions, and the program instructions are sent to the one or more processing units. Reception of one or more pupil images of one or more cells to be overlaid from the detector, wherein the one or more pupil images are generated using one or more broadband illumination beams from one or more broadband illumination sources, To generate a sample overlay measurement based on selected portions of one or more pupil images corresponding to selected wavelengths of the spectrum of the primary diffraction region, Overlay measurement system.

12. To generate an overlay 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 primary diffraction region, The overlay measurement system according to claim 11, further comprising identifying a region associated with the selected wavelength, wherein the identified region corresponds to a stability region, and the stability region corresponds to a region insensitive to variations in the overlay measurement.

13. The lighting subsystem further comprises, One or more broadband illumination sources configured to generate one or more broadband illumination beams, An overlay measurement system according to claim 11, comprising: one or more illumination optical systems configured to direct one or more broadband illumination beams toward the overlay target on the sample when performing a measurement recipe, wherein the overlay target according to the measurement recipe includes one or more illumination optical systems having one or more cells having periodic feature portions formed as an overlapping lattice structure, and the periodic feature portions of the overlay target function as diffraction gratings that generate diffracted light by separating the one or more broadband illumination beams into a plurality of wavelengths.

14. The overlay measurement system according to claim 13, wherein the one or more broadband illumination sources include a rotating quadrupole illumination source that provides oblique illumination beams along two orthogonal directions in the pupil plane.

15. The system further comprises a light-gathering subsystem, the light-gathering subsystem, A detector positioned on the pupil plane, wherein the detector generates one or more pupil images of the one or more cells to be overlaid based on illumination by the one or more broadband illumination beams, and the light distribution on the pupil plane according to the measurement recipe includes primary diffraction regions from the one or more broadband illumination beams, and the spectra of the primary diffraction regions are spatially dispersed on the pupil plane. One or more focusing optical systems configured to direct at least the primary diffraction area toward the detector, The overlay measurement system according to claim 11, comprising:

16. The overlay measurement system according to claim 15, wherein the detector comprises a charge-coupled element or a complementary metal-oxide-semiconductor detector.

17. The one or more processing units described above are: When carrying out the aforementioned measurement recipe, the generated overlay measurement is stored in memory. The overlay measurement system according to claim 11, further configured to adjust one or more process parameters based on the stored generated whole pupil landscape.

18. The one or more processing units described above are: When carrying out the aforementioned measurement recipe, the generated overlay measurement is stored in memory. The overlay measurement system according to claim 11, further configured to adjust one or more recipe parameters based on the stored generated whole pupil landscape.

19. The one or more processing units described above are: The received pupil images are sliced, The overlay measurement system according to claim 11, further configured to generate additional overlay measurements of the sample based on selected portions of one or more sliced ​​pupil images corresponding to selected wavelengths of the spectrum of the primary diffraction region via a multi-wavelength algorithm.

20. The sample is the overlay measurement system according to claim 11, comprising a substrate.

21. The sample comprises a wafer, as described in claim 20, for the overlay measurement system.

22. Generating one or more broadband illumination beams using one or more broadband illumination sources, When performing the measurement recipe, the generated one or more broadband illumination beams are directed towards an overlay target on the sample, wherein the overlay target according to the measurement recipe includes one or more cells having periodic feature portions formed as an overlapping grid structure. The process involves generating diffracted light using the periodic feature portion of the overlay target, wherein the periodic feature portion of the overlay target functions as a diffraction grating that generates the diffracted light by separating the broadband illumination beam into multiple wavelengths. The method involves generating one or more pupil images of one or more cells to be overlaid using detectors positioned on the pupil surface based on illumination by one or more broadband illumination beams, wherein the light distribution on the pupil surface according to the measurement recipe includes primary diffraction regions, and the spectra of the primary diffraction regions are spatially dispersed on the pupil surface. To generate an overlay measurement of the sample based on a selected portion of one or more pupil images corresponding to a selected wavelength of the spectrum of the primary diffraction region, A method that includes this.

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