Single cell scatterometry overlay with sensitivity calibration

Abstract

A metrology system may receive metrology data for a first set of overlay targets, the first set of overlay targets including at least two cells having different expected offsets. The system may further receive metrology data for a second set of overlay targets, wherein the metrology data for the second set of overlay targets is based on fewer cells than the first set of overlay targets. The system may further generate a sensitivity metric at a location of the first set of overlay targets based on the metrology data for the first set of overlay targets, generate an overlay measurement for the first set of overlay targets based on the sensitivity metric and the metrology data from the first set of overlay targets, and generate overlay measurements of the first set of overlay targets and the second set of overlay targets based on the sensitivity metric and the metrology data from the second set of overlay targets.

Description

Technical Field

[0001] The present disclosure relates generally to scatterometry overlay metrology, and more particularly to single-cell scatterometry overlay metrology. Background Art

[0002] Scatterometry overlay metrology techniques typically generate overlay measurements based on data collected from two or more cells of an overlay target, where each cell includes a grating-on-grating structure with a different intentional offset. However, this approach requires alignment of the metrology tool to each desired cell, which negatively impacts measurement throughput and may introduce inaccuracies due to navigation calibration errors and / or unexpected differences between cells. In addition, such dual-cell designs may be relatively large, which may make it impractical to place targets in some areas of the sample (e.g., within a die, etc.), and may further result in reduced yield. Therefore, there is a desire to develop systems and methods to overcome the above-mentioned drawbacks. Summary of the invention

[0003] According to one or more illustrative embodiments of the present disclosure, a metrology system is disclosed. In one illustrative embodiment, the system includes a controller. In another illustrative embodiment, the controller receives metrology data associated with a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlapping features on two layers of the sample. In another illustrative embodiment, the controller receives metrology data associated with a second set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets. In another illustrative embodiment, the controller generates a sensitivity metric at a location of the first set of overlay targets based on the metrology data of the first set of overlay targets. In another illustrative embodiment, the controller generates an overlay measurement of the first set of overlay targets based on the sensitivity metric and the metrology data from the first set of overlay targets. In another illustrative embodiment, the controller generates an overlay measurement of the first set of overlay targets based on the sensitivity metric and the metrology data from the second set of overlay targets. In another illustrative embodiment, the controller generates an overlay measurement of the first set of overlay targets and the second set of overlay targets based on the sensitivity metric and the metrology data from the second set of overlay targets.

[0004] According to one or more illustrative embodiments of the present disclosure, a metrology system is disclosed. In one illustrative embodiment, the system includes a metrology subsystem that generates metrology data associated with a sample. In another illustrative embodiment, the system includes a controller communicatively coupled to the metrology subsystem. In another illustrative embodiment, the controller receives metrology data associated with a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlapping features on two layers of the sample. In another illustrative embodiment, the controller receives metrology data associated with a second set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets. In another illustrative embodiment, the controller generates a sensitivity metric at a location of the first set of overlay targets based on the metrology data of the first set of overlay targets. In another illustrative embodiment, the controller generates an overlay measurement of the first set of overlay targets based on the sensitivity metric and the metrology data from the first set of overlay targets. In another illustrative embodiment, the controller generates overlay measurements of the first set of overlay targets and the second set of overlay targets based on the sensitivity metric and the metrology data from the second set of overlay targets.

[0005] According to one or more illustrative embodiments of the present disclosure, a method is disclosed. In one illustrative embodiment, the method includes generating metrology data associated with a first set of overlay targets and a second set of overlay targets on a sample, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlapping features on two layers of the sample, and wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets. In another illustrative embodiment, the method includes generating a sensitivity metric at a location of the first set of overlay targets based on the metrology data of the first set of overlay targets. In another illustrative embodiment, the method includes generating an overlay measurement of the first set of overlay targets based on the sensitivity metric and the metrology data from the first set of overlay targets. In another illustrative embodiment, the method includes generating an overlay measurement of the second set of overlay targets based on the sensitivity metric and the metrology data from the second set of overlay targets.

[0006] According to one or more illustrative embodiments of the present disclosure, a sample is disclosed. In one illustrative embodiment, the sample includes a plurality of overlay targets distributed across a plurality of fields. In another illustrative embodiment, the plurality of overlay targets include a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlapping features on two layers of the sample. In another illustrative embodiment, the plurality of overlay targets further include a second set of overlay targets, wherein each of the second set of overlay targets includes fewer cells than the first set of overlay targets. In another illustrative embodiment, metrology data associated with diffraction of the first set of overlay targets provides overlay measurements at locations of the first set of overlay targets. In another illustrative embodiment, metrology data associated with diffraction of the second set of overlay targets and sensitivity metrics from the metrology data associated with the first set of overlay targets provide overlay measurements at locations of the second set of overlay targets.

[0007] 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 present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0009] Figure 1A is a block diagram of an overlay metrology system according to one or more embodiments of the present disclosure.

[0010] Figure 1B is a simplified schematic diagram of an overlay metrology subsystem in accordance with one or more embodiments of the present disclosure.

[0011] Figure 2A is a top view of a unit cell of an overlay target having a grating-on-grating structure according to one or more embodiments of the present disclosure.

[0012] Figure 2B According to one or more embodiments of the present disclosure Figure 2A Side view of a unit cell in .

[0013] Figure 3A is a top down conceptual view of an overlay target having two cells with equal and opposite non-zero intended offsets according to one or more embodiments of the present disclosure.

[0014] Figure 3B is a top-down conceptual view of an overlay target having a unit cell according to one or more embodiments of the present disclosure.

[0015] Figure 4 is a conceptual illustration of metrology data associated with first order diffraction captured in a field plane in accordance with one or more embodiments of the present disclosure.

[0016] Figure 5 is a conceptual illustration of metrology data associated with first order diffraction captured in a pupil plane, according to one or more embodiments of the present disclosure.

[0017] Figure 6 is a flow chart illustrating steps performed in a method for efficient scatterometry overlay metrology based on sensitivity calibration in accordance with one or more embodiments of the present disclosure.

[0018] Figure 7 is a simplified top view of the distribution of calibration targets and efficiency targets in four fields on a sample according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0019] Reference will now be made in detail to the disclosed subject matter as 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 described herein are to be regarded as illustrative and not 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.

[0020] Embodiments of the present disclosure relate to systems and methods for performing scatterometry overlay metrology (SCOL) measurements of a single-cell overlay target on a sample based on calibrating the single-cell overlay target with data from a multi-cell overlay target on the sample.

[0021] In general, the SCOL technique may utilize an overlay target comprising two or more cells per direction, wherein each of the cells comprises overlapping features on two or more layers of a sample, and wherein the cells are fabricated to have different expected offsets between overlapping features. In a general sense, the features associated with each layer are 180 degree rotationally symmetric, such that when there is no expected offset, the cell is 180 degree rotationally symmetric. In some embodiments, the features of the cell are periodic and may be characterized by at least one pitch or spatial frequency. Thus, such periodic features may produce discrete diffraction orders. For example, the cell may comprise a grating structure (or grating) on ​​each layer of interest, wherein the overlapping grating structure may be referred to as a grating-on-grating structure. However, it should be understood that the features on a particular sample layer may be characterized by multiple pitches along a particular direction and / or multiple pitches along different directions. For example, the features of the grating-on-grating structure may be segmented to provide multiple pitches in any combination of directions, or otherwise distributed to provide a spatial frequency suitable for producing diffraction of incident light. Furthermore, any reference to the term "grating-on-grating structure" in this disclosure is merely illustrative and should not be construed as limiting the present disclosure. Rather, any such reference may be understood to encompass or extend to any suitable 180-degree rotationally symmetric feature suitable for SCOL technology. For example, for illustrative purposes, various examples herein may refer to diffraction orders. However, SCOL measurements may be performed on one or more cells containing non-periodic overlapping features based on the entire reflected signal (e.g., the entire pupil plane).

[0022] SCOL measurements are based on metrology data generated by illuminating a cell and collecting the resulting light from the cell. In the case of a grating-on-grating structure, this resulting light may include one or more diffraction orders. As an illustration, a first-order SCOL technique may be based on metrology data associated with first-order diffraction from a grating-on-grating structure, where the first-order diffraction may be resolvable in the pupil plane (e.g., as a diffraction lobe) and / or the field plane (e.g., as a region of constant intensity). As another illustration, a zero-order SCOL technique may be based on metrology data associated with zero-order light from an overlay target, such as, but not limited to, zero-order diffraction or opposite-order diffraction from a grating-on-grating structure (e.g., positive first-order diffraction from a grating structure in one layer and negative first-order diffraction from a grating structure in another layer). In general, various non-limiting examples of SCOL technology are described in the following patents: Adel et al., “Diffraction order control in overlay metrology—a review of the roadmap options” (Proc. Of SPIE Vol. 6922, 692202-1 (2008)); U.S. Patent No. 7,317,531, entitled “Apparatus and methods for detecting overlay errors using scatterometry” and issued on January 8, 2008; U.S. Patent No. 10,197,389, entitled “Approaches in first order scatterometry overlay based on introduction of auxiliary electromagnetic fields” and issued on February 5, 2019; and International Publication No. WO 2017 / 044283; all patents are incorporated herein by reference in their entirety.

[0023] It should be recognized herein that SCOL techniques typically require an overlay target having multiple cells, where each cell has a different expected offset (e.g., expected physical overlay). In such a configuration, metrology data from the various cells is used to generate unintended overlay (e.g., unintended physical overlay) measurements at the location of the overlay target. Different SCOL techniques based on different diffraction orders typically require different numbers of cells in the overlay target to generate measurements. Continuing with the above description, a first-order SCOL technique based on cells having a grating-on-grating structure may typically require a two-cell overlay target and generate measurements based on positive and negative first-order diffraction from each cell.

[0024] Consider herein that metrology data collected in the SCOL technique associated with a plurality of cells of an overlay target can generally be divided into a plurality of components, wherein a first set of components (referred to herein as K signals) depends on the actual overlay value at the location of the overlay target, while a second set of components (referred to herein as G signals) does not depend on the actual overlay value. Rather, the G signal depends on the physical properties of the overlay target design and is related to the sensitivity of the target to overlay variations. For this reason, this G signal is referred to herein as a sensitivity metric.

[0025] Note that a SCOL measurement at a particular location on the sample requires both a K signal and a G signal. For example, the overlay measurement (OVL) may be calculated as: OVL = K / G. However, since the G signal (e.g., a sensitivity metric) does not directly depend on the actual overlay at a particular location of the overlay target, the G signal may be obtained from another source and therefore need not be measured at every overlay target. As a result, when the G signal is obtained from another source, the number of cells required to obtain the overlay measurement for the overlay target may be reduced, which may 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 may be used.

[0026] In various embodiments of the present disclosure, a sample may include a first set of overlay targets designed to provide a sensitivity metric (e.g., a G signal) and a second set of overlay targets that do not provide a sensitivity metric. In this way, overlay measurements at the locations of the second set of overlay targets can utilize the sensitivity metrics associated with the first set of overlay targets. Metrology data from the first set of overlay targets can also provide sufficient information to generate overlay measurements at corresponding locations. Using this technique, as the number of the first set of overlay targets decreases relative to the number of the second set of overlay targets, the measurement throughput across the sample generally increases. In some embodiments, similar performance benefits can be obtained by simply reducing the number of measurements of some overlay targets. For example, a sample may include a common overlay target design across the sample that is suitable for providing sensitivity metrics, but these sensitivity metrics are only obtained for a subset of targets. As an illustration, a sample may include twin cell overlay targets distributed across the sample. In this configuration, measurements from two cells may be performed on a first set of overlay targets (e.g., a first subset of common overlay target designs) to obtain both overlay measurements and sensitivity metrics at these locations, while measurements from one of the cells may be performed on a second set of overlay targets (e.g., a second subset of common overlay target designs) to obtain overlay measurements based on the sensitivity metrics from the first set of overlay targets.

[0027] Consider further herein that sensitivity metrics (e.g., G signals) are related to physical properties of the overlay target design. As a result, variations in those sensitivity metrics across a wafer may be related to variations in the physical properties of the overlay target across the wafer, which typically occur over much larger length scales than overlay variations. For example, overlay variations may vary significantly in each lithography exposure field, while the physical properties of the overlay target (and thus the sensitivity metrics) may vary relatively slowly across several fields. Thus, a sensitivity metric measured at one location may be related to multiple targets within a field or potentially between fields.

[0028] The sensitivity metrics from the first set of overlay targets may be applied to the second set of overlay targets using any suitable technique, such as, but not limited to, nearest neighbor techniques, polynomial fitting, or interpolation.

[0029] Reference Figures 1A to 7 , according to one or more embodiments of the present disclosure, systems and methods for efficient SCOL metering are described in more detail.

[0030] Figure 1A is a block diagram of an overlay metrology system 100 according to one or more embodiments of the present disclosure.

[0031] In various embodiments, the overlay metrology system 100 includes an overlay metrology subsystem 102 to generate metrology data from an overlay target 104 on a sample 106. For example, the overlay target 104 may include one or more cells each including a grating-on-grating structure. The overlay metrology subsystem 102 may be a SCOL metrology subsystem to generate metrology data associated with diffraction orders from the overlay target 104.

[0032] Figure 2A to 2B An overlay target 104 suitable for SCOL metrology techniques is depicted in accordance with one or more embodiments of the present disclosure.

[0033] Figure 2A is a top view of a unit cell 202 of an overlay target 104 having a grating-on-grating structure according to one or more embodiments of the present disclosure. Figure 2B According to one or more embodiments of the present disclosure Figure 2A 202 in FIG.

[0034] In one embodiment, the cell 202 includes a first layer of printed elements 204 located on a first layer 206 of the sample 106 and a second layer of printed elements 208 located on a second layer 210 of the sample 106, and the first layer 206 and the second layer 210 are oriented such that the regions including the first layer of printed elements 204 and the second layer of printed elements 208 overlap to form a grating-on-grating structure. Figure 2B Further depicted is substrate 212 beneath first layer printed elements 204 and second layer printed elements 208 .

[0035] The first layer printed elements 204 and the second layer printed elements 208 in any particular cell 202 can be designed to have a plurality of printed elements along any direction (e.g., Figure 2B The expected offset (f0) of the first layer of printed elements 204 and the second layer of printed elements 208 is any expected offset (f0) in the X direction corresponding to the measurement direction. For example, the expected zero offset (f0=0) can provide that the first layer of printed elements 204 and the second layer of printed elements 208 completely overlap when the physical overlay is also zero (e.g., no overlay error). In this configuration, the relative offset between the first layer of printed elements 204 and the second layer of printed elements 208 indicates the overlay error during production. As another example, the expected non-zero offset (f0≠0) can provide that the first layer of printed elements 204 and the second layer of printed elements 208 exhibit this expected offset when the physical overlay is zero (e.g., no overlay error).

[0036] In general, the overlay target 104 may be formed of any number of cells 202 that may have any desired combination of offsets (eg, values ​​of f0). As a non-limiting illustration, Figure 3Ais a top-down conceptual view of an overlay target 104 having two cells 202 with equal and opposite non-zero intended offsets according to one or more embodiments of the present disclosure. Specifically, Figure 3A The first cell 202 in has the expected offset +f0, and Figure 3A The second cell 202 in has a desired offset of -f0, where f0 can be any non-zero number. As another non-limiting illustration, Figure 3B is a top-down conceptual view of an overlay target 104 having a single cell 202 according to one or more embodiments of the present disclosure. In this configuration, the cell 202 may have any desired offset including zero values ​​(f0=0) and non-zero values ​​(f0≠0).

[0037] Although not explicitly illustrated, the overlay target 104 can be suitable for overlay measurement along multiple directions (e.g., orthogonal directions). Generally speaking, the measurement directions can correspond to the periodic directions of the first layer of printed elements 204 and the second layer of printed elements 208 (e.g., the periodic directions of the grating structure on the grating). As an illustration, Figure 2A and 2B The cell 202 depicted in shows periodicity along the X direction and is suitable for overlay measurement along the X direction.

[0038] In some embodiments, the overlay target 104 includes a plurality of Figure 2A and 2B The periodicity of one or more cells 202 along the second direction (eg, the X direction depicted in FIG. 1 ) and the periodicity of one or more cells 202 along the second direction (eg, Figure 2A and 2B In some embodiments, the overlay target 104 includes one or more cells 202 having periodicity in both directions. For example, the first layer of printed elements 204 and the second layer of printed elements 208 may include structures having periodicity in both the X direction and the Y direction (e.g., a hatching pattern, a grid of square or rectangular structures, etc.).

[0039] General reference Figure 2A and 2B , it should be understood that Figure 2A and 2Band the associated descriptions are merely illustrative and should not be construed as limiting the present disclosure. For example, the first layer 206 and the second layer 210 can generally have any thickness. As another example, the sample 106 can include any number of layers between the first layer of printed elements 204 and the second layer of printed elements 208 and / or between the first layer of printed elements 204 and the substrate 212. As another example, the first layer of printed elements 204 and the second layer of printed elements 208 can generally include any 180 degree rotationally symmetric features, and need not include gratings on gratings or even periodic features.

[0040] Reference Figure 1B , various aspects of the overlay metrology subsystem 102 are described in greater detail according to one or more embodiments of the present disclosure. Figure 1B is a simplified schematic diagram of the overlay metrology subsystem 102 in accordance with one or more embodiments of the present disclosure.

[0041] In various embodiments, the overlay metrology subsystem 102 may be configured according to a metrology recipe (e.g., an overlay recipe) to generate overlay measurements associated with an overlay target 104 having a design based on the metrology recipe. For example, the overlay metrology subsystem 102 may direct an illumination beam 108 from an illumination source 110 to the overlay target 104 on the sample 106 (e.g., via an illumination pathway 112), collect light or other radiation (referred to herein as measurement light 114) emitted from the overlay target 104 via a collection pathway 116, and generate metrology data from at least one detector 118 based on the measurement light 114. For example, the metrology data may be associated with diffraction of the illumination beam 108 from the overlay target 104. The illumination pathway 112 and the collection pathway 116 may further include additional optical elements at any suitable locations, such as, but not limited to, a lens 120 and a beam manipulation component 122 (e.g., a polarizer, a spectral filter, a spatial filter, a beam blocker, an aperture, etc.). In some embodiments, as Figure 1B , the overlay metrology subsystem 102 includes one or more beam splitters 124 to allow simultaneous illumination and collection through a common objective lens 126 or other focusing element. In some embodiments, the overlay metrology subsystem 102 includes a translation stage 128 that includes any number of linear or rotary actuators to hold and / or position the sample 106.

[0042] The overlay metrology subsystem 102 may include one or more detectors 118 located at any suitable location to collect metrology data. For example, the overlay metrology subsystem 102 may include at least one detector 118 located at a field plane 130 (e.g., a plane conjugate to the sample 106), such as Figure 1B. As another example, although not illustrated, the overlay metrology subsystem 102 may include at least one detector 118 located at a pupil plane 132 (e.g., a diffraction plane corresponding to the angular distribution of light from the sample 106). Further, although not illustrated, the overlay metrology subsystem 102 may include multiple channels, each with a separate detector 118. In this manner, the overlay metrology subsystem 102 may use multiple detectors 118 to provide multiple simultaneous measurements at any combination of the field plane 130 or the pupil plane 132. For example, the overlay metrology subsystem 102 may include one or more beam splitters 124 (e.g., a non-polarizing beam splitter, a polarizing beam splitter, a dichroic mirror providing spectral selectivity, etc.) to split the measurement light 114 into different channels for detection. The overlay metrology subsystem 102 may further include optical components to modify the properties of the measurement light 114 within each channel, such as, but not limited to, polarizers, polarization rotators, spectral filters, spatial filters, or pupil filters (e.g., beam blocks or apertures in the pupil plane to block or pass selected diffraction orders).

[0043] Some embodiments of the present disclosure are directed to providing a recipe for configuring the overlay metrology subsystem 102 to facilitate overlay measurements based on selected diffraction orders. The metrology recipe may include a set of parameters for controlling various aspects of the overlay measurement, such as, but not limited to, illumination of the sample 106, collection of light from the sample 106, or position of the sample 106 during measurement. In this manner, the overlay metrology subsystem 102 may be configured to provide a selected type of measurement for a selected overlay target design. For example, the metrology recipe may include parameters of the illumination beam 108, such as, but not limited to, illumination wavelength, illumination pupil distribution (e.g., distribution of illumination angles and associated illumination intensities at those angles), polarization of incident illumination, or spatial distribution of illumination. By way of another example, the metrology recipe may include collection parameters, such as, but not limited to, collection pupil distribution (e.g., desired distribution of angular light from the overlay target 104 for measurement and associated filtered intensities at those angles), collection field aperture settings to select portions of interest of the overlay target 104, polarization of collected light, wavelength filters, or parameters for controlling one or more detectors. By way of another example, the metrology recipe may include various parameters associated with the design of the overlay target 104, such as, but not limited to, the location and orientation of sample features (e.g., the pitch of grating features along a particular direction). By way of another example, the metrology recipe may include various parameters associated with the location of the sample 106 during measurement, such as, but not limited to, sample height, sample orientation, whether the sample 106 is stationary during measurement, or whether the sample 106 is in motion during measurement (along with associated parameters describing speed, scanning mode, etc.).

[0044] In this manner, the overlay metrology subsystem 102 can be configured according to a metrology recipe to provide a selected light distribution in the collection pupil when analyzing a specific overlay target 104 having a known design. This distribution of light in the collection pupil can then be further modified by various optical devices as desired to produce the desired overlay measurement.

[0045] In some embodiments, the overlay metrology system 100 further includes a controller 134 having one or more processors 136 configured to execute program instructions stored on a memory 138 (e.g., a memory medium). The controller 134 may be communicatively coupled with any of the components of the overlay metrology system 100, such as, but not limited to, the detector 118. In this manner, the controller 134 may generate overlay measurements based on the detection signals according to a metrology recipe.

[0046] The one or more processors 136 of the controller 134 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 136 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In one embodiment, the one or more processors 136 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 that is configured to operate or operate in conjunction with the stack metrology system 100 as described throughout this disclosure.

[0047] In addition, the different subsystems of the overlay metrology system 100 may include processors or logic elements suitable for implementing at least a portion of the steps described in the present disclosure. Therefore, the above description should not be interpreted as limiting the various embodiments of the present disclosure and is merely considered as an illustration. In addition, the steps described throughout the present disclosure may be implemented by a single controller 134 or, alternatively, multiple controllers. In addition, the controller 134 may include one or more controllers housed in a common housing or multiple housings. In this way, any controller or combination of controllers can be individually packaged as a module suitable for integration into the overlay metrology system 100.

[0048] The memory 138 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 136. For example, the memory 138 may include a non-transitory memory medium. By way of another example, the memory 138 may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical storage device (e.g., a disk), a tape, a solid-state hard drive, and the like. It should be further noted that the memory 138 may be housed in a common controller housing with the one or more processors 136. In one embodiment, the memory 138 may be located remotely relative to the physical location of the one or more processors 136 and the controller 134. For example, the one or more processors 136 of the controller 134 may access a remote memory (e.g., a server) that may be accessed via a network (e.g., the Internet, an intranet, etc.).

[0049] Now for general reference Figures 2A to 5 , according to one or more embodiments of the present disclosure, overlay metrology with shared sensitivity metrics is described in more detail. Note that, Figures 2A to 5 The use of the first-order SCOL technique is described; however, this is for illustrative purposes only and should not be construed as limiting. In particular, the systems and methods disclosed herein can be extended to other SCOL techniques (e.g., zero-order SCOL techniques), and such techniques are within the spirit and scope of the present disclosure.

[0050] Furthermore, each cell 202 should be designed such that when there is no overlay error (OVL=0) and the expected offset is zero (f0=0), the cell will be 180 degree rotationally symmetric (e.g., invariant to 180 degree rotation). Note that this condition does not imply that the expected offset is zero. Rather, the first layer printed elements 204 and the second layer printed elements 208 can be designed to satisfy 180 degree rotational symmetry under these conditions. In practice, the two cells 202 have equal and opposite non-zero expected offsets, such as Figure 3A For example, the first cell 202 may have an expected offset of +f0, and the second cell 202 may have an expected offset of -f0.

[0051] In this configuration, the overlay target 104 is unchanged under the following conditions:

[0052]

[0053] where k x , k yIn this manner, rotating the cell 202 having the intended offset f0 printed with the unintended actual overlay OVL provides the opposite sensed offset and actual overlay (f0→-f0 and OVL→-OVL), and further provides that the resulting pupil plane distribution of light collected from the cell 202 is rotated 180 degrees (k x , k y →-k x , -k y ).

[0054] In the case where the cell 202 comprises a first order SCOL of a grating-on-grating structure, the metrology data associated with a particular cell 202 having an expected offset f0 may include a signal associated with positive first order diffraction and the signal associated with the negative first order diffraction Thus, metrology data from such an overlay target 104 may include a signal associated with the positive first order diffraction from the first cell 202. The signal associated with the minus first order diffraction from the first cell 202 is The signal associated with the positive first-order diffraction from the second cell 202 is and the signal associated with the minus first order diffraction from the second cell 202

[0055] Furthermore, when the overlay target 104 is illuminated by an illumination having a 180 degree rotational symmetry, the collected signal will obey

[0056]

[0057] Expanding the metrology data serially into linear order with overlay (OVL) and expected offset (f0), 180 degree symmetry of each cell 202 and illumination provides:

[0058]

[0059] Wherein P is the pitch between the first layer printing elements 204 and the second layer printing elements 208 .

[0060] When OVL, f0>>P, equations (3) to (6) are simplified to:

[0061]

[0062] Where A and B are constants.

[0063] Metrology data (eg, signals described by equations (3)-(10)) may generally be collected in a field plane 130 (eg, a plane conjugate to the sample 106) or a pupil plane 132 (eg, a diffraction plane).

[0064] Figure 4 is a conceptual illustration of metrology data associated with first order diffraction captured in field plane 130 according to one or more embodiments of the present disclosure. A field plane image of a cell 202 produced using a single diffraction order (e.g., having a periodic structure such as a grating structure on a grating) can generally have uniform intensity across the entire cell 202, depending on the interference between the first layer of printed elements 204 and the second layer of printed elements 208. In this configuration, overlay measurements can be based on the relative intensity of each cell 202 based on different diffraction orders. As a graphical illustration, Figure 4 A first field plane image 402 and a second field plane image 404 based on diffraction orders of the first cell 202a from the overlay target 104 are depicted. The first cell 202a has a first order diffraction order corresponding to the positive first order diffraction order. and negative first order diffraction The associated expected offset is +f0. Similarly, these images may be captured simultaneously in different channels of the overlay metrology subsystem 102, or sequentially in a common channel. Figure 4 Also depicted are a third field plane image 406 and a fourth field plane image 408 based on diffraction orders from the second cell 202b of the overlay target 104, the second cell 202b having a positive first diffraction order, respectively. and negative first order diffraction The associated expected offset is −f0. Similarly, these images may be captured simultaneously in different channels of the overlay metrology subsystem 102, or sequentially in a common channel.

[0065] Figure 5 1 is a conceptual illustration of metrology data associated with first order diffraction captured in pupil plane 132 according to one or more embodiments of the present disclosure. A first pupil distribution 502 (e.g., distribution of light in pupil plane 132) depicts diffraction lobes from a first cell 202a of an overlay target 104, the first cell 202a having a positive first order diffraction lobes. and negative first order diffraction The second pupil distribution 504 depicts the diffraction lobes of the second cell 202b from the overlay target 104, which has a positive first order diffraction angle of +f0. and negative first order diffraction The expected offset associated with these four metrology data signals ( and ) can be captured using any suitable technique. For example, the metrology data signal in the first pupil distribution 502 and can be captured as a first measurement, while the metrology data signal in the second pupil distribution 504 and May be captured as a second measurement.

[0066] Regardless of the collection technique, overlay measurements may be generated based on the metrology data using a variety of techniques or concepts, all of which are within the spirit and scope of the present disclosure.

[0067] As an illustration, equations (11) through (16) illustrate a common non-limiting technique for generating an overlay measurement from such metrology data based on the generation of a differential signal.

[0068] For example, the following differential signal can be defined as follows:

[0069]

[0070] These differential signals can then be combined into so-called K and G signals:

[0071]

[0072] The overlay measurement (OVL) can then be generated as

[0073]

[0074] As long as G≠0.

[0075] Assuming OVL<<P, equations (13) and (14) indicate that the K signal depends on the actual value of the overlay OVL measured at the location of the overlay target 104, while the G signal does not depend on the actual value. Instead, the G signal depends on This is negligible under these conditions. In this case, Equation 15 simplifies to

[0076]

[0077] The G signal may be associated with properties of the overlay target 104 itself, and may represent the sensitivity of a particular overlay target 104 to overlay changes. In other words, the G signal may represent the linear response of the measured metrology data to overlay changes. For these reasons, the G signal may be referred to as a sensitivity metric.

[0078] It should be understood that the G signal as described in equations (11) to (16) is a non-limiting example of a sensitivity metric, and any suitable sensitivity metric is within the spirit and scope of the present disclosure. In this manner, the present disclosure is not limited to a specific definition of a differential signal (e.g., equations (11) and (12)), a K signal, or a G signal.

[0079] Consider that the sensitivity metric (e.g., but not limited to, the G signal of equation (14)) may depend on various characteristics of the overlay target 104 itself and / or measurement conditions (e.g., parameters of a metering recipe). For example, the sensitivity metric may be affected by physical characteristics of the overlay target 104 (e.g., but not limited to, the height of the overlay target 104, the height of the first layer printed elements 204 and the second layer printed elements 208, the thickness of any constituent materials, the refractive index of any constituent materials, the pitch of the first layer printed elements 204 and the second layer printed elements 208, or the physical layout of the first layer printed elements 204 and the second layer printed elements 208 (e.g., strips on strips, grooves, etc.)). As another example, the sensitivity metric may be affected by parameters of the illumination beam 108 (e.g., but not limited to, the wavelength or the angle of incidence).

[0080] Thus, such a sensitivity metric may be a function of position on the sample 106 (e.g., a function of the sample coordinates). Furthermore, the sensitivity metric may generally vary over similar length scales because these underlying properties typically vary much more slowly than the overlay (e.g., overlay signature) across the sample 106. For example, the overlay signature may vary rapidly across each field, and typically have a repeating pattern within each field. In contrast, the sensitivity metric may vary more slowly within each field and also between fields.

[0081] As a result, sensitivity metrics measured on different overlay targets 104 in the same area of ​​the sample 106 may be similar, even though the overlay targets 104 belong to different fields and / or the actual overlays at corresponding locations are substantially different.

[0082] In various embodiments of the present disclosure, a sensitivity metric is measured involving a first set of overlay targets 104 (e.g., a subset of all overlay targets 104 on a sample 106), and is then used to generate (e.g., estimate, model, etc.) sensitivity metrics at locations of a second set of overlay targets 104. For ease of description, the first set of overlay targets 104 is referred to herein as calibration targets, and the second set of overlay targets 104 is referred to herein as efficiency targets.

[0083] The systems and methods disclosed herein may provide numerous benefits of complete characterization of a set of calibration targets across the sample 106. For example, a reduced number of measurements of an efficiency target may be required to produce an overlay measurement because the sensitivity metric is obtained from measurements of the calibration targets, which may substantially improve measurement efficiency. As another example, an efficiency target may require fewer cells 202 than a calibration target.

[0084] As an illustration, a first-level SCOL technique may require two cells 202 for the calibration target (e.g., Figure 3A) and a unit cell 202 for efficiency goals (e.g., as Figure 3B ). For example, the efficiency target may include a unit cell 202 that does not have an expected offset (eg, f0=0). When the G signal is taken from a calibration target, the overlay (OVL) may be calculated as:

[0085]

[0086] and

[0087]

[0088] More generally, the efficiency target and the overlay (OVL) of the unit cell 202 with a non-zero expected offset (f0≠0) can be calculated as:

[0089]

[0090] General reference Figures 3A to 5 and equations (2) to (19), the references to the first-order SCOL technique provided herein are for illustrative purposes only and should not be construed as limiting. Rather, the systems and methods disclosed herein can be extended to any suitable type of SCOL technique. As another example, a zero-order SCOL technique may require four cells 202 for a calibration target and two cells 202 for an efficiency target.

[0091] Reference Figure 6 , Figure 6 is a flow chart illustrating steps performed in a method 600 for efficient SCOL metrology based on sensitivity calibration in accordance with one or more embodiments of the present disclosure. Applicants note that the embodiments and enabling techniques previously described in the context of the overlay metrology system 100 should be interpreted as extending to the method 600. However, it should be further noted that the method 600 is not limited to the architecture of the overlay metrology system 100.

[0092] In various embodiments, the method 600 includes step 602 of generating metrology data associated with a first set of overlay targets 104 (e.g., calibration targets) and a second set of overlay targets 104 (e.g., efficiency targets) on a sample 106, wherein each of the first set of overlay targets 104 includes at least two cells 202 having different expected offsets between overlay features on two layers of the sample 106, and wherein the metrology data associated with the second set of overlay targets 104 is based on fewer cells 202 than the metrology data associated with the first set of overlay targets 104. For example, the first set of overlay targets 104 may each include two grating-on-grating structures having different expected offsets (e.g., in different cells 202), while the second set of overlay targets 104 may each include a single grating-on-grating structure (e.g., as an overlay target 104 having a single cell 202). Furthermore, such a single-cell overlay target 104 in the second set of overlay targets 104 may have, but need not have, an unintended offset (eg, f0=0).

[0093] In various embodiments, the method 600 includes step 604 of generating sensitivity metrics at locations of the first set of overlay targets 104 based on metrology data of the first set of overlay targets 104. In various embodiments, the method 600 includes step 606 of generating overlay measurements of the first set of overlay targets 104 based on the sensitivity metrics and metrology data from the first set of overlay targets 104. In various embodiments, the method 600 includes step 608 of generating overlay measurements of the second set of overlay targets 104 based on the sensitivity metrics and metrology data from the second set of overlay targets 104.

[0094] For the selected metrology measurement technique, the calibration target and the efficiency target may generally have any suitable design and / or number of cells 202. For example, the metrology data associated with the overlay target 104 may generally be a first order diffraction based on a first order SCOL technique, a zero order signal of a zero order SCOL technique (e.g., a zero order diffraction from an associated grating-on-grating structure, or a combination of higher order diffraction from the first layer of printed elements 204 and the second layer of printed elements 208 emanating from the grating-on-grating structure parallel to the zero order diffraction, etc.), etc.

[0095] In steps 606 and 608, any sensitivity metric suitable for overlaying the target 104 may be utilized. For example, the sensitivity metric may be, but need not be, a G signal as described by equations (7) through (14).

[0096] Furthermore, in some embodiments, the efficiency target has fewer grating structures (e.g., cells 202) on the grating than the calibration target. Figures 3A to 3BAs described by equations (7) to (14), the calibration target may have two grating-on-grating structures with different expected offsets (e.g., ±f0≠0 or any other suitable offset), while the efficiency target may have a single grating-on-grating structure with zero expected offset or non-zero expected offset.

[0097] As previously described, reducing the number of grating structures (e.g., cells 202) on the grating of the efficiency targets can beneficially reduce the overall size of the targets and thus allow for more flexible placement of these targets. Although overlay targets 104 can generally be placed at any suitable location including scribe lines or the die, it can often be desirable to limit the number and / or size of overlay targets 104 within a die. However, it may be the case that the reduced size of the efficiency targets can allow for more flexibility with respect to placement within a die. In some embodiments, sample 106 includes one or more calibration targets within a scribe line and efficiency targets distributed in any combination of scribe lines or within a die.

[0098] In some embodiments, the calibration target and the efficiency target have the same design (e.g., have a common number of grating-on-grating structures). In such a configuration, metrology data (e.g., in step 602) may be generated for a subset of the grating-on-grating structures in the efficiency target. This may allow for improved measurement efficiency for a wide variety of samples 106.

[0099] The calibration targets and efficiency targets may also have any suitable layout on the sample 106. In a general sense, the more calibration targets are needed, the less benefit there is in using efficiency targets. However, because the sensitivity metric varies slowly across the sample 106 and may be continuous across multiple fields, the sensitivity metric of a calibration target in one field may be used to generate the sensitivity metric used at the location of an efficiency target in the same or a different field.

[0100] Figure 7 is a simplified top view of the distribution of calibration targets and efficiency targets in four fields 702 on the sample 106 according to one or more embodiments of the present disclosure. It should be understood that Figure 7 The target distribution in is provided for illustration purposes only and should not be construed as limiting. Rather, any distribution of calibration targets and efficiency targets is within the spirit and scope of the present disclosure.

[0101] Figure 7 Four fields 702 labeled F1, F2, F3, and F4 are depicted, each field having four dies 704, and each field having the same distribution of overlay targets 104 (labeled 1 to 13). Figure 7 In a non-limiting configuration, the calibration targets 104a each include two cells 202 (eg, two grating-on-grating structures), such as Figure 3A, and the efficiency targets 104b each include a unit cell 202 (e.g., a single grating-on-grating structure). Each of the fields 702 includes two calibration targets 104a (labeled 1 and 7 in F1) in the scribe lines (e.g., the area between the dies 704), one of which is located in the center of the field 702 and one in the corner. Each of the fields 702 also includes 11 efficiency targets 104b (labeled 2 to 7 and 8 to 13 in F1) distributed within the die 704 and in the scribe lines (e.g., near the corners of the die 704). In this configuration, the maximum distance between the calibration target 104a and the efficiency target 104b is the length of one die 704.

[0102] Again, general reference Figure 6 , the sensitivity metric at the location of the efficiency target may be calculated using any technique (e.g., in step 608). In various embodiments, the method 600 includes generating a model of the sensitivity metric across the overlay metrology system 100 based on the metrology data of the calibration target. For example, the sensitivity metric at the location of the efficiency target may be calculated based on interpolation, fitting (e.g., polynomial fitting), or nearest neighbor techniques.

[0103] Consider herein that the technique used to calculate the sensitivity metric at the location of the efficiency target may depend on the configuration of the overlay metrology subsystem 102 used to generate the metrology data (eg, in step 602 ).

[0104] For example, when metrology data is generated based on measurements in the field plane 130 (e.g., Figure 5 ), both the K signal and the G signal are substantially constant within each cell 202, but may exhibit some variation due to edge effects or other irregularities. In this case, the G signal (or more generally the sensitivity metric) may be generated based on the average intensity, the intensity in a selected region of interest, or any suitable technique. The G signal (or more generally the sensitivity metric) may then be modeled across samples 106 using any suitable technique, including but not limited to interpolation, fitting (e.g., polynomial fitting), or nearest neighbor techniques.

[0105] As another example, when metrology data is generated based on measurements in pupil plane 132, the G signal varies across pupil plane 132 and is therefore a function of pupil coordinates. In this case, each region of pupil plane 132 may have a different G signal behavior across sample 106. In some embodiments, a model of the G signal (or more generally a sensitivity metric) may be constructed for each pixel across pupil plane 132 and used to calculate the sensitivity metric at the location of the efficiency target. In some embodiments, a nearest neighbor technique is used, where the sensitivity metric at the location of a particular efficiency target is determined based on the values ​​at the N nearest neighbor calibration targets (e.g., the average of the N nearest neighbors or any suitable weighting scheme). In this technique, the value of N may be determined based on any factors, including, but not limited to, the rate of change of the sensitivity metric across sample 106, the density of calibration targets, and the like.

[0106] In some embodiments, based on measurements at the location of the calibration target, the G signal is modeled as a function of pupil and wafer coordinates by using polynomials, splines, or any other modeling approach. This model can then be used to provide the G signal at the location of the efficiency target.

[0107] The subject matter described herein sometimes illustrates different components contained in or connected to other components. It should be understood that these depicted architectures are only exemplary, and in fact many other architectures that realize the same functionality can be implemented. In a conceptual sense, any component arrangement that realizes the same functionality is effectively "associated" so that the desired functionality is realized. Therefore, any two components combined to realize a specific functionality herein can be considered to be "associated" with each other so that the desired functionality is realized, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to realize the desired functionality. Specific examples that can be coupled include but are not limited to components that can physically interact and / or physically interact and / or components that can wirelessly interact and / or wirelessly interact and / or components that can logically interact and / or logically interact.

[0108] It is believed that many of the advantages of the present disclosure and its attendant advantages will be appreciated from the foregoing description, and it will be apparent that various changes may be made in the form, construction, 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 it is intended that such changes be covered and included by the appended claims. Furthermore, it should be understood that the present disclosure is defined by the appended claims.

Claims

1. A metering system, comprising: a controller communicatively coupled to the metering subsystem, the controller comprising one or more processors configured to execute program instructions, the program instructions causing the one or more processors to: receiving metrology data associated with a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlay features on two layers of a sample; receiving metrology data associated with a second set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets; generating a sensitivity metric at a location of the first set of overlay targets based on the metrology data associated with the first set of overlay targets; generating an overlay measurement of the first set of overlay targets based on the sensitivity metric and the metrology data associated with the first set of overlay targets; and Overlay measurements of the first set of overlay targets and the second set of overlay targets are generated based on the sensitivity metric associated with the second set of overlay targets and the metrology data. 2 . The metrology system of claim 1 , wherein the cells of at least one of the first set of overlay targets or the second set of overlay targets are 180 degree rotationally symmetric.

3. The metrology system of claim 1, wherein a first set of overlay targets comprises two cells having different desired offsets, and wherein the second set of overlay targets comprises a single cell.

4. The metrology system of claim 3, wherein the cells of the first set of overlay targets and the second set of overlay targets comprise grating-on-grating structures, wherein the metrology data of the first set of overlay targets and the second set of overlay targets comprise first-order diffraction from the corresponding cells.

5. The metrology system of claim 1, wherein a first set of overlay targets includes four cells having different expected offsets, wherein the second set of overlay targets includes two of the cells having different expected offsets.

6. The metrology system of claim 5, wherein the cells of the first set of overlay targets and the second set of overlay targets comprise grating-on-grating structures, wherein the metrology data of the first set of overlay targets and the second set of overlay targets comprise zero-order light from the corresponding cells.

7. The metrology system of claim 1, wherein a first set of overlay targets and the second set of overlay targets have a common number of cells, wherein the metrology data associated with the second set of overlay targets is based on a subset of the cells.

8. The metrology system of claim 1 , wherein the generating the overlay measurements of the first set of overlay targets and the second set of overlay targets based on the sensitivity metric and the metrology data from the second set of overlay targets comprises: The sensitivity metrics at the locations of the second set of overlay targets are calculated based on the sensitivity metrics at the locations of the first set of overlay targets.

9. The metrology system of claim 1, wherein the cells of the first set of overlay targets and the second set of overlay targets comprise grating-on-grating structures, wherein component gratings of the grating-on-grating structures have a common pitch.

10. The metrology system of claim 9, wherein the metrology data associated with any of the grating structures on the grating includes data associated with a positive first order diffraction (I +1 ) and negative first order diffraction (I -1 ) associated measurement data.

11. The metrology system according to claim 10, wherein the positive first-order diffraction (I +1 ) and the negative first order diffraction (I -1 )The metering data associated with the field is resolved in the field plane.

12. The metrology system according to claim 10, wherein the positive first-order diffraction (I +1 ) and the negative first order diffraction (I -1 )The metrology data associated with the image is resolved in the pupil plane.

13. The metrology system of claim 1, wherein each of the first set of overlay targets comprises a first on-grating grating structure having a first expected offset (f1) and a second on-grating grating structure having a second expected offset (f2), wherein the metrology data associated with each of the first set of overlay targets comprises a positive first-order diffraction from the first on-grating grating structure. The negative first-order diffraction from the grating structure on the first grating The positive first-order diffraction from the grating structure on the second grating and the negative first-order diffraction from the grating structure on the second grating 14. The metrology system according to claim 13, wherein the first expected deviation (f1) and the second expected deviation (f2) have equal magnitude and opposite direction, such that f1 = f0 and f2 = -f0.

15. The metrology system of claim 14, wherein the sensitivity metric (G) for a particular one of the first set of overlay targets is calculated as wherein based on the metrology data associated with the particular one of the first set of overlay targets, and 16. The metrology system of claim 15, wherein an overlay measurement (OVL) of the particular one of the first set of overlay targets is calculated as in 17. The metrology system of claim 1, wherein the sensitivity metric is independent of a physical overlay at the location of the first set of overlay targets.

18. The metrology system of claim 17, wherein the sensitivity metric corresponds to a linear response of the metrology data in response to changes in the physical overlay at the locations of the first set of overlay targets.

19. The metrology system of claim 1, wherein the second set of overlay targets is larger than the first set of overlay targets.

20. A metering system comprising: a metrology subsystem configured to generate metrology data associated with the sample; and a controller communicatively coupled to the metering subsystem, the controller comprising one or more processors configured to execute program instructions, the program instructions causing the one or more processors to: receiving metrology data associated with a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlay features on two layers of the sample; receiving metrology data associated with a second set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets; generating a sensitivity metric at a location of the first set of overlay targets based on the metrology data associated with the first set of overlay targets; generating an overlay measurement of the first set of overlay targets based on the sensitivity metric and the metrology data associated with the first set of overlay targets; and Overlay measurements of the first set of overlay targets and the second set of overlay targets are generated based on the sensitivity metric associated with the second set of overlay targets and the metrology data.

21. The metrology system of claim 20, wherein the generating the overlay measurements of the first set of overlay targets and the second set of overlay targets based on the sensitivity metric and the metrology data from the second set of overlay targets comprises: The sensitivity metrics at the locations of the second set of overlay targets are calculated based on the sensitivity metrics at the locations of the first set of overlay targets.

22. The metrology system of claim 20, wherein the cells of the first set of overlay targets and the second set of overlay targets comprise grating-on-grating structures, wherein the grating-on-grating structures have a common pitch.

23. The metrology system of claim 22, wherein the metrology data associated with any of the grating structures on the grating includes data associated with a positive first order diffraction (I +1 ) and negative first order diffraction (I -1 ) associated data.

24. The metrology system of claim 23, wherein the positive first-order diffraction (I +1 ) and the negative first order diffraction (I -1 )The metering data associated with the field is resolved in the field plane.

25. The metrology system of claim 23, wherein the positive first-order diffraction (I +1 ) and the negative first order diffraction (I -1 )The metrology data associated with the image is resolved in the pupil plane.

26. A method comprising: generating metrology data associated with a first set of overlay targets and a second set of overlay targets on a sample, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlay features on two layers of the sample, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets; generating a sensitivity metric at a location of the first set of overlay targets based on the metrology data associated with the first set of overlay targets; generating an overlay measurement of the first set of overlay targets based on the sensitivity metric and the metrology data associated with the first set of overlay targets; and An overlay measurement of the second set of overlay targets is generated based on the sensitivity metric associated with the second set of overlay targets and the metrology data.

27. A sample comprising: A plurality of overlay targets distributed across a plurality of fields, wherein the plurality of overlay targets include: a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells having different expected offsets between overlay features on two layers of the sample; and a second set of overlay targets, wherein each of the second set of overlay targets includes fewer cells than the first set of overlay targets; wherein the metrology data associated with the diffraction of the first set of overlay targets provides an overlay measurement at the location of the first set of overlay targets; and Wherein metrology data associated with diffraction of the second set of overlay targets and sensitivity metrics from the metrology data associated with the first set of overlay targets provide overlay measurements at locations of the second set of overlay targets.

Images