System and method for suppressing tool-introduced offsets in scanning overlay metrology

Abstract

An overlay metrology system and method for generating an overlay measurement of an overlay target including cells having structures in an inverted order is disclosed. The overlay metrology system may include a lighting subsystem and a light collecting subsystem. The light collection subsystem may include one or more detectors to collect measurement light from a sample. In accordance with a metrology recipe, the sample may include an overlap target having first cells of a first cell type and second cells of a second cell type, where the second cell type includes structures in an inverted order with respect to the first cell type. The dosing recipe may include: receiving a detection signal; generating an overlap measurement for each cell based on the detection signal; and generating an overlay measurement associated with the overlay target based on a value indicative of an average value of the overlay measurements for each cell.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 427,538, filed on November 23, 2022, entitled “STEM AND METHOD FOR SUPPRESSION OF TOOL INDUCED SHIFT IN SCANNING OVERLAY METROLOGY,” and named after Itay Gdor, Yuval Lubashevsky, Vladimir Levinski, Daria Negri, Alon Yagil, and Nickolai Isakovich, pursuant to 35 U.S.C. §119(e), the entire text of which is incorporated herein by reference. Technical Field

[0003] The present invention relates generally to overlay metrology, and more particularly to an overlay metrology system and method for reducing tool introduced offset errors in overlay measurements of overlay targets. Background Art

[0004] The demand for decreasing feature size and increasing feature density has resulted in an increased need for accurate and efficient overlay metrology.Overlay metrology refers to the measurement of the relative alignment of layers on a sample, such as, but not limited to, a semiconductor device.

[0005] Overlay targets are typically formed on the surface of the sample and may include cells with grating structures with various pitches in the overlay layer. The sample is typically mounted on a translation stage and translated so that the overlay target is sequentially moved into the measurement field of view. In a typical metrology system employing the Move and Measure (MAM) method, the sample is static during each measurement. However, the time required to allow the translation stage to settle before measurement can adversely affect throughput.

[0006] In addition, various sources may introduce errors into the overlay metrology data, such as tool introduced offset (TIS) errors. For example, illumination non-uniformity may cause TIS errors. For example, contaminants such as particles or dust may settle on the filter and cause a non-uniform distribution of the illumination beam. In another example, the illumination beam may not be properly aligned with the sample during measurement, further contributing to TIS errors.

[0007] Therefore, there is a need to provide a system and method for solving the above-mentioned drawbacks. Summary of the invention

[0008] According to one or more illustrative embodiments of the present disclosure, an overlap metering system is disclosed. In one illustrative embodiment, the overlap metering system includes a controller. In another illustrative embodiment, the controller may include one or more processors, the one or more processors being configured to execute program instructions that cause the one or more processors to execute a metering recipe. In another illustrative embodiment, the metering recipe may include: receiving a detection signal from each unit from the one or more detectors; generating an overlap measurement for each unit based on the detection signal; and generating an overlap measurement associated with an overlap target based on a value indicating an average of the overlap measurements for each unit. In another illustrative embodiment, according to the metering recipe, the sample may include an overlap target having a first unit of a first unit type and a second unit of a second unit type, wherein the second unit type includes structures in a reverse order relative to the first unit type.

[0009] According to one or more illustrative embodiments of the present disclosure, an overlay metrology system is disclosed. In one illustrative embodiment, the overlay metrology system includes an illumination subsystem and a light collection subsystem. The light collection subsystem may include one or more detectors for collecting measurement light from a sample. According to a metrology recipe, the sample may include an overlay target having a first cell of a first cell type and a second cell of a second cell type, wherein the second cell type includes structures in a reverse order relative to the first cell type. The metrology recipe may include: receiving a detection signal from each cell from the one or more detectors; generating an overlay measurement for each cell based on the detection signal; and generating an overlay measurement associated with the overlay target based on a value indicating an average of the overlay measurements for each cell.

[0010] According to one or more illustrative embodiments of the present disclosure, an overlapping target is disclosed. In one illustrative embodiment, the overlapping target includes at least four units, including a first unit and a second unit. The first unit may include a first layer and a second layer of structures having a first pitch and a second pitch, respectively. The layers may be in a first order along the depth direction of the sample. The second unit may include a layer of structures having the first pitch and the second pitch in an inverted order relative to the first order. Both the first unit type and the second unit type may include a first pitch and a second pitch, but the order of the pitches may be inverted relative to each other.

[0011] A method for generating an overlay measurement associated with an overlapping target is disclosed. The method includes receiving first and second detection signals from first and second cells of two or more cells of the overlapping target from one or more detectors. The first and second cells are defined as first and second cell types characterized by an order of structures in a layer, the order being characterized by a pitch of the structures in the layer. An overlay measurement for the first cell is generated based on the first detection signal, and an overlay measurement for the second cell is generated based on the second detection signal. Both the first and second cell types include a first pitch and a second pitch, but the first pitch and the second pitch of the first cell type are in an inverted order relative to the first pitch and the second pitch in the second cell type, as defined relative to a depth direction of a sample. An overlay measurement associated with the overlapping target is generated based on a value indicating an average of the overlay measurement of the first cell and the overlay measurement of the second cell.

[0012] It should be understood that both the foregoing general description and the following "detailed description" are exemplary and illustrative only and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0014] Figure 1A is a conceptual diagram of an overlay metering system according to one or more embodiments of the present disclosure.

[0015] Figure 1B is a schematic diagram of an optical subsystem according to one or more embodiments of the present disclosure.

[0016] Figure 2A is a conceptual diagram of an illumination pupil plane distribution of a circular illumination light beam according to one or more embodiments of the present disclosure.

[0017] Figure 2B According to one or more embodiments of the present disclosure Figure 2A Conceptual diagram of the distribution of diffraction orders of a circular illumination beam in the collecting pupil plane.

[0018] Figure 3 is a schematic diagram of overlapping targets according to one or more embodiments of the present disclosure.

[0019] Figure 4 is a top view of overlapping targets according to one or more embodiments of the present disclosure.

[0020] Figure 5is a graph of data depicting TIS error for various wavelengths for a single-unit target and a multi-unit inverted pitch target according to one or more embodiments of the present disclosure.

[0021] Fig. 6A is a top view of overlapping targets according to one or more embodiments of the present disclosure.

[0022] Figure 6B is a top view of overlapping targets according to one or more embodiments of the present disclosure.

[0023] Figure 6C is a top view of overlapping targets according to one or more embodiments of the present disclosure.

[0024] Fig.6D is a schematic diagram of overlapping targets according to one or more embodiments of the present disclosure.

[0025] Fig. 6E is a schematic diagram of overlapping targets according to one or more embodiments of the present disclosure.

[0026] Figure 7 is a process flow diagram depicting a method of overlay metering using two or more units according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0027] The present disclosure has been particularly shown and described with respect to specific embodiments and specific features thereof. The embodiments described herein should be regarded as illustrative rather than restrictive. It should be readily apparent to one of ordinary skill in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings.

[0028] A variety of overlay metrology techniques may be used to perform overlay metrology. For example, techniques include a static move and measure mode in which the sample is static during measurement and a scanning mode in which the illumination beam is scanned across the sample during measurement. Scanning-based scatterometry techniques include a fast detector to capture a time-varying interference signal generated when scanning the sample. The detector may be placed in the pupil plane at an overlapping position between selected diffraction orders to capture the time-varying interference signal when scanning the sample. Various non-limiting scanning scatterometry overlay metrology techniques are described in the following cases: U.S. Patent Publication No. 2022 / 0034652, filed on February 17, 2021; U.S. Patent Application No. 17 / 119,536, filed on December 11, 2020; U.S. Patent Application No. 17 / 708,958, filed on March 30, 2022; and U.S. Patent Application No. 17 / 709,104, filed on March 30, 2022; the entire texts of the U.S. Patent Applications are incorporated herein by reference in their entirety. It should be noted that such scanning examples are non-limiting and that embodiments herein may include one or more detectors in a field plane and may include various types of detectors, such as one or more diode array sensors.

[0029] Ideally, the time-varying diffraction signal would follow a trivial mathematical equation, but practically speaking, the diffraction signal may include TIS errors. TIS errors may be caused by a variety of factors. For example, TIS errors may be caused by non-uniformity of the illumination beam, errors in the scanning speed during scanning overlay metrology, and / or errors in the alignment of the illumination beam with the sample. Non-uniformity of the illumination beam may be caused by contaminants on components (e.g., filters, lenses) of the illumination subsystem of the overlay metrology system. TIS may also be caused by other factors, such as misalignment of the illumination beam relative to the sample. For the diffraction signal of a single unit, TIS errors may be difficult to determine using a scanning pattern.

[0030] Embodiments of the present disclosure relate to using an overlay metrology system to produce overlay measurements of an overlay target with suppressed TIS error. It is contemplated herein that the TIS error is related to the order of the gratings of the cells, such that reversing the order of the gratings produces an opposite amount of TIS error. In an embodiment, using this principle, the TIS error can be "cancelled" by averaging the overlap of cells with gratings of opposite (i.e., reversed) order. For example, an overlay target may include a first cell and a second cell. The structures of the cells (e.g., gratings) may be distributed in different layers of a sample such that the structures overlap each other in each cell. The first cell may include a structure having a first pitch in a first layer and a structure having a second pitch in a second layer. The second cell may also include the same pitch, but in reverse order. Since the TIS errors of such cells will have opposite magnitudes, the overlay measurements of each cell may be averaged to produce an overlay measurement with suppressed TIS error.

[0031] Figure 1A A conceptual diagram illustrating an overlay metering system 100 in accordance with one or more embodiments of the present disclosure.

[0032] The overlay metrology system 100 includes an optical subsystem 102 configured to acquire one or more images from a sample 104 for determining an overlay measurement.

[0033] In an embodiment, the overlay metrology system 100 includes a controller 122. The controller 122 may include one or more processors 124 and a memory 126. For example, the controller 122 may be configured to generate an overlay measurement based on a signal received from a detector of the optical subsystem 102.

[0034] Figure 1B A simplified schematic diagram illustrating optical subsystem 102 in accordance with one or more embodiments of the present disclosure.

[0035] In an embodiment, the optical subsystem 102 includes an illumination subsystem 106 and a light collection subsystem 110 .

[0036] The illumination subsystem 106 is configured to generate illumination in the form of one or more illumination beams 108 to illuminate the sample 104. The light collection subsystem 110 is configured to collect light from the illuminated sample 104 (e.g., according to a dosing recipe). In addition, the one or more illumination beams 108 may be spatially confined so that they may illuminate selected portions of the sample 104. For example, each of the one or more illumination beams 108 may be spatially confined to illuminate a specific cell of an overlapping target.

[0037] For example, the overlay metrology system 100 can be configured to image a particular type of sample according to a metrology recipe. For example, the overlay metrology system 100 can be designed (configured) and / or programmed (e.g., programmed via program instructions) to calculate overlay measurements of a particular type of features (e.g., grating-on-grating targets) of the sample 104 according to a metrology recipe.

[0038] As previously mentioned herein, the overlay metrology system 100 may include one or more detectors 112. Depending on the embodiment, the one or more detectors 112 may be used for scanning overlay metrology, static overlay metrology, or both and use imaging and / or scatterometry techniques unless otherwise mentioned. In scanning overlay metrology embodiments, the one or more detectors 112 may generally include any type of optical detector known in the art suitable for capturing interference signals generated when the sample 104 is translated by the translation stage 116 and / or when the one or more illumination beams 108 are scanned by the optical subsystem 102. For example, the one or more detectors 112 may be a diode array sensor and / or a charge coupled device (CCD) sensor.

[0039] In an embodiment of scanning overlay metrology, as an example, one or more detectors 112 are positioned in the collection pupil plane 114, such as Figure 1B By way of another example, one or more detectors 112 are positioned in the light collection field plane 150. In this example, the one or more detectors 112 may be able to image the entire field plane of the entire overlapping target. The field plane is conjugate to the object plane so that the sample 104 can be imaged from a top-down perspective.

[0040] In an embodiment, the optical subsystem 102 may include a translation stage 116 to scan the sample 104 through a measurement field of view of the optical subsystem 102 during overlay measurements.

[0041] For example, performing scan-based overlay metrology may include receiving detection signals from one or more detectors 112 while the sample 104 is in motion, such that the detection signals are time-varying interference signals.

[0042] For static overlay metrology, in an embodiment, one or more detectors include a multi-pixel sensor. For example, the multi-pixel sensor may be at least one of a (multi-pixel) charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device. For example, the multi-pixel sensor may be a charge coupled device (CCD) in one embodiment and a complementary metal oxide semiconductor (CMOS) device in another embodiment.

[0043] In an embodiment, the optical subsystem 102 may perform scatterometry overlay measurements on portions of the sample 104 having overlapping targets, such as, but not limited to, grating-on-grating targets.

[0044] In an embodiment, the structure of the unit cell may be configured to generate Moire diffraction orders (eg, +1 Moire order diffraction and -1 Moire order diffraction).

[0045] It is recognized herein that the distribution of diffraction orders of the illumination beam 108 produced by a periodic structure (e.g., a grating-on-grating structure) may be affected by a variety of parameters, such as, but not limited to, the wavelength of the illumination beam 108, the angle of incidence of the illumination beam 108 in both elevation and azimuth directions, the period (i.e., pitch) of the periodic structure, or the numerical aperture (NA) of the collecting lens. Thus, the illumination subsystem 106, the collecting subsystem 110, and the overlap target 302 may be configured to provide an overlap distribution of zero-order diffraction and first-order diffraction in the collection pupil plane 114 of the collecting subsystem 110. For example, the illumination subsystem 106 and / or the collecting subsystem 110 may be configured to produce measurements on a grating-on-grating structure having a selected range of periodicity that provides an overlap distribution. Furthermore, various components of the illumination subsystem 106 and / or the collecting subsystem 110 (e.g., a stop, pupil, or the like) may be adjustable to provide an overlap distribution for a given structure.

[0046] The collection subsystem 110 may be configured to collect at least one of the 0th order of diffraction (eg, specular reflection) and + / −1st diffraction orders associated with diffraction of the illumination beam 108 from the sample 104 .

[0047] In an embodiment, the optical subsystem 102 includes an objective lens 136 to focus the illumination beam 108 onto the sample 104 (e.g., onto an overlapping target having structures positioned on two or more layers of the sample 104). The objective lens 136 may be configured to collect measurement light emitted from the sample 104 in response to the illumination beam 108 as the sample 104 is scanned along a scan direction.

[0048] The optical subsystem can implement a variety of illumination beam distributions. For example, the illumination beam 108 can be circular, annular, and / or the like.

[0049] Figure 2A Conceptual diagram illustrating an illumination pupil plane distribution 200 for a circular illumination beam 204 in accordance with one or more embodiments of the present disclosure.

[0050] Figure 2B Describe one or more embodiments of the present disclosure Figure 2A 1. Conceptual diagram of a collection pupil plane distribution 202 of diffraction orders of a circular illumination beam 204. For example, the circular illumination beam 204 may become a measurement beam after emanating from the sample 104 and form circular diffraction orders in the collection pupil plane 114. The circular diffraction orders are illustrated by a zero (0) order circular diffraction order 206a, a first (+1) order circular diffraction order 206c, and a first (-1) order circular diffraction order 206b. One or more detectors 112 may be placed to capture overlapping regions 208a, 208b of such diffraction orders. For example, the detectors 112 (e.g., diode array sensors) may be placed in the pupil plane 114 such that the one or more detectors 112 substantially capture light from detected regions 210c, 210b. It should be noted that the detected regions 210c, 210b may be of any size, such as less than, equal to, or greater than the overlapping regions 208a, 208b.

[0051] Figure 3 Schematic diagram illustrating an overlay target 302 of a sample 104 in accordance with one or more disclosed embodiments. The illumination beam 108 is scanned along a scan direction 318. Scanning the overlay target 302 by a length equal to the pitch of the grating-on-grating structure may result in a 2π phase shift in each of the + / - 1 diffraction orders (in opposite directions), and the intensity captured by each of the one or more detectors 112 may oscillate via interference fringes.

[0052] As shown, the illumination beam 108 may occupy a field of view that is smaller than the overlapping target 302 itself. However, it should be understood that Figure 3 The overlapping target 302 and associated description in are provided for illustrative purposes only and should not be construed as limiting. For example, the overlapping target may include cells configured to be scanned along more than one scanning direction. For example, the overlapping target may include a first cell grouping having a periodicity along the X direction and a second cell grouping having a periodicity along the Y direction. In this way, all cells within a particular cell grouping may be imaged / detected while the sample 104 is scanned along a corresponding scanning direction associated with the grouping. By way of another example, a diagonal target suitable for performing metrological measurements in orthogonal directions in a single scan is generally described in U.S. Patent Publication No. 2021 / 0364935, published on November 25, 2021, the entire text of which is incorporated herein by reference.

[0053] For purposes of this disclosure, some concepts may be better understood in terms of cell "types" rather than repeatedly detailing the limitations of each cell. For example, a first cell type and a second cell type are defined such that the second cell type has structures with pitches in the opposite order to the first cell type. It should be noted that the first cell type may be referred to as a "P / Q" cell and the second cell type may be referred to as a "Q / P" cell. For example, the first pitch may be "P" and the second pitch may be "Q". This concept may also be described in terms of "first" and "second" pitches. In an embodiment, the first cell type is characterized by an order of structures in a layer, the order being characterized by the pitch of the structures in the layer. The second cell type is characterized by a second order of second structures in a layer of a sample, the second order being characterized by a second pitch of the second structures in the layer. The pitch of the first cell type and the second pitch of the second cell type both include structures with a first pitch and structures with a second pitch, but wherein the first pitch and the second pitch of the first cell type are in an inverted order relative to the structures with the first pitch and the second pitch in the second cell type. This order may be defined relative to the depth direction of the sample. For example, an upper layer of a sample may be "above" relative to a lower layer. In this regard, a grating structure having a first pitch may be above or below a grating structure having a second pitch, and in an inverted order in one cell type compared to another cell type.

[0054] Reference again Figure 3 , unless otherwise mentioned, the first cell 304 belongs to the first cell type and the second cell 306 belongs to the second cell type.

[0055] In an embodiment, the overlapping target 302 includes a first unit 304 and a second unit 306. The first unit 304 includes a first layer having a structure 310 with a first pitch and a second layer having a structure 308 with a second pitch. With respect to the depth direction of the sample 104, the structure 310 is on top of the structure 308. In an embodiment, the layer of the second unit 306 includes a structure 312 with a first pitch and a structure 314 with a second pitch in reverse order. It should be noted that the order is not necessarily limited to Figure 3 For example, the first unit 304 and the second unit 306 may include any number of layers, such as any number of intermediate layers between the structures 308, 310, 312, 314.

[0056] By way of another example, cells 304, 306 may include three or more layers of varying pitches (e.g., four or more, five or more, six or more, or the like) such that overlap between many layers may be measured. For example, a second cell may include all three layers in a reversed order (e.g., pitches 3, 2, 1 rather than pitches 1, 2, 3).

[0057] However, it should be noted that the three or more pitches may alternatively be in different layers, such that no cell has more than two pitches. For example, the methods herein (e.g., using two cells, one with a reversed order of pitches) may be applied to three or more pitches as follows: two cells have pitches in the first and second layers of the sample (but in reversed order); two additional cells have pitches in the first and third layers; and the last two cells have pitches in the second and third layers. In this regard, the overlap between all three layers may be determined.

[0058] Figure 4 A top view of an overlay target 400 is illustrated in accordance with one or more embodiments of the present disclosure. Figure 4 The cells 304, 306 may be illustrated in a side-by-side (i.e., parallel) configuration rather than a sequential configuration. It should be noted that the illumination beam 108 may need to be scanned twice (e.g., in a "c" shape) across the overlapping target 400. For example, after scanning the first cell 304, the illumination beam may move down and then scan across the second cell 306. In other embodiments, two illumination beams 108 are used to scan two parallel cells simultaneously.

[0059] Figure 5 A data graph 500 is illustrated depicting TIS error for various wavelengths for a single-unit target and a multi-unit inverted pitch target in accordance with one or more embodiments of the present disclosure.

[0060] As shown, TIS error increases as wavelength increases from 500 nm to 580 nm. Using embodiments of the present disclosure, TIS error can be suppressed by more than 70%, but is not limited to such suppression levels. As shown, the multi-cell TIS error 504 tolerated by the present disclosure is significantly lower than the single-cell TIS error 502 of other methods (e.g., methods not necessarily based on the present disclosure).

[0061] The following formula is consistent with overlapping targets with two or more layers (e.g. Figure 3 Compared to the formula shown in U.S. Patent Application No. 17 / 709,200 filed on March 30, 2022 (the entire text of which is hereby incorporated by reference), the following formula may be similar, except for the additional TIS error term. However, the following formula indicates how equal ratios of the first cell type and the second cell type allow the TIS error term to be canceled.

[0062] Before understanding the second unit, it is possible to understand the second unit by first referring to the single unit (e.g. Figure 3 For purposes of the following formulas, the first cell 304 includes a first (top) layer having structures 310 with a first pitch (p1) and a second (bottom) layer having structures 308 with a second pitch (p2).

[0063] The interference intensity can be modeled as varying as a function of grating position (X)*2*pi / pitch. The interference intensity (eg, corresponding to a time-varying signal) measured by the detector in the overlap between the zero-order diffraction and the first-order diffraction from the structure 310 having the first pitch (P1) is:

[0064]

[0065] The interference intensity measured in the overlap between the zeroth order diffraction and the first order diffraction from the structure 308 having the second pitch (P2) is:

[0066]

[0067] Where P 1 is the first pitch of the elements in the first layer; P 2 is the second pitch of the elements in the second layer; A 0 , A 1 Corresponding to the pitch P 1 The intensity of the associated zeroth and first diffraction orders; A 0 ′、A 1 ' respectively corresponds to the second pitch P 2 the intensities of the associated zeroth and second diffraction orders; Yes and IP1± The phase term associated with the signal; θ is related to I P2± The phase term associated with the signal; X is the X-direction variable (i.e., the scan position at a given point in time); X 0 is the position in the X direction at time 0 (ie, the starting position); and DC is a constant offset similar to using direct current instead of alternating current.

[0068] In general, the overlap of the first unit 304 is:

[0069]

[0070] Unfortunately, if the illumination is not perfectly uniform, another ρ (which is associated with the TIS error) is added to the interference equation:

[0071]

[0072] This additional phase (ρ 1 and 2 ) eventually adds a constant value to the resulting OVL (also known as TIS error) over time:

[0073]

[0074] The above process is for a first cell 304, which may be referred to as a "P / Q" cell. To overcome TIS errors, the order of the pitches of the structure of the first cell 304 may be reversed to produce a second cell 306. The second cell 306 is a second type of cell, which may be referred to as a "Q / P" cell.

[0075] The resulting equation for the overlap of such units is:

[0076]

[0077] Therefore, by averaging the two results, the TIS error due to lighting pollution can be estimated:

[0078]

[0079] Figures 6A to 6E A top view illustrating overlapping targets according to one or more embodiments of the present disclosure.

[0080] Fig. 6A A top view of a Knight overlay target 602 is illustrated in accordance with one or more embodiments of the present disclosure.

[0081] In an embodiment, the two or more units sequentially include at least three units (i.e., X1, X2, and Y1) and a fourth unit (i.e., Y2) adjacent to a third unit (i.e., Y1) of the at least three units. The first unit (X1) and the second unit (X2) of the at least three units are configured to be used with a scanning direction (e.g., an X scanning direction), while the fourth unit and the third unit are configured to be used with a different scanning direction (e.g., a Y scanning direction).

[0082] Figure 6B A top view of a denim overlay target 604 is illustrated in accordance with one or more embodiments of the present disclosure.

[0083] It should be noted that periodicity along the scan direction may include periodicity at a non-zero angle relative to the scan direction.

[0084] Figure 6B A potential problem with the denim target 604 shown in FIG. 6 is TIS error. Thus, for a pitch that is angled (e.g., 45 degrees) relative to the scan direction, four cells ( Figure 6C ) may be more desirable to reduce the number of scans and still obtain overlap in two directions (e.g., X-direction overlap and Y-direction overlap) with reduced TIS error in a single scan.

[0085] Figure 6C A top view of a Bishop overlap target 606 is illustrated according to one or more embodiments of the present disclosure. In an embodiment, two or more cells include four cells 304, 614, 306, 616 aligned in a row. The four cells include a first cell 304 (of a first cell type) and a corresponding third cell 305 (of a second cell type). Both the first cell 304 and the third cell 306 include a periodic structure at +45 degrees to the scan direction. It should be noted in this example that the second cell 614 does not correspond to the first cell 304 as in other examples of the present disclosure, but rather, it corresponds to the fourth cell 616. The second cell 614 and the corresponding fourth cell 616 may include a periodic structure at -45 degrees and include pitches in an inverted order relative to each other. The second cell 614 and the corresponding fourth cell 616 may correspond to an X direction ( Figure 6C In the horizontal direction, the first unit 304 and the corresponding third unit 306 may correspond to the overlapping diffraction orders in the Y direction ( Figure 6C In this regard, Figure 6C The overlapping target can allow a "single" scan to produce overlap in both the X and Y directions.

[0086] Fig.6D A schematic diagram illustrating a waffle overlap target 608 in accordance with one or more embodiments of the present disclosure.

[0087] In an embodiment, two or more cells of the overlapping target include waffle cells 610 having a periodic structure at +45 degrees and -45 degrees to the scan direction in the same layer such that a waffle pattern is formed.

[0088] Fig. 6E A schematic diagram illustrating a waffle overlap target 612 according to one or more embodiments of the present disclosure. In an embodiment, two waffle cells 610 may be placed sequentially and / or in parallel.

[0089] In embodiments, scanning may be performed 1) by adjusting the optics of the optical subsystem 102 (e.g., the objective 136 or any other optics); and / or 2) by moving the sample 104 via the translation stage 116. It should be noted that adjusting the illumination beam 108 to scan the sample 104 may result in TIS errors, as doing so may result in vertical alignment errors of the illumination beam 108 and the sample 104 due to imperfect beam translation. The amount of TIS error may vary depending on the amount of beam translation performed. In embodiments, this TIS error may be addressed by using more than one pair of cells (e.g., a first cell type 304 and a corresponding second cell type 306) to address differences in the alignment of the illumination beam 108. For example, an overlapping target used with an illumination beam 108 translated using optics may include multiple pairs of cells 304, 306 aligned in a row.

[0090] Figure 7 A process flow diagram illustrating a method 700 of overlay metrology using two or more units in accordance with one or more embodiments of the present disclosure. It should be noted that the embodiments and implementation techniques described previously herein in the context of the overlay metrology system 100 should be interpreted as extending to the method 700. It should be further noted herein that the steps of the method 700 may be implemented in whole or in part by the overlay metrology system 100. However, it should be further recognized that the method 700 is not limited to the overlay metrology system 100, as additional or alternative system-level embodiments may implement all or a portion of the steps of the method 700.

[0091] At step 702, a first detection signal from the first unit 304 is received from one or more detectors 112. For example, the first detection signal may be a signal generated by one or more detectors 112. For example, when scanning the first unit 304, one detector 112 may be positioned at Figure 2B In each overlapping region 208a, 208b shown in. For example, the controller 122 may be configured to receive such a first detection signal (eg, as data to be stored on a memory).

[0092] At step 704 , a second detection signal is received from the one or more detectors 112 during a scan of the second unit 306 .

[0093] At step 706, an overlay measurement associated with the overlay target 302 is generated based on a value indicating an average of the overlay measurement of the first cell 304 and the overlay measurement of the second cell 306. For example, the first cell 304 may be of the first cell type previously described and the second cell 306 may be of the second cell type previously described (i.e., having a reverse pitch order). In this regard, by averaging the results, the overlay may have a reduced TIS error.

[0094] In an optional step, a tool introduced offset (TIS) error of the overlay target 302 is determined based on the difference between the overlay measurement of the first unit and the overlay measurement of the second unit. The TIS error may be a function of subtracting half the absolute value of the second overlay measurement from the overlay measurement of the first unit.

[0095] In an optional step, at least one of intensity or phase information associated with the time-varying interference signal is extracted using a phase lock technique; and an overlay error between a first layer and a second layer of the sample is determined based on at least one of the intensity or phase information. For example, generating an overlay measurement associated with an overlay target may include such an optional step. Such optional steps are described in additional detail in one or more references previously incorporated herein by reference.

[0096] Reference again Figure 1A to 1B , additional components of the optical subsystem 102 are described in accordance with one or more embodiments of the present disclosure. For example, a controller 122 and a processor 124 and various optical components generally used for overlay metrology (i.e., not specifically used for scanning or static overlay metrology unless otherwise noted) are described in detail below.

[0097] In an embodiment, the controller 122 generates (or determines) an overlap measurement between layers (e.g., a first layer and a second layer) of the overlapping target 302 along a measurement direction based on a comparison of the detection signals. For example, the controller 122 may compare the magnitude and / or phase of the detection signals to generate the overlap measurement. For example, U.S. Patent No. 10,824,079, issued on November 3, 2020 (the entire text of which is incorporated herein by reference) generally describes diffraction orders in a light collecting pupil and further provides a specific relationship between overlap and measured intensity in a pupil plane. It is contemplated herein that the systems and methods disclosed herein may extend the teachings of U.S. Patent No. 10,824,079 to detection signals captured by one or more detectors placed in an overlap region between a 0 diffraction order and a + / - 1 diffraction order. In particular, it is contemplated herein that the overlap on a sample may be proportional to the relative phase shift between the two detection signals. In another example, the relative intensities of the diffraction orders in the pupil plane may be extracted from the detection signals. In this way, overlay algorithms known in the art based on relative intensity differences of diffraction orders may be applied to generate overlay measurements.

[0098] In an embodiment, the overlay metrology system 100 includes a controller 122 communicatively coupled to the optical subsystem 102. The controller 122 may include one or more processors 124 and a memory device 126 or memory. For example, the one or more processors 124 may be configured to execute a set of program instructions maintained in the memory device 126.

[0099] The one or more processors 124 of the controller 122 may generally include any processor or processing component 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 124 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 124 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a network-linked computer, or any other computer system configured to execute a program configured to operate or operate in conjunction with the overlay metering system 100, as described throughout this disclosure. In addition, different subsystems of the overlay metering system 100 may include processors or logic elements suitable for implementing at least a portion of the steps described in this disclosure. Therefore, the above description should not be construed as limiting the embodiments of the present disclosure, but is merely illustrative. Furthermore, the steps described throughout the present disclosure may be performed by a single controller or alternatively multiple controllers. Additionally, the controller 122 may include one or more controllers housed in a common housing or within multiple housings. In this manner, any controller or combination of controllers may be individually packaged as a module suitable for integration into the system 100. Furthermore, the controller 122 may analyze or otherwise process data received from the one or more detectors 112 and feed the data to additional components within the overlay metering system 100 or external to the overlay metering system 100.

[0100] Furthermore, the memory device 126 may include any storage media known in the art suitable for storing program instructions that are executable by the associated one or more processors 124. For example, the memory device 126 may include a non-transitory storage medium. As additional examples, the memory device 126 may include, but is not limited to, a read-only memory, a random access memory, a magnetic or optical storage device (e.g., a disk), a tape, a solid-state drive, and the like. It should be further noted that the memory device 126 may be housed in a common controller housing with the one or more processors 124.

[0101] In this regard, the controller 122 may perform any of the various processing steps associated with overlay metrology. For example, the controller 122 may be configured to generate control signals to direct or otherwise control the optical subsystem 102, or any component thereof. For example, the controller 122 may be configured to direct the translation stage 116 to translate the sample 104 along one or more measurement paths or scan zones to scan one or more overlay targets through the measurement field of view of the optical subsystem 102. By another example, the controller 122 may be configured to receive signals corresponding to detection signals from the one or more detectors 112. By another example, the controller 122 may generate correctable terms for one or more additional manufacturing tools based on the overlay measurements from the optical subsystem 102 as feedback and / or feedforward control of the one or more additional manufacturing tools.

[0102] In an embodiment, the controller 122 captures detection signals detected by the one or more detectors 112. The controller 122 may generally use any technique known in the art (such as, but not limited to, one or more phase-locked loops) to capture data, such as, but not limited to, the magnitude or phase of the detection signal. In addition, the controller 122 may use any combination of hardware (e.g., circuitry) or software techniques to capture the detection signal (e.g., the detection signal) or any data associated with the detection signal.

[0103] Reference again Figure 1B , various components of the optical subsystem 102 are described in more detail according to one or more embodiments of the present disclosure.

[0104] In an embodiment, the illumination subsystem 106 includes an illumination source 128 configured to generate at least one illumination beam 108. The illumination from the illumination source 128 may include light of one or more selected wavelengths, including but not limited to ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0105] In an embodiment, the illumination subsystem 106 includes one or more optical components adapted to modify and / or adjust the illumination beam 108 and direct the illumination beam 108 to the sample 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., to collimate the illumination beam 108, relay the illumination pupil plane 120 and / or the illumination field plane 132, or the like). In another embodiment, the illumination subsystem 106 includes one or more illumination control optics 134 to shape or otherwise control the illumination beam 108. For example, the illumination control optics 134 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0106] In an embodiment, the illumination subsystem 106 illuminates the sample 104 with two or more illumination beams 108. Furthermore, the two or more illumination beams 108 may (but need not) be incident on different portions of the sample 104 (e.g., different cells of the overlapping target 302) within the measurement field of view (e.g., the field of view of the objective lens 136). It is contemplated herein that a variety of techniques may be used to generate the two or more illumination beams 108. In one embodiment, the illumination subsystem 106 includes two or more apertures at the illumination field plane 132. In another embodiment, the illumination subsystem 106 includes one or more beam splitters to separate illumination from the illumination source 128 into the two or more illumination beams 108. In another embodiment, at least one illumination source 128 directly generates the two or more illumination beams 108. In a general sense, each illumination beam 108 may be considered part of a different illumination channel, regardless of the techniques used to generate the various illumination beams 108.

[0107] The collection subsystem 110 may include one or more optical components suitable for modifying and / or conditioning the collected light 138 from the sample 104. In one embodiment, the collection subsystem 110 includes one or more collection lenses 140 (e.g., to collimate the illumination beam 108, relay a pupil and / or field plane, or the like), which may include (but need not include) an objective lens 136. In another embodiment, the collection subsystem 110 includes one or more collection control optics 142 to shape or otherwise control the collected light 138. For example, the collection control optical device 142 may include (but is not limited to) one or more field apertures, one or more pupil apertures, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more trackers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like). In another example, the collection subsystem 110 may include one or more collection field planes 150.

[0108] In an embodiment, the collection subsystem 110 includes two or more collection channels 144, each having a separate detector 112 (or multiple detectors 112). For example, the optical subsystem 102 may include one or more beam splitters 146 configured to split the collected light 138 into the collection channels 144. In addition, the beam splitter 146 may be a polarizing beam splitter, a non-polarizing beam splitter, or a combination thereof.

[0109] In an embodiment, the plurality of light collection channels 144 are configured to collect light from a plurality of illumination beams 108 on the sample 104. For example, in the case where the overlapping target 302 has two or more cells distributed in parallel in a direction different from the scanning direction, the optical subsystem 102 can simultaneously illuminate the different cells with different illumination beams 108 and simultaneously capture the detection signal associated with each illumination beam 108. Additionally, in some embodiments, the plurality of illumination beams 108 directed to the sample 104 can have different polarizations. In this way, the diffraction orders associated with each of the illumination beams 108 can be separated. For example, the polarization beam splitter 146 can efficiently separate the diffraction orders associated with the different illumination beams 108. By way of another example, a polarizer can be used in one or more light collection channels 144 to isolate the desired diffraction orders for measurement.

[0110] Reference again Figure 1AIt should be noted herein that one or more components of the overlay metrology system 100 may be communicatively coupled to various other components of the system 100 in any manner known in the art. For example, the one or more processors 124 may be communicatively coupled to each other and to other components via a wired (e.g., copper wire, fiber optic cable, and the like) or wireless connection (e.g., RF coupling, IR coupling, WiMax, Bluetooth, 3G, 4G, 4G LTE, 5G, and the like). By way of another example, the controller 122 may be communicatively coupled to one or more components of the optical subsystem 102 via any wired or wireless connection known in the art.

[0111] In one embodiment, the one or more processors 124 may include any one or more processing components known in the art. In this sense, the one or more processors 124 may include any microprocessor-type device configured to execute software algorithms and / or instructions. In one embodiment, the one or more processors 124 may be composed of the following: a desktop computer, a large computer system, a workstation, an image computer, a parallel processor, or other computer systems (e.g., network-linked computers) configured to execute programs configured to operate the overlap metering system 100, as described throughout the present disclosure. It should be recognized that the steps described throughout the present disclosure may be implemented by a single computer system or alternatively multiple computer systems. In addition, it should be recognized that the steps described throughout the present disclosure may be implemented on any one or more of the one or more processors 124. In general, the term "processor" can be broadly defined to cover any device having one or more processing elements that execute program instructions from the memory 126. In addition, different subsystems of the overlap metering system 100 may include processors or logic elements suitable for implementing at least a portion of the steps described throughout the present disclosure. Therefore, the above description should not be interpreted as a limitation of the present disclosure, but only as an illustration.

[0112] Those skilled in the art will recognize that for the sake of conceptual clarity, the components (e.g., operations), devices, objects, and the accompanying discussions described herein are used as examples, and various configuration modifications are carefully considered. Therefore, as used herein, the specific examples set forth and the accompanying discussions are intended to represent their more general classes. In general, the use of any specific example is intended to represent its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be considered limiting.

[0113] Those skilled in the art will appreciate that there are various carriers (e.g., hardware, software, and / or firmware) that can implement the processes and / or systems and / or other techniques described herein, and that the preferred carrier will vary depending on the context in which the processes and / or systems and / or other techniques are deployed. For example, if the implementer determines that speed and accuracy are most important, then the implementer may choose a primarily hardware and / or firmware carrier; alternatively, if flexibility is most important, then the implementer may choose a primarily software implementation; or again alternatively, the implementer may choose some combination of hardware, software, and / or firmware. Thus, there are several possible carriers that can implement the processes and / or devices and / or other techniques described herein, and none of the carriers is inherently better than another, as any carrier to be utilized depends on the context in which the carrier will be deployed and the implementation's specific considerations (e.g., speed, flexibility, or predictability), any of which may vary.

[0114] The previous description is presented to enable one of ordinary skill in the art to make and use the invention, as provided in the context of specific applications and their requirements. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the specific embodiments shown and described, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0115] With respect to the terms used herein for substantially any plural and / or singular terms, those skilled in the art may translate from the plural to the singular and / or from the singular to the plural, depending on the context and / or application. For clarity, various singular / plural permutations are not explicitly set forth herein.

[0116] All methods described herein may include storing the results of one or more steps of the method embodiment in a memory. The result may include any result described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the result has been stored, the result may be accessed in the memory and used by any of the method or system embodiments described herein, formatted to display to the user, used by another software module, method or system, and the like. In addition, the result may be stored "permanently", "semi-permanently", "temporarily" or stored for a period of time. For example, the memory may be a random access memory (RAM), and the result may not necessarily be retained in the memory indefinitely.

[0117] It is further contemplated that each of the above-described method embodiments may include any other steps of any other method described herein. In addition, each of the above-described method embodiments may be performed by any of the systems described herein.

[0118] The subject matter described herein sometimes illustrates different components contained in or connected to other components. It should be understood that such depicted architectures are exemplary only, and in fact many other architectures that realize the same functionality can be implemented. In a conceptual sense, any component arrangement for realizing the same functionality is effectively "associated" so as to realize the desired functionality. Therefore, any two components combined to realize a specific functionality herein can be regarded as "associated" with each other so as to realize the desired functionality, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be regarded as "connected" or "coupled" to realize the desired functionality, and any two components that can be so associated can also be regarded as "coupleable" to each other to realize the desired functionality. Specific examples that can be coupled include but are not limited to physically coordinated and / or physically interactive components, and / or wirelessly interactive and / or wirelessly interactive components, and / or logically interactive and / or logically interactive components.

[0119] In addition, it should be understood that the present invention is defined by the appended claims. Those skilled in the art will understand that in general, the terms used herein and particularly in the appended claims (e.g., the body of the appended claims) are generally intended to be "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "having" should be interpreted as "having at least", the term "includes" should be interpreted as "including but not limited to", etc.). Those skilled in the art will further understand that if a specific number of an introduced claim recitation is intended, then such intent is to be explicitly stated in the claim, and if such statement is not made, then such intent does not exist. For example, to aid understanding, the appended claims may contain the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be interpreted as implying that the introduction of a claim recitation by the indefinite article "a" or "an" limits any particular claim containing the introduced claim recitation to inventions containing only one such recitation, even if the same claim contains the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" (e.g., "a" should generally be interpreted as meaning "at least one" or "one or more"); the same is true for the use of definite articles to introduce claim recitations. In addition, even if a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that the recitation should generally be interpreted to mean at least the recited number (e.g., the mere recitation of "two recitations" without other modifiers generally means at least two recitations, or two or more recitations). Furthermore, in examples where conventional expressions similar to “at least one of A, B, and C, and the like” are used, such construction is generally contemplated in the sense that one skilled in the art would understand the conventional expressions (e.g., “a system having at least one of A, B, and C” would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). In examples where conventional expressions similar to “at least one of A, B, or C, and the like” are used, such construction is generally contemplated in the sense that one skilled in the art would understand the conventional expressions (e.g., “a system having at least one of A, B, or C” would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). Those skilled in the art will further understand that, in fact, any transitional conjunction and / or phrase presenting two or more alternatives, whether in the description, claims or drawings, should be understood to consider the possibility of including one of the items, any one of the items, or both of the items. For example, the phrase "A or B" will be understood to include the possibility of "A" or "B" or "A and B".

[0120] It is believed that the present disclosure and its many attendant advantages will be appreciated from the foregoing description, and it will be appreciated 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 the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. An overlapping metering system, comprising: A controller comprising one or more processors configured to execute program instructions that cause the one or more processors to execute a metering recipe by: receiving, from one or more detectors, a first detection signal from a first unit of two or more units of the overlapping target; receiving, from the one or more detectors, a second detection signal from a second unit of the two or more units; generating an overlay measurement of the first cell based on the first detection signal; generating an overlap measurement of the second cell based on the second detection signal; and generating an overlap measure associated with the overlap target based on a value indicative of an average of the overlap measure of the first cell and the overlap measure of the second cell, wherein the first cell is defined as a first cell type characterized by an order of structures in a layer, the order being characterized by a pitch of the structures in the layer, wherein the second cell is defined as a second cell type characterized by a second order of second structures in the layer, the second order being characterized by a second pitch of the second structures in the layer, wherein the pitch of the first unit type and the second pitch of the second unit type both include a first pitch and a second pitch, but wherein if defined relative to a depth direction of the sample, then the first pitch and the second pitch of the first unit type are in a reverse order relative to the first pitch and the second pitch in the second unit type.

2. The overlay metrology system of claim 1 , wherein the controller is configured to execute the program instructions that cause the one or more processors to execute the metrology recipe by determining a tool introduced offset (TIS) error of the overlay target based on a difference between the overlay measurement of the first unit and the overlay measurement of the second unit.

3. The overlay metrology system of claim 1, wherein the one or more detectors include at least one detector positioned in a pupil plane.

4. The overlay metrology system of claim 1, wherein the one or more detectors include at least one detector positioned in a field plane.

5. The overlay metrology system of claim 1, wherein the one or more detectors include at least one diode array sensor.

6. The overlay metrology system of claim 1, wherein the one or more detectors include at least one charge coupled device (CCD) sensor.

7. The overlay metrology system of claim 1, wherein an illumination pupil plane distribution of the illumination beam is circular.

8. The overlay metrology system of claim 1, wherein the illumination pupil plane distribution of the illumination beam is annular.

9. The overlay metrology system of claim 1, wherein the structures of the two or more cells of the overlay target are at a 45 degree angle relative to a scan direction.

10. The overlay metrology system of claim 9, wherein the two or more cells of the overlay target include waffle cells having a periodic structure at +45 degrees and -45 degrees to the scan direction in the same layer such that a waffle pattern is formed.

11. The overlay metrology system of claim 9, wherein the two or more cells include four cells in a row, wherein the four cells in the row include two first cell types adjacent to each other having the structure at a positive angle relative to the scanning direction and two second cell types adjacent to each other having the structure at a negative angle relative to the scanning direction.

12. The overlay metrology system of claim 9, wherein the two or more units include at least three units in a row and a fourth unit adjacent to a third unit of the at least three units, wherein a first and a second unit of the at least three units are configured for use with the scan direction, and the fourth unit and the third unit are configured for use with a different scan direction orthogonal to the scan direction.

13. The overlay metrology system of claim 1, wherein the two or more units include three or more layers of varying pitches.

14. The overlay metering system of claim 1, wherein the receiving the first detection signal and the receiving the second detection signal generally comprise: A time-varying interference signal is received while scanning the overlapping object along a scanning direction.

15. The overlay metrology system of claim 1, wherein the first position including the first detector includes the position of a +1 moiré order diffraction, and wherein the second position including the second detector includes the position of a -1 moiré order diffraction.

16. The overlay metering system of claim 1, wherein the controller is configured to execute the program instructions that cause the one or more processors to execute the metering recipe by: extracting at least one of intensity or phase information associated with the time-varying interference signal using a phase lock-in technique; and An overlay error between a first layer and a second layer of the sample is determined based on at least one of intensity or phase information.

17. An overlay metering system comprising: Lighting subsystem, which includes: an illumination source configured to generate an illumination beam; A photon collection system, comprising: one or more detectors; and an objective lens configured to collect measurement light emitted from the sample in response to the illumination beam while scanning the sample along a scanning direction, wherein according to a metrology recipe, the sample comprises an overlapping target, wherein the overlapping target comprises two or more cells having a structure having a periodicity along the scanning direction; and a controller communicatively coupled to the collection subsystem, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to perform the metering recipe by: receiving, from the one or more detectors, a first detection signal from a first unit of the two or more units; receiving, from the one or more detectors, a second detection signal from a second unit of the two or more units; generating an overlay measurement of the first cell based on the first detection signal; generating an overlay measurement of the second cell based on the second detection signal; and generating an overlap measure associated with the overlap target based on a value indicative of an average of the overlap measure of the first cell and the overlap measure of the second cell, wherein the first unit is defined as a first unit type characterized by an order of the structures in a layer, the order being characterized by a pitch of the structures in the layer, wherein the second unit is defined as a second unit type characterized by a second order of second structures in the layer, the second order being characterized by a second pitch of the second structures in the layer, wherein the pitch of the first cell type and the second pitch of the second cell type both include a first pitch and a second pitch, but wherein if defined relative to a depth direction of the sample, then the first pitch and the second pitch of the first cell type are in a reverse order relative to the first pitch and the second pitch in the second cell type.

18. The overlay metrology system of claim 17, wherein the controller is configured to execute the program instructions that cause the one or more processors to execute the metrology recipe by determining a tool introduced offset (TIS) error of the overlay target based on a difference between the overlay measurement of the first unit and the overlay measurement of the second unit.

19. The overlay metrology system of claim 17, wherein the one or more detectors include at least one detector positioned in a pupil plane.

20. The overlay metrology system of claim 17, wherein the one or more detectors include at least one detector positioned in a field plane.

21. The overlay metrology system of claim 17, wherein the one or more detectors include at least one diode array sensor.

22. The overlay metrology system of claim 17, wherein the one or more detectors comprises at least one charge coupled device (CCD) sensor.

23. The overlay metrology system of claim 17, wherein an illumination pupil plane distribution of the illumination beam is circular.

24. The overlay metrology system of claim 17, wherein an illumination pupil plane distribution of the illumination beam is annular.

25. The overlay metrology system of claim 17, wherein the structures of the two or more cells of the overlay target are at a 45 degree angle relative to the scan direction.

26. The overlay metrology system of claim 25, wherein the two or more cells of the overlay target include waffle cells having a periodic structure at +45 degrees and -45 degrees to the scan direction in the same layer such that a waffle pattern is formed.

27. The overlay metrology system of claim 25, wherein the two or more cells comprise at least four cells in a row, wherein the at least four cells in the row comprise at least two first cell types adjacent to each other having the structure at a positive angle relative to the scan direction and at least two second cell types adjacent to each other having the structure at a negative angle relative to the scan direction.

28. The overlay metering system of claim 25, wherein the two or more units include at least three units in a row and a fourth unit adjacent to a third unit of the at least three units, wherein the first unit and the second unit of the at least three units are configured for use with the scanning direction, and the fourth unit and the third unit are configured for use with a different scanning direction orthogonal to the scanning direction.

29. The overlay metrology system of claim 17, wherein the two or more units include three or more layers of varying pitch.

30. The overlay metering system of claim 17, wherein said receiving said first detection signal and said receiving said second detection signal substantially comprise: A time-varying interference signal is received while scanning the overlapping object along the scanning direction.

31. The overlay metrology system of claim 17, wherein the first position including the first detector includes the position of a +1 moiré order diffraction, and wherein the second position including the second detector includes the position of a -1 moiré order diffraction.

32. The overlay metering system of claim 17, wherein the controller is configured to execute the program instructions that cause the one or more processors to execute the metering recipe by: extracting at least one of intensity or phase information associated with the time-varying interference signal using a phase lock-in technique; and An overlay error between a first layer and a second layer of the sample is determined based on at least one of intensity or phase information.

33. An overlapping target, comprising: Four units, aligned in a row, comprising: The first unit and the third unit include a periodic structure at +45 degrees to the scanning direction; and The second unit and the fourth unit include a periodic structure that is -45 degrees to the scanning direction, wherein the first unit and the second unit belong to a first unit type, and the third unit and the fourth unit belong to a second unit type, wherein the first cell type is characterized by an order of structures in a layer, the order being characterized by a pitch of the structures in the layer, wherein the second cell type is characterized by a second order of second structures, the second order being characterized by a second pitch of the second structures in the layer, wherein the pitch of the first unit type and the second pitch of the second unit type both include a first pitch and a second pitch, but wherein if defined relative to a depth direction of the sample, then the first pitch and the second pitch of the first unit type are in a reverse order relative to the first pitch and the second pitch in the second unit type.

34. A method comprising: receiving, from one or more detectors, a first detection signal from a first cell of two or more cells of an overlapping target including a sample having a periodic structure along a scan direction; receiving, from the one or more detectors, a second detection signal from a second unit of the two or more units; generating an overlay measurement of the first cell based on the first detection signal; generating an overlap measurement of the second cell based on the second detection signal; and generating an overlap measure associated with the overlap target based on a value indicative of an average of the overlap measure of the first cell and the overlap measure of the second cell, wherein the first unit is defined as a first unit type characterized by an order of the structures in a layer, the order being characterized by a pitch of the structures in the layer, wherein the second unit is defined as a second unit type characterized by a second order of second structures in the layer, the second order being characterized by a second pitch of the second structures in the layer, wherein the pitch of the first cell type and the second pitch of the second cell type both include a first pitch and a second pitch, but wherein if defined relative to a depth direction of the sample, then the first pitch and the second pitch of the first cell type are in a reverse order relative to the first pitch and the second pitch in the second cell type.

35. The method of claim 34, further comprising: A tool introduced offset (TIS) error of the overlay target is determined based on a difference between the overlay measurement of the first unit and the overlay measurement of the second unit.

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