Systems and methods for reducing device-induced errors in scanning overlay metrology

Abstract

An overlay metrology system and method are disclosed for generating overlay measurements of an overlay target including cells with a reverse-order structure. The overlay metrology system may include an illumination subsystem and a collection subsystem. The collection subsystem may include one or more detectors for collecting measurement light from a sample. 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, the second cell type including a reverse-order structure relative to the first cell type, according to a metrology recipe. The metrology recipe may include receiving detection signals, generating an overlay measurement for each cell based on the detection signals, and generating an overlay measurement associated with the overlay target based on a value indicating an average of the overlay measurements for each cell.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application No. 63 / 427,538, filed November 23, 2022, in the names of Itay Gdor, Yuval Lubashevsky, Vladimir Levinski, Daria Negri, Alon Yagil, and Nickolai Isakovich, entitled "STEM AND METHOD FOR SUPPRESSION OF TOOL INDUCED SHIFT IN SCANNING OVERLAY METROLOGY," which is incorporated by reference in its entirety.

[0002] The present invention relates generally to overlay metrology, and more particularly to a system and method for overlay metrology that reduces apparatus-induced error in overlay measurement of an overlay target. [Background technology]

[0003] The demand for smaller feature sizes and increased feature densities has driven the demand for accurate and efficient overlay metrology, which refers to the measurement of the relative alignment of layers on a sample, such as, but not limited to, a semiconductor device.

[0004] The overlay target is typically formed on the surface of a sample and may contain cells with grating structures with varying pitches in overlapping layers. The sample is typically mounted on a translation stage and translated to sequentially move the overlay target into the measurement field of view. In typical metrology systems using a move and measure (MAM) approach, the sample remains stationary during each measurement. However, the time required for the translation stage to stabilize before a measurement can adversely affect throughput.

[0005] Additionally, various sources can introduce errors into overlay metrology data, such as instrument-induced error (TIS) errors. For example, non-uniformity in illumination can cause TIS errors. For example, contaminants such as particles or dust can adhere to the filter, causing an uneven distribution in the illumination beam. Another example is that the illumination beam may not be properly aligned with the sample during measurement, further introducing TIS errors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2022 / 0328365 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, it would be desirable to provide a system and method to overcome the above-mentioned deficiencies. [Means for solving the problem]

[0008] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the overlay metrology system includes a controller. In another exemplary embodiment, the controller may include one or more processors configured to execute program instructions that cause the one or more processors to execute a metrology recipe. In another exemplary embodiment, the metrology recipe may include receiving detection signals from one or more detectors from each cell, generating an overlay measurement for each cell based on the detection signals, and generating an overlay measurement associated with the overlay target based on a value indicating an average of the overlay measurements for each cell. In another exemplary embodiment, according to the 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, the second cell type including a reverse-order structure relative to the first cell type.

[0009] An overlay metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the overlay metrology system includes an illumination subsystem and a collection subsystem. The collection subsystem may include one or more detectors to collect measurement light from a sample. 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, the second cell type including a reverse order of structure relative to the first cell type, according to a metrology recipe. The metrology recipe may include receiving detection signals from one or more detectors from each cell, generating an overlay measurement value for each cell based on the detection signals, and generating an overlay measurement value 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 exemplary embodiments of the present disclosure, an overlay target is disclosed. In one exemplary embodiment, the overlay target includes at least four cells, including a first cell and a second cell. The first cell may include a first layer and a second layer of structure 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 cell may include layers of structure having the first pitch and the second pitch in a reverse order relative to the first order. The first cell type and the second cell type may both include the first pitch and the second pitch, but the order of the pitches may be reversed relative to each other.

[0011] A method for generating an overlay measurement associated with an overlay target is disclosed. The method includes receiving first and second detection signals from one or more detectors from first and second cells of two or more cells of the overlay target. The first and second cells are defined as first and second cell types characterized by the order of structures in a layer, and the order is characterized by the pitch of the structures in the layer. An overlay measurement of the first cell is generated based on the first detection signal, and an overlay measurement of 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 second pitch of the first cell type are in reverse order relative to the first pitch and second pitch of the second cell type defined with respect to the depth direction of the sample. An overlay measurement associated with the overlay 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 is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of 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.

[0013] The many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Brief explanation of the drawings]

[0014] [Figure 1A] FIG. 1 is a conceptual diagram of an overlay metrology system in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram of an optical subsystem in accordance with one or more embodiments of the present disclosure. [Figure 2A] FIG. 1 is a conceptual diagram of an illumination pupil plane distribution of a circular illumination beam, in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 2B is a conceptual diagram of a collection pupil plane distribution of diffraction orders of the circular illumination beam of FIG. 2A in accordance with one or more embodiments of the present disclosure. [Figure 3] FIG. 1 is a schematic diagram of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 4] FIG. 1 is a top view of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 5] 10 is a data graph illustrating TIS error for various wavelengths for a single-cell target and a multi-cell inverted-pitch target in accordance with one or more embodiments of the present disclosure. [Figure 6A] FIG. 1 is a top view of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 6B] FIG. 1 is a top view of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 6C] FIG. 1 is a top view of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 6D] FIG. 1 is a schematic diagram of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 6E] FIG. 1 is a schematic diagram of an overlay target in accordance with one or more embodiments of the present disclosure. [Figure 7]FIG. 1 is a process flow diagram illustrating a method for overlay metrology using two or more cells in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present disclosure has been particularly shown and described with respect to certain embodiments and certain features thereof. The embodiments described herein are to be considered illustrative and not restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made therein without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings.

[0016] Overlay metrology can be performed using a variety of overlay metrology techniques. For example, techniques include a static move-and-measure mode, in which the sample remains stationary during measurement, and a scan mode, in which an illumination beam scans the sample during measurement. Scanning-based scatterometry techniques include a high-speed detector for capturing the time-varying interference signal generated as the sample is scanned. The detector can be positioned in the pupil plane at the overlap between selected diffraction orders to capture the time-varying interference signal as the sample is scanned. Various non-limiting scanning scattering overlay metrology techniques are described in U.S. Patent Application Publication No. 2022 / 0034652, filed February 17, 2021, U.S. Patent Application No. 17 / 119,536, filed December 11, 2020, U.S. Patent Application No. 17 / 708,958, filed March 30, 2022, and U.S. Patent Application No. 17 / 709,104, filed March 30, 2022, all of which are incorporated by reference in their entirety. It should be noted that such scanning examples are non-limiting and embodiments herein may include one or more detectors in the field plane, and may include various types of detectors, such as one or more diode array sensors.

[0017] Ideally, the time-varying diffraction signal follows a simple mathematical equation; however, in reality, the diffraction signal may contain TIS errors. TIS errors can be caused by a variety of factors. For example, TIS errors can be caused by nonuniformity 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. Nonuniformity of the illumination beam can be caused by contaminants on components (e.g., filters, lenses) in the illumination subsystem of the overlay metrology system. TIS errors can also be caused by other factors, such as misalignment of the illumination beam with respect to the sample. For single-cell diffraction signals, TIS errors can be difficult to determine using scanning mode.

[0018] Embodiments of the present disclosure relate to using an overlay metrology system to generate overlay measurements of an overlay target with suppressed TIS errors. Herein, TIS errors are believed to be correlated with the order of the cell grid, and reversing the grid order results in TIS errors of opposite magnitude. Using this principle, in embodiments, TIS errors can be "cancelled out" by averaging overlays of cells with opposite (i.e., reverse) grid order. For example, an overlay target may include a first cell and a second cell. The cell structures (e.g., grids) may be distributed on different layers of the sample, such that the structures overlap each other in each cell. The first cell may include structures with a first pitch on the first layer and structures with a second pitch on the second layer. The second cell may also include the same pitch, but in reverse order. Because the TIS errors of such cells will be of opposite magnitude, the overlay measurements of each cell may be averaged to generate overlay measurements with suppressed TIS errors.

[0019] FIG. 1A shows a conceptual diagram of an overlay metrology system 100 in accordance with one or more embodiments of the present disclosure.

[0020] Overlay metrology system 100 includes an optical subsystem 102 configured to acquire one or more images from a sample 104 for use in determining overlay measurements.

[0021] In an embodiment, overlay metrology system 100 includes a controller 122. Controller 122 may include one or more processors 124 and memory 126. For example, controller 122 may be configured to generate overlay measurements based on signals received from detectors of optical subsystem 102.

[0022] FIG. 1B shows a simplified schematic diagram of optical subsystem 102 in accordance with one or more embodiments of the present disclosure.

[0023] In an embodiment, the optical subsystem 102 includes an illumination subsystem 106 and a collection subsystem 110 .

[0024] 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 collection subsystem 110 is configured to collect light from the illuminated sample 104 (e.g., according to a metrology recipe). Furthermore, the one or more illumination beams 108 may be spatially restricted to illuminate selected portions of the sample 104. For example, each of the one or more illumination beams 108 may be spatially restricted to illuminate a specific cell of an overlay target.

[0025] For example, overlay metrology system 100 may be configured to image a particular type of sample according to a metrology recipe. For example, overlay metrology system 100 may be designed (configured) and / or programmed (e.g., programmed via program instructions) to calculate overlay measurements of a particular type of feature (e.g., a grating-over-grating target) of sample 104 according to the metrology recipe.

[0026] As previously described herein, overlay metrology system 100 may include one or more detectors 112. Depending on the embodiment, and unless otherwise specified, one or more detectors 112 may be used for scanning overlay metrology, static overlay metrology, or both, and may be used in conjunction with imaging and / or scatterometry techniques. In embodiments for scanning overlay metrology, one or more detectors 112 may generally include any type of photodetector known in the art suitable for capturing interference signals generated when sample 104 is translated by translation stage 116 and / or when one or more illumination beams 108 are scanned by optical subsystem 102. For example, one or more detectors 112 may be diode array sensors and / or charge-coupled device (CCD) sensors.

[0027] In an embodiment for scanning overlay metrology, one or more detectors 112 may be positioned at a collection pupil plane 114, as shown in FIG. 1B , for example. As another example, one or more detectors 112 may be positioned at a collection field plane 150. In such an example, one or more detectors 112 may be able to image the entire field plane of the entire overlay target. The field plane is conjugate with the object plane so that the sample 104 can be imaged from above.

[0028] In an embodiment, the optical subsystem 102 may include a translation stage 116 for scanning the sample 104 through a measurement field of view of the optical subsystem 102 during overlay measurements.

[0029] For example, performing scanning-based overlay metrology may include receiving detection signals from one or more detectors 112 while the sample 104 is moving, such that the detection signals are time-varying interference signals.

[0030] For static overlay metrology, in an embodiment, the one or more detectors include a multi-pixel sensor. For example, the multi-pixel sensor may be 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.

[0031] In an embodiment, the optical subsystem 102 may perform scatterometry overlay measurements on a portion of the sample 104 having an overlay target, such as, but not limited to, a grating-over-grating target.

[0032] In an embodiment, the structure of the cells may be configured to produce Moire diffraction orders (eg, +1st and -1st Moire diffraction orders).

[0033] It is recognized herein that the distribution of diffraction orders of the illumination beam 108 produced by a periodic structure (e.g., a grating-over-grating structure) can be affected by various 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 the elevation and azimuth directions, the period (i.e., pitch) of the periodic structure, or the numerical aperture (NA) of the collection lens. Accordingly, the illumination subsystem 106, the collection subsystem 110, and the overlay target 302 may be configured to provide an overlapping distribution of zeroth and first diffraction orders at the collection pupil plane 114 of the collection subsystem 110. For example, the illumination subsystem 106 and / or the collection subsystem 110 may be configured to generate measurements on a grating-over-grating structure having a selected range of periodicity that provides the overlapping distribution. Furthermore, various components of the illumination subsystem 106 and / or the collection subsystem 110 (e.g., an aperture, a pupil, etc.) may be adjustable to provide the overlapping distribution for a given structure.

[0034] The collection subsystem 110 may be configured to collect at least one of a zeroth diffraction order (eg, specular reflection) and + / −1st diffraction orders from the sample 104 associated with the diffraction of the illumination beam 108 .

[0035] In an embodiment, the optical subsystem 102 includes an objective lens 136 for focusing the illumination beam 108 onto the sample 104 (e.g., onto an overlay 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.

[0036] The optical subsystem may implement various illumination beam distributions. For example, the illumination beam 108 may be circular, annular, etc.

[0037] FIG. 2A shows a conceptual diagram of an illumination pupil plane distribution 200 of a circular illumination beam 204, in accordance with one or more embodiments of the present disclosure.

[0038] 2B shows a conceptual diagram of a collection pupil plane distribution 202 of diffraction orders of the circular illumination beam 204 of FIG. 2A in accordance with one or more embodiments of the present disclosure. For example, after the circular illumination beam 204 emanates from the sample 104, it may become a measurement beam and form circular diffraction orders at the collection pupil plane 114. The circular diffraction orders are illustrated by a zeroth (0) circular diffraction order 206a, a first (+1) circular diffraction order 206c, and a first (-1) circular diffraction order 206b. One or more detectors 112 may be positioned to capture overlapping regions 208a, 208b of such diffraction orders. For example, the detector 112 (e.g., a diode array sensor) may be positioned at the pupil plane 114 such that the one or more detectors 112 generally capture light from detection regions 210c, 210b. It should be noted that the detection regions 210c, 210b can be any size, such as smaller than, equal to, or larger than the overlapping regions 208a, 208b.

[0039] 3 shows a schematic diagram of an overlay target 302 on a sample 104, in accordance with one or more embodiments of the present disclosure. An illumination beam 108 is scanned along a scan direction 318. Scanning the overlay target 302 a length equal to the pitch of the grating-over-grating structure may result in a phase shift of 2π (in opposite directions) in each of the + / -1 diffraction orders, and the intensity captured by each of the one or more detectors 112 may oscillate through the interference pattern.

[0040] As shown, the illumination beam 108 may occupy a field of view smaller than the overlay target 302 itself. However, it should be understood that the overlay target 302 of FIG. 3 and the associated description are provided for illustrative purposes only and should not be construed as limiting. For example, an overlay target may include cells configured to be scanned along multiple scan directions. For example, the overlay target may include a first group of cells having periodicity along the X direction and a second group of cells having periodicity along the Y direction. In this manner, all cells within a particular cell group can be simultaneously imaged / detected while the sample 104 is scanned along the corresponding scan direction associated with that group. As another example, diagonal targets suitable for metrology measurements in orthogonal directions in a single scan are generally described in U.S. Patent Application Publication No. 2021 / 0364935, published November 25, 2021, and incorporated herein by reference in its entirety.

[0041] For purposes of this disclosure, some concepts may be better understood by referring to the "types" of cells rather than repeatedly detailing the limitations of each cell. For example, a first cell type and a second cell type may be defined such that the second cell type has a structure with a pitch that is the opposite order of the first cell type. Note that the first cell type may be referred to as a "P / Q" cell and the second cell type as a "Q / P" cell. For example, the first pitch may be "P" and the second pitch may be "Q." This concept may be described with reference to "first" and "second" pitches. In embodiments, the first cell type is characterized by the order of structures within a layer, which is characterized by the pitch of the structures within the layer. The second cell type is characterized by the second order of structures within a layer of the sample, which is characterized by the second pitch of the second structures within the layer. The pitch of the first cell type and the second pitch of the second cell type both include structures having the first pitch and structures having the second pitch, but the first pitch and second pitch of the first cell type are in reverse order relative to the first pitch and second pitch of the second cell type. This order may be defined with respect to the depth direction of the sample. For example, an upper layer of the sample may be "above" a lower layer in a relative sense. In this regard, the lattice structure having the first pitch may be above or below the lattice structure having the second pitch, and the order may be reversed in one cell type compared to the other cell type.

[0042] Referring again to FIG. 3, unless otherwise noted, the first cell 304 is of a first cell type and the second cell 306 is of a second cell type.

[0043] In an embodiment, the overlay target 302 includes a first cell 304 and a second cell 306. The first cell 304 includes a first layer with structures 310 having a first pitch and a second layer with structures 308 having a second pitch. The structures 310 are located on top of the structures 308 with respect to the depth of the sample 104. In an embodiment, the layers of the second cell 306 include, in reverse order, structures 312 having a first pitch and structures 314 having a second pitch. Note that the order is not necessarily limited to the example shown in FIG. 3 . For example, the first cell 304 and the second cell 306 may include any number of layers, such as any number of intermediate layers between the structures 308, 310, 312, and 314.

[0044] As another example, cells 304, 306 may include three or more layers (e.g., four or more, five or more, six or more, etc.) of different pitches, thereby allowing overlay between many layers to be measured. For example, a second cell may include all three layers in reverse order (e.g., with a pitch of 3, 2, 1 instead of a pitch of 1, 2, 3).

[0045] 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 the pitches in reverse order) can be applied to more than two pitches, such as two cells with pitches in the first and second layers of a sample (but in reverse order), two additional cells with pitches in the first and third layers, and two final cells with pitches in the second and third layers. In this regard, the overlay between all three layers can be determined.

[0046] 4 shows a top view of an overlay target 400 in accordance with one or more embodiments of the present disclosure. FIG. 4 may show the cells 304, 306 in a side-by-side (i.e., parallel) configuration rather than a sequential configuration. Note that the illumination beam 108 may need to be scanned twice across the overlay target 400, e.g., in a "c" shape. For example, after scanning the first cell 304, the illumination beam may move downward and then be scanned across the second cell 306. In other embodiments, two illumination beams 108 are used to simultaneously scan two parallel cells.

[0047] FIG. 5 shows a data graph 500 illustrating TIS error for various wavelengths for a single-cell target and a multi-cell inverted-pitch target, in accordance with one or more embodiments of the present disclosure.

[0048] As shown, the TIS error increases as the wavelength increases from 500 nm to 580 nm. Using embodiments of the present disclosure, the TIS error can be suppressed by greater than 70%, but is not limited to such a suppression level. As shown, the multi-cell TIS error 504 enabled 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).

[0049] The following equations pertain to overlay targets having two or more layers, such as overlay target 302 of Figure 3. The following equations may be compared to and similar to the equations set forth in U.S. patent application Ser. No. 17 / 709,200, filed March 30, 2022, which is incorporated herein by reference in its entirety, except for the additional TIS error term. However, the following equations show how an equal ratio of a first cell type to a second cell type allows the TIS error term to cancel out.

[0050] Canceling out TIS errors can be better understood by first understanding the TIS error terms for a single cell (e.g., the first cell 304 of FIG. 3) before understanding the second cell. For purposes of the following equations, the first cell 304 has a first (top) layer with structures 310 having a first pitch (p1) and a second (bottom) layer with structures 308 having a second pitch (p2).

[0051] The interference intensity can be modeled as a function of grating position (X)*2*pi / Pitch. The interference intensity measured by a detector at the overlap of the zeroth and first diffraction orders (e.g., corresponding to a time-varying signal) from structure 310 having a first pitch (P1) is:

number

[0052] The interference intensity measured at the overlap of the zeroth and first order diffractions from the structures 308 having the second pitch (P2) is:

number

[0053] where P1 is a first pitch of elements in a first layer, P2 is a second pitch of elements in a second layer, and A0, A1 correspond to the intensities of the zeroth and first diffraction orders, respectively, associated with pitch P1;

number

[0054] In general, the overlay of the first cell 304 is as follows:

number

[0055] Unfortunately, if the illumination is not perfectly uniform, another term, ρ, associated with the TIS error, is added to the interference equation.

number

number

[0056] This additional phase (ρ1 and ρ2) ultimately adds a constant value to the resulting OVL over time, also known as the TIS error.

number

[0057] The above equation is for a first cell 304, which may also be referred to as a "P / Q" cell. To overcome TIS errors, the order of pitches in the structure of the first cell 304 may be reversed to create a second cell 306. The second cell 306 is a second type of cell, which may also be referred to as a "Q / P" cell.

[0058] The resulting overlay formula for such a cell is:

number

[0059] Therefore, by averaging both results, TIS errors caused by illumination contamination can be eliminated.

number

[0060] 6A-6E show top views of an overlay target according to one or more embodiments of the present disclosure.

[0061] FIG. 6A shows a top view of a night overlay target 602 in accordance with one or more embodiments of the present disclosure.

[0062] In an embodiment, the two or more cells include at least three cells in sequence (i.e., X1, X2, and Y1) and a fourth cell (i.e., Y2) adjacent to the third cell (i.e., Y1) of the at least three cells. The first cell (X1) and the second cell (X2) of the at least three cells are configured for use with a scanning direction (e.g., an X scanning direction), and the fourth cell and the third cell are configured for use with a different scanning direction (e.g., a Y scanning direction).

[0063] FIG. 6B shows a top view of a denim overlay target 604 in accordance with one or more embodiments of the present disclosure.

[0064] Note that periodicity along the scan direction may include periodicity at a non-zero angle relative to the scan direction.

[0065] A potential issue with the denim overlay target 604 shown in Figure 6B is TIS error. Therefore, for a pitch 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 overlay in two directions (e.g., X-direction overlay and Y-direction overlay) in a single scan, which also reduces TIS error.

[0066] 6C shows a top view of a Bishop overlay target 606 according to one or more embodiments of the present disclosure. In an embodiment, the two or more cells include four aligned cells 304, 614, 306, 616. The four cells include a first cell 304 (of a first cell type) and a corresponding third cell 306 (of a second cell type). The first cell 304 and the third cell 306 both include periodic structures at a positive 45-degree angle from the scan direction. Note that in this example, the second cell 614 corresponds to the fourth cell 616, rather than the first cell 304 as in other examples of the present disclosure. The second cell 614 and the corresponding fourth cell 616 include periodic structures at a negative 45-degree angle and may include pitches in reverse order relative to each other. The second cell 614 and the corresponding fourth cell 616 may correspond to diffraction orders that exhibit overlay in the X direction (horizontal in FIG. 6C), while the first cell 304 and the corresponding third cell 306 may correspond to diffraction orders that exhibit overlay in the Y direction (vertical in FIG. 6C). In this regard, the overlay target of FIG. 6C may enable a "single" scan to generate overlay in both the X and Y directions.

[0067] FIG. 6D shows a schematic diagram of a waffle overlay target 608 in accordance with one or more embodiments of the present disclosure.

[0068] In an embodiment, two or more cells of the overlay target include waffle cells 610 having periodic structures in the same layer at positive and negative 45 degrees from the scanning direction, thereby forming a waffle pattern.

[0069] 6E shows a schematic diagram of a waffle overlay target 612, according to one or more embodiments of the present disclosure. In an embodiment, two waffle cells 610 may be arranged sequentially and / or in parallel.

[0070] In embodiments, scanning may be performed by 1) adjusting the optics of the optical subsystem 102 (e.g., the objective lens 136 or any other optics) and / or 2) moving the sample 104 via the translation stage 116. Note that adjusting the illumination beam 108 to scan the sample 104 can result in a TIS error because imperfect beam translation can cause errors in the vertical alignment of the illumination beam 108 and the sample 104. The amount of TIS error can vary as a function of the amount of beam translation performed. In embodiments, this TIS error can be addressed by using multiple pairs of cells (e.g., a first cell type 304 and a corresponding second cell type 306) to account for differences in the alignment of the illumination beam 108. For example, an overlay target for use with an illumination beam 108 translated using an optics system may include multiple pairs of aligned cells 304, 306.

[0071] 7 shows a process flow diagram of a method 700 for overlay metrology using two or more cells, in accordance with one or more embodiments of the present disclosure. It is noted that embodiments and enabling techniques described herein above in the context of overlay metrology system 100 should be construed to extend to method 700 as well. It is further noted herein that the steps of method 700 may be performed in whole or in part by overlay metrology system 100. However, it is further recognized that method 700 is not limited to overlay metrology system 100, in that additional or alternative system-level embodiments may perform all or a portion of the steps of method 700.

[0072] In step 702, a first detected signal from the first cell 304 is received from one or more detectors 112. For example, the first detected signal may be a signal generated by one or more detectors 112. For example, when the first cell 304 is scanned, one detector 112 may be positioned in each overlapping region 208a, 208b shown in FIG. 2B. For example, the controller 122 may be configured to receive such first detected signals (e.g., as data stored in memory).

[0073] In step 704 , a second detected signal is received from one or more detectors 112 during scanning of the second cell 306 .

[0074] In step 706, an overlay measurement associated with the overlay target 302 is generated based on a value indicating the 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 described above, and the second cell 306 may be of the second cell type described above (i.e., with an inverse pitch order). In this regard, by averaging the results, the overlay can reduce TIS errors.

[0075] In an optional step, a tool-induced error (TIS) error of the overlay target 302 is determined based on the difference between the overlay measurement of the first cell and the overlay measurement of the second cell. The TIS error may be a function of half the absolute value of the overlay measurement of the first cell minus the second overlay measurement.

[0076] In an optional step, at least one of intensity or phase information associated with the time-varying interference signal is extracted using a phase-locking technique, and an overlay error between the first and second layers of the sample is determined based on the 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 further detail in one or more of the references previously incorporated by reference herein.

[0077] 1A-1B, additional components of the optical subsystem 102 are described in accordance with one or more embodiments of the present disclosure. For example, the controller 122 and processor 124, as well as various optical components, are described in detail below for general overlay metrology (i.e., not specific to scanning or static overlay metrology, unless otherwise noted).

[0078] In an embodiment, the controller 122 generates (or determines) an overlay measurement between layers (e.g., between a first layer and a second layer) of the overlay target 302 along the measurement direction based on a comparison of the detected signals. For example, the controller 122 may compare the magnitude and / or phase of the detected signals to generate the overlay measurement. For example, U.S. Pat. No. 10,824,079, issued November 3, 2020, and incorporated herein by reference in its entirety, generally describes diffraction orders at a collection pupil and further provides a specific relationship between overlay and measured intensity at the pupil plane. It is contemplated herein that the systems and methods disclosed herein may extend the teachings of U.S. Pat. No. 10,824,079 to detection signals captured by one or more detectors positioned in the overlap region between the 0th and + / -1st diffraction orders. In particular, it is contemplated herein that overlay on a sample may be proportional to the relative phase shift between two detected signals. In another example, the relative intensities of the diffraction orders at the pupil plane may be extracted from the detected signals. In this way, any overlay algorithm based on relative intensity differences of diffraction orders known in the art may be applied to generate overlay measurements.

[0079] In an embodiment, overlay metrology system 100 includes a controller 122 communicatively coupled to optical subsystem 102. Controller 122 may include one or more processors 124 and a memory device 126, or memory. For example, one or more processors 124 may be configured to execute a set of program instructions stored in memory device 126.

[0080] The one or more processors 124 of the controller 122 may generally include any processor or processing element known in the art. For 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 memory). In one embodiment, the one or more processors 124 may be embodied as a desktop computer, mainframe computer system, workstation, image computer, parallel processor, networked computer, or any other computer system configured to execute programs configured to operate or in conjunction with the overlay metrology system 100, as described throughout this disclosure. Furthermore, different subsystems of overlay metrology system 100 may include processors or logic elements suitable for performing at least some of the steps described in this disclosure. Accordingly, the above description should not be construed as a limitation on embodiments of the present disclosure, but merely as examples. Furthermore, the steps described throughout this disclosure may be performed by a single controller, or alternatively, by multiple controllers. Additionally, controller 122 may include one or more controllers housed within 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 system 100.Additionally, the controller 122 may analyze or otherwise process data received from one or more detectors 112 and provide the data to additional components within the overlay metrology system 100 or external to the overlay metrology system 100 .

[0081] Additionally, memory device 126 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 124. For example, memory device 126 may include a non-transitory memory medium. As additional examples, memory device 126 may include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, and the like. It is further noted that memory device 126 may be housed within a common controller housing along with one or more processors 124.

[0082] In this regard, the controller 122 may perform any of a variety of 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 swaths to scan one or more overlay targets through a measurement field of view of the optical subsystem 102. As another example, the controller 122 may be configured to receive signals corresponding to detection signals from the one or more detectors 112. As another example, the controller 122 may generate correctable values ​​for one or more additional manufacturing devices as feedback and / or feedforward control of the one or more additional manufacturing devices based on the overlay measurements from the optical subsystem 102.

[0083] In an embodiment, the controller 122 captures the detected signals detected by the one or more detectors 112. The controller 122 may generally capture data such as, but not limited to, the magnitude or phase of the detected signals using any technique known in the art, such as, but not limited to, one or more phase-locked loops. Additionally, the controller 122 may capture the detected signals (e.g., the detection signals) or any data associated with the detected signals using any combination of hardware (e.g., circuitry) or software techniques.

[0084] Referring again to FIG. 1B, various components of optical subsystem 102 are described in more detail, in accordance with one or more embodiments of the present disclosure.

[0085] 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 one or more selected wavelengths of light, including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0086] In an embodiment, the illumination subsystem 106 includes one or more optical components suitable for modifying and / or conditioning the illumination beam 108 and for directing the illumination beam 108 toward the sample 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., for collimating the illumination beam 108 or for relaying the illumination pupil plane 120 and / or the illumination field plane 132, etc.). In another embodiment, the illumination subsystem 106 includes one or more illumination control optics 134 for shaping or otherwise controlling the illumination beam 108. For example, the illumination control optics 134 may include, but are not limited to, one or more field diaphragms, one or more pupil diaphragms, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, etc.).

[0087] 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 be incident on different portions of the sample 104 (e.g., different cells of the overlay target 302) within the measurement field of view (e.g., the field of view of the objective lens 136), although this is not required. It is contemplated herein that the two or more illumination beams 108 may be generated using various techniques. In one embodiment, the illumination subsystem 106 includes two or more apertures in the illumination field plane 132. In another embodiment, the illumination subsystem 106 includes one or more beam splitters for splitting 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 can be considered to be part of a different illumination channel, regardless of the technique by which the various illumination beams 108 are generated.

[0088] The collection subsystem 110 may include one or more optical elements 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 or to relay a pupil plane and / or a field plane, etc.), which may, but need not, include the objective lens 136. In another embodiment, the collection subsystem 110 includes one or more collection control optics 142 for shaping or otherwise controlling the collected light 138. For example, the collection control optics 142 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, etc.). In another example, the collection subsystem 110 may include one or more collection viewing planes 150 .

[0089] In an embodiment, the collection subsystem 110 includes two or more collection channels 144, each having a respective detector 112 (or multiple detectors 112). For example, the optical subsystem 102 may include one or more beam splitters 146 positioned to split the collected light 138 among the collection channels 144. Furthermore, the beam splitters 146 may be polarizing beam splitters, non-polarizing beam splitters, or a combination thereof.

[0090] In embodiments, the multiple collection channels 144 are configured to collect light from multiple illumination beams 108 on the sample 104. For example, if the overlay target 302 has two or more parallel cells distributed in a direction different from the scanning direction, the optical subsystem 102 may simultaneously illuminate different cells with different illumination beams 108 and simultaneously capture detection signals associated with each illumination beam 108. Furthermore, in some embodiments, the multiple illumination beams 108 directed at the sample 104 may have different polarizations. In this manner, the diffraction orders associated with each illumination beam 108 can be separated. For example, a polarizing beam splitter 146 may efficiently separate the diffraction orders associated with the different illumination beams 108. As another example, a polarizer may be used in one or more collection channels 144 to isolate desired diffraction orders for measurement.

[0091] 1A , it is noted herein that one or more components of overlay metrology system 100 may be communicatively coupled to various other components of system 100 in any manner known in the art. For example, one or more processors 124 may be communicatively coupled to each other and to the other components via wired (e.g., copper wire, fiber optic cable, etc.) or wireless connections (e.g., RF coupling, IR coupling, WiMax, Bluetooth, 3G, 4G, 4G LTE, and 5G, etc.). As another example, controller 122 may be communicatively coupled to one or more components of optical subsystem 102 via any wired or wireless connection known in the art.

[0092] In one embodiment, the one or more processors 124 may include any one or more processing elements 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 comprise a desktop computer, mainframe computer system, workstation, image computer, parallel processor, or other computer system (e.g., networked computer) configured to execute programs configured to operate the overlay metrology system 100 as described throughout this disclosure. It should be appreciated that the steps described throughout this disclosure may be performed by a single computer system or, alternatively, by multiple computer systems. Furthermore, it should be appreciated that the steps described throughout this disclosure may be performed in any one or more of the one or more processors 124. In general, the term “processor” may be broadly defined to encompass any device having one or more processing elements that execute program instructions from memory 126. Additionally, different subsystems of overlay metrology system 100 may include processors or logic elements suitable for performing at least some of the steps described throughout this disclosure. Accordingly, the above description should not be construed as a limitation on the present disclosure, but merely as an example.

[0093] Those skilled in the art will recognize that the components (e.g., operations), devices, objects, and their accompanying descriptions described herein are used as examples for conceptual clarity, and that various configurational variations are possible. Accordingly, the specific examples used herein and the accompanying descriptions are intended to be representative of their more general genus. In general, the use of any specific example is intended to be representative of that genus, and the absence of a particular component (e.g., operation), device, or object should not be construed as limiting.

[0094] Those skilled in the art will understand that there are various means (e.g., hardware, software, and / or firmware) by which the processes and / or systems and / or other techniques described herein may be implemented, and that the preferred means will vary depending on the context in which the processes and / or systems and / or other techniques are deployed. For example, if an implementer determines that speed and accuracy are most important, the implementer may select a primarily hardware and / or firmware means; alternatively, if flexibility is most important, the implementer may select a primarily software implementation, or, still alternatively, the implementer may select some combination of hardware, software, and / or firmware. Thus, there are multiple possible means by which the processes and / or devices and / or other techniques described herein may be implemented, and any means utilized is a choice that depends on the context in which the means is deployed and the implementer's particular concerns (e.g., speed, flexibility, or predictability); no means is inherently better than another, in that these concerns may vary.

[0095] The foregoing description is presented to enable one skilled in the art to make and use the invention in the context of a particular application and its 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. Thus, the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0096] With respect to the use of virtually any plural and / or singular term herein, those skilled in the art can convert from plural to singular and / or from singular to plural as appropriate depending on the context and / or application. The various singular / plural permutations are not expressly set forth herein for the sake of clarity.

[0097] All of the methods described herein may include storing results of one or more steps of a method embodiment in memory. The results may include any of the results 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 results are stored, they can be accessed in memory, used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. Furthermore, the results may be stored "permanently," "semi-permanently," "temporarily," or for a period of time. For example, the memory may be random access memory (RAM), and the results may not necessarily be retained in memory indefinitely.

[0098] It is further contemplated that each of the above method embodiments may include any other step(s) of any other method(s) described herein. Furthermore, each of the above method embodiments may be performed by any of the systems described herein.

[0099] The subject matter described herein may depict different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that many other architectures that achieve the same functionality may actually be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is substantially "associated" such that the desired functionality is achieved. Thus, any two components combined herein to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intervening components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" with each other to achieve the desired functionality, and any two components that can be associated in this way can also be considered to be "couplable" with each other to achieve the desired functionality. Examples of what can be coupled include, but are not limited to, physically compatible and / or physically interacting components, wirelessly interacting and / or wirelessly interacting components, and / or logically interacting and / or logically interacting components.

[0100] It should further be understood that the present invention is defined by the appended claims. Those skilled in the art will generally understand that the terms used herein, particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "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," and 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 introduced claim recitations are intended, such intention will be explicitly stated in the claim, and that, absent such recitation, no such intention exists. For example, as an aid to understanding, the following appended claims may include the introductory phrases "at least one" and "one or more" to introduce the claim recitations. However, the use of such phrases should not be construed as limiting any particular claim containing such introduced claim recitation to an invention containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should generally be interpreted to mean "at least one" or "one or more"). The same applies to definite articles used to introduce claim recitations. In addition, even when a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that such a recitation should generally be interpreted to mean at least the recited number (e.g., the mere recitation of "two recitations" without any other modifier generally means at least two recitations, or more than two recitations).Furthermore, when phrases similar to "at least one of A, B, and C, and the like" are used, generally such configurations are intended in the sense that one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having only A, only B, only C, a combination of A and B, a combination of A and C, a combination of B and C, and / or a combination of A, B, and C, etc.). When phrases similar to "at least one of A, B, or C, and the like" are used, generally such configurations are intended in the sense that one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having only A, only B, only C, a combination of A and B, a combination of A and C, a combination of B and C, and / or a combination of A, B, and C, etc.). Those skilled in the art will further appreciate that virtually any disjunctive word and / or phrase presenting two or more alternative terms in the description, claims, or drawings should be understood to contemplate the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" is understood to include the possibilities of "A" or "B" or "A and B."

[0101] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in form, construction, and arrangement of components can be made without departing from the disclosed subject matter or sacrificing all of its important advantages. The described forms are merely illustrative, and it is the intent of the following claims to encompass and cover all such modifications. It is to be further understood that the invention is defined by the appended claims.

Claims

1. 1. An overlay metrology system, comprising: a controller, the controller including one or more processors; receiving a first detection signal from the one or more detectors from a first cell of the two or more cells of the overlay target; receiving a second detection signal from the one or more detectors from a second cell of the two or more cells; generating an overlay measurement of the first cell based on the first detection signal; generating an overlay measurement for the second cell based on the second detection signal; generating an overlay measurement associated with the overlay target based on a value indicative of an average of the overlay measurement of the first cell and the overlay measurement of the second cell; a controller comprising the one or more processors configured to execute program instructions that cause a metrology recipe to be executed by Equipped with the first cell is defined as a first cell type characterized by an order of structures within a layer, the order being characterized by a pitch of the structures within the layer; the second cell is defined as a second cell type characterized by a second order of second structures within the layer, the second order being characterized by a second pitch of the second structures within the layer; the pitch of the first cell type and the second pitch of the second cell type both comprise a first pitch and a second pitch, but 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 of the second cell type defined with respect to the depth direction of the sample. Overlay measurement system.

2. 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 equipment caused error (TIS) error of the overlay target based on a difference between the overlay measurement of the first cell and the overlay measurement of the second cell.

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

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

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

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

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

8. The overlay metrology system of claim 1 , wherein the illumination beam has an illumination pupil plane distribution that 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 with respect to a scan direction.

10. 10. The overlay metrology system of claim 9, wherein the two or more cells of the overlay target comprise waffle cells having periodic structures in the same layer at positive 45 degrees and negative 45 degrees from the scanning direction, thereby forming a waffle pattern.

11. 10. The overlay metrology system of claim 9, wherein the two or more cells comprise four cells in a row, the four cells in a row comprising two adjacent first cell types having the structures at a positive diagonal angle with respect to the scan direction and two adjacent second cell types having the structures at a negative diagonal angle with respect to the scan direction.

12. 10. The overlay metrology system of claim 9, wherein the two or more cells comprise at least three cells aligned in a row and a fourth cell adjacent to a third cell of the at least three cells, wherein a first and second cell of the at least three cells are configured to be used in the scan direction, and the fourth cell and the third cell are configured to be used in a different scan direction orthogonal to the scan direction.

13. The overlay metrology system of claim 1 , wherein the two or more cells comprise three or more layers of different pitches.

14. 10. The overlay metrology system of claim 1, wherein said receiving the first detected signal and said receiving the second detected signal generally comprises receiving a time-varying interference signal as the overlay target is scanned along a scan direction.

15. 2. The overlay metrology system of claim 1, wherein the first location comprising the first detector comprises a location of +1 order Moire diffraction, and the second location comprising the second detector comprises a location of −1 order Moire diffraction.

16. The controller instructs the one or more processors to: extracting at least one of intensity or phase information associated with the time-varying interference signal using a phase-locked technique; determining the overlay error between the first and second layers of the sample based on at least one of intensity or phase information; 2. The overlay metrology system of claim 1, configured to execute the program instructions that cause the metrology recipe to be executed by:

17. 1. An overlay metrology system, comprising: a lighting subsystem comprising: an illumination source configured to generate an illumination beam a lighting subsystem comprising: a collection subsystem, one or more detectors; an objective lens configured to collect measurement light emitted from the sample in response to the illumination beam as the sample is scanned along a scan direction, the sample comprising an overlay target according to a metrology recipe, the overlay target comprising two or more cells with a structure having a periodicity along the scan direction; and a collection subsystem comprising: a controller communicatively coupled to the collection subsystem, the controller instructing one or more processors to: receiving a first detection signal from the one or more detectors from a first cell of the two or more cells; receiving a second detection signal from the one or more detectors from a second cell of the two or more cells; generating an overlay measurement of the first cell based on the first detection signal; generating an overlay measurement for the second cell based on the second detection signal; generating an overlay measurement associated with the overlay target based on a value indicative of an average of the overlay measurement of the first cell and the overlay measurement of the second cell; a controller comprising the one or more processors configured to execute program instructions that cause the metrology recipe to be executed by Equipped with the first cell is defined as a first cell type characterized by an order of the structures within a layer, the order being characterized by a pitch of the structures within the layer; the second cell is defined as a second cell type characterized by a second order of second structures within the layer, the second order being characterized by a second pitch of the second structures within the layer; the pitch of the first cell type and the second pitch of the second cell type both comprise a first pitch and a second pitch, but 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 of the second cell type defined with respect to the depth direction of the sample. Overlay measurement system.

18. 20. 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 equipment caused error (TIS) error of the overlay target based on a difference between the overlay measurement of the first cell and the overlay measurement of the second cell.

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

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

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

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

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

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

25. 20. 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 with respect to the scanning direction.

26. 26. The overlay metrology system of claim 25, wherein the two or more cells of the overlay target comprise waffle cells having periodic structures in the same layer at positive 45 degrees and negative 45 degrees from the scanning direction, thereby forming a waffle pattern.

27. 26. The overlay metrology system of claim 25, wherein the two or more cells comprise at least four cells in a row, the at least four cells in a row comprising at least two adjacent first cell types having the structures at a positive diagonal angle with respect to the scan direction and at least two adjacent second cell types having the structures at a negative diagonal angle with respect to the scan direction.

28. 26. The overlay metrology system of claim 25, wherein the two or more cells comprise at least three cells aligned in a row and a fourth cell adjacent a third cell of the at least three cells, the first cell and the second cell of the at least three cells being configured to be used in the scan direction, and the fourth cell and the third cell being configured to be used in a different scan direction orthogonal to the scan direction.

29. 20. The overlay metrology system of claim 17, wherein the two or more cells comprise three or more layers of different pitches.

30. 20. The overlay metrology system of claim 17, wherein said receiving said first detected signal and said receiving said second detected signal generally comprises receiving a time-varying interference signal as said overlay target is scanned along said scan direction.

31. 18. The overlay metrology system of claim 17, wherein the first location comprising the first detector comprises a location of +1 order Moire diffraction, and the second location comprising the second detector comprises a location of −1 order Moire diffraction.

32. The controller instructs the one or more processors to: extracting at least one of intensity or phase information associated with the time-varying interference signal using a phase-locked technique; determining the overlay error between the first and second layers of the sample based on at least one of intensity or phase information; 20. The overlay metrology system of claim 17, configured to execute the program instructions that cause the metrology recipe to be executed by:

33. an overlay target, Four cells aligned in a row, a first cell and a third cell each having a periodic structure at a positive 45° angle from the scanning direction; a second cell and a fourth cell each having a periodic structure at an angle of negative 45 degrees from the scanning direction; Four aligned cells comprising: Equipped with the first cell and the second cell are of a first cell type, and the third cell and the fourth cell are of a second cell type; the first cell type is characterized by an order of structures within a layer, the order being characterized by a pitch of the structures within the layer, 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 within the layer; the pitch of the first cell type and the second pitch of the second cell type both comprise a first pitch and a second pitch, but 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 of the second cell type defined with respect to the depth direction of the sample. Overlay target.

34. 1. A method comprising: receiving a first detection signal from one or more detectors from a first cell of two or more cells of an overlay target of a sample comprising a structure having periodicity along a scan direction; receiving a second detection signal from the one or more detectors from a second cell of the two or more cells; generating an overlay measurement of the first cell based on the first detection signal; generating an overlay measurement for the second cell based on the second detection signal; generating an overlay measurement associated with the overlay target based on a value indicative of an average of the overlay measurement of the first cell and the overlay measurement of the second cell; Including, the first cell is defined as a first cell type characterized by an order of the structures within a layer, the order being characterized by a pitch of the structures within the layer; the second cell is defined as a second cell type characterized by a second order of second structures within the layer, the second order being characterized by a second pitch of the second structures within the layer; the pitch of the first cell type and the second pitch of the second cell type both comprise a first pitch and a second pitch, but 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 of the second cell type defined with respect to the depth direction of the sample. method.

35. determining a tool-induced error (TIS) error of the overlay target based on a difference between the overlay measurement of the first cell and the overlay measurement of the second cell; 35. The method of claim 34, further comprising:

Images