Imaging overlay targets using moire elements and rotationally symmetric arrays - Patents.com

Abstract

The metrology target may include a first rotationally symmetric working zone with one or more instances of a first pattern and a second rotationally symmetric working zone with one or more instances of a second pattern, wherein at least one of the first and second patterns is a Moiré pattern formed from a first grating structure on the first specimen layer having a first pitch along the measurement direction and a second grating structure on the second specimen layer having a second pitch along the measurement direction that is different from the first pitch. The centers of rotational symmetry of the first and second working zones may be intentionally overlapped when the overlay error between the first and second specimen layers is zero. A difference between the centers of rotational symmetry of the first and second working zones may indicate an overlay error between the first and second specimen layers.

Description

[Technical field]

[0001] This disclosure relates generally to imaging overlay metrology, and more specifically to imaging overlay targets having Moire elements. [Background technology]

[0002] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62 / 898,980, filed September 11, 2019, and entitled “IMAGING OVERLAY TARGETS INCLUDING MOIRE ELEMENTS AND ROTATIONAL SYMMETRY ARRANGEMENTS” by Yoel Feler, Mark Ghinovker, Diana Shaphirov, Evgeni Gurevich and Vladimir Levinski, which is incorporated herein by reference in its entirety.

[0003] This application also claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62 / 954,256, filed December 27, 2019, entitled “IMAGING OVERLAY TARGETS INCLUDING MOIRE ELEMENTS AND ROTATIONAL SYMMETRY ARRANGEMENTS” by Yoel Feler, Mark Ghinovker, Diana Shaphirov, Evgeni Gurevich and Vladimir Levinski, which is incorporated herein by reference in its entirety.

[0004] As design rules shrink and specifications for overlay metrology become tighter, there is an increasing demand for sensitivity and robustness in overlay metrology methods. Typically, overlay metrology is performed by creating dedicated metrology targets with features fabricated in multiple sample layers of interest. Analysis of the fabricated metrology targets can then provide a measurement of the overlay error (e.g., relative alignment error) between the sample layers of interest. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 7,440,105 [Patent Document 2] U.S. Patent No. 7,349,105 [Patent Document 3] US Patent Application Publication No. 2018 / 0188663 [Patent Document 4] U.S. Patent No. 7,068,833 [Patent Document 5] U.S. Patent No. 6,921,916 [Patent Document 6] U.S. Patent No. 7,177,457 Summary of the Invention [Problem to be solved by the invention]

[0006] Although a variety of overlay metrology target designs have been proposed, there is a continuing need for improved metrology target designs and measurement methods that allow for accurate and efficient analysis of the produced metrology targets. [Means for solving the problem]

[0007] In accordance with one or more exemplary embodiments of the present disclosure, a metrology target is disclosed. In an exemplary embodiment, the target has a rotationally symmetric first working zone having one or more instances of a first pattern therein. In an exemplary embodiment, the target has a rotationally symmetric second working zone having one or more instances of a second pattern therein. In an exemplary embodiment, at least one of the first and second patterns is a Moiré pattern formed by a first grating structure on the first specimen layer having a first pitch along the measurement direction and a second grating structure on the second specimen layer having a second pitch along the measurement direction that is different from the first pitch. In an exemplary embodiment, the rotationally symmetric center of the first working zone and the rotationally symmetric center of the second working zone overlap when an overlay error between the first and second specimen layers is zero. Additionally, in one demonstrative embodiment, a difference between the centers of rotational symmetry of the first working zone and the centers of rotational symmetry of the second working zone along the measurement direction is indicative of an overlay error between the first and second specimen layers along the measurement direction.

[0008] A metrology system is disclosed in accordance with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, the system includes a controller configured to be coupled to an imaging system. In an exemplary embodiment, the controller receives an image of a metrology target on the specimen. In an exemplary embodiment, the target has a rotationally symmetric first working zone having one or more instances of a first pattern therein. In an exemplary embodiment, the target has a rotationally symmetric second working zone having one or more instances of a second pattern therein. In an exemplary embodiment, at least one of the first and second patterns is a Moiré pattern formed by a first grating structure on the first specimen layer having a first pitch along the measurement direction and a second grating structure on the second specimen layer having a second pitch along the measurement direction that is different from the first pitch. In an exemplary embodiment, the controller determines a difference between the axes of symmetry of the first and second working zones along the measurement direction in the image. Additionally, in one demonstrative embodiment, the controller calculates overlay error along the measurement direction for the first and second specimen layers by adjusting for the difference along the measurement direction between the axes of symmetry of the first and second working zones with a moiré gain based on the pitch of the moiré pattern.

[0009] In accordance with one or more exemplary embodiments of the present disclosure, a metrology target is disclosed. In an exemplary embodiment, the target has a rotationally symmetric working zone with one or more instances of a moiré pattern present therein. In an exemplary embodiment, the moiré pattern presents a grating structure on a first specimen layer with a first pitch (p1) along a measurement direction and a grating structure on a second specimen layer with a second pitch (p2) along the measurement direction that is different from the first pitch. In an exemplary embodiment, an overlay error along the measurement direction for the first specimen layer and the second specimen layer corresponds to a difference between an axis of symmetry of an image of the first working zone with an imaging system of a first optical configuration and an axis of symmetry of an image of the first working zone with an imaging system of a second optical configuration adjusted by a moiré gain based on a pitch value of the first moiré pattern. Also, in one illustrative embodiment, moire fringes can be detected with the first optical configuration, and at least one of a grating structure having a first pitch and a grating structure having a second pitch can be detected with the second optical configuration.

[0010] A metrology system is disclosed according to one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, the system includes an imaging system. In an exemplary embodiment, the imaging system includes an illumination source that generates illumination. In an exemplary embodiment, the imaging system includes one or more illumination optics that direct illumination from the illumination source to a metrology target. In an exemplary embodiment, the metrology target has a rotationally symmetric working zone with one or more instances of a moiré pattern present therein. In an exemplary embodiment, the moiré pattern includes a grating structure on a first specimen layer having a first pitch (p1) along a measurement direction and a grating structure on a second specimen layer having a second pitch (p2) along the measurement direction that is different from the first pitch. In an exemplary embodiment, the imaging system includes a detector that generates an image of the metrology target based on illumination from the illumination source, and the optical configuration of the imaging system is configurable. In some illustrative embodiments, the optical configuration includes a wavelength of the illumination, a polarization of the illumination incident on the metrology target, an angle of the illumination incident on the metrology target, or a focal position of the metrology target relative to the detector. In some illustrative embodiments, the system includes a controller configured to be coupled to the imaging system. In some illustrative embodiments, the controller receives a first image of the metrology target on the specimen using a first optical configuration. In some illustrative embodiments, the controller identifies a first axis of symmetry of the working zone along the measurement direction based on the first image. In some illustrative embodiments, the controller receives a second image of the metrology target on the specimen using a second optical configuration different from the first optical configuration. In some illustrative embodiments, the controller identifies a second axis of symmetry of the working zone along the measurement direction based on the second image.In one example embodiment, the controller determines an optical overlay measurement based on the difference between the first and second axes of symmetry, and in one example embodiment, the controller calculates an overlay error along the measurement direction for the first and second sample layers by adjusting the difference between the axes of symmetry in the first and second images by a moiré gain based on the pitch of the moiré pattern.

[0011] A method for designing a moire metrology target in accordance with one or more exemplary embodiments of the present disclosure is disclosed. In an exemplary embodiment, the method receives a design of a metrology target, the target having working zones with one or more non-overlapping instances of a moire pattern, the moire pattern being comprised of a first grating structure on a first specimen layer having a first pitch (p1) along a measurement direction and a second grating structure on a second specimen layer having a second pitch (p2) along the measurement direction that is different from the first pitch. In an exemplary embodiment, the method receives an optical configuration of an imaging system for imaging the metrology target. In an exemplary embodiment, the method performs a design of experiments to select a set of target design parameters for the metrology target, in particular a set of target design parameters including the first pitch and the second pitch, that when imaged by the imaging system results in a moire fringe pattern that meets selected design criteria.

[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] Those skilled in the art will be able to better appreciate the many advantages of the present disclosure by reviewing the accompanying drawings, in which: [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram of a weighing system according to one or more embodiments of the present disclosure. [Figure 2A] FIG. 13 is a top view block diagram of a metrology target having a moiré pattern based on a grating-over-grating structure within multiple rotationally symmetric working zones in accordance with one or more embodiments of the present disclosure. [Figure 2B] FIG. 2B is a conceptual diagram of a multi-layer grating structure in the Moire pattern of FIG. 2A in accordance with one or more embodiments of the present disclosure. [Figure 2C] FIG. 2C is a top view of a metrology target according to FIGS. 2A and 2B for measurement along two orthogonal directions in accordance with one or more embodiments of the present disclosure. [Figure 3A] FIG. 1 is a flow diagram depicting steps performed in a method for measuring overlay in accordance with one or more embodiments of the present disclosure. [Figure 3B] FIG. 13 is a flow diagram illustrating a method for identifying an axis of symmetry for a working group. [Figure 4] FIG. 2D is a top view of the metrology target of FIG. 2C with additional markings illustrating application of the method according to one or more embodiments of the present disclosure. [Diagram 5] FIG. 2 is a top view of a metrology target in accordance with one or more embodiments of the present disclosure, the target having a first working zone with two instances of a first moiré pattern and a second working zone with two instances of a second moiré pattern. [Figure 6] FIG. 2 is a top view of a metrology target in accordance with one or more embodiments of the present disclosure, the metrology target having a first working zone with two instances of a first moiré pattern and a second working zone with a single instance of a second moiré pattern. [Figure 7]FIG. 2A is a top view of a hybrid metrology target for measurements along two orthogonal directions in accordance with one or more embodiments of the present disclosure, where the measurements in each direction rely on one working zone having one or more moiré patterns and another working zone having one or more single layer structures. [Figure 8] FIG. 2 is a top view of a metrology target for measurement along a single direction in accordance with one or more embodiments of the present disclosure, the metrology target having a first working zone with two instances of a first moiré pattern and a second working zone with two instances of a single layer grating structure. [Figure 9] FIG. 1 illustrates a top view of a metrology target for measurement along a single direction in accordance with one or more embodiments of the present disclosure. [Figure 10] FIG. 2 illustrates a top view of a moiré rain box metrology target in accordance with one or more embodiments of the present disclosure showing a single instance of a moiré pattern in a first working zone and a non-periodic monolayer structure surrounding the moiré pattern in a second working zone. [Figure 11A] FIG. 1 is a block diagram of a top view of a three-layer metrology target in accordance with one or more embodiments of the present disclosure having a moiré pattern based on a grating-over-grating structure across multiple layers. [Figure 11B] FIG. 11B is a conceptual diagram of a multi-layer grating structure in the moire pattern of FIG. 11A in accordance with one or more embodiments of the present disclosure. [Figure 11C] FIG. 11C is a top view of a metrology target according to FIGS. 11A and 11B for measurement along two orthogonal directions in accordance with one or more embodiments of the present disclosure. [Figure 12A] FIG. 2 is a top view block diagram of a triple moire metrology target in accordance with one or more embodiments of the present disclosure. [Figure 12B] FIG. 12B is a conceptual diagram of a multi-layer grating structure in the moire pattern of FIG. 12A in accordance with one or more embodiments of the present disclosure. [Figure 13A]FIG. 1 illustrates a top view of a metrology target, in accordance with one or more embodiments of the present disclosure, suitable for performing overlay measurements along a single direction based on images generated with multiple optical configurations and having a single Moiré pattern. [Figure 13B] FIG. 1 illustrates a top view of a metrology target in accordance with one or more embodiments of the present disclosure, suitable for performing overlay measurements along a single direction based on images generated with multiple optical configurations, and having a working zone with two instances of a Moiré pattern. [Figure 14] FIG. 1 is a flow diagram depicting steps performed in a method for measuring overlay in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Reference will now be made in detail to the subject matter disclosed and illustrated in the accompanying drawings. The present disclosure has been specifically shown and described with reference to certain embodiments and specific features thereof. The embodiments described herein are to be understood as illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the present disclosure.

[0016] Embodiments of the present disclosure are directed to overlay metrology targets having moiré patterns and methods of measuring overlay based on such targets. For example, grating structures may be provided on different specimen layers with different periodicities to provide a moiré pattern on the metrology target that includes grating-over-grating structures formed by the grating structures. Additionally, for purposes of this disclosure, "grating" or "grating structure" may describe any periodic structure or sequence of elements, including, but not limited to, line-space patterns. In an image of the moiré pattern, moiré fringes will appear at a moiré pitch that is related to the spatially varying overlap between gratings on different specimen layers. Typically, the moiré pitch is a longer pitch than either grating structure and is related to the pitch difference between the grating structures. For example, the moiré pitch (p M )of p M =(p1 p2) / (p1-p2) (1) where p1 is the period of the first grating structure on the first layer and p2 is the period of the second grating structure on the second layer.

[0017] In accordance with the present invention, metrology targets exhibiting moiré patterns can facilitate sensitive overlay metrology. Specifically, a physical shift of one grating relative to another grating in the moiré pattern along the periodicity direction (e.g., an overlay error associated with a relative shift of two specimen layers on a specimen) will result in a corresponding lateral shift of the moiré fringes along the measurement direction. Furthermore, the magnitude of the shift of the moiré fringes is typically greater than the magnitude of the physical shift. Specifically, the magnitude of the shift of the moiré fringes is proportional to the physical shift (e.g., an overlay error) according to a conditional moiré factor that depends on the reference coordinate system. Continuing with the above example, a shift of the second layer relative to the first layer will result in a shift of the moiré fringes from a nominal position (e.g., a position without overlay error), M = p1 / (p1-p2) (2) This results in a conditional moiré factor (M) of 1. It should be noted that in the context of this disclosure, the designations "first layer," "second layer," "third layer," etc. are intended merely to distinguish between various specimen layers and do not indicate a physical order between layers on the specimen. Thus, the "first layer" may be above or below the "second layer" on the specimen.

[0018] In this case, overlay metrology can be performed by measuring the shift of the moiré fringes along the periodic direction of the associated lattice structure on the metrology target and adjusting the value by a moiré gain, which will depend on the specific design of the metrology target and the specific measurement being performed. For example, it may be desirable to measure the shift of the moiré fringes relative to another structure or set of moiré fringes, since absolute measurement of the shift of a single moiré fringe may be difficult, impractical or impossible depending on the target design. The use of moiré patterns in overlay metrology is generally described in U.S. Pat. No. 6,399,433, published Oct. 21, 2008, U.S. Pat. No. 6,399,433, published Mar. 25, 2008, and U.S. Pat. No. 6,399,433, published Jul. 5, 2018, all of which are incorporated herein in their entirety.

[0019] It is further recognized herein that arranging the elements of a metrology target in a symmetrical configuration can facilitate determining the relative positions of the elements by relying on the exploitation of that symmetry. For example, an overlay metrology target can be formed such that the centers of symmetry of the elements on a first specimen layer overlap the centers of symmetry of the elements on a second specimen layer. Any differences between the centers of symmetry of the elements in a first layer relative to a second layer in the constructed metrology target can then be attributed to overlay error. The exploitation of symmetry in overlay metrology targets (e.g., Advanced Imaging Metrology (AIM) targets) is generally described in U.S. Pat. No. 6,393,433 issued Jun. 27, 2006, U.S. Pat. No. 6,393,433 issued Jul. 26, 2005, and U.S. Pat. No. 6,393,433 issued Feb. 13, 2007, all of which are incorporated herein in their entireties.

[0020] Embodiments of the present disclosure are directed to an overlay metrology target having at least one working zone with one or more moiré patterns arranged in a symmetrical distribution. For example, the moiré patterns in the working zones can be mirror symmetric or rotationally symmetric (e.g., 90° rotationally symmetric, 180° rotationally symmetric, etc.) distributions. In this way, the advantages of the moiré patterns and the symmetry in the metrology target can be combined and utilized together to achieve accurate and robust overlay metrology.

[0021] It is recognized herein that the effect of physical overlay error on a working group containing one or more instances of a Moiré pattern will be a shift in the center of symmetry due to shifts in the Moiré fringes, as described herein, and therefore any overlay metrology based on that center of symmetry will need to be adjusted based on a Moiré gain factor, which is further recognized to be dependent on the specific arrangement of elements within the overlay metrology target.

[0022] 1 is a block diagram of a metrology system 100 in accordance with one or more embodiments of the present disclosure, which may generate one or more images of a specimen 102 on at least one detector 104 using any method known in the art.

[0023] In one embodiment, the metrology system 100 includes an illumination source 106 that generates an illumination beam 108. The illumination beam 108 may include one or more designated wavelengths, including, but not limited to, vacuum ultraviolet radiation (VUV), deep ultraviolet radiation (DUV), ultraviolet (UV) radiation, visible radiation, infrared (IR) radiation, etc. Additionally, the illumination beam 108 generated by the illumination source 106 may include any range of designated wavelengths. Additionally, in one embodiment, the illumination source 106 may include a spectrally tunable illumination source, such that the illumination beam 108 generated has a tunable spectrum.

[0024] Further, the illumination beam 108 generated by the illumination source 106 may have any temporal profile. For example, the illumination source 106 may generate a continuous illumination beam 108, a pulsed illumination beam 108, a modulated illumination beam 108, etc. Additionally, the illumination beam 108 may be delivered from the illumination source 106 via free space propagation or via an optical waveguiding (e.g., optical fiber, light pipe, etc.).

[0025] In some embodiments, an illumination beam 108 is directed from the illumination source 106 to the specimen 102 via an illumination path 110. One or more lenses 112 or additional illumination optics 114 may be provided on the illumination path 110 to modify and / or dim the illumination beam 108. For example, the one or more illumination optics 114 may include, but are not limited to, 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, one or more shutters (e.g., mechanical shutters, electro-optical shutters, acousto-optical shutters, etc.), etc. Alternatively, the illumination optics 114 may include an aperture stop to control the angle of illumination on the specimen 102 and / or a field stop to control the spatial extent of the illumination on the specimen 102. As an example, the illumination path 110 may include an aperture stop located at a plane conjugate to the back focal plane of the objective 116, thereby providing telecentric illumination of the specimen. In some embodiments, the metrology system 100 includes an objective 116 that focuses the illumination beam 108 onto the specimen 102.

[0026] In one embodiment, the specimen 102 is disposed on a specimen stage 118. The specimen stage 118 may include any device suitable for positioning the specimen 102 within the metrology system 100. For example, the specimen stage 118 may include any combination of a linear translation stage, a rotation stage, a tip / tilt stage, etc.

[0027] In some embodiments, the detector 104 is configured to capture radiation (e.g., sample light 120) emanating from the sample 102 via a collection path 122. For example, the collection path 122 may include, but is not limited to, a collection lens (e.g., objective lens 116 depicted in FIG. 1 ), one or more additional collection path lenses 124, etc. In this case, the detector 104 may receive radiation reflected or scattered from the sample 102 (e.g., via specular reflection, diffuse reflection, etc.) and radiation generated by the sample 102 (e.g., luminescence associated with absorption of the illumination beam 108, etc.).

[0028] Further, the collection path 122 may include any number of collection optics 126, including but not limited to one or more collection path lenses 124, one or more filters, one or more polarizers, one or more beam blocks, etc., to direct and / or modify the illumination collected by the objective lens 116. Additionally, the collection path 122 may include a field stop to control the spatial extent of the sample in the image on the detector 104, and an aperture stop to control the angular extent of the illumination from the sample, which may be used to generate an image on the detector 104. In one embodiment, the collection path 122 may include an aperture stop that is conjugate to the back focal plane of the objective lens 116 optics, thereby providing telecentric imaging of the sample.

[0029] The detector 104 may include any type of optical detector known in the art suitable for receiving and measuring illumination from the specimen 102. For example, the detector 104 may include a charge-coupled device (CCD), a complementary metal-oxide semiconductor (CMOS) sensor, a photomultiplier tube (PMT) array, an avalanche photodiode (APD) array, or other sensor suitable for generating one or more images of the stationary specimen 102 (e.g., in a static mode of operation). Additionally, the detector 104 may include a multi-tap sensor having multiple taps per pixel, including, but not limited to, a multi-tap CMOS sensor, in which charge in a multi-tap pixel may be directed to any designated tap during an exposure window depending on one or more drive signals for the pixel. Thus, a multi-tap sensor having an array of multi-tap pixels may generate multiple images during a single readout phase, each associated with a different tap of an associated pixel. Additionally, for purposes of this disclosure, an output tap connected to an associated pixel may be referred to as a tap of a multi-tap sensor, where each tap of the multi-tap sensor may be read out (e.g., during a readout phase) to generate a separate image.

[0030] According to another example, the detector 104 can include a sensor suitable for generating one or more images of the moving specimen 102 (e.g., a scanning mode of operation). For example, the detector 104 can include a line sensor having rows of pixels. In this case, the metrology system 100 can generate successive images (e.g., strip images), one row at a time, by translating the specimen 102 through a measurement field of view along a scan direction perpendicular to the pixel rows and by successive clocking of the line sensor during successive exposure windows.

[0031] In another embodiment, the detector 104 may include a TDI sensor having multiple pixel rows and readout rows. The TDI sensor may be operated similarly to a line sensor, except that charge is moved sequentially from one pixel row to the next in accordance with a clocking signal until the charge reaches a readout row where the row of the image is generated. By synchronizing the charge transfer (e.g., in accordance with a clocking signal) with the motion of the sample along the scan direction, charge can be continuously accumulated across pixel rows, providing a relatively high signal-to-noise ratio compared to a line sensor.

[0032] In some embodiments, the detector 104 may include a spectroscopic detector suitable for identifying wavelengths of radiation emanating from the sample 102. In some embodiments, the metrology system 100 may include multiple detectors 104 (e.g., multiple beam paths generated by one or more beam splitters) to facilitate multiple metrology measurements by the metrology system 100. For example, the metrology system 100 may include one or more detectors 104 suitable for static mode imaging and one or more detectors 104 suitable for scanning mode imaging. In some embodiments, the metrology system 100 may include one or more detectors 104 suitable for both static and scanning imaging modes.

[0033] According to one embodiment, as depicted in FIG. 1, a beam splitter 128 is provided in the metrology system 100 oriented such that the objective lens 116 can simultaneously direct the illumination beam 108 onto the sample 102 and collect the radiation emanating from the sample 102.

[0034] In some embodiments, the angle of incidence of the illumination beam 108 on the specimen 102 can be adjusted. For example, the path of the illumination beam 108 through the beam splitter 128 and the objective lens 116 can be adjusted to control the angle of incidence of the illumination beam 108 on the specimen 102. In this case, the path of the illumination beam 108 can be a nominal path through the beam splitter 128 and the objective lens 116 such that the illumination beam 108 exhibits an orthogonal angle of incidence on the specimen 102. In other embodiments, the position and / or angle of the illumination beam 108 on the beam splitter 128 can be modified (e.g., by a rotatable mirror, a spatial light modulator, a freeform illumination source, etc.) to control the angle of incidence of the illumination beam 108 on the specimen 102. In some embodiments, the illumination source 106 directs one or more illumination beams 108 at an angle (e.g., at a glancing angle, a 45 degree angle, etc.) to the specimen 102.

[0035] In some embodiments, the metrology system 100 includes a controller 130. In some embodiments, the controller 130 includes one or more processors 132 configured to execute program instructions stored on a storage medium 134. The one or more processors 132 in the controller 130 may perform any of the various processing steps described elsewhere in this disclosure. The controller 130 may be configured to receive data, including, but not limited to, an image of the specimen 102 (from the detector 104).

[0036] The one or more processors 132 of the controller 130 may include any processing element known in the art. In this sense, the one or more processors 132 may include any microprocessor-based device configured to execute algorithms and / or instructions. According to certain embodiments, the one or more processors 132 may be a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other computer system (e.g., a networked computer) configured to execute programs and to operate the metering system 100 as described elsewhere in this disclosure. It is further recognized that the term "processor" may be broadly defined to encompass any device having one or more processing elements that execute program instructions obtained from a non-transitory storage medium 134. Additionally, the steps described elsewhere in this disclosure may be performed by a single controller 130 or, alternatively, by multiple controllers. Additionally, one or more of the controllers included in the controller 130 may be housed within a common housing or may be housed in multiple housings, such that any controller or combination of controllers may be individually packaged as a module suitable for incorporation into the metering system 100. Additionally, data received from the detector 104 may be analyzed by the controller 130 and the data may be sent to additional components within or external to the metering system 100.

[0037] The storage medium 134 may include any storage medium known in the art suitable for storing program instructions executable by one or more cooperating processors 132. For example, the storage medium 134 may include a non-transitory storage medium. In another embodiment, the storage medium 134 may include, but is not limited to, a read-only memory, a random access memory, a magnetic or optical storage device (e.g., disk), a magnetic tape, a solid-state drive, and the like. It is further noted that the storage medium 134 may be housed in a common controller housing with one or more processors 132. In some embodiments, the storage medium 134 may be located remotely relative to the physical location of one or more processors 132 and the controller 130. For example, the controller 130 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.) from one or more processors 132. Thus, the above description should be taken as merely illustrative and not as a limitation on the present invention.

[0038] Additionally, in some embodiments, the controller 130 is communicatively coupled to one or more components of the weighing system 100 such that the controller 130 can send and / or receive data to any component of the weighing system 100. Additionally, the controller 130 can control, e.g., command, any component of the weighing system 100 by generating one or more drive signals to associated components. For example, the controller 130 can be communicatively coupled to the detector 104 such that the controller 130 can receive one or more images from the detector 104.

[0039] Additionally, the controller 130 may provide one or more drive signals to the detector 104 to implement any of the detection techniques described herein. In another example, the controller 130 may be communicatively coupled to any combination of components, including but not limited to the illumination source 106, the illumination optics 114, the collection optics 126, the detector 104, etc. to control the optical configuration for the image.

[0040] 2A-14, metrology of overlay targets having moiré patterns based on a grating-over-grating structure in one or more rotationally symmetric working zones will now be described in more detail. FIGS. 2A-6 depict overlays using metrology targets with moiré patterns in two working zones. FIGS. 7-10 depict overlays using metrology targets with a moiré pattern in one working zone and a single layer structure (e.g., not a grating-over-grating structure) in a second working zone. FIGS. 11A-12B depict overlays using metrology targets with moiré patterns in two working zones and three or more layers, where one layer acts as a reference layer. FIGS. 13A-14 depict overlays using a single working zone with one or more moiré patterns where the overlay can be determined based on imaging under different optical conditions.

[0041] Figure 2A is a top block diagram of a metrology target 202 having a moiré pattern based on a grating-over-grating structure within a number of rotationally symmetric working zones in accordance with one or more embodiments of the present disclosure, and Figure 2B is a conceptual diagram of a multi-layer grating structure in the moiré pattern of Figure 2A in accordance with one or more embodiments of the present disclosure.

[0042] In one embodiment, a first working zone 204 on a metrology target 202 is formed by two instances of a first moiré pattern 206 arranged such that the first working zone 204 is rotationally symmetric. In another embodiment, a second working zone 208 on a metrology target 202 is formed by two instances of a second moiré pattern 210 arranged such that the second working zone 208 is rotationally symmetric. In the context of this disclosure, a working zone is a group of features that are intended to be analyzed together. For example, characteristics of one working zone can be compared to characteristics of another working zone to perform overlay metrology.

[0043] In general, the centers of rotational symmetry of the various working zones in the metrology target 202 can be independent. However, it may be desirable to design the metrology target 202 such that the centers of symmetry of some or all of the working zones coincide (within a specified tolerance) in the absence of overlay errors. Such a target design can minimize errors that may occur due to rotational misalignment between the metrology system (e.g., metrology system 100) and the wafer axis. In one embodiment, working zones with the same orientation (e.g., X-direction overlay metrology) have the same center of symmetry. Additionally, the centers of symmetry of working zones for overlay metrology along different directions may, but need not, coincide.

[0044] As depicted in FIG. 2A , in a situation where there is no overlay error, the first working zone 204 and the second working zone 208 are symmetrical about a 180° rotation about the center of symmetry 212.

[0045] The metrology target 202 of FIG. 2A may have rotational symmetry characteristics similar to those of advanced imaging metrology (AIM) targets as outlined in U.S. Patent No. 6,399,433 issued June 27, 2006, U.S. Patent No. 6,399,433 issued July 26, 2005, and U.S. Patent No. 6,399,433 issued February 13, 2007. However, unlike typical AIM targets in which each working zone has features in a single layer, at least one working zone of the metrology target 202 (e.g., first working zone 204 and second working zone 208) has a moiré pattern formed by a grating structure in multiple layers of interest. As depicted in FIG. 2B, a first moiré pattern 206 is formed by a first grating structure 214 in a first layer (Layer A) having a pitch Q and a second grating structure 216 in a second layer (Layer B) having a pitch P, where P ≠ Q. Additionally, a second Moire pattern 210 is formed by a third grating structure 218 in the first layer (Layer A) having a pitch T, and a fourth grating structure 220 in the second layer (Layer B) having a pitch S, where S ≠ T. In general, the values ​​of P, Q, S, and T can be varied independently such that a more comprehensive Moire AIM target is depicted in Figures 2A and 2B.

[0046] As discussed earlier in this application in connection with equations (1) and (2), in this case, the moiré pitch (p M1 )teeth p M1 =QP / (QP) (3) and the moire pitch (p M2 )teeth p M2 =ST / (ST) (4) It becomes.

[0047] And the conditional moiré factor (M1) in the first working zone 204, in relation to the misalignment of layer A with respect to layer B, is: M1=P / (PQ) (5) and the conditional moiré factor (M2) in the second working zone 208, in relation to the shift of layer A relative to layer B, is given by: M2 = S / (ST) (6) Similarly, a shift of layer B relative to layer A will result in M1=Q / (QP) and M2=T / (TS).

[0048] In some embodiments, the first moiré pattern 206 and / or the second moiré pattern 210 include a grating-over-grating structure in which individual gratings overlap one another. For example, the first grating structure 214 and the second grating structure 216 of the first moiré pattern 206 may be overlapped on the specimen 102. Similarly, the third grating structure 218 and the fourth grating structure 220 of the second moiré pattern 210 may be overlapped on the specimen 102. In this case, the size of the metrology target 202 may be minimized, and the space on the specimen 102 may be efficiently utilized.

[0049] As contemplated herein, metrology targets 202 having adjacent moiré patterns are susceptible to crosstalk. Furthermore, the severity of the crosstalk may depend on a number of factors, including, but not limited to, stack thickness, material properties, grating design, and metrology system (e.g., metrology system 100) conditions. In certain embodiments, exclusion zones are provided between working zones of the metrology target 202 or between moiré patterns associated with different working zones to reduce crosstalk to within a specified tolerance. For example, instances of the first moiré pattern 206 and the second moiré pattern 210 may be separated by a sufficiently wide exclusion zone 222 to reduce crosstalk between corresponding moiré fringes to within a specified tolerance. In certain embodiments, the exclusion zone 222 may be in the range of 0.25-0.5 μm or greater.

[0050] The exclusion zone 222 may be empty or may be filled with sub-resolution assist features, such as those that may be required by certain design rules. In one embodiment, the exclusion zone 222 is filled with sub-resolution assist features oriented orthogonal to the measurement direction (here, the X-direction). In general, as long as each working zone is rotationally symmetric, the elements (including the moiré pattern) within each working zone may be arranged according to any 2D distribution suitable for mitigating crosstalk to within a specified tolerance.

[0051] Further, while FIG. 2A illustrates working zones for measurements along a single direction (e.g., X-direction), metrology targets 202 and methods for measurements along additional directions (e.g., Y-direction) are within the spirit and scope of the present disclosure. In some embodiments, the metrology target 202 includes a third working zone 224 and a fourth working zone 226 suitable for measurements along the Y-direction. Additionally, the features within the third working zone 224 and / or the fourth working zone 226 may include any features suitable for overlay metrology and may, but need not, include one or more moiré patterns. Also, in some embodiments, not shown, the metrology target 202 includes working zones having 2D moiré patterns with periodic features along multiple directions (e.g., X-direction and Y-direction). In this case, the 2D moiré patterns may exhibit moiré fringes along the multiple directions simultaneously and may therefore be suitable for simultaneous overlay metrology along multiple directions.

[0052] Figure 2C is a top view of a metrology target 202 according to Figures 2A and 2B for measurement along two orthogonal directions in accordance with one or more embodiments of the present disclosure. Specifically, the metrology target 202 depicted in Figure 2C represents an example where P=T and Q=S. Additionally, Figure 2C illustrates a situation where there is no overlay error along the X or Y directions, where the axis of symmetry of the first working zone 204 and that of the second working zone 208 overlap along both the X and Y directions (e.g., the axis of symmetry of the first working zone 204 and that of the second working zone 208 overlap).

[0053] It should be understood, however, that FIG. 2C and the associated description are presented for illustrative purposes only and should not be taken as limiting.

[0054] In one embodiment, the metrology target 202 has a first working zone 204 with two instances of the first moiré pattern 206 for measurements along the X direction, a second working zone 208 with two instances of the second moiré pattern 210, a third working zone 224 with two instances of the first moiré pattern 206 for measurements along the Y direction, and a fourth working zone 226 with two instances of the second moiré pattern 210 for measurements along the vertical direction, where the third working zone 224 and fourth working zone 226 are rotated versions of the first working zone 204 and second working zone 208, respectively.

[0055] FIG. 3A is a flow diagram illustrating steps performed in an overlay metrology method 300 according to one or more embodiments of the present disclosure. For example, the method 300 may be applied to measure overlay based on a metrology target, such as, but not limited to, the metrology target 202 depicted in FIGS. 2A-2C. Applicant notes that the embodiments and enabling technologies described herein above in the context of the metrology system 100 should be understood to extend to the method 300. However, it is further noted that the method 300 is not limited to the metrology system 100 of that architecture. Additionally, the method 300 may be applied to measure overlay along one or more measurement directions.

[0056] In one embodiment, the method 300 includes receiving, at step 302, an image of a first working zone of a metrology target, the first working zone containing one or more instances of a first moiré pattern interspersed with gratings in two specimen layers, and receiving, at step 304, an image of a second working zone of the metrology target, the second working zone containing one or more instances of a second moiré pattern interspersed with gratings in the two specimen layers.

[0057] The images of the first moiré pattern 206 and the second moiré pattern 210 may be associated into separate images or into a single common image. In some embodiments, an image of the entire metrology target 202 is acquired (e.g., by metrology system 100) so that the first working zone 204 and the second working zone 208 may be analyzed based on the same image. In some embodiments, separate images of the metrology target 202 (or its components) are generated and used to analyze the first working zone 204 and the second working zone 208. In this case, the images may be generated using different imaging conditions (e.g., different illumination wavelengths, illumination angles of incidence, polarization, focus, etc.).

[0058] In some embodiments, the method 300 includes identifying a first axis of symmetry for the first working zone that is orthogonal to the measurement direction at step 306. In some embodiments, the method 300 includes identifying a second axis of symmetry for the second working zone that is orthogonal to the measurement direction at step 308. In some embodiments, the method 300 includes measuring the difference between the first and second axes of symmetry at step 310. Furthermore, an axis of symmetry that is orthogonal to another direction (e.g., an orthogonal direction) can be identified and its intersection point found to find the center of symmetry 212 for one or more working zones.

[0059] Identifying the axis of symmetry for the first working zone 204 and the second working zone 208 in step 302 or step 304 may be accomplished using any technique known in the art, such as a technique suitable for measuring the center of symmetry of a typical AIM target lacking a Moiré pattern.

[0060] Figure 3B is a flow diagram illustrating a method 312 of identifying an axis of symmetry of a working group perpendicular to a measurement direction, where method 312 may be associated with step 306 and / or step 308. Figure 4 is a top view of the metrology target 202 of Figure 2C with additional markings illustrating application of method 312 in accordance with one or more embodiments of the present disclosure.

[0061] In one embodiment, a region of interest (ROI) is selected in which at least a portion of the elements in the working group lie, step 314. For example, ROI 402, represented by a solid box in FIG. 4, selects portions of the first moiré pattern 206 in the first working zone 204, and ROI 404, represented by a dashed box, selects portions of the second moiré pattern 210 in the second working zone 208.

[0062] Additionally, in one embodiment, a measurement signal is generated based on the ROI at step 316. For example, each value of the measurement signal along the measurement direction may include an average (or cumulative) intensity value along an orthogonal direction within the ROI.

[0063] As contemplated herein, the moire fringes associated with a moire pattern (e.g., first moire pattern 206 or second moire pattern 210) may have a relatively low contrast with respect to the grating structures forming the moire pattern that may be seen in an image of the metrology target 202. In some embodiments, step 318 separates the moire fringes in the measurement signal. For example, step 318 may take into account one or more orders of moire fringes (e.g., first order, second order, etc.). Separating the moire fringes may reduce noise and increase the accuracy and / or sensitivity of the symmetry axis determination in steps 306 and / or 308, which may improve the accuracy and / or robustness of the symmetry axis determination.

[0064] The separation of the moiré fringes in step 318 can be performed using any technique known in the art. In one embodiment, the measured signal is filtered to separate the moiré fringes. For example, the spatial frequency content of the measured signal can be analyzed using 1D or 2D Fourier filtering or other frequency-based decomposition techniques (e.g., decomposing the measured signal into sine and / or cosine signals). Furthermore, frequency selective filters can be used to separate the spatial frequencies of the moiré fringes (e.g., first order moiré fringes, second order moiré fringes, etc.).

[0065] 3B , in one embodiment of method 312, an axis of symmetry 406 of the working zone perpendicular to the measurement direction can be identified based on the measurement signal at step 320. The axis of symmetry 406 of the working zone perpendicular to the measurement direction can be identified using any technique known in the art (e.g., at step 306 or 308 of method 300 or at step 320 of method 312). In one embodiment, the axis of symmetry is identified by correlating a portion of an image of the first moiré pattern 206 (e.g., the ROI at step 314) with a symmetrical version of the image. For example, the axis of symmetry 406 of the first working zone 204 can be identified by generating a copy of the portion of the image that includes the first working zone 204, rotating the image copy according to the rotational symmetry of the metrology target 202 (e.g., 90°, 180°, etc.), and performing a correlation between the original image and the image copy at various points as a function of position along the measurement direction. In this case, the location along the measurement direction where the correlation between the original image and its rotated version is highest can be associated with the axis of symmetry 406 of the first working zone 204. Alternatively, if the working zone has reflection symmetry (i.e., mirror symmetry), the axis of symmetry 406 of the working zone can be determined by correlating a reflection copy of the working zone with itself.

[0066] As previously described herein, the axis of symmetry 406 for any number of working zones may be identified by applying the steps of method 312. For example, both steps 306 and 308 may incorporate application of method 312.

[0067] However, as can be appreciated, this method 312 of identifying the axis of symmetry 406 of the working zone along the measurement direction is presented for illustrative purposes only and should not be taken as limiting. On the contrary, any technique known in the art can be used to identify the axis of symmetry 406. According to one embodiment, the axis of symmetry 406 of the working group along the measurement direction can be applied by first determining a region of interest (e.g., ROI 402 in step 314), performing a spatial frequency filtering operation on the entire ROI to isolate one or more orders of moiré fringes along the measurement direction (e.g., by treating features as having infinite dimensions along the orthogonal direction and applying a 1D filtering operation similar to step 318), and then correlating the ROI with a rotated version of itself to identify the axis of symmetry 406.

[0068] Additionally, in one embodiment of method 300, at step 322, the overlay error between the two specimen layers along the measurement direction is calculated by dividing the difference between the axes of symmetry of the first and second working zones 204 and 208 perpendicular to the measurement direction by a moiré gain factor. For example, FIG. 4 illustrates a case without overlay error, where both the first working zone 204 and the second working zone 208 have axes of symmetry 406 perpendicular to the measurement direction (e.g., X-direction) and overlap. In contrast, if there is a physical overlay error, the axes of symmetry 406 will not overlap.

[0069] Due to the presence of Moiré fringes, the difference between the symmetry axes identified in step 310 is not equal to the physical overlay error between the first and second sample layers. Instead, the difference between the symmetry axes corresponds to a relative shift of the Moiré fringes. Therefore, the physical overlay error along the measurement direction can be determined by dividing the difference between the symmetry axes perpendicular to the measurement direction by the Moiré gain for a particular layout of the metrology target 202.

[0070] It is recognized herein that the Moiré gain depends on the specific layout of the metrology target 202. For example, the Moiré gain factor (M g ) relates the overlay to a shift of layer A relative to layer B, M g =M1-M2=P / (PQ)-S / (ST)=-(Q / (QP)-T / (TS)) (7) Similarly, the Moiré gain factor for the shift of layer A relative to layer B can be characterized as -M g =M2-M1.

[0071] As evidenced by equation (7), the moiré gain is affected by the conditional moiré factors of the first moiré pattern 206 and the second moiré pattern 210, which are in turn a function of the specific values ​​of the grating pitches P, Q, S, and T. Thus, by appropriately selecting the values ​​of the grating pitches P, Q, S, and T, the composite moiré gain, and thus the sensitivity to physical overlay errors, can be optimized, e.g., increased. For example, selecting the values ​​of the grating pitches P, Q, S, and T such that the moiré gain of the first working zone 204 and that of the second working zone 208 have different signs, can generally increase the composite moiré gain.

[0072] 5 and 6, it is contemplated herein that the method 300 is not limited to the specific geometry of the metrology target 202 depicted in FIG 2A. In general, any number of instances of a moiré pattern (e.g., first moiré pattern 206 or second moiré pattern 210) may reside within a working zone (e.g., first working zone 204 or second working zone 208) as long as the working zone is rotationally and / or reflectively symmetric.

[0073] FIG. 5 illustrates a top view of a metrology target 202 in accordance with one or more embodiments of the present disclosure having a first working zone 204 having two instances of a first moiré pattern 206 therein and a second working zone 208 having two instances of a second moiré pattern 210 therein.

[0074] FIG. 6 illustrates a top view of a metrology target 202 in accordance with one or more embodiments of the present disclosure having a first working zone 204 having two instances of a first moiré pattern 206 therein and a second working zone 208 having a single instance of a second moiré pattern 210 therein.

[0075] 7-10, the generic moiré metrology target 202 and method 300 depicted in FIG. 2A can be further expanded into a hybrid metrology target, i.e., one that has one or more instances of a moiré pattern in one working zone and one or more instances of a single layer structure (e.g., no grating-over-grating structure and no moiré pattern) in a second working zone.

[0076] 7 illustrates a top view of a hybrid metrology target 202 for measurements along two orthogonal directions according to one or more embodiments of the present disclosure, where measurements in each direction rely on one working zone with one or more moiré patterns and another working zone with one or more single layer structures. Specifically, the metrology target 202 depicted in FIG. 7 represents a variation of FIG. 2A, where T=0 and there is no grating structure on layer A associated with the second working zone 208. Thus, the moiré gain (M g ) is related to the shift of layer A relative to layer B, M g =P / (PQ)-S / (ST)=P / (PQ)-S / (S-0)=P / (PQ)-1=-Q / (QP)=-(Q / (QP)-0 / (0-S))=-(Q / (QP)-T / (TS)) (8) 7. Additionally, the third working zone 224 and the fourth working zone 226 of the metrology target 202 depicted in FIG. 7 are rotated versions of the first working zone 204 and the second working zone 208 for performing similar measurements along the Y direction. However, it should be understood that FIG. 7 and the associated description are presented for illustrative purposes only and should not be taken as limiting. The hybrid target is not limited to the layout depicted in FIG. 7. For example, any rotationally symmetric distribution of features may be present in the working zones along the X or Y direction. According to another example, the single layer of features in the second working zone 208 may include non-periodic features and thus is not limited to the lattice structure depicted in FIG. 7.

[0077] FIG. 8 illustrates a top view of a metrology target 202 for measurements along a single direction (e.g., the X-direction) in accordance with one or more embodiments of the present disclosure, including a first working zone 204 having two instances of a first moiré pattern 206 therein, and a second working zone 208 having two instances of a single layer grating structure (e.g., on layer A or layer B).

[0078] 9 is a top view of a metrology target 202 for metrology along a single direction (e.g., the X direction) in accordance with one or more embodiments of the present disclosure. Specifically, there is a single instance of a moiré pattern 902 in the first working zone 204, and there are two instances of a single layer grating structure (e.g., on layer A or layer B) in the second working zone 208.

[0079] In accordance with the present contemplation, the examples depicted in Figures 8 and 9 have two non-moiré patterns in one working zone and one or more moiré patterns in another working zone. However, it will be appreciated that further variations are within the spirit and scope of the present disclosure. In general, any number of moiré patterns may be present in any rotationally symmetric distribution in the first working zone 204, and any number of non-moiré patterns may be present in any rotationally symmetric distribution in the second working zone 208.

[0080] As discussed herein above, a working zone having one or more non-moiré patterns (e.g., a reference for a working zone with one or more moiré patterns) therein may have any rotationally symmetric distribution of periodic or non-periodic features. Additionally, a working zone with non-moiré features may, but is not required to, partially or completely overlap a working zone with a moiré pattern.

[0081] FIG. 10 illustrates a top view of a moiré rain box metrology target 202 in accordance with one or more embodiments of the present disclosure, with a single instance of a moiré pattern 1002 in the first working zone 204 and a non-periodic monolayer structure surrounding the moiré pattern 1002 in the second working zone 208. Because the moiré pattern 1002 of FIG. 10 has a grating-over-grating structure that is periodic in only the X direction, the metrology target 202 of FIG. 10 can be used to perform overlay metrology in the X direction (e.g., according to method 300). However, it can be appreciated that the example metrology target 202 of FIG. 10 is provided for illustrative purposes only and should not be construed as limiting. In one embodiment, not shown, a moiré rain box target can have a 2D moiré pattern with a grating-over-grating structure that is periodic along both the X and Y directions, thereby performing overlay metrology along both the X and Y directions.

[0082] Next, as shown in Figures 11A-12B, in some embodiments, a reference layer is provided on the metrology target 202. In this case, structures in the reference layer can be optically interacted with structures in additional layers to provide a device-like metrology target (e.g., a target having features exhibiting a size, density, and / or pitch similar to the device features). Device-like metrology targets with reference layers are generally described in US Patent Application Publication No. 2013 / 0133999, published July 5, 2018, the entirety of which is incorporated herein by reference.

[0083] FIG. 11A is a top block diagram of a three layer metrology target 202 having a moiré pattern based on a grating-over-grating structure across multiple layers in accordance with one or more embodiments of the present disclosure. FIG. 11B is a conceptual diagram of a multi-layer grating structure in the moiré pattern of FIG. 11A in accordance with one or more embodiments of the present disclosure. In one embodiment, the metrology target 202 has a first working zone 204 with two instances of a first moiré pattern 1102 and a second working zone 208 with two instances of a second moiré pattern 1104. As depicted in FIG. 11B, the first moiré pattern 1102 is formed by a grating structure 1106 in a first layer (Layer A) having a pitch P, a grating structure 1108 in a reference layer (Layer B) having a pitch Q, and there is no grating structure in a third layer (Layer C) such that P≠Q. Furthermore, the second moiré pattern 1104 is formed by a grating structure 1110 in the reference layer (layer B) with pitch x·Q and a grating structure 1112 in the third layer (layer C) with pitch x·P, where x is a positive number (e.g. a rational number). In this case, the structures in the reference layer are incorporated into both the first moiré pattern 1102 and the second moiré pattern 1104. Furthermore, the reference layer structures do not need to have the same pitch as the first moiré pattern 1102 and the second moiré pattern 1104.

[0084] In accordance with the present contemplation, the metrology target 202 of FIG. 11A is suitable for performing overlay metrology between layers A and C. In this metrology target 202, the moiré gain (M g )but M g =Q / (PQ) (9) It becomes.

[0085] 11C is a top view of a metrology target 202 according to FIGS. 11A and 11B for measurements along two orthogonal directions in accordance with one or more embodiments of the present disclosure. Specifically, the metrology target 202 depicted in FIG. 11C illustrates an example where x=1.

[0086] As can be appreciated, Figures 11A-11C and the associated description are presented for illustrative purposes only and should not be construed as limiting. In some embodiments, the metrology target 202 has at least one working zone with a Moiré pattern having three overlapping gratings in three layers, including a reference layer, where the overlay between the other two pairs of layers can be restored algorithmically (e.g., by filtering one or more metrology signals to isolate or suppress desired spatial frequencies and / or Moiré fringes) or physically (e.g., using additional working zones).

[0087] FIG 12A is a top view block diagram of a triple moiré metric target 202 in accordance with one or more embodiments of the present disclosure. FIG 12B is a conceptual diagram of a multi-layer grating structure in the moiré pattern of FIG 12A in accordance with one or more embodiments of the present disclosure. In one embodiment, the metric target 202 has a first working zone 1202 with two instances of a first moiré pattern 1204 therein, a second working zone 1206 with two instances of a second moiré pattern 1208 therein, and a third working zone 1210 with two instances of a third moiré pattern 1212. As depicted in FIG 12B, the first moiré pattern 1204 is formed by a grating structure 1214 in a first layer (Layer A) having a pitch P, a grating structure 1216 in a second layer (Layer B) having a pitch Q, and there is no grating structure in a third layer (Layer C) such that P≠Q. The second moiré pattern 1208 is formed by a grating structure 1218 in the first layer (Layer A) having a pitch T and a grating structure 1220 in the second layer (Layer B) having a pitch S, where T ≠ S. The third moiré pattern 1212 is formed by a grating structure 1222 in the third layer (Layer C) having a pitch T and a grating structure 1224 in the second layer (Layer B) having a pitch S.

[0088] In accordance with the present contemplation, the metrology target 202 of FIG. 12A is suitable for performing overlay metrology between layers A and C or between layers A and B. In this metrology target 202, the moire gain (M g )but M g =P / (PQ)-S / (ST) (10) It becomes.

[0089] In this metrology target 202, the moire gain (M g )but M g =T / (ST) (11) It becomes.

[0090] It should be understood that FIGS. 12A and 12B and the associated description are presented for illustrative purposes only and should not be construed as limiting. For example, the triple moiré metrology target 202 may generally have further variations of lattice structure arrangements across three layers. In one embodiment, the triple moiré metrology target 202 may have a first working zone 1202 having a moiré pattern based on lattice structures on layers A and B, a second working zone 1206 having lattice structures on layers B and C, and a third working zone 1210 having lattice structures on layers A and C. Such targets may also be suitable for overlay metrology between layers A and B and between layers B and C. Furthermore, the metrology target 202 may generally have any number of layers. For example, an N-fold metrology target 202 having N layers with lattice structures on selected layers may provide overlay metrology between the selected layers.

[0091] 13A-14, metrology of an overlay target for metrology along a single direction having a single working zone with one or multiple instances of a Moiré pattern will now be described in more detail.

[0092] It is contemplated herein that the information content of an image of a moiré pattern 1302 may vary depending on the optical conditions under which the image is generated, including, but not limited to, the wavelength of the illumination used to generate the image (e.g., the wavelength of illumination beam 108), the angle of incidence of that illumination, and the focal position of a detector used to generate the image (e.g., detector 104). For example, a moiré fringe may be observable in one optical configuration but not in another. Similarly, one or more of the underlying grating structures may be visible in one optical configuration but not in another. Thus, two images of a single moiré pattern captured under different optical configurations may have different axes of symmetry, much like those described in connection with FIGS. 2A-6.

[0093] Figure 13A illustrates a top view of a metrology target 202 according to one or more embodiments of the present disclosure, having a single moiré pattern 1302 suitable for performing overlay metrology along a single direction based on images generated with multiple optical configurations. For example, the metrology target 202 of Figure 13A may be suitable for metrology along a single direction (e.g., X-direction) based on images generated under conditions in which moiré fringes can be detected and at least one of the gratings beneath the moiré pattern 1302 can be detected.

[0094] As contemplated by the present application, the metrology target 202 depicted in FIG. 13A can be approximately 3-4 times smaller than targets designed using conventional techniques, thereby significantly reducing the required space on the specimen 102 dedicated to metrology.

[0095] Figure 13B illustrates a top view of a metrology target 202 according to one or more embodiments of the present disclosure, having a working zone 1304 with two instances of a moiré pattern 1302 suitable for performing overlay metrology along a single direction based on images generated with multiple optical configurations. Similar to Figure 13A, the metrology target 202 depicted in Figure 13B may be suitable for metrology along a single direction (e.g., X-direction) based on images generated under conditions in which moiré fringes can be detected and at least one of the underlying gratings of the moiré pattern 1302 can be detected.

[0096] Additionally, the use of multiple instances of the moiré pattern 1302 in the metrology target 202 depicted in Figure 13B provides flexibility in the spreading of the metrology target 202 across the specimen 102. That is, different elements, including but not limited to device features, can be located between different features of the metrology target 202.

[0097] 14 is a flow diagram depicting steps performed in an overlay metrology method 1400 in accordance with one or more embodiments of the present disclosure. Applicant notes that the embodiments and enabling technologies described herein above in the context of metrology system 100 should be understood to extend to the method 1400. However, it is further noted that the method 1400 is not limited to metrology system 100 of such architecture.

[0098] In one embodiment, the method 1400 includes receiving, at step 1402, a first image of a metrology target on a specimen with one or more instances of a moiré pattern (e.g., first moiré pattern 206) using a first optical configuration. In one embodiment, the method 1400 also includes determining, at step 1404, a first axis of symmetry of the working zone along the measurement direction based on the first image. In one embodiment, the method 1400 also includes receiving, at step 1406, a second image of the metrology target on the specimen using a second optical configuration different from the first optical configuration. In one embodiment, the method 1400 also includes determining, at step 1408, a second axis of symmetry of the working zone along the measurement direction based on the second image.

[0099] Moreover, the images generated in steps 1402 and 1406 based on different optical configurations may be generated sequentially or simultaneously, for example, with associated optical conditions (e.g., by metrology system 100) generated sequentially or simultaneously.

[0100] In addition, in one embodiment of the method 1400, at step 1410, a difference between the first and second axes of symmetry is determined.

[0101] As contemplated herein, it may be desirable to fill spatial frequencies in the first or second image to isolate the desired signal. The techniques described in accordance with step 318 of FIG. 3B for isolating the moire fringes can be used to generally isolate any specified set of spatial frequencies, including but not limited to spatial frequencies associated with one of the lattice structures within the moire fringes, or spatial frequencies associated with any specified order of the moire fringes.

[0102] For example, it may be desirable to provide a first optical configuration in which only the moiré fringes can be resolved, and any underlying grating structures are not required, although if one or both of the underlying grating structures are visible, then the moiré fringes may be isolated prior to identifying the axis of symmetry. For example, it may be desirable to provide a second optical configuration in which only one of the underlying grating structures (e.g., one that acts as a "reference layer" as described herein above) can be resolved, although if the moiré fringes and other grating structures can be resolved, then the desired grating structure may be isolated.

[0103] Additionally, in one embodiment of the method 1400, at step 1412, the overlay error associated with the misalignment of the second specimen layer relative to the first specimen layer is calculated by dividing the difference between the first and second axes of symmetry by the moiré gain.

[0104] As recognized herein, method 1400 can be quite similar to method 300, supra. However, depending on which structures in the two images are resolved (e.g., in steps 1402 and 1404), the moiré gains can be different. For example, if one optical configuration resolves those moiré fringes and a second optical configuration resolves whether layer A was received in that optical configuration, then the moiré gains (M g )of M g =P / (PQ) (10) Similarly, if one optical configuration resolves these moiré fringes and a second optical configuration resolves the reception or non-reception of layer B in the optical configuration, then the moiré gain (M g )of M g =Q / (QP) (11) can be characterized as:

[0105] The method 1400 can be applied to any type of metrology target having a moiré pattern, including but not limited to any of the targets described herein, using different optical configurations that result in different image content to generate additional information based on any working zones that have an inherent moiré pattern.

[0106] 2A-14 are presented for illustrative purposes only and should not be construed as limiting. In some embodiments, a metrology target 202 may have a working zone with one or more instances of a moiré pattern that may include gratings on three or more layers, each having a different pitch. In this case, an image of the moiré pattern may include double, triple or more scattered signals associated with moiré fringes due to interference between the three or more gratings. In accordance with further contemplation herein, moiré patterns based on three or more overlapping gratings may be incorporated into metrology targets 202 of various designs, suitable for analysis using multiple algorithms. For example, the method 1400 may be applied to extract the overlay between two specimen layers of such a metrology target 202 based on multiple images of the moiré pattern with different optical configurations selected to detect the moiré fringes between the different specimen layers and / or to detect any of the underlying grating structures. As an example, different optical configurations can be generated in which different moiré patterns (e.g., interference between different specimen layers) are visible. As another example, any of the techniques described in connection with step 318 of method 312 for separating moiré fringes as described herein above (e.g., Fourier filtering) can be applied to separate selected spatial frequencies, such as, but not limited to, spatial frequencies associated with any of the underlying grating structures and / or moiré fringes between different specimen layers. As another example, method 300 can be applied to generate overlay measurements between two specimen layers based on a comparison along a measurement direction of the axis of symmetry of a working group with the moiré pattern to the axis of symmetry of another working group. In this case, additional layers of the moiré pattern can be used as reference layers. Moreover, the overlay measurements can be based on any combination of the techniques listed above.

[0107] It is recognized herein that the specific design parameters of the grating-over-grating moiré patterns described herein may affect various aspects of the associated moiré fringes, including, but not limited to, the number of moiré fringes, the period of the moiré fringes, the order of the moiré fringes (e.g., first order, second order, etc.), the contrast of the moiré fringes, the crosstalk between adjacent moiré patterns, etc. For example, the moiré fringes may be generally affected by target design parameters (e.g., pitch of the grating structures, duty cycle of the grating structures, feature segmentation to provide features with design level dimensions, exclusion zone size, overall dimensions of the target, etc.), metrology tool parameters, stack parameters (e.g., that include information about the printing / patterning process), and / or lithography tool parameters.

[0108] Thus, in some embodiments, one or more aspects of the metrology target design, metrology tool metrology recipe, lithography tool recipe, etc. are selected based on simulation and / or measurement of test targets. For example, a design of experiments can be generated where a set of candidate parameters (e.g., target design parameters, metrology tool parameters, lithography tool parameters, etc.) are systematically varied. The performance of each set of candidate parameters can be evaluated through some combination of simulation and test target creation / measurement. A set of parameters can then be selected from the set of candidate parameters based on some selected metric or combination of metrics, such as, but not limited to, moiré fringe pattern contrast, moiré fringe period, generation of a selected moiré fringe order, overlay accuracy, measurement repeatability, robustness to variations in the optical configuration of the imaging system, robustness to variations in the moiré pattern, etc.

[0109] In some embodiments, a Maxwell-based simulation is used to optimize parameters of the grating structure on one or more working zones in which at least one Moiré pattern resides. The Maxwell-based simulation may include any type of simulation incorporating Maxwell's equations, such as, but not limited to, Rigorous Coupled Wave Analysis (RCWA) simulation. For example, the Maxwell-based simulation may be performed using AcuRate™ software from KLA Corporation, although this is not required. Furthermore, optical crosstalk between adjacent Moiré patterns may be simulated using a Maxwell-based approximation or a simpler approximation, such as the Kirchhoff approximation, which assumes Fourier optical effects.

[0110] In some embodiments, tool parameters (e.g., metrology tool parameters, lithography tool parameters, etc.) are optimized by first identifying a specified number of candidate sets of target design parameters based on simulation, creating only the selected candidate sets, and measuring their performance using various tool parameters. The best combination of design parameters and tool parameters can then be selected based on a desired performance metric. In this case, the number of test specimens to be created can be narrowed down using simulation, allowing efficient selection of optimal parameters.

[0111] The subject matter described herein sometimes depicts various components being included in or connected to other components. As will be appreciated, the illustrated architectures are merely exemplary, and in fact many other architectures can be implemented to achieve the same functionality. Conceptually, any arrangement of components that achieves the same functionality provides the desired functionality in an effective "association." Thus, any two components in this application that are combined to achieve a particular function can be viewed as "associated" with each other to achieve the desired functionality, regardless of the architecture or intervening components. Similarly, any two components that are so associated can be viewed as "connected" or "coupled" to each other to achieve the desired functionality, and any two components that can be so associated can be viewed as "combinable" with each other to achieve the desired functionality. Examples of what is connectable include, but are not limited to, physically interactable and / or physically interacting components, and / or wirelessly interactable and / or wirelessly interacting components, and / or logically interactable and / or logically interacting components.

[0112] 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 the form, construction and arrangement of the parts may be made without departing from the disclosed subject matter or sacrificing all of its essential advantages. The described form is merely exemplary, and it is the intent of the following claims to encompass and embrace all such modifications. The invention is further defined by the appended claims.

Claims

1. A weighing target, a first working zone within which one or more instances of a first pattern reside, the first working zone being rotationally symmetric; a second working zone within which one or more instances of a second pattern reside, the second working zone being rotationally symmetric; At least one of the first pattern and the second pattern is on a first sample layer and has a first pitch (p １ a first grating structure on the second sample layer and having a second pitch (p ２ a second grating structure having a pitch different from the first pitch, wherein a center of rotational symmetry of the first working zone and a center of rotational symmetry of the second working zone overlap when an overlay error between the first specimen layer and the second specimen layer is zero, and a difference between the centers of rotational symmetry of the first working zone and the centers of rotational symmetry of the second working zone along the measurement direction indicates an overlay error between the first specimen layer and the second specimen layer along the measurement direction; The overlay error along the measurement direction corresponds to a shift of the second specimen layer relative to the first specimen layer, and the overlay error along the measurement direction determines the difference between the center of rotational symmetry of the first working zone and the center of rotational symmetry of the second working zone by M. ｇ = p １ / (p １ -p ２ ) is adjusted by a moire gain of 0.015 μm.

2. 2. The metrology target of claim 1, wherein said first grating structure and said second grating structure fully overlap.

3. 2. The metrology target of claim 1, wherein at least one of the first working zone and the second working zone are rotationally symmetric about at least one of 90° and 180°.

4. 2. The metrology target of claim 1, wherein at least one of the first working zone and the second working zone includes features disposed diagonally about the center of rotational symmetry.

5. 2. The metrology target of claim 1, The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern being on a first sample layer and having a first pitch (p １ ) and a grating structure on the second sample layer having the second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ a third grating structure on the second sample layer and having a fourth pitch (p ４ and a fourth grating structure having a first pitch different from the second pitch, the fourth grating structure having a second pitch different from the third pitch.

6. 6. The metrology target of claim 5, wherein the overlay error along the measurement direction corresponds to a shift of the second specimen layer relative to the first specimen layer, and the first working zone is determined by a first conditional moiré factor M １ = p １ / (p １ -p ２ ), and the second working zone has a second conditional moiré factor M ２ = p ３ / (p ３ -p ４ ), and the overlay error along the measurement direction is determined by the difference between the center of rotational symmetry of the first working zone and the center of rotational symmetry of the second working zone, M ｇ = M １ -M ２ The metric target corresponds to the one adjusted by the moire gain.

7. 7. The metrology target of claim 6, further comprising: １ and M. ２ and a metric target with opposite signs.

8. 6. The metric target of claim 5, wherein said first pitch is equal to said third pitch and said second pitch is equal to said fourth pitch.

9. 10. The metrology target of claim 1, wherein at least one instance of the first pattern is separated from at least one instance of the second pattern by an exclusion zone to reduce crosstalk.

10. 10. The metrology target of claim 9, wherein the exclusion zone is at least 0.25 μm.

11. 2. The metric target of claim 1, wherein two instances of said first pattern reside within said first working zone and two instances of said second pattern reside within said second working zone.

12. 2. The metric target of claim 1, wherein two instances of said first pattern reside within said first working zone and one instance of said second pattern reside within said second working zone.

13. 13. The metrology target of claim 12, wherein said first pattern comprises said Moire pattern formed from said first grating structure and said second grating structure.

14. 13. The metrology target of claim 12, wherein the second pattern comprises the Moire pattern formed from the first grating structure and the second grating structure.

15. 2. The metrology target of claim 1, The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern being on a first sample layer and having a first pitch (p １ ) and a grating structure on the second sample layer having the second pitch (p ２ ) wherein the second pitch is different from the first pitch, A metrology target, the second pattern being on the first specimen layer and defining a second working zone containing one or more instances of a reference structure along the measurement direction.

16. 16. The metrology target of claim 15, wherein the reference structure comprises: A metrology target comprising a grating structure having a third pitch.

17. 2. The metrology target of claim 1, The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ ) and a grating structure on the second sample layer having a fourth pitch (p ４ ) wherein the fourth pitch is different from the third pitch; The method further includes a third working zone having one or more instances of a third moiré pattern therein, the third moiré pattern having a fifth pitch (p ５ ) on the third sample layer and a grating structure having a sixth pitch (p ６ ), wherein the sixth pitch is different from the fifth pitch, and a difference along the measurement direction between the center of rotational symmetry of the first working zone and the center of rotational symmetry of the third working zone is indicative of an overlay error between the first specimen layer and the third specimen layer along the measurement direction.

18. 2. The metrology target of claim 1, The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ ) on the third sample layer and a fourth pitch (p ４ ) wherein the fourth pitch is different from the third pitch; The method further includes a third working zone having one or more instances of a third moiré pattern therein, the third moiré pattern having a fifth pitch (p ５ ) and a grating structure on the third sample layer having a sixth pitch (p ６ ), wherein the sixth pitch is different from the fifth pitch, and a difference along the measurement direction between the center of rotational symmetry of the second working zone and the center of rotational symmetry of the third working zone is indicative of an overlay error between the second specimen layer and the third specimen layer along the measurement direction.

19. 2. The metrology target of claim 1, The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ ) on the third sample layer and a fourth pitch (p ４ ) wherein the fourth pitch is different from the third pitch; The method further includes a third working zone having one or more instances of a third moiré pattern therein, the third moiré pattern having a fifth pitch (p ５ ) and a grating structure on the third sample layer having a sixth pitch (p ６ ), wherein the sixth pitch is different from the fifth pitch, and a difference along the measurement direction between the centers of rotational symmetry of the first working zone and the centers of rotational symmetry of the second working zone is indicative of an overlay error between the first specimen layer and the second specimen layer along the measurement direction.

20. 10. The metrology target of claim 1, further comprising: a first additional working zone within which resides one or more instances of a first additional pattern, the first additional working zone being rotationally symmetric; a second additional working zone within which resides one or more instances of a second additional pattern, the second additional working zone being rotationally symmetric; a center of rotational symmetry of the first additional working zone and a center of rotational symmetry of the second additional working zone overlap when the overlay error between the first specimen layer and the second specimen layer is zero, and a difference along the measurement direction between the center of rotational symmetry of the first additional working zone and the center of rotational symmetry of the second additional working zone indicates an overlay error between the first specimen layer and the second specimen layer along the additional measurement direction.

21. 21. A metrology target as described in claim 20, wherein at least one of the first additional pattern and the second additional pattern is a moire pattern formed from a first additional grating structure on the first sample layer having a first additional pitch along the additional measurement direction and a second additional grating structure on the second sample layer having a second additional pitch along the additional measurement direction, wherein the second additional pitch is different from the first additional pitch.

22. 1. A weighing system comprising: a controller configured to be coupled to the imaging system, the controller having one or more processors, the one or more processors executing program instructions to: is a metric target on the specimen, a first working zone within which one or more instances of a first pattern reside, the first working zone being rotationally symmetric; a second working zone within which one or more instances of a second pattern reside, the second working zone being rotationally symmetric; at least one of the first pattern and the second pattern is a moiré pattern formed from a first grating structure on a first sample layer and having a first pitch along a measurement direction, and a second grating structure on a second sample layer and having a second pitch along the measurement direction, the second pitch being different from the first pitch; Receive an image of a weighing target; determining a difference between axes of symmetry of the first working zone and the second working zone along the measurement direction in the image; calculating an overlay error along the measurement direction for the first specimen layer and the second specimen layer by adjusting the difference along the measurement direction between the axes of symmetry of the first working zone and the second working zone with a moiré gain based on the pitch of the moiré patterns; The configured metering system.

23. 23. The metrology system of claim 22, wherein determining the difference between the axes of symmetry of the first working zone and the second working zone along the measurement direction in the image comprises: generating a first measurement signal based on an intensity of the image along the measurement direction for the first working zone; determining a first axis of symmetry for the first working zone based on the first measurement signal; generating a second measurement signal based on an intensity of the image along the measurement direction for the second working zone; determining a second axis of symmetry for the second working zone based on the second measurement signals; A metrology system for determining the difference between the first axis of symmetry and the second axis of symmetry.

24. 24. The weighing system of claim 23, further comprising: filtering the first measurement signal to separate a moire fringe signal associated with a moire period of the moire pattern prior to identifying the first axis of symmetry; A metrology system further comprising: filtering the second measurement signal prior to identifying the second axis of symmetry to isolate a moire fringe signal associated with a moire period of the moire pattern.

25. 23. A weighing system according to claim 22, comprising: The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern being on a first sample layer and having a first pitch (p １ ) and a grating structure on the second sample layer having the second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ a third grating structure on the second sample layer and having a fourth pitch (p ４ and a fourth lattice structure having a fourth pitch, the fourth pitch being different from the third pitch.

26. 26. The metrology system of claim 25, wherein the overlay error along the measurement direction corresponds to a shift of the second specimen layer relative to the first specimen layer, and the first working zone is determined by a first conditional moiré factor M １ = p １ / (p １ -p ２ ), and the second working zone has a second conditional moiré factor M ２ = p ３ / (p ３ -p ４ ), and the overlay error along the measurement direction is determined by the difference between the center of rotational symmetry of the first working zone and the center of rotational symmetry of the second working zone, M ｇ = M １ -M ２ A weighing system that corresponds to a moire gain adjustment.

27. 27. The weighing system of claim 26, further comprising: １ and M. ２ A measuring system in which and have opposite signs.

28. 23. A weighing system according to claim 22, comprising: The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern being on a first sample layer and having a first pitch (p １ ) and a grating structure on the second sample layer having the second pitch (p ２ ) wherein the second pitch is different from the first pitch, A metrology system, wherein the second pattern defines a second working zone containing one or more instances of a reference structure on the first specimen layer along the measurement direction.

29. 29. The metrology system of claim 28, wherein the overlay error along the measurement direction corresponds to a shift of the second specimen layer relative to the first specimen layer, and the overlay error along the measurement direction determines the difference between the centers of rotational symmetry of the first working zone and the centers of rotational symmetry of the second working zone by M. ｇ = p １ / (p １ -p ２ ) a weighing system that corresponds to the moire gain adjustment.

30. 23. A weighing system according to claim 22, comprising: The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ ) and a grating structure on the second sample layer having a fourth pitch (p ４ ) wherein the fourth pitch is different from the third pitch, The target further comprises a third working zone having one or more instances of a third moiré pattern therein, the third moiré pattern having a fifth pitch (p ５ ) on the third sample layer and a grating structure having a sixth pitch (p ６ ) and the sixth pitch is different from the fifth pitch, The one or more processors further execute program instructions to: determining a difference between the axes of symmetry of the first working zone and the third working zone along the measurement direction in the image; calculating an overlay error for the first specimen layer and the third specimen layer along the measurement direction by adjusting the difference along the measurement direction between the axes of symmetry of the first working zone and the third working zone with a moiré gain based on the pitch of the first moiré pattern and the second moiré pattern; The configured metering system.

31. 23. A weighing system according to claim 22, comprising: The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ ) on the third sample layer and a fourth pitch (p ４ ) wherein the fourth pitch is different from the third pitch, The target further comprises a third working zone having one or more instances of a third moiré pattern therein, the third moiré pattern having a fifth pitch (p ５ ) and a grating structure on the third sample layer having a sixth pitch (p ６ ) wherein the sixth pitch is different from the fifth pitch, and the sixth pitch is different from the fifth pitch; The one or more processors further execute program instructions to: determining a difference between the axes of symmetry of the second working zone and the third working zone along the measurement direction in the image; calculating an overlay error for the second and third specimen layers along the measurement direction by adjusting the difference along the measurement direction between the axes of symmetry of the second and third working zones with a moiré gain based on the pitches of the second and third moiré patterns; The configured metering system.

32. 23. A weighing system according to claim 22, comprising: The first pattern includes one or more instances of a first moiré pattern, the first moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ ) wherein the second pitch is different from the first pitch, The second pattern includes one or more instances of a second moiré pattern, the second moiré pattern having a third pitch (p ３ ) on the third sample layer and a fourth pitch (p ４ ) wherein the fourth pitch is different from the third pitch, The target further comprises a third working zone having one or more instances of a third moiré pattern therein, the third moiré pattern having a fifth pitch (p ５ ) and a grating structure on the third sample layer having a sixth pitch (p ６ ) wherein the sixth pitch is different from the fifth pitch, and the sixth pitch is different from the fifth pitch; The one or more processors further execute program instructions to: determining a difference between the axes of symmetry of the second working zone and the third working zone along the measurement direction in the image; calculating an overlay error along the measurement direction for the second and third specimen layers by adjusting the difference along the measurement direction between the axes of symmetry of the first and second working zones with a moiré gain based on the pitch of the first and second moiré patterns; The configured metering system.

33. A weighing target, A first working zone having one or more instances of a first moiré pattern therein and being rotationally symmetric, the first moiré pattern being on a first sample layer and having a first pitch (p １ ) and a grating structure on the reference sample layer having a second pitch (p ２ a first working zone having a lattice structure therein having a lattice structure having a thickness of 100 nm; a second working zone having one or more instances of a second moiré pattern therein, the second moiré pattern having a third pitch (p ３ ) and a grating structure on the reference sample layer having a fourth pitch (p ４ a second working zone having a fourth lattice structure therein, the fourth lattice structure having a first thickness of 100 nm and a second thickness of 100 nm; a center of rotational symmetry of the first working zone and a center of rotational symmetry of the second working zone overlap when an overlay error between the first and second specimen layers is zero, and a difference between the centers of rotational symmetry of the first working zone and the centers of rotational symmetry of the second working zone along the measurement direction indicates an overlay error between the first and second specimen layers along the measurement direction; The overlay error along the measurement direction corresponds to a shift of the second specimen layer relative to the first specimen layer, and the overlay error along the measurement direction determines the difference between the center of rotational symmetry of the first working zone and the center of rotational symmetry of the second working zone by M. ｇ = p １ / (p １ -p ２ ) is adjusted by a moire gain of 0.015 μm.

34. 34. A metric target according to claim 33, comprising: ３ = n p １ And p ４ = n p ２ where n is a positive number.

35. 35. The metrology target of claim 34, wherein n=1.

36. 1. A weighing system comprising: a controller configured to be coupled to an imaging system, the controller having one or more processors, the one or more processors executing program instructions to: is a metric target on the specimen, A first working zone having one or more instances of a first moiré pattern therein and being rotationally symmetric, the first moiré pattern being on a first sample layer and having a first pitch (p １ ) and a grating structure on the reference sample layer having a second pitch (p ２ a first working zone having a lattice structure therein having a lattice structure having a thickness of 100 nm; a second working zone having one or more instances of a second moiré pattern therein, the second moiré pattern having a third pitch (p ３ a third grating structure on the reference sample layer and having a fourth pitch (p ４ a second working zone having a fourth lattice structure therein, the fourth lattice structure having a first thickness of 100 nm and a second thickness of 100 nm; a center of rotational symmetry of the first working zone and a center of rotational symmetry of the second working zone overlap when an overlay error between the first specimen layer and the second specimen layer is zero. Receive an image of a weighing target; determining a difference between axes of symmetry of the first working zone and the second working zone along the measurement direction in the image; calculating an overlay error for the first and second specimen layers along the measurement direction by adjusting the difference along the measurement direction between the axes of symmetry of the first and second working zones with a moiré gain based on the pitches of the first and second moiré patterns; The configured metering system.

37. 37. The metrology system of claim 36, wherein determining the difference between the axes of symmetry of the first working zone and the second working zone along the measurement direction in the image comprises: generating a first measurement signal based on an intensity of the image along the measurement direction for the first working zone; determining a first axis of symmetry for the first working zone based on the first measurement signal; generating a second measurement signal based on an intensity of the image along the measurement direction for the second working zone; determining a second axis of symmetry for the second working zone based on the second measurement signals; A metrology system for determining the difference between the first axis of symmetry and the second axis of symmetry.

38. 38. The weighing system of claim 37, further comprising: filtering the first measurement signal to separate a moire fringe signal associated with a moire period of the first moire pattern prior to identifying the first axis of symmetry; A metrology system that filters the second measurement signal prior to identifying the second axis of symmetry to isolate a moire fringe signal associated with a moire period of the second moire pattern.

39. 37. A weighing system according to claim 36, comprising: ３ = n p １ And p ４ = n p ２ A metric system where n is a positive number.

40. 40. The weighing system of claim 39, wherein n=1.

41. 40. The metrology system of claim 39, wherein the overlay error along the measurement direction corresponds to a shift of the second specimen layer relative to the first specimen layer, and the Moire gain is M ｇ = p １ / (p １ -p ２ ) a weighing system.

42. A weighing target, The moiré pattern has one or more instances of the moiré pattern in a rotationally symmetric working zone, the moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ a grating structure having a second pitch different from the first pitch, an overlay error along the measurement direction for the first specimen layer and the second specimen layer corresponding to a difference between an axis of symmetry of the working zone imaged with an imaging system of a first optical configuration and an axis of symmetry of the working zone imaged with an imaging system of a second optical configuration, moiré fringes detectable with the first optical configuration, and at least one of the grating structure having the first pitch and the grating structure having the second pitch detectable with the second optical configuration.

43. 43. The metrology target of claim 42, wherein the grating structure having the first pitch is detectable with the second optical configuration, the overlay error along the measurement direction corresponds to a shift of the second specimen layer relative to the first specimen layer, and the overlay error along the measurement direction corresponds to a difference in the axes of symmetry of the working zones. ｇ = p １ / (p １ -p ２ ) is adjusted by a moire gain of 0.015 μm.

44. 43. The metrology target of claim 42, wherein individual optical configurations of the first optical configuration and the second optical configuration include a wavelength of illumination, a polarization of the illumination, an angle of the illumination, or a focal position of the metrology target relative to a detector.

45. 43. The metrology target of claim 42, wherein a single instance of said Moiré pattern resides within said working zone.

46. 43. The metrology target of claim 42, wherein at least two instances of said Moiré pattern reside within said working zone.

47. 1. A weighing system comprising: An imaging system, an illumination source for generating illumination; one or more illumination optics for directing illumination from the illumination source onto a metrology target, the metrology target comprising: The moiré pattern has one or more instances of the moiré pattern embedded therein and having a rotationally symmetric working zone, the moiré pattern having a first pitch (p １ ) and a grating structure on the second sample layer having a second pitch (p ２ and a lattice structure having a second pitch different from the first pitch. one or more illumination optical systems; and a detector that generates an image of the metrology target based on the illumination from the illumination source; an imaging system capable of configuring an optical configuration of the imaging system, the optical configuration including a wavelength of the illumination, a polarization of the illumination incident on the metrology target, an angle of the illumination incident on the metrology target, or a focal position of the metrology target relative to the detector; a controller configured to be coupled to the imaging system; the controller having one or more processors, the one or more processors executing program instructions to receiving a first image of the metrology target on a specimen using a first optical configuration; identifying a first axis of symmetry of the working zone along the measurement direction based on the first image; receiving a second image of the metrology target on the specimen using a second optical configuration different from the first optical configuration; determining a second axis of symmetry of the working zone along the measurement direction based on the second image; determining an optical overlay measurement based on a difference between the first axis of symmetry and the second axis of symmetry; calculating an overlay error along the measurement direction for the first sample layer and the second sample layer by adjusting the difference between the axes of symmetry in the first image and the second image by a moiré gain based on the pitch of the moiré pattern; The configured metering system.

48. 48. The metrology system of claim 47, wherein the grating structure having the first pitch is detectable with the second optical configuration, the overlay error along the measurement direction corresponds to a shift of the second sample layer relative to the first sample layer, and the Moire gain is M ｇ = p １ / (p １ -p ２ ) a weighing system.

49. 48. The weighing system of claim 47, wherein said first image and said second image are generated sequentially.

50. 48. The weighing system of claim 47, wherein said first image and said second image are generated simultaneously.

51. 48. The weighing system of claim 47, further comprising: filtering the first image to isolate a moire fringe signal associated with a moire period of the moire pattern prior to identifying the first axis of symmetry; A metrology system that filters the second image prior to identifying the second axis of symmetry to isolate signals associated with one of the grating structure having the first pitch and the grating structure having the second pitch.

52. 1. A method for designing a moire metrology target, comprising: is a metric target, a working zone having one or more non-overlapping instances of a moiré pattern therein, the moiré pattern having a first pitch (p) on a first sample layer along a measurement direction; １ a first grating structure on the second sample layer and having a second pitch (p ２ a second grating structure having a pitch different from the first pitch, an overlay error along the measurement direction for the first and second sample layers corresponding to a difference between an axis of symmetry of the working zone imaged with an imaging system of a first optical configuration and an axis of symmetry of the working zone imaged with an imaging system of a second optical configuration, moiré fringes are detectable with the first optical configuration, and at least one of the first grating structure having the first pitch and the second grating structure having the second pitch are detectable with the second optical configuration. Receive the design of the weighing target, receiving an optical configuration of an imaging system for imaging the metrology target; A method of selecting a set of target design parameters for the metrology target that, when imaged by the imaging system, results in a moire fringe pattern that meets selected design criteria by performing an experimental design method, the set of target design parameters including the first pitch and the second pitch.

53. 53. The method of claim 52, wherein the selected design criteria for the moiré fringe pattern comprises: The method includes at least one of the following: contrast of the moire fringe pattern, overlay accuracy, metrology repeatability, moire fringe period, and generation of a selected moire fringe order.

54. 53. The method of claim 52, wherein the set of target design parameters further includes at least one of a critical dimension of the first grating structure, a critical dimension of the second grating structure, a segmentation period of the first grating structure, a segmentation period of the second grating structure, a size of the first grating structure, and a size of the second grating structure.

55. 53. The method of claim 52, wherein the crosstalk is simulated using at least one of a Maxwell-based simulation and a Kirchhoff approximation.

56. 53. The method of claim 52, wherein the imaging system comprises: an illumination source for generating illumination; one or more illumination optics that direct illumination from the illumination source onto a metrology target; a detector that generates an image of the metrology target based on the illumination from the illumination source; an optical configuration of the imaging system can be configured, the optical configuration including a wavelength of the illumination, a polarization of the illumination incident on the metrology target, an angle of the illumination incident on the metrology target, or a focal position of the metrology target relative to the detector, and the set of target design parameters further includes the optical configuration of the imaging system.

57. 53. The method of claim 52, wherein the experimental design comprises: simulating an image of the metric target with a plurality of candidate sets of target design parameters; selecting a set of target design parameters from among the plurality of candidate sets of target design parameters based on the selected design criteria.

58. 58. The method of claim 57, wherein simulating an image of the metric target with the plurality of candidate sets of target design parameters comprises: A method of simulating images of the metrology target with a plurality of candidate sets of target design parameters using Maxwell-based simulation.

59. 53. The method of claim 52, wherein the experimental design comprises: generating a test metrology target with a plurality of candidate sets of target design parameters; imaging the test metrology target; Analyzing an image of the test metrology target with the selected design criteria; A method of selecting a set of target design parameters from among the plurality of candidate sets of target design parameters based on the analysis of the image of the test metrology target.

60. 53. The method of claim 52, wherein the experimental design comprises: simulating an image of the metric target with a plurality of candidate sets of target design parameters; Narrowing the plurality of candidate sets of target design parameters to N sets of target design parameters based on the selected design criteria; generating a test metrology target having the N sets of target design parameters with a plurality of candidate sets of metrology tool parameters; imaging the test metrology target; Analyzing an image of the test metrology target with the selected design criteria; A method for selecting a set of target design parameters and a set of metrology tool parameters based on the analysis of the image of the test metrology target.

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