System and method for isolating specific Fourier pupil frequencies in overlay metrology - Patents.com

Abstract

The system includes an illumination source configured to generate an illumination beam, a collection subsystem including an objective lens, one or more detectors disposed at a collection pupil plane, a light modulator, and a controller. The light modulator is configured to direct one or more selected portions of the measurement light to the one or more detectors. The controller includes one or more processors configured to execute program instructions that cause the one or more processors to execute a metrology recipe by receiving detection signals from the one or more detectors associated with the one or more selected portions of the measurement light directed to the one or more detectors and generating overlay measurements associated with at least two layers of the specimen based on the detection signals.

Description

[Technical field]

[0001] The present invention relates generally to overlay metrology, and more particularly to a system and method for overlay metrology using light modulation. [Background technology]

[0002] Overlay metrology generally refers to the measurement of the relative alignment between layers on a specimen, such as, but not limited to, a semiconductor device. Overlay measurements or overlay error measurements usually refer to the measurement of misalignment between features fabricated on two or more specimen layers. In a general sense, proper alignment of features fabricated on multiple specimen layers is required for a device to function properly.

[0003] The demand for smaller feature sizes and higher feature densities has correspondingly increased the demand for accurate and efficient overlay metrology. Metrology systems typically generate metrology data related to a sample by measuring or otherwise inspecting dedicated metrology targets (i.e., overlay targets) distributed across the sample. The sample is therefore typically mounted on a translation stage and translated such that the metrology targets are moved sequentially into the measurement field of view. In typical metrology systems employing the Move and Measure (MAM) approach, the sample remains stationary during each measurement. However, the time required for the translation stage to settle prior to a measurement can negatively impact throughput. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0364279 [Patent Document 2] US Patent Application Publication No. 2012 / 0033193 Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to provide a system and method for addressing the above-mentioned shortcomings. [Means for solving the problem]

[0006] An overlay metrology system is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination source configured to generate an illumination beam. In another exemplary embodiment, the system includes a collection subsystem having an objective lens configured to collect measurement light emitted from the sample in response to the illumination beam according to a metrology recipe, where the sample includes an overlay target including at least two layers according to the metrology recipe. In another exemplary embodiment, the system includes one or more detectors disposed at a first pupil plane. In another exemplary embodiment, the system includes a light modulator disposed at a second pupil plane, where the light modulator is configured to direct one or more selected portions of the measurement light in the second pupil plane to the one or more detectors. In another exemplary embodiment, the system includes a controller communicatively coupled to the collection subsystem, the controller including one or more processors configured to execute program instructions, the program instructions causing the one or more processors to execute the metrology recipe by receiving detection signals from the one or more detectors, where the detection signals are related to the one or more selected portions of the measurement light directed to the one or more detectors. In another illustrative embodiment, the one or more processors are further configured to execute program instructions that cause the one or more processors to execute the metrology recipe by generating overlay measurements associated with at least two layers of the specimen based on the detection signals in accordance with the metrology recipe.

[0007] An overlay metrology system having a field plane detector is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the system includes an illumination source configured to generate an illumination beam. In another exemplary embodiment, the system includes a collection subsystem having an objective lens configured to collect measurement light emitted from a specimen in response to the illumination beam according to a metrology recipe, where the specimen includes an overlay target including at least two layers according to the metrology recipe. In another exemplary embodiment, the system includes one or more detectors disposed at a collection field plane. In another exemplary embodiment, the system includes a light modulator disposed at a collection pupil plane, where the light modulator is configured to direct one or more selected portions of the measurement light in the collection pupil plane to the one or more detectors. In another exemplary embodiment, the system includes a controller communicatively coupled to the collection subsystem, the controller including one or more processors configured to execute program instructions, where the program instructions cause the one or more processors to execute a metrology recipe by receiving detection signals from the one or more detectors, where the detection signals are related to the one or more selected portions of the measurement light directed to the one or more detectors. In another illustrative embodiment, the one or more processors are further configured to execute program instructions that cause the one or more processors to execute the metrology recipe by generating overlay measurements associated with at least two layers of the specimen based on the detection signals in accordance with the metrology recipe.

[0008] A method for overlay metrology is disclosed according to one or more exemplary embodiments of the present disclosure. In one exemplary embodiment, the method includes directing, using a light modulator disposed in a second pupil plane, one or more selected portions of the measurement light in the second pupil plane, the one or more selected portions emanating from the sample, to one or more detectors disposed in a first pupil plane. In another exemplary embodiment, the method includes receiving detection signals from the one or more detectors associated with the one or more selected portions of the measurement light. In another exemplary embodiment, the system includes generating an overlay measurement associated with two layers of the sample based on the detection signals.

[0009] 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.

[0010] Many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Brief description of the drawings]

[0011] [Figure 1A] FIG. 1 is a conceptual diagram of a system for overlay metrology in accordance with one or more embodiments of the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram of an overlay metrology tool having a transmissive light modulator in a collection pupil plane in accordance with one or more embodiments of the present disclosure. [Figure 1C] FIG. 1 is a schematic diagram of an overlay metrology tool having a reflective light modulator in a collection pupil plane in accordance with one or more embodiments of the present disclosure. [Diagram 2] FIG. 1 illustrates a side view of one cell of a sample overlay target in accordance with one or more embodiments of the present disclosure. [Figure 3A]1 shows a schematic diagram of an illumination pupil plane distribution of a circular illumination beam in accordance with one or more embodiments of the present disclosure. [Figure 3B] 3B shows a schematic diagram of a collection pupil plane distribution of diffraction orders of the circular illumination beam of FIG. 3A in accordance with one or more embodiments of the present disclosure. [Figure 3C] 1 shows a schematic diagram of an illumination pupil plane distribution of an annular illumination beam in accordance with one or more embodiments of the present disclosure. [Figure 3D] 3D shows a schematic diagram of a collection pupil plane distribution of diffraction orders of the annular illumination beam of FIG. 3C in accordance with one or more embodiments of the present disclosure. [Figure 3E] 1 illustrates a simulated collection pupil distribution of a moiré target of a sample in accordance with one or more embodiments of the present disclosure. [Figure 4] 4 illustrates a graphical representation of simulated intensity signals of various regions of FIG. 3 measured across the X-direction of the sample, in accordance with one or more embodiments of the present disclosure. [Diagram 5] 1 illustrates a flowchart of a method for overlay metrology using a light modulator in a collection pupil plane in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present disclosure has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments described herein are considered to be illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings.

[0013] 1-5, a system and method for overlay metrology having a light modulator in a collection pupil plane is disclosed in accordance with one or more embodiments of the present disclosure.

[0014] Embodiments of the present disclosure are directed to using a light modulator in a collection pupil plane of an overlay metrology tool to filter and / or align a portion of light (herein referred to as measurement light) collected from a sample during an overlay measurement on one or more detectors. In this manner, the light modulator may actively control the portion of the measurement light that is incident on the detector during a measurement.

[0015] It is contemplated herein that the light modulators in the collection pupil may be implemented using a variety of overlay metrology target designs, measurement techniques, and corresponding overlay metrology tools.

[0016] In some embodiments, an image-based overlay metrology tool includes a light modulator in the collection pupil. For example, the image-based overlay metrology tool may illuminate an overlay target (e.g., an Advanced Imaging Metrology (AIM) target, a Box-in-Box metrology target, etc.) and capture an overlay signal including an image of the overlay target based on various imaging techniques, including but not limited to bright-field imaging or dark-field imaging. Thus, the overlay may be determined by measuring the relative positions (e.g., field plane distribution) of the overlay target features in the captured image. It is contemplated herein that a light modulator disposed in the collection pupil of the image-based overlay metrology tool may enable adjustment of pupil-based filtering of the measurement light that contributes to the generated image. For example, in the case of an overlay target having periodic features designed to generate discrete diffraction orders, a light modulator in the collection pupil may facilitate dynamic selection or blocking of diffraction orders that may contribute to the generated detection signal (e.g., image).

[0017] Additionally, collection pupil control using light modulators may be implemented in scanning or static measurement modes associated with imaging and / or scatterometry techniques. As an example, some scanning-based scatterometry techniques include a high-speed photodetector at a selected location of the collection pupil to capture a time-varying interference signal generated as the sample moves continuously and is scanned relative to the illumination beam. Various non-limiting scanning scatterometry overlay metrology techniques are described in U.S. Patent Application Publication No. 2022 / 0034652, filed February 17, 2021, U.S. Patent Application No. 17 / 119,536, filed December 11, 2020, U.S. Patent Application No. 17 / 708,958, filed March 30, 2022, and U.S. Patent Application No. 17 / 709,104, filed March 30, 2022, all of which are incorporated herein by reference in their entirety. For example, high-speed photodetectors may be placed at each overlap between selected diffraction orders to capture time-varying interference signals in these regions. It is contemplated herein that an optical modulator in the collection pupil of a scanning overlay metrology tool may enable adjustment of the control of the measurement light incident on the high-speed photodetectors. In some embodiments, such an optical modulator ensures proper alignment of the high-speed photodetectors by directing the measurement light in a selected portion of the collection pupil plane (e.g., a location that includes a time-varying interference signal indicative of overlay) to the photodetectors. In this manner, errors in the physical placement of the photodetectors in the collection pupil plane may be corrected. In some embodiments, an optical modulator in the collection pupil plane filters the measurement light incident on the photodetectors. For example, the signal-to-noise ratio (SNR) of the time-varying signal may be improved by filtering out portions of the measurement light that do not include the time-varying signal.

[0018] FIG. 1A is a conceptual diagram of a system for overlay metrology in accordance with one or more embodiments of the present disclosure.

[0019] In one embodiment, the system 100 includes an overlay metrology tool 102 for performing overlay measurements on a specimen 104 .

[0020] In an embodiment, as shown in FIG. 1A, the overlay metrology tool 102 includes an illumination subsystem 106 and a collection subsystem 110, which may include one or more detectors 112 and a light modulator 148 (e.g., in a collection pupil plane 114).

[0021] In one embodiment, as described above, the overlay metrology system 100 (or overlay metrology tool 102) includes an illumination subsystem 106 configured to generate illumination in the form of one or more illumination beams 108 to illuminate the specimen 104, and a collection subsystem 110 to collect light from the illuminated specimen 104 (e.g., according to a metrology recipe). Additionally, the one or more illumination beams 108 may be spatially restricted such that they illuminate selected portions of the specimen 104. For example, each of the one or more illumination beams 108 may be spatially restricted to illuminate a particular cell 204 of the overlay target 202.

[0022] It should be noted that descriptions / limitations of a specimen (e.g., features / layers / targets of the specimen) in this disclosure may be construed as descriptions / limitations according to a "metrology recipe." For example, system 100 may be configured for a particular type of specimen or feature of the specimen according to a metrology recipe. For example, system 100 may be designed (configured) and / or programmed (e.g., program instructions) to calculate overlay measurements of a particular type of feature of a specimen (e.g., grating-over-grating targets), which is what "according to a metrology recipe," etc., may mean.

[0023] 1A-1C, the one or more detectors 112 and the light modulator 148 of the overlay metrology tool 102 will be described in more detail in accordance with one or more embodiments of the present disclosure.

[0024] As mentioned above, in an embodiment, the system 100 may further include a light modulator 148. The light modulator 148 may generally be configured to selectively direct (e.g., transmit, reflect, direct, align, filter, etc.) one or more selected portions of the light (e.g., measurement light) in the collection pupil plane 114 to one or more detectors 112. In this manner, the light modulator 148 may enable a particular / selected portion of the distribution of the measurement light in the collection pupil plane to be selected / directed to be incident on the detector 112 (or one or more detectors 112).

[0025] 1B is a schematic diagram of an overlay metrology tool 102 having a transmissive light modulator 148 in the collection pupil plane 114, in accordance with one or more embodiments of the present disclosure. For example, the light modulator 148 of FIG. 1A may be a transmissive light modulator 148 (as shown in FIG. 1B). In one embodiment, the transmissive light modulator 148 is a deformable optical component.

[0026] FIG. 1C is a schematic diagram of an overlay metrology tool 102 having a reflective light modulator 148 in the collection pupil plane 114, according to one or more embodiments of the present disclosure. For example, the light modulator 148 of FIG. 1A may be a transmissive light modulator 148 configured to selectively transmit one or more selected portions of the light (e.g., measurement light) at the collection pupil plane 114 to one or more detectors 112. In this regard, the light modulator 148 may be a reflective light modulator 148 configured to selectively reflect one or more selected portions of the light (e.g., measurement light) at the collection pupil plane 114 to one or more detectors 112. In one embodiment, the reflective light modulator 148 is a Micro-Electro-Mechanical System (MEMS) device. In another embodiment, the reflective light modulator 148 is a Digital Light Processing (DLP) device. For example, the DLP may include a Digital Micromirror Device (DMD), which may be a MEMS device. In another embodiment, the light modulator includes at least one of a spatial light modulator, a microelectromechanical system (MEMS) device, or a deformable optical component.

[0027] Referring again generally to the light modulator, in other embodiments, the light modulator 148 is dynamically adjustable. For example, the light modulator 148 may be configured to be dynamically adjustable to provide dynamic selection of a selected portion of the measurement light directed to one or more detectors. For example, the overlay metrology tool 102 may be configured to adjust (e.g., dynamically select) one or more selected portions of the measurement light directed to one or more detectors before (e.g., prior to) the sample 104 entering the measurement field of view and / or before a measurement is obtained (e.g., before a detection signal is received).

[0028] Referring now generally to the detector 112, as discussed above, in some embodiments, the system 100 may include one or more detectors 112. In some embodiments, unless otherwise noted, the one or more detectors 112 may be used with imaging and / or scatterometry techniques for scanning overlay metrology, static overlay metrology, or both. For example, the one or more detectors 112 may be positioned in a collection pupil plane for scanning overlay metrology. In another example, the one or more detectors 112 may be positioned in a collection field plane for static overlay metrology. In scanning overlay metrology embodiments, the detector 112 may generally include any type of optical detector known in the art suitable for capturing interference signals generated when the sample 104 is translated by the translation stage 116 and / or when the one or more illumination beams 108 are scanned by a beam scanning subsystem.

[0029] In a scanning overlay metrology embodiment, by way of example, one or more detectors 112 are positioned in a collection pupil plane 114 (eg, a first pupil plane) as shown in FIGS. 1B and 1C.

[0030] For example, in the case of scanning overlay metrology, the one or more detectors 112 may include at least one of a photodiode, an avalanche photodiode, or a photomultiplier tube. For example, the one or more detectors 112 may include, but are not limited to, a high-speed photodiode. In another example, the one or more detectors 112 include one (or more) photodiodes. In another example, the one or more detectors 112 include one (or more) avalanche photodiodes. In another example, the one or more detectors 112 include one (or more) photomultiplier tubes.

[0031] In another embodiment in the context of scanning overlay metrology, the overlay metrology tool 102 may include a translation stage 116 for scanning the sample 104 through a measurement field of view of the overlay metrology tool 102 during measurement.

[0032] For example, scanning overlay metrology may mean receiving detection signals from one or more detectors 112 while the sample 104 is moving relative to the one or more detectors 112 such that the detection signals are time-varying interference signals.

[0033] Now, referring to overlay metrology in general (and not specifically to scanning overlay metrology), in another embodiment, sensor elements of one or more detectors underfill the first pupil plane, and the light modulator 148 directs selected portions of the measurement light to the locations of those sensor elements. Underfill may mean that the entire portion / extent of the distribution of light at the first pupil plane is not completely filled by the sensor elements of the one or more detectors, such that part of the distribution goes undetected.

[0034] In another embodiment, the sensor elements of one or more detectors are not aligned to the desired portion of the pupil plane. For example, for various reasons (such as, but not limited to, changes in wavelength, differences in characteristics of overlay targets, and other reasons that cause changes in the pupil range where detection is desired), the pupil portion / range where detection is desired may change and may not necessarily coincide with the detection target range (e.g., detection portion 310a and detection portion 310b in FIG. 3B). In this case, the light modulator 148 may be configured (controlled) to dynamically adjust to select for the detection target range. For example, the light modulator 148 may "direct" (transmit, reflect, align, direct, selectively block, filter, etc.) light such that the desired range of the pupil plane directed to the one or more detectors is the same as the selected portion 308 in the detection portion 310 shown in FIG. 3B (or at least a portion of the desired / selected range 308 is within the detection portion 310).

[0035] In another embodiment, in a scanning overlay metrology mode, the one or more detectors generate detection signals while the sample is stationary, e.g., the sample may be stationary while generating / receiving detection signals according to a metrology recipe, as opposed to an "on-the-fly" scanning method / system in which the sample may be continuously translated during generation of detection signals of the overlay targets, for example.

[0036] For static overlay metrology, in one embodiment, the light modulator 148 is in a collection pupil plane 114 and the one or more detectors 112 are in a collection field plane 150. In this regard, the one or more detectors 112 may be capable of imaging an entire field plane that is conjugate to the object plane in a general sense such that the sample 104 can be imaged from a top-down view (not shown).

[0037] For static overlay metrology, in some embodiments, the one or more detectors include a multi-pixel sensor. For example, the multi-pixel sensor can be at least one of a Charge-Coupled Device (CCD) or a Complementary Metal-Oxide-Semiconductor (CMOS) device. For example, the multi-pixel sensor can be a Charge-Coupled Device (CCD) in one embodiment and a Complementary Metal-Oxide-Semiconductor (CMOS) device in another embodiment.

[0038] Various elements will now be described with reference to scatterometry overlay metrology.

[0039] In some embodiments, the overlay metrology tool 102 as a whole may perform scatterometry overlay measurements (according to a metrology recipe) on portions of the sample 104 having an overlay target, such as, but not limited to, a grating-over-grating structure.

[0040] It is recognized herein that the distribution of diffraction orders of the illumination beam 108 by a periodic structure (such as a grating-over-grating structure) may be affected by various parameters, such as, but not limited to, the wavelength of the illumination beam 108, the angle of incidence of the illumination beam 108 in both the elevation and azimuth directions, the period (i.e., pitch) of the periodic structure, or the numerical aperture (NA) of the collection lens. Thus, in embodiments of the present disclosure, the illumination subsystem 106, the collection subsystem 110, and the overlay target 202 may be configured to exhibit an overlap distribution of zeroth and first diffraction orders in the collection pupil plane 114 of the collection subsystem 110. For example, the illumination subsystem 106 and / or the collection subsystem 110 may be configured to generate measurements for a grating-over-grating structure having a selected periodicity range that exhibits an overlap distribution. Additionally, various components (e.g., aperture, pupil, etc.) of the illumination subsystem 106 and / or the collection subsystem 110 may be adjustable to exhibit an overlap distribution of a given structure (e.g., a grating-over-grating) with a given periodicity.

[0041] The collection subsystem 110 may collect at least one of a 0th diffraction order (e.g., specular reflection) and + / -1 diffraction orders associated with the diffraction of the illumination beam 108 from the sample 104. Additionally, the collection subsystem 110 may include one or more detectors 112 positioned within the collection pupil plane 114 (e.g., at a location of overlap between the 0th diffraction order and the + / -1 diffraction order). For example, in some embodiments, the range 332 (described in more detail later in this disclosure) in FIG. 3E may be a location of overlap between the 0th diffraction order and the + / -1 diffraction order (e.g., in some cases, overlap with the 0th diffraction order and the + / -2 diffraction order) such that absolute grating position information (e.g., indicative of an overlay measurement) may be determined / generated (e.g., by the controller 122).

[0042] In another embodiment, the overlay metrology tool 102 includes an objective lens 136 for focusing the illumination beam 108 onto the sample 104 (e.g., an overlay target 202 having overlay target elements disposed on two or more layers of the sample 104). For example, the objective lens 136 may be configured to collect measurement light emitted from the sample 104 in response to the illumination beam 108 according to a metrology recipe. For example, the sample 104 may include an overlay target 202 formed of one or more cells 204, each cell 204 including a grating-over-grating structure formed from grating structures on two layers of the sample according to a metrology recipe (as shown in FIG. 2 ).

[0043] 2-4, various non-limiting embodiments of scanning scatterometry overlay metrology using an optical modulator 148 in the collection pupil plane 114 to detect signals from an overlay target 202 on the sample 104 will be described in more detail in accordance with one or more embodiments of the present disclosure. It should be noted that FIGS. 2-4 and the accompanying descriptions in the context of scanning scatterometry overlay metrology are non-limiting examples and descriptions, and that scanning scatterometry overlay metrology may be implemented in many and varied ways using the present disclosure.

[0044] FIG. 2 is a side view of one cell 204 of an overlay target 202 of a sample 104 in accordance with one or more embodiments of the present disclosure in the context of scatterometry overlay metrology.

[0045] In some embodiments, the scatterometry-based overlay metrology tool includes a light modulator in the collection pupil. In one example, the scatterometry-based overlay metrology tool may illuminate an overlay target (e.g., a grating-over-grating metrology target, etc.) and capture an overlay signal that includes an angular distribution of light emitted from the overlay target related to the diffraction, scattering, and / or reflection of the illumination beam. In this case, the overlay may be determined based on the angular distribution of the captured / measured light (e.g., pupil plane distribution).

[0046] In one embodiment, the grating structures on two layers (e.g., the first layer 210 and the second layer 214) in the overlay target 202 of the sample 104 have a common pitch (e.g., the periodic distance between elements 212).

[0047] In another embodiment, the grating structures on the two layers in the overlay target of the sample 104 have different pitches, and the grating-over-grating structures form a Moiré structure (as shown in FIG. 2).

[0048] In one embodiment, the cells 204 include first layer printed elements 208 disposed on a first layer 210 of the sample 104 and second layer printed elements 212 disposed on a second layer 214 of the sample 104, which are oriented such that the areas including the first layer printed elements 208 and the areas including the second layer printed elements 212 overlap to form a lattice-over-lattice structure. Additionally, as illustrated in FIG. 2, the first layer printed elements 208 may, but are not required to, be designed to include a selected amount of intended offset (due to pitch differences) from the second layer printed elements 212 along a measurement direction (e.g., the X-direction in FIG. 2), which may facilitate measurement of overlay errors associated with deviations from the intended offset along the measurement direction. As described in more detail below, it should be understood that the overlay target 202 may generally be formed from any number of cells 204, and that any particular cell 204 may include a lattice-over-lattice feature having periodicity along any direction.

[0049] For example, many scatterometry overlay metrology techniques typically determine overlay by illuminating an overlay target having a two-layer grating structure (e.g., a grating-over-grating structure), where the overlay measurement is based on the asymmetry between the positive (e.g., +1) and negative (e.g., -1) diffraction orders. For example, various scatterometry techniques are described in U.S. patent application Ser. No. 17 / 068,328, filed October 12, 2020, U.S. Pat. No. 10,824,079, issued November 3, 2020, U.S. Pat. No. 10,197,389, issued February 9, 2019, and Adel et al., “Diffraction order control in overlay metrology: a review of the roadmap options,” Proc. SPIE. 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 692202 (2008), all of which are incorporated by reference in their entireties herein. It is contemplated herein that an optical modulator positioned within the collection pupil of a scatterometry overlay metrology tool may enable control and / or filtering of the diffraction orders directed to one or more detectors during measurement.

[0050] However, it should be understood that the overlay target 202 of FIG. 2 (and associated elements of FIGS. 3A-4) and associated description are provided for illustrative purposes only and should not be construed as limiting. Rather, the overlay target 202 may include any suitable design (e.g., a grating-over-grating overlay target design, grating next to grating, three-layer grating). For example, the overlay target 202 may include any number of cells 204 suitable for measurements along two directions. Furthermore, the cells 204 may be distributed in any pattern or arrangement. For example, metrology target designs suitable for scanning metrology are outlined in U.S. Pat. No. 11,073,768, issued July 27, 2021, which is incorporated herein by reference in its entirety. In one embodiment, the overlay target 202 includes one or more cell groups distributed along a scanning direction (e.g., a direction of motion of the sample 104), where the cells 204 within each particular cell group are oriented to have a periodic grating-over-grating structure along a common direction. For example, a first cell group may include one or more cells 204 with periodicity along the X direction, and a second cell group may include one or more cells 204 with periodicity along the Y direction. In this manner, all cells 204 in a particular cell group may be imaged / detected simultaneously while the sample 104 is scanned through the measurement field of view of the collection subsystem 110. As another example, diagonal targets suitable for orthogonal measurements in a single scan are outlined in U.S. Patent Application Publication No. 2021 / 0364935, published Nov. 25, 2021, and incorporated herein by reference in its entirety. Additionally, the illumination beam is not limited to those shown in FIGS. 3A and 3C, but may be of any number of configurations / shapes, and the detector 112 is not limited to the locations, sizes, etc. of the illustrated ranges (e.g., first detection range 330a and second detection range 330b). In some embodiments, the size and shape of the diffraction orders at the collection pupil plane 114 may generally be related to the size and shape of the illumination beam 108 on the sample 104.For example, although not shown, if the illumination beam 108 is elongated, the diffraction orders may be elongated as well (eg, in orthogonal directions).

[0051] 3A-3E, various examples of illumination pupil plane distributions (shown in FIGS. 3A and 3C) and corresponding collection pupil plane distributions (shown in FIGS. 3B and 3D) of diffraction orders of an illumination beam distribution are illustrated in accordance with one or more further embodiments of the present disclosure. In particular, a selected portion of the measurement light (e.g., selected portion 308a in FIG. 3B, which is directed / directable by the light modulator 148) and a detected portion of the measurement light (e.g., detected portion 310a, which is detected / detectable by the detector 112) and a diffraction order (e.g., 1 (-1) circular diffraction order 306b, which emanates from the overlay target) are illustrated in FIGS. 3A-3E in accordance with one or more embodiments of the present disclosure. FIGS. 3A-3B relate to a diffraction order corresponding to a circular illumination beam 304, and FIGS. 3C-3E relate to a diffraction order corresponding to an annular illumination beam 324.

[0052] In an embodiment, as described above, the optical modulator 148 may be configured to direct (e.g., transmit, reflect, align, direct, selectively block, etc.) one or more selected portions (ranges) of light to one or more detection portions (ranges) to be detected by the one or more detectors 112. In this regard, the selected portion may be a portion (e.g., of the measurement light) that is selected for detection by directing (using the optical modulator) the selected portion to the portion (range) to be detected (e.g., to the detection portion corresponding to that to be detected by the detector 112). Alternatively or additionally (e.g., described with respect to one selected portion for clarity, but not limited to a singular portion), the selected portion may be a filtered / unfiltered portion, such that only the selected portion is detected by the detector 112 (e.g., adjacent portions around the selected portion are not detected by the detector (e.g., filtered out by the optical modulator 148)). For example, although not shown, in some embodiments, a simulated distribution of light at the collection pupil plane 114 of the detector 112 (rather than the pupil plane of the light modulator as FIG. 3B was originally intended to illustrate) may be illustrated by modifying FIG. 3B such that distribution 302 is completely (or nearly completely) absent of light in all portions / ranges except for selected (overlapping) portions 308 (e.g., first selected portion 308a and second selected portion 308b in FIG. 3B). Further, for such examples, detected portion 310 is the portion / range that is detected (e.g., will be detected as a detected signal (e.g., a time-varying interference signal)) by each detector 112. Note that in some embodiments of the above example, the detection portion 310 is larger than the selected portion 308 (as shown in FIG. 3B ) so that a smaller amount of measurement light than the theoretical maximum detection portion / range detectable by the detector 112 is actually detected (e.g., increasing the signal-to-noise ratio by allowing irrelevant and / or undesired portions to be filtered out and the desired portion to be reliably detected (with a margin of error)).However, it should be noted that any configuration may be used, for example, any configuration of selected portions that are larger, smaller, and / or equal, fully overlapping and / or partially overlapping with the detection portion may be used.

[0053] Generally, by way of example, and not by way of limitation to these examples, the one or more selected portions may be first selected portion 308a, second selected portion 308b of FIG. 3B, first selected portion 328a, second selected portion 328b of FIG. 3D, and / or selected portion 332 of FIG. 3E.

[0054] Further, the one or more detection portions may be, but are not limited to, the first detection portion 310a, the second detection portion 310b of FIG. 3B, the first detection portion 330a, the second detection portion 330b of FIG. 3D, and / or the detection portion 334 of FIG. 3E. For example, the one or more detectors 112 may be a first photodiode 112 configured to detect an average intensity of light within a detection range 330a, and a second photodiode 112 configured to detect an average intensity of light within a detection range 330b. Further, the controller 122 may be configured to generate an overlay measurement related to two layers of the sample 104 based on the detection signals (of the first photodiode 112 and the second photodiode 112).

[0055] In one embodiment, the illumination subsystem 106 illuminates the overlay target 202 at normal incidence (or near normal incidence) with one or more illumination beams 108. Additionally, the one or more illumination beams 108 may illuminate the overlay target 202 at a limited range of incidence angles, as illustrated by the limited size of the distribution 302 at the collection pupil plane 114 in FIG. 3B. In this regard, the overlay target 202 may diffract the one or more illumination beams 108 into discrete diffraction orders 306 (306a, 306b, 306c).

[0056] 3A shows a schematic diagram of an illumination pupil plane distribution 300 of a circular illumination beam 304, in accordance with one or more embodiments of the present disclosure. In one embodiment, the illumination beam 108 of the system 100 is circular (as illustrated by the circular illumination beam 304).

[0057] 3B shows a schematic diagram of a collection pupil plane distribution 302 of diffraction orders of the circular illumination beam 304 of FIG. 3A in accordance with one or more embodiments of the present disclosure. For example, the circular illumination beam 304 may form circular diffraction orders in the collection pupil plane 114 as shown in FIG. 3B by a zeroth (0) circular diffraction order 306a, a first (+1) circular diffraction order 306c, and a first (-1) circular diffraction order 306b when the overlay target 202 is illuminated by the circular illumination beam 304.

[0058] 3C shows a schematic diagram of an illumination pupil plane distribution 320 of an annular illumination beam 324, in accordance with one or more embodiments of the present disclosure. In one embodiment, the illumination beam 108 of the system 100 is annular (e.g., ring-shaped), as illustrated by the annular illumination beam 324.

[0059] 3D shows a schematic diagram of a collection pupil plane distribution of diffraction orders of the annular illumination beam of FIG. 3C in accordance with one or more embodiments of the present disclosure. For example, the annular illumination beam 324 may form annular diffraction orders in the collection pupil plane 114 as shown in FIG. 3D by the zeroth (0) annular diffraction order 326a, the first (+1) annular diffraction order 326c, and the first (-1) annular diffraction order 326b when the overlay target 202 is illuminated by the annular illumination beam 324.

[0060] In another example, the selected portion of the measurement light 138 directed to the one or more detectors 112 may include overlapping regions of annular diffraction orders from a Moiré structure (e.g., the overlapping rings of Figures 3D and 3E).

[0061] 3E is a diagram illustrating a simulated pupil distribution 346 of a moiré target of a sample in accordance with one or more embodiments of the present disclosure. For example, the simulated pupil distribution 346 may be the simulated distribution of the moiré overlay target 202 shown in FIG. 2 and may be theoretically captureable within the collection pupil plane 114. Additionally, the simulated pupil distribution 346 may be the simulated pupil distribution of the collection pupil plane distribution 322 shown in FIG. 3D of the diffraction orders of the annular illumination beam 324.

[0062] For example, Figure 3E may be a top view of a collection pupil in collection pupil plane 114 (e.g., any collection pupil plane 114) of overlay metrology tool 102, in accordance with one or more embodiments of the present disclosure. In this regard, collection pupil plane 114 may correspond to collection pupil plane 114 in collection subsystem 110 as illustrated in Figure 1B or 1C.

[0063] In an embodiment, each ring or partial ring shown in FIG. 3E may be a diffraction order of diffraction of a grating element (eg, element 212) of FIG.

[0064] For example, the simulated pupil distribution 346 may include a zeroth (0) annular diffraction order 336, a second (top) layer annular diffraction order 340 of a first (+1) order, a second (−1) layer annular diffraction order 338 of a first (−1) order, a first (bottom) layer annular diffraction order 344 of a first (+1) order, and a first layer annular diffraction order 342 of a first (−1) order. For example, the second (top) layer annular diffraction order 340 of a first (+1) order may be a first diffraction order from element 212 of the second layer (top layer) 214 of FIG. 2. Additionally, the first layer annular diffraction order 344 of a first (+1) order may be a first diffraction order from element 208 of the first layer (bottom layer) 210 of FIG. 2. In this regard, the detection range 334 may detect overlap of diffraction orders of multiple layers (e.g., the first layer 210 and the second layer 214) of the overlay target 202 to generate, for example, an overlay measurement (misregistration) between the layers.

[0065] For example, according to the metrology recipe, the first diffraction orders (e.g., the second (top) layer annular diffraction order 340 of 1st (+1), the second (-1) layer annular diffraction order 338 of 1st (+1), the first (bottom) layer annular diffraction order 344 of 1st (+1), and the first layer annular diffraction order 342 of 1st (-1)) may partially overlap with the zeroth diffraction order 336, as shown in FIG. 3E. For example, as shown in FIG. 3E, the second layer annular diffraction order 340 of 1st (+1) and the first layer annular diffraction order 344 of 1st (+1) overlap with each other (indicated by the two left selected portions 334). Similarly, the first (-1) diffraction order overlaps with the zeroth (0) annular diffraction order 336 (indicated by the two right selected portions 334).

[0066] FIG. 4 shows a graphical representation 400 of simulated intensity signals of various regions of FIG. 3E measured across the X-direction of the sample 104 in accordance with one or more embodiments of the present disclosure.

[0067] For example, Figure 4 may be a chart of simulated detected signals received by one or more detectors 112 at a collection pupil plane 114 (e.g., of a moiré overlay target 202 including layers with gratings of different pitches) and measured across an X-direction (e.g., the X-direction in Figure 2) of the sample 104. In another example, the detected signals may be received as the sample is moving (e.g., in a fast scanning system) such that the detected signals are time-varying signals (e.g., interference signals).

[0068] In some embodiments, the first signal 402 may be a simulated signal of an average intensity (e.g., light intensity) of at least one of the four detection portions (ranges) 334 shown in Figure 3E, measured across the X direction. Additionally, the second signal 404 may be an average intensity of the entire simulated distribution 346 of Figure 3E, measured across the X direction.

[0069] It should be noted that the selected portion 332 may be selected or configured to be selected such that the signal-to-noise ratio (SNR) of the signal is improved / higher as shown by the first signal 402 compared to the second signal 404. Note that in the example of Figure 4, the first signal 402 associated with the detected portion 334 (and the selected portion 332) has a large oscillation intensity that has a higher SNR than the second signal 404 associated with the average intensity over the collection pupil range.

[0070] In some embodiments, and as is evident from FIG. 4, it is contemplated that selection on one or more selected portions of the pupil plane may be necessary to generate meaningful information.

[0071] For example, by selecting for one or more selected portions of the pupil plane, the signal contributions according to their position can be separated, thus simplifying the computations for determining / generating the overlay measurement.

[0072] The following equations relate to an overlay target having two or more layers, with a first (top) layer having a first pitch (p1) and a second (bottom) layer having a second pitch (p2), as shown in Figure 2. For example, the following equations may be used for Diffraction-Based Overlay (DBO) measurements. In another example, the following equations may be used for Robust Advanced Imaging Metrology (rAIM) targets.

[0073] The intensity measured at the overlap between the zeroth and first diffraction orders (eg, corresponding to a time-varying signal) from a grating with pitch 1 is:

number

[0074] The intensity measured at the overlap between the zeroth and first diffraction orders (eg, corresponding to a time-varying signal) from a grating with pitch 2 is:

number

[0075] The center of symmetry of p1 can be characterized as follows:

number

[0076] The center of symmetry of p2 can be characterized as follows:

number

[0077] The overlay measurements for plus and minus (taken separately to remove the X0 dependency) are as follows:

number

[0078] The final (overall) overlay measurements are:

number

[0079] where P1 is the pitch of the elements of the first layer, P2 is the pitch of the elements of the second layer, A0, A1 correspond to the intensity of the zeroth and first diffraction orders, respectively, associated with pitch P1, A0', A1' correspond to the intensity of the zeroth and second diffraction orders, respectively, associated with pitch P2, and φ is the linear function of l p1± is the phase term associated with the signal, and θ is p2± is the phase term associated with the signal, X is the variable in the X direction, X0 is the position in the X direction at time 0, and DC is a constant offset similar to using direct current rather than alternating current.

[0080] The X direction in FIG. 4 may be the scan direction of the overlay metrology system 100 across the elements 212 (grid) of the cell 204, such as the X direction shown in FIG.

[0081] In some embodiments, advantages of directing a selected portion (e.g., within detection portion 334) to one or more detectors as shown in Figures 3A-4 include at least one of: a higher signal-to-noise ratio in the detected signal; obtaining overlap of diffraction orders related to information about absolute diffraction grating position and overlay measurements; and excluding portions (ranges) of the pupil (e.g., irrelevant ranges) from the detected signal that would add offset and / or error due to contributions from undesired diffraction orders.

[0082] 3E shows a distribution of diffraction orders (e.g., the zeroth (0) annular diffraction order 336) distributed along a direction of periodicity (e.g., the X-direction here) of the grating-over-grating structure at the collection pupil plane 114. Specifically, the first diffraction orders 338, 340 are distributed on opposite sides of the zeroth (0) annular diffraction order 336.

[0083] In another embodiment, the overlay metrology tool 102 includes one or more detectors 112 arranged in overlapping regions (overlapping diffraction orders) of the collection pupil plane 114. For example, a first detector can be arranged in the first overlapping region (i.e., the top right detection portion 334), and a second detector can be arranged in the second overlapping region (i.e., the top left detection portion 334). Each of the one or more detectors 112 can then capture a time-varying interference signal as the sample 104 is scanned. Specifically, the overlay target 202 can be scanned along the direction of the periodicity of the structure (e.g., the X direction of the grating-over-grating structure in FIG. 2), where the phase of the + / -1 diffraction orders (e.g., diffraction orders 338, 340) relative to the zeroth diffraction order (e.g., the zeroth (0) annular diffraction order 336) shifts in the opposite direction. Therefore, scanning the overlay target 202 a length equal to the pitch of the grating-over-grating structure may result in a phase shift of 2π (in opposite directions) in each of the + / -1 diffraction orders, and the intensity captured by each of the detectors 112 may oscillate through the interference fringes.

[0084] For example, in some embodiments, the light modulator 148 needs to be dynamically adjustable, e.g., the light modulator 148 needs to be configured to be able to adjust one or more selected portions of the measurement light before a measurement (e.g., before receiving a detection signal), such as before a fast-scanning measurement during a scanning mode and / or before a move-and-measure (MAM) measurement in a stationary mode.

[0085] In the same example, in a general sense, the bandwidth or response time of the detector 112 should be sufficient to resolve the time frequency of the interference fringes. For example, if the scanning speed along the measurement direction is 10 centimeters per second and the target pitch is 1 micrometer, the interference signal will oscillate at a rate on the order of 100 kHz. In one embodiment, the detector 112 includes a detector having a bandwidth of at least 1 GHz. However, it should be understood that this value is not required. Rather, the bandwidth of the detector 112, the translation speed along the measurement direction, and the pitch of the grating-over-grating structure may be selected together to provide a desired sampling rate of the interference signal.

[0086] In another embodiment, one or more detectors 112 are disposed at (or near) the first pupil plane, and the light modulator is disposed at the second pupil plane. For example, but not limited to, the second pupil plane may be the collection pupil plane 114 in which (or near) the light modulator 148 resides in FIGS. 1B-1C. It should be noted that one or more collection channel beam splitters (not shown) may be disposed before or after the light modulator 148 such that at least one detector of the two or more detectors 112 is disposed in a separate collection channel 144 and may detect a separate detection portion (e.g., separate detection portion 334) of the collection pupil plane 114. In this regard, the first pupil plane may be at multiple physical locations (e.g., where each detector 112 is disposed) of the collection pupil plane split into multiple channels 144. It should be noted that the first pupil plane (where the detectors are disposed) is different from the second pupil plane (where the light modulator is disposed).

[0087] Alternatively, two or more detectors may each be located within the same collection channel 144 .

[0088] In an embodiment, the one or more detectors may be two or more detectors. In other embodiments, the one or more detectors may be four or more detectors. For example, four separate detectors 112 of the four or more detectors may be positioned (or light may be directed to them) such that each of the four separate detectors 112 detects a detection signal corresponding to one of the four detection portions 334 (e.g., the overlapping range of the zeroth diffraction order and the first diffraction order) shown in FIG. 3E.

[0089] Reference will now be made to method 500 in relation to overlay metrology generally, unless otherwise indicated. FIG. 5 illustrates a flow chart of method 500 for overlay metrology using a light modulator in collection pupil plane 114, in accordance with one or more embodiments of the present disclosure. It is noted that the embodiments and enabling techniques described herein above in relation to system 100 should be construed as extending to method 500. It is further noted herein that the steps of method 500 may be implemented in whole or in part by system 100. However, it is further recognized that method 500 is not limited to system 100 in that additional or alternative system-level embodiments may perform all or a portion of the steps of method 500.

[0090] In one embodiment, the method 500 includes a step 502 of directing one or more selected portions of the measurement light in the second pupil plane, the selected portions emanating from the sample, to one or more detectors disposed in the first pupil plane using a light modulator disposed in the second pupil plane. For example, the selected portions 332 as shown in FIG. 3E may be directed using a light modulator 148 disposed in the second collection pupil plane 114. For example, the second collection pupil plane 114 may be any collection pupil plane 114 (e.g., the collection pupil plane 114 shown in FIG. 1B). For example, the controller 122 may be configured to execute program instructions that cause the light modulator 148 to direct one or more selected portions 332 of the measurement light in the second pupil plane to one or more detectors disposed in the first pupil plane.

[0091] For example, the top right selected portion 332 of the distribution 346 in FIG. 3E may be the range desired to be directed to one or more detectors 112, but the actual distribution (not shown) may differ from the distribution 346 due to changes (e.g., caused by differences in wavelength, angle of incidence, pitch of the sample, or any other possible cause) and / or a different type of selected portion (not shown) may be desired to be directed. In such an example, the light modulator 148 may be configured (e.g., controlled by a controller) to make adjustments (e.g., change which micromirrors of the MEMS reflect light to one or more detectors) to accommodate the changes and / or to select a different selected portion to be directed. For example, the selected portion 334 of the diffraction orders may be moving in the collection pupil plane (e.g., due to a change in wavelength) and the light modulator 148 may need to adjust the direction in which it directs the measurement light so that the desired range of the pupil plane 114 can be detected by one or more detectors 112 and / or may need to selectively block undesired ranges of the measurement light.

[0092] In another embodiment, the method 500 includes receiving 504 a detection signal associated with one or more selected portions of the measurement light from one or more detectors. For example, the detectors 112 may be positioned within a detection range (e.g., detection range 334) of the collection pupil plane 114 such that light (e.g., measurement light) directed by the light modulator 148 is directed (e.g., allowed to pass / transmit, directed, aligned, selectively blocked from being transmitted / reflected, etc.) to the one or more detectors 112. For example, light within the detection range 334 associated with the detector 112 may be detected as a detection signal. For example, the controller 122 may be configured to execute program instructions that cause the detection signal to be received from the one or more detectors 112.

[0093] For example, in a scanning overlay metrology embodiment, the reception of the detection signal may occur when the sample 104 is moving relative to the one or more detectors 112 such that the detection signal is a time-varying interference signal. For example, the plotted signal in FIG. 4 may be such a time-varying signal. A "time-varying signal" may refer to a signal acquired by an "on-the-fly" overlay metrology method / system acquired over a scanning direction (e.g., X-direction in FIG. 2) over time. For example, the time-varying signal may be a signal acquired by a fast diode, which may correspond to the diffraction overlap range 334 of the collection pupil plane distribution 346 as the measurement light is scanned across one or more gratings (e.g., element 212) of the sample 104 as shown in FIG. 2.

[0094] In another embodiment, referring back to overlay metrology generally, the method 500 includes generating overlay measurements associated with two layers of the specimen based on the detection signals 506. For example, the controller 122 may be configured to execute program instructions that cause the generating overlay measurements associated with two layers of the specimen based on the detection signals.

[0095] For example, in scanning overlay metrology embodiments, overlay targets and / or algorithms associated with static measurements of stationary samples, such as, but not limited to, those described in the above-referenced U.S. Patent Application Publication No. 2019 / 0004439, may be extended to scanning formats.

[0096] As mentioned above, Figures 2-4 relating to scanning scatterometry overlay metrology are intended to be non-limiting examples, and it should be understood that a light modulator in the collection plane may be used for collection pupil plane control of any overlay metrology technique.

[0097] 1A-1C, additional components of the overlay metrology tool 102, in accordance with one or more embodiments of the present disclosure, are described in detail below. For example, the controller 122, the processor 124, and various optical components are described in detail below with respect to overlay metrology generally (i.e., not specifically with respect to scanning or static overlay metrology, unless otherwise noted).

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

[0099] The one or more processors 124 of the controller 122 may generally include any processor or processing element known in the art. For purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 124 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In one embodiment, the one or more processors 124 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute programs configured to operate or operate in conjunction with the system 100 as described throughout this disclosure. Additionally, the various different subsystems of the system 100 may include processors or logic elements suitable for performing at least some of the steps described in this disclosure. Therefore, the above description should not be construed as limiting the embodiments of the present disclosure, but merely as illustrative. Furthermore, the steps described throughout the present disclosure may be performed by one controller or may be performed by multiple controllers. Furthermore, the controller 122 may include one or more controllers housed in a common housing or in multiple housings. In this manner, any controller or combination of controllers may be packaged separately as a module suitable for integration into the system 100.Additionally, the controller 122 may analyze or otherwise process data received from one or more detectors 112 and provide the data to additional components within the system 100 or external to the system 100 .

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

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

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

[0103] In another embodiment, the controller 122 generates (or determines) an overlay measurement between layers (e.g., the first layer 210 and the second layer 214) of the overlay target 202 along the measurement direction based on a comparison between the detection signals. For example, the controller 122 may compare the magnitude and / or phase of the detection signals to generate the overlay measurement. For example, U.S. Pat. No. 10,824,079, issued Nov. 3, 2020, which is incorporated herein by reference in its entirety, outlines the electric field of the diffraction orders in the collection pupil and further provides a specific relationship between overlay and the measured intensity in the pupil plane. It is contemplated herein that the systems and methods disclosed herein may extend the teachings of U.S. Pat. No. 10,824,079 to detection signals captured by a detector positioned in the overlap region between the 0th and + / -1th diffraction orders. In particular, it is contemplated herein that the overlay on the sample may be proportional to the relative phase shift between the two detection signals. In another example, the relative intensities of the diffraction orders in the pupil plane may be extracted from the detection signals. In this manner, any overlay algorithm based on the relative intensity differences of the diffraction orders known in the art may be applied to generate an overlay measurement.

[0104] Additionally, the controller 122 may calibrate or otherwise correct the overlay measurements based on known, assumed, or measured features of the specimen that may also affect the detected signal, such as, but not limited to, sidewall angle or other specimen asymmetries.

[0105] 1B (and 1C), various components of the overlay metrology tool 102 are described in more detail, in accordance with one or more embodiments of the present disclosure.

[0106] In one embodiment, the illumination subsystem 106 includes an illumination source 128 configured to generate at least one illumination beam 108. The illumination from the illumination source 128 may include one or more selected wavelengths of light, including, but not limited to, ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0107] The illumination source 128 may include any type of illumination source suitable for providing at least one illumination beam 108. In one embodiment, the illumination source 128 is a laser source. For example, the illumination source 128 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, and the like. In this regard, the illumination source 128 may provide an illumination beam 108 having high coherence (e.g., high spatial coherence and / or temporal coherence). In another embodiment, the illumination source 128 includes a Laser-Sustained Plasma (LSP) source. For example, the illumination source 128 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements capable of emitting broadband illumination when excited into a plasma state by a laser light source.

[0108] In another embodiment, the illumination subsystem 106 includes one or more optical components suitable for directing the illumination beam 108 to the sample 104 as well as modifying and / or conditioning the illumination beam 108. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., for collimating the illumination beam 108, relaying the illumination pupil plane 120 and / or the illumination field plane 132, etc.). In another embodiment, the illumination subsystem 106 includes one or more illumination control optics 134 for shaping or otherwise controlling the illumination beam 108. For example, the illumination control optics 134 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., stationary mirrors, translating mirrors, scanning mirrors, etc.).

[0109] In some embodiments, the illumination subsystem 106 illuminates the sample 104 with two or more illumination beams 108. Additionally, the two or more illumination beams 108 may, but need not, be incident on different portions of the sample 104 (e.g., different cells 204 of the overlay target 202) within the measurement field of view (e.g., the field of view of the objective lens 136). It is contemplated herein that the two or more illumination beams 108 may be generated using a variety of techniques. In one embodiment, the illumination subsystem 106 includes two or more openings in the illumination field plane 132. In another embodiment, the illumination subsystem 106 includes one or more beam splitters for splitting illumination from the illumination source 128 into the two or more illumination beams 108. In another embodiment, at least one illumination source 128 directly generates the two or more illumination beams 108. In a general sense, each illumination beam 108 may be considered to be part of a different illumination channel, regardless of the technique by which the various illumination beams 108 are generated.

[0110] The collection subsystem 110 may include one or more optical elements suitable for modifying and / or conditioning the light 138 collected from the sample 104. In one embodiment, the collection subsystem 110 includes one or more collection lenses 140 (e.g., for collimating the illumination beam 108, relaying pupil and / or field planes, etc.), which may, but need not, include the objective lens 136. In another embodiment, the collection subsystem 110 includes one or more collection control optics 142 for shaping or otherwise controlling the collected light 138. For example, the collection control optics 142 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., stationary mirrors, translating mirrors, scanning mirrors, etc.). In another example, the collection subsystem 110 may include one or more collection field surfaces 150. It should be noted that the location of the light modulators may be located before and / or after the collection control optics 142 and / or one or more collection lenses 140, and is not limited to the locations shown in Figures 1B or 1C.

[0111] In another embodiment, the collection subsystem 110 includes two or more collection channels 144, with each collection channel 144 having a separate detector 112 (or multiple detectors 112). For example, the overlay metrology tool 102 may include one or more beam splitters 146 positioned to split the collected light 138 among the collection channels 144. Additionally, the beam splitters 146 may be polarizing beam splitters, non-polarizing beam splitters, or a combination thereof.

[0112] In one embodiment, the multiple collection channels 144 are configured to collect light from multiple illumination beams 108 on the sample 104. For example, if the overlay target 202 has two or more cells 204 distributed in a direction different from the scanning direction, the overlay metrology tool 102 may simultaneously illuminate different cells 204 with different illumination beams 108 and simultaneously capture detection signals associated with each illumination beam 108. Furthermore, in some embodiments, the multiple illumination beams 108 directed at the sample 104 may have separate polarizations. In this manner, the diffraction orders associated with each of the illumination beams 108 may be separated. For example, the polarizing beam splitter 146 may efficiently separate the diffraction orders associated with the different illumination beams 108. As another example, a polarizer may be used in one or more collection channels 144 to separate desired diffraction orders for measurement.

[0113] 1A , it is noted herein that one or more components of the system 100 may be communicatively coupled to various other components of the system 100 in any manner known in the art. For example, the one or more processors 124 may be communicatively coupled to each other and to other components via wired (e.g., copper wire, fiber optic cable, etc.) or wireless (e.g., RF coupling, IR coupling, WiMax, Bluetooth, 3G, 4G, 4G LTE, 5G, etc.) connections. As another example, the controller 122 may be communicatively coupled to one or more components of the overlay metrology tool 102 via any wired or wireless connection known in the art.

[0114] In one embodiment, the one or more processors 124 may include any one or more processing elements known in the art. In this sense, the one or more processors 124 may include any microprocessor-type device configured to execute software algorithms and / or instructions. In one embodiment, the one or more processors 124 may be comprised of a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or other computer system (e.g., a networked computer) configured to execute a program configured to operate the system 100 as described throughout this disclosure. It should be appreciated that the steps described throughout this disclosure may be performed by one computer system or, alternatively, by multiple computer systems. Furthermore, it should be appreciated that the steps described throughout this disclosure may be performed by any one or more of the one or more processors 124. In general, the term "processor" may be broadly defined to encompass any device having one or more processing elements that executes program instructions from the memory 126. Furthermore, the various different subsystems of the system 100 may include processors or logic elements suitable for performing at least some of the steps described throughout this disclosure. Therefore, the above description should not be construed as a limitation on the present disclosure, but merely as illustrative.

[0115] Those skilled in the art will recognize that the components (e.g., operations), devices, objects, and the accompanying discussion described herein are used as examples for conceptual clarity, and that various configuration changes are contemplated. As a result, when used herein, the specific exemplars described and the accompanying discussion are intended to be representative of their more general genus. In general, the use of any specific exemplar is intended to be representative of that genus, and the absence of a specific component (e.g., operation), device, and object should not be considered limiting.

[0116] Those skilled in the art will appreciate that there are a variety of vehicles (e.g., hardware, software, and / or firmware) by which the processes and / or systems and / or other techniques described herein may be implemented, and that the preferred vehicle will vary depending on the context in which the processes and / or systems and / or other techniques are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may select a primarily hardware and / or firmware vehicle. Alternatively, if flexibility is paramount, the implementer may select a primarily software implementation. Or, still further alternatively, the implementer may select some combination of hardware, software, and / or firmware. Thus, there are a number of vehicles by which the processes and / or devices and / or other techniques described herein may be implemented, and no vehicle utilized is inherently better than another in that the choice is dependent on the context in which the vehicle is to be deployed and the specific concerns of the implementer (e.g., speed, flexibility, predictability), all of which may vary.

[0117] The preceding description is presented to enable any person skilled in the art to make and use the invention provided in the context of a particular application and its requirements. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the specific embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0118] With respect to the use of substantially any plural and / or singular term herein, those skilled in the art can translate from the plural to the singular and / or from the singular to the plural as appropriate to the context and / or application. For the sake of clarity, the various singular / plural permutations are not expressly set forth herein.

[0119] All of the methods described herein may include storing results of one or more steps of the method embodiments in memory. The results may include any of the results described herein and may be stored in any manner known in the art. The memory may include any memory described herein, or any other suitable storage medium known in the art. After storing the results, they may be accessed in the memory and used by any of the method or system embodiments described herein, formatted for display to a user, used by other software modules, methods, or systems, etc. Furthermore, the results may be stored "permanently," "semi-permanently," "temporarily," or for a period of time. For example, the memory may be a random access memory (RAM), and the results may not necessarily remain in memory indefinitely.

[0120] It is further contemplated that each of the method embodiments described above may include any other step(s) of any other method(s) described herein. Additionally, each of the method embodiments described above may be performed by any of the systems described herein.

[0121] The subject matter described herein may illustrate various components that are contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, an arrangement of components to achieve the same functionality is effectively "associated" with one another such that a desired functionality is achieved. Thus, any two components that are combined herein to achieve a particular functionality may be considered to be "associated" with one another such that a desired functionality is achieved, regardless of architecture or intervening components. Similarly, any two components so associated may also be considered to be "connected" or "coupled" with one another to achieve a desired functionality, and any two components so associateable may also be considered to be "couplable" with one another to achieve a desired functionality. Specific examples of couplable include, but are not limited to, physically joinable and / or physically interacting components, and / or wirelessly interactable and / or wirelessly interacting components, and / or logically interacting and / or logically interacting components.

[0122] It should further be understood that the present invention is defined by the appended claims. In general, those skilled in the art will understand that the terms used herein, and particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "including but not limited to," etc.). Those skilled in the art will further understand that if a certain number of introduced claim recitations is intended, such intention will be explicitly stated in the claim, and that in the absence of such recitation, no such intention exists. For example, to aid in understanding, the following appended claims may include the use of the introductory phrases "at least one" and "one or more" to introduce the claim recitations. However, the use of such phrases should not be construed as suggesting that introducing a claim statement with the indefinite article "a" or "an" limits any particular claim containing the claim statement so introduced to an invention containing only one such statement, even when the same claim contains the introductory phrase "one or more" or "at least one" and an indefinite article, such as "a" or "an" (e.g., "a" and / or "an" should generally be construed to mean "at least one" or "one or more"). The same applies to the use of definite articles used to introduce claim statements. Moreover, those skilled in the art will recognize that when a particular number of claim statements introduced is explicitly stated, such a statement should generally be construed to mean at least the stated number (e.g., a minimal statement of "two statements" without other qualifiers generally means at least two statements, or more than two statements).When a conventional expression similar to "at least one of A, B, or C, etc." is used, such a structure is generally intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, or C" would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). When a conventional expression similar to "at least one of A, B, or C, etc." is used, such a structure is generally intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, or C" would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). Those skilled in the art will further appreciate that virtually any disjunctive word and / or phrase presenting two or more alternative terms, whether in the specification, claims, or drawings, should be understood to contemplate the possibility of including one of those terms, either of those terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B," or "A and B."

[0123] It will be believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in form, structure, and arrangement of the components may be made without departing from the subject matter disclosed or sacrificing all of the advantages of the materials. The described forms are merely illustrative, and it is the intent of the following claims to embrace and include such modifications. It will be further understood that the invention is defined by the claims.

Claims

1. 1. An overlay metrology system, comprising: an illumination source configured to generate an illumination beam, the illumination beam including one or more illumination beams, each of which is spatially restricted to illuminate a particular cell of the overlay target; a light collection subsystem comprising: an objective configured to collect measurement light emitted from a specimen in response to the illumination beam according to a metrology recipe, the specimen including the overlay target including at least two layers according to the metrology recipe; and one or more detectors positioned at a first pupil plane; a light collection subsystem comprising: a light modulator disposed at a second pupil plane, the light modulator configured to direct one or more selected portions of the measurement light in the second pupil plane to the one or more detectors; a controller communicatively coupled to the light collection subsystem, the controller including one or more processors configured to execute program instructions, the program instructions causing the one or more processors to: by receiving, from the one or more detectors, detection signals related to the one or more selected portions of the measurement light directed to the one or more detectors; and an overlay metrology system that executes the metrology recipe by generating overlay measurements associated with the at least two layers of the specimen based on the detection signals.

2. 10. The overlay metrology system of claim 1, wherein the receiving of the detected signal occurs while the specimen is moving relative to the one or more detectors in accordance with the metrology recipe such that the detected signal is a time-varying interference signal.

3. 2. The overlay metrology system of claim 1, wherein the light modulator is configured to be dynamically adjustable to provide dynamic selection of the one or more selected portions of the measurement light directed to the one or more detectors.

4. The overlay metrology system of claim 1 , wherein the light modulator comprises at least one of a spatial light modulator, a micro-electro-mechanical system (MEMS) device, or a deformable optical component.

5. The overlay metrology system of claim 1 , wherein the one or more detectors are two or more detectors distributed across the first pupil plane.

6. the receiving of the detected signals occurs while the sample is moving relative to the two or more detectors in accordance with the metrology recipe such that the detected signals are time-varying interference signals; the optical modulator is configured to be dynamically adjustable to provide dynamic selection of the one or more selected portions of the measurement light directed to the two or more detectors; The overlay metrology system of claim 5 , wherein the light modulator comprises at least one of a spatial light modulator, a micro-electro-mechanical system (MEMS) device, a digital light processing (DLP) device, or a deformable optical component.

7. The overlay metrology system of claim 6 , wherein at least one of the two or more detectors comprises at least one of a photodiode, an avalanche photodiode, or a photomultiplier tube.

8. the one or more selected portions of the measurement light; the selected diffraction order, or The overlay metrology system of claim 6 , comprising at least one of the diffraction orders that overlap.

9. The overlay metrology system of claim 1 , wherein the one or more selected portions of the measurement light directed to the one or more detectors are reflected off the light modulator.

10. The overlay metrology system of claim 1 , wherein the one or more selected portions of the measurement light directed to the one or more detectors are transmitted by the light modulator.

11. The overlay metrology system of claim 1 , wherein the one or more detectors generate the detection signals when the sample is stationary.

12. The overlay metrology system of claim 1 , wherein the one or more detectors include a multi-pixel sensor.

13. 13. The overlay metrology system of claim 12, wherein the multi-pixel sensor is at least one of a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device.

14. sensor elements of the one or more detectors underfill the first pupil plane; The overlay metrology system of claim 1 , wherein the light modulator directs the one or more selected portions of the measurement light to the location of the sensor element.

15. 10. The overlay metrology system of claim 1, wherein grating structures on the at least two layers of the specimen in the overlay target have a common pitch.

16. the grating structures on the at least two layers of the sample in the overlay target have different pitches; The overlay metrology system of claim 1 , wherein the grating-over-grating structure formed from the grating structure is a Moire structure.

17. the illumination beam is annular; 17. The overlay metrology system of claim 16, wherein the one or more selected portions of the measurement light directed to the one or more detectors include an overlap region of annular diffraction orders from the Moiré structure.

18. the illumination beam is circular; 2. The overlay metrology system of claim 1, wherein the one or more selected portions of the measurement light directed to the one or more detectors include overlap regions of circular diffraction orders from Moiré structures on the at least two layers of the specimen.

19. 1. An overlay metrology system having a field plane detector, comprising: an illumination source configured to generate an illumination beam, the illumination beam including one or more illumination beams, each of which is spatially restricted to illuminate a particular cell of the overlay target; a light collection subsystem comprising: an objective configured to collect measurement light emitted from a specimen in response to the illumination beam according to a metrology recipe, the specimen including the overlay target comprising at least two layers according to the metrology recipe; and one or more detectors disposed in a collection field plane of the collection subsystem; a collection subsystem comprising: a light modulator disposed at a collection pupil plane, the light modulator configured to direct one or more selected portions of the measurement light in the collection pupil plane to the one or more detectors; a controller communicatively coupled to the light collection subsystem, the controller including one or more processors configured to execute program instructions, the program instructions causing the one or more processors to: by receiving, from the one or more detectors, detection signals related to the one or more selected portions of the measurement light directed to the one or more detectors; and an overlay metrology system that executes the metrology recipe by generating overlay measurements associated with the at least two layers of the specimen based on the detection signals.

20. said receiving said detection signal occurs while said sample is stationary; 20. The overlay metrology system of claim 19, wherein the one or more detectors comprise at least one of a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device.

21. 1. A method for overlay metrology, comprising: illuminating the sample with one or more illumination beams, each of the one or more illumination beams being spatially restricted to illuminate a specific cell of the overlay target; directing, using a light modulator disposed in a second pupil plane, one or more selected portions of the measurement light in the second pupil plane, the one or more selected portions emanating from the sample, to one or more detectors disposed in a first pupil plane; receiving a detection signal associated with the one or more selected portions of the measurement light from the one or more detectors; and generating an overlay measurement relating to two layers of the sample based on the detection signal.

22. 22. The method of claim 21, wherein the receiving of the detected signal occurs when the sample is moving relative to the one or more detectors such that the detected signal is a time-varying interference signal.

23. 22. The method of claim 21 , wherein the directing the one or more selected portions of the measurement light comprises dynamically adjusting the light modulator to provide dynamic selection of the one or more selected portions of the measurement light directed to the one or more detectors.

24. 22. The method of claim 21, wherein the light modulator comprises at least one of a spatial light modulator, a micro-electro-mechanical system (MEMS) device, or a deformable optical component.

25. 22. The method of claim 21, wherein the one or more selected portions of the measurement light directed to the one or more detectors are reflected off the light modulator.

26. 22. The method of claim 21, wherein the one or more selected portions of the measurement light directed to the one or more detectors are transmitted by the light modulator.

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