Classifications

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Definitions

• the present disclosure relates generally to overlay metrology and, more particularly, to machine learning for target feature focus.
• Image-based overlay metrology may typically include determining relative offsets between two or more layers on a sample based on relative imaged positions of features of an overlay target in the different layers of interest.
• the accuracy of the overlay measurement may thus be sensitive to image quality associated with imaged features on each sample layer, which may vary based on factors such as a depth of field or location of the plane (e.g., focal position) with respect to the sample.
• overlay metrology procedures typically include tradeoffs between image quality at particular sample layers and throughput. For example, it may be the case that overlay measurements based on separate images of each sample layer may provide the highest quality images of overlay target features. However, capturing multiple images per target may reduce throughput.
• overlay measurements based on a single image capturing features on multiple layers may provide relatively higher throughput, but may require reference measurements based on external tools or fullwafer measurements to provide a desired measurement accuracy. Therefore, it would be desirable to provide a system and method for curing defects such as those identified above.
• the metrology system includes a controller communicatively coupled to one or more through-focus imaging metrology sub-systems, wherein the controller includes one or more processors configured to execute a set of program instructions stored in memory, and wherein the set of program instructions is configured to cause the one or more processors to: receive a plurality of training images captured at one or more focal positions, the plurality of training images including one or more training features of a training specimen; generate a machine learning classifier based on the plurality of training images captured at one or more focal positions; receive one or more target feature selections for one or more target overlay measurements corresponding to one or more target features of a target specimen; determine one or more target focal positions based on the one or more target feature selections using the machine learning classifier; receive one or more target images captured at the one or more target focal positions, the one or more target images including the one or more target features of the target specimen; and determine one or more overlay measurements based
• the metrology system includes one or more through-focus imaging metrology sub-systems.
• the metrology system includes a controller communicatively coupled to the one or more metrology sub-systems, wherein the controller includes one or more processors configured to execute a set of program instructions stored in memory, and wherein the set of program instructions is configured to cause the one or more processors to: receive a plurality of training images captured at one or more focal positions, the plurality of training images including one or more training features of a training specimen; generate a machine learning classifier based on the plurality of training images captured at one or more focal positions; receive one or more target feature selections for one or more target overlay measurements corresponding to one or more target features of a target specimen; determine one or more target focal positions based on the one or more target feature selections using the machine learning classifier; receive one or more target images captured at the one or more target focal positions, the one or more target images including
• the method includes receiving a plurality of training images captured at one or more focal positions, the plurality of training images including one or more training features of a training specimen.
• the method includes generating a machine learning classifier based on the plurality of training images captured at one or more focal positions.
• the method includes receiving one or more target feature selections for one or more target overlay measurements corresponding to one or more target features of a target specimen.
• the method includes determining one or more target focal positions based on the one or more target feature selections using the machine learning classifier.
• the method includes receiving one or more target images captured at the one or more target focal positions, the one or more target images including the one or more target features of the target specimen. In another embodiment, the method includes determining one or more overlay measurements based on the one or more target images.
• FIG. 1 is a conceptual view illustrating a metrology system, in accordance with one or more embodiments of the present disclosure.
• FIG. 2 is a simplified schematic view illustrating a metrology system, in accordance with one or more embodiments of the present disclosure.
• FIG. 3 is a flow diagram illustrating steps performed in a method for measuring overlay, in accordance with one or more embodiments of the present disclosure.
• FIG. 4 is a flow diagram illustrating steps performed in a method for measuring overlay, in accordance with one or more embodiments of the present disclosure.
• Embodiments of the present disclosure are directed to systems and methods through-focus imaging of an overlay target on a sample to provide self-referenced overlay measurement recipes for additional overlay targets on the sample as well as processmonitoring between wafers.
• Semiconductor devices are typically formed as multiple patterned layers of patterned material on a substrate. Each patterned layer may be fabricated through a series of process steps such as, but not limited to, one or more material deposition steps, one or more lithography steps, or one or more etching steps. Further, features within each patterned layer must typically be fabricated within selected tolerances to properly construct the final device. For example, overlay errors associated with relative misregistrations of features on different sample layers must be well characterized and controlled within each layer and relative to previously fabricated layers. [0011] Accordingly, overlay targets may be fabricated on one or more sample layers to enable efficient characterization of the overlay of features between the layers. For example, an overlay target may include fabricated features on multiple layers arranged to facilitate accurate overlay measurements. In this regard, overlay measurements on one or more overlay targets distributed across a sample may be used to determine the overlay of corresponding device features associated with a semiconductor device being fabricated.
• Image-based overlay metrology tools typically capture one or more images of an overlay target and determine an overlay between sample layers based on relative positions of imaged features of the overlay target on layers of interest.
• features of overlay targets suitable for image-based overlay e.g., box-in-box targets, advanced imaging metrology (AIM) targets, or the like
• the overlay may be determined based on relative positions of features on layers of interest within one or more images of the overlay target.
• overlay targets may be designed to facilitate overlay measurements between any number of sample layers in either a single measurement step or multiple measurement steps.
• an overlay target may have different sections (e.g., cells, or the like) to facilitate overlay measurements between selected layers.
• overlay between all layers of interest may be determined based on measurements of multiple portions of the overlay target.
• the accuracy of image-based overlay may depend on multiple factors associated with image quality such as, but not limited to, resolution or aberrations.
• the system resolution may impact the accuracy at which positions of features may be determined (e.g., edge positions, centers of symmetry, or the like).
• aberrations in an imaging system may distort the sizes, shapes, and spacings of features such that position measurements based on an image may not accurately represent the physical sample.
• image quality may vary as a function of focal position. For example, features outside of a focal volume of an imaging system may appear blurred and/or may have a lower contrast between overlay target features and background space than features within the focal volume, which may impact the accuracy of positional measurements (e.g., edge measurements, or the like).
• capturing separate images of features on different layers of a sample may provide accurate overlay metrology measurements.
• a focal position e.g., an object plane
• an image-based overlay metrology system may be adjusted to correspond to the depth of imaged features on each layer of interest.
• features on each layer of interest may be imaged under conditions designed to mitigate focal positiondependent effects.
• Embodiments of the present disclosure are directed to overlay measurements at multiple focal positions, where the multiple focal positions are determined in real-time by the metrology system and may correspond to the one or more varying depths at which one or more portions of one or more metrology targets is located.
• an overlay measurement may be generated for an overlay target based on multiple images captured at multiple focal positions (e.g., including focal depths corresponding to locations of overlay target features), where the metrology system determines the multiple focal positions in real-time (e.g., such as through the use of a machine learning classifier).
• Additional embodiments of the present disclosure are directed to translating one or more portions of the metrology system along one or more adjustment axes. For example, it may be the case that an optimal coordinate position at which a particular overlay measurement is taken may be different from the optimal coordinate position of a subsequent overlay measurement.
• Additional embodiments of the present disclosure are directed to generating control signals based on the overlay measurements across the sample provided to process tools (e.g., lithography tools, metrology tools, or the like) as feedback and/or feedforward data.
• process tools e.g., lithography tools, metrology tools, or the like
• FIG. 1 is a conceptual view illustrating an overlay metrology system 100, in accordance with one or more embodiments of the present disclosure.
• the system 100 may include, but is not limited to, one or more metrology sub-systems 102.
• the system 100 may additionally include, but is not limited to, a controller 104, wherein the controller includes one or more processors 106, a memory 108, and a user interface 110.
• the one or more metrology sub-systems 102 may include any metrology subsystem known in the art including, but not limited to, an optical metrology sub-system.
• the metrology sub-system 102 may include, but is not limited to, an opticalbased metrology system a broadband metrology system (e.g., broadband plasma metrology system) or a narrowband inspection system (e.g., laser-based metrology system).
• the metrology sub-system 102 may include a scatterometry-based metrology system.
• the one or more metrology sub-systems 102 may include any through-focus imaging metrology subsystem (e.g., an imaging metrology sub-system configured to construct one or more images of a specimen, where the one or more images are of a desired focus and are constructed using a plurality of images of the sample captured at different focal positions).
• any through-focus imaging metrology subsystem e.g., an imaging metrology sub-system configured to construct one or more images of a specimen, where the one or more images are of a desired focus and are constructed using a plurality of images of the sample captured at different focal positions.
• the controller 104 is communicatively coupled to the one or more metrology sub-systems 102.
• the one or more processors 106 of the controller 104 may be configured to generate and provide one or more control signals configured to make one or more adjustments to one or more portions of the one or more metrology sub-systems 102.
• the controller 104 is configured to receive a plurality of training images captured at one or more focal positions, wherein the plurality of training images includes one or more training features of a training specimen.
• the controller 104 may be configured to receive the plurality of training images from the one or more metrology sub-systems 102.
• the controller 104 may be configured to generate a machine learning classifier based on the plurality of training images.
• the controller 104 may be configured to use as inputs to the machine learning classifier the plurality of training images.
• the controller 104 may be configured to receive one or more target feature selections for one or more target overlay measurements, wherein the one or more target feature selections correspond to one or more target features of the target specimen.
• the controller 104 may be configured to receive one or more target feature selections from a user via the user interface 110.
• the controller 104 may be configured to determine one or more target focal positions based on the one or more target feature selections.
• the controller 104 may be configured to determine one or more target focal positions using the machine learning classifier.
• the controller 104 may be configured to receive one or more target images captured at the one or more target focal positions.
• the controller 104 may be configured to receive one or more target images including the one or more target features at the one or more target focal positions.
• the controller 104 may be configured to determine one or more overlay measurements based on the one or more target images. For example, the controller 104 may be configured to determine overlay between a first layer of the target specimen and a second layer of the target specimen based on one or more target features formed on each of the first layer and the second layer.
• FIG. 2 illustrates a simplified schematic view of the system 100, in accordance with one or more embodiments of the present disclosure.
• the system 100 as depicted in FIG. 2 includes an optical metrology sub-system 102 such that system 100 operates as an optical inspection system.
• the optical inspection sub-system 102 may include any optical-based inspection known in the art.
• the metrology sub-system 102 may include, but is not limited to, an illumination source 112, an illumination arm 111 , a collection arm 113, and a detector assembly 126.
• metrology sub-system 102 is configured to inspect and/or measure the specimen 120 disposed on the stage assembly 122.
• the illumination source 112 may include any illumination source known in the art for generating illumination 101 including, but not limited to, an illumination source configured to provide wavelengths of light including, but not limited to, vacuum ultraviolet radiation (VUV), deep ultraviolet radiation (DUV), ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.
• the metrology sub-system 102 may include an illumination arm 111 configured to direct illumination 101 to the specimen 120.
• illumination source 112 of the metrology sub-system 102 may be configured in any orientation known in the art including, but not limited to, a dark-field orientation, a light-field orientation, and the like.
• one or more optical elements 114, 124 may be selectably adjusted in order to configure the metrology sub-system 102 in a dark-field orientation, a bright- field orientation, and the like.
• the specimen 120 may include any specimen known in the art including, but not limited to, a wafer, a reticle, a photomask, and the like.
• the specimen 120 may include any specimen having one or more overlay metrology targets known in the art to be suitable for image-based overlay metrology.
• the specimen 120 may include an overlay metrology target that includes target features in one or more layers which may have been printed in one or more lithographically distinct exposures.
• the targets and/or the target features may possess various symmetries such as two-fold or four-fold rotation symmetry, reflection symmetry.
• the specimen 120 is disposed on a stage assembly 122, wherein the stage assembly 122 is configured to facilitate movement of specimen 120 (e.g., movement along one or more of an x-direction, a y-direction, or a z-direction).
• the stage assembly 122 is an actuatable stage.
• the stage assembly 122 may include, but is not limited to, one or more translational stages suitable for selectably translating the specimen 120 along one or more linear directions (e.g., x-direction, y-direction and/or z-direction).
• the stage assembly 122 may include, but is not limited to, one or more rotational stages suitable for selectively rotating the specimen 120 along a rotational direction.
• the stage assembly 122 may include, but is not limited to, a rotational stage and a translational stage suitable for selectably translating the specimen 120 along a linear direction and/or rotating the specimen 120 along a rotational direction. It is noted herein that the system 100 may operate in any metrology mode known in the art.
• the illumination arm 111 may include any number and type of optical components known in the art.
• the illumination arm 111 includes one or more optical elements 114, a set of one or more optical elements 115, a beam splitter 116, and an objective lens 118.
• the illumination arm 111 may be configured to focus illumination 101 from the illumination source 112 onto the surface of the specimen 120.
• the one or more optical elements 114 may include any optical elements known in the art including, but not limited to, one or more mirrors, one or more lenses, one or more polarizers, one or more beam splitters, wave plates, and the like.
• the metrology sub-system 102 includes a collection arm 113 configured to collect illumination reflected or scattered from specimen 120.
• the collection arm 113 may direct and/or focus the reflected and scattered light to one or more sensors of a detector assembly 126 via one or more optical elements 124.
• the one or more optical elements 124 may include any optical elements known in the art including, but not limited to, one or more mirrors, one or more lenses, one or more polarizers, one or more beam splitters, wave plates, and the like.
• detector assembly 126 may include any sensor and detector assembly known in the art for detecting illumination reflected or scattered from the specimen 120.
• the detector assembly 126 of metrology sub-system 102 is configured to collect inspection data of the specimen 120 based on illumination reflected or scattered from the specimen 120. In another embodiment, the detector assembly 126 is configured to transmit collected/acquired images and/or metrology data to the controller 104. [0035]
• the metrology system 100 may be configured to image the specimen 120 at any selected measurement plane (e.g., at any position along a z-direction). For example, a location of an object plane associated with an image generated on the detector assembly 126 with respect to the specimen 120 may be adjusted using any combination of components of the metrology system 100.
• the location of the object plane associated with an image generated on the detector assembly 126 with respect to the specimen 120 may be adjusted by controlling a position of the stage assembly 122 with respect to the objective lens 118.
• the location of the object plane associated with an image generated on the detector assembly 126 with respect to the specimen 120 may be adjusted by controlling a position of the objective lens 118 with respect to the specimen 120.
• the objective lens 118 may be mounted on a translation stage configured to adjust a position of the objective lens 118 along one or more adjustment axes (e.g., an x-direction, a y-direction, or a z-direction).
• the location of the object plane associated with an image generated on the detector assembly 126 with respect to the specimen 120 may be adjusted by controlling a position of the detector assembly 126.
• the detector assembly 126 may be mounted on a translation stage configured to adjust a position of the detector assembly 126 along the one or more adjustment axes.
• the location of the object plane associated with an image generated on the detector assembly 126 with respect to the specimen 120 may be adjusted by controlling a position of the one or more optical elements 124.
• one or more optical elements 124 may be mounted on translation stages configured to adjust positions of the of the one or more optical elements 124 along the one or more adjustment axes.
• the controller 104 may be configured to perform any of the foregoing adjustments by providing one or more control signals to one or more portions of the metrology sub-system 102.
• the controller 104 of system 100 may include one or more processors 106 and memory 108.
• the memory 108 may include program instructions configured to cause the one or more processors 106 to carry out various process steps described throughout the present disclosure.
• the program instructions are configured to cause the one or more processors 106 to adjust one or more characteristics of the metrology sub-system 102 in order to perform one or more of the process steps of the present disclosure.
• the controller 104 may be configured to receive data including, but not limited to, imagery data associated with the specimen 120 from the detector assembly 126.
• the one or more processors 106 of the controller 104 may include any processor or processing element known in the art.
• 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)).
• the one or more processors 106 may include any device configured to execute algorithms and/or instructions (e.g., program instructions stored in memory).
• the one or more processors 106 may be embodied as a desktop computer, mainframe computer system, workstation, image computer, parallel processor, networked computer, or any other computer system configured to execute a program configured to operate or operate in conjunction with the metrology system 100, as described throughout the present disclosure
• different components of the system 100 may include a processor or logic elements suitable for carrying out at least a portion of the steps described in the present disclosure. Therefore, the above description should not be interpreted as a limitation on the embodiments of the present disclosure but merely as an illustration. Further, the steps described throughout the present disclosure may be carried out by a single controller 104 or, alternatively, multiple controllers. Additionally, the controller 104 may include one or more controllers housed in a common housing or within multiple housings. In this way, any controller or combination of controllers may be separately packaged as a module suitable for integration into metrology system 100. Further, the controller 104 may analyze data received from the detector assembly 126 and feed the data to additional components within the metrology system 100 or external to the metrology system 100.
• the memory 108 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 106.
• the memory 108 may include a non-transitory memory medium.
• the memory 108 may include, but is not limited to, a read-only memory (ROM), a random-access memory (RAM), a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid-state drive and the like.
• ROM read-only memory
• RAM random-access memory
• magnetic or optical memory device e.g., disk
• magnetic tape e.g., magnetic tape
• solid-state drive e.g., solid-state drive and the like.
• memory 108 may be housed in a common controller housing with the one or more processors 106.
• the memory 108 may be located remotely with respect to the physical location of the one or more processors 106 and controller 104.
• the one or more processors 106 of controller 104 may access a remote memory (e.g.
• the user interface 110 is communicatively coupled to the controller 104.
• the user interface 110 may include, but is not limited to, one or more desktops, laptops, tablets, and the like.
• the user interface 110 includes a display used to display data of the system 100 to a user.
• the display of the user interface 110 may include any display known in the art.
• the display may include, but is not limited to, a liquid crystal display (LCD), an organic light-emitting diode (OLED) based display, or a CRT display.
• LCD liquid crystal display
• OLED organic light-emitting diode
• CRT display Those skilled in the art should recognize that any display device capable of integration with a user interface 110 is suitable for implementation in the present disclosure.
• a user may input selections and/or instructions responsive to data displayed to the user via a user input device of the user interface 110
• the controller 104 is communicatively coupled to one or more elements of the metrology system 100.
• the controller 104 may transmit and/or receive data from any component of the metrology system 100.
• the controller 104 may direct or otherwise control any component of the metrology system 100 by generating one or more control signals for the associated components.
• the controller 104 may be communicatively coupled to the detector assmebly 126 to receive one or more images from the detector assembly 126.
• FIG. 3 illustrates a method 300 of measuring overlay, in accordance with one or more embodiments of the present disclosure.
• a plurality of training images captured at one or more focal positions is received.
• a plurality of training images 125 may be received by the controller 104 from the metrology sub-system 102.
• the plurality of training images 125 may include optical training images.
• the controller 104 may be configured to receive one or more training images 125 from a source other than the one or more metrology sub-systems 102.
• the controller 104 may be configured to receive one or more training images 125 of features of a specimen 120 from an external storage device and/or memory 108.
• controller 104 may be further configured to store received training images 125 in memory 108.
• the plurality of training images 125 may include one or more training features of a training specimen.
• the plurality of training images 125 may include images captured at multiple depths of the training specimen.
• the one or more training features of the training specimen may include one or more training target features formed at different layers of the training specimen.
• the metrology sub-system 102 may be configured to capture the plurality of training images 125 at one or more focal positions corresponding to the depth (e.g., position along the z-direction) of a particular training feature.
• the metrology sub-system 102 may be configured to capture the plurality of training images 125 within a focus training range, wherein the focus training range comprises a plurality of focal positions corresponding to a plurality of depths of the one or more training features.
• the focus training range may be provided by a user via the user interface 110.
• a machine learning classifier is generated based on the plurality of training images.
• the controller 104 may be configured to generate a machine learning classifier based on the plurality of training images.
• the controller 104 may be configured to generate the machine learning classifier via any one or more techniques known in the art, including, without limitation, supervised learning, unsupervised learning, and the like.
• the plurality of training images 125 may include varying degrees of focus based on the focal position at which each of the plurality of training images was captured (e.g., the plurality of training images may include a plurality of through-focus images of one or more features of the sample).
• the controller 104 may receive one or more optimal focus tolerances such that the controller 104 may determine one or more training images of the plurality of training images that fall within the one or more optimal focus tolerances.
• the plurality of training images 125 and the one or more optimal focus tolerances may be used as inputs to train the machine learning classifier.
• the controller 104 may be further configured to store the plurality of training images 125, the optimal focus tolerances, and the generated machine learning classifier, in memory 108.
• the one or more optimal focus tolerances may be configured such that the machine learning classifier may be configured to determine one or more target focal positions for one or more target overlay measurements.
• the one or more optimal focus tolerances may be configured to ensure that one or more target images that may be subsequently captured at the one or more target focal positions are of sufficient quality for overlay measurement by the controller 104.
• the one or more optimal focus tolerances may be provided by a user via the user interface 110.
• the controller 104 may be configured to determine the one or more optimal focus tolerances using any technique known in the art.
• the controller 104 may be configured to determine the one or more optimal focus tolerances based on a contrast precision function (e.g., a function configured to determine a focus at which noise is minimal based on a plurality of images captured at multiple focal positions).
• the controller 104 may be configured to determine the one or more optimal focus tolerances using a Linnik interferometer integrated into or generated by one or more portions of the metrology sub-system 102.
• one or more portions of the metrology sub-system 102 may be configured to illuminate the sample, where the controller 104 may be configured to generate a Linnik interferogram (e.g., a low coherence interferogram) based on illumination collected by the detector assembly 126.
• the controller 104 may be configured to determine a peak (e.g., a point having the greatest contrast of all collected images) of the interferogram and may associate the peak with the through-focus position along a z-axis of the sample.
• the embodiments of the present disclosure are not limited to the controller 104 generating or referencing a Linnik interferogram in order to determine the one or more optimal focus tolerances.
• the controller 104 may be configured to generate a machine learning classifier configured to determine best focus and/or best position based on a plurality of training images generated using one or more signals indicative of illumination (e.g., illumination generated by a bright field and/or dark field microscopy device) emanating from various focal positions and/or positions (e.g., a coordinate position on an x-axis and/or a y-axis, where the plurality of training images may be captured at various coordinate positions along one or both of such axes, such as via a translatable stage).
• illumination e.g., illumination generated by a bright field and/or dark field microscopy device
• focal positions e.g., a coordinate position on an x-axis and/or a y-axis, where the plurality of training images may be captured at various coordinate positions along one
• the controller 104 may be configured to determine best focus and/or best position based on image contrast and/or contrast precision of the plurality of training images.
• the machine learning classifier may be configured to determine the one or more optimal focus tolerances based on the plurality of training images, where the plurality of training images constitute focus slice images generated at various focal positions along a z-axis of the sample, and where the controller 104 may be configured to classify and/or label each focus slice image with a corresponding best focus based on image contrast and/or contrast precision of the focus slice images.
• the controller 104 may be configured to determine the one or more optimal focus tolerances by interpolation based on the plurality of training images.
• the machine learning classifier may be configured to determine the one or more optimal focus tolerances based on the plurality of training images, where the plurality of training images include images captured at various focal positions along a z-axis of the sample, and where the focus of the plurality of training images is varied using a coarse focusing mechanism.
• a coarse focusing mechanism or any other general focusing mechanism known in the art to be suitable for the purposes contemplated by the present disclosure, may permit the machine learning classifier to determine the one or more optimal focus tolerances in a more accurate manner (e.g., more accurate relative to other methods of focus adjustment described herein or known in the art).
• the course focusing mechanism may be configured to permit the controller 104 to determine and/or set a coarse focus (e.g., a general focal position, which may later be finely adjusted (see Step 308 below)).
• a coarse focus e.g., a general focal position, which may later be finely adjusted (see Step 308 below)
• the coarse focusing system may include any coarse focusing mechanism known in the art to be suitable for the purposes contemplated by the present disclosure, including, without limitation, a lens triangulation mechanism, a bi-cell detector apparatus, and/or any range finding system.
• the machine learning classifier generated in step 304 may include any type of machine learning algorithm/classifier and/or deep learning technique or classifier known in the art including, but not limited to, a random forest classifier, a support vector machine (SVM) classifier, an ensemble learning classifier, an artificial neural network (ANN), and the like.
• the machine learning classifier may include a deep convolutional neural network (CNN).
• CNN deep convolutional neural network
• the machine learning classifier may include ALEXNET and/or GOOGLENET.
• the machine learning classifier may include any algorithm, classifier, or predictive model, including, without limitation, any algorithm, classifier, or predictive model configured to generate a Linnik interferogram and to determine the one or more target focal positions for one or more target overlay measurements using the Linnik interferogram.
• the machine learning classifier may comprise a neural network having multiple layers and receptors.
• the machine learning classifier may comprise a neural network having approximately five layers and approximately fifty receptors.
• Step 306 one or more target feature selections for one or more target overlay measurements corresponding to one or more target features of a target specimen are received.
• the controller 104 may be configured to receive the one or more target feature selections for one or more target overlay measurements from a user via the user interface 110.
• the one or more target feature selections may include one or more signals configured to direct the system 100 to capture one or more target images including the one or more target features of the target specimen.
• the controller 104 may be configured to determine one or more expected depths of the one or more target features within the target specimen.
• the controller 104 may be provided the one or more expected depths of the one or more target features for overlay measurement by a user via the user interface 110.
• the controller 104 may determine the one or more expected depths of the one or more target features for overlay measurement by reference to one or more design files or other data corresponding to the target specimen stored in memory 108. In another embodiment, the controller 104 may determine the one or more expected depths of the one or more target features for overlay measurement based on the Linnik interferogram. For example, the controller 104 may determine the one or more expected depths by reference to the peak of the Linnik interferogram associated with the through- focus position along the z-axis of the sample.
• one or more target focal positions based on the one or more target feature selections are determined using the machine learning classifier.
• the controller 104 may be configured to determine the one or more target focal positions based on the one or more target feature selections using the machine learning classifier.
• the controller 104 may provide the one or more expected depths of the one or more target features of the target specimen as an input to the machine learning classifier.
• the machine learning classifier may be configured to provide the one or more target focal positions based on the plurality of training images 125 and the optimal focus tolerances.
• the machine learning classifier may be configured to determine one or more target focal positions for one or more target overlay measurements by determining one or more focal positions within 1 micron of a focal position provided by the contrast precision function, the Linnink interferogram function, or any other method described herein.
• the controller 104 may be configured to determine and/or provide one or more control signals to one or more portions of the one or more metrology sub-systems 102, wherein the one or more control signals are configured to cause the one or more portions of the one or more metrology sub-systems 102 to be translated along one or more adjustment axes (e.g., an x-direction, a y-direction, and/or a z-direction).
• the controller 104 may be configured to provide one or more control signals to the stage assembly 122 and/or the detector assembly 126 such that the target specimen is located at one of the one or more determined target focal positions.
• the controller 104 may be configured to provide one or more control signals to at least one of the optical elements 114, 115, the beam-splitter 116, the objective lens 118, or the optical elements 124, in order to enable the metrology sub-system 102 to capture one or more target images at the one or more target focal positions.
• the machine learning classifier may be configured to determine (and the controller 104 may be configured to provide) one or more control signals to the coarse focusing system, where the one or more control signals may be configured to cause the coarse focusing system adjust focus to a focal position within ⁇ 2 micrometers of the target focal position.
• the machine learning classifier may be configured to determine the one or more optimal focus tolerances by determining one or more fine- focus adjustments to modify the focal position determined by the course focusing system.
• Step 310 one or more target images of the one or more target features captured at the one or more target focal positions are received.
• the controller 104 may be configured to receive one or more target images 135 from the metrology sub-system 102.
• target images may refer to images of the one or more target features captured at the one or more target focal positions and with which one or more overlay measurements will be determined.
• target images may be distinguished from “training images” which may be regarded as images of training features which may be used as inputs to train the machine learning classifier.
• the controller 104 may be configured to receive one or more target images 135 from a source other than the one or more metrology sub-systems 102.
• the controller 104 may be configured to receive one or more target images 135 of a specimen 120 from an external storage device and/or memory 108.
• one or more overlay measurements are determined based on the one or more target images.
• the controller 104 may be configured to determine an overlay between a first layer of the target specimen and a second layer of the target specimen based on a first overlay measurement corresponding to one or more target features formed on the first layer of the target specimen and a second overlay measurement corresponding to one or more target features formed on the second layer of the target specimen.
• the controller 104 may be configured to determine an offset (e.g., PPE) between the first layer and the second layer.
• the one or more overlay measurements may include any overlay measurement known in the art to be suitable for the purposes contemplated by the present disclosure, including those overlay measurements configured for use with specific target features of a specimen.
• the controller 104 may be configured to utilize one or more overlay algorithms stored in memory 108 or otherwise provided to the controller 104 in order to determine the one or more overlay measurements.
• the method 300 may include a Step 312.
• one or more control signals are provided.
• one or more control signals for adjusting one or more process tools e.g., lithographic tools
• the controller 104 may provide one or more control signals (or corrections to the control signals) to one or more portions of one or more process tools for adjusting the one or more parameters (e.g., fabrication settings, configuration, and the like) of the one or more process tools such that one or more parameters of the one or more process tools are adjusted.
• the controller 104 may determine the one or more control signals based on the one or more overlay measurements of the specimen.
• the control signals may be provided by the controller 104 as part of a feedback and/or feedforward control loop.
• the controller 104 may cause the one or more process tools to execute one or more adjustments to the one or more parameters of the process tools based on the control signals, or the controller 104 may alert a user to make the one or more adjustments to the one or more parameters.
• the one or more control signals may compensate for errors of one or more fabrication processes of the one or more process tools, and thus may enable the one or more process tools to maintain overlay within selected tolerances across multiple exposures on subsequent samples in the same or different lots.
• FIG. 4 illustrates a method 400 for measuring overlay, in accordance with one or more embodiments of the present disclosure.
• Step 402 one or more target feature selections for one or more target overlay measurements corresponding to one or more target features of a target specimen are received.
• the controller 104 may be configured to receive the one or more target feature selections for one or more target overlay measurements from a user via the user interface 110.
• the one or more target feature selections may include one or more signals configured to direct the system 100 to capture one or more target images including the one or more target features of the target specimen.
• the controller 104 may be configured to determine one or more expected positions (e.g., positions along an x-direction, a y-direction, and/or a z-direction) of the one or more target features within the target specimen.
• the controller 104 may be provided the one or more expected positions of the one or more target features for overlay measurement by a user via the user interface 110. In another embodiment, the controller 104 may determine the one or more expected depths of the one or more target features for overlay measurement by reference to one or more design files or other data corresponding to the target specimen stored in memory 108. [0061] In Step 404, one or more target focal positions based on the one or more target feature selections are determined. For example, the controller 104 may be configured to determine one or more target focal positions using the machine learning classifier based on the one or more target feature selections, where the one or more target feature selections correspond to one or more target features for one or more overlay measurements.
• the controller 104 may provide the one or more expected depths of the one or more target features of the target specimen as an input to the machine learning classifier.
• the machine learning classifier may be configured to provide the one or more target focal positions based on the plurality of training images 125 and the optimal focus tolerances.
• the controller 104 may be configured to determine and/or provide one or more control signals to one or more portions of the one or more metrology sub-systems 102, wherein the one or more control signals are configured to cause the one or more portions of the one or more metrology sub-systems 102 to be translated along one or more adjustment axes (e.g., an x-direction, a y-direction, and/or a z-direction).
• the controller 104 may be configured to determine and/or provide one or more control signals to one or more portions of the one or more metrology sub-systems 102, wherein the one or more control signals are configured to cause the one or more portions of the one or more metrology sub-systems 102 to be translated along one or more adjustment axes (e.g., an x-direction, a y-direction, and/or a z-direction).
• the controller 104 may be configured to provide one or more control signals to the stage assembly 122 and/or the detector assembly such that the one or more target features for overlay measurements are centered within a field of view of one or more components of the metrology sub-system 102.
• the controller 104 may be configured to provide one or more control signals to one or more portions of the metrology sub-system 102 such that the target images 135 include the one or more target features at one or more centers of the target images 135.
• the controller 104 may be configured to provide one or more control signals to the stage assembly 122 such that the target specimen is located at one of the one or more determined target focal positions.
• the controller 104 may be configured to provide one or more control signals to at least one of the optical elements 114, 115, the beam-splitter 116, the objective lens 118, or the optical elements 124, in order to enable the metrology subsystem 102 to capture one or more target images at the one or more target focal positions.
• the controller 104 may be configured to provide the one or more control signals to the one or more portions of the one or more metrology subsystems 102 simultaneously.
• the controller 104 may be configured to provide one or more control signals configured to cause simultaneous adjustments to the stage assembly 122 along an x-direction and/or a y-direction and to one or more other portions of the metrology sub-system 102 (e.g., the detector assembly 126 and/or the objective lens 118) along a z-direction.
• the metrology sub-system 102 e.g., the detector assembly 126 and/or the objective lens 118
• the controller 104 may be configured to use the machine learning classifier to determine the one or more control signals configured to cause the translation of one or more portions of the one or more metrology sub-systems 102.
• the machine learning classifier may be configured to associate one or more positions (e.g., positions along an x-axis and/or a y-axis) with a desired the one or more target features.
• the machine learning classifier may be configured to determine a position (e.g., a coordinate position on an x-axis and/or a y-axis) automatically center the one or more target features within a field of view.
• Step 408 one or more target images of the one or more target features captured at the one or more target focal positions are received.
• the controller 104 may be configured to receive one or more target images 135 from the metrology sub-system 102.
• 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.
• the results can 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 another software module, method, or system, and the like.
• the results may be stored “permanently,” “semi-permanently,” temporarily,” or for some period of time.
• the memory may be random access memory (RAM), and the results may not necessarily persist indefinitely in the memory.
• each of the embodiments of the method described above may include any other step(s) of any other method(s) described herein.
• each of the embodiments of the method described above may be performed by any of the systems described herein.
• any two components so associated can also be viewed as being “connected,” or “coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “couplable,” to each other to achieve the desired functionality.
• Specific examples of couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

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