High resolution evaluation of optical metrology targets for process control

Abstract

A metrology system may include an optical metrology subsystem for generating an optical metrology measurement of an optical metrology based on a characteristic of an optical metrology target associated with at least one optical pitch; and an additional metrology subsystem for generating an additional metrology measurement of the optical metrology target, where the additional metrology measurement has a higher resolution than the optical metrology measurement, and where the additional metrology subsystem further measures a deviation of the optical metrology target from a reference design. The system may further include a controller to generate an accuracy measurement of the optical metrology target based on the measurement, identify a change in a lithographic process based on the deviation, correlate the accuracy measurement with the change, and generate a measurement of the accuracy of the optical metrology target based on the measurement. And adjusting at least one of the optical metrology subsystem, a lithographic tool, or the reference design based on the correlation.

Description

Technical Field

[0001] The present disclosure relates generally to optical metrology, and more particularly to process control based on high resolution evaluation of optical metrology targets. Background Art

[0002] Optical metrology may refer to metrology based on the use of light, which typically includes wavelengths in the ultraviolet (UV) to infrared (IR) wavelengths. Many optical metrology techniques rely on the measurement of specialized metrology targets with features designed to facilitate the measurement. However, the accuracy of measurements based on such targets may vary in response to deviations in the manufacturing process. Therefore, there is a need to develop systems and methods to evaluate optical metrology targets. Summary of the invention

[0003] According to one or more illustrative embodiments of the present disclosure, a metrology system is disclosed. In one illustrative embodiment, the system includes a controller coupled to an optical metrology subsystem and an additional metrology subsystem. In another illustrative embodiment, the optical metrology subsystem may be configured according to a first metrology recipe to generate optical metrology measurements of one or more optical metrology targets on one or more samples, wherein the optical metrology measurements are based on features of the optical metrology targets associated with at least one optical pitch. In another illustrative embodiment, the additional metrology subsystem may be configured according to a second metrology recipe to generate additional metrology measurements of the one or more optical metrology targets, wherein the additional metrology measurements have a higher resolution than the optical metrology measurements. In another illustrative embodiment, the additional metrology subsystem further measures deviations of the one or more optical metrology targets from a reference design, wherein the deviations include deviations of the features associated with the at least one optical pitch relative to the reference design. In another illustrative embodiment, the controller compares the optical metrology measurements with the additional metrology measurements to generate accuracy measurements of the one or more optical metrology targets. In another illustrative embodiment, the controller identifies changes in the photolithography process used to manufacture the one or more samples based on the deviations of the one or more optical metrology targets from the reference design. In another illustrative embodiment, the controller correlates the accuracy measurements of the one or more optical metrology targets with the variation of the lithography process based on the deviations of the one or more optical metrology targets from the reference design. In another illustrative embodiment, the controller adjusts at least one of the optical metrology subsystem, the lithography tool, or the reference design based on the correlation.

[0004] According to one or more illustrative embodiments of the present disclosure, a method is disclosed. In one illustrative embodiment, the method includes generating optical metrology measurements of one or more optical metrology targets on one or more samples using an optical metrology subsystem according to a first metrology recipe, wherein the one or more optical metrology targets include features associated with at least one optical pitch, and wherein the optical metrology measurements are based on the features of the optical metrology targets having at least one optical pitch. In another illustrative embodiment, the method includes generating additional metrology measurements of the one or more optical metrology targets using an additional metrology subsystem configurable according to a second metrology recipe, wherein the additional metrology measurements have a higher resolution than the optical metrology measurements. In another illustrative embodiment, the method includes comparing the optical metrology measurements with the additional metrology measurements to generate an accuracy measurement of the one or more optical metrology targets. In another illustrative embodiment, the method includes measuring deviations of the one or more optical metrology targets from a reference design using the additional metrology subsystem, wherein the deviations include deviations of the optically resolvable features from the reference design. In another illustrative embodiment, the method includes identifying changes in a photolithography process used to manufacture the one or more samples based on the deviations of the one or more optical metrology targets from the reference design. In another illustrative embodiment, the method includes correlating the accuracy measurements of the one or more optical metrology targets with the variation of the lithography process based on the deviations of the one or more optical metrology targets from the reference design. In another illustrative embodiment, the method includes adjusting at least one of the optical metrology subsystem, the lithography tool, or the reference design based on the correlation.

[0005] According to one or more illustrative embodiments of the present disclosure, a metrology system is disclosed. In one illustrative embodiment, the system includes an optical metrology subsystem that can be configured according to a first metrology recipe to generate optical metrology measurements of one or more optical metrology targets on one or more samples, wherein the optical metrology measurements are based on features of the optical metrology targets associated with at least one optical pitch. In another illustrative embodiment, the system includes an additional metrology subsystem that can be configured according to a second metrology recipe to generate additional metrology measurements of the one or more optical metrology targets, wherein the additional metrology measurements have a higher resolution than the optical metrology measurements. In another illustrative embodiment, the additional metrology subsystem further measures deviations of the one or more optical metrology targets from a reference design, wherein the deviations include deviations of the features associated with the at least one optical pitch relative to the reference design. In another illustrative embodiment, the system includes a controller. In another illustrative embodiment, the controller compares the optical metrology measurements with the additional metrology measurements to generate accuracy measurements of the one or more optical metrology targets. In another illustrative embodiment, the controller identifies changes in the photolithography process used to manufacture the one or more samples based on the deviations of the one or more optical metrology targets from the reference design. In another illustrative embodiment, the controller correlates the accuracy measurements of the one or more optical metrology targets with the variation of the lithography process based on the deviations of the one or more optical metrology targets from the reference design. In another illustrative embodiment, the controller adjusts at least one of the optical metrology subsystem, the lithography tool, or the reference design based on the correlation.

[0006] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and do not necessarily restrict the invention as claimed.The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0008] Figure 1A is a block diagram illustration of a metering system according to one or more embodiments of the present disclosure.

[0009] Figure 1B is a conceptual diagram of an optical metrology subsystem according to one or more embodiments of the present disclosure.

[0010] Figure 1C is a conceptual diagram of an additional metering subsystem according to one or more embodiments of the present disclosure.

[0011] Figure 2is a conceptual diagram depicting an error driver for process monitoring using an optical metrology target according to one or more embodiments of the present disclosure.

[0012] Figure 3 is a flow chart illustrating steps performed in a method according to one or more embodiments of the present disclosure.

[0013] Figure 4A is a simplified top view of a first design of an optical metrology target in accordance with one or more embodiments of the present disclosure.

[0014] Figure 4B According to one or more embodiments of the present disclosure Figure 4A A simplified side view of a first design of an optical metrology target depicted in FIG.

[0015] Figure 5A is a simplified top view of a first design of an optical metrology target in accordance with one or more embodiments of the present disclosure.

[0016] Figure 5B According to one or more embodiments of the present disclosure Figure 5A A simplified side view of a first design of an optical metrology target depicted in FIG.

[0017] Fig. 6A is a simplified top view of a first design of an optical metrology target in accordance with one or more embodiments of the present disclosure.

[0018] Figure 6B According to one or more embodiments of the present disclosure Fig. 6A A simplified side view of a first design of optical metrology target 104 is depicted in FIG.

[0019] Figure 7 is a conceptual diagram illustrating drift monitoring based on deviation of an optical metrology target from a reference design according to one or more embodiments of the present disclosure.

[0020] Figure 8 Included are conceptual diagrams depicting performance of relatively high-quality reference designs of optical metrology targets and conceptual diagrams depicting performance of relatively low-quality reference designs of optical metrology targets in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0021] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments described herein are to be regarded as illustrative and not restrictive. It will be readily apparent to one of ordinary skill in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the present disclosure.

[0022] Embodiments of the present disclosure are directed to systems and methods for high-resolution evaluation of metrology targets suitable for optical metrology (referred to herein as optical metrology targets).

[0023] Metrology systems in many applications including but not limited to semiconductor manufacturing typically generate measurements on metrology targets on a sample, where the metrology targets are designed to facilitate robust and accurate measurements. As an illustration, semiconductor manufacturing typically involves sequential deposition and patterning of layers on a sample to form a device. In this context, metrology can typically be used to monitor various steps of a semiconductor manufacturing process to ensure that the steps are performed within manufacturing tolerances and / or to provide feedback for controlling manufacturing tools. These metrology measurements should typically characterize features that will ultimately form a device, such features being referred to herein as device features. Although metrology measurements can be performed directly on device features in some applications, it is typically necessary to perform metrology measurements on separate metrology targets distributed throughout the sample. The metrology of device features typically must be highly customized to a specific layout and is slow and / or destructive in many cases. In contrast, metrology targets can be designed to provide high throughput and / or non-destructive measurements representative of device features. For example, a metrology target suitable for overlay measurements (e.g., measurements of alignment or misalignment of different lithography exposures on one or more layers) may include target features associated with different lithography exposures arranged to facilitate robust and accurate overlay measurements.

[0024] Various metrology targets and associated metrology techniques have been developed for different situations or applications. For example, some metrology targets are designed for high-resolution measurements using high-resolution metrology tools, such as, but not limited to, particle-based metrology tools (e.g., electron beam metrology tools, ion beam metrology tools, or the like) or X-ray metrology tools. However, such techniques may suffer from relatively low throughput and may be destructive in some cases. As another example, some metrology targets are designed for optical measurements based on wavelengths ranging from ultraviolet (UV) to infrared (IR) spectra using optical metrology tools. Optical metrology techniques generally provide relatively high throughput and non-destructive measurements. However, optical metrology techniques generally require that features on the optical metrology target (referred to herein as optical features or coarse features) have a size and / or pitch on the order of the wavelength of light used for measurement. Such optical features may be substantially larger than the corresponding size and / or pitch of device features.

[0025] One challenge of metrology based on optical metrology targets is to ensure that the measurements accurately represent the device features of interest. For example, even if the features of the optical metrology targets are substantially larger to be compatible with optical measurement techniques, it may be desirable to provide measurements with accuracy within the scale of the device features. This may require that the features of the optical metrology targets be manufactured within specific tolerances. Therefore, deviations of the optical metrology targets from the reference design may reduce the accuracy of the target-based measurements and thus reduce the effectiveness of process control based on these measurements.

[0026] During lithographic exposure, the accuracy with which features on a photomask (e.g., a reticle) can be imaged onto a sample can depend on a range of factors, including, but not limited to, the optical properties of the lithographic tool (e.g., wavelength, numerical aperture, depth of field, or the like) and the properties of the pattern (e.g., feature size, feature density, feature orientation, or the like). In this way, optical features on a sample can be printed with properties that are different from device features.

[0027] Therefore, some optical metrology target designs additionally include features (e.g., fine features) having sizes and / or pitches corresponding to device features to make the properties of the printed optical features correspond more accurately to the properties of the printed device features. For example, the optical features may be segmented to include fine features having sizes and / or pitches similar to the device features.

[0028] However, it remains the case that aberrations and / or temporal variations in lithographic exposure may affect optical features differently than fine features. Thus, variations in the lithographic process (e.g., drift, offset, or the like) may affect optical features differently than fine features.

[0029] Therefore, it is desirable to evaluate the performance of optical metrology targets to ensure that constituent features are printed according to a reference design and therefore accurately measured. The resulting information can be used for process control during manufacturing (e.g., as data in feedback and / or feedforward process control loops) and / or to compare the performance of different target designs.

[0030] Embodiments of the present disclosure are directed to directly measuring deformation of an optical metrology target (e.g., deviation of an optical metrology target from a reference design) using high-resolution metrology techniques (e.g., but not limited to, particle-based metrology techniques or X-ray metrology techniques). For example, deformations such as, but not limited to, feature asymmetry or pitch-dependent pattern placement error (PPE) may be measured. It is contemplated herein that such deformations may represent a significant contribution to the errors associated with optical metrology.

[0031] Furthermore, direct measurement of such deformation of the optical target may be performed at any stage of the manufacturing process, including but not limited to, before the etching step (e.g., an after-development inspection (ADI) step) or after the etching step (e.g., an after-etch inspection (AEI) step) directly after photoresist exposure. It is contemplated herein that directional measurement of deformation of an optical metrology target as disclosed herein may provide performance advantages over alternative techniques for evaluating optical overlay targets.

[0032] In an embodiment, the metrology system includes an optical metrology subsystem and an additional metrology subsystem with a higher resolution than the optical metrology tool. The additional metrology subsystem may include, but is not limited to, a particle beam metrology subsystem or an X-ray metrology subsystem.

[0033] In an embodiment, the optical metrology subsystem generates optical overlay measurements of a series of optical overlay targets. For example, the optical overlay targets may include features having at least one optical pitch, wherein the optical metrology subsystem generates the optical overlay measurements based on light diffracted and / or scattered by the at least one optical pitch (e.g., a pitch that can be resolved by the optical metrology system). In an embodiment, the additional metrology subsystem further generates additional overlay measurements of at least some of the optical metrology targets. For example, the additional metrology subsystem may measure deviations of the optical metrology targets, including but not limited to asymmetry or PPE of features associated with the at least one optical pitch. As another example, the additional metrology subsystem may measure etch bias (e.g., the difference between developed resist before etching and etched pattern).

[0034] In an embodiment, the metrology system measures deviations of the one or more overlay targets from a reference design based on the additional measurements, wherein the deviations include deviations of the features associated with the at least one optical pitch from the reference design.

[0035] In an embodiment, the metrology system further identifies variations in a lithography process used to manufacture the one or more samples based on the deviations of the one or more overlay targets from the reference design. For example, the deviations of the overlay targets may be associated with drifts in the lithography process.

[0036] In an embodiment, the metrology system further relates the accuracy measurement of the one or more overlay targets to the variation of the lithography process based on the deviation of the one or more overlay targets from the reference design. In this way, the accuracy of the overlay measurement in the presence of variation of the lithography process can be evaluated.

[0037] In an embodiment, the metrology system further takes one or more actions based on these correlations. For example, in an initial design phase, optical overlay targets with different reference designs may be evaluated and a preferred design may be selected. For example, a preferred design may provide relatively high accuracy despite changes in the lithography process. As another example, in a high volume manufacturing phase, the reference design of the optical overlay target may be switched and / or the metrology recipe used to characterize the optical overlay target using the optical metrology subsystem may be updated to improve performance in response to changes in the lithography process.

[0038] Reference Figures 1A to 8 , describe in more detail systems and methods for evaluating optical metrology targets according to one or more embodiments of the present disclosure.

[0039] Figure 1A is a block diagram illustration of a metering system 100 according to one or more embodiments of the present disclosure.

[0040] In an embodiment, the metrology system 100 includes an optical metrology subsystem 102 adapted to generate optical metrology measurements of an optical metrology target 104 on a sample 106 .

[0041] The optical metrology target 104 may include any number or arrangement of target features suitable for characterization by the optical metrology subsystem 102. In an embodiment, the optical metrology target 104 includes features associated with at least one optical pitch, wherein the optical metrology subsystem 102 generates optical metrology measurements based on the at least one optical pitch. In some embodiments, the optical metrology target 104 further includes features associated with at least one fine pitch that is smaller than the optical pitch. For example, the fine pitch may be similar to or representative of the pitch of a design feature that the optical metrology target 104 is designed to characterize. In this way, features having a fine pitch may be printed (e.g., exposed in a photolithography process) with characteristics similar to device features.

[0042] The optical metrology subsystem 102 may include any combination of components suitable for generating optical metrology measurements of the optical metrology target 104. For example, the optical metrology subsystem 102 may include an imaging subsystem and provide optical metrology measurements based on one or more images of the optical metrology subsystem 102, wherein at least one optical pitch is resolved. In the case where the optical metrology target 104 further includes features with fine pitch, the fine pitch may not be resolved in the image. As another example, the optical metrology subsystem 102 may include a scatterometry subsystem and provide optical metrology measurements based on relative intensities of diffraction orders from at least one optical pitch (e.g., as measured in a pupil plane). In the case where the optical metrology target 104 further includes features with fine pitch, diffraction may not be collected or may not be utilized in the measurement.

[0043] The optical metrology subsystem 102 may utilize light having any wavelength or combination of wavelengths to generate optical metrology measurements of the optical metrology target 104. For example, the optical metrology subsystem 102 may utilize light having a wavelength in the UV to IR spectral region.

[0044] In an embodiment, the metrology system 100 includes an additional metrology subsystem 108, which may be referred to as a high-resolution metrology subsystem. For example, the additional metrology subsystem 108 may include an imaging system suitable for resolving the position and / or profile of the optical metrology target 104. As an illustration, the additional metrology subsystem 108 may be suitable for measuring characteristics of the optical metrology target 104, including but not limited to the sidewall angle of a constituent feature (and thus the asymmetry of the feature) or the PPE of the constituent feature. Furthermore, in the case where the optical metrology target 104 includes fine features at a fine pitch, the additional metrology subsystem 108 may provide such characteristics for the fine features.

[0045] The additional metrology subsystem 108 may include any combination of components suitable for resolving the position and / or profile of the optical metrology target 104. For example, the additional metrology subsystem 108 may include a particle-based metrology subsystem, such as, but not limited to, an electron beam metrology subsystem (e.g., a scanning electron microscope or the like) or an ion beam metrology subsystem. As another example, the additional metrology subsystem 108 may include an X-ray metrology subsystem.

[0046] In an embodiment, the additional metrology subsystem 108 has a higher resolution than the optical metrology subsystem 102 and can individually characterize features of the optical metrology target 104 on one or more sample layers. For example, it may be the case that the optical metrology subsystem 102 can generate optical metrology measurements based on two diffraction orders of the optical metrology target 104. In this case, the optical metrology subsystem 102 does not necessarily need to resolve aspects of individual features of the optical metrology target 104, such as sidewall angles or the like. Rather, the additional metrology subsystem 108 can fully resolve such aspects of the individual features.

[0047] Some embodiments of the present disclosure are directed to providing recipes for configuring the optical metrology subsystem 102 and / or the additional metrology subsystem 108. The metrology recipe may include a set of parameters for controlling various aspects of a metrology measurement. Furthermore, the optical metrology subsystem 102 and the additional metrology subsystem 108 may utilize different metrology recipes (e.g., first and second recipes or the like).

[0048] For example, the metrology recipe may include parameters such as, but not limited to, illumination of the optical metrology target 104, collection of light from the sample, or position of the sample during measurement. In this way, the optical metrology subsystem 102 can be configured to provide a selected type of measurement for a selected target design (e.g., a reference design).

[0049] By way of illustration, a metrology recipe for a light-based metrology subsystem (e.g., the optical metrology subsystem 102 or the additional X-ray-based metrology subsystem 108) may include parameters of an illumination beam, such as, but not limited to, illumination wavelength, illumination pupil distribution (e.g., distribution of illumination angles and associated illumination intensities at those angles), polarization of incident illumination, or spatial distribution of illumination. Similarly, a metrology recipe for a particle-based metrology subsystem (e.g., the additional particle-based metrology subsystem 108) may include illumination parameters such as, but not limited to, acceleration voltage, beam current, spot size of the illumination beam, or scanning speed.

[0050] As another illustration, a metrology recipe for a light-based metrology subsystem may include collection parameters such as, but not limited to, a collection pupil distribution (e.g., a desired distribution of angular light from the optical metrology target 104 to be used for measurement and the associated filter intensities at the angles), a collection field stop setting for selecting portions of the optical metrology target 104 of interest, polarization of the collection light, wavelength filters, or parameters for controlling one or more detectors. Similarly, a metrology recipe for a particle-based metrology subsystem may include collection parameters such as, but not limited to, voltages applied to a collection lens or detector type.

[0051] By way of another example, the metrology recipe may include various parameters associated with the design of the optical metrology target 104, such as, but not limited to, the location and orientation of sample features (e.g., the pitch of grating features along a particular direction). By way of another example, the metrology recipe may include various parameters associated with the location of the sample 106 during measurement, such as, but not limited to, sample height, sample orientation, whether the sample 106 is stationary during measurement, or whether the sample 106 is in motion during measurement (along with associated parameters describing speed, scanning pattern, or the like).

[0052] In an embodiment, the metering system 100 includes a controller 110 communicatively coupled to any components therein. In some embodiments, the controller 110 includes one or more processors 112. For example, the one or more processors 112 may be configured to execute a set of program instructions maintained in a memory 114 or a memory device. The one or more processors 112 of the controller 110 may include any processing element known in the art. In this sense, the one or more processors 112 may include any microprocessor-type device configured to execute algorithms and / or instructions.

[0053] The one or more processors 112 of the controller 110 may include any processor or processing element known in the art. For the purposes of the present 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 112 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In some embodiments, the one or more processors 112 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 a program configured to operate the metering system 100 or operate in conjunction with the metering system 100, as described throughout the present disclosure. In addition, different subsystems of the metering system 100 may include processors or logic elements suitable for performing at least a portion of the steps described in the present disclosure. Therefore, the above description should not be construed as limiting the embodiments of the present disclosure but only as an illustration. Furthermore, the steps described throughout this disclosure may be performed by a single controller or, alternatively, by multiple controllers. Additionally, the controller 110 may include one or more controllers housed in a common housing or multiple housings. In this manner, any controller or combination of controllers may be individually packaged as a module suitable for integration into the metering system 100.

[0054] The memory 114 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 112. For example, the memory 114 may include a non-transitory storage medium. By way of another example, the memory 114 may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical storage device (e.g., a disk), a tape, a solid-state drive, and the like. It should be further noted that the memory 114 may be housed in a common controller housing with the one or more processors 112. In some embodiments, the memory 114 may be remotely located relative to the physical location of the one or more processors 112 and the controller 110. For example, the one or more processors 112 of the controller 110 may access a remote memory (e.g., a server) that is accessible via a network (e.g., the Internet, an intranet, and the like).

[0055] The controller 110 may direct (e.g., via control signals) and / or receive data from any component or subsystem of the metrology system 100, such as, but not limited to, the light metrology subsystem 102 or the additional metrology subsystem 108. The controller 110 may be further configured to perform any of the various process steps described in the present disclosure.

[0056] Reference Figure 2 , describes in more detail high resolution evaluation of an optical metrology target 104 for facilitating process control according to one or more embodiments of the present disclosure. Figure 2 is a conceptual diagram depicting an error driver for process monitoring using an optical metrology target according to one or more embodiments of the present disclosure.

[0057] As previously described herein, it may be desirable to evaluate the printing characteristics of the optical metrology target 104 to ensure that metrology measurements based on the target remain accurate (eg, within an accuracy metric).

[0058] An option for evaluating the optical metrology target 104 is to use optical techniques. Optical techniques for evaluation of metrology targets are generally described in D. Kandel et al., Overlay Accuracy Fundamentals, Proc. SPIE 8324, Metrology, Inspection, and Process Control for Microlithography XXVI, 832417 (April 5, 2012); A. Shchegrov et al., On Product Overlay Metrology Challenges in Advanced Nodes, Proc. SPIE 11325, Metrology, Inspection, and Process Control for Microlithography XXVI, 832417 (April 5, 2012); Microlithography XXXIV, 113251P (March 20, 2020); and E. Amit et al., Overlay Accuracy Calibration, Journal of the International Society for Optical Engineering 8681, Metrology, Inspection, and Process Control for Microlithography XXVII, 86811G (April 18, 2013), the entire contents of which are incorporated herein by reference. However, the wavelength of light used for such optical evaluations can limit the achievable resolution.

[0059] A second option for evaluating the optical metrology target 104 is to utilize an external reference, such as an additional target or a portion of the target suitable for characterization by a high-resolution metrology tool (e.g., a particle beam metrology tool, an X-ray metrology tool, or the like. For example, a high-resolution target may include fine features having a size and / or pitch similar to device features and may generally have a small size suitable for measurement using a high-resolution metrology tool. Techniques for external reference-based high-resolution measurement evaluation and / or calibration of the optical metrology target 104 are generally described in U.S. Pat. No. 11,075,126, entitled MISREGISTRATION MEASUREMENTS USING COMBINED OPTICAL AND ELECTRONBEAM TECHNOLOGY, issued on July 27, 2021; OPTICAL IMAGING METROLOGY CALIBRATION USING HIGH VOLTAGE SCANNING ELECTRON MICROSCOPE AT AFTER-DEVELOPMENT INSPECTION FOR ADVANCED PROCESSES, by N. Gutman et al., Journal of the International Society for Optical Engineering, 11325, Metrology, Inspection, and Process Control for Microlithography. Microlithography) XXXIV, 113251X (March 20, 2020); and S. Czerkas et al., HIGH VOLTAGE SCANNING ELECTRON MICROSCOPE OVERLAY METROLOGY ACCURACY FOR AFTER DEVELOPMENT INSPECTION, Journal of the International Society for Optical Engineering 11611, Metrology, Inspection, and Process Control for Semiconductor Manufacturing XXXV, 116110B (February 22, 2021), the entire contents of which are incorporated herein by reference.

[0060] exist Figure 2, a bar graph 202 depicts the relative contributions of different target quality errors (e.g., deviations from a reference design, deformations, or the like) associated with accuracy instabilities of an optical metrology target 104 characterized using optical techniques and a dedicated high-resolution target characterized using a high-resolution metrology subsystem. In particular, the bar graph 202 depicts the relative contributions of target asymmetry and PPE. However, Figure 2 It is provided for illustrative purposes only and should not be construed as limiting. Rather, any contribution to target mass error, including but not limited to etch bias, is within the spirit and scope of the present disclosure.

[0061] like Figure 2 As depicted in , high-resolution characterization of a dedicated high-resolution target can provide significantly more accurate deformation measurements, such as asymmetry or PPE, than corresponding optical measurements of the optical metrology target 104. Figure 2 However, it is contemplated herein that measurements of external features (eg, dedicated high-resolution targets) may not be able to capture the deformation of optical features of the optical metrology target 104 and therefore may not be able to adequately assess the performance of the optical metrology target 104.

[0062] For example, it may be the case that optical features having a size and / or pitch suitable for optical characterization may be more sensitive to process deviations (e.g., variations in the lithography process) than fine features. In fact, lithography processes are typically designed to make device features (and thus corresponding fine features of the optical metrology target 104) relatively insensitive to process variations to minimize the impact of such process variations on the device features. Therefore, fine features associated with a dedicated high-resolution metrology target may also be insensitive to process variations.

[0063] Embodiments of the present disclosure are directed to using high-resolution metrology tools to directly measure deformation (eg, deviation from a reference design) of an optical metrology target 104. In this manner, high-resolution metrology tools may be used to capture deformation of optical features suitable for optical characterization.

[0064] Figure 2 The left panel 206 of further depicts a portion of the optical metrology target 104, which includes an optical feature 208 segmented into fine features 210. In an embodiment, the optical feature 208 is evaluated as well as any fine features 210 using a high-resolution metrology tool (e.g., the additional metrology subsystem 108). In addition, such features may, but need not, be evaluated using more than one region of interest (ROI). For example, a first ROI 212 (e.g., a fine pitch ROI) may be suitable for capturing the PPE and / or asymmetry of the fine features 210, while a second ROI 214 (e.g., an optical ROI) may be suitable for capturing the PPE and / or asymmetry of the optical feature 208.

[0065] Reference Figure 3 , Figure 3 is a flow chart illustrating steps performed in method 300 according to one or more embodiments of the present disclosure. Applicants note that the embodiments and enabling techniques previously described herein in the context of metering system 100 should be interpreted as extending to method 300. However, it should be further noted that method 300 is not limited to the architecture of metering system 100.

[0066] In an embodiment, method 300 includes step 302 of generating optical metrology measurements of one or more optical metrology targets 104 on one or more samples using optical metrology subsystem 102 according to a first metrology recipe, wherein the optical metrology measurements are based on features of optical metrology target 104 having at least one optical pitch.

[0067] The optical metrology target 104 may be based on any type of target design suitable for characterization by the optical metrology subsystem 102. Furthermore, the optical metrology target 104 may include features having any number of different pitches. For example, the optical metrology target 104 may include features having one or more optical pitches (e.g., Figure 2 As another example, the optical metrology target 104 may include features with a fine pitch that may be similar to or representative of the pitch of device features (e.g., as shown in FIG. Figure 2 In some cases, optical metrology target 104 includes optical features distributed at an optical pitch, where the optical features are segmented into smaller fine features distributed at a fine pitch.

[0068] Furthermore, any suitable technique may be used to determine the optical metrology measurement.For example, step 302 may include generating the optical metrology measurement using a model-based or model-free technique.

[0069] Figures 4A to 6B Various non-limiting illustrations of designs (eg, reference designs) for optical metrology targets 104 according to one or more embodiments of the present disclosure are depicted. Specifically, Figures 4A to 6B Various designs of optical metrology targets 104 suitable for overlay measurements (e.g., overlay targets) are depicted. Figures 4A to 6B In each of the embodiments, the optical metrology target 104 includes a first layer feature 402 on a first layer 404 of the sample 106 and a second layer feature 406 on a second layer 408 of the sample 106. In this manner, Figures 4A to 6BDepicts a variation of the optical metrology target 104 suitable for overlay measurement between a first layer 404 and a second layer 408. Furthermore, the first layer 404 and the second layer 408 may correspond to any suitable layers. In some embodiments, the first layer 404 is a process layer and includes first layer features 402 formed by development (e.g., photolithography exposure) and etching steps, while the second layer 408 is a resist layer and includes second layer features 406 formed by a development step. This configuration may correspond to an after-development inspection (ADI) step. In some embodiments, both the first layer 404 and the second layer 408 are process layers such that both the first layer features 402 and the second layer features 406 are formed by development and etching steps. This configuration may correspond to an after-etch inspection (AEI) step.

[0070] However, Figures 4A to 6B The depiction of the optical metrology target 104 in is illustrative only and should not be construed as limiting. For example, an optical metrology target 104 suitable for overlay measurement may include features associated with different exposures in a single layer (e.g., based on a multi-patterning technique) or features associated with different exposures in three or more layers for overlay measurement between any of the three or more layers. As another example, the optical metrology target 104 is not limited to overlay metrology, and the optical metrology target 104 associated with any type of optical metrology measurement is within the spirit and scope of the present disclosure. In some embodiments, the optical metrology target 104 is formed as a hybrid target suitable for both optical and particle beam-based metrology techniques. Non-limiting examples of hybrid targets are generally described in U.S. Patent Application No. 17 / 487,725, filed on September 28, 2021, the entire contents of which are incorporated herein by reference.

[0071] Figure 4A is a simplified top view of a first design of an optical metrology target 104 in accordance with one or more embodiments of the present disclosure. Figure 4B According to one or more embodiments of the present disclosure Figure 4A A simplified side view of a first design of optical metrology target 104 is depicted in FIG.

[0072] exist Figure 4A and 4B , the first layer features 402 and the second layer features 406 have a common pitch (eg, optical pitch) and are arranged in non-overlapping regions of the optical metrology target 104. This arrangement may be suitable for, but is not limited to, imaging-based optical metrology. For example, Figure 4A and 4B May represent a unit of an Advanced Imaging Metrology (AIM) optical metrology target 104 .

[0073] Figure 5Ais a simplified top view of a first design of an optical metrology target 104 in accordance with one or more embodiments of the present disclosure. Figure 5B According to one or more embodiments of the present disclosure Figure 5A A simplified side view of a first design of optical metrology target 104 is depicted in FIG.

[0074] exist Figure 5A and 5B , the first layer features 402 and the second layer features 406 have a common pitch (eg, optical pitch) and are arranged in an overlapping region of the optical metrology target 104. This arrangement may be suitable for, but is not limited to, optical metrology based on scatterometry. For example, Figure 5A and 5B Cells of the scatterometry optical metrology target 104 may be represented, where different cells may have different intentional offsets between the first layer features 402 and the second layer features 406 .

[0075] Fig. 6A is a simplified top view of a first design of an optical metrology target 104 in accordance with one or more embodiments of the present disclosure. Figure 6B According to one or more embodiments of the present disclosure Fig. 6A A simplified side view of a first design of optical metrology target 104 is depicted in FIG.

[0076] exist Fig. 6A and 6B , first layer features 402 and second layer features 406 have different pitches and are arranged in an overlapping region of the optical metrology target 104 to form a Moiré structure. This configuration can generate diffraction orders associated with each of the different pitches and Moiré diffraction orders associated with double diffraction (e.g., combined diffraction) from each of the structures, where optical overlay metrology measurements can be generated based on any of the diffraction orders, either individually or in combination, using different techniques. For example, both pitches of the first layer features 402 and the second layer features 406 can be optical pitches, such that optical overlay metrology measurements can be generated based on diffraction from these structures. As another example, the pitch of the first layer features 402 and / or the second layer features 406 can be below the imaging resolution of the optical metrology subsystem 102, but the Moiré diffraction orders can be optical pitches and used to generate optical overlay metrology measurements.

[0077] In addition, the general reference Figures 4A to 6B Although not shown, any of the first layer features 402 or the second layer features 406 may be further segmented to include fine structures distributed at a fine pitch, as previously described herein.

[0078] In an embodiment, the method 300 includes a step 304 of generating additional metrology measurements of the one or more overlay targets using an additional metrology subsystem 108 that may be configured according to a second metrology recipe, wherein the additional metrology measurements have a higher resolution than the optical metrology measurements. For example, in the case of an image-based optical metrology subsystem 102, the additional metrology subsystem 108 may have a higher imaging resolution than the optical metrology subsystem 102. As another example, in the case of a scatterometry-based optical metrology subsystem 102, the additional metrology subsystem 108 may have a higher measurement accuracy than the optical metrology subsystem 102.

[0079] In an embodiment, the method 300 includes a step 306 of comparing the optical metrology measurements with additional metrology measurements to generate an accuracy (or inaccuracy) measurement of one or more optical metrology targets 104. In this way, various errors associated with the optical metrology measurements may be determined. Such errors may be systematic and occur consistently for all optical metrology targets 104, may depend on the position of the optical metrology target 104 on the sample 106 (e.g., position within an exposure field and / or position across the sample 106), and / or may be time-varying (e.g., may vary for an optical metrology target 104 in a consistent position across multiple samples 106 in the same or different batches).

[0080] In an embodiment, the method 300 includes a step 308 of measuring deviations of one or more optical metrology targets 104 from a reference design using an additional metrology subsystem 108, wherein the deviations include deviations of optically resolvable features from the reference design. In an embodiment, the method 300 includes a step 310 of identifying variations in a lithography process used to fabricate one or more samples 106 based on the deviations of the one or more optical metrology targets from the reference design. In a manner similar to step 306, variations in the lithography process may depend on the position of the optical metrology target 104 on the sample 106, and / or may vary in time. Such variations in the lithography process may induce the deviations measured in step 308. In this way, the deviations of the optical metrology target 104 from the reference design measured in step 308 may serve as an indicator of variations in the lithography process.

[0081] The reference design may include designed (e.g., ideal) sizes, orientations, and / or placements of all features of the optical metrology target 104. For example, the reference design may include characteristics such as, but not limited to, sidewall angles or design symmetry or asymmetry of any feature (e.g., features associated with optical pitch and / or features associated with fine pitch).

[0082] Thus, step 308 may include measuring deviations from any design characteristics of any of the features of the optical metrology target 104, such as, but not limited to, deviations from placement of any feature (e.g., PPE of the feature), deviations from one or more sidewall angles, deviations from symmetry of any or a combination of features (e.g., unintended asymmetry, pitch splitting, asymmetric pitch walk, asymmetric profile error (EPE)), or etch bias errors.

[0083] Step 308 may include individual measurements of specific features and / or groups of features. For example, step 308 may include layer-specific deviation measurements. In this case, features on different layers of sample 106 may exhibit different printing errors, which may be identified in step 308. As an illustration, Figure 3 A through 5B depict asymmetric first layer features 402, but symmetric second layer features 406. In situations where all features are desired to be symmetric (eg, in a reference design), such asymmetry of first layer features 402 may be identified in step 308.

[0084] As another example, step 308 may include pitch specific deviation measurements. In this case, features associated with different pitches may exhibit different printing errors, which may be identified in step 308. For example, an optical metrology target 104 including optical features distributed at an optical pitch segmented into fine features distributed at a fine pitch may exhibit different printing errors for optical and fine features, which may be identified in step 308.

[0085] In an embodiment, method 300 includes step 312 of correlating the accuracy measurements of one or more optical metrology targets 104 with variations (e.g., drift) in the lithography process based on deviations of the one or more optical metrology targets 104 from a reference design. In this way, the impact of variations in the lithography process on the accuracy of the optical overlay measurements can be determined.

[0086] Figure 7 is a conceptual diagram illustrating excursion monitoring (eg, monitoring process variation) based on deviation of optical metrology target 104 from a reference design according to one or more embodiments of the present disclosure.

[0087] Panel 702 depicts drift monitoring based on using optical techniques to evaluate optical metrology target 104. In particular, panel 702 illustrates a single representative optical feature 704 having a size and / or pitch suitable for optical characterization (additional structures not shown in the figure).

[0088] Panel 706 depicts excursion monitoring based on evaluating a high resolution metrology target using a high resolution metrology tool. In particular, panel 706 illustrates a plurality of representative fine features 708 having a size and / or pitch similar to corresponding device features.

[0089] Panel 710 depicts drift monitoring of the optical metrology target 104 based on drift monitoring based on evaluating the optical metrology target 104 using a high resolution metrology tool as disclosed herein (e.g., additional metrology subsystem 108). In particular, panel 710 illustrates optical features 704 and constituent fine features 712 that can be resolved using additional metrology subsystem 108 but not necessarily by optical metrology subsystem 102.

[0090] In each panel, row 714 depicts a side profile of a first representative target measured by a corresponding tool. Row 716 depicts a side profile of a second representative target measured by a corresponding tool, where the second representative target exhibits asymmetry errors due to process variations.

[0091] Next, row 718 depicts a conceptual diagram of the measurement inaccuracies of respective targets that may be measured by respective tools in response to process deviations. Furthermore, such process deviations may occur spatially (e.g., as a function of location on the sample 106) and / or across time (e.g., across multiple samples 106). As depicted in panel 710, based on monitoring the drift of the optical metrology target 104 based on evaluating the optical metrology target 104 for drift monitoring using the high resolution metrology tool disclosed herein (e.g., additional metrology subsystem 108), a highly sensitive assessment of the asymmetry of the optical feature 704 is provided in addition to the characteristics of the fine feature 712. Thus, this technique may provide a highly sensitive assessment of the inaccuracy of the associated optical metrology target 104 in response to process variations.

[0092] Reference again Figure 3 In an embodiment, method 300 includes step 314 of adjusting at least one of an optical metrology subsystem, a lithography tool, or a reference design based on the correlation.

[0093] It is contemplated herein that correlation between accuracy measurements of one or more optical metrology targets 104 as measured in step 312 and variations (eg, drift) in the lithography process based on deviations of one or more optical metrology targets 104 from a reference design may be used in a variety of ways.

[0094] For example, step 314 may include evaluating a reference design. As an illustration, Figure 8A conceptual graph 802 depicting the performance of an optical metrology target 104 relative to a low quality reference design and a conceptual graph 804 depicting the performance of an optical metrology target 104 relative to a high quality reference design according to one or more embodiments of the present disclosure are included. In each graph 802, 804, the optical metrology targets 104 distributed across the samples 106 (e.g., within various fields 806) are depicted as circles, where the shading / color of each circle is associated with the deviation (e.g., PPE or the like) of one aspect of the associated optical metrology target 104 relative to the reference design. The 3σ variation of the relative low quality reference design in graph 802 is 0.33, while the 3σ variation of the relative high quality reference design in graph 804 is 0.07. Figure 8 The average value (M) of the optical metrology measurement is further described.

[0095] In a similar manner, step 314 may include evaluating a metrology recipe (e.g., a first metrology recipe of the optical metrology subsystem 102) used to determine the optical metrology measurement in step 302. As previously described herein, the metrology recipe may include various configurations of the optical metrology subsystem 102 that may affect the measurement (e.g., wavelength, polarization, field of view, or the like). For example, it may be the case that some metrology recipes may provide more accurate measurements than other recipes. In this manner, step 314 may include adjusting the metrology recipes of the optical metrology subsystem to select a metrology recipe that provides a relatively higher accuracy. As another example, it may be the case that different metrology recipes may have different sensitivities to variations in the photolithography process associated with the fabrication of the sample 106. In this manner, step 314 may include adjusting the metrology recipe of the optical metrology subsystem to reduce the sensitivity of the optical metrology measurement to variations in the photolithography process associated with the fabrication of the sample 106.

[0096] As another example, step 314 may include selecting a reference design and / or a metrology recipe (e.g., from a variety of alternative reference designs). For example, the reference design and / or the metrology recipe may be selected before initiating a large number of manufacturing batches. In the present application, the manufacturing tool may use the reference design selected in step 314 to manufacture the optical metrology target 104 and / or may utilize the metrology recipe selected in step 314 for process control.

[0097] As another example, step 314 may include switching reference designs (e.g., switching from one reference design to an alternate reference design). For example, over a large number of manufacturing batches, steps 302-314 may be used to evaluate reference designs and / or metrology recipes and determine when the reference designs and / or metrology recipes do not meet selected metrics. As an illustration, an initial reference design and / or metrology recipe for the optical metrology target 104 may be adapted to process variations during a first phase of a large number of manufacturing batches. However, over time, it may be the case that process variations change such that a different reference design and / or metrology recipe may provide better performance.

[0098] As another example, step 314 may include adjusting the lithography tool to compensate for variations in the lithography process. For example, step 314 may reduce or in some cases eliminate such variations in future lithography exposures.

[0099] Reference Figures 1A to 1C , additional aspects of the metering system 100 according to one or more embodiments of the present disclosure are described in more detail.

[0100] Figure 1B is a conceptual diagram of an optical metrology subsystem 102 according to one or more embodiments of the present disclosure.

[0101] The optical metrology subsystem 102 may generate one or more images of the sample 106 on at least one detector 116 using any method known in the art. In an embodiment, the detector 116 is located at a field plane to generate an image of one or more features on the sample 106. In an embodiment, the detector 116 is located at a pupil plane to generate an image based on the angle of light emitted from the sample 106 (e.g., based on reflection, diffraction, scattering, or the like). In this regard, the optical metrology subsystem 102 may operate as a scatterometry-based metrology tool.

[0102] In an embodiment, the optical metrology subsystem 102 includes an illumination source 118 for generating an illumination beam 120. The illumination beam 120 may include light of one or more selected wavelengths, including but not limited to vacuum ultraviolet radiation (VUV), deep ultraviolet radiation (DUV), ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation. The illumination light source 118 may further generate the illumination beam 120 including any range of selected wavelengths. In an embodiment, the illumination light source 118 may include a spectrally tunable illumination light source to generate the illumination beam 120 having a tunable spectrum.

[0103] The illumination source 118 can further generate an illumination beam 120 having any temporal profile. For example, the illumination source 118 can generate a continuous illumination beam 120, a pulsed illumination beam 120, or a modulated illumination beam 120. Additionally, the illumination beam 120 can be delivered from the illumination source 118 via free space propagation or light guides (e.g., optical fibers, light pipes, or the like).

[0104] In an embodiment, the illumination light source 118 directs an illumination beam 120 to the sample 106 via an illumination path 122. The illumination path 122 may include one or more lenses 124 or additional illumination optical components 126 suitable for modifying and / or adjusting the illumination beam 120. For example, the one or more illumination optical components 126 may include, but are not limited to, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more shutters (e.g., mechanical shutters, electrical shutters, acoustic shutters, or the like). By way of another example, the one or more illumination optical components 126 may include an aperture stop to control the illumination angle on the sample 106 and / or a field stop to control the spatial extent of the illumination on the sample 106. In one example, the illumination path 122 includes an aperture stop located at a plane conjugate to the back focal plane of the objective 128 to provide telecentric illumination of the sample. In an embodiment, the optical metrology subsystem 102 includes an objective lens 128 to focus the illumination beam 120 onto the sample 106 .

[0105] In an embodiment, the sample 106 is disposed on a sample stage 130. The sample stage 130 may include any device suitable for positioning the sample 106 within the metrology system 100. For example, the sample stage 130 may include any combination of a linear translation stage, a rotation stage, a tip / tilt stage, or the like.

[0106] In an embodiment, the detector 116 is configured to capture radiation (e.g., sample light 132) emitted from the sample 106 through a collection path 134. For example, the collection path 134 may include, but need not include, a collection lens (e.g., objective lens 128 as illustrated in FIG. 1 ) or one or more additional collection path lenses 136. In this regard, the detector 116 may receive radiation that is reflected or scattered (e.g., via specular reflection, diffuse reflection, and the like) from the sample 106 or generated by the sample 106 (e.g., luminescence associated with absorption of the illumination beam 120 or the like).

[0107] The collection path 134 may further include any number of collection optical components 138 for directing and / or modifying the illumination collected by the objective 128, including but not limited to one or more collection path lenses 136, one or more filters, one or more polarizers, or one or more beam stops. Additionally, the collection path 134 may include a field stop for controlling the spatial extent of the sample imaged on the detector 116 or an aperture stop for controlling the angular extent of illumination from the sample used to produce an image on the detector 116. In an embodiment, the collection path 134 includes an aperture stop located in a plane conjugate to the back focal plane of the optical elements of the objective 128 to provide telecentric imaging of the sample.

[0108] Detector 116 may include any type of optical detector known in the art suitable for measuring illumination received from sample 106. For example, detector 116 may include a sensor suitable for producing one or more images of static specimen 106 (e.g., in a static mode of operation), such as, but not limited to, a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS) sensor, a photomultiplier tube (PMT) array, or an avalanche photo diode (APD) array.

[0109] By way of another example, the detector 116 may include a sensor suitable for generating one or more images of the sample 106 in motion (e.g., a scanning mode of operation). For example, the detector 116 may include a line sensor including a row of pixels. Accordingly, the optical metrology subsystem 102 may generate a continuous image (e.g., a strip image) one row at a time by translating the sample 106 through the measurement field of view in a scanning direction perpendicular to the row of pixels during continuous exposure windows and continuously clocking the line sensor.

[0110] In another example, the detector 116 may include a TDI sensor including a plurality of pixel rows and a readout row. The TDI sensor may operate in a manner similar to a line sensor, except that a clock signal may continuously move charge from one pixel row to the next pixel row until the charge reaches the readout row, where a line image is generated. By synchronizing the charge transfer (e.g., based on a clock signal) with the movement of the sample along the scan direction, charge may continue to accumulate across the pixel rows to provide a relatively high noise ratio compared to a line sensor.

[0111] In embodiments, the detector 116 may include a spectral detector suitable for identifying wavelengths of radiation emitted from the sample 106. In embodiments, the optical metrology subsystem 102 may include multiple detectors 116 (e.g., associated with multiple beam paths produced by one or more beam splitters to facilitate multiple metrology measurements by the optical metrology subsystem 102). For example, the optical metrology subsystem 102 may include one or more detectors 116 suitable for static mode imaging and one or more detectors 116 suitable for scanning mode imaging. In embodiments, the optical metrology subsystem 102 may include one or more detectors 116 suitable for both static and scanning imaging modes.

[0112] In an embodiment, Figure 1B , the optical metrology subsystem 102 includes a beam splitter 140 oriented so that an objective lens 128 can simultaneously direct an illumination beam 120 to a sample 106 and collect radiation emitted from the sample 106. In this regard, the metrology system 100 can be configured in a reflected illumination mode.

[0113] In an embodiment, the angle of incidence of the illumination beam 120 on the sample 106 is adjustable. For example, the path of the illumination beam 120 through the beam splitter 140 and the objective lens 128 can be adjusted to control the angle of incidence of the illumination beam 120 on the sample 106. In this regard, the illumination beam 120 can have a nominal path through the beam splitter 140 and the objective lens 128 such that the illumination beam 120 has a normal angle of incidence on the sample 106. By way of another example, the angle of incidence of the illumination beam 120 on the sample 106 can be controlled by modifying the position and / or angle of the illumination beam 120 on the beam splitter 140 (e.g., by a rotatable mirror, a spatial light modulator, a free-form illumination light source, or the like). In an embodiment, the illumination light source 118 directs one or more illumination beams 120 to the sample 106 at an angle (e.g., a grazing angle, a 45 degree angle, or the like).

[0114] Figure 1C is a conceptual diagram of an additional metering subsystem 108 according to one or more embodiments of the present disclosure.

[0115] In an embodiment, the additional metrology subsystem 108 includes an illumination source 118. In an embodiment, the illumination source 118 includes a particle source (e.g., an electron beam source, an ion beam source, or the like) such that the illumination beam 120 includes a particle beam (e.g., an electron beam, a particle beam, or the like). The illumination source 118 may include any particle source known in the art that is suitable for generating the illumination beam 120. For example, the illumination source 118 may include, but is not limited to, an electron gun or an ion gun. In an embodiment, the illumination source 118 is configured to provide a particle beam with tunable energy. For example, the illumination source 118 including an electron source may, but is not limited to, provide an accelerating voltage in the range of 0.1 kV to 30 kV. As another example, the illumination source 118 including an ion source may, but need not, provide an ion beam with an energy in the range of 1 keV to 50 keV.

[0116] In an embodiment, the illumination path 122 includes one or more particle focusing elements (e.g., a lens 124 or the like) and / or a corrective element (e.g., an stigmator or the like). For example, the one or more particle focusing elements may include, but are not limited to, a single particle focusing element or one or more particle focusing elements forming a composite system. In an embodiment, the one or more particle focusing elements include an objective lens 128 configured to direct the illumination beam 120 to the sample 106. Furthermore, the one or more particle focusing elements may include any type of electron lens known in the art, including, but not limited to, electrostatic, magnetic, single-potential, or double-potential lenses. It should be noted herein that Figure 1CThe description of the voltage contrast imaging inspection system depicted in and the associated description above are provided for illustrative purposes only and should not be construed as limiting. For example, the additional metrology subsystem 108 may include any excitation source known in the art suitable for generating inspection data on the sample 106. In an embodiment, the additional metrology subsystem 108 includes two or more particle beam sources (e.g., electron beam sources or ion beam sources) for generating two or more particle beams. In a further embodiment, the additional metrology subsystem 108 may include one or more components (e.g., one or more electrodes) configured to apply one or more voltages to one or more locations of the sample 106. Accordingly, the additional metrology subsystem 108 can generate voltage contrast imaging data.

[0117] In an embodiment, the additional metrology subsystem 108 includes one or more particle detectors 116 for imaging or otherwise detecting particles emitted from the sample 106. In an embodiment, the detector 116 includes an electron collector (e.g., a secondary electron collector, a backscattered electron detector, or the like). In an embodiment, the detector 116 includes a photon detector (e.g., a light detector, an x-ray detector, a scintillation element coupled to a photomultiplier tube (PMT) detector, or the like) for detecting electrons and / or photons from the sample surface.

[0118] The subject matter described herein sometimes illustrates different components contained in or connected to other components. It should be understood that such depiction architecture is for illustration only, and in fact many other architectures that realize the same functionality can be implemented. Conceptually, any arrangement of components that realize the same functionality is effectively "associated" so that the desired functionality is realized. Therefore, any two components combined to realize a specific functionality herein can be considered to be "associated" with each other so that the desired functionality is realized, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to realize the desired functionality. The specific instance of "coupleable" includes but is not limited to physically interactable and / or physically interactive components and / or wirelessly interactive and / or wirelessly interactive components and / or logically interactive and / or logically interactive components.

[0119] It is believed that the present disclosure and its many attendant advantages will be understood from the above description, and it should be understood that various changes may be made to the form, construction and arrangement of components without departing from the present disclosure or sacrificing all of its material advantages. The forms described are for illustration only, and the appended claims are intended to cover and encompass such changes. In addition, it should be understood that the present disclosure is defined by the appended claims.

Claims

1. A metering system, comprising: a controller communicatively coupled to an optical metrology subsystem and an additional metrology subsystem, wherein the optical metrology subsystem is configurable according to a first metrology recipe to generate optical metrology measurements of one or more optical metrology targets on one or more samples, wherein the optical metrology measurements are based on features of the optical metrology targets associated with at least one optical pitch, wherein the additional metrology subsystem is configurable according to a second metrology recipe to generate additional metrology measurements of the one or more optical metrology targets, wherein the additional metrology measurements have a higher resolution than the optical metrology measurements, wherein the additional metrology subsystem further measures deviations of the one or more optical metrology targets from a reference design, wherein the deviations include deviations of the features associated with the at least one optical pitch relative to the reference design, wherein the controller includes one or more processors configured to execute program instructions that cause the one or more processors to: comparing the optical metrology measurement to the additional metrology measurement to generate an accuracy measurement of the one or more optical metrology targets; identifying variations in a photolithography process used to fabricate the one or more samples based on the deviations of the one or more optical metrology targets from the reference design; correlating the accuracy measurements of the one or more optical metrology targets with the variations of the photolithography process based on the deviations of the one or more optical metrology targets from the reference design; and At least one of the optical metrology subsystem, the lithography tool, or the reference design is adjusted based on the correlation.

2. The metrology system of claim 1 , wherein measuring a deviation of the one or more optical metrology targets from a reference design based on the additional measurements comprises: At least one of a sidewall angle, an asymmetry, a pattern placement error, or an etch bias of the feature associated with the at least one optical pitch is measured.

3. The metrology system of claim 1 , wherein the one or more optical metrology targets further include features associated with a fine pitch that is smaller than the at least one optical pitch, wherein measuring a deviation of the one or more optical metrology targets from a reference design based on the additional measurements comprises: At least one of a sidewall angle, an asymmetry, a pattern placement error, or an etch bias of the feature associated with the fine pitch is measured.

4. The metrology system of claim 1 , wherein measuring a deviation of the one or more optical metrology targets from a reference design based on the additional measurements comprises: Layer-specific deviations of the one or more optical measurement targets are measured.

5. The metrology system of claim 1 , wherein the one or more optical metrology targets include features distributed at one or more pitches, wherein measuring a deviation of the one or more optical metrology targets from a reference design based on the additional measurements comprises: A pitch-specific deviation of the one or more optical metrology targets is measured.

6. The metrology system of claim 1 , wherein identifying variations in the photolithography process used to fabricate the one or more samples based on the deviations of the one or more optical metrology targets from the reference design comprises: Variations in the lithographic process between different spatial locations of a particular sample across the one or more samples are identified.

7. The metrology system of claim 1 , wherein the one or more samples include two or more samples, wherein identifying a variation in the photolithography process used to fabricate the one or more samples based on the deviation of the one or more optical metrology targets from the reference design comprises: Variations in the lithography process over time are identified for at least two of the two or more samples.

8. The metrology system of claim 1 , wherein adjusting at least one of the optical metrology subsystem, the lithography tool, or the reference design based on the correlation comprises: The first metrology recipe is adjusted to reduce sensitivity of the optical metrology measurement to the variation of the photolithography process.

9. The metrology system of claim 8, wherein adjusting the first metrology recipe to reduce sensitivity of the optical metrology measurement to offset comprises: At least one of an illumination wavelength, an illumination polarization, an illumination angle, or a field of view of the optical metrology subsystem is adjusted.

10. The metrology system of claim 1 , wherein adjusting at least one of the optical metrology subsystem, the lithography tool, or the reference design based on the correlation comprises: The lithography tool is adjusted to compensate for the variation in the lithography process.

11. The metrology system of claim 1 , wherein adjusting at least one of the optical metrology subsystem, the lithography tool, or the reference design based on the correlation comprises: switching the reference design to an alternative reference design; and The lithography tool is directed to fabricate one or more additional optical metrology targets on one or more additional samples based on the alternative reference design.

12. The metrology system of claim 1, wherein the optical metrology subsystem generates the optical metrology measurements based on one or more images of the one or more optical metrology targets.

13. The metrology system of claim 1, wherein the optical metrology subsystem generates the optical metrology measurements based on one or more scatterometry measurements of the one or more optical metrology targets.

14. The metrology system of claim 1, wherein the at least one optical pitch comprises a single optical pitch, wherein the one or more optical metrology targets comprise features having the single optical pitch on at least two layers.

15. The metrology system of claim 1, wherein the at least one optical pitch comprises a first optical pitch and a second optical pitch.

16. The metrology system of claim 15, wherein the first optical pitch and the second optical pitch are resolvable using the optical metrology subsystem.

17. The metrology system of claim 1, wherein the one or more optical targets include features having a first pitch and a second pitch, wherein at least one of the first pitch or the second pitch cannot be resolved using the optical metrology subsystem, wherein the optical pitch includes a moiré pitch based on the first pitch and the second pitch and is capable of being resolved by the optical metrology subsystem.

18. The metering system of claim 1, wherein the additional metering subsystem comprises: At least one of a particle beam metrology system or an X-ray metrology system.

19. A method comprising: generating, using an optical metrology subsystem, optical metrology measurements of one or more optical metrology targets on one or more samples according to a first metrology recipe, wherein the one or more optical metrology targets include features associated with at least one optical pitch, wherein the optical metrology measurements are based on the features of the optical metrology targets having the at least one optical pitch; generating additional metrology measurements of the one or more optical metrology targets using an additional metrology subsystem configurable according to a second metrology recipe, wherein the additional metrology measurements have a higher resolution than the optical metrology measurements; comparing the optical metrology measurement to the additional metrology measurement to generate an accuracy measurement of the one or more optical metrology targets; measuring deviations of the one or more optical metrology targets from a reference design using the additional metrology subsystem, wherein the deviations include deviations of optically resolvable features from the reference design; identifying variations in a photolithography process used to fabricate the one or more samples based on the deviations of the one or more optical metrology targets from the reference design; correlating the accuracy measurements of the one or more optical metrology targets with the variations of the photolithography process based on the deviations of the one or more optical metrology targets from the reference design; and At least one of the optical metrology subsystem, the lithography tool, or the reference design is adjusted based on the correlation.

20. A metering system comprising: an optical metrology subsystem configurable according to a first metrology recipe to produce optical metrology measurements of one or more optical metrology targets on one or more samples, wherein the optical metrology measurements are based on characteristics of the optical metrology targets associated with at least one optical pitch; an additional metrology subsystem configurable according to a second metrology recipe to generate additional metrology measurements of the one or more optical metrology targets, wherein the additional metrology measurements have a higher resolution than the optical metrology measurements, wherein the additional metrology subsystem further measures deviations of the one or more optical metrology targets from a reference design, wherein the deviations include deviations of the features associated with the at least one optical pitch relative to the reference design; and a controller communicatively coupled to the optical metrology subsystem and the additional metrology subsystem, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to: comparing the optical metrology measurement to the additional metrology measurement to generate an accuracy measurement of the one or more optical metrology targets; identifying variations in a photolithography process used to fabricate the one or more samples based on the deviations of the one or more optical metrology targets from the reference design; correlating the accuracy measurements of the one or more optical metrology targets with the variations of the photolithography process based on the deviations of the one or more optical metrology targets from the reference design; and At least one of the optical metrology subsystem, the lithography tool, or the reference design is adjusted based on the correlation.

21. The metrology system of claim 20, wherein the optical metrology subsystem generates the optical metrology measurements based on one or more images of the one or more optical metrology targets.

22. The metrology system of claim 20, wherein the optical metrology subsystem generates the optical metrology measurements based on one or more scatterometry measurements of the one or more optical metrology targets.

23. The metrology system of claim 20, wherein the at least one optical pitch comprises a single optical pitch, wherein the one or more optical metrology targets comprise features having the single optical pitch on at least two layers.

24. The metrology system of claim 20, wherein the at least one optical pitch comprises a first optical pitch and a second optical pitch.

25. The metrology system of claim 24, wherein the first optical pitch and the second optical pitch are resolvable using the optical metrology subsystem.

26. The metrology system of claim 20, wherein the one or more optical targets include features having a first pitch and a second pitch, wherein at least one of the first pitch or the second pitch is not resolvable using the optical metrology subsystem, wherein the optical pitch includes a moiré pitch based on the first pitch and the second pitch and is resolvable by the optical metrology subsystem.

27. The metering system of claim 20, wherein the additional metering subsystem comprises: At least one of a particle beam metrology system or an X-ray metrology system.

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