Scattering overlay metrology with orthogonal fine pitch segmentation

Abstract

A superimposed metrology target may include a grating overlying grating structure formed of a lower grating structure having a first coarse pitch in a first sample layer and an upper grating structure having a second coarse pitch in a second sample layer, where the upper and lower grating structures overlap on the sample. At least one of the upper grating structure or the lower grating structure may include features having a fine pitch less than a wavelength of an illumination beam and are arranged to rotate from the first coarse pitch relative to at least one of specular reflection from a top surface of the sample or zero order diffraction from the one or more grating structures or a first order diffraction of the illumination beam associated with at least one of the first coarse pitch and the second coarse pitch. A superposition between the first layer and the second layer of the sample may be determined from an image of the grating structure based on the first order diffraction.

Description

Technical Field

[0001] The present disclosure relates generally to scatter superposition metrology, and more particularly to scatter superposition metrology of targets with orthogonal fine pitch. Background Art

[0002] Superposition metrology techniques utilizing grating-on-grating structures, such as but not limited to scatter superposition (SCOL) or Moiré techniques, provide relatively compact superposition targets. However, such techniques may suffer from reduced contrast or signal-to-noise ratio due to the presence of unwanted signals, such as but not limited to specular reflections (e.g., DC signals). Therefore, it is desirable to develop systems and methods that address the above-mentioned deficiencies. Summary of the invention

[0003] According to one or more illustrative embodiments, a superposition metrology system is disclosed. In one illustrative embodiment, the system includes an illumination source configured to generate an illumination beam. In another illustrative embodiment, the system includes one or more illumination optics to direct the illumination beam to a sample having a field of view including one or more superposition targets when implementing a metrology recipe. In another illustrative embodiment, a particular superposition target of the one or more superposition targets according to the metrology recipe includes one or more grating-overlying grating structures formed by a lower grating structure having a first coarse pitch and an upper grating structure having a second coarse pitch, wherein the upper grating structure and the lower grating structure overlap on the sample. In another illustrative embodiment, at least one of the upper grating structure or the lower grating structure further includes features having a fine pitch less than a wavelength of the illumination beam and arranged to rotate a first order diffraction of the illumination beam associated with at least one of the first coarse pitch or the second coarse pitch relative to at least one of a specular reflection from a top surface of the sample or a zero order diffraction from the one or more grating-overlying grating structures. In another illustrative embodiment, the system includes an objective lens to collect light from the sample within the field of view when implementing the metrology recipe. In another illustrative embodiment, the system includes a polarizer arranged to pass a portion of the light from the sample associated with first order diffraction. In another illustrative embodiment, the system includes a detector to generate an image of the sample including the one or more superposition targets. In another illustrative embodiment, the system includes a controller executing program instructions that cause the one or more processors to determine a superposition measurement of the sample based on the image of the one or more superposition targets.

[0004] According to one or more illustrative embodiments, a superposition metrology target is disclosed. In one illustrative embodiment, the target includes one or more grating-overlying grating structures formed by a lower grating structure having a first coarse pitch in a first layer of a sample and an upper grating structure having a second coarse pitch in a second layer of the sample, wherein the upper grating structure and the lower grating structure overlap on the sample. In another illustrative embodiment, at least one of the upper grating structure or the lower grating structure further includes features having a fine pitch less than a wavelength of an illumination beam and arranged to rotate a first order diffraction of the illumination beam associated with at least one of the first coarse pitch or the second coarse pitch relative to at least one of a specular reflection from a top surface of the sample or a zero order diffraction from the one or more grating structures. In another illustrative embodiment, a superposition between the first layer and the second layer of the sample can be determined from an image of the one or more grating structures based on the first order diffraction.

[0005] According to one or more illustrative embodiments, a superposition metrology method is disclosed. In one illustrative embodiment, the method includes fabricating one or more superposition targets on a sample. In another illustrative embodiment, a particular superposition target of the one or more superposition targets includes one or more grating-overlying grating structures formed of a lower grating structure having a first coarse pitch and an upper grating structure having a second coarse pitch, wherein the upper grating structure and the lower grating structure overlap on the sample. In another illustrative embodiment, at least one of the upper grating structure or the lower grating structure further includes features having a fine pitch less than a wavelength of an illumination beam and arranged to rotate a first order diffraction of the illumination beam associated with at least one of the first coarse pitch or the second coarse pitch relative to at least one of a specular reflection from a top surface of the sample or a zero order diffraction from the one or more grating-overlying grating structures. In another illustrative embodiment, the method includes illuminating the one or more of the superposition targets using the illumination beam. In another illustrative embodiment, the method includes generating an image of the sample through a polarizer aligned to pass the first order diffraction. In another illustrative embodiment, the method includes determining an overlay measurement based on the image of the sample.

[0006] According to one or more illustrative embodiments, a superposition metrology system is disclosed. In one illustrative embodiment, the system includes an illumination source configured to generate at least one illumination beam. In another illustrative embodiment, the system includes one or more illumination optics to direct the illumination beam at an oblique angle to a sample having a field of view including one or more superposition targets when implementing a metrology recipe. In another illustrative embodiment, a particular superposition target of the one or more superposition targets includes one or more corrugated grating overlying grating structures formed by a lower grating structure having a first coarse pitch and an upper grating structure having a second coarse pitch different from the first pitch, wherein the upper grating structure and the lower grating structure overlap on the sample. In another illustrative embodiment, the system includes an objective lens to collect light diffraction from the sample within the field of view when implementing the metrology recipe, wherein at least one of specular reflection from the sample or zero-order diffraction from the one or more superposition targets is outside the collection numerical aperture of the objective lens. In another illustrative embodiment, the system includes a detector to generate an image of the sample including the one or more superposition targets. In another illustrative embodiment, the system includes a controller to determine an overlay measurement of the sample based on the image of the one or more overlay targets.

[0007] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and do not necessarily limit the invention as claimed.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0009] Figure 1A is a conceptual diagram illustrating a superposition metering system according to one or more embodiments of the present disclosure.

[0010] Figure 1B is a conceptual diagram illustrating a superposition metrology subsystem according to one or more embodiments of the present disclosure.

[0011] Figure 2 is a top view of a polarization rotating feature located on a first layer of a stacking target according to one or more embodiments of the present disclosure.

[0012] Figure 3A Describes one or more embodiments of the present disclosure in conjunction with Figure 2 The coarse spacing associated with the periodicity of the structure within the structure is defined by the X-direction polarized light.

[0013] Figure 3B Describes one or more embodiments of the present disclosure along the Figure 2 The effective medium representation of the structure within the coarse spacing of light polarized in the Y direction is defined.

[0014] Figure 4 According to one or more embodiments of the present disclosure, after being illuminated by an illumination beam, Figure 2 Conceptual illustration of the electric field directions of the various diffraction orders produced by the polarization rotation feature illustrated in FIG.

[0015] Figure 5 is a top view of a 2D polarization rotation feature suitable for superimposed measurement along two measurement directions according to one or more embodiments of the present disclosure.

[0016] Figure 6 is a top view of polarization rotating features arranged with fine pitch periodicity at a 45 degree angle relative to coarse pitch according to one or more embodiments of the present disclosure.

[0017] Figure 7 is a top view of a non-segmented 2D polarization rotation feature according to one or more embodiments of the present disclosure.

[0018] Fig. 8A is a top view of a stacking target suitable for polarization-based isolation of first-order diffraction along a single measurement direction in accordance with one or more embodiments of the present disclosure.

[0019] Figure 8B is a top view of a 2D stacking target suitable for polarization-based isolation of first-order diffraction along two measurement directions according to one or more embodiments of the present disclosure.

[0020] Fig. 9 Depicts the use of a superposition target including a polarization rotation feature in a grating-on-grating structure for zero-order SCOL techniques in accordance with one or more embodiments of the present disclosure.

[0021] Fig.10 is a conceptual side view of a grating-on-grating structure illustrating a non-limiting component of a ripple signal in accordance with one or more embodiments of the present disclosure.

[0022] Fig.11 is a flow chart illustrating steps performed in a method for high-throughput overlay metrology according to one or more embodiments of the present disclosure.

[0023] Fig.12 is a series of high-level diagrams illustrating high-throughput imaging of multiple superimposed objects in a single image grab in accordance with one or more embodiments of the present disclosure.

[0024] Fig.13A is a top view of a collection pupil of a superposition metrology subsystem according to one or more embodiments of the present disclosure.

[0025] Fig. 13B is a conceptual diagram of generating two illumination beams from an incoherent light source according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0026] 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 specific embodiments and specific features of the present disclosure. The embodiments described herein should be regarded as illustrative rather than restrictive. It should be readily apparent to those skilled in the art that various changes and modifications in form and details may be made without departing from the spirit and scope of the present disclosure.

[0027] Embodiments of the present disclosure relate to systems and methods for overlay metrology using an overlay target having a grating-on-grating structure, wherein selected diffraction orders for measurement are optically isolated using polarization control. In other words, some embodiments of the present disclosure relate to systems and methods for overlay metrology using an overlay target having a grating-on-grating structure, wherein polarization control is used to block at least a portion of unwanted optical signals emanating from a sample (e.g., light from the sample that cannot contribute to the overlay measurement). As a non-limiting illustration, in some overlay measurement techniques, it may be desirable to block pure reflections from the sample that do not interact with the two gratings of the grating-on-grating structure (e.g., reflections from the top surface of the sample), which are referred to herein as DC signals to distinguish this signal from zero-order diffraction from the two gratings. It is contemplated herein that such DC signals may be relatively strong compared to the various diffraction orders from the grating-on-grating structure and may therefore reduce the contrast of the measurement.

[0028] For purposes of this disclosure, the term "grating-on-grating structure" is used to refer to a set of features in the overlap region of two or more layers of a sample, where the features on each of the layers have a periodicity that can be characterized by at least one pitch or spatial frequency. In this way, the features in the overlap region are described as grating structures. However, it should be understood that the grating structure on a particular sample layer can be characterized by multiple pitches along a particular direction and / or multiple pitches along different directions. Thus, the constituent features of the grating-on-grating structure can be segmented to provide multiple pitches in any combination of directions or otherwise distributed to provide a spatial frequency suitable for producing diffraction of incident light.

[0029] Additionally, optical isolation of selected diffraction orders from a superimposed target comprising a grating-on-grating structure can also block signals from other features on the sample (e.g., device features, dummy features, or the like), allowing multiple superimposed targets within the field of view to be characterized simultaneously. This measurement method enables extremely high throughput measurements.

[0030] An overlay target and / or an overlay metrology tool suitable for characterizing the overlay target may be configured according to a metrology recipe suitable for generating overlay measurements based on a desired technique. More generally, an overlay metrology tool may be configured according to a variety of metrology recipes to perform overlay measurements using a variety of techniques and / or to perform overlay measurements on a variety of overlay targets having different designs.

[0031] For example, a metrology recipe may include various aspects of an overlay target or design of an overlay target, including but not limited to the layout of target features, feature size, or feature spacing on one or more sample layers. As another example, a metrology recipe may include illumination parameters, 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, spatial distribution of illumination, or sample height. As another example, a recipe for an overlay metrology tool may include collection parameters, such as but not limited to collection pupil distribution (e.g., desired distribution of angular light from the sample to be used for measurement and associated filtering intensities at those angles), collection field stop settings that select portions of the sample of interest, polarization or wavelength filters for the collected light.

[0032] Some embodiments of the present disclosure relate to a superposition target suitable for providing polarization-based optical isolation of selected diffraction orders from an overlying grating structure (e.g., but not limited to first order diffraction) of a grating. Some embodiments of the present disclosure relate to a superposition measurement technique (e.g., which may be implemented using a metrology recipe) suitable for measuring superposition on a superposition target based on polarization-based optical isolation of selected diffraction orders. Some embodiments of the present disclosure relate to a superposition metrology tool that may be configured (e.g., based on a metrology recipe) to perform superposition metrology based on polarization-based optical isolation of selected diffraction orders.

[0033] In some embodiments, a superposition target suitable for polarization isolation-based superposition metrology based on first-order diffracted light includes at least one grating-on-grating structure, wherein the grating on the first layer includes features that impart different phase changes on orthogonal polarized light components of the first-order diffracted light. The use of polarization target features to provide control of the amplitude and phase of diffraction orders is generally described in U.S. Patent No. 10,337,991, issued on July 2, 2019, the entire contents of which are incorporated herein by reference. It is contemplated herein that some embodiments of the present disclosure may extend the use of the polarization target features described in U.S. Patent No. 10,337,991 to multiple superposition metrology techniques utilizing grating-on-grating structures and further extend the use of the polarization target features described in U.S. Patent No. 10,337,991 to high-throughput superposition measurements based on simultaneous imaging of multiple superposition targets in a single image grab.

[0034] The grating-on-grating structure may be formed from periodic structures (e.g., gratings or, more generally, grating structures) from different lithographic exposures on two layers in the overlap region of the superposition target (e.g., upper and lower layers). Thus, light incident on the grating-on-grating structure may interact with the gratings on each layer, such that the diffraction orders emanating from the superposition target may be affected, among other things, by the relative position of the grating structures. Thus, superposition measurements associated with the relative registration (or offset) of the sample layers may be based on one or more diffraction orders of light interacting with the grating structure in each of the layers of interest.

[0035] For example, such a grating on a first layer of a stacking target may include features arranged to provide a phase shift of π for a first order diffraction along the Y direction relative to a phase shift of a first order diffraction along the X direction. In other words, the grating on the first layer may have a different effective dielectric constant along the X direction relative to the orthogonal Y direction. In this way, the grating on the first layer may operate as a wave plate for first order diffraction but not for other light from the sample, such as but not limited to zero order diffraction, DC signal, or higher order diffraction. Thus, the grating on the first layer may rotate the polarization of the first order diffracted light relative to other light. Additionally, the grating on the second layer of the stacking target may have any design and need not affect the polarization of the light. In this way, such a stacking target may be formed on a process layer with a relatively high contrast between the grating features and the surrounding material necessary to modify the polarization of the first order diffraction, along with the first layer and the second layer in the resist layer. For the purposes of this disclosure, the term process layer refers to a layer having one or more features that is manufactured using various processing steps, including but not limited to a photolithography step (e.g., in a photomask deposited on the layer), followed by an etching step. In this way, features in the process layer can have a different material than the surrounding material, which can be air (e.g., unfilled) or additional material such as, but not limited to, oxide. For purposes of this disclosure, features in the resist layer refer to features in the photoresist produced by photolithographic exposure prior to the etching step.

[0036] An overlay metrology tool configured (e.g., according to a metrology recipe) to perform overlay metrology using such an overlay target can illuminate the overlay target using linearly polarized light and include a polarizer in a collection path with orthogonal polarization. In this way, the collection path can selectively pass first-order diffraction that has been rotated by the first layer of polarization of the overlay target and can block non-rotated light, including but not limited to DC signals or diffraction other than first-order diffraction. As a result, the signal associated with the first-order diffraction can have a high contrast and / or a high signal-to-noise ratio.

[0037] It is contemplated herein that superposition metrology based on polarization-based isolation of first order diffraction can be implemented in any superposition technique (and associated superposition target design) based on first order diffraction. It is contemplated herein that this technique can be particularly beneficial, but not limited to, mitigating DC reflections that can reduce the contrast and / or signal-to-noise ratio of superposition measurements.

[0038] Some embodiments of the present disclosure relate to scatter superposition (SCOL) techniques and associated superposition targets. SCOL superposition metrology techniques can utilize superposition targets comprising grating-on-grating structures, wherein constituent grating features have a common spacing. Such targets are referred to herein as SCOL targets.

[0039] It is recognized herein that conventional zero-order SCOL metrology techniques are based on a grating-on-grating target design, where the upper and bottom gratings have the same pitch. Additionally, every photon emitted from any point in the illumination pupil is scattered on both the upper and lower gratings and vice versa, so that the measured zero-order signal contains superposition information due to the combination of ±1, ±2, ... diffraction orders from the upper and bottom gratings.

[0040] One problem with this approach is the large DC signal due to pure zero-order reflections together with algorithm inaccuracies stemming from various combinations of diffraction orders contributing to the measurement signal. In particular, a model based on a relatively small number of cells with a predefined offset between the upper grating structure and the lower grating cannot actually account for all of these possible combinations of diffraction orders contributing to the measurement signal. For example, the number of cells associated with a measurement and therefore reflected in this model may be limited by considerations such as, but not limited to, target size and mobile acquisition measurement (MAM) throughput considerations.

[0041] It is further recognized that similar problems arise when using a ripple overlay target with a relatively large gain (e.g., >300). Additionally, ripple targets with gains of about 10 to about 300 to about 400 may be impractical due to inherent ambiguity in overlay measurements with these values. For example, addressing a DC signal using techniques such as dark field illumination may be impractical or impossible.

[0042] Some embodiments of the present disclosure relate to a SCOL target in which a grating in one layer can rotate the polarization of the first order diffraction (e.g., DC signal, zeroth order diffraction, or higher order diffraction) relative to other light from the sample. In this way, a superposition metrology tool can provide polarization-based isolation of the first order diffraction. This target can be used with any SCOL superposition technique that utilizes the first order diffraction.

[0043] Some embodiments of the present disclosure relate to a ripple superposition technique and an associated superposition target. The ripple superposition metrology technique may utilize a superposition target comprising one or more grating-on-grating structures, wherein the constituent gratings have different pitches. Such a target is referred to herein as a ripple target and provides diffraction from two gratings (e.g., double diffraction) in addition to typical diffraction orders from each of the gratings. For example, based on a gain factor associated with the difference between the pitches of the constituent gratings, the ripple target may produce ripple diffraction orders with relatively small diffraction angles. The ripple target may be used in a variety of measurement modes. Therefore, even if the pitch of the constituent gratings is indistinguishable, an image of the ripple target may include a periodic signal based on this ripple diffraction order (e.g., a signal with the ripple pitch). In addition, since the ripple pitch is typically larger than the pitch associated with the constituent gratings (e.g., by a gain factor), the ripple superposition technique may provide a superposition measurement with sensitivity amplified by the gain factor. The ripple target may also be characterized by pupil-based measurement techniques.

[0044] Some embodiments of the present disclosure relate to high-throughput overlay measurements based on simultaneous capture of signals from multiple overlay targets, sometimes hundreds of overlay targets or more. It is contemplated herein that an overlay target comprising a grating-on-grating structure, wherein one grating rotates the polarization of a first order diffraction relative to other light from the overlay target, can enable isolated imaging of the target based on this first order diffraction. For example, an overlay measurement based on illumination with linearly polarized light and collection using crossed polarizers (e.g., polarizers oriented in the collection path to exclude non-rotated polarization) can optically isolate the first order diffraction from the overlay target and block other light, including but not limited to additional light from the overlay target and light from device features. Thus, an image having a field of view comprising multiple overlay targets can display the overlay targets with high contrast.

[0045] It should be noted that the use of a polarization rotating target (e.g., within a process layer) provides first order diffraction from two layers with perpendicular polarizations. This can be beneficial for a variety of superposition metrology techniques in general. For example, this can be beneficial for optical SCOL techniques, where the ripple signal is obtained as interference in the field of the +1 order of a grating structure in two layers in one detector and the -1 order of a grating structure in two layers in a second detector. Then, a polarizer aligned at a suitable angle can be used to equalize the amplitude of the diffraction orders from the grating structure and thus improve the signal-to-noise ratio. Similar techniques can be applied in typical imaging superposition metrology techniques in order to equalize the contrast of signals from layers formed of different materials (e.g., from grating structures in resist and process layers).

[0046] Reference Figures 1A to 13B , describes in more detail systems and methods for superposition metrology using polarization-based isolation of selected diffraction orders of light according to one or more embodiments of the present disclosure.

[0047] Figure 1A is a conceptual diagram illustrating an overlay metrology system 100 according to one or more embodiments of the present disclosure.

[0048] In some embodiments, the overlay metrology system 100 includes an overlay metrology subsystem 102 to acquire an overlay signal from an overlay target based on any number of overlay recipes. For example, the overlay metrology subsystem 102 may direct at least one illumination beam 104 to an overlay target 106 on a sample 108 and may further collect light or other electromagnetic radiation (referred to herein as sample light 110) emitted from the overlay target 106, wherein at least a portion of the sample light 110 is used to generate one or more images of the overlay target 106. In this manner, one or more overlay measurements of the sample 108 (e.g., overlay measurements associated with registration or offset of two or more layers of the sample 108) may be generated based on at least one image of the overlay target 106.

[0049] Additionally, the overlay metrology subsystem 102 may be configured to generate images based on any number of metrology recipes that define measurement parameters for image acquisition and / or design parameters of the overlay target 106 to be imaged. For example, a metrology recipe may include various aspects of the overlay target 106 or the design of the overlay target 106, including but not limited to the layout of target features on one or more sample layers, feature size, or feature spacing. As another example, a metrology recipe may include illumination parameters, 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, spatial distribution of illumination, or sample height. As another example, a metrology recipe may include collection parameters, such as but not limited to collection pupil distribution (e.g., desired distribution of angular light from the sample 108 to be measured and associated filtering intensities at those angles), collection field stop settings for selecting portions of the sample of interest, polarization or wavelength filters for the collection light.

[0050] The overlay metrology subsystem 102 may be any type of overlay metrology tool known in the art suitable for generating an overlay signal suitable for determining an overlay associated with an overlay target 106 on a sample 108 .

[0051] In some embodiments, the overlay metrology subsystem 102 generates an image of the overlay target 106, wherein one or more features of the overlay target 106 are unresolved. For example, the overlay metrology subsystem 102 may be configured (e.g., based on a metrology recipe) to form an image of the overlay target 106 based on light from a single diffraction order or light from multiple diffraction orders that are not combined in a manner to provide a resolved image of the overlay target 106 or selected features therein. As an illustration, an image of the overlay target 106 associated with the zero-order SCOL technique may include an unresolved grating-on-grating structure, wherein the unresolved grating-on-grating structure is represented as a grayscale region. In this configuration, the intensity of a particular grayscale region is affected by the physical overlay of the grating-on-grating structure (e.g., a physical offset associated with an expected offset (if applicable) and an unintended overlay error). In this manner, the overlay metrology subsystem 102 may generate an overlay measurement of the sample 108 (e.g., a measure of an unintended overlay error) based on the imaged intensities of the unresolved grating-on-grating features in multiple cells of the overlay target 106. As another illustration, an image of the superimposed target 106 associated with the moire technique may include an unresolved grating-on-grating structure, but may include resolved periodic signals associated with diffraction (eg, double diffraction) of the moires that constitute the grating.

[0052] Figure 1B 1 is a conceptual diagram illustrating a superposition metrology subsystem 102 according to one or more embodiments of the present disclosure. In some embodiments, the superposition metrology subsystem 102 includes an illumination source 112 configured to generate an illumination beam 104. The illumination beam 104 may include one or more selected wavelengths of light, including but not limited to ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0053] In some embodiments, the overlay metrology subsystem 102 directs the illumination beam 104 to the sample 108 or a portion of the sample 108 including at least one overlay target 106 via an illumination path 114. The illumination path 114 may include one or more optical components suitable for modifying and / or adjusting the illumination beam 104 and directing the illumination beam 104 to the sample 108. For example, the illumination path 114 may include, but need not include, one or more lenses 116 (e.g., to collimate the illumination beam 104, relay a pupil and / or field plane, or the like), one or more illumination polarizers 118 to adjust the polarization of the illumination beam 104, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like). In some embodiments, the overlay metrology subsystem 102 includes an objective lens 120 to focus the illumination beam 104 onto a sample 108 (e.g., an overlay target 106 having overlay target elements located on two or more layers of the sample 108). In some embodiments, the sample 108 is disposed on a sample stage 122 suitable for fixing the sample 108 and further configured to position the sample 108 relative to the illumination beam 104.

[0054] In some embodiments, the superposition metrology subsystem 102 includes one or more detectors 124 configured to capture sample light 110 emitted from the sample 108 through a collection path 126 and generate one or more superposition signals indicative of a superposition of two or more layers of the sample 108. The collection path 126 may include a plurality of optical elements to direct and / or modify the illumination collected by the objective 120, including but not limited to one or more lenses 128, one or more filters, one or more collection polarizers 130, one or more beam blocks, or one or more beam splitters. For example, the detector 124 may receive an optical image of the sample 108 provided by an element in the collection path 126 (e.g., the objective 120, the one or more lenses 128, or the like). As another example, the detector 124 may receive radiation reflected or scattered (e.g., via specular reflection, diffuse reflection, and the like) from the sample 108. As another example, detector 124 may receive radiation from one or more diffraction orders of superposition target 106 (eg, 0th diffraction order, ±1st diffraction orders, ±2nd diffraction orders, and the like).

[0055] The illumination path 114 and collection path 126 of the superposition metrology subsystem 102 may be oriented in a wide range of configurations suitable for illuminating the superposition target 106 with the illumination beam 104 and collecting sample light 110 in response to the incident illumination beam 104. For example, Figure 1B, the superposition metrology subsystem 102 may include a beam splitter 132 oriented so that the objective 120 can simultaneously direct the illumination beam 104 to the superposition target 106 and collect radiation emitted from the sample 108. As another example, the illumination path 114 and the collection path 126 may contain non-overlapping optical paths.

[0056] Reference Figures 2 to 10 , describes in more detail the design of a stacking target 106 suitable for first-order diffraction polarization-based isolation according to one or more embodiments of the present disclosure. Figures 2 to 7 Various non-limiting examples of features suitable for rotating the polarization of the first order diffraction relative to other sample light 110 are described, such as but not limited to a DC signal, zero order diffraction, or higher order diffraction. Such features are referred to herein as polarization rotating features. It is contemplated herein that the stacking target 106 according to the systems and methods disclosed herein may be formed of or otherwise include a grating-on-grating structure, wherein at least one of the layers includes a polarization rotating feature. Next, Figures 8A to 10 Various non-limiting examples of superimposed targets 106 that include polarization rotation features are depicted.

[0057] In some embodiments, the overlay target 106 includes at least one grating-on-grating structure, wherein features on at least one of the layers of the sample 108 rotate the polarization of first-order diffraction relative to other light emitted from the grating-on-grating structure, such as but not limited to DC reflection, zeroth-order diffraction, or higher-order diffraction.

[0058] The grating-on-grating structure may have any combination or orientation of features suitable for providing rotation of the first order diffraction. In some embodiments, the grating-on-grating structure comprises features with coarse pitch on at least one sample layer, which are further segmented in orthogonal directions (e.g., by fine pitch). Additionally, the fine pitch may be smaller than the wavelength of light, such that the orthogonal segmentation at the fine pitch may provide different effective dielectric constants for light polarized in orthogonal directions.

[0059] Figure 2 is a top view of a polarization rotating feature 202 located on a first layer of a superimposed target 106 in accordance with one or more embodiments of the present disclosure.

[0060] Now specific reference Figure 2, the polarization rotating features 202 include grating structures 204 of a first material type separated by regions of a second material type (which are referred to herein as surrounding material 206). For the purposes of this disclosure, the term grating structure 204 is used herein to refer to a set of features patterned in a sample layer having a periodicity that can be characterized by at least one pitch or spatial frequency. In a general sense, the grating structure 204 on any particular layer may have multiple periodicities (and associated pitches) in any particular direction and / or may have periodicity in multiple directions.

[0061] The polarization rotation feature 202 can be characterized by a coarse pitch 208 (e.g., a coarse period) and a fine pitch 210 (e.g., a fine period, a divided pitch, a divided period, or the like). In particular, the features within the coarse pitch 208 are further arranged into two regions 212a, 212b having an orthogonal periodicity to the fine pitch 210. For example, Figure 2 Box 214 in illustrative embodiment depicts features within a period associated with coarse pitch 208 divided into a first region 212a characterized by segmentation along the X direction using fine pitch 210 and a second region 212b characterized by segmentation along the Y direction using fine pitch 210.

[0062] After careful consideration, this article Figure 2 The polarization rotation feature 202 illustrated in FIG. 1 operates as a wave plate to impart different phases to light having orthogonal polarizations along the fine pitch 210. In this manner, the polarization rotation feature 202 can alter or rotate the polarization of incident light (e.g., the illumination beam 104). For example, the polarization rotation feature 202 can operate as a half-wave plate for first-order diffraction because the polarization rotation feature 202 changes the phase of the first-order diffraction by π along the Y direction, while the phase of the first-order diffraction along the X direction remains unchanged.

[0063] Figure 3A Describes a method for using a Figure 2 The structure within the period associated with the coarse pitch 208 (e.g., Figure 2 An effective medium representation of the features within box 214 in FIG. Figure 3B Describes a method for using a Figure 2 The structure within the coarse spacing 208 (eg, Figure 2 An effective medium representation of the features within box 214 in FIG.

[0064] exist Figure 3A and 3B In this case, the effective dielectric constant is defined by the following formula:

[0065] ε1=∈ Gr ·η+∈ sur·(1-η) (1)

[0066]

[0067] where ∈ Gr is the dielectric constant of the grating structure 204 of the first material type, ∈ sur is the dielectric constant of the surrounding material 206 of the second material type, and n is a fraction of the coarse pitch 208 associated with the segmentation having the fine pitch 210 along the x-direction (e.g., relative to the coarse pitch 208). Figure 2 In other words, n corresponds to the duty cycle of the orthogonal fine division.

[0068] As shown in equations (1) and (2) together with Figures 3A to 3B As illustrated, arranging features on the layers of superposition target 106 to provide regions of coarse pitch 208 and orthogonal fine pitch 210 directions both effectively operate as wave plates and provide different phase shifts for light polarized in orthogonal directions. Figure 4 According to one or more embodiments of the present disclosure, after being illuminated by the illumination beam 104, Figure 2 A conceptual illustration of the electric field directions of the various diffraction orders generated by the polarization rotation feature 202 described in FIG. Figure 4 As described in , the zeroth order diffraction 402 may have the same electric field direction as the incident illumination beam 104 , while the first order diffraction 404 may be polarized orthogonally to the zeroth order diffraction 402 .

[0069] In some embodiments, Figure 4 As described in FIG. 1 , the superimposed metrology subsystem 102 configured according to the metrology recipe provides a direction (e.g., Figure 2 404). In some embodiments, the overlay metrology subsystem 102 is further configured according to the metrology recipe to provide a crossed collection polarizer 130 in the collection path 126 that is oriented to isolate the first order diffraction 404.

[0070] Reference Figure 5 , Figure 5 2 is a top view of a 2D polarization rotation feature 202 suitable for performing overlay measurements along two measurement directions according to one or more embodiments of the present disclosure. The 2D polarization rotation feature 202 can be suitable for use in an overlay target 106 for overlay measurements along two dimensions (e.g., the 2D overlay target 106). As an illustration, Figure 5 The 2D polarization rotation feature 202 described in Figure 2 The extension of the polarization rotation feature described in the figure along the Y direction. For example, Figure 5 The 2D polarization rotation features 202 are formed in alternating rows from Figure 2 2 and a shifted version of the polarization rotation features 202 in the staggered rows. Specifically, the polarization rotation features 202 in the staggered rows are shifted in the X direction by half of the coarse pitch 208. In this way, the features within the coarse pitch 208 along the Y direction are also divided into regions 212a, 212c with orthogonal fine pitch periodicity in a manner similar to the X direction.

[0071] General Reference Figures 2 to 5 , it should be understood that Figures 2 to 5 This is provided for illustrative purposes only and should not be construed as limiting. The polarization rotation feature 202 may have any arrangement suitable for rotating the first order diffraction 404 , such as but not limited to the zeroth order diffraction 402 , relative to the other sample light 110 .

[0072] For example, the fine pitch 210 need not be the same for two orthogonal directions (eg, the fine pitch 210 need not be the same for the first region 212a and the second region 212b). Figure 2 However, without explicit description, the first region 212a may have a first fine pitch 210 and the second region 212b may have a second fine pitch 210 having a value different from the first fine pitch 210. However, the fine pitch 210 in any direction should be sufficiently smaller than the wavelength of the illumination beam 104 (e.g., according to the metering recipe) to satisfy the effective medium condition so that equations (1) and (2) are valid. In addition, the duty cycle (e.g., associated with the value of η) should be the same for different measurement directions. Consider Figure 5 As an illustration, the duty cycle along the X direction associated with regions 212a, 212b should be the same as the duty cycle along the Y direction associated with regions 212a, 212c.

[0073] As another example, the polarization rotation feature 202 can have any duty cycle (eg, any value of η). However, in some designs, a duty cycle that deviates from 1:1 (eg, a value of η=0.5) may reduce the effectiveness of rotating the first order diffraction by the polarization rotation feature 202.

[0074] For example, the polarization rotation features 202 can be arranged to provide fine pitch periodicity in any two orthogonal directions. As an illustration, Figure 6is a top view of polarization rotating features 202 periodically arranged with fine pitch at a 45 degree angle relative to coarse pitch 208 according to one or more embodiments of the present disclosure. Specifically, grating structure 204 is oriented at angles of 45 degrees and 135 degrees relative to coarse pitch 208 (here in the X direction).

[0075] As described previously herein, the illumination beam 104 should be polarized at 45 degrees relative to both directions of the fine pitch periodicity. Figure 6 In the embodiment of the present invention, the illumination beam 104 should be polarized in the X or Y direction. Similarly, the superposition metrology subsystem 102 should include a collection polarizer 130 in orthogonal polarization to capture the rotational first order diffraction.

[0076] As another example, the polarization rotating feature 202 need not be segmented into separate regions (e.g., Figures 2 to 3B and Figure 5 Specifically, the polarization rotation feature 202 imparts different phases to the orthogonal polarizations sufficient to rotate the first order diffraction relative to other sample light 110, such as but not limited to a DC signal, a zero order diffraction, or a higher order diffraction. In other words, the polarization rotation feature 202 can have any size, orientation, or distribution, as long as the effective dielectric constant distribution of the X and Y polarizations is similar to but not limited to Figures 3A to 3B Different phases are imparted to orthogonal polarizations in the manner of equations (1) to (2).

[0077] As an illustration, Figure 7 FIG. 2 is a top view of a portion of a 2D polarization rotation feature 202 without segmentation according to one or more embodiments of the present disclosure. For example, the 2D polarization rotation feature 202 includes features with different orientations and spacings along the X and Y directions, so that the 2D polarization rotation feature 202 can be similar to Figure 5 The 2D polarization rotation feature 202 is operated in this manner. In addition, Figure 7 Box 702 in FIG. 1 depicts one period (eg, coarse pitch 208) of the 2D polarization rotation feature 202, where Figure 7 The ellipses in indicate that the illustrated pattern repeats in two dimensions.

[0078] 8-10 , various non-limiting examples of superimposed targets 106 incorporating polarization rotation features 202 in accordance with one or more embodiments of the present disclosure are described in greater detail.

[0079] It is contemplated herein that the effectiveness of the polarization rotation feature 202 in achieving polarization-based isolation of the first order diffraction when rotating the first order diffraction may depend on the specific layout and composition of the polarization rotation feature 202 .

[0080] For example, in a surrounding material 206 (∈ sur =1.45) and a 1:1 duty cycle (η=0.5) silicon grating structure 204 (∈ Gr =3.8) provides effective dielectric constant values ​​of ε1=2.63 and ε2=2.1. This is similar to the contrast obtained using a typical resist layer target. However, fabricating the polarization rotating feature 202 with the same 1:1 duty cycle in the resist layer (e.g., ε Gr =1.4 and∈ sur =1) provides effective dielectric constant values ​​of ε1 = 1.2 and ε2 = 1.17, which provides minimal contrast and thus relatively poor rotation of the first order diffraction 404. Thus, the polarization rotation feature 202 may be suitable for use in process layers, but may be impractical for use in resist layers (or may be effective at polarization rotations below the application tolerance).

[0081] Therefore, it may not be practical to utilize the polarization rotation feature 202 in the overlay target 106 where features on different sample layers (or more generally, features associated with different lithographic exposures) are in a non-overlapping or side-by-side region when one of the sample layers is a resist layer. In this configuration, the amplitude of the first order diffraction from the feature in the resist layer may have a relatively small amplitude due to the relatively small refractive index difference between the feature and the surrounding medium. Thus, in this configuration, the signal-to-noise ratio may be low.

[0082] However, it is contemplated herein that the polarization rotation feature 202 may be well suited for, but not limited to, an overlay target 106 having a grating-on-grating structure. In this configuration, it may be sufficient to provide the polarization rotation feature 202 for first order diffraction on one layer (e.g., a process layer) of the overlay target 106. Thus, the features on the second layer (e.g., a resist layer or a process layer) may have any suitable pattern or orientation without any polarization rotation requirements.

[0083] It is further contemplated herein that any overlay target 106 design including at least one grating-on-grating structure may incorporate polarization rotating features 202 in at least one layer.

[0084] Fig. 8Ais a top view of a stack target 106 suitable for polarization-based isolation of first order diffraction along a single measurement direction according to one or more embodiments of the present disclosure. Features in a first sample layer are depicted in a first panel 802 and features in a second sample layer are depicted in a second panel 804. In this manner, features in the first panel 802 may constitute a lower grating structure 806 and features in the second panel 804 may constitute an upper grating structure 808. In combination, the lower grating structure 806 and the upper grating structure 808 may form a grating-on-grating structure.

[0085] In some embodiments, the overlay target 106 includes polarization rotation features 202 in a first layer, which may be a process layer so that the features have high contrast. For example, the first panel 802 includes Figure 2 806 . The overlay target 106 may then include any suitable grating structure on a second layer, which may be any type of layer, including, but not limited to, a resist layer or a process layer. In this manner, the polarization rotating features 202 may be located in both the first and second layers (e.g., the lower and upper grating structures 806, 808) or only in the first layer (e.g., the lower grating structure 806). For example, the second panel 804 illustrates an unsegmented feature characterized by a pitch 810. This pitch 810 may have different values ​​depending on the particular technology. For example, an overlay target 106 suitable for SCOL technology may provide (e.g., according to a metering recipe) that the pitch 810 of the upper grating structure 808 is equal to the coarse pitch 208 of the polarization rotating features 202 in the lower grating structure 806. In another example, an overlay target 106 suitable for a moire technique may provide (eg, according to a metrology recipe) an upper grating structure 808 with a pitch 810 that is different than the coarse pitch 208 of the polarization rotation features 202 in the lower grating structure 806 to provide moire gain.

[0086] Figure 8B 8 is a top view of a 2D stacking target 106 suitable for polarization-based isolation of first order diffraction along two measurement directions according to one or more embodiments of the present disclosure. For example, the third panel 812 includes Figure 5 810. The overlay target 106 may then include any suitable grating structure on a second layer, which may be any type of layer, including but not limited to a resist layer or a process layer. For example, the fourth panel 814 illustrates an undivided hatch feature characterized by a spacing 810.

[0087] Although not explicitly illustrated, it should be understood that an overlay target 106 suitable for overlay measurements in one or two dimensions may be produced based on any design of polarization rotation features 202 in at least one layer. In the case where polarization rotation features 202 are located on more than one layer, the polarization rotation features 202 may be adjusted to provide the desired polarization rotation of the first order diffraction as a whole.

[0088] Reference Figures 9 to 10 , using an overlay target 106 including polarization rotation features 202 in a grating-on-grating structure is described for a variety of non-limiting overlay techniques. It is contemplated herein that an overlay target 106 including polarization rotation features 202 in a grating-on-grating structure may be used in any overlay technique that utilizes first order diffraction from a grating-on-grating structure.

[0089] Fig. 9 Depicts the use of a superimposed target 106 including a polarization rotation feature 202 in a grating-on-grating structure for zero-order SCOL techniques in accordance with one or more embodiments of the present disclosure. Specifically, Fig. 9 is a conceptual side view of a grating-on-grating structure illustrating a non-limiting component of a zero-order SCOL signal in accordance with one or more embodiments of the present disclosure.

[0090] In the zero-order SCOL technique, a superposition measurement may be generated based on measurements of zero-order signals from multiple grating-on-grating structures in different cells of the superposition target 106, where the grating-on-grating structures in the different cells have a common pitch but different predetermined offsets between constituent grating features. For example, the zero-order SCOL technique may utilize measurements from four or more cells having grating-on-grating structures with different predetermined offsets.

[0091] It should be noted herein that the term zero-order signal from a grating structure is different from zero-order diffraction. Specifically, a zero-order signal in the context of SCOL measurement includes multiple signals emitted from a grating-on-grating structure at a common angle. For example, a zero-order signal from a grating-on-grating structure in response to an illumination beam 104 at a normal incidence angle may include multiple light signals emitted from a sample 108 at a normal exit angle.

[0092] like Fig. 9 , the illumination beam 104 may interact with various features of the sample 108 to produce a zero-order signal. For example, the zero-order signal may include a specular reflection (e.g., a DC signal 904) from a top surface 902 of the sample 108 or other interfaces between sample layers not explicitly shown. As another example, the zero-order signal may include a zero-order diffraction 906 from the upper grating structure 808, which may propagate along the same path as the DC signal 904.

[0093] The zero-order signal may further include various signals associated with the combined interaction between the upper grating structure 808 and the lower grating structure 806. Fig. 9 , a portion of the illumination beam 104 may pass through the upper grating structure 808 (e.g., as a transmitted zeroth order diffraction) to reach the lower grating structure 806. The lower grating structure 806 may then generate various reflected diffraction orders from this portion of the illumination beam 104, which may then interact with the upper grating structure 808 again before exiting the sample 108.

[0094] For example, the zero-order signal from the grating-overlying grating structure may include the zero-order diffraction 908 from the lower grating structure 806, which passes through the upper grating structure 808 (e.g., as the zero-order diffraction). As another example, the zero-order signal from the grating-overlying grating structure may include double diffraction with a common diffraction order and opposite signs from the lower grating structure 806 and the upper grating structure 808, which exit the sample 108 at a normal exit angle. As an illustration, Fig. 9 Light + / -1 diffraction 910 is depicted as being associated with the +1 diffraction order 912 from the lower grating structure 806 and the -1 diffraction order 914 from the upper grating structure 808. Although not shown, the light associated with the -1 diffraction order from the lower grating structure 806 and the +1 diffraction order from the upper grating structure 808 may follow a symmetric path. As another illustration, Fig. 9 Depicted is a + / -2nd order diffraction 916 associated with a -2nd diffraction order 918 from the lower grating structure 806 and a +2nd diffraction order 920 from the upper grating structure 808. Although not shown, the light associated with the +2nd diffraction order from the lower grating structure 806 and the -2nd diffraction order from the upper grating structure 808 may follow a symmetric path. Thus, the zeroth order SCOL signal may include + / -N double diffraction signals that follow similar patterns for the additional diffraction orders.

[0095] It should be understood that the grating overlying grating structure can generate various additional diffraction orders from the lower grating structure 806 and the upper grating structure 808 alone or in combination. For the sake of clarity, Fig. 9 The diffraction orders are not explicitly stated.

[0096] It is contemplated herein that the zero-order SCOL technique may provide relatively high accuracy and relatively low tool-induced errors (e.g., tool-induced shift (TIS) errors, TIS 3σ errors, or the like). However, this approach may suffer from relatively strong unwanted signals associated with the DC signal 904 and the like, as well as algorithmic inaccuracies associated with multi-order diffraction signals, which may be difficult, impractical, or sometimes impossible to interpret under typical measurement constraints, such as, but not limited to, the target size or the number of cells within the target required for measurement.

[0097] It is further contemplated herein that a grating-on-top grating structure having a polarization rotation feature 202 to rotate the polarization of the first order diffraction from the lower grating structure 806 and / or the upper grating structure 808 can be used to achieve optical isolation of this first order diffraction using the collection polarizer 130 in the superposition metrology subsystem 102 as disclosed herein. For example, using a grating-on-top grating structure having a polarization rotation feature 202 to rotate the polarization of the first order diffraction from the lower grating structure 806 and / or the upper grating structure 808 coupled to the collection polarizer 130 can achieve optical isolation of the + / -1 diffraction 910 from other zero-order SCOL signals, which can provide enhanced contrast or signal-to-noise ratio of the associated superposition measurement. As an illustration, as Fig. 8A The overlay target 106 configured as described in may include a grating-on-grating structure, wherein the pitch 810 of the upper grating structure 808 is equal to the coarse pitch 208 of the lower grating structure 806 .

[0098] Fig.10 Depicting the use of an overlay target 106 including a polarization rotation feature 202 in a grating-on-grating structure for a corrugation technique. Specifically, Fig.10 2 is a conceptual side view of a grating-on-grating structure illustrating a non-limiting component of a moire signal according to one or more embodiments of the present disclosure. For example, a grating-on-grating structure suitable for moire technology (e.g., a moire grating-on-grating structure) may provide an upper grating structure 808 having a pitch 810 that is different from the coarse pitch 208 of the lower grating structure 806.

[0099] Similar to Fig. 9 As described in the foregoing, illuminating the corrugated grating overlying grating structure using the illumination beam 104 can generate various zero-order signals at a normal exit angle, including but not limited to a DC signal 904 associated with the top surface 902 of the sample 108, a zero-order diffraction 906 from the upper grating structure 808, and a zero-order diffraction 908 from the lower grating structure 806.

[0100] Additionally, the corrugated grating overlying grating structure may produce corrugated diffraction associated with double diffraction from both the lower grating structure 806 and the upper grating structure 808. For example, Fig.10Depicted are corrugation diffraction orders 1002 associated with +1 order diffraction 1004 from the lower grating structure 806 and -1 order diffraction 1006 from the upper grating structure 808. Although not explicitly shown, additional corrugation diffraction orders based on the -1 order diffraction and +1 order diffraction from the lower grating structure 806 may be generated using a symmetric path. Since the pitch 810 of the upper grating structure 808 is different from the coarse pitch 208 of the lower grating structure 806, the corrugation diffraction orders 1002 emanate from the grating overlying grating structure at a non-normal angle. In particular, the exit angles of the corrugation diffraction orders 1002 may be based on the difference between these pitches, wherein as the difference between the pitches increases, the exit angles further deviate from the normal exit angle.

[0101] It is contemplated herein that for some applications it may be desirable to provide a corrugated grating overlying grating structure in which the spacings of the upper grating structure 808 and the lower grating structure 806 are close together to provide high gain and corrugation diffraction with a low corrugation spacing that is easily distinguishable even if the underlying spacings of the upper grating structure 808 and the lower grating structure 806 are indistinguishable.

[0102] However, at high gain values, the corrugation diffraction orders 1002 may overlap with various zero-order signals (e.g., the DC signal 904, the zero-order diffraction 906 from the upper grating structure 808, and the zero-order diffraction 908 from the lower grating structure 806), which may make it impractical to optically isolate the corrugation diffraction orders 1002 from the zero-order signals. Additionally, corrugation techniques with gains in the range of approximately 10 to approximately 300 may introduce ambiguity issues in the superposition measurements, which may also make these gain factors impractical.

[0103] In some embodiments, the overlay target 106 includes a grating-overlying grating structure having a polarization rotation feature 202 in at least one layer to rotate the polarization of the first order diffraction from the lower grating structure 806 and / or the upper grating structure 808. In this way, the corrugated diffraction orders 1002 formed by the first order diffraction from both the lower grating structure 806 and the upper grating structure 808 can be optically isolated using the collecting polarizer 130, which can provide an enhanced contrast or signal-to-noise ratio of the associated overlay measurement. With further consideration, this technique may be suitable for, but not limited to, corrugated grating-overlying grating structures having relatively high gain (e.g., 300 or more).

[0104] In some embodiments, the ripple gain may be high enough that the ripple spacing increases to the point where the change in the signal associated with the superposition is negligible for a given cell size of the superposition target 106. In this case, the image of this grating-on-grating structure may appear as grayscale intensity values. Thus, a superposition measurement may be generated based on the signals generated from multiple (e.g., two or more) grating-on-grating structures (e.g., multiple cells of the superposition target 106) having different predetermined offsets. For example, these grayscale measurements may be fit to a sine function with the ripple spacing to determine the superposition.

[0105] General Reference Fig. 9 and 10 , it should be understood that Fig. 9 and 10 and the associated descriptions are provided for illustrative purposes only and should not be construed as limiting. Specifically, the superposition target 106 including a grating-on-grating structure having polarization rotation features 202 on at least one sample layer can be used in any superposition technique utilizing first order diffraction.

[0106] Reference Figures 11 to 12 , describes in more detail techniques for characterizing a stacking target 106 that provides polarization rotation of first-order diffraction relative to other sample light 110 in accordance with one or more embodiments of the present disclosure.

[0107] It is contemplated herein that selective rotation of the first order diffraction of the stacking target 106 and optical isolation of the first order diffraction using the collection polarizer 130 of the stacking metrology subsystem 102, as disclosed herein, enables high throughput imaging of multiple stacking targets 106 within a single field of view. For example, selective rotation of the first order diffraction of the stacking target 106 and optical isolation of the first order diffraction using the collection polarizer 130 of the stacking metrology subsystem 102, as disclosed herein, enables the first order diffraction to be isolated not only from additional sample light 110 from the stacking target 106, but also from sample light 110 associated with device features. Thus, such stacking targets 106 can be imaged with high contrast regardless of placement on the sample 108.

[0108] Fig.11 1 is a flow chart illustrating steps performed in a method 1100 for high-throughput overlay metrology according to one or more embodiments of the present disclosure. Applicants of the present invention illustrate that the embodiments and heuristic techniques previously described herein in the context of an overlay metrology system 100 should be interpreted as extending to the method 1100. However, it should be further noted that the method 1100 is not limited to the architecture of the overlay metrology system 100.

[0109] In some embodiments, method 1100 includes step 1102 of fabricating a plurality of overlay targets 106 on a sample 108, wherein the overlay targets 106 include a grating-on-grating structure having polarization rotation features 202 on at least one layer to rotate first order diffraction relative to at least one of specular reflection or zero order diffraction.

[0110] The overlay targets 106 or portions thereof may be dispersed across the sample 108 in any suitable location. Different units (e.g., different grating-on-grating structures) need not be adjacent to each other. In some embodiments, different units (e.g., different grating-on-grating structures) of one or more overlay targets 106 are distributed across the sample 108. In this configuration, various units of various overlay targets 106 may be imaged simultaneously in a large field of view and overlay measurements may be based on reconstruction of data from the various units.

[0111] It is further contemplated herein that a particular unit of the superimposed target 106 (e.g., Fig. 8A and 8B ) can be fabricated in relatively small sizes because the constituent grating structures need not be individually resolvable. For example, as previously described herein, a grating-overlying grating structure suitable for SCOL techniques may appear as a single grayscale intensity associated with actual registration between the upper grating structure 808 and the lower grating structure 806 (e.g., due to intentionally predetermined offsets and / or unintentional superposition errors). As another example, a periodic signal associated with the corrugation diffraction order 1002 (e.g., at the corrugation pitch) may be visible even if the constituent grating structures are not resolvable.

[0112] As an illustration, a cell of the overlay target 106 comprising a grating-on-grating structure may have, but need not have, a size of approximately 5 microns or less on a side. Thus, the cell is not limited to placement in a scribe street, but may be placed within a die on the sample 108, which may beneficially increase measurement accuracy due in part to a reduced distance between the cell and the device feature of interest.

[0113] In some embodiments, the method 1100 includes a step 1104 of illuminating a plurality of overlay targets 106 using an illumination beam 104. In some embodiments, the method 1100 includes a step 1106 of generating an image of the sample 108 through a polarizer aligned with the first order diffraction of the illumination beam 104 at the coarse pitch 208. For example, the overlay metrology subsystem 102 may be configured (e.g., according to a metrology recipe) to image a relatively large field of view of the sample 108 including the plurality of overlay targets 106 (or portions thereof) through a collection polarizer 130 aligned to pass the first order diffraction when rotated by the overlay targets 106. The resulting image may then display the overlay targets 106 with high contrast. In some embodiments, the method 1100 includes a step 1108 of determining an overlay measurement based on the image of the sample 108.

[0114] Fig.12 is a series of high-level diagrams illustrating high-throughput imaging of multiple overlay targets 106 in a single image grab in accordance with one or more embodiments of the present disclosure.

[0115] Panel 1202 depicts a field of view 1204 of an overlay metrology subsystem 102 that may, but need not, be used to perform step 1104 of illuminating a sample 108 and / or step 1106 of imaging the sample 108. Panel 1206 depicts a die 1208 within the field, which may include various overlay targets 106 or portions thereof (e.g., individual cells having a grating-on-grating structure). In some embodiments, the various overlay targets 106 or portions thereof are arranged in subsections 1210 of the die 1208 such that separate overlay measurements may be generated based on the overlay targets 106 or portions thereof in respective subsections 1210. Panel 1212 depicts different overlay measurements in each of the subsections 1210.

[0116] After careful consideration, this article Fig.12 The description and Fig.11 The superposition measurement technique described in can achieve superposition measurement with large throughput and high accuracy. In a general sense, any number of superposition targets 106 can be imaged simultaneously in a single grab. For example, the field size can be about a few millimeters or larger, and the cell size (e.g., the size of the grating structure overlying the grating) can be, but need not be, about 5 microns or less. In some applications, the cell size can be about 3 microns or less. In some applications, the cell size can be greater than 5 microns. Therefore, the number of superposition targets 106 that can be imaged simultaneously can be about tens, hundreds, or more. In addition, since the collection polarizer 130 can pass the first order diffraction from the superposition target 106 rotated by the superposition target 106 and block other light sources (e.g., DC signal 904, zero order diffraction 908 from the lower grating structure 806, zero order diffraction 906 from the upper grating structure 808, light from device features, or the like), a large field of view image can display these superposition targets 106 with high contrast, which can achieve superposition measurement with high sensitivity and / or signal-to-noise ratio.

[0117] After further careful consideration, Fig.12 The superposition measurement technique depicted in is not necessarily limited to the superposition target 106 having the polarization rotation feature 202 described previously herein. Rather, this technique may be suitable for any superposition target 106 that provides a diffraction order of interest in the collection aperture of the superposition metrology subsystem 102.

[0118] As an illustration, Fig.13A and 13BThe configuration of the overlay metrology subsystem 102 is illustrated for measuring a corrugated overlay target 106 having a relatively small gain (e.g., a gain of about 10 or less) that does not necessarily include a polarization rotation feature 202. For example, Fig.13A and 13B A configuration of the overlay metrology subsystem 102 for measuring a corrugated overlay target 106 having only a process pitch is illustrated.

[0119] Fig.13A FIG. 1 is a top view of the collection pupil 1302 of the superposition metrology subsystem 102 according to one or more embodiments of the present disclosure. Fig.13A In the embodiment, two oblique illumination beams 104 are used to illuminate a target 106 including one or more superimposed targets (e.g., Fig.12 ) such that the zero-order diffraction lobes 1304 and the DC signal 904 from the upper and lower grating structures are located outside the boundary 1306 of the collection pupil 1302, but wherein the first-order diffraction 1308 from the upper and lower grating structures (e.g., the upper grating structure 806 and the lower grating structure 808) are within the boundary 1306 of the collection pupil 1302. For example, Fig.13A A configuration is illustrated in which the +1 order diffraction lobe from one of the illumination beams 104 and the -1 order diffraction lobe from the other illumination beam 104 overlap in the center of the boundary 1306 of the collection pupil 1302. In this configuration, the collection polarizer 130 is not necessary because the first order diffraction of interest is isolated using optical and / or mechanical techniques.

[0120] After careful consideration, this article Fig.13A The configuration described in can be suitable for large field imaging of many overlay targets 106 (e.g., up to 100 or more overlay targets 106 simultaneously) or portions thereof (e.g., cells having any type of corrugated grating overlying grating structure), where the cells can appear as grayscale intensity values ​​based on the actual registration between the associated layers of the sample 108. Thus, overlay measurements can be generated based on multiple cells (e.g., two or more cells) having a grating overlying grating structure with a predetermined offset. In particular, the obtained intensity values ​​of the cells in each overlay target 106 can be fit to a sinusoidal function having a pitch corresponding to the corrugation pitch of the overlay target 106.

[0121] Fig. 13B 1 is a conceptual diagram of generating two illumination light beams 104 from an incoherent light source according to one or more embodiments of the present disclosure. For example, light 1310 from an incoherent light source may be incident on a diffraction grating 1312 or other dispersive optical device so that the two illumination light beams 104 may be formed as + / - 1st order diffracted light beams of the incoherent light 1310. Fig. 13BA beam block 1314 for blocking zero-order light 1316 and a lens 1318 for collimating the two illumination beams 104 are further illustrated.

[0122] However, it should be understood that Fig.13A and 13B It is provided for illustrative purposes only and should not be construed as limiting. Fig.12 The techniques described in can be used with any type of overlay target 106 and configuration of the overlay metrology subsystem 102 suitable for providing imaging of a large field of view on the sample 108 using light isolated from the overlay target 106 to the diffraction orders of interest.

[0123] Reference again Figure 1A and 1B , describes in greater detail additional aspects of the superposition metrology subsystem 102 according to one or more embodiments of the present disclosure.

[0124] The illumination source 112 may include any type of illumination source suitable for providing the illumination beam 104. In some embodiments, the illumination source 112 is a laser source. For example, the illumination source 112 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, or the like. In this regard, the illumination source 112 may provide an illumination beam 104 having high coherence (e.g., high spatial coherence and / or temporal coherence). In some embodiments, the illumination source 112 includes a laser sustained plasma (LSP) source. For example, the illumination source 112 may include, but is not limited to, an LSP lamp, an LSP bulb, or an LSP chamber suitable for housing one or more elements that, when excited into a plasma state by a laser source, can emit broadband illumination. In some embodiments, the illumination source 112 includes a lamp source. For example, the illumination source 112 may include, but is not limited to, an arc lamp, a discharge lamp, an electrodeless lamp, or the like. In this regard, the illumination source 112 may provide an illumination beam 104 having low coherence (eg, low spatial coherence and / or temporal coherence).

[0125] In some embodiments, the overlay metering system 100 includes a controller 134 communicatively coupled to the overlay metering subsystem 102. The controller 134 may be configured to direct the overlay metering subsystem 102 to generate an overlay signal based on one or more selected recipes. The controller 134 may be further configured to receive data including, but not limited to, the overlay signal from the overlay metering subsystem 102. Additionally, the controller 134 may be configured to determine an overlay associated with the overlay target 106 based on the acquired overlay signal.

[0126] In some embodiments, the controller 134 includes one or more processors 136. For example, the one or more processors 136 may be configured to execute a set of program instructions maintained in a memory device 138 or memory. The one or more processors 136 of the controller 134 may include any processing element known in the art. In this sense, the one or more processors 136 may include any microprocessor-type device configured to execute algorithms and / or instructions. In addition, the memory device 138 may include any storage medium known in the art suitable for storing program instructions that can be executed by the associated one or more processors 136. For example, the memory device 138 may include a non-transitory memory medium. As an additional example, the memory device 138 may include, but is not limited to, a read-only memory, a random access memory, a magnetic or optical memory device (e.g., a disk), a tape, a solid-state hard drive, and the like. It should be further noted that the memory device 138 may be housed in a common controller housing with the one or more processors 136.

[0127] The subject matter described herein sometimes illustrates different components contained in or connected to other components. It should be understood that such depicted architecture is for demonstration 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 "coupled" to each other to realize the desired functionality. Specific examples that can be coupled include but are not limited to physically interacting and / or physically interacting components and / or wirelessly interacting and / or wirelessly interacting components and / or logically interacting and / or logically interacting components.

[0128] It is believed that the present disclosure and its many attendant advantages will be understood from the above description, and it should be appreciated that various changes may be made in the form, construction and arrangement of components without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are for illustration only, and the appended claims are intended to cover and include such changes. In addition, it should be understood that the invention is defined by the appended claims.

Claims

1. A superposition metering system, comprising: an illumination source configured to generate an illumination beam; One or more illumination optics for directing the illumination beam to a sample having a field of view including one or more overlay targets when implementing a metrology recipe, wherein a particular overlay target of the one or more overlay targets according to the metrology recipe comprises: one or more grating-overlying grating structures formed of a lower grating structure having a first coarse pitch and an upper grating structure having a second coarse pitch, wherein the upper grating structure and the lower grating structure overlap on the sample, wherein at least one of the upper grating structure or the lower grating structure further includes features having a fine pitch less than a wavelength of the illumination beam and arranged to rotate first order diffraction of the illumination beam associated with at least one of the first coarse pitch or the second coarse pitch relative to at least one of specular reflection from a top surface of the sample or a zero order diffraction from the one or more grating-overlying grating structures; an objective lens for collecting light from the sample within the field of view when implementing the metrology recipe; a polarizer arranged to pass a portion of the light from the sample associated with first order diffraction; a detector for generating an image of the sample including the one or more superimposed targets; and A controller is communicatively coupled to the detector, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to determine an overlay measurement of the sample based on the image of the one or more overlay targets.

2. The overlay metrology system of claim 1, wherein at least one of the one or more overlay targets comprises two or more of the one or more grating structures in different cells in non-adjacent portions of a die on the sample.

3. The overlay metrology system of claim 1, wherein the image contains more than 100 overlay objects.

4. The superposition metrology system of claim 1, wherein the first coarse spacing and the second coarse spacing of at least one of the one or more superposition targets are equal to form at least one scatter superposition (SCOL) target.

5. The superposition metrology system of claim 4, wherein the at least one SCOL target comprises two or more grating overlying grating structures having different predetermined offsets between the constituent upper and lower grating structures.

6. The superposition metrology system of claim 4, wherein a portion of the image containing the at least one SCOL target is based on at least one of +1st order diffraction from the lower grating structure combined with -1st order diffraction from the upper grating structure or -1st order diffraction from the lower grating structure combined with +1st order diffraction from the upper grating structure.

7. The overlay metrology system of claim 1, wherein the first coarse pitch and the second coarse pitch of at least one of the one or more overlay targets are different to form at least one corrugated target.

8. The superposition metrology system of claim 7, wherein the at least one corrugated target comprises two or more grating overlying grating structures having different predetermined offsets between the constituent upper and lower grating structures.

9. The superposition metrology system of claim 7, wherein a portion of the image containing the at least one corrugated target is based on at least one of a corrugation diffraction order formed by a +1st order diffraction from the lower grating structure combined with a -1st order diffraction from the upper grating structure or a corrugation diffraction order formed by a -1st order diffraction from the lower grating structure combined with a +1st order diffraction from the upper grating structure.

10. The overlay metrology system of claim 1, wherein the one or more grating-on-grating structures in the one or more overlay targets are unresolved in the image of the one or more overlay targets and appear in grayscale intensity.

11. The overlay metrology system of claim 1 , wherein the features having the fine pitch are located only in the lower grating structure in at least one of the one or more overlay targets.

12. The superposition metrology system of claim 11, wherein the lower grating structure is in a process layer of the sample.

13. The superposition metrology system of claim 12, wherein the lower grating structure is in a resist layer of the sample.

14. The overlay metrology system of claim 12, wherein the lower grating structure is in an additional process layer of the sample.

15. The overlay metrology system of claim 1, wherein the features having the fine pitch are arranged in two zones within the first coarse pitch, wherein a direction of the fine pitch in a first of the two zones is orthogonal to a direction of the fine pitch in a second of the two zones.

16. The overlay metrology system of claim 15, wherein the two zones have a 1:1 duty cycle within the first coarse spacing.

17. The overlay metrology system of claim 15, wherein the fine pitch in the first zone is equal to the fine pitch in the second zone.

18. The overlay metrology system of claim 15, wherein the fine pitch in the first zone has a different value than the fine pitch in the second zone.

19. The overlay metrology system of claim 15, wherein a direction of the fine pitch in the first zone is parallel to a direction of at least one of the first coarse pitch or the second coarse pitch.

20. The overlay metrology system of claim 15, wherein a direction of the fine pitch in the first zone is at a 45 degree angle to a direction of at least one of the first coarse pitch or the second coarse pitch.

21. A superimposed metrology target, comprising: One or more grating-overlying grating structures formed by a lower grating structure having a first coarse pitch in a first layer of a sample and an upper grating structure having a second coarse pitch in a second layer of the sample, wherein the upper grating structure and the lower grating structure overlap on the sample, wherein at least one of the upper grating structure or the lower grating structure further includes features having a fine pitch less than a wavelength of an illumination beam and is arranged to rotate a first order diffraction of the illumination beam associated with at least one of the first coarse pitch or the second coarse pitch relative to at least one of a specular reflection from a top surface of the sample or a zero order diffraction from the one or more grating structures, wherein an overlay between the first layer and the second layer of the sample is determinable from an image of the one or more grating structures based on the first order diffraction.

22. The stacking metrology target of claim 21, wherein the first coarse spacing and the second coarse spacing are equal to form a scatter stacking (SCOL) target.

23. The superposition metrology target of claim 22, wherein the SCOL target comprises two or more grating overlying grating structures having different predetermined offsets between the constituent upper and lower grating structures.

24. The stacked metrology target of claim 21, wherein the first coarse pitch and the second coarse pitch are different to form a corrugated target.

25. The superimposed metrology target of claim 24, wherein the corrugated target comprises two or more grating overlying grating structures having different predetermined offsets between the constituent upper and lower grating structures.

26. The overlay metrology target of claim 21, wherein the features having the fine pitch are located only in the lower grating structure in at least one of the one or more overlay targets.

27. The stacking metrology target of claim 26, wherein the lower grating structure is in a process layer of the sample.

28. The superposition metrology target of claim 27, wherein the lower grating structure is in a resist layer of the sample.

29. The overlay metrology target of claim 27, wherein the lower grating structure is in an additional process layer of the sample.

30. The overlay metrology target of claim 21, wherein the features having the fine pitch are arranged in two zones within each coarse pitch, wherein a direction of the fine pitch in a first of the two zones is orthogonal to a direction of the fine pitch in a second of the two zones.

31. The overlay metrology target of claim 30, wherein the two zones have a 1:1 duty cycle within the first coarse spacing.

32. The overlay metrology target of claim 30, wherein the fine pitch in the first zone is equal to the fine pitch in the second zone.

33. The overlay metrology target of claim 30, wherein the fine pitch in the first zone has a different value than the fine pitch in the second zone.

34. The overlay metrology target of claim 30, wherein a direction of the fine pitch in the first region is parallel to a direction of at least one of the first coarse pitch or the second coarse pitch.

35. The overlay metrology target of claim 30, wherein a direction of the fine pitch in the first zone is at a 45 degree angle to a direction of at least one of the first coarse pitch or the second coarse pitch.

36. A superposition measurement method, comprising: One or more overlay targets are fabricated on the sample, wherein a specific overlay target among the one or more overlay targets comprises: one or more grating-overlying grating structures formed of a lower grating structure having a first coarse pitch and an upper grating structure having a second coarse pitch, wherein the upper grating structure and the lower grating structure overlap on the sample, wherein at least one of the upper grating structure or the lower grating structure further comprises features having a fine pitch less than a wavelength of an illumination beam and arranged to rotate first order diffraction of the illumination beam associated with at least one of the first coarse pitch or the second coarse pitch relative to at least one of specular reflection from a top surface of the sample or a zero order diffraction from the one or more grating-overlying grating structures; illuminating the one or more of the superimposed targets using the illumination beam; producing an image of the sample through a polarizer aligned to pass the first order diffraction; and An overlay measurement is determined based on the image of the sample.

37. The overlay metrology method of claim 36, wherein at least one of the one or more overlay targets comprises two or more of the one or more grating structures in different cells in non-adjacent portions of a die on the sample.

38. The overlay metrology method of claim 36, wherein the image contains more than 100 overlay objects.

39. The superposition metrology method of claim 36, wherein the first coarse spacing and the second coarse spacing of at least one of the one or more superposition targets are equal to form at least one scatter superposition (SCOL) target.

40. The superposition metrology method of claim 39, wherein the at least one SCOL target comprises two or more grating overlying grating structures having different predetermined offsets between the constituent upper and lower grating structures.

41. The superposition metrology method of claim 39, wherein a portion of the image containing the at least one SCOL target is based on at least one of +1st order diffraction from the lower grating structure combined with -1st order diffraction from the upper grating structure or -1st order diffraction from the lower grating structure combined with +1st order diffraction from the upper grating structure.

42. The overlay metrology method of claim 36, wherein the first coarse pitch and the second coarse pitch of at least one of the one or more overlay targets are different to form at least one corrugated target.

43. The superposition metrology system of claim 42, wherein a portion of the image including the at least one corrugation target is based on at least one of a corrugation diffraction order formed by a +1st order diffraction from the lower grating structure combined with a -1st order diffraction from the upper grating structure or a corrugation diffraction order formed by a -1st order diffraction from the lower grating structure combined with a +1st order diffraction from the upper grating structure.

44. The overlay metrology method of claim 36, wherein the one or more grating-on-grating structures in the one or more overlay targets are unresolved and appear in grayscale intensity in the image of the one or more overlay targets.

45. The overlay metrology method of claim 36, wherein the features having the fine pitch are located only in the lower grating structure in at least one of the one or more overlay targets.

46. ​​A superimposed metering system comprising: an illumination source configured to generate at least one illumination beam; One or more illumination optics for directing the illumination beam at an oblique angle to a sample having a field of view including one or more overlay targets when implementing a metrology recipe, wherein a particular overlay target of the one or more overlay targets according to the metrology recipe comprises: one or more corrugated grating overlying grating structures formed of a lower grating structure having a first coarse pitch and an upper grating structure having a second coarse pitch different from the first pitch, wherein the upper grating structure and the lower grating structure overlap on the sample; an objective lens for collecting light diffraction from the sample within the field of view when implementing the metrology recipe, wherein at least one of specular reflection from the sample or zeroth order diffraction from the one or more superimposed targets is outside a collection numerical aperture of the objective lens; a detector for generating an image of the sample including the one or more superimposed targets; and A controller is communicatively coupled to the detector, the controller comprising one or more processors configured to execute program instructions that cause the one or more processors to determine an overlay measurement of the sample based on the image of the one or more overlay targets.

Images