Systems and methods for device-like overlay target measurements

Abstract

A method can include illuminating a target of an overlay target of a specimen with one or more broadband illumination beams from one or more broadband illumination sources. The overlay target can include one or more sets of superlens features. Each set of superlens features can include one or more first features having a coarse pitch and one or more second features having a fine pitch. The one or more first features and the one or more second features of each set of superlens features can operate as a superlens array to produce a periodic light distribution at a measurement plane. The method can further include generating one or more images of the periodic light distribution at the measurement plane. The method can further include generating an overlay measurement of the specimen based on the one or more images of the periodic light distribution at the measurement plane.

Description

Technical Field

[0001] This disclosure generally relates to superposition measurement, and more specifically, to a system and method for measuring superposition targets in a device-like manner. Background Technology

[0002] Overlap metrology generally refers to the measurement of the relative alignment of layers on a sample (e.g., but not limited to semiconductor devices). Overlap measurement, or measurement of overlap error, typically refers to the measurement of misalignment of manufacturing features on two or more sample layers. Generally, proper alignment of manufacturing features on multiple sample layers and proper operation of the alignment apparatus are necessary.

[0003] The need to reduce feature size and increase feature density has led to a corresponding increase in demand for accurate and efficient overlay metrology. Metrology systems typically generate sample-associated metrological data by measuring or otherwise verifying specific metrological targets that span the sample distribution.

[0004] Many current targets do not conform to design rules and are incompatible with processes. For example, gratings may have dimensions that do not conform to design rules. For instance, the typical size of a feature or space in a target may be hundreds of nanometers compared to a design-rule feature of tens of nanometers. Furthermore, the pitch of segmented features may be similar to the design rules, but the space between such features does not conform to the design rules, for example, having a size of hundreds of nanometers. This results in defective targets with suboptimal metrological performance. Additionally, even high-quality targets may fail to reflect device overlays because overlays induced by scanners and other processes can depend on feature size, density, and pitch. Current targets that are compatible with processes, such as critical-size (CD) modulation targets, have measurability problems. For example, even using dark imaging optical configurations, the printed pattern of a CD modulation target is almost unmeasurable.

[0005] Therefore, it would be advantageous to provide a system and method for measuring targets using a device stack that overcomes the shortcomings of the aforementioned prior methods. Summary of the Invention

[0006] According to one or more embodiments of this disclosure, a stacked metrology target is disclosed. In one embodiment, the stacked metrology target includes one or more first exposure structures. In another embodiment, the stacked metrology target includes one or more second exposure structures, wherein at least one of the one or more first exposure structures or the one or more second exposure structures includes one or more superlens feature sets. In another embodiment, each superlens feature set includes one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more second features are positioned relative to the one or more first features, wherein the fine pitch is smaller than the coarse pitch. In another embodiment, the one or more first features and the one or more second features of each superlens feature set operate as a superlens array to generate a periodic light distribution at a measurement plane that is different from the plane of at least one of the one or more superlens feature sets, wherein the periodic light distribution has the coarse pitch.

[0007] According to one or more embodiments of this disclosure, a superlens feature set is disclosed. In an embodiment, the superlens feature set includes one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more second features are positioned relative to the one or more first features, and wherein the fine pitch is smaller than the coarse pitch. In an embodiment, the one or more first features and the one or more second features operate as a superlens array to generate a periodic light distribution at a measurement plane different from the plane of the superlens feature set, wherein the periodic light distribution has the coarse pitch.

[0008] According to one or more embodiments of this disclosure, a superposition metrology system is disclosed. In one embodiment, the system includes an illumination subsystem comprising: one or more broadband illumination sources configured to generate one or more broadband illumination beams; and one or more illumination optics configured to guide the one or more broadband illumination beams onto a superposition target on a sample during metrology formulation, wherein the superposition target according to the metrology formulation includes one or more sets of superlens features, wherein each set of superlens features includes one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more first features and the one or more second features of each set of superlens features operate as a superlens array to generate a periodic light distribution at a measurement plane that is different from a plane of at least one of the one or more sets of superlens features, wherein the periodic light distribution has the coarse pitch. In another embodiment, the system includes a collection subsystem comprising: a detector configured to generate one or more images of the periodic light distribution at the measurement plane; and one or more collection optics. In one embodiment, the system includes a controller communicatively coupled to the detector, the controller including one or more processors configured to execute program instructions to cause the one or more processors to: receive one or more images of the periodic light distribution at the measurement plane from the detector; and generate a superimposed measurement of the sample based on the one or more images of the periodic light distribution at the measurement plane.

[0009] According to one or more embodiments of this disclosure, a superposition metrology system is disclosed. In one embodiment, the system includes a controller communicatively coupled to a detector. In another embodiment, the controller includes one or more processors configured to execute program instructions to cause the one or more processors to: receive from the detector one or more images of a periodic light distribution at a measurement plane, wherein the superposition target according to the metrology formula includes one or more sets of superlens features, wherein each set of superlens features includes one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more first features and the one or more second features of each set of superlens features operate as a superlens array to generate the periodic light distribution at the measurement plane in a plane different from at least one of the one or more sets of superlens features, wherein the periodic light distribution has the coarse pitch; and generate a superposition measurement of a sample based on the one or more images of the periodic light distribution at the measurement plane.

[0010] According to one or more embodiments of this disclosure, a method is disclosed. In an embodiment, the method includes: illuminating a stacked target of a sample with one or more broadband illumination beams from one or more broadband illumination sources, wherein the stacked target according to a metrological formulation comprises one or more sets of superlens features, wherein each set of superlens features comprises one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more first features and the one or more second features of each set of superlens features operate as a superlens array to generate a periodic light distribution at a measurement plane that is different from a plane of at least one of the one or more sets of superlens features, wherein the periodic light distribution has the coarse pitch; generating one or more images of the periodic light distribution at the measurement plane; receiving the one or more images of the periodic light distribution at the measurement plane; and generating a stacked measurement of the sample based on the one or more images of the periodic light distribution at the measurement plane.

[0011] It should be understood that the above general description and the following detailed description are for illustrative purposes only and do not necessarily limit the invention. 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. Attached Figure Description

[0012] Those skilled in the art can better understand the many advantages of this disclosure by referring to the accompanying drawings.

[0013] Figure 1A This is a conceptual diagram of the critical size (CD) modulation feature set of the superimposed measurement target.

[0014] Figure 1B yes Figure 1A The image shows a comparative simulation of the critical size (CD) modulation feature set of the superimposed measurement target.

[0015] Figure 2 This is a conceptual diagram of a superlens feature set according to one or more embodiments of the present disclosure.

[0016] Figure 3 It is a top view of a superimposed target containing a set of superlens features according to one or more embodiments of the present disclosure.

[0017] Figure 4 This is a conceptual diagram of a two-dimensional feature set according to one or more embodiments of the present disclosure.

[0018] Figure 5A This is a simplified schematic diagram of a stacked metering system including a stacked metering subsystem according to one or more embodiments of the present disclosure.

[0019] Figure 5BThis is a conceptual diagram of a stacked target containing a set of superlens features according to one or more embodiments of the present disclosure.

[0020] Figure 6 This is a flowchart depicting a method for measuring overlapping pairs according to one or more embodiments of the present disclosure. Detailed Implementation

[0021] The objectives of this disclosure will now be explained in detail with reference to the accompanying drawings. This disclosure has been specifically shown and described with respect to particular embodiments and their specific features. The embodiments set forth herein should be considered illustrative rather than restrictive. Those skilled in the art will readily understand that various changes and modifications in form and detail may be made without departing from the spirit and scope of this disclosure.

[0022] Embodiments of this disclosure relate to a system and method for superimposing a measurement device onto a target, providing sufficient target contrast and addressing measurement problems associated with CD-modulated targets. For example, the system and method can enhance target contrast by generating a focusing effect. For instance, the variability of the duty cycle within each pitch of a periodic target can be designed such that the phase distribution of the corresponding portion of a 0th-order plane wave passes through the target and returns in a manner similar to a lens phase distribution.

[0023] Figure 1A It is a CD modulation feature set 100 containing device target designs with detail pitch critical size (CD) modulation.

[0024] CD modulation feature set 100 may include coarse pitch 102 between isolation features 104 (e.g., 104a, 104b, or similar) having spaces filled with densely packed features 106 (e.g., 106a, 106b, 106c, 106d, 106e, or similar) conforming to predefined design rules. For example, dense features 106a to 106e may be positioned between isolation features 104a and 104b such that the coarse pitch 102 and the densely packed features 106a to 106e having fine pitch 108 all conform to the design rules. Segmented scattering measurement stack targets are generally discussed in U.S. Patent No. 8,913,237, issued December 16, 2014, the entire contents of which are incorporated herein by reference.

[0025] As discussed earlier in this article, it includes CD modulation feature set 100 (such as... Figure 1A The target shown in the figure is process-compatible. However, it should be noted that the CD modulation feature set 100 (such as...) Figure 1A The target shown in the image encounters measurability problems when used in imaging-based systems. For example, Figure 1B yes Figure 1AThe contrast simulation of CD modulation feature set 100 shown in the figure. The contrast of the printed pattern of the target of CD modulation feature set 100 is so low that the signal is almost unmeasurable even when using a dark field imaging optical configuration.

[0026] Figure 2 It is a superlens feature set 200 according to one or more embodiments of the present disclosure.

[0027] In an embodiment, the superlens feature set 200 includes one or more first features 202 having a coarse pitch 204.

[0028] In an embodiment, the superlens feature set 200 includes one or more second features 206 having a fine pitch 208. For example, one or more second features 206 may be positioned relative to one or more first features 202, wherein the fine pitch 208 is smaller than the coarse pitch 204. Furthermore, it is conceivable that one or more first features 202 may have a first critical size value set and one or more second features 206 may have a second critical size value set different from the first critical size value set.

[0029] Here, it can be considered that the coarse pitch 204 and the fine pitch 208 can be configured such that their ratio is an integer (N). Therefore, within the coarse pitch 204, N symmetrical second features 206 with different geometric properties can be printed such that the distance between the centers of adjacent features corresponds to the fine pitch 208. In this regard, the geometric properties of the second features 206 can be configured such that the N second features 206 within the coarse pitch 204 can act as individual lenses that focus reflected light (e.g., order 0 light) at a measurement plane 210 at a certain distance above the target.

[0030] In this embodiment, the first feature 202 and the second feature 206 operate as a lens array to enhance contrast. For example, the first feature 202 and the second feature 206 may form a superlens feature set 200 composed of sub-resolution features to focus incident light (e.g., order 0 light) onto the measurement plane 210 in a periodic distribution with a coarse pitch 204. In this respect, the position of the periodic light distribution in the measurement plane 210 may indicate the position of the superlens feature set 200. It is conceivable that the fine pitch and / or CD of any of the second features 206 may be sub-resolution features.

[0031] In this embodiment, the operating period of the second feature 206 can be varied. For example, the operating period of the second feature 206 can be varied to resemble a lens phase distribution, where the lens phase distribution is based on the lens focal length F. For example, the phase difference can be shifted to the focal position so that the measurement plane 210 of the target 201 is positioned at the lens focal length F.

[0032] Figure 3 It is included according to one or more embodiments of this disclosure. Figure 2 The superimposed target 201 of one or more superlens feature sets 200 shown in the figure. Here, it can be considered that... Figure 3 The overlapping target 201 in the image is suitable for image-based overlapping.

[0033] In an embodiment, the stacked target 201 comprises four units 303a to 303d, denoted herein as quadrants of the stacked target 201. Each unit 303a to 303d may include a first exposure structure 305 and a second exposure structure 307. At least one of the first exposure structure 305 or the second exposure structure 307 may include one or more superlens feature sets 200. For example, in a non-limiting example, the photoresist layer and the process layer may include superlens features. Although Figure 3 The first exposure structure 305 and the second exposure structure 307, depicting each unit 303a to 303d, include superlens features; however, it is conceivable that either the first or second exposure structure may contain a set of superlens features. For example, in a non-limiting example, the photoresist layer may contain standard periodic features without a lensing effect, and the process layer may contain superlens features, or vice versa. In this regard, this can be achieved by moving the sample upwards to the cone 540 ( Figure 5B The bottom of the image (as shown in the image) is used to image standard periodic features that do not have a lens effect.

[0034] It is conceivable that the first exposure structure 305 can be associated with a first photolithographic exposure and the second exposure structure 307 can be associated with a second photolithographic exposure, wherein the first and second photolithographic exposures can be on the same layer (or on different layers, such as...). Figure 3 (as shown in the image).

[0035] Furthermore, cells 303b and 303d can be configured to provide stacked measurements along the X direction, such as... Figure 3 As illustrated in the diagram. For example, overlay measurements along the X-direction can be performed by directly comparing the relative positions of the first layer superlens feature set 200 and the second layer superlens feature set 200 within each cell or between cells 303b and 303d. In another example, overlay measurements along the X-direction can be performed by comparing symmetrical points (e.g., rotational symmetry, reflection symmetry, mirror symmetry, or similar) between the first layer superlens feature sets 200 distributed across cells 303b and 303d with symmetrical points between the second layer printed superlens feature sets 200 distributed across cells 303b and 303d. Similarly, cells 303a and 303c can be configured to provide overlay measurements along the Y-direction, as... Figure 3 As explained in the text.

[0036] It should be understood that Figure 3For illustrative purposes only and should not be construed as limiting. The superimposed target 201 may include any design of patterned elements for use in imaging or scattering measurement modes. For example, in some embodiments, the superlens feature set 200 is a non-overlapping structure, such as... Figure 3 As shown in the figure. To give another example, in some embodiments, the superlens feature set 200 may be an overlapping structure.

[0037] The phase distribution of the lens can be defined by equation (1), as shown and described below:

[0038] Equation (1)

[0039] Where F is the focal length of the lens, λ is the wavelength, and x is the distance.

[0040] Here, it can be considered that features 202 and 206 of the superlens feature set are smaller than the wavelength of the incident light (e.g., the illumination of the system), making the effective medium theory applicable to describe electromagnetic scattering. Therefore, using the effective medium approximation, the phase distribution of the portion of the zero-order plane wave that passes through the target and returns can be described using equation (2), as shown and described below:

[0041] Equation (2)

[0042] Where H is the target height and n eff These are the polarization-dependent effective refractive indices for Y and X polarization, respectively, as given by equations (3a) and (3b), as shown and described below:

[0043] Equation (3a)

[0044] Equation (3b)

[0045] in and η(x) represents the dielectric constant of the inclusion (e.g., silicon or the like) and the surrounding layer (e.g., oxide layer or the like), respectively, and η(x) is the segmented duty cycle in the x-direction.

[0046] It can be considered that, although the effective medium theory is used to describe electromagnetic scattering, other models / theories can be used, such as, but not limited to, numerical scattering or similar theories.

[0047] As discussed earlier herein, it can be considered that the superlens feature set 200, including the first feature 202 and the second feature 206, can act as a superlens array (e.g., a lens array with coarse pitch) that produces a periodic light distribution at a measurement plane 210 that can be imaged by the system. For example, the superlens array may have a predefined focal length F. Therefore, at the focal length F of the superlens feature set 200, a periodic signal 212 with enhanced contrast (e.g., an image relative to the superlens feature set 200 itself) can be detected to determine the grating position measurement. For example, for Y-polarization, n from equation (3a) eff Substituting into equation (2) and making it equal to equation (1) produces equation (4), as shown and described below:

[0048] Equation (4)

[0049] in,

[0050] In a non-limiting example, for instance, an estimate of the focal length F for silicon in oxides gives a value of approximately 1 μm. For example, for... Approximately 15 and Approximately 2.5 n eff It is approximately 1.5 (from dense to isolated structures). Therefore, the lens focal length F can be... The coarse pitch is approximately 1 μm and H is approximately 50 nm.

[0051] It should be noted that a one-dimensional grating can be associated with the dependence of the target design on the polarization direction of the illumination light. For example, a one-dimensional grating requires measuring targets with different X and Y polarizations (i.e., dual grasp), which increases measurement time. Therefore, in some cases, using a two-dimensional target to reduce measurement time and target size may be preferred.

[0052] Figure 4 It is a two-dimensional feature set 400 according to one or more embodiments of this disclosure.

[0053] In an embodiment, the superlens feature set 400 includes target features 402 in the y-direction having a target pitch 404.

[0054] In an embodiment, the superlens feature set 400 includes design rule features 406 in the x-direction with design rule pitch 408 (or fine pitch).

[0055] In this embodiment, the target feature 402 and the design rule feature 406 may have the same pitch in both the x and y directions. In this respect, the specific structure within each unit cell will provide a polarization-independent response. Furthermore, it is possible to configure the printed structure based on 90-degree rotational invariance.

[0056] although Figure 4 The superlens feature set 400 includes radial spatial modulation with circular inclusions, but it is conceivable that the features may have any size, shape, or similar. For example, inclusions may include, but are not limited to, square inclusions, square lattice structures, hexagonal structures, triangular structures, and similar structures suitable for a predetermined physical response.

[0057] Furthermore, it is worth considering here that overlapping targets (similar to) Figure 3 The target shown may include a first exposure structure and a second exposure structure, wherein at least one of the first exposure structure or the second exposure structure includes one or more superlens feature sets 400.

[0058] The phase function of a zero-order plane wave used for focusing a two-dimensional target can be described by equation (5), as shown and described below:

[0059] Equation (5)

[0060] Note the phase distribution This can be any general function suitable for focusing purposes and is therefore not limited to radial functions. For example, this generalization can also be readily extended to cylindrical lenses. Similar to the 1D case, the phase distribution on the target can be described by the theory of effective media, as shown and described by the following equation (6):

[0061] Equation (6)

[0062] In the case of two-dimensional periodic structures, it should be noted that the analytical closed-form expression for the unknown effective medium is not provided in the literature. However, using the Green's function method for periodic media, a corresponding expression for a structure whose form is symmetric about a 90° rotation can be obtained, and it has the following expression, as shown and described below with respect to equation (7):

[0063] Equation (7)

[0064] Where η = S(x,y) / (coarse pitch) 2 And S(x,y) is an inclusion. The spatially dependent area. Assume the parameter η can vary from approximately 0.1 to 0.7 (e.g., due to the printability and geometry of the inclusions). n eff It is approximately 1 and the corresponding focal length (under the same conditions as in the example of a one-dimensional target) is approximately 1.5 μm.

[0065] Figure 5AThis is a conceptual diagram of a superimposed metering system 500 for performing superimposed metering on superimposed target 201 using metering subsystem 502, according to one or more embodiments of the present disclosure.

[0066] It should be noted that, for the purposes of this disclosure, the term "overlap" is generally used to describe the relative position of features on a sample fabricated by two or more photolithographic patterning steps, while the term "overlap error" describes the deviation of a feature from its nominal arrangement. In this context, overlap measurement can be expressed as a measurement of relative positions or overlap errors associated with those relative positions. For example, a multilayer device may contain features patterned on multiple sample layers using different photolithographic steps for each layer, where the alignment of features between layers must typically be tightly controlled to ensure proper performance of the resulting device. Thus, overlap measurement characterizes the relative position of features on two or more of the sample layers. As another example, multiple photolithographic steps can be used to fabricate features on a single sample layer. Such techniques (often referred to as dual patterning or multipatterning techniques) facilitate the fabrication of highly dense features at near-photolithographic system resolution. Overlap measurement in this context characterizes the relative position of features from different photolithographic steps on this single layer. It should be understood that the examples and descriptions throughout this disclosure relating to specific applications of overlap metrology are illustrative only and should not be construed as limiting the scope of this disclosure.

[0067] As used throughout this disclosure, the term "sample" generally refers to a substrate (e.g., a wafer or the like) formed of a semiconductor or non-semiconductor material. For example, semiconductor or non-semiconductor materials may include, but are not limited to, single-crystal silicon, gallium arsenide, and indium phosphide. A sample may contain one or more layers. For example, such layers may include, but are not limited to, photoresists, dielectric materials, conductive materials, and semiconducting materials. Many different types of such layers are known in the art, and as used herein, the term "sample" is intended to encompass a sample on which all types of such layers can be formed. The one or more layers formed on the sample may be patterned or unpatterned. For example, a sample may contain multiple dies, each having repeatably patterned features. The formation and processing of such material layers can ultimately result in a completed device. Many different types of devices can be formed on a sample, and as used herein, the term "sample" is intended to encompass a sample on which any type of device known in the art is manufactured. Furthermore, for the purposes of this disclosure, the terms "sample" and "wafer" should be interpreted interchangeably. Furthermore, for the purposes of this disclosure, the terms “patterning device,” “mask,” and “photomask” should be interpreted as interchangeable.

[0068] In an embodiment, the overlay metrology system 500 includes a metrology subsystem 502 for acquiring overlay signals from overlay targets 201 based on various overlay formulations. For example, the metrology subsystem 502 may direct illumination to sample 504 and may further collect light or other radiation emitted from sample 504 to generate overlay signals suitable for determining overlays of two or more sample layers. The metrology subsystem 502 may be any type of overlay metrology subsystem known in the art, suitable for generating overlay signals suitable for determining overlays associated with overlay targets 201 on sample 504. The metrology subsystem 502 may operate selectively in an imaging mode or a non-imaging mode. For example, in an imaging mode, as previously discussed herein, the overlay target 201 may include one or more superlens feature sets 200 configured to generate a periodic light distribution at measurement plane 210, wherein the metrology subsystem 502 may be configured to image the periodic light distribution at measurement plane 210. In this respect, an image of the periodic light distribution at plane 210 has a better quality than an image of the target itself (e.g., ...). Figure 1B (As shown in the image) Enhanced contrast.

[0069] Furthermore, the metrology subsystem 502 can be configured to generate a pairing signal based on various formulations, which define measurement parameters for obtaining a pairing signal suitable for determining the pairing of pairing target 201. For example, the formulation of the metrology subsystem 502 may include, but is not limited to, illumination wavelength, detection wavelength of light emitted from sample 504, size or shape of the illumination spot on sample 504, incident illumination angle, incident illumination polarization, collected light polarization, position of the incident illumination beam on pairing target 201, position of pairing target 201 in the focal volume of metrology subsystem 502, or similar parameters.

[0070] In an embodiment, the metrology subsystem 502 includes an illumination subsystem comprising an illumination source 514 configured to generate at least one illumination beam 516 and one or more illumination optics 522. For example, the illumination subsystem may include one or more broadband illumination sources 514 configured to generate one or more broadband illumination beams 516. In this regard, the metrology subsystem 502 may include one or more apertures at an illumination pupil plane for splitting illumination from the illumination source 514 into one or more illumination beams 516 or illumination lobes. In this regard, the metrology subsystem 502 may provide dipole illumination, orthogonal illumination, or the like. Furthermore, the spatial profile of one or more illumination beams 516 on the sample 504 may be controlled by a field plane aperture to have any selected spatial profile.

[0071] The illumination source 514 may comprise any type of illumination source suitable for providing at least one broadband illumination beam 516. In an embodiment, the illumination source 514 is a laser source. For example, the illumination source 514 may comprise a broadband laser source.

[0072] In one embodiment, the metrology subsystem 502 guides an illumination beam 516 to a sample 504 via an illumination path 518. The illumination path 518 may include one or more optical components suitable for modifying and / or adjusting the illumination beam 516 and guiding it to the sample 504. In one embodiment, the illumination path 518 includes one or more illumination path lenses 520 (e.g., for collimating the illumination beam 516, for relay pupils and / or field planes, or the like). In another embodiment, the illumination path 518 includes one or more illumination path optics 522 for shaping or otherwise controlling the illumination beam 516. For example, the illumination path optics 522 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translation mirrors, scanning mirrors, or the like).

[0073] In one embodiment, the metrology subsystem 502 includes an objective lens 524 for focusing an illumination beam 516 onto a sample 504 (e.g., a stacked target 201 having stacked target features located on two or more layers of the sample 504). In another embodiment, the sample 504 is placed on a sample stage 526 adapted to fix the sample 504 and further configured to position the sample 504 relative to the illumination beam 516.

[0074] Figure 5B This is a conceptual diagram of a stacked target containing a set of superlens features according to one or more embodiments of the present disclosure.

[0075] Figure 5B A cone 540 depicts the lens focal length F and represents the numerical aperture of the objective lens 534 of the metrology subsystem 502, wherein the objective lens 534 has a focal length f0. It is conceivable that, for a typical setup with an infinitely corrected objective lens, the target feature is placed at f0. However, in this disclosure discussed herein, the system is shifted such that f0 is placed on the measurement plane rather than at the sample feature. In this respect, the superlens feature set 200 operates as a superlens array to generate a periodic light distribution at the measurement plane 210, which can be imaged by the system at the measurement plane 210.

[0076] It is conceivable that the measurement plane 210 may be located above or below the superlens feature set 200 and may further be located within the volume of the sample or completely outside the sample. Furthermore, it should be noted that if the target 201 comprises multiple sample layers containing one or more superlens feature sets 200, then each superlens feature set 200 may have the same or different measurement plane 210. However, it is conceivable that overlapping measurement planes may be beneficial, as it will provide high-contrast signals for both layers in a single image.

[0077] In an embodiment, the metrology subsystem 502 includes one or more detectors 528 configured to capture light (e.g., collection light 530) emitted from a sample 504 (e.g., a stacked target 201 on the sample 504) via a light-collecting path 532. The light-collecting path 532 may include one or more optical elements suitable for modifying and / or adjusting the collection light 530 from the sample 504. In an embodiment, the light-collecting path 532 includes one or more light-collecting path lenses 534 (e.g., for collimating the illumination beam 516, for relaying pupils and / or field planes or the like), which may include (but may not include) objective lenses 524. In an embodiment, the light-collecting path 532 includes one or more light-collecting path optics 536 for shaping or otherwise controlling the collection light 530. For example, the light-collecting path optics 536 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translation mirrors, scanning mirrors, or the like).

[0078] Detector 528 can be located at any selected location within the light-collecting path 532. In an embodiment, the metrology subsystem 502 includes detector 528 configured to generate an image of a periodic light distribution at measurement plane 210. Generally, detector 528 can capture any combination of light reflected (or transmitted), scattered, or diffracted from sample 504.

[0079] The metrology subsystem 502 may generally include any number or type of detectors 528 suitable for capturing light from the sample 504 indicating a stacked pair. In embodiments, detectors 528 include one or more detectors 528 suitable for characterizing static samples. In this respect, the metrology subsystem 502 can operate in a static mode, wherein the sample 504 is static during measurement. For example, detectors 528 may include a two-dimensional pixel array, such as, but not limited to, a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) device. In this respect, detectors 528 can generate a two-dimensional image in a single measurement.

[0080] In an embodiment, detector 528 includes one or more detectors 528 suitable for characterizing moving sample 504 (e.g., scanned sample). In this regard, metrology subsystem 502 can operate in a scan mode, wherein sample 504 is scanned relative to a measurement field during measurement. For example, detector 528 may include a 2D pixel array having a capture time and / or refresh rate sufficient to capture one or more images within selected image tolerances (e.g., image blur, contrast, sharpness, or the like) during scanning. As another example, detector 528 may include a line scan detector for continuously generating images one row of pixels at a time. As yet another example, detector 528 may include a time delay integration (TDI) detector. The TDI detector generates continuous images of sample 504 when the movement of sample 504 is synchronized with a charge transfer frequency signal in the TDI detector. Specifically, the TDI detector acquires charge from exposure on a column of pixels and includes clock pulses for transferring charge between adjacent columns of pixels along the scan direction. Charge continuously accumulates during scanning as the movement of sample 504 along the scan direction is synchronized with charge transfer in the TDI detector. This process continues until the charge reaches the last column of pixels and is subsequently read out from the detector. In this way, the image of the object accumulates over a longer timeframe than that available by a simple line-scan camera. This relatively long acquisition time reduces the level of photon noise in the image. Furthermore, the synchronized movement of the image and the charge prevents blurring of the recorded image.

[0081] In an embodiment, the metrology subsystem 502 includes a scanning subsystem for scanning the sample 504 relative to the measurement field during metrological measurements. For example, the sample stage 526 can position and orient the sample 504 within the focal volume of the objective lens 524. In an embodiment, the sample stage 526 includes one or more adjustable stages, such as, but not limited to, linear translation stages, rotation stages, or tilt / flip stages. In an embodiment, although not shown, the scanning subsystem includes one or more beam scanning optics (e.g., rotatable mirrors, galvanometers, or the like) for scanning the illumination beam 516 relative to the sample 504.

[0082] The illumination path 518 and light-collecting path 532 of the metrology subsystem 502 can be adapted to various configuration orientations for illuminating the sample 504 with the illumination beam 516 and collecting light emitted from the sample 504 in response to the incident illumination beam 516. For example, as Figure 4 As described, the metrology subsystem 502 may include a beam splitter 538, which is oriented such that the common objective lens 524 can simultaneously direct the illumination beam 516 to the sample 504 and collect light from the sample 504. As another example, the illumination path 518 and the light-collecting path 532 may contain non-overlapping optical paths.

[0083] In an embodiment, the metrology subsystem 502 may provide overlay data to one or more process subsystems. Overlay data from the overlay metrology subsystem may generally include any output of overlay metrology information having sufficient information to determine the overlay (or overlay error) associated with various lithography steps. For example, the overlay data may include, but is not required to include, one or more datasets, one or more images, one or more detector readings, or the like. This overlay data may then be used for various purposes, including, but not limited to, diagnostic information for the lithography subsystem or for the generation of process control correctable values. For example, overlay data of samples in a batch may be used to generate feedback correctable values ​​for controlling the lithography exposure of subsequent samples in the same batch. In another example, overlay data of samples in a batch may be used to generate feedforward correctable values ​​for controlling the lithography exposure of the same or similar samples in subsequent lithography steps to address any deviations in the current exposure.

[0084] In an embodiment, the stacked metering system 500 includes a controller 508. The controller 508 may include one or more processors 510 and / or memory media 512 (e.g., memory 512). The controller 508 may include one or more processors 510 configured to execute program instructions held on the memory media 512 or memory. In this regard, the one or more processors 510 of the controller 508 may perform any of the various process steps described herein. Furthermore, the controller 508 may be communicatively coupled to the metering subsystem 502 or any component thereof.

[0085] One or more processors 510 of controller 508 may comprise any processor or processing element known in the art. For the purposes of this disclosure, the terms “processor” or “processing element” may be broadly defined to cover any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this regard, one or more processors 510 may comprise any means configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In embodiments, one or more processors 510 may embody a desktop computer, a host computer system, a workstation, a graphics computer, a parallel processor, a network computer, or any other computer system configured to execute programs (which are configured to operate or be combined with the metering system 500) as described throughout this disclosure.

[0086] Furthermore, different subsystems of the stacked metering system 500 may include processors or logic elements suitable for implementing at least a portion of the steps described in this disclosure. Therefore, the above description should not be construed as limiting the embodiments of this disclosure, but is merely illustrative. Additionally, the steps described throughout this disclosure may be implemented by a single controller 508 or, alternatively, multiple controllers. Furthermore, controller 508 may include one or more controllers housed within a common housing or multiple housings. In this manner, any controller or combination of controllers may be individually packaged as a module suitable for integration into the stacked metering system 500.

[0087] Memory media 512 may comprise any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 510. For example, memory media 512 may comprise non-transitory memory media. As another example, memory media 512 may comprise, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical storage devices (e.g., magnetic disks), magnetic tape, solid-state drives, and the like. It should be further noted that memory media 512 may be housed in a common controller housing with one or more processors 510. In embodiments, memory media 512 may be remotely located relative to the physical location of one or more processors 510 and controller 508. For example, one or more processors 510 of controller 508 may access remote storage (e.g., a server) accessible via a network (e.g., the Internet, an intranet, and the like).

[0088] Figure 6 This is a flowchart depicting a method 600 for measuring stacked pairs according to one or more embodiments of the present disclosure. The applicant emphasizes that the embodiments and implementation techniques previously described herein in the context of the stacked pair metrology system 500 should be interpreted as extending to method 600. However, it should be further noted that method 600 is not limited to the architecture of the stacked pair metrology system 500.

[0089] In one embodiment, method 600 includes step 602: illuminating a sample with one or more broadband illumination beams, wherein the sample, as a stacked metrological target, comprises one or more sets of superlens features forming a lens array. The lens array can produce a periodic light distribution at the measurement plane 210. In another embodiment, the duty cycle of the second feature 206 can be adjusted to resemble a lens phase distribution, wherein the lens phase distribution is based on the lens focal length.

[0090] In an embodiment, method 600 includes step 604: generating an image of a periodic light distribution at the measurement plane.

[0091] In an embodiment, method 600 includes step 606: receiving one or more images of a periodic light distribution at a measurement plane from one or more detectors.

[0092] In one embodiment, method 600 includes step 608: determining a sample overlay measurement based on an image of a periodic light distribution at the measurement plane. In this regard, the measurement of the process-compatible overlay target 201 can be attributed to the enhanced contrast of the periodic light distribution at the measurement plane 210 (rather than an image of sample features), thereby improving the accuracy of the overlay measurement.

[0093] Those skilled in the art will recognize that, for the sake of clarity, the components (e.g., operations), devices, objects, and accompanying discussions described herein are used as examples and various configuration modifications may be considered. Therefore, as used herein, the specific examples and accompanying discussions are intended to represent their more general categories. In general, the use of any particular example is intended to represent its category, and the omission of specific components (e.g., operations), devices, and objects should not be considered as limitation.

[0094] Those skilled in the art will understand that various tools (e.g., hardware, software, and / or firmware) exist to implement the processes and / or systems and / or other technologies described herein, and preferred tools will vary depending on the context in which the processes and / or systems and / or other technologies are deployed. For example, if the implementer determines that speed and accuracy are of utmost importance, then the implementer may choose a tool that is primarily hardware and / or firmware; alternatively, if flexibility is of utmost importance, then the implementer may choose a software-based implementation; or alternatively, the implementer may choose a combination of hardware, software, and / or firmware. Therefore, several feasible tools exist to implement the processes and / or apparatuses and / or other technologies described herein, and none of these tools is inherently superior to the others, because any tool to be used depends on the context in which the tool will be deployed and the implementer's specific considerations (e.g., speed, flexibility, or predictability), any of which can vary.

[0095] The foregoing description is presented to enable those skilled in the art to make and use the invention in the context of a particular application and its requirements. As used herein, directional terms (e.g., “top,” “bottom,” “above,” “below,” “up,” “down,” “downward,” and “towards”) are intended to provide relative positions for descriptive purposes and are not intended to specify an absolute frame of reference. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the invention is not intended to be limited to the specific embodiments shown and described, but is given the broadest scope consistent with the principles and novel features disclosed herein.

[0096] Regarding the use of generally plural and / or singular terms in this document, those skilled in the art can appropriately convert plural to singular and / or singular to plural depending on the context and / or application. For clarity, various singular / plural arrangements are not explicitly described herein.

[0097] All methods described herein may include storing the results of one or more steps of the method embodiments in memory. The results may include any of the results described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the results are stored, they may be accessed in memory and used by any of the methods or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. Furthermore, the results may be stored “permanently,” “semi-permanently,” “temporarily,” or for a period of time. For example, the memory may be random access memory (RAM), and the results may not necessarily remain in memory indefinitely.

[0098] It can be further considered that each of the embodiments of the above methods may include any other steps of any other method described herein. Furthermore, each of the embodiments of the above methods may be performed by any of the systems described herein.

[0099] The objectives described herein sometimes refer to different components contained within or connected to other components. It should be understood that such depicted architectures are illustrative only, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components achieving the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components combined herein to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “coupled” with each other to achieve the desired functionality, and any two components that can be suchly associated can also be considered “coupleable” with each other to achieve the desired functionality. Specific instances of “coupleable” include, but are not limited to, physically mating and / or physically interacting components and / or wirelessly interacting and / or logically interacting components.

[0100] Furthermore, it should be understood that the invention is defined by the appended claims. Those skilled in the art will understand that, generally, the terms used herein and especially in the appended claims (e.g., the body of the appended claims) are intended to be “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “at least having,” the term “include” should be interpreted as “including but not limited to,” etc.). Those skilled in the art will further understand that if a particular number of claims is to be introduced, then this intention must be explicitly stated in the claims, and if such a statement is not made, then this intention does not exist. For example, to aid understanding, the appended claims may contain the use of the introductory phrases “at least one” and “one or more” to introduce the claims. However, the use of such phrases should not be construed as implying that the introduction of a claim statement by the indefinite article "a" limits any particular claim containing such an introduction to an invention containing only one such statement, even if the same claim contains the introductory phrase "a or more" or "at least one" and an indefinite article such as "a" (e.g., "a" should generally be interpreted as meaning "at least one" or "a or more"); the same applies to the use of definite articles introducing claim statements. Furthermore, even if a specific number of claim statements is explicitly stated, those skilled in the art will recognize that such a statement should generally be interpreted as meaning at least a number of statements (e.g., a bare statement of "two statements" without other modifiers generally means at least two statements or two or more statements). Furthermore, in examples where the convention of "at least one of A, B, and C and similar items" is used, this construction is generally intended to be understood in the sense commonly understood by those skilled in the art (e.g., "a system having at least one of A, B, and C" would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and similar items). In examples where the convention of "at least one of A, B, or C and similar items" is used, this construction is generally intended to be understood in the sense commonly understood by those skilled in the art (e.g., "a system having at least one of A, B, or C" would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, and similar items). Those skilled in the art should further understand that, regardless of the specific embodiments, claims, or figures, virtually any extractive terms and / or phrases presenting two or more alternatives should be understood to contemplate the possibility of including one, any one, or both of the items. For example, the phrase “A or B” should be understood as including the possibility of “A” or “B” or “A and B”.

[0101] It is believed that this disclosure and its many accompanying advantages will be understood from the foregoing description, and it should be understood that various changes can be made to the form, construction, and arrangement of the components without departing from the disclosed objectives or sacrificing all its important advantages. The forms described are for illustrative purposes only, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A stacked measurement target, comprising: One or more first exposure structures; and One or more second exposure structures, wherein the one or more first exposure structures or at least one of the one or more second exposure structures comprises one or more superlens feature sets. Each hyperlens feature set includes: One or more first features having a coarse pitch; and One or more second features having a fine pitch, wherein the one or more second features are positioned relative to the one or more first features, wherein the fine pitch is smaller than the coarse pitch. The one or more first features and the one or more second features of each superlens feature set are operated as a superlens array to generate a periodic light distribution at a measurement plane that is different from the plane of at least one of the one or more superlens feature sets, wherein the periodic light distribution has the coarse pitch.

2. The stacked measurement target according to claim 1, wherein the working period of the one or more second features is varied to resemble a lens phase distribution, wherein the lens phase distribution provides the lens focal length.

3. The stacked measurement target according to claim 2, wherein the measurement plane is arranged at the focal length of the lens.

4. The stacked measurement target according to claim 1, wherein the one or more first features have a first critical size value set, and wherein the one or more second features have a second critical size value set different from the first critical size value set.

5. The stacked measurement target according to claim 1, wherein the one or more first features and the one or more second features comprise two-dimensional features.

6. The stacked measurement target according to claim 5, wherein the two-dimensional feature comprises a two-dimensional circular inclusion.

7. The stacked metering target according to claim 1, wherein the one or more first exposure structures and the one or more second exposure structures do not overlap.

8. The stacking metrology target according to claim 1, wherein the one or more first exposure structures are located on a first layer of the sample and the one or more second exposure structures are located on a second layer of the sample.

9. The stacked metrology target according to claim 8, wherein the first layer comprises a process layer and the second layer comprises a photoresist layer.

10. The stacking metrology target of claim 9, wherein the one or more first exposure structures of the process layer comprise the one or more superlens feature sets.

11. The stacked metrology target of claim 9, wherein the one or more second exposure structures of the photoresist layer comprise the one or more superlens feature sets.

12. The stacking metrology target according to claim 9, wherein the one or more first exposure structures of the process layer and the one or more second exposure structures of the photoresist layer comprise the one or more superlens feature sets.

13. A feature set of a superlens, comprising: One or more first features having a coarse pitch; and One or more second features having a fine pitch, wherein the one or more second features are positioned relative to the one or more first features, wherein the fine pitch is smaller than the coarse pitch. The one or more first features and the one or more second features operate as a superlens array to generate a periodic light distribution at a measurement plane that is different from the plane of the superlens feature set, wherein the periodic light distribution has the coarse pitch.

14. The superlens feature set of claim 13, wherein the working period of the one or more second features is varied to resemble a lens phase distribution, wherein the lens phase distribution provides the lens focal length.

15. A stacked metering system, comprising: The lighting subsystem includes: One or more broadband lighting sources configured to produce one or more broadband lighting beams; and One or more illumination optics configured to guide one or more broadband illumination beams onto a stacked target on a sample during the implementation of a metrology formulation, wherein the stacked target according to the metrology formulation comprises one or more sets of superlens features, wherein each set of superlens features comprises one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more first features and the one or more second features of each set of superlens features operate as a superlens array to generate a periodic light distribution at a measurement plane that is different from the plane of at least one of the one or more sets of superlens features, wherein the periodic light distribution has the coarse pitch. The collection subsystem includes: A detector configured to generate one or more images of the periodic light distribution at the measurement plane; and One or more collecting optical elements; and A controller communicatively coupled to the detector, the controller comprising one or more processors configured to execute program instructions to cause the one or more processors to: Receive one or more images of the periodic light distribution at the measurement plane from the detector; and The superimposed measurement of the sample is generated based on one or more images of the periodic light distribution at the measurement plane.

16. The stacking metering system of claim 15, wherein the one or more processors are further configured to execute program instructions to cause the one or more processors to: The working cycle of one or more second features is adjusted to resemble a lens phase distribution, wherein the lens phase distribution provides the lens focal length.

17. The stacking measurement system according to claim 16, wherein the measuring plane is arranged at the focal length of the lens.

18. The stacking metering system of claim 15, wherein the one or more first features and the one or more second features comprise two-dimensional features.

19. A stacked metering system, comprising: A controller communicatively coupled to a detector, the controller comprising one or more processors configured to execute program instructions to cause the one or more processors to: One or more images of a periodic light distribution at a measurement plane are received from the detector, wherein the superimposed target according to the metrological formula comprises one or more sets of superlens features, wherein each set of superlens features comprises one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more first features and the one or more second features of each set of superlens features operate as a superlens array to generate the periodic light distribution at the measurement plane in a plane different from at least one of the one or more sets of superlens features, wherein the periodic light distribution has the coarse pitch; and The sample overlay measurement is generated based on one or more images of the periodic light distribution at the measurement plane.

20. The stacking metering system of claim 19, wherein the one or more processors are further configured to execute program instructions to cause the one or more processors to: The working cycle of one or more second features is adjusted to resemble a lens phase distribution, wherein the lens phase distribution provides the lens focal length.

21. The stacking measurement system according to claim 20, wherein the measuring plane is arranged at the focal length of the lens.

22. A method comprising: A stacked target of a sample is illuminated by one or more broadband illumination beams from one or more broadband illumination sources, wherein the stacked target according to the metrological formulation comprises one or more sets of superlens features, wherein each set of superlens features comprises one or more first features having a coarse pitch and one or more second features having a fine pitch, wherein the one or more first features and the one or more second features of each set of superlens features operate as a superlens array to generate a periodic light distribution at a measurement plane that is different from the plane of at least one of the one or more sets of superlens features, wherein the periodic light distribution has the coarse pitch. One or more images of the periodic light distribution are generated at the measurement plane; Receive one or more images of the periodic light distribution at the measurement plane; and The superimposed measurement of the sample is generated based on one or more images of the periodic light distribution at the measurement plane.

23. The method of claim 22, further comprising: The working cycle of one or more second features is adjusted to resemble a lens phase distribution, wherein the lens phase distribution provides the lens focal length.

24. The method of claim 23, wherein the measuring plane is arranged at the focal length of the lens.

Images