Overlay metrology systems and methods for semiconductor manufacturing

Abstract

Measuring overlay is described. A sensor generates a signal comprising an intensity modulated fringe pattern (e.g., an interference pattern) based on the interference of +nth and -nth diffraction radiation for a given direction of diffraction received from a first metrology mark in a first layer of a substrate and a second metrology mark in a second layer that is below the first mark. The first and second marks are arranged in non-overlapping positions in the first and second layers. A partitioned wedge directs + / - nth orders of the diffracted radiation from segments of each mark that correspond to a first direction of the diffracted radiation, and segments that correspond to a second direction of the diffracted radiation, onto different areas of the sensor. Parameters associated with fringes in the intensity modulated fringe pattern are determined, and overlay values are determined based on the parameters.

Description

OVERLAY METROLOGY SYSTEMS AND METHODS FOR SEMICONDUCTOR MANUFACTURINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the priority benefit of U.S. Provisional Patent Application Number 63 / 777,798, filed March 26, 2025, the content of which is incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] This description relates to overlay metrology systems and methods for semiconductor manufacturing.BACKGROUND

[0003] A lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device (e.g., a mask) may include or provide a pattern corresponding to an individual layer of the IC (“design layout”), and this pattern can be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g., silicon wafer) that has been coated with a layer of radiation-sensitive material (“resist”), by methods such as irradiating the target portion through the pattern on the patterning device. In general, a single substrate includes a plurality of adjacent target portions to which the pattern is transferred successively by the lithographic projection apparatus, one target portion at a time. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred onto one target portion in one operation. Such an apparatus is commonly referred to as a stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, a projection beam scans over the patterning device in a given reference direction (the “scanning” direction) while synchronously moving the substrate parallel or anti-parallel to this reference direction. Different portions of the pattern on the patterning device are transferred to one target portion progressively.

[0004] Prior to transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures, such as priming, resist coating, and a soft bake. After exposure, the substrate may be subjected to other procedures (“post-exposure procedures”), such as a post-exposure bake (PEB), development, a hard bake and measurement / inspection of the transferred pattern. This array of procedures is used as a basis to make an individual layer of a device, e.g., an IC. The substrate may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, deposition, chemo-mechanical polishing, etc., all intended to finish the individual layer of the device. If several layers are required in the device, then the whole procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present in each target portion on the substrate. These devicesare then separated from one another by a technique such as dicing or sawing, such that the individual devices can be mounted on a carrier, connected to pins, etc.

[0005] Thus, manufacturing devices, such as semiconductor devices, typically involves processing a substrate (e.g., a semiconductor wafer) using a number of fabrication processes to form various features and multiple layers of the devices. Such layers and features are typically manufactured and processed using, e.g., deposition, lithography, etch, deposition, chemical-mechanical polishing, and ion implantation. Multiple devices may be fabricated on a plurality of dies on a substrate and then separated into individual devices. This device manufacturing process may be considered a patterning process. A patterning process involves a patterning step, such as optical and / or nanoimprint lithography using a patterning device in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, deposition, etc.

[0006] Lithography is a central step in the manufacturing of device such as ICs, where patterns formed on substrates define functional elements of the devices, such as microprocessors, memory chips, etc. Similar lithographic techniques are also used in the formation of flat panel displays, micro-electro mechanical systems (MEMS) and other devices.

[0007] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements have continually been reduced while the number of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as “Moore ’s law”. At the current state of technology, layers of devices are manufactured using lithographic projection apparatuses that project a design layout onto a substrate using illumination from a deepultraviolet or extreme ultraviolet illumination source, creating individual functional elements having dimensions well below 100 nm, i.e. less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source).

[0008] This process in which features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus are printed, is commonly known as low-ki lithography, according to the resolution formula CD = k| / Z / NA. where I is the wavelength of radiation employed, NA is the numerical aperture of projection optics in the lithographic projection apparatus, CD is the “critical dimension’-generally the smallest feature size printed-and ki is an empirical resolution factor. In general, the smaller ki the more difficult it becomes to reproduce a pattern on the substrate that resembles the shape and dimensions planned by a designer in order to achieve particular electrical functionality and performance. To overcome these difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase shifting patterning devices, optical proximity correction (OPC, sometimes also referred to as “optical and process correction”) in the design layout, or othermethods generally defined as “resolution enhancement techniques” (RET). Overlay metrology plays a key part in these fine tuning steps.SUMMARY

[0009] Measuring overlay using a microscope based sensor is described. The signal from the sensor is an intensity modulated fringe pattern (e.g., an interference pattern). The sensor is configured to generate the intensity modulated fringe pattern based on diffracted radiation received from a metrology target with a specific design. The metrology target comprises a first metrology mark in a first layer of a patterned substrate and a second metrology mark that is below the first metrology mark, in a second layer of the patterned substrate. The first metrology mark comprises a first segment associated with a first direction of the diffracted radiation and a second segment associated with a second direction of the diffracted radiation. The second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of the diffracted radiation. The first and third segments, and the second and fourth segments, are arranged in non-overlapping positions in the first and second layers. A partitioned wedge is configured to direct + / -nth orders of the diffracted radiation from the first and third segments, and thus from the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation, onto different areas of the sensor for generating the intensity modulated fringe pattern. Overlay is determined based on the intensity modulated fringe pattern. This makes overlay measurements insensitive (or at least less sensitive compared to prior systems) to system vibrations and / or isoplanatic aberrations, among other advantages.

[0010] According to an embodiment, an overlay metrology system is provided. The system comprises a radiation sensor configured to generate a metrology signal based on diffracted radiation received from a metrology target in a patterned substrate. The metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation from the metrology target. The metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate. The first metrology mark comprises a first segment associated with a first direction of the diffracted radiation and a second segment associated with a second direction of the diffracted radiation. The first metrology mark is above the second metrology mark in the patterned substrate. The second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of the diffracted radiation. The first and third segments, and the second and fourth segments, are arranged in nonoverlapping positions in the first and second layers. The system comprises a partitioned wedge configured to direct + / - nth orders of the diffracted radiation from: the first and third segments, and thus from the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation, onto different areas of the radiation sensor for generating the intensity modulated fringe pattern. The system comprises one or more processors operativelycoupled to the radiation sensor. The one or more processors are configured to determine parameters associated with fringes in the intensity modulated fringe pattern, and determine one or more overlay values for the metrology target based on the parameters.

[0011] In some embodiments, the first and third segments, and the second and fourth segments, are arranged symmetrically about an axis of the metrology target in the non-overlapping positions in the first and second layers. The axis is orthogonal to a plane of the patterned substrate. The intensity modulated fringe pattern comprises individual intensity modulated fringe sub-patterns for interfering + / - nth orders of the diffracted radiation from each of: the first and third segments, and thus the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation. The one or more processors are configured to determine the one or more overlay values based on the individual intensity modulated fringe sub-patterns.

[0012] In some embodiments, the + / - nth orders of the diffracted radiation comprise + / - first order diffracted radiation.

[0013] In some embodiments, the first and third segments are associated with an x direction, and the second and fourth segments are associated with a y direction. In some embodiments, the first segment is a top x segment, the third segment is a bottom x segment, the second segment is a top y segment, and the fourth segment is a bottom y segment. In some embodiments, the partitioned wedge comprises an eight fold wedge or a four fold wedge. The eight fold wedge is configured to direct Oth order x, Oth order y, interfering + / - 1st order diffracted radiation associated with the top x segment, interfering + / -1st order diffracted radiation associated with the bottom x segment, interfering + / - 1st order diffracted radiation associated with the top y segment, and interfering + / - 1st order diffracted radiation associated with the bottom y segment to different areas of the radiation sensor. The interfering + / - 1st order diffracted radiation associated with the top x segment, and the interfering + / - 1st order diffracted radiation associated with the bottom x segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top x segment and the + / - 1st order diffracted radiation associated with the bottom x segment are naturally separated by their relative positions in a plane of the patterned substrate. The interfering + / - 1st order diffracted radiation associated with the top y segment, and the interfering + / - 1st order diffracted radiation associated with the bottom y segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top y segment and the + / - 1st order diffracted radiation associated with the bottom y segment are naturally separated by their relative positions in the plane of the patterned substrate.

[0014] In some embodiments, the Oth order x, and Oth order y diffracted radiation are completely or partially blocked by one or more additional components of the system at an exit pupil plane or any equivalent plane in the radiation sensor. In some embodiments, x and y -1st and +lst orders of diffracted radiation all share a same first wedge angle but with angles of opposite sign for x and y directions, and Oth order x and y diffracted radiation also shares a same second wedge angle but with angles of oppositesign for x and y directions. In some embodiments, + / -lst order x and Oth order y diffracted radiation share a same first wedge angle, and + / -lst order y and Oth order x diffracted radiation share a same second wedge angle.

[0015] In some embodiments, the Oth orders of diffracted radiation as used for generation of the + / -nth orders of diffracted radiation are pointwise coherent, and thus the + / - nth orders of the diffracted radiation from the first and third segments, and from the second and fourth segments, are also pointwise coherent.

[0016] In some embodiments, the one or more overlay values comprise an x direction overlay value and a y direction overlay value.

[0017] In some embodiments, the parameters associated with fringes in the intensity modulated fringe pattern comprise amplitude and position offset.

[0018] In some embodiments, the second metrology mark comprises the third segment associated with the first direction of the diffracted radiation in the second layer, and the fourth segment associated with the second direction of the diffracted radiation in a third layer that is below the second layer of the metrology target.

[0019] In some embodiments, the first and second segments of the first metrology mark are combined, and the third and fourth segments of the second metrology mark are combined, such that the first and second metrology marks each comprise two dimensional gratings, and such that separate x and y segments are not required.

[0020] In some embodiments, the system comprises a radiation source operatively coupled to the one or more processors and the radiation sensor. The radiation source is configured to irradiate the two or more metrology targets with radiation.

[0021] In some embodiments, the radiation sensor comprises a camera.

[0022] In some embodiments, the one or more processors are further configured to determine an alignment value for the first layer and / or the second layer based on the diffracted radiation received from the metrology target. In some embodiments, the one or more processors are configured to determine an overlay value as a difference between two alignment values, one for each of two directions of the diffracted radiation.

[0023] In some embodiments, the metrology signal is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.

[0024] According to another embodiment, a target for a metrology system is provided. The target comprises a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate. The first metrology mark comprises a first segment associated with a first direction of diffracted radiation, and a second segment associated with a second direction of the diffracted radiation. The first metrology mark is above the second metrology mark in the patterned substrate. The second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of thediffracted radiation. The first and third segments, and the second and fourth segments, are arranged in non-overlapping positions in the first and second layers. A radiation sensor is configured to generate a metrology signal based on the diffracted radiation received from the first and second marks of the metrology target. The metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation. One or more processors are operatively coupled to the radiation sensor and configured to determine parameters associated with fringes in the intensity modulated fringe pattern, and determine one or more overlay values for the metrology target based on the parameters.

[0025] According to another embodiment, a metrology method comprising one or more of the operations described above is provided.

[0026] According to another embodiment, a non-transitory computer readable medium having instructions thereon is provided. The instructions when executed by a computer comprising one or more processors, cause the computer to perform a method comprising one or more of the operations described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above aspects and other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

[0028] Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.

[0029] Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0030] Fig. 3 schematically depicts an example metrology system, according to an embodiment.

[0031] Fig. 4 schematically depicts an example metrology technique, according to an embodiment.

[0032] Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.

[0033] Fig. 6 illustrates a metrology method, according to an embodiment.

[0034] Fig. 7 illustrates an example embodiment of a metrology target, according to an embodiment.

[0035] Fig. 8 illustrates metrology target concepts, according to an embodiment.

[0036] Fig. 9 illustrates a metrology target (with x and y segments in top and bottom layers of the target - see Fig. 7 for additional detail), an eight fold portioned wedge (also see Fig. 3), and an image comprising an intensity modulated fringe pattern, according to an embodiment.

[0037] Fig. 10 illustrates the aberration insensitivity of the present techniques, according to an embodiment.

[0038] Fig. 11 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0039] In semiconductor device manufacturing, determining overlay typically includes determining the (relative) positions of different metrology marks of a metrology target, such as a diffraction based overlay target, in different layers of a semiconductor device structure. In order to meet smaller and smaller node sizes, and / or to make more efficient use of limited substrate real estate, smaller and smaller metrology (overlay, etc.) targets, multi-purpose targets (e.g., one metrology target that can be used for both overlay and alignment), and / or other space saving techniques are needed. Smaller targets and / or targets that can be used for multiple purposes facilitate a need for less targets, placement of targets in a field with a limited area, placement of targets closer to the edges of a substrate, and / or other advantages.

[0040] Existing metrology systems often utilize separate sensors and metrology targets for overlay and alignment operations. This can cause differences between aligned position and overlay, even when measuring the same marks, which can degrade On Product Overlay (OPO) and / or have other negative effects. Also, current overlay measurement solutions are sensitive to surrounding structures, so that more real estate on a substrate is required for a given overlay target and / or an overlay target may be more difficult to place on a substrate among the surrounding structures because of the sensitivity to scattering from the surrounding structures. For example, an overlay target may be made large so that a region of interest within the target, surrounded by a buffer portion of the target that separates the region of interest from other structures beyond the target, may be used. As another example, an overlay target may be placed some distance away from other structures on a substrate. Further, current overlay measurement systems are often sensitive to vibrations, aberrations, and / or other environmental factors.

[0041] In contrast to prior systems (which operate in a dark-field mode), the present systems and methods are configured for determining overlay using a fringe pattern (or fringe patterns) in images detected with a microscope based sensor. Using specific measures, overlay measurements can be made insensitive (or at least less sensitive compared to prior systems) to system vibrations and / or isoplanatic aberrations, among other advantages. The present systems and methods have these and other advantages because sensor output signals are generated based on diffracted radiation received from a metrology target having pads with different segments (e.g., gratings) in first and second metrology marks in first and second layers of a patterned substrate. Signal formation and related signal processing are performed for gratings in the pads. Overlay can be determined based on this signal processing (and alignment can be similarly determined).

[0042] By way of a brief introduction, the following description relates generally to semiconductor device manufacturing and patterning processes. Although specific reference may be made in this text to the measurement of overlay and the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that the description has many other possible applications. For example, it may be employed in the measurement of other parameters (e.g., alignment, etc.). It may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer”or “die” in this text should be considered as interchangeable with the more general terms “mask”, “substrate” and “target portion”, respectively.

[0043] Fig. 1 schematically depicts an embodiment of a lithographic apparatus LA. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation, or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT (e.g., WTa, WTb or both) configured to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies and often referred to as fields) of the substrate W. The projection system is supported on a reference frame RF. As depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array, or employing a reflective mask).

[0044] The illuminator IL receives a beam of radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising for example suitable directing mirrors and / or a beam expander. In other cases, the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0045] The illuminator IL may alter the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non-zero within an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a plurality of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in a pupil plane of the illuminator IL may be referred to as an illumination mode.

[0046] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as o-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. Forexample, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator.

[0047] The illuminator IL may be operable to alter the polarization of the beam and may be operable to adjust the polarization using adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as a polarization mode. The use of different polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across a pupil plane of the illuminator IL. The polarization direction of radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen in dependence on the illumination mode. For multi-pole illumination modes, the polarization of each pole of the radiation beam may be generally perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, for a dipole illumination mode, the radiation may be linearly polarized in a direction that is substantially perpendicular to a line that bisects the two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as X-polarized and Y-polarized states. For a quadrupole illumination mode, the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as XY polarization. Similarly, for a hexapole illumination mode the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as TE polarization.

[0048] In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0049] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, forexample with respect to the projection system. Any use of the terms “reticle” or “mask” may be considered synonymous with the more general term “patterning device.”

[0050] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of the substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in a target portion of the device, such as an integrated circuit.

[0051] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.

[0052] The term “projection system” should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” may be considered as synonymous with the more general term “projection system”.

[0053] The projection system PS may comprise a plurality of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct for aberrations (phase variations across the pupil plane throughout the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system where its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and / or deform one or more optical elements. Displacement of an optical element may be in any direction (x, y, z, or a combination thereof). Tilting of an optical element is typically out of a plane perpendicular to the optical axis, by rotating about an axis in the x and / or y directions although a rotation about the z axis may be used for a non-rotationally symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and / or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and / orby using one or more heating elements to heat one or more selected regions of the optical element. In general, it may not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). The transmission map of a projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithography apparatus LA. Using a computational lithography technique, the patterning device MA may be designed to at least partially correct for apodization.

[0054] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g., two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system without a substrate that is dedicated to, for example, facilitating measurement, and / or cleaning, etc.). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0055] In operation of the lithographic apparatus, a radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a shortstroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0056] The depicted apparatus may be used in at least one of the following modes. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). Thesubstrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0057] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0058] The substrate may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multilayer IC, so that the term substrate may also refer to a substrate that already includes multiple processed layers.

[0059] The terms “radiation” and “beam” used with respect to lithography encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0060] Various patterns on or provided by a patterning device may have different process windows, i.e., a space of processing variables under which a pattern will be produced within specification. Examples of pattern specifications that relate to potential systematic defects include checks for necking, line pull back, line thinning, CD, edge placement, overlapping, resist top loss, resist undercut and / or bridging. The process window of the patterns on a patterning device or an area thereof may be obtained by merging (e.g., overlapping) process windows of each individual pattern. The boundary of the process window of a group of patterns comprises boundaries of process windows of some of the individual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0061] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and postexposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input / output port I / O 1 , 1 / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0062] In order that a substrate that is exposed by the lithographic apparatus is exposed correctly and consistently and / or in order to monitor a part of the patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties such as alignment, overlay (which can be, for example, between structures in overlying layers or between structures in a same layer that have been provided separately to the layer by, for example, a double patterning process), line thickness, critical dimension (CD), focus offset, a material property, etc. Accordingly, a manufacturing facility in which lithocell LC is located also typically includes a metrology system that measures some or all of the substrates W (Fig. 1) that have been processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example it may be part of the lithographic apparatus LA (such as alignment sensor AS (Fig. 1)).

[0063] The one or more measured parameters may include, for example, overlay between successive layers formed in or on the patterned substrate, alignment, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. This measurement is often performed on a dedicated metrology target provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and / or at other times.

[0064] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image-based measurement tool and / or various specialized tools. A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this may be termed diffraction-based metrology. One such application of this diffractionbased metrology is in the measurement of overlay and / or alignment (e.g., as described below).

[0065] Thus, in a device fabrication process (e.g., a patterning process or a lithography process), a substrate or other objects may be subjected to various types of measurement during or after the process. The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two or more layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes. Examples of measurement include optical imaging (e.g., optical microscope), non-imaging optical measurement (e.g., measurement based on diffraction such as the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profiling using a stylus, atomic force microscopy (AFM)), and / or non-optical imaging (e.g., scanning electron microscopy (SEM)).

[0066] Metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, an adjustment may be made to exposure of a subsequent substrate (especially if the inspection can be done soon and fast enough that one or more other substrates of the batch are still to be exposed) and / or to subsequent exposure of the exposed substrate. Also, an already exposed substrate may be stripped and reworked to improve yield, or discarded, thereby avoiding performing further processing on a substrate known to be faulty. In a case where only some target portions of a substrate are faulty, further exposures may be performed only on those target portions which meet specifications. Other manufacturing process adjustments are contemplated.

[0067] A metrology system may be used to determine one or more properties of the substrate structure, and in particular, how one or more properties of different substrate structures vary, or different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or the lithocell LC, or may be a stand-alone device.

[0068] To enable metrology, often one or more targets are specifically provided on the substrate. A target may include an overlay target, for example, an alignment mark, and / or other targets. Typically, the target is specially designed and may comprise one or more periodic structures. For example, the target on a substrate may comprise one or more 1-D periodic structures (e.g., geometric features such as gratings) in one or more layers of the substrate, which are printed such that after development, the periodic structural features are formed of solid resist lines. As another example, the target may comprise one or more 2-D periodic structures (e.g., gratings) in one or more layers, which are printed such that after development, the one or more periodic structures are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0069] Fig. 3 depicts an example metrology system 10 that may be used to detect overlay, alignment, and / or perform other metrology operations. It comprises a radiation source 2 which projects or otherwise irradiates radiation 8 onto a substrate W. Substrate W may typically include a metrology target 30 such as an overlay target, an alignment mark, and / or other structures. Diffracted or otherwise redirected radiation 8 is passed to a radiation sensor 4 such as a camera, a spectrometer detector, and / orother sensors, which measures a spectrum (intensity) of the specular reflected and / or diffracted radiation, as shown, e.g., in the graph on the left of Fig. 4. System 10 may include one or more optical components such as a wedge 6, one or more lenses, one or more mirrors, etc., configured to direct diffracted or otherwise redirected radiation 8 (or portions thereof) to sensor 4 (or onto specific areas thereof), and / or radiation 8 from source 2 onto substrate W. Sensor 4 may generate a metrology signal conveying overlay data, alignment data, and / or other data indicative of properties of the diffracted and / or reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in Fig.4, or by other operations. Note that these are generalized examples. Often, illumination of a target such as overlay target and / or an alignment mark is done orthogonal to the target and / or mark, and not at an angle as shown in Fig. 3.

[0070] As in the lithographic apparatus LA in Fig. 1, one or more substrate tables (not shown in Fig.4) may be provided to hold the substrate W during metrology operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where metrology system 10 is integrated with the lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a metrology system 10, and / or another measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest of a structure (e.g., an overlay target and / or an alignment mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at different locations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to the focus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. Provided the relative position of the substrate and the optical system is correct, it does not matter in principle which one of those is moving, or if both are moving, or a combination of a part of the optical system is moving (e.g., in the Z and / or tilt direction) with the remainder of the optical system being stationary and the substrate is moving (e.g., in the X and Y directions, but also optionally in the Z and / or tilt direction).

[0071] For typical metrology measurements, a target 30 on substrate W may be a 1-D grating, which is printed such that after development, the bars are formed of solid resist lines (e.g., which may be covered by a deposition layer), and / or other materials. Or the target 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and / or other features in the resist. The bars, pillars, vias, and / or other features may be etched into or on the substrate (e.g., into one or more layers on the substrate), deposited on a substrate, covered by a deposition layer, and / or have other properties. In some embodiments (e.g., as described below), target 30 may include structuresin more than one layer of a substrate. Target 30 (e.g., of bars, pillars, vias, etc.) is sensitive to changes in processing in the patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in target 30. Accordingly, the measured data from target 30 may be used to determine an adjustment for one or more of the manufacturing processes, and / or used as a basis for making the actual adjustment. Note that in this example, target 30 may represent one or more layers comprising one or more metrology marks.

[0072] For example, the measured data from target 30 may indicate overlay for layers of a semiconductor device, alignment, and / or other information. The measured data from target 30 may be used (e.g., by the one or more processors) for determining one or more semiconductor device manufacturing process parameters based the alignment, overlay, and / or other information, and / or determining an adjustment for a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology target (e.g., an overlay target and / or an alignment mark) design, a semiconductor device design, an intensity of the radiation, an incident angle of the radiation, a wavelength of the radiation, a pupil size and / or shape, a resist material, and / or other process parameters.

[0073] Fig. 5 illustrates a plan view of a typical target 30 (e.g., an overlay target, an alignment mark, etc.), or a portion thereof, and the extent of a radiation illumination spot S in the system of Fig. 3. Typically, to obtain a diffraction spectrum that is free of interference from surrounding structures, the target 30, in an embodiment, comprises one or more periodic structures (e.g., gratings) larger than the width (e.g., diameter) of the illumination spot S. The width of spot S may be smaller than the width and length of the target 30. The target 30, in other words, is ‘underfilled’ by the illumination, and the diffraction signal is essentially free from any signals from product features and the like outside the target itself. The illumination arrangement may be configured to provide illumination of a uniform intensity across a back focal plane of an objective, for example. Alternatively, by, for example, including an aperture in the illumination path, illumination may be restricted to on axis or off axis directions.

[0074] Fig. 6 illustrates a metrology method 600. In some embodiments, method 600 is performed as part of a semiconductor device manufacturing process. In some embodiments, one or more operations of method 600 may be implemented in or by (metrology) system 10 illustrated in Fig. 3 and 4, a computer system (e.g., as illustrated in Fig. 11 and described below), and / or in or by other systems, for example. In some embodiments, method 600 comprises irradiating (operation 602) a metrology target in a patterned substrate (such as a semiconductor wafer) with radiation, directing (operation 604) diffracted radiation from the metrology target onto different areas of a radiation sensor with a partitioned wedge, generating (operation 606) a metrology signal comprising an intensity modulated fringe pattern based on the received diffracted radiation, determining (operation 608) parameters associated with fringes in the intensity modulated fringe pattern, and determining (operation 610) an overlay value,and / or an overlay value and two related alignment values, based on the metrology signal, and / or other operations.

[0075] The operations of method 600 presented below are intended to be illustrative. In some embodiments, method 600 may be accomplished with one or more additional operations not described, and / or without one or more of the operations discussed. For example, in some embodiments, method 600 may include an additional operation comprising determining an adjustment for a semiconductor device manufacturing process. Additionally, the order in which the operations of method 600 are illustrated in Fig. 6 and described below is not intended to be limiting.

[0076] In some embodiments, one or more portions of method 600 may be implemented in and / or controlled by one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and / or other mechanisms for electronically processing information - see the description of processors PRO). The one or more processing devices may include one or more devices executing some or all of the operations of method 600 in response to (machine readable) instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software to be specifically designed for execution of one or more of the operations of method 600 (e.g., see discussion related to Fig. 11 below).

[0077] Operation 602 comprises irradiating a metrology target in a patterned substrate with radiation. The metrology target comprises one or more structures in the patterned substrate capable of providing a diffraction signal (e.g., a metrology target or some other structure(s)). For operation 602, the metrology target is included in multiple layers of a substrate in a semiconductor device structure. In some embodiments, the metrology target comprises one or more geometric features such as ID or 2D features, and / or other geometric features. By way of several non-limiting examples, a metrology target may comprise a fine-pitched series of lines and / or edges, a set of multiple fine-pitched series of lines and / or edges, and / or other features. In some embodiments, the metrology target can be any structure in a pattern design layout capable of generating a wide angle diffraction signal. In some embodiments, the metrology target is associated with an overlay and / or alignment measurement for the patterned substrate. For example, the metrology target may be or include a dedicated overlay target comprising diffraction gratings in the different layers. The radiation may be diffracted by the diffraction grating(s).

[0078] In operation 602, a radiation source (e.g., source 2 shown in Fig. 3) is configured to irradiate a metrology target (e.g., target 30 shown in Fig. 3) in a patterned substrate (e.g., substrate W shown in Fig. 3) with radiation (e.g., radiation 8 shown in Fig. 3). The metrology target is configured to diffract the radiation. The metrology target comprises a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate. The first metrology mark comprises a first segment associated with a first direction of the diffracted radiation and a second segment associated with a second direction of the diffracted radiation. The second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourthsegment associated with the second direction of the diffracted radiation. In some embodiments, the first and third segments are associated with an x direction, and the second and fourth segments are associated with a y direction, for example.

[0079] The first metrology mark is above the second metrology mark in the patterned substrate. As such, the first segment may be a top x segment, the third segment may be a bottom x segment, the second segment may be a top y segment, and the fourth segment may be a bottom y segment. In addition, the first and third segments (i.e., the top and bottom x segments), and the second and fourth segments (i.e., the top and bottom y segments), are arranged in non-overlapping positions in the first and second layers. Note that in the following discussion and corresponding figures 7-10, the abbreviations “T” may indicate top, “B” may indicate bottom, “E” may indicate empty, “L” may indicate layer (e.g., LI, L2, L3), “BF” may indicate bright-field, and “O” may indicate orders (of diffraction).

[0080] For example, Fig. 7 illustrates a possible embodiment of metrology target 30 (also see Fig. 3). Fig. 7 illustrates a top view 702, and a perspective view 704 of target 30. Target 30 comprises a first metrology mark 726 (indicated by a first dash pattern) in a first (e.g., upper or top) layer 706 (indicated by a second dash pattern) of a patterned substrate (e.g., W shown in Fig. 1, 3, and 5) and a second metrology mark 728 in a second (e.g., bottom or lower) layer 708. First metrology mark 726 in the first (top or upper) layer 706 and / or second metrology mark 728 in the second (bottom or lower) layer 708 can include one or more segments 732, 734, 736, and 738. In this example, two differently oriented gratings (e.g., in x and y directions) make up each metrology mark 726 and 728. First metrology mark 726 comprises a first segment 732 associated with a first direction of diffracted radiation and a second segment 734 associated with a second direction of the diffracted radiation. Second metrology mark 728 comprises a third segment 736 associated with the first direction of the diffracted radiation and a fourth segment 738 associated with the second direction of the diffracted radiation. In some embodiments, the first and third segments 732 and 736 are associated with an x direction of the diffracted radiation, and the second and fourth segments 734 and 738 are associated with a y direction, for example, as shown in Fig. 7. First metrology mark 726 is above second metrology mark 728 in the patterned substrate. As such, first segment 732 may be a top x segment, third segment 736 may be a bottom x segment, second segment 734 may be a top y segment, and fourth segment 738 may be a bottom y segment. In addition, the first and third segments 732 and 736 (i.e., the top and bottom x segments), and the second and fourth segments 734 and 738 (i.e., the top and bottom y segments), are arranged in non-overlapping positions in the first and second layers 706 and 708 (e.g., as indicated by the blank or open areas in each of layers 706 and 708 in Fig. 7).

[0081] In some embodiments, as shown in Fig. 7, the first and third segments 732 and 736, and the second and fourth segments 734 and 738, are arranged symmetrically about an axis 750 of metrology target 30 in the non-overlapping positions in the first and second layers 706 and 708. Axis 750 isorthogonal to a plane (e.g., a plane parallel to layers 706 and 708) of the patterned substrate (e.g., substrate W shown in Fig. 3).

[0082] In some embodiments (conceptually shown in inset 790 in Fig. 7), the second metrology mark 728 comprises the third segment 736 associated with the first direction (e.g., the x direction) of the diffracted radiation in second layer 708, and fourth segment 738 associated with the second direction (e.g., the y direction) of the diffracted radiation in a third layer that is below second layer 708 of metrology target 30 (e.g., so that target 30 comprises three layers instead of two).

[0083] In some embodiments, the first and second segments 732 and 734 of first metrology mark 726 are combined, and third and fourth segments 736 and 738 of second metrology mark 728 are combined, such that first and second metrology marks 728 and 728 each comprise two dimensional gratings, and such that separate x and y segments are not required. Also note, that even though just two layers, or three layers, with one overlay value (for each of two directions x and y) is described, these concepts can be generalized by N layers with N-l overlay values. And following that generalization, the layers need not necessarily be consecutive layers.

[0084] These targets (e.g., target 30 and similar targets) are suited for the sensor concept described herein in view of overlay metrology, whereas traditional uDBO targets are not suited for this type of overlay metrology. Several additional signal processing measures have to be taken when using the traditional uDBO targets, and even then, their performance is limited in terms of robustness of overlay inference. Target 30 and similar targets have several advantages over the use of typical micro diffraction based overlay (pDBO) targets, including insensitivity to vibrations, insensitivity to (isoplanatic) aberrations, and / or other advantages. In addition, target 30 and similar targets can also deal with non-isoplanatic aberrations, which requires knowledge of offset in the X / Y position of the target with respect to a so-called nodal point, which is the origin in field-space with respect to which the field-dependence of these non-isoplanatic aberrations is modelled.

[0085] Returning to Fig. 6 and operation 602, the radiation (e.g., radiation 8 shown in Fig. 3) may have a target wavelength and / or wavelength range, a target intensity, and / or other characteristics. The target wavelength and / or wavelength range, the target intensity, etc., may be entered and / or selected by a user, determined by the system based on previous metrology measurements, and / or determined in other ways. In some embodiments, the radiation comprises light and / or other radiation. In some embodiments, the light comprises visible light, infrared light, near infrared light, and / or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry. In some embodiments, the radiation comprises two incident mutually coherent beams oriented at different angles relative to the target. The two incident beams are configured to be diffracted by the first and second metrology marks of the target to form the diffracted radiation.

[0086] The radiation may be generated by a radiation source (e.g., source 2 shown in Fig. 3 and described above) of the metrology system (e.g., system 10 shown in Fig. 3), and / or other components. The radiation source may be operatively coupled to one or more processors (e.g., processor(s) PROdescribed herein), one or more radiation sensors (e.g., sensor 4 as described herein), and / or other components. In some embodiments, the radiation may be directed by the radiation source (e.g., by way of one or more lenses, mirrors, and / or other components) onto a metrology target (e.g., metrology target 30 shown in Fig. 3 and Fig. 7), sub-portions (e.g., something less than the whole) of a metrology target, multiple metrology targets, and / or onto a substrate in other ways.

[0087] In some embodiments, metrology target 30 (Fig. 3, Fig. 7) may be substantially stationary while irradiation occurs, a radiation sensor generates a metrology signal, an image of the metrology target is generated based on a metrology signal and / or other information, and / or other operations are performed. In some embodiments, characteristics of the radiation (e.g., wavelength, intensity, etc.) may be varied by the radiation source over time (whether in a stationary or a scanning mode). This may create and / or supplement time varying radiation for analysis. This may also facilitate analysis of individual portions of a feature, comparison of one portion of a feature to another and / or to other features, and / or other analysis.

[0088] Operation 604 comprises directing diffracted radiation (e.g., diffracted radiation 8 shown in Fig. 3) from the metrology target (e.g., target 30 shown in Fig. 3 and Fig. 7) onto different areas of the radiation sensor (e.g., sensor 4 shown in Fig. 3) with a partitioned wedge (e.g., wedge 6 shown in Fig.3) and / or other components. An example partitioned wedge is shown in Fig. 9 and 10, and further described below. For areas of the wedge which have the same slope the radiation related to these areas will be directed to the same location on the radiation sensor. Interference takes place at the radiation sensor, and therefore the + / - nth order diffracted radiation is directed to the same area on the radiation sensor. Equivalently formulated as a sentence of two steps, (1) first certain portions of the radiation are directed to the same area on the radiation sensor; and (2) interference at the radiation of these directed portions of radiation then occurs.

[0089] The partitioned wedge is configured to direct + / - nth orders of the diffracted radiation from: the first and third segments (e.g., segments 732 and 736 in Fig. 7), and thus from the first direction (e.g., the x direction in Fig. 7) of the diffracted radiation, and the second and fourth segments (e.g., segments 734 and 738 in Fig. 7), and thus the second direction (e.g., the y direction in Fig. 7) of the diffracted radiation, onto the different areas of the radiation sensor (which is then used for generating the intensity modulated fringe pattern). In some embodiments, the + / - nth orders of the diffracted radiation comprise + / - first order diffracted radiation, and / or diffracted radiation of other orders.

[0090] In some embodiments, the partitioned wedge (e.g., wedge 6 shown in Fig. 3, and the partitioned wedge described below with respect to Figs. 9 and 10) comprises an eight fold wedge or a four fold wedge. The eight fold wedge may be configured to direct Oth order x, Oth order y, interfering + / - 1st order diffracted radiation associated with the top x segment (e.g., segment 732 from Fig. 7), interfering + / - 1st order diffracted radiation associated with the bottom x segment (e.g., segment 736), interfering + / - 1st order diffracted radiation associated with the top y segment (e.g., segment 734), and interfering + / - 1st order diffracted radiation associated with the bottom y segment (e.g., segment 738) to differentareas of the radiation sensor (e.g., sensor 4 shown in Fig. 3). The interfering + / - 1st order diffracted radiation associated with the top x segment, and the interfering + / - 1st order diffracted radiation associated with the bottom x segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top x segment and the + / - 1st order diffracted radiation associated with the bottom x segment are naturally separated by their relative positions in a plane of the patterned substrate (e.g., substrate W shown in Fig. 3). The interfering + / - 1st order diffracted radiation associated with the top y segment, and the interfering + / - 1st order diffracted radiation associated with the bottom y segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top y segment and the + / - 1st order diffracted radiation associated with the bottom y segment are naturally separated by their relative positions in the plane of the patterned substrate (e.g., see Fig. 9 and related discussion below). The Oth order x, and Oth order y diffracted radiation may be completely or partially blocked by one or more additional components of the system (e.g., one or more optical components of system 10 shown in Fig. 3) at an exit pupil plane or any equivalent plane in the radiation sensor (e.g., sensor 4 shown in Fig. 3).

[0091] The Oth orders of diffracted radiation as used for generation of the + / - nth orders of diffracted radiation for overlay inference in the related direction of the at least two directions are pointwise coherent, and thus the + / - nth orders of the diffracted radiation from the diffraction gratings at the first and third segments, and from the diffraction gratings as the second and fourth segments, are also pointwise coherent. Because of the point-wise spatial coherence of the +nth and -nth diffraction orders, an interference pattern can be realized at the radiation sensor, which may be referred to as a (singlepitch) fringe pattern in case of exactly two + / - nth diffraction orders giving rise to the interference.

[0092] In some embodiments, the areas of the wedge where x and y -1st and +lst orders of diffracted radiation reside, may all share a same first wedge angle but with angles of opposite sign for x and y directions. In addition, Oth order x and y diffracted radiation may also share a same second wedge angle, but with angles of opposite sign for x and y directions. In some embodiments, + / - 1st order x and Oth order y diffracted radiation share a same first wedge angle, and + / - 1 st order y and Oth order x diffracted radiation share a same second wedge angle. In some embodiments, the Oth order for y and the + / - 1st orders for x do not share any coherence property (this relates to the point-wise spatial coherence property that applies between + / - 1st order and Oth order that are related to the same direction, either x or y). But important to realize here is that the Oth order for y will generate a (substantially) uniform background image for all pads (e.g., segments), so there will be overlap with the pads related to diffraction in the x-direction. The Oth order y-image will add to the DC-component of the fringe-image for x, and that is not ideal (since it will “eat away” some of the dynamic range at the detector).

[0093] Note that for the Oth orders it is only essential that images generate based on this radiation received by the sensor (e.g., sensor 4 shown in Fig. 3) do not overlap with 1st order images. The Oth order images are not used in further processing to determine overlay (as described herein).

[0094] Operation 606 comprises generating a metrology signal based on the received diffracted radiation (e.g., diffracted radiation 8 received from metrology target 30 in patterned substrate W shown in Fig. 3). The metrology signal is generated by a radiation sensor (e.g., radiation sensor 4 shown in Fig. 3). The radiation sensor may comprise a camera, and / or other components, for example. The spatial resolution of the camera (pixel size) or similar sensor must be good enough (pixel size small enough) to resolve the fringes in the fringe-images. That will also depend on the magnification of the imaging optics, for example.

[0095] The radiation sensor is configured for detecting diffracted (e.g., reflected and / or transmitted) radiation from the metrology target. In some embodiments, detecting such radiation comprises detecting changes in intensity or amplitude, and / or other characteristics of the (diffracted) radiation received from one or more geometric features (e.g., of the gratings as described above) in the target. Changes in intensity or amplitudes may correspond to one or more dimensions of a feature in the target, for example.

[0096] The metrology signal comprises measurement information pertaining to the metrology target (e.g., target 30 shown in Fig. 3 and Fig. 7). For example, the metrology signal may be an overlay signal comprising overlay measurement information, an alignment signal comprising alignment measurement information, a combination thereof, and / or other metrology signals. For overlay, the radiation sensor measures two alignment signals, one for the mark area in the top-layer and one for the mark area in the bottom-layer, and subtraction of these two alignment signals yields the overlay signal for the overlay error between these two layers. Here, the metrology signal comprises overlay and alignment position information for the first and second layers (as described above) conveyed by diffracted radiation from the metrology target. A metrology signal comprises an electronic signal that represents and / or otherwise corresponds to the diffracted radiation from a metrology target. The metrology signal may depend on an overlay value for one or more layer pairs, for example, on an alignment value, and / or on another information. Generating the metrology signal comprises sensing the diffracted radiation and converting the sensed diffracted radiation into the electronic signal. In some embodiments, generating the metrology signal comprises sensing different portions of the diffracted radiation from different portions and / or different geometries of the metrology target (e.g., different gratings in different layers), and combining the different portions of the sensed radiation to form the metrology signal.

[0097] Here, the metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation from the metrology target (e.g., target 30). An example of an intensity modulated fringe pattern is shown and described in PCT International Application Publication No. WO2024 / 208554, titled “Overlay Metrology Based on a Fringe Pattern,” relevant aspects of which are incorporated by reference herein. The intensity modulated fringe pattern may be detected in the form of an image or images such that one or more images showing intensity modulated fringe patterns are output by the radiation sensor. In some embodiments, the intensity modulated fringe pattern comprises individual intensity modulated fringe sub-patterns for interfering + / - nth orders of the diffracted radiation fromeach of the first and third segments (e.g., segments 732 and 736 shown in Fig. 7), and thus the first direction (e.g., the x direction) of the diffracted radiation, and the second and fourth segments (e.g., segments 734 and 738 shown in Fig. 7), and thus the second direction (e.g., the y direction) of the diffracted radiation. Separate signals for the fringe sub-patterns are generated with the partitioned wedge (e.g., wedge 6 shown in Fig. 3, Fig. 9, and Fig. 10), for example. The separate signals and subpatterns comprise an intensity modulated fringe pattern for each of the segments of the metrology marks (comprising top and bottom x and y segments as described above) of the target (e.g., target 30 shown in Fig. 3 and Fig. 7).

[0098] Operation 608 comprises determining parameters associated with fringes in the intensity modulated fringe pattern. The parameters are determined by one or more processors PRO (see Fig. 3 and Fig. 11). As part of operation 608 (and operation 610 described below), the one or more processors are operatively coupled to the radiation sensor (e.g., sensor 4 shown in Fig. 3), the source (e.g., source 2 shown in Fig. 3), and / or other components of the system (e.g., system 10 shown in Fig. 3). The parameters associated with fringes in the intensity modulated fringe pattern comprise amplitude and position offset and / or other parameters (additional information related to these parameters is provided in the discussion of Figs. 8-10 below).

[0099] Operation 610 comprises determining an overlay value, and / or an overlay value and its two related alignment values (e.g., two alignment values relating to one overlay value described above), and / or other operations. The overlay value, and / or an overlay value and its two related alignment values are determined by one or more processors PRO (see Fig. 3 and Fig. 11). The one or more processors are configured to determine an overlay value and / or an alignment value for the first layer and / or the second layer (e.g., layer 706 and / or layer 708 shown in Fig. 7) of the substrate (e.g., substrate W shown in Fig. 3) based on the diffracted radiation received from the metrology target (e.g., target 30 shown in Fig. 3 and Fig. 7). The one or more processors are configured to determine the one or more (e.g., overlay and / or alignment) values based on the individual intensity modulated fringe sub-patterns (see Fig. 9-10, and related discussion below).

[0100] As described above, each metrology mark (e.g., mark 726 and mark 728 shown in Fig. 7) comprises top and bottom segments (e.g., top and bottom x and y gratings - segments 732 -738 shown in Fig. 7) related to a given direction (e.g., x or y) in a two-dimensional plane of the patterned substrate. The given direction comprises a direction for which a measurement will reveal information to estimate the overlay and or alignment value in that direction. The one or more processors are configured to determine an overlay value, and / or an overlay value and its two related alignment values in the given direction in the two-dimensional plane of the patterned substrate, based on the intensity modulated fringe pattern associated with corresponding metrology mark segments. For example, in some embodiments, the one or more processors are configured to determine overlay values comprising an x direction overlay value and a y direction overlay value. In some embodiments, the one or moreprocessors are configured to determine an overlay value as a difference between two alignment values, one for each of two directions (e.g., x and y) of the diffracted radiation.

[0101] Fig. 8-10 provide several additional details related to the techniques described above for method 600 shown in Fig. 6.

[0102] For example, Fig. 8 illustrates metrology target concepts 800. Fig. 8 illustrates target 30, with x and y segments 732-738 in top and bottom layers of target 30 (see Fig. 7 for additional detail). There are two segments per layer, per overlay direction (e.g., x and y). These may also be termed pads, each with a grating in only a single layer, one pad with a grating in the top layer, the other pad with a grating in the bottom layer. The radiation sensor (e.g., sensor 4 in Fig. 4) may detect a fringe-based image (showing an intensity modulated fringe pattern) due to the interference of the two ±lst diffraction orders, for example, as generated by each of the gratings (or segments) - again see PCT International Application Publication No. WO2024 / 208554 for examples. The fringe amplitude (or intensity) together with a fringe position offset (e.g., an x or y position offset of a fringe or fringes in the actual image) yields a complex-valued AC-signal, denoted by SAC. The gratings (e.g., segments 732-738) are assumed to be symmetric, which implies that they have equal complex-valued field amplitudes for +lst and -1st diffracted orders of radiation described by equations Eq. 1 and Eq. 2 below.EropJ=^Top^X=Erop.X Eq. 1EBotx = EBotx* = EBot,x Eq. 2Eq. 1 and Eq. 2 are generated for the x direction. Eq. 1 and Eq. 2 may be similarly generated for the y direction. For the sake of simplicity, it is assumed that without any overlay error, the grating of a segment in the top-layer and the related grating of a segment in the bottom-layer are exactly “in-phase” with each other (referred to above as “coherent” top-to-bottom in target 30), assuming that they will be in-phase at the level of the masks (reticles) that are used for the two layers in the lithographic steps (note that in the case that there is a non-zero phase-offset of these gratings at the level of the masks, it is trivial to include this known value of the latter phase-offset in the signal processing). In equations Eq. 3, Eq. 4, and Eq. 5 discussed below, “o” indicates overlay (in the x direction in this example, but may also be determined in the same way for the y direction), Ki is a known diffraction factor (e.g., proportional to 1 / grating pitch), e4rais a phase factor associated with the lateral displacement of a given segment, E is a complex valued amplitude of the electric field, and AC (later denoted SAC, signal-of-AC) is the complex-valued amplitude of the Fourier component of the fringe-image related to l / (grating pitch) (in a given sub-image - see Fig. 9). This notation has to do with DC (direct, which is nonalternating) and AC (alternating) behavior of a signal, a terminology that is often used in the area of signal processing.

[0103] Target 30 may not be exactly in the center of an incident beam of radiation, thus generating some positional offset denoted by AXAI which leads to a phase-factor in Fourier space, with the phase being linear in spatial frequency, and being proportional to the product of spatial frequency times AXAI . In this example, the Ax for the top x segment may be thought of as an alignment value in x (AXAI), and the bottom x segment or grating has a positional offset which is the sum of the positional offset that is common with that of the segment in the top layer and the overlay value (which is an additional shift of the bottom layer with respect to the top layer).

[0104] The AC-signals (SAC) - equation Eq. 3 shown below for both grating pads have an amplitude given by the diffraction efficiency of the respective single grating (or segment), and a phase which is 2x the linear phase shift for an in-plane position offset denoted by AxTopand AxBotrespectively, and with K i>xbeing the length of the 1st order diffraction vector for the gratings (segments).i 12 A ■ „ A phase \ SACTop X= iFrop^le 711 1,X XTop> AxTop I A _. ,2 , . „ phase / • -> o — &XBot&XTopEq. 3SACBotiX= |ESot,x| - > A%SotJThe in-plane position offsets for the two gratings are given by, with AXAI an “align position” or common position offset of the target as a whole, equations Eq. 4 and Eq. 5 shown below (which could be similarly defined for the y direction).Axrop= AXAIEq. 4AxBot= AXAI+ o Eq. 5Eq. 4 and Eq. 5 show two alignment signals (or values), from which an overlay value is derived by subtraction of the former two alignment values. Subtraction of the two respective “top” and “bottom” position offsets yields the overlay value for that direction (x or y). On each of the two segments in a mark 726 and 728 of target 30 a micro-alignment - see Eq. 3 (i.e., an alignment on a single segment) is carried out using a single image comprising both segments (e.g., as described above, the individual intensity modulated fringe sub-patterns for interfering + / - nth orders of the diffracted radiation from each of the first and third segments (e.g., segments 732 and 736 shown in Fig. 7), and thus the first direction (e.g., the x direction) of the diffracted radiation, and the second and fourth segments (e.g., segments 734 and 738 shown in Fig. 7), and thus the second direction (e.g., the y direction) of the diffracted radiation).

[0105] Fig. 9 illustrates target 30 (with x and y segments 732-738 in top and bottom layers of target 30 - see Fig. 7 for additional detail), an eight fold portioned wedge 6 (also see Fig. 3), and an image 900 comprising an intensity modulated fringe pattern. Individual top x 902, bottom x 904, top y 906, andbotom y 908 paterns comprise sub-paterns, as described above. Image 900 includes a dark field x sub-image 910 (or sub-patern, where only the top x 902 and botom x 904 areas have an image fringe patern) and a dark field y sub-image 912 (or sub-patern, where only the top y 906 and botom y 908 areas have an image fringe patern). The unnumbered top y and botom y areas in dark field x sub-image 910, and top x and botom x in dark field y-sub-image 912 only comprise a (constant) average intensity signal, which is not used for the techniques described herein. The bright-field x sub image 920 and the bright-field y sub image 922 are also unused. In some embodiments, the Oth order diffracted beams can also be blocked at an exit pupil plane, so as not to bother with any bright-field image on the detector (since these areas will be completely dark in such case).

[0106] Eight fold portioned wedge 6 may be used when the four Oth orders (two for x, and two for y) are not blocked by a beam stop in an exit pupil plane, for example. In the blocking case, a simpler four fold wedge with 4 quadrants could be sufficient (like a four fold wedge in prior metrology systems, but with only two angles, one angle with “+”-sign for the two quadrants along the main diagonal, and the same angle but with sign for the two quadrants along the off-diagonal). In Fig. 9, that would mean that each segment containing a 1st order expands to cover its full quadrant in which it is located.

[0107] In the eight fold partitioned wedge 6 in Fig. 9, dividing lines 950 indicate partitions of wedge 6 into eight different areas that are used to direct diffracted radiation to different areas on the radiation sensor (e.g., sensor 4 shown in Fig. 3), which facilitates specific interferences for the generation of the intensity modulated fringe patern (including the sub-paterns) shown in image 900. Wedge 6 may be positioned at or near an exit pupil plane of a metrology system (e.g., system 10 shown in Fig. 3), for example, for joint x and y direction dark-field imaging.

[0108] Eight fold partitioned wedge 6 is configured to direct + / - nth orders of the diffracted radiation from: the first and third segments (e.g., segments 732 and 736 in Fig. 7), and thus from the first direction (e.g., the x direction in Fig. 7) of the diffracted radiation, and the second and fourth segments (e.g., segments 734 and 738 in Fig. 7), and thus the second direction (e.g., the y direction in Fig. 7) of the diffracted radiation, onto the different areas of the radiation sensor (which is then used for generating the intensity modulated fringe patern in image 900). In some embodiments, the + / - nth orders of the diffracted radiation comprise + / - first order diffracted radiation, and / or diffracted radiation of other orders, for example.

[0109] In this example, wedge 6 is configured to direct Oth order x, Oth order y, interfering + / - 1st order diffracted radiation associated with the top x segment (e.g., segment 732 from Fig. 7), interfering + / -1st order diffracted radiation associated with the botom x segment (e.g., segment 736), interfering + / -1st order diffracted radiation associated with the top y segment (e.g., segment 734), and interfering + / -1st order diffracted radiation associated with the botom y segment (e.g., segment 738) to different areas of the radiation sensor (e.g., sensor 4 shown in Fig. 3). The + / - 1st order diffracted radiation associated with the top x segment (e.g., segment 732 from Fig. 7), and + / - 1st order diffracted radiation associated with the botom x segment (e.g., segment 736) are subject to the same wedge angle. Also, the + / - 1storder diffracted radiation associated with the top y segment (e.g., segment 734), and the + / - 1st order diffracted radiation associated with the bottom y segment (e.g., segment 738) are subject to the (another) same wedge angle. The interfering + / - 1st order diffracted radiation associated with the top x segment, and the interfering + / - 1st order diffracted radiation associated with the bottom x segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top x segment and the + / - 1st order diffracted radiation associated with the bottom x segment are naturally separated by their relative positions in a plane of the patterned substrate (e.g., substrate W shown in Fig. 3). The interfering + / - 1st order diffracted radiation associated with the top y segment, and the interfering + / - 1st order diffracted radiation associated with the bottom y segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top y segment and the + / - 1st order diffracted radiation associated with the bottom y segment are naturally separated by their relative positions in the plane of the patterned substrate (e.g., see Fig. 9 and related discussion below). In this example, on wedge 6, corresponding solid arrows are arranged in pairs, with a pair of arrows 970 and a pair of arrows 980 directing + / 1storder x and y diffracted radiation respectively, onto the radiation detector to form corresponding subimages (or sub-patterns) 902-908.

[0110] The fringe amplitude (or intensity) together with a fringe position offset (e.g., an x or y position offset of a fringe or fringes in the actual sub-images 902-908) yields a complex-valued AC-signal, denoted by SAC shown in Fig. 8. Using these SAC signals, overlay (e.g., “o” in Eqs. 3-5) can be determined for each direction (e.g., x and y) as described above. It should be noted that the use of the eight fold wedge is a good way to reduce crosstalk between x and y segments of a target.

[0111] Using these techniques, overlay determinations are largely insensitive to vibrations. For this discussion, vibrations are separated into out-of-plane (Az(t)) and in-plane vibrations (Ax(t), Ay (t)) (with xy being the 2D wafer plane, z being the normal to the 2D wafer plane, and with t referring to time). For out-of-plane vibrations, the two + / -lst diffraction orders may be symmetrically positioned with respect to an optical axis which is located at the center of an exit pupil of the metrology system (e.g., system 10 shown in Fig. 3), both for the x and for the y direction, the radiation sensor is basically insensitive to out-of-plane vibrations (as it is to any even aberration). For in-plane vibrations, fringes in an intensity modulated fringe pattern are sensitive to in-plane vibrations. These vibrations will both reduce the fringe amplitude as well as cause a fringe shift. The latter fringe shift can be seen as part of the overall “align position” offset (e.g., AxAior AyAi), since it is common to both segments in a mark of target 30 (Fig. 3, 7, etc.). Upon subtraction of the two phases (one phase for each segment) as described above, this overall position offset cancels out. Further, the vibration-induced amplitude reduction is irrelevant since via the two micro-alignments, only phase-offset is used for the inference of overlay.

[0112] Fig. 10 illustrates the aberration insensitivity of the present techniques. Fig. 10 illustrates target 30, partitioned wedge 6, and dark field x sub-image 910 (or sub-pattern, where only the top x 902 andbotom x 904 areas have an image fringe patern). Note that this discussion is easily adjusted for the y direction, even though it is not shown in Fig. 10. Fig. 10 is focused on the dark-field image in the x-direction only, and a corresponding exit pupil, in view of its odd aberration (in)sensitivity on top of its natural even aberration insensitivity. The fringe-patern (AC-signal) in sub-image 910 is realized via the cross-interference of the two 1st diffraction orders in the exit pupil of the metrology system, which are symmetrically positioned with respect to an optical axis (which is located in the center of the exit pupil). Such a symmetric alignment implies that the two orders are suffering from an identical effect due to even aberrations, whereas the effect due to odd aberrations is equal in size but has opposite signs for the two orders. Upon interference, the even aberrations therefore cancel out, and the (in magnitude identical) odd aberrations add together to twice the effect. Conveniently, the remaining odd aberrations affect the phase of the two segments (top x and botom x) in the same way, so that after the subtraction of the two respective phases according to equation Eq. 6, the odd aberrations are also canceled out.Si4CTopjc = IE’TOP'XI e4711 K1^4XT°P e4711> K1>xAxTop+ xodd(Kl x) A O = AxBot-SACBotiX=K1,xAxBot+ xodd(K1>x) xTopEq. 6As a result of the above argumentation, the present techniques are insensitive to (isoplanatic) aberrations. Note that with some extra measures, mitigation of field-dependent non-isoplanatic aberrations is possible for the presented overlay inference methodology.

[0113] Returning to Fig. 6, in some embodiments, operation 610 comprises determining an adjustment for a semiconductor device manufacturing process. In some embodiments, operation 610 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on an overlay value, an alignment value, and / or other information. The one or more parameters may include a parameter of the radiation (the radiation used for determining overlay and / or alignment), an overlay and / or alignment inspection location on a layer of a semiconductor device structure, and / or other parameters. In some embodiments, process parameters can be interpreted broadly to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation (used for exposing resist, etc.), an incident angle of the radiation (used for exposing resist, etc.), a wavelength of the radiation (used for exposing resist, etc.), a pupil size and / or shape, a resist material, or any other material as used in the layer stack on top of the substrate, and the optical constants of refractive index (n) and absorption coefficient (k) of each of these material for the multiple wavelengths as used in a given metrology tool, and / or other parameters.

[0114] A parameter of the radiation used for determining overlay and / or alignment, for example, may include a wavelength, an intensity, an angle of incidence, and / or parameters of the radiation. Theseparameters may be adjusted to better measure features with specific shapes, enhance the intensity of reflected radiation, increase and / or otherwise enhance (e.g., maximize) phase and / or amplitude shifts (if any) in reflected radiation from one area of a feature to the next, and / or for other purposes. This may enable and / or enhance detection of more subtle deviations, make phase and / or amplitude shifts easier to detect, and / or have other advantages.

[0115] In some embodiments, operation 610 includes determining a process adjustment based on the one or more determined semiconductor device manufacturing process parameters, adjusting a semiconductor device manufacturing apparatus based on the determined adjustment, and / or other operations. For example, based on a measured overlay and / or alignment value, a lithography exposure may be corrected. As another example, if a determined overlay and / or alignment value is not within process tolerances, the misalignment may be caused by one or more manufacturing processes whose process parameters have drifted and / or otherwise changed so that the process is no longer producing acceptable devices (e.g., overlay and / or alignment measurements may breach a threshold for acceptability), which observations may require a rework of the few last steps of wafer processing. One or more new or adjusted process parameters may be determined based on the overlay and / or alignment determination. The new or adjusted process parameters may be configured to cause a manufacturing process to again produce acceptable devices. For example, a new or adjusted process parameter may cause a previously unacceptable overlay and / or alignment value to be adjusted back into an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. If there is a difference, that difference may be used to determine an adjustment for an apparatus that is used to produce the devices (e.g., parameter “x” should be increased / decreased / changed so that it matches the new or adjusted version of parameter “x” determined as part of operation 610), for example. In some embodiments, operation 610 may include electronically adjusting an apparatus (e.g., based on the determined process parameters). Electronically adjusting an apparatus may include sending an electronic signal, and / or other communications to the apparatus, for example, which causes a change in the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and / or other adjustments.

[0116] Fig. 11 is a diagram of an example computer system CS that may be used for one or more of the operations described herein. Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. Astorage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0117] Computer system CS may be coupled via bus BS to a display DS, such as a flat panel or touch panel display for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[0118] In some embodiments, portions of one or more methods and / or one or more operations of such method(s) may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions included in main memory MM causes processor PRO to perform the process steps (operations). One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, this description is not limited to any specific combination of hardware circuitry and software.

[0119] The term “computer-readable medium” or “machine-readable medium” refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a hard disk, a magnetic medium, an optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non-transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the operations described. Transitory computer-readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[0120] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions intoits dynamic memory and send the instructions. Computer system CS can receive the data and convert the data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0121] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0122] Network link NDL typically provides data communication through one or more networks to other data devices. For example, network link NDL may provide a connection through local network LAN to a host computer HC. This can include data communication services provided through the worldwide packet data communication network, now commonly referred to as the “Internet” INT Local network LAN (Internet) may use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network data link NDL and through communication interface CI, which carry the digital data to and from computer system CS, are exemplary forms of carrier waves transporting the information.

[0123] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0124] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. An overlay metrology system, comprising: a radiation sensor configured to generate a metrology signal based on diffracted radiation received from a metrology target in a patterned substrate, the metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation from the metrology target, wherein: the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate; the firstmetrology mark comprises a first segment associated with a first direction of the diffracted radiation and a second segment associated with a second direction of the diffracted radiation; the first metrology mark is above the second metrology mark in the patterned substrate; the second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of the diffracted radiation; and the first and third segments, and the second and fourth segments, are arranged in non-overlapping positions in the first and second layers; a partitioned wedge configured to direct + / - nth orders of the diffracted radiation from: the first and third segments, and thus from the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation, onto different areas of the radiation sensor for generating the intensity modulated fringe pattern; and one or more processors operatively coupled to the radiation sensor, the one or more processors configured to determine parameters associated with fringes in the intensity modulated fringe pattern, and determine one or more overlay values for the metrology target based on the parameters.2. The system of clause 1, wherein: the first and third segments, and the second and fourth segments, are arranged symmetrically about an axis of the metrology target in the non-overlapping positions in the first and second layers, wherein the axis is orthogonal to a plane of the patterned substrate; the intensity modulated fringe pattern comprises individual intensity modulated fringe sub-patterns for interfering + / - nth orders of the diffracted radiation from each of: the first and third segments, and thus the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation; and the one or more processors are configured to determine the one or more overlay values based on the individual intensity modulated fringe sub-patterns.3. The system of any of the previous clauses, wherein the + / - nth orders of the diffracted radiation comprise + / - first order diffracted radiation.4. The system of any of the previous clauses, wherein the first and third segments are associated with an x direction, and the second and fourth segments are associated with a y direction.5. The system of any of the previous clauses, wherein the first segment is a top x segment, the third segment is a bottom x segment, the second segment is a top y segment, and the fourth segment is a bottom y segment.6. The system of any of the previous clauses, wherein the partitioned wedge comprises an eight fold wedge or a four fold wedge.7. The system of any of the previous clauses, wherein: the eight fold wedge is configured to direct Oth order x, Oth order y, interfering + / - 1st order diffracted radiation associated with the top x segment, interfering + / - 1st order diffracted radiation associated with the bottom x segment, interfering + / - 1st order diffracted radiation associated with the top y segment, and interfering + / - 1st order diffracted radiation associated with the bottom y segment to different areas of the radiation sensor; the interfering + / - 1st order diffracted radiation associated with the top x segment, and the interfering + / - 1st order diffracted radiation associated with the bottom x segment, are directed jointly in the same directiontoward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top x segment and the + / - 1st order diffracted radiation associated with the bottom x segment are naturally separated by their relative positions in a plane of the patterned substrate; and the interfering + / - 1st order diffracted radiation associated with the top y segment, and the interfering + / - 1st order diffracted radiation associated with the bottom y segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top y segment and the + / - 1st order diffracted radiation associated with the bottom y segment are naturally separated by their relative positions in the plane of the patterned substrate.8. The system of any of the previous clauses, wherein the Oth order x, and Oth order y diffracted radiation are completely or partially blocked by one or more additional components of the system at an exit pupil plane or any equivalent plane in the radiation sensor.9. The system of any of the previous clauses, wherein x and y -1st and +lst orders of diffracted radiation all share a same first wedge angle but with angles of opposite sign for x and y directions, and Oth order x and y diffracted radiation also shares a same second wedge angle but with angles of opposite sign for x and y directions.10. The system of any of the previous clauses, wherein + / - 1 st order x and Oth order y diffracted radiation share a same first wedge angle, and + / -lst order y and Oth order x diffracted radiation share a same second wedge angle.11. The system of any of the previous clauses, wherein the one or more overlay values comprise an x direction overlay value and a y direction overlay value.12. The system of any of the previous clauses, wherein Oth orders of diffracted radiation as used for generation of the + / - nth orders of diffracted radiation are pointwise coherent, and thus the + / - nth orders of the diffracted radiation from the first and third segments, and from the second and fourth segments, are also pointwise coherent.13. The system of any of the previous clauses, wherein the parameters associated with fringes in the intensity modulated fringe pattern comprise amplitude and position offset.14. The system of any of the previous clauses, wherein the second metrology mark comprises the third segment associated with the first direction of the diffracted radiation in the second layer, and the fourth segment associated with the second direction of the diffracted radiation in a third layer that is below the second layer of the metrology target.15. The system of any of the previous clauses, wherein the first and second segments of the first metrology mark are combined, and the third and fourth segments of the second metrology mark are combined, such that the first and second metrology marks each comprise two dimensional gratings, and such that separate x and y segments are not required.16. The system of any of the previous clauses, further comprising a radiation source operatively coupled to the one or more processors and the radiation sensor, the radiation source configured to irradiate the two or more metrology targets with radiation.17. The system of any of the previous clauses, wherein the radiation sensor comprises a camera. 18. The system of any of the previous clauses, wherein the one or more processors are further configured to determine an alignment value for the first layer and / or the second layer based on the diffracted radiation received from the metrology target.19. The system of any of the previous clauses, wherein the one or more processors are configured to determine an overlay value as a difference between two alignment values, one for each of two directions of the diffracted radiation.20. The system of any of the previous clauses, wherein the metrology signal is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.21. A target for a metrology system, comprising: a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate; wherein: the first metrology mark comprises a first segment associated with a first direction of diffracted radiation, and a second segment associated with a second direction of the diffracted radiation; the first metrology mark is above the second metrology mark in the patterned substrate; the second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of the diffracted radiation; and the first and third segments, and the second and fourth segments, are arranged in non-overlapping positions in the first and second layers; and wherein a radiation sensor is configured to generate a metrology signal based on the diffracted radiation received from the first and second marks of the metrology target, the metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation; and one or more processors operatively coupled to the radiation sensor are configured to determine parameters associated with fringes in the intensity modulated fringe pattern, and determine one or more overlay values for the metrology target based on the parameters.22. The target of any of the previous clauses, wherein the first and third segments are associated with an x direction, and the second and fourth segments are associated with a y direction.23. The target of any of the previous clauses, wherein the first segment is a top x segment, the third segment is a bottom x segment, the second segment is a top y segment, and the fourth segment is a bottom y segment.24. The target of any of the previous clauses, wherein: the second metrology mark comprises the third segment associated with the first direction of the diffracted radiation in the second layer, and the fourth segment associated with the second direction of the diffracted radiation in a third layer that is below the second layer of the metrology target; or the first and second segments of the first metrology mark are combined, and the third and fourth segments of the second metrology mark are combined, such that the first and second metrology marks each comprise two dimensional gratings, and such that separate x and y segments are not required.25. The target of any of the previous clauses, wherein: the first and third segments, and the second and fourth segments, are arranged symmetrically about an axis of the metrology target in the non-overlapping positions in the first and second layers, wherein the axis is orthogonal to a plane of the patterned substrate.26. An overlay metrology method, comprising: generating, with a radiation sensor, a metrology signal based on diffracted radiation received from a metrology target in a patterned substrate, the metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation from the metrology target, wherein: the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate; the first metrology mark comprises a first segment associated with a first direction of the diffracted radiation and a second segment associated with a second direction of the diffracted radiation; the first metrology mark is above the second metrology mark in the patterned substrate; the second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of the diffracted radiation; and the first and third segments, and the second and fourth segments, are arranged in non-overlapping positions in the first and second layers; directing, with a partitioned wedge, + / - nth orders of the diffracted radiation from: the first and third segments, and thus from the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation, onto different areas of the radiation sensor for generating the intensity modulated fringe pattern; and determining, with one or more processors operatively coupled to the radiation sensor, parameters associated with fringes in the intensity modulated fringe pattern, and determining one or more overlay values for the metrology target based on the parameters.27. The method of clause 26, wherein: the first and third segments, and the second and fourth segments, are arranged symmetrically about an axis of the metrology target in the non-overlapping positions in the first and second layers, wherein the axis is orthogonal to a plane of the patterned substrate; the intensity modulated fringe pattern comprises individual intensity modulated fringe sub-patterns for interfering + / - nth orders of the diffracted radiation from each of: the first and third segments, and thus the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation; and the one or more processors are configured to determine the one or more overlay values based on the individual intensity modulated fringe sub-patterns.28. The method of any of the previous clauses, wherein the + / - nth orders of the diffracted radiation comprise + / - first order diffracted radiation.29. The method of any of the previous clauses, wherein the first and third segments are associated with an x direction, and the second and fourth segments are associated with a y direction.30. The method of any of the previous clauses, wherein the first segment is a top x segment, the third segment is a bottom x segment, the second segment is a top y segment, and the fourth segment is a bottom y segment.31. The method of any of the previous clauses, wherein the partitioned wedge comprises an eight fold wedge or a four fold wedge.32. The method of any of the previous clauses, wherein: the eight fold wedge is configured to direct Oth order x, Oth order y, interfering + / - 1st order diffracted radiation associated with the top x segment, interfering + / - 1st order diffracted radiation associated with the bottom x segment, interfering + / - 1st order diffracted radiation associated with the top y segment, and interfering + / - 1st order diffracted radiation associated with the bottom y segment to different areas of the radiation sensor; the interfering + / - 1st order diffracted radiation associated with the top x segment, and the interfering + / - 1st order diffracted radiation associated with the bottom x segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top x segment and the + / - 1st order diffracted radiation associated with the bottom x segment are naturally separated by their relative positions in a plane of the patterned substrate; and the interfering + / - 1st order diffracted radiation associated with the top y segment, and the interfering + / - 1st order diffracted radiation associated with the bottom y segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top y segment and the + / - 1st order diffracted radiation associated with the bottom y segment are naturally separated by their relative positions in the plane of the patterned substrate.33. The method of any of the previous clauses, wherein the Oth order x, and Oth order y diffracted radiation are completely or partially blocked by one or more additional components of the system at an exit pupil plane or any equivalent plane in the radiation sensor.34. The method of any of the previous clauses, wherein x and y -1st and +lst orders of diffracted radiation all share a same first wedge angle but with angles of opposite sign for x and y directions, and Oth order x and y diffracted radiation also shares a same second wedge angle but with angles of opposite sign for x and y directions.35. The method of any of the previous clauses, wherein + / -lst order x and Oth order y diffracted radiation share a same first wedge angle, and + / - 1 st order y and Oth order x diffracted radiation share a same second wedge angle.36. The method of any of the previous clauses, wherein the one or more overlay values comprise an x direction overlay value and a y direction overlay value.37. The method of any of the previous clauses, wherein Oth orders of diffracted radiation as used for generation of the + / - nth orders of diffracted radiation are pointwise coherent, and thus the + / - nth orders of the diffracted radiation from the first and third segments, and from the second and fourth segments, are also pointwise coherent.38. The method of any of the previous clauses, wherein the parameters associated with fringes in the intensity modulated fringe pattern comprise amplitude and position offset.39. The method of any of the previous clauses, wherein the second metrology mark comprises the third segment associated with the first direction of the diffracted radiation in the second layer, and the fourth segment associated with the second direction of the diffracted radiation in a third layer that is below the second layer of the metrology target.40. The method of any of the previous clauses, wherein the first and second segments of the first metrology mark are combined, and the third and fourth segments of the second metrology mark are combined, such that the first and second metrology marks each comprise two dimensional gratings, and such that separate x and y segments are not required.41. The method of any of the previous clauses, further comprising irradiating, with a radiation source operatively coupled to the one or more processors and the radiation sensor, the two or more metrology targets with radiation.42. The method of any of the previous clauses, wherein the radiation sensor comprises a camera. 43. The method of any of the previous clauses, further comprising determining, with the one or more processors, an alignment value for the first layer and / or the second layer based on the diffracted radiation received from the metrology target.44. The method of any of the previous clauses, wherein the one or more processors are configured to determine an overlay value as a difference between two alignment values, one for each of two directions of the diffracted radiation.45. The method of any of the previous clauses, wherein the metrology signal is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.46. A method for a metrology system, comprising: forming a metrology target comprising a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate; wherein: the first metrology mark comprises a first segment associated with a first direction of diffracted radiation, and a second segment associated with a second direction of the diffracted radiation; the first metrology mark is above the second metrology mark in the patterned substrate; the second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of the diffracted radiation; and the first and third segments, and the second and fourth segments, are arranged in nonoverlapping positions in the first and second layers; and wherein a radiation sensor is configured to generate a metrology signal based on the diffracted radiation received from the first and second marks of the metrology target, the metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation; and one or more processors operatively coupled to the radiation sensor are configured to determine parameters associated with fringes in the intensity modulated fringe pattern, and determine one or more overlay values for the metrology target based on the parameters.47. The method of any of the previous clauses, wherein the first and third segments are associated with an x direction, and the second and fourth segments are associated with a y direction.48. The method of any of the previous clauses, wherein the first segment is a top x segment, the third segment is a bottom x segment, the second segment is a top y segment, and the fourth segment is a bottom y segment.49. The method of any of the previous clauses, wherein: the second metrology mark comprises the third segment associated with the first direction of the diffracted radiation in the second layer, and thefourth segment associated with the second direction of the diffracted radiation in a third layer that is below the second layer of the metrology target; or the first and second segments of the first metrology mark are combined, and the third and fourth segments of the second metrology mark are combined, such that the first and second metrology marks each comprise two dimensional gratings, and such that separate x and y segments are not required.50. The method of any of the previous clauses, wherein: the first and third segments, and the second and fourth segments, are arranged symmetrically about an axis of the metrology target in the nonoverlapping positions in the first and second layers, wherein the axis is orthogonal to a plane of the patterned substrate.

[0125] The concepts disclosed herein may be associated with any generic metrology and / or imaging system for measuring and / or imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths.

[0126] While the concepts disclosed herein may be used for metrology and / or imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of metrology and / or imaging systems, e.g., those used for metrology and / or imaging on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments.

[0127] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

1. CLAIMS1. An overlay metrology system, comprising:a radiation sensor configured to generate a metrology signal based on diffracted radiation received from a metrology target in a patterned substrate, the metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation from the metrology target, wherein:the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate;the first metrology mark comprises a first segment associated with a first direction of the diffracted radiation and a second segment associated with a second direction of the diffracted radiation;the first metrology mark is above the second metrology mark in the patterned substrate;the second metrology mark comprises a third segment associated with the first direction of the diffracted radiation and a fourth segment associated with the second direction of the diffracted radiation; andthe first and third segments, and the second and fourth segments, are arranged in non-overlapping positions in the first and second layers;a partitioned wedge configured to direct + / - nth orders of the diffracted radiation from:the first and third segments, and thus from the first direction of the diffracted radiation, andthe second and fourth segments, and thus the second direction of the diffracted radiation,onto different areas of the radiation sensor for generating the intensity modulated fringe pattern; andone or more processors operatively coupled to the radiation sensor, the one or more processors configured to determine parameters associated with fringes in the intensity modulated fringe pattern, and determine one or more overlay values for the metrology target based on the parameters.

2. The system of claim 1, wherein:the first and third segments, and the second and fourth segments, are arranged symmetrically about an axis of the metrology target in the non-overlapping positions in the first and second layers, wherein the axis is orthogonal to a plane of the patterned substrate;the intensity modulated fringe pattern comprises individual intensity modulated fringe subpatterns for interfering + / - nth orders of the diffracted radiation from each of:the first and third segments, and thus the first direction of the diffracted radiation, and the second and fourth segments, and thus the second direction of the diffracted radiation; andthe one or more processors are configured to determine the one or more overlay values based on the individual intensity modulated fringe sub-patterns.

3. The system of claim 1 or 2, wherein the + / - nth orders of the diffracted radiation comprise + / - first order diffracted radiation.

4. The system of any of claims 1-3, wherein the first and third segments are associated with an x direction, and the second and fourth segments are associated with a y direction.

5. The system of claim 4, wherein the first segment is a top x segment, the third segment is a bottom x segment, the second segment is a top y segment, and the fourth segment is a bottom y segment.

6. The system of claim 5, wherein the partitioned wedge comprises an eight fold wedge or a four fold wedge.

7. The system of claim 6, wherein:the eight fold wedge is configured to direct 0thorder x, 0thorder y, interfering + / - 1storder diffracted radiation associated with the top x segment, interfering + / - 1storder diffracted radiation associated with the bottom x segment, interfering + / - 1storder diffracted radiation associated with the top y segment, and interfering + / - 1storder diffracted radiation associated with the bottom y segment to different areas of the radiation sensor;the interfering + / - 1st order diffracted radiation associated with the top x segment, and the interfering + / - 1st order diffracted radiation associated with the bottom x segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top x segment and the + / - 1st order diffracted radiation associated with the bottom x segment are naturally separated by their relative positions in a plane of the patterned substrate; and the interfering + / - 1st order diffracted radiation associated with the top y segment, and the interfering + / - 1st order diffracted radiation associated with the bottom y segment, are directed jointly in the same direction toward the radiation sensor, whereby the + / - 1st order diffracted radiation associated with the top y segment and the + / - 1st order diffracted radiation associated with the bottom y segment are naturally separated by their relative positions in the plane of the patterned substrate.

8. The system of claim 7, wherein the 0thorder x, and 0thorder y diffracted radiation are completely or partially blocked by one or more additional components of the system at an exit pupil plane or any equivalent plane in the radiation sensor.

9. The system of claim 7 or 8, wherein x and y -1st and +lst orders of diffracted radiation all share a same first wedge angle but with angles of opposite sign for x and y directions, and Oth order x and y diffracted radiation also shares a same second wedge angle but with angles of opposite sign for x and y directions.

10. The system of claims 7 or 8, wherein + / - 1st order x and Oth order y diffracted radiation share a same first wedge angle, and + / -1 st order y and Oth order x diffracted radiation share a same second wedge angle.

11. The system of any of claims 4-10, wherein the one or more overlay values comprise an x direction overlay value and a y direction overlay value.

12. The system of any of claims 1-11, wherein Oth orders of diffracted radiation as used for generation of the + / - nth orders of diffracted radiation are pointwise coherent, and thus the + / - nth orders of the diffracted radiation from the first and third segments, and from the second and fourth segments, are also pointwise coherent.

13. The system of any of claims 1-12, wherein the parameters associated with fringes in the intensity modulated fringe pattern comprise amplitude and position offset.

14. The system of any of claims 1-13, wherein the second metrology mark comprises the third segment associated with the first direction of the diffracted radiation in the second layer, and the fourth segment associated with the second direction of the diffracted radiation in a third layer that is below the second layer of the metrology target.

15. The system of any of claims 1-13, wherein the first and second segments of the first metrology mark are combined, and the third and fourth segments of the second metrology mark are combined, such that the first and second metrology marks each comprise two dimensional gratings, and such that separate x and y segments are not required.

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