Overlay and alignment metrology systems and methods for semiconductor manufacturing

Abstract

Measuring overlay and alignment with a single system is described. Sensor output signals are generated based on diffracted radiation received from a metrology target having pads with different portions (e.g., gratings) in first and second metrology marks in first and second layers of a patterned substrate. Various sensor signals are combined for the realization of the joint detection of both overlay and alignment with said single system. Signal formation and related signal processing are described for gratings in the pads, for which a system of non-linear equations is derived from which overlay and alignment can be determined jointly (e.g., at the same time). Signal formation operations and the system of non-linear equations are configured to account for 4D aberrations associated with an imaging lens. An approach where 4D aberrations are taken into account enables the use of simpler optics as compared to prior systems, for example.

Description

OVERLAY AND ALIGNMENT METROLOGY SYSTEMS AND METHODS FOR SEMICONDUCTOR MANUFACTURINGCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Application No. 63 / 527,541, filed July 18, 2023, and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This description relates generally to overlay and alignment 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 devices are 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, microelectro 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 deep-ultraviolet 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 = kjxk / 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 other methods generally defined as “resolution enhancement techniques” (RET). Metrology plays a key part in these fine tuning steps.SUMMARY

[0009] Measuring overlay and alignment using a microscope based sensor is described. This provides the ability to measure overlay and alignment with a single system, among other advantages. Sensor output signals are generated based on diffracted radiation received from a metrology target having pads with different portions (e.g., gratings) in first and second metrology marks in first and second layers out of a multi-layer stack of a patterned substrate. Signal formation and related signal processing are described for gratings in the pads, for which a system of non-linear equations is derived from which overlay and alignment can be determined. Signal formation operations and the system of non-linear equations are configured to account for four dimensional (4D) aberrations associated with an imaging lens. Therefore, signal formation for 4D non-isoplanatic aberrations and finite targets is also described, albeit within a scalar diffraction based description with a windowing approach for the pads in view of a transparent description of the physics of image formation. An approach where 4D aberrations are taken into account enables the use of simpler optics (even for an extended wavelength range 400-1600nm) as compared to prior systems, for example.

[0010] According to an embodiment, a metrology system is provided. The metrology system comprises an imaging lens configured to transmit diffracted radiation received from a target. The target comprises a first metrology mark (e.g., having multiple gratings) in a first layer of a patterned substrate and a second metrology mark (e.g., also having multiple gratings) in a second layer of the patterned substrate. The imaging lens contributes to, affects, and / or impacts aberrations in the diffracted radiation wavefront through its aberrations, and as the diffracted radiation wavefront is subject to interference yielding an image at a detection plane, thereby impacting a quality of the image.

[0011] The system comprises a first radiation sensor in a first portion of the metrology system. The first radiation sensor is configured to generate a first image based metrology signal based on interference of coherent diffracted radiation for -i-nth and -nth diffraction orders of higher than Oth order diffracted radiation. This diffracted radiation is received from the metrology target through the imaging lens. The first image based metrology signal comprises an intensity modulated fringe pattern realized through the interference of the two diffraction orders of the diffracted radiation, which is superimposed on a background signal.

[0012] The system comprises a second radiation sensor in a second portion of the metrology system. The second radiation sensor is configured to generate at least two second image based metrology signals based on separate dark field imaging with the -i-nth and -nth diffraction orders received from the metrology target through the imaging lens. Separate signals are generated with a partitioned wedge with at least a twofold partitioning. The at least two second image based metrology signals comprise an intensity modulated pattern for each of the metrology marks of target. Note: the pads here refer to portions of the marks in the two layers of the patterned substrate, as defined above.

[0013] The system comprises one or more processors operatively coupled to the first radiation sensor, and the second radiation sensor (with the second radiation sensor being associated with the at least twofold partitioned wedge). The one or more processors are configured to obtain aberration information associated with the imaging lens. The one or more processors are configured to determine a set of window functions for each measured signal associated with multiple pads of the target. Each pad comprises at least portions (e.g., one or more gratings) of the first and second metrology marks. The multiple pads relate to a given direction in a two-dimensional plane of the patterned substrate. The given direction comprises a direction in which measurement is performed. The one or more processors are configured to determine an overlay value, and / or an overlay value and an alignment value in the given direction (either x- or y-direction) in the two-dimensional plane of the patterned substrate, based on the intensity modulated fringe pattern, and at least two separate patterns of dark field imaging realized with the -i-nth and -nth diffraction orders separately, the aberration information, and the set of window functions.

[0014] In some embodiments, the -i-nth and -nth diffraction orders of higher than Oth order diffracted radiation comprise -4-lst and -1st diffraction orders.

[0015] In some embodiments, the one or more processors are configured to determine a plurality of field dependent image based functions based on the intensity modulated fringe pattern on top of a background signal, the at least two separate patterns realized with the -i-nth and -nth diffraction separately, the aberration information, and the set of window functions. The overlay value, and / or the overlay value and the alignment value associated with a given direction may be determined by “solving” the plurality of field dependent image based functions. In some embodiments, “solving” comprises fitting the plurality of determined field dependent image based functions to parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, in addition to some nuisance parameters which affect the measured signals, but are not key performance parameters like overlay and alignment values.

[0016] In some embodiments, the set of window functions for each measured signal is associated with at least two given directions (x and y) for four pads of the target, with two of the four pads associated with a first given direction, and another two of the four pads associated with a second given direction.

[0017] In some embodiments, the one or more processors are configured to determine, for each of the at least two given directions: an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a first pad and an amplitude of each of the at least two diffracted -i-nth and - nth radiation received from a second pad, a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the first pad, and a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the second pad, and / or a phase offset due to and linear in an alignment error between diffracted -i-nth and -nth radiation, the phase offset being identical for the second pad and the first pad of the target, based onthe intensity modulated fringe pattern and / or based on the at least two second image based metrology signals comprising an intensity modulated pattern for each of the at least two metrology marks of target, and fit the plurality of determined field dependent image based functions to their parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value which are the key performance parameters, using the amplitudes, phases, and / or phase offsets.

[0018] In some embodiments, the one or more processors are configured to determine the overlay value and the alignment value, and the plurality of field dependent image based functions are fitted sequentially such that: the alignment value is determined based on the signal from the first radiation sensor using overlay information derived from the signals from the second radiation sensor, after determining the overlay value based on the signals from the second radiation sensor.

[0019] In some embodiments, the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted simultaneously such that the alignment value is determined at the same time as the overlay value.

[0020] In some embodiments, a quantity of the plurality of field dependent image based functions corresponds to a number of known variables in the plurality of field dependent image based functions. In some embodiments, a number of unknows in the plurality of field dependent image based functions is less than or equal to a quantity of the plurality of field dependent image based functions.

[0021] In some embodiments, the system comprises the partitioned wedge with the least a twofold partitioning. The first and second portions of the metrology system are configured such that, in the first portion, the first radiation sensor has a single branch, and, in the second portion, the second radiation sensor has two branches related to the twofold partitioning with the partitioned wedge. The partitioned wedge comprises a starting point of the two branches.

[0022] In some embodiments, the aberration information comprises an aberration function. In some embodiments, the aberration information is determined based on a physics-based or machine-learning based electronic model configured to simulate the imaging lens. In some embodiments, the aberration information is four dimensional (4D) with two dimensions for the dependence on the 2D field space (real space) and with two dimensions for the dependence on the 2D pupil space of the imaging lens (Fourier space). In some embodiments, the aberration information is known for the imaging lens, and is obtained by the one or more processors from electronic storage.

[0023] In some embodiments, the target comprising the first metrology mark in the first layer of the patterned substrate and the second metrology mark in the second layer comprises multiple pads. Each pad comprises a top grating in the second layer and a bottom grating in the first layer.

[0024] In some embodiments, the system comprises a radiation source operatively coupled to the one or more processors and the radiation sensors. The radiation source is configured to irradiate the target with radiation. In some embodiments, the radiation from the radiation source comprises two incidentmutually 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 to form the diffracted radiation. In some embodiments, the different angles comprise azimuths of 0 and 180 degrees at a same tilt angle.

[0025] In some embodiments, the diffracted radiation comprises two first order diffracted radiation beams. The first radiation sensor is configured to generate the intensity modulated fringe pattern based on the two first order diffracted radiation beams.

[0026] In some embodiments, a window function in the set of window functions is determined based on physical edges of the first and second metrology marks and / or pads of the first and second metrology marks. In some embodiments, a window function in the set of window functions is determined based on the geometry of a pad, for instance, as it was designed for the manufacturing of the mask.

[0027] In some embodiments, the second metrology mark is above the first metrology mark in the patterned substrate. In some embodiments, the target comprises at least one pad of the part of the second metrology mark of that pad is shifted in the xy-plane along the given direction relative to the part of the first metrology mark of that same pad by a known bias amount. In some embodiments, pads comprise gratings. In some embodiments, pads of the first and second metrology marks comprise gratings. In some embodiments, the target comprises a diffraction-based overlay metrology target. In some embodiments, the target comprises a Micro Diffraction Based Overlay (pDBO) target.

[0028] In some embodiments, the first and / or second radiation sensor comprises an interferometer.

[0029] In some embodiments, the overlay value and / or the alignment value is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.

[0030] According to another embodiment, a metrology method comprising one or more of the operations described above is provided.

[0031] 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

[0032] 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.

[0033] Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.

[0034] Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0035] Fig. 3 schematically depicts an example metrology system, according to an embodiment.

[0036] Fig. 4 schematically depicts an example metrology technique, according to an embodiment.

[0037] Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.

[0038] Fig. 6 illustrates a metrology method, according to an embodiment.

[0039] Fig. 7 illustrates an example embodiment of a metrology target, according to an embodiment.

[0040] Fig. 8 illustrates another example metrology system, according to an embodiment.

[0041] Fig. 9 illustrates yet another example metrology system, according to an embodiment.

[0042] Fig. 10 illustrates additional possible components of one or more of the metrology systems shown in Fig. 3, Fig. 8, and / or Fig. 9, according to an embodiment.

[0043] Fig. 11 illustrates determining overlay and / or overlay and alignment values in a given direction in a two-dimensional plane of a patterned substrate based on an intensity modulated fringe pattern, and at least two separate dark field patterns realized with -i-nth and -nth diffraction orders separately, aberration information, and a set of window functions, according to an embodiment.

[0044] Fig. 12 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0045] 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.

[0046] 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.

[0047] In contrast to prior systems, the present systems and methods are configured for determining overlay and / or alignment using a microscope based sensor, therefore being able to determine overlayand alignment with a single system, and using the same physical target for overlay, alignment, and / or other metrology operations. The present systems and methods may also use smaller marks, and / or marks positioned relatively close to other structures in a substrate, for determining overlay and / or alignment.

[0048] 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 portions (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, for which a system of non-linear equations is derived. Overlay and / or alignment can be determined from these equations. Signal formation operations and the system of non-linear equations are also configured to account for four dimensional (4D) aberrations associated with an imaging lens.

[0049] Concepts related to those described herein are discussed in applicant’s US Provisional Patent Application Nos. 63 / 457,680 (filed April 6, 2023) titled “Overlay Metrology Based on a Fringe Pattern”; and 63 / 450,243 (filed March 6, 2023) titled “Multi-layer Metrology Systems and Methods”; which are both hereby incorporated by reference in their entireties.

[0050] By way of a brief introduction, the following description relates generally to semiconductor device manufacturing and patterning processes. More particularly, the following paragraphs describe several components of a system and / or related systems. As described above these systems and methods may be used for measuring overlay and / or alignment in a semiconductor device manufacturing process, for example, or for other operations.

[0051] 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. 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.

[0052] The term “projection optics” should be broadly interpreted as encompassing various types of optical systems, including refractive optics, reflective optics, apertures and catadioptric optics, for example. The term “projection optics” may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, collectively or singularly. The term “projection optics” may include any optical component in the lithographic projection apparatus, no matter where the optical component is located on an optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, adjusting and / or projecting radiation from the source before the radiation passes the patterning device,and / or optical components for shaping, adjusting and / or projecting the radiation after the radiation passes the patterning device. The projection optics generally exclude the source and the patterning device.

[0053] 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).

[0054] 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.

[0055] 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.

[0056] 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 intensitydistribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, 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.

[0057] 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.

[0058] 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.

[0059] 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 desiredposition, for example 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.”

[0060] 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.

[0061] 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 phaseshift, 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.

[0062] 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”.

[0063] 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 moresides of the optical element and / or by 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.

[0064] 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.

[0065] 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 short-stroke 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.

[0066] 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 patternimparted to the radiation beam is projected onto a target portion C at one time (i.e., a single static exposure). The substrate 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.

[0067] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0068] 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 multi-layer IC, so that the term substrate may also refer to a substrate that already includes multiple processed layers.

[0069] 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.

[0070] 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 theindividual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0071] 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 post-exposure 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 / Ol, I / 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.

[0072] 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)).

[0073] 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.

[0074] 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 diffraction-based metrology is in the measurement of overlay and / or alignment (e.g., as described below).

[0075] 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)).

[0076] 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.

[0077] 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.

[0078] 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).

[0079] Fig. 3 depicts an example inspection (metrology) system 10 that may be used to detect overlay, alignment, and / or perform other metrology operations. It comprises a radiation source 2which projects or otherwise irradiates radiation 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. The redirected radiation is passed to a radiation sensor such as a spectrometer detector 4 and / or other sensors, which measures a spectrum (intensity as a function of wavelength) of the specular reflected and / or diffracted radiation, as shown, e.g., in the graph on the left of Fig. 4. The sensor may generate a metrology signal conveying overlay data, alignment data, and / or other data indicative of properties of the 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.

[0080] 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 inspection 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 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).

[0081] 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), target30 may include structures in 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 targets.

[0082] 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.

[0083] Fig. 5 illustrates a plan view of a typical target 30 (e.g., an overlay target, an alignment mark, etc.), and the extent of a radiation illumination spot S in the system of Fig. 4. 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.

[0084] 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 (and / or by one or more of the systems shown in Fig. 8-10 described below), a computer system (e.g., as illustrated in Fig. 12 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, transmitting (operation 604) diffracted radiation from the metrology target with an imaging lens, generating (operation 606) a first image based metrology signal, generating (operation 608) at least two second image based metrologysignals, determining (operation 610) an overlay value, and / or an overlay value and an alignment value, and / or other operations.

[0085] 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.

[0086] 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. 13 below).

[0087] Operation 602 comprises irradiating a metrology target in a patterned substrate with radiation. In some embodiments, 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)). 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 comprises metrology marks in different layers of the patterned substrate, and / or other features. In some embodiments, the metrology target is associated with an alignment and / or overlay 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).

[0088] In some embodiments, the metrology target may be included in multiple layers of a substrate in a semiconductor device structure, for example. 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 line, an edge, 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.

[0089] In some embodiments, the radiation source (e.g., source 2 shown in Fig. 3) is configured to irradiate 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 with radiation. In someembodiments, the second metrology mark is directly above the first metrology mark in the patterned substrate in a second layer of a semiconductor structure, though the first metrology mark in the first layer may be shifted relative to the second metrology mark by a known bias amount. Specifically, a lateral shift over a known bias is applied to the pattern of the pad in the second layer / mark with respect to the pattern in the same pad in the first layer / mark.

[0090] In some embodiments, the first and second metrology marks together comprise a diffractionbased overlay metrology target including gratings and / or other structures. The gratings may have the same pitch, different pitches, and / or other features. In some embodiments, the first and second metrology marks form a Micro Diffraction Based Overlay (pDBO) target, with the first and second metrology marks comprising gratings in the first and second layers of the patterned substrate.

[0091] For example, Fig. 7 illustrates a possible embodiment of metrology target 30. Target 30 comprises a first metrology mark 702 in a first (e.g. lower or bottom) layer of a patterned substrate (e.g., W shown in Fig. 1, 3, and 5) and a second metrology mark 704 in a second (e.g., upper or top) layer. First metrology mark 702 in the first (lower or bottom) layer and / or second metrology mark 704 in the second (upper or top) layer can include one or more gratings 714 (e.g., two or more differently oriented gratings in each metrology mark) and / or other structures. Target 30 comprises multiple pads 706, 708, 710, 712. In some embodiments, pads 706, 708, 710, 712 comprise gratings 714. In this example each pad comprises a top grating in the second layer and a bottom grating in the first layer (see gratings 714) - one grating of the top metrology mark 704 and one grating of the bottom metrology mark 702. In this example, second metrology mark 704 is above first metrology mark 702 in the patterned substrate (e.g., W). In some embodiments, target 30 comprises at least one pad 706-712 that is shifted relative to a different pad by a known bias amount. For example, there may be a positive bias (e.g., +20nm in x) and / or a negative bias (in x and / or y) between pads.

[0092] Returning to Fig. 6, the radiation 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.

[0093] 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. In some embodiments, the different angles comprise azimuths of 0 and 180 degrees at a same tilt angle, for example.

[0094] The radiation may be generated by a radiation source (e.g., source 2 shown in Fig. 3 and 4 and described above) of the metrology system, and / or other components. The radiation source may be operatively coupled to one or more processors (e.g., processor(s) PRO described herein), one or moreradiation sensors (e.g., as described below), 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, a modulator, and / or other components) onto a metrology target, sub-portions (e.g., something less than the whole) of a metrology target, multiple metrology targets, and / or onto the substrate in other ways.

[0095] In some embodiments, the metrology target 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.

[0096] Operation 604 comprises transmitting the diffracted radiation from the metrology target with an imaging lens of the metrology system and / or other components. The imaging lens is configured to transmit diffracted radiation received from the 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 as described above). The imaging lens contributes to, affects, and / or impacts aberrations in the diffracted radiation wavefront through its aberrations, and as the diffracted radiation wavefront is subject to interference yielding an image at a detection plane, thereby impacting a quality of the image.

[0097] Operations 606 and 608 are performed by first and second radiation sensors. The first and / or second radiation sensors may each form a portion of detector 4 shown in Fig. 3, for example. The first and / or second radiation sensors may comprise an interferometric microscopy detector, a camera, and / or other components, for example. In some embodiments, the first and / or second radiation sensor comprises an interferometer. The first and / or second sensors are configured for detecting reflected and / or transmitted radiation from the metrology target. In some embodiments, a metrology signal comprises overlay and / or alignment position information for the first and second layers conveyed by radiation from the metrology target.

[0098] In some embodiments, detecting such radiation comprises detecting (1) changes in amplitude (or intensity, which is amplitude-squared); and / or (2) changes in phase-shifts (which are differences in phase) in (diffracted) radiation received from one or more geometric features.

[0099] Here we refer to the information present in the complex-valued field with both amplitude and phase information. We could also refer to the asymmetries in detected intensities of the diffracted radiation, which is the typical property of the diffracted radiation used in uDBO. One or more phase and / or changes in amplitudes may correspond to one or more dimensions of a feature. For example, the phase and / or amplitude of reflected radiation (either real-valued intensity-based or complex-value field-based) from one side of a feature may be different relative to the phase and / or amplitude ofreflected radiation from another side of the feature. In this example, one pad may reside at one side of a feature, where the feature is the whole target. Detecting the one or more phase shifts and amplitude changes and asymmetries in the radiation from the metrology mark comprises measuring local phase shifts (e.g., local phase deltas) and / or amplitude variations that correspond to different portions of a metrology mark. For example, the radiation from a specific area of a mark may comprise a sinusoidal waveform having a certain phase and / or amplitude. The radiation from a different area of the mark may also comprise a sinusoidal waveform, but one with a different phase and / or amplitude. Detecting radiation also comprises measuring a phase and / or amplitude difference in radiation of different diffraction orders. Detecting the one or more local phase and / or amplitude shifts may be performed using various signal processing techniques like Fourier transformations and / or Hilbert transformations, for example. Interferometry techniques and / or other operations may be used to measure phase and / or amplitude differences in reflected radiation of different diffraction orders.

[0100] A metrology signal comprises measurement information pertaining to the metrology target. For example, a metrology signal may be an alignment signal comprising alignment measurement information, an overlay signal comprising overlay measurement information, a combination thereof, and / or other metrology signals. A metrology signal comprises an electronic signal that represents and / or otherwise corresponds to the 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 which may be less interesting in terms of lithographic performance, and this particular type of information is therefore often referred to as nuisance parameters, for example. Generating the metrology signal comprises sensing the radiation and converting the sensed radiation into the electronic signal. In some embodiments, generating the metrology signal comprises sensing different portions of the 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. This sensing and converting may be performed by components similar to and / or the same as radiation sensor detector 4 and / or processors PRO shown in Fig. 3, and / or other components.

[0101] Operation 606 comprises generating a first image based metrology signal with a first radiation sensor in a first portion of a metrology system. The first radiation sensor is configured to generate a first image based metrology signal based on interference of coherent diffracted radiation for +nth and -nth diffraction orders of higher than Oth order diffracted radiation, as received from the metrology target and after being propagated through the imaging lens towards the signal detecting device. In some embodiments, the -i-nth and -nth diffraction orders of higher than Oth order diffracted radiation comprise +1 st and -1st diffraction orders, for example. The first image based metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation superimposed on a background signal, and / or other information. In some embodiments, the diffracted radiation comprises two first order diffracted radiation beams (as described above), and the first radiationsensor is configured to generate the intensity modulated fringe pattern based on the two first order diffracted radiation beams. In some embodiments, the intensity modulated fringe pattern comprises a one or more dimensional interference pattern. In some embodiments, the first radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation as generated through superposition from the first metrology mark and from the second metrology mark.

[0102] Operation 608 comprises generating at least two second image based metrology signals with a second radiation sensor in a second portion of the metrology system, and / or other components. The second radiation sensor is configured to generate at least two second image based metrology signals based on separate dark field imaging with the +nth and -nth diffraction orders received from the metrology target through the imaging lens. Separate signals are generated with a partitioned wedge with at least a twofold partitioning, for example. The at least two second image based metrology signals comprise an intensity modulated pattern for each of the metrology pads (comprising patterning on the two layers) of the target. In some embodiments, the first and second portions of the metrology system are configured such that, in the first portion, the first radiation sensor has a single branch, and, in the second portion, the second radiation sensor has two branches related to the twofold partitioning with the partitioned wedge. The partitioned wedge comprises a starting point of the two branches, for example.

[0103] Operation 610 comprises determining (operation 610) an overlay value, and / or an overlay value and an alignment value, and / or other metrics. As part of operation 610, one or more processors (e.g., processor(s) PRO described herein) are operatively coupled to the first radiation sensor and the second radiation sensor (the second radiation sensor associated with the at least twofold partitioned wedge), the source, and / or other components.

[0104] The one or more processors are configured to obtain aberration information associated with the imaging lens. In some embodiments, the aberration information may be four dimensional (4D), for example. Two of these four dimensions relate to the 2D coordinates in the field space of the sample (real space) which is parallel to the sample’s surface. The other two of these four dimensions relate to the 2D coordinates in the pupil space (back focal plane) which is numerically to be considered as a Fourier space. In some embodiments, the aberration information comprises an aberration function. In some embodiments, the aberration information is known for the imaging lens, and is obtained by the one or more processors from electronic storage. In some embodiments, the aberration information is determined based on an electronic model configured to simulate the imaging lens and / or other information. The electronic model is based on a physical description of the impact of these 4D or 2D aberrations on the complex-valued wavefront. The latter physical description is most often given in terms of a transfer function in Fourier space, which is a Fourier transform of a point-spread function in the real space. The former transfer function has a phase factor, the argumentof which is known as the (2D or 4D) aberration function, which is typically expanded into Zernike polynomials (2D) or Hopkins polynomials (4D).

[0105] The one or more processors are configured to determine a set of window functions for each measured signal associated with multiple pads of the target. A window function in the set of window functions is determined based on physical edges of each pad in the metrology target. The first and the second metrology marks (which are referred to here as layers in the description above) are measured together, not separately. The measured signal can be seen as an addition of a wavefront generated by the first layer and a wavefront generated by the second layer. In some embodiments, the window function in the set of window functions is determined based on geometry of a pad. The window functions may be configured in this way because only diffracted radiation from the pads, (i.e., and not from surrounding structures around the target) is of interest when determining overlay and / or alignment, for example.

[0106] As described above, each pad comprises at least portions of the first and second metrology marks (e.g., a top grating and a bottom grating). The multiple pads relate to a given direction in a two-dimensional plane of the patterned substrate. The given direction comprises a direction for which the measurement will reveal information to estimate the overlay and or alignment value in that direction. For example, in some embodiments, the set of window functions for each measured signal is associated with at least two given directions for four pads of the target, with two of the four pads associated with a first given direction, and another two of the four pads associated with a second given direction.

[0107] The one or more processors are configured to determine an overlay value, and / or an overlay value and an alignment value in the given direction in the two-dimensional plane of the patterned substrate, based on the intensity modulated fringe pattern, and at least two separate dark field patterns realized with the -i-nth and -nth diffraction orders separately, the aberration information, the set of window functions, and / or other information. In some embodiments, the one or more processors are configured to determine a plurality of field dependent image based functions based on the intensity modulated fringe pattern, the at least two separate patterns realized with the -i-nth and -nth diffraction separately, the aberration information, the set of window functions, and or other information. The one or more processors are configured to determine the overlay value, and / or the overlay value and the alignment value associated with a given direction, by “solving” the plurality of field dependent image based functions. “Solving” may comprise fitting the plurality of determined field dependent image based functions to parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, and / or other “solving” operations.

[0108] A quantity of the plurality of field dependent image based functions may correspond to a number of known variables in the plurality of field dependent image based functions. In some embodiments, a number of unknows in the plurality of field dependent image based functions is less than or equal to a quantity of the plurality of field dependent image based functions. In someembodiments, the one or more processors are configured to determine the overlay value and the alignment value by fitting the plurality of field dependent image based functions sequentially such that the alignment value is determined based on the signal from the first radiation sensor using overlay information derived from the signals from the second radiation sensor, after determining the overlay value based on the signals from the second radiation sensor. In some embodiments, the one or more processors are configured to determine the overlay value and the alignment value by fitting the plurality of field dependent image based functions simultaneously such that the alignment value is determined at the same time as the overlay value.

[0109] In some embodiments, the one or more processors are configured to determine, for each of the at least two given directions: an amplitude of each of the at least two diffracted +nth and -nth radiation received from a first pad and an amplitude of each of the at least two diffracted -i-nth and - nth radiation received from a second pad, a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the second pad, and a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the first pad, and / or a phase offset due to and linear in an alignment error between diffracted -i-nth and -nth radiation. The phase offset is identical for the second pad and the first pad of the target. These determinations are based on the intensity modulated fringe pattern and / or based on the at least two second image based metrology signals comprising an intensity modulated pattern for each of the at least two metrology marks of target , and / or other information. The one or more processors are configured to fit the plurality of determined field dependent image based functions to their parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, using the amplitudes and phase differences.

[0110] Fig. 8 - Fig. 11 provide several examples of various components and / or operations described above.

[0111] Fig. 8 illustrates an example metrology system 800. System 800 is the same as or similar to system 10 described above with respect to Fig. 3, with one or more components of system 800 being similar to and / or the same as one or more components of system 10 (and Fig. 8 illustrating additional possible components of the system). In some embodiments, one or more components of system 800 may replace, be used with, and / or otherwise augment one or more components of system 10. In Fig. 8, radiation may be generated and directed to a metrology target (e.g., target 30) by a radiation source such as source 2 shown in Fig. 3 (but not repeated in Fig. 8).

[0112] In this example, metrology target 30 on substrate W comprises 2-D gratings (or multiple 1-D gratings) in multiple layers of substrate W (though only one layer is shown in Fig. 8 for simplicity). A grating may be formed of solid resist pillars, bars, vias, and / or other features, for example. Metrology target 30 may be 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 metrology target 30.Accordingly, the measured data from metrology 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. Again note that in this example, metrology target 30 may represent one or more layers comprising one or more metrology marks.

[0113] Fig. 8 illustrates one or more lenses 802, 804 (one or both of which may be considered an imaging lens) configured to receive reflected plus and minus first order radiation 806 and 808, respectively, from metrology target 30 (e.g., the first and second metrology marks in different layers described above) and direct the received reflected radiation 806 and 808 toward radiation sensor 4 (which includes first and second sensors as described above). Metrology target 30 has a certain position 816 with respect to radiation sensor 4. There is a phase difference 814 between radiation 806 and 808. In this example, a phase fit 810 may be performed, including generating and / or analyzing a two dimensional (2D) interference (or fringe) pattern 812 (e.g., as described herein), and / or other operations.

[0114] Fig. 8 also illustrates an example of tilted fringes in interference pattern 850, which can be used to determine overlay as described herein. Interference pattern 850 is intensity modulated and is generated based on + / - 1storder diffracted radiation from two (x) pads of metrology target 30. For example, radiation received by a radiation sensor (e.g., sensor 4 shown in Fig. 3) comprises diffracted radiation. The radiation sensor (and / or one or more processors PRO of the radiation sensor - see Fig. 3 and Fig. 12) is configured to generate a metrology signal, which comprises an intensity modulated fringe pattern such as interference (or fringe) patterns 812 and / or 850. In Fig. 8 and interference patterns 812 and 850, the darker and lighter lines that run at an angle through each rectangle are fringes. Intensity modulation comprises variation in the intensity of radiation reflected by target 30 and received by sensor 4 from across a grating. In Fig. 8, intensity modulation is illustrated by how dark or how light the varying darker and lighter lines are. The intensity modulated interference (or fringe) patterns 812 and / or 850 may comprise a one, two, or more dimensional interference pattern.

[0115] Fig. 9 illustrates yet another example metrology system 900. System 900 is the same as or similar to system 10 described above with respect to Fig. 3, and / or system 800 shown in Fig. 8, with one or more components of system 900 being similar to and / or the same as one or more components of system 10 and / or system 800 (and Fig. 9 illustrating additional possible components of the system). In some embodiments, one or more components of system 900 may replace, be used with, and / or otherwise augment one or more components of system 10 and / or system 800. In Fig. 9, radiation 902 may be generated and directed to a metrology target (e.g., target 30, a pDBO target in this example) by a radiation source such as source 2 (also shown in Fig. 3). In this example, metrology target 30 on substrate W comprises gratings in multiple layers of substrate W (though only one layer is shown in Fig. 9 for simplicity).

[0116] Fig. 9 illustrates one or more lenses 904, 906, 908, 910 (note that lenses 908 and / or 910 may be considered an imaging lens in this example); mirrors 903, 905, and 907; a detection pupil 912; animage plane 914; and an illumination pupil 916 and / or other components configured to direct (and / or are otherwise associated with directing) radiation 902 from source 2 to metrology target 30, and direct diffracted radiation 902 from metrology target 30 toward radiation sensor 4 (which may include first and second sensors as described above).

[0117] Fig. 10 illustrates additional possible components of one or more of the metrology systems described herein (e.g., those shown in Fig. 3, Fig. 8, and / or Fig. 9). As shown in Fig. 10, + / - 1storder diffracted radiation (in this example) may pass through a detection pupil 1000 (which may be similar to and / or the same as detection pupil 912 shown in Fig. 9), where a splitter 1002 (e.g., a nonpolarizing beam splitter) splits the radiation for first and second portions 1004 and 1006 of the metrology system (e.g., system 10, 800, and / or 900). In some embodiments, the first and second portions 1004 and 1006 of the metrology system are configured such that, in first portion 1004, a first radiation sensor 1010 (as described above) has a single branch (e.g., as shown by the single row of arrows). This may be an alignment portion or branch, for example. In second portion 1006, a second radiation sensor 1012 has two branches (e.g., as indicated by the arrows splitting in two different directions). The two branches are created by twofold partitioning with a partitioned wedge 1020. The partitioned wedge 1020 comprises (e.g., creates, includes, and / or surrounds in this example) a starting point of the two branches, for example. The second portion may be an overlay portion, for example.

[0118] First portion 1004 (e.g., an alignment branch) and first radiation sensor 1010 are configured for generating a first image based metrology signal. First radiation sensor 1010 is configured to generate a first image based metrology signal based on interference of coherent diffracted radiation for -i-nth and -nth (+ / - 1stin this example) diffraction orders of higher than Oth order diffracted radiation, as received from the metrology target through the imaging lens (e.g., as described above). The first image based metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation superimposed on a background signal, and / or other information. In some embodiments, the diffracted radiation comprises two first order diffracted radiation beams (as described above), and the first radiation sensor is configured to generate the intensity modulated fringe pattern based on the two first order diffracted radiation beams.

[0119] At least two second image based metrology signals are generated with second radiation sensor 1012 in second portion 1006 of the metrology system, and / or other components. Second radiation sensor 1012 is configured to generate at least two second image based metrology signals based on separate dark field imaging with the -i-nth and -nth diffraction orders (+ / - 1stin this example) received from the metrology target through the imaging lens. Separate signals are generated with partitioned wedge 1020 with at least a twofold partitioning, for example. The at least two second image based metrology signals comprise an intensity modulated pattern for each of the metrology marks of the target.

[0120] Fig. 11 illustrates determining overlay and / or overlay and alignment values in a given direction in a two-dimensional plane of a patterned substrate based on an intensity modulated fringepattern 1101, and at least two separate dark field patterns realized with the +nth and -nth diffraction orders separately, the aberration information, and the set of window functions. As described above, the one or more processors are configured to determine (e.g., to measure, acquire through measurements, identify in acquired measurements, etc.) a plurality of field dependent image based functions based on the intensity modulated fringe pattern, the at least two separate patterns realized with the -i-nth and -nth diffraction separately, the aberration information, the set of window functions, and or other information. The one or more processors are configured to determine (e.g., to estimate from the measured field dependent image based functions, to infer from these measurements, etc.) the overlay value, and / or the overlay value and the alignment value associated with a given direction, by “solving” the plurality of field dependent image based functions. “Solving” may comprise fitting the plurality of determined field dependent image based functions to parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, and, in addition, a number of nuisance parameters, and / or other solving operations. The quantity of the plurality of field dependent image based functions corresponds to a number of known variables in the plurality of field dependent image based functions. In some embodiments, a number of unknows in the plurality of field dependent image based functions is less than or equal to a quantity of the plurality of field dependent image based functions.

[0121] In some embodiments, the one or more processors are configured to determine (e.g., a kind of intermediate action, where the one or more processors start from the measurements - from the latter the one or more processors determine the intermediate variables, and from these variables, the one or more processors determine, estimate, and / or infer the parameters of interest, being overlay, or overlay and alignment, for a given direction), for each of at least two given directions (e.g., x and y in this example): an amplitude of each of the at least two diffracted -i-nth and -nth radiation (e.g., +lstand - 1storder diffracted radiation in this example) received from a first pad (see Fig. 7 for an example of a pad) and an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a second pad, a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the second pad, and a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the first pad, and / or a phase offset due to and linear in an alignment error between diffracted -i-nth and -nth radiation. The phase offset is identical for the second pad and the first pad of the target. These determinations (and / or estimations, inferences, etc.) are based on the intensity modulated fringe pattern and / or based on the at least two second image based metrology signals comprising an intensity modulated pattern for each of the at least two metrology marks of target , and / or other information. The one or more processors are configured to fit the plurality of determined field dependent image based functions to their parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, using the amplitudes, phases, and / or phase offsets.

[0122] In Fig. 11, X and Y represent physical directions on a target. The +lstand -1stare example diffracted radiation orders, p indicates a coordinate or position at an exit pupil, E indicates a complexvalued electromagnetic field, H indicates a 2D vector in the real space of the sample and image, I is image intensity, Al is alignment position, o is overlay, and W indicates a window function. Two contributions to the 1st order of diffraction from the top grating and the bottom grating of a target can be written as (in terms of their amplitudes r and t and their phases <prand <pt): EtOp= rand Ebot= t where o and d are the (un-scaled versions of) overlay and the overlay bias, respectively, where p is the pitch of the gratings as present in the respective pads at the top layer and the bottom layer, and where 2ji / p is a scaling factor. The total E field, E, is Etop+ Ebot. In addition, “A” may be used to indicate t / r, short-hand notation for the overlay-stack-phase may be A<pr-t= (pt-(pr, and a notation for generalized bias may be kd. A pad- window function may be written as W / ft( (H-Hkd) for a kth pad, centered around the position Hkd. Further, p+ist = -p ist is the 2D vector describing the position of the -4-lst and -1st orders within the NA of the imaging lens in a symmetric alignment imaging setting, which should not be considered limiting the scope of the invention (with an entrance pupil of two-by-two mutually coherent delta-functions, two mutually coherent ones for each direction of overlay, x & y). It should be noted that the size of the +1 st and -1st orders may be finite, and in such case they are build up by pairs of mutually coherent delta-functions, but there is no intended phase relation between different pairs that make up the finite size of the +1 st and -1st orders.

[0123] In some embodiments, 4D aberrations may be described by a wave-aberration function W4Dp,H), for example, with p indicating a 2D (Fourier space) coordinate at an exit pupil and H indicating a 2D (real space) coordinat in an object field.

[0124] Fig. 11 illustrates several examples of measurements that may be made and inserted into the field dependent image based functions as known variables. Fig. 11 illustrates X and Y pads 1102 (of a target such as target 30 described above) and their relative offsets (e.g., = / - d), with k = -1 and k = +1 for the generic biases denoted kd. Fig. 11 illustrates various measurements 1104 associated with an alignment portion (or branch) - see Fig. 10 - of the metrology system (e.g., system 10, 800, 900 shown in Fig. 3, 8, 9) system that may be determined, and various measurements 1106 associated with an overlay portion (or branch, again see Fig. 10). Measurements 1104 include alignment related measurements from a main diagonal 1110, and an off diagonal 1112. Note that 1110 indicates two separate measurements, and also 1112 denotes two separate measurements, each time one measurement per pad.

[0125] Measurements 1106 include pDBO (in this example) measurements 1114, 1116, 1118, 1120 made based on signals from different wedges or wedge quadrants (NW, NE, SW, and SE).

[0126] Fig. 11 also shows a derived equation 1150 showing that overlay and alignment are partially disentangled (they are in some way entangled in the alignment signals of the first sensor, which is why they are jointly determined / estimated, and not separately), corresponding measurements 1152,and corresponding unknowns 1154. As shown by reference numerals 1156 and 1158, overlay (o) is encoded in interference between a top and bottom grating of a pDBO target (in this example). This encoding is different for both 1storders of diffraction, assuming that <pr-t4= 0. As indicated at 1160, alignment yields an overall phase shift (with cc indicating a complex conjugate - a mathematical expression that the previous expression is related but after complex conjugation.

[0127] Equation 1150 contains enough information for fitting the unknown parameters (i.e., 1154). The set of 4D aberrations are known (as described above), and the simplified pad model in terms of the expressions for Ek<rlstis sufficiently accurate to determine overlay and / or alignment. For example, here there are eight parameters for pDBO (X gratings [r, A, <pr-t(which may be considered nuisance parameters here) and o (a parameter of interest)]x; and Y gratings [r, A, <pr-t(which may be considered nuisance parameters here) and o (a parameter of interest)],. There are also eight measurements that can be made for pDBO (see measurements associated with NW, NE, SW, and SE quadrants described above). For alignment, there are 10 parameters (X gratings [r, A, <pr-t(which may be considered nuisance parameters here) and o, HAI (parameter of interests)]x; and Y gratings [r, A, <pr-t(which may be considered nuisance parameters here) and o, HAI (parameters of interest)],. There are also as many as twelve measurements that can be made for alignment (see measurements associated with alignment described above). Equations for each of the unknowns, given the numbers of measurable parameters, can be generated and “solved” (sequentially or simultaneously as described above).

[0128] 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.

[0129] 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. These parameters may be adjusted to better measure features with specific shapes, enhance the intensity ofreflected 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.

[0130] 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 604 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, that causes a change in the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and / or other adjustments.

[0131] Fig. 12 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. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0132] Computer system CS may be coupled via bus BS to a display DS, such as a cathode ray tube (CRT) or 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.

[0133] 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.

[0134] 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 floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other 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.

[0135] 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 theinstructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infrared transmitter to 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.

[0136] 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 to a corresponding type of telephone line. 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.

[0137] 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.

[0138] 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 nonvolatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0139] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. A metrology system, comprising: an imaging lens configured to transmit diffracted radiation received from a target comprising 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 imaging lens contributing toaberrations in the diffracted radiation, as the diffracted radiation is subject to interference yielding an image at a detection plane, thereby impacting a quality of the image; a first radiation sensor in a first portion of the metrology system, the first radiation sensor configured to generate a first image based metrology signal based on interference of coherent diffracted radiation for +nth and -nth diffraction orders of higher than Oth order diffracted radiation, as received from the metrology target through the imaging lens, the first image based metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation superimposed on a background signal; a second radiation sensor in a second portion of the metrology system, the second radiation sensor configured to generate at least two second image based metrology signals based on separate dark field imaging with the -i-nth and - nth diffraction orders received from the metrology target through the imaging lens, wherein separate signals are generated with a partitioned wedge with at least a twofold partitioning, the at least two second image based metrology signals comprising an intensity modulated pattern for each of the metrology marks of target; and one or more processors operatively coupled to the first radiation sensor, and the second radiation sensor, the second radiation sensor associated with the at least twofold partitioned wedge, the one or more processors configured to: obtain aberration information associated with the imaging lens, determine a set of window functions for each measured signal associated with multiple pads of the target, each pad comprising at least portions of the first and second metrology marks, the multiple pads relate to a given direction in a two-dimensional plane of the patterned substrate, the given direction comprising a direction in which measurement is performed; and determine an overlay value, and / or an overlay value and an alignment value in the given direction in the two-dimensional plane of the patterned substrate, based on the intensity modulated fringe pattern, and at least two separate dark field patterns realized with the -i-nth and -nth diffraction orders separately, the aberration information, and the set of window functions.2. The system of clause 1 , wherein the -i-nth and -nth diffraction orders of higher than Oth order diffracted radiation comprise +1 st and -1st diffraction orders.3. The system of any of the previous clauses, wherein the one or more processors are configured to determine a plurality of field dependent image based functions based on the intensity modulated fringe pattern, the at least two separate patterns realized with the -i-nth and -nth diffraction separately, the aberration information, and the set of window functions, and determine the overlay value, and / or the overlay value and the alignment value associated with a given direction, by solving the plurality of field dependent image based functions.4. The system of any of the previous clauses, wherein solving comprises fitting the plurality of determined field dependent image based functions to parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value.5. The system of any of the previous clauses wherein the set of window functions for each measured signal is associated with at least two given directions for four pads of the target, with two of the fourpads associated with a first given direction, and another two of the four pads associated with a second given direction.6. The system of any of the previous clauses, wherein the one or more processors are configured to: determine, for each of the at least two given directions: an amplitude of each of the at least two diffracted +nth and -nth radiation received from a first pad and an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a second pad, a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the second pad, and a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the first pad, and / or a phase offset due to and linear in an alignment error between diffracted -i-nth and -nth radiation, the phase offset being identical for the second pad and the first pad of the target, based on the intensity modulated fringe pattern and / or based on the at least two second image based metrology signals comprising an intensity modulated pattern for each of the at least two metrology marks of target , and fit the plurality of determined field dependent image based functions to their parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, using the amplitudes, phases, and / or phase offsets.7. The system of any of the previous clauses, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted sequentially such that: the alignment value is determined based on the signal from the first radiation sensor using overlay information derived from the signals from the second radiation sensor, after determining the overlay value based on the signals from the second radiation sensor.8. The system of any of the previous clauses, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted simultaneously such that the alignment value is determined at the same time as the overlay value.9. The system of any of the previous clauses, wherein a quantity of the plurality of field dependent image based functions corresponds to a number of known variables in the plurality of field dependent image based functions.10. The system of any of the previous clauses, wherein a number of unknows in the plurality of field dependent image based functions is less than or equal to a quantity of the plurality of field dependent image based functions.11. The system of any of the previous clauses, further comprising the partitioned wedge with the least a twofold partitioning, wherein the first and second portions of the metrology system are configured such that, in the first portion, the first radiation sensor has a single branch, and, in the second portion, the second radiation sensor has two branches related to the twofold partitioning with the partitioned wedge, the partitioned wedge comprising a starting point of the two branches.12. The system of any of the previous clauses, wherein the aberration information comprises an aberration function.13. The system of any of the previous clauses, wherein the aberration information is determined based on an electronic model configured to simulate the imaging lens.14. The system of any of the previous clauses, wherein the aberration information is four dimensional (4D).15. The system of any of the previous clauses, wherein the target comprising the first metrology mark in the first layer of the patterned substrate and the second metrology mark in the second layer comprises multiple pads, and wherein each pad comprises a top grating in the second layer and a bottom grating in the first layer.16. The system of any of the previous clauses, wherein the aberration information is known for the imaging lens, and is obtained by the one or more processors from electronic storage.17. The system of any of the previous clauses, further comprising a radiation source operatively coupled to the one or more processors and the radiation sensors, the radiation source configured to irradiate the target with radiation.18. The system of any of the previous clauses, wherein the radiation from the radiation source comprises two incident mutually coherent beams oriented at different angles relative to the target, the two incident beams configured to be diffracted by the first and second metrology marks to form the diffracted radiation, wherein the different angles comprise azimuths of 0 and 180 degrees at a same tilt angle.19. The system of any of the previous clauses, wherein the diffracted radiation comprises two first order diffracted radiation beams, the first radiation sensor configured to generate the intensity modulated fringe pattern based on the two first order diffracted radiation beams.20. The system of any of the previous clauses, wherein a window function in the set of window functions is determined based on physical edges of the first and second metrology marks.21. The system of any of the previous clauses, wherein the window function in the set of window functions is determined based on geometry of a pad.22. The system of any of the previous clauses, wherein the window function is equal to 1 when there are no aberrations associated with the imaging lens and the target is infinite in size.23. The system of any of the previous clauses, wherein the second metrology mark is above the first metrology mark in the patterned substrate.24. The system of any of the previous clauses, wherein the target comprises at least one pad that is shifted relative to a different pad by a known bias amount.25. The system of any of the previous clauses, wherein pads comprise gratings.26. The system of any of the previous clauses, wherein the target comprises a diffraction-based overlay metrology target.27. The system of any of the previous clauses, wherein pads of the first and second metrology marks comprise gratings.28. The system of any of the previous clauses, wherein the target comprises a Micro Diffraction Based Overlay (pDBO) target.29. The system of any of the previous clauses, wherein the first and / or second radiation sensor comprises an interferometer.30. The system of any of the previous clauses, wherein the overlay value and / or the alignment value is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.31. A metrology method, comprising: transmitting, with an imaging lens, diffracted radiation received from a target comprising 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 imaging lens contributing to aberrations in the diffracted radiation, as the diffracted radiation is subject to interference yielding an image at a detection plane, thereby impacting a quality of the image; generating, with a first radiation sensor in a first portion of a metrology system, a first image based metrology signal based on interference of coherent diffracted radiation for +nth and -nth diffraction orders of higher than Oth order diffracted radiation, as received from the metrology target through the imaging lens, the first image based metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation superimposed on a background signal; generating, with a second radiation sensor in a second portion of the metrology system, at least two second image based metrology signals based on separate dark field imaging with the -i-nth and -nth diffraction orders received from the metrology target through the imaging lens, wherein separate signals are generated with a partitioned wedge with at least a twofold partitioning, the at least two second image based metrology signals comprising an intensity modulated pattern for each of the metrology marks of target; obtaining, with one or more processors operatively coupled to the first radiation sensor, and the second radiation sensor, aberration information associated with the imaging lens, determining, with the one or more processors, a set of window functions for each measured signal associated with multiple pads of the target, each pad comprising at least portions of the first and second metrology marks, the multiple pads relate to a given direction in a two-dimensional plane of the patterned substrate, the given direction comprising a direction in which measurement is performed; and determining, with the one or more processors, an overlay value, and / or an overlay value and an alignment value in the given direction in the two- dimensional plane of the patterned substrate, based on the intensity modulated fringe pattern, and at least two separate dark field patterns realized with the -i-nth and -nth diffraction orders separately, the aberration information, and the set of window functions.32. The method of clause 31, wherein the -i-nth and -nth diffraction orders of higher than Oth order diffracted radiation comprise +1 st and -1st diffraction orders.33. The method of any of the previous clauses, further comprising determining, with the one or more processors, a plurality of field dependent image based functions based on the intensity modulated fringe pattern, the at least two separate patterns realized with the +nth and -nth diffraction separately, the aberration information, and the set of window functions, and determine the overlay value, and / or the overlay value and the alignment value associated with a given direction, by solving the plurality of field dependent image based functions.34. The method of any of the previous clauses, wherein solving comprises fitting the plurality of determined field dependent image based functions to parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value.35. The method of any of the previous clauses, wherein the set of window functions for each measured signal is associated with at least two given directions for four pads of the target, with two of the four pads associated with a first given direction, and another two of the four pads associated with a second given direction.36. The method of any of the previous clauses, further comprising: determining, with the one or more processors, for each of the at least two given directions: an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a first pad and an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a second pad, a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the second pad, and a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the first pad, and / or a phase offset due to and linear in an alignment error between diffracted -i-nth and -nth radiation, the phase offset being identical for the second pad and the first pad of the target, based on the intensity modulated fringe pattern and / or based on the at least two second image based metrology signals comprising an intensity modulated pattern for each of the at least two metrology marks of target, and fitting, with the one or more processors, the plurality of determined field dependent image based functions to their parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, using the amplitudes, phases, and / or phase offsets.37. The method of any of the previous clauses, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted sequentially such that: the alignment value is determined based on the signal from the first radiation sensor using overlay information derived from the signals from the second radiation sensor, after determining the overlay value based on the signals from the second radiation sensor.38. The method of any of the previous clauses, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted simultaneously such that the alignment value is determined at the same time as the overlay value.39. The method of any of the previous clauses, wherein a quantity of the plurality of field dependent image based functions corresponds to a number of known variables in the plurality of field dependent image based functions.40. The method of any of the previous clauses, wherein a number of unknows in the plurality of field dependent image based functions is less than or equal to a quantity of the plurality of field dependent image based functions.41. The method of any of the previous clauses, further comprising configuring the first and second portions of the metrology system such that, in the first portion, the first radiation sensor has a single branch, and, in the second portion, the second radiation sensor has two branches related to the twofold partitioning with the partitioned wedge, the partitioned wedge comprising a starting point of the two branches.42. The method of any of the previous clauses, wherein the aberration information comprises an aberration function.43. The method of any of the previous clauses, wherein the aberration information is determined based on an electronic model configured to simulate the imaging lens.44. The method of any of the previous clauses, wherein the aberration information is four dimensional (4D).45. The method of any of the previous clauses, wherein the target comprising the first metrology mark in the first layer of the patterned substrate and the second metrology mark in the second layer comprises multiple pads, and wherein each pad comprises a top grating in the second layer and a bottom grating in the first layer.46. The method of any of the previous clauses, wherein the aberration information is known for the imaging lens, and is obtained by the one or more processors from electronic storage.47. 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 sensors, the target with radiation.48. The method of any of the previous clauses, wherein the radiation from the radiation source comprises two incident mutually coherent beams oriented at different angles relative to the target, the two incident beams configured to be diffracted by the first and second metrology marks to form the diffracted radiation, wherein the different angles comprise azimuths of 0 and 180 degrees at a same tilt angle.49. The method of any of the previous clauses, wherein the diffracted radiation comprises two first order diffracted radiation beams, the first radiation sensor configured to generate the intensity modulated fringe pattern based on the two first order diffracted radiation beams.50. The method of any of the previous clauses, wherein a window function in the set of window functions is determined based on physical edges of the first and second metrology marks.51. The method of any of the previous clauses, wherein the window function in the set of window functions is determined based on geometry of a pad.52. The method of any of the previous clauses, wherein the window function is equal to 1 when there are no aberrations associated with the imaging lens and the target is infinite in size.53. The method of any of the previous clauses, wherein the second metrology mark is above the first metrology mark in the patterned substrate.54. The method of any of the previous clauses, wherein the target comprises at least one pad that is shifted relative to a different pad by a known bias amount.55. The method of any of the previous clauses, wherein pads comprise gratings.56. The method of any of the previous clauses, wherein the target comprises a diffraction-based overlay metrology target.57. The method of any of the previous clauses, wherein pads of the first and second metrology marks comprise gratings.58. The method of any of the previous clauses, wherein the target comprises a Micro Diffraction Based Overlay (pDBO) target.59. The method of any of the previous clauses, wherein the first and / or second radiation sensor comprises an interferometer.60. The method of any of the previous clauses, wherein the overlay value and / or the alignment value is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.61. A non-transitory computer readable medium having instructions thereon, the instructions when executed by a computer comprising one or more processors, causing the computer to perform a method, comprising: obtaining aberration information associated with an imaging lens, determining, with the one or more processors, a set of window functions for each measured signal associated with multiple pads of a metrology target, each pad comprising at least portions of first and second metrology marks, the multiple pads relate to a given direction in a two-dimensional plane of a patterned substrate, the given direction comprising a direction in which measurement is performed; and determining, with the one or more processors, an overlay value, and / or an overlay value and an alignment value in the given direction in the two-dimensional plane of the patterned substrate, based on an intensity modulated fringe pattern, and at least two separate dark field patterns realized with -i-nth and -nth diffraction orders separately, the aberration information, and the set of window functions, wherein: the imaging lens is configured to transmit diffracted radiation received from the target comprising the 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 imaging lens contributing to aberrations in the diffracted radiation, as the diffracted radiation is subject to interference yielding an image at a detection plane, thereby impacting a quality of the image; a first image based metrology signal is generated with a first radiation sensor in a first portion of a metrology system, based on interference of coherent diffracted radiation for -i-nth and -nth diffraction orders of higher than Oth order diffracted radiation, as received from the metrology target through the imaging lens, the firstimage based metrology signal comprising the intensity modulated fringe pattern for the diffracted radiation superimposed on a background signal; and at least two second image based metrology signals are generated with a second radiation sensor in a second portion of the metrology system, based on separate dark field imaging with the +nth and -nth diffraction orders received from the metrology target through the imaging lens, wherein separate signals are generated with a partitioned wedge with at least a twofold partitioning, the at least two second image based metrology signals comprising an intensity modulated pattern for each of the metrology marks of target.62. The medium of clause 61, wherein the -i-nth and -nth diffraction orders of higher than Oth order diffracted radiation comprise +1 st and -1st diffraction orders.63. The medium of any of the previous clauses, the method further comprising determining, with the one or more processors, a plurality of field dependent image based functions based on the intensity modulated fringe pattern, the at least two separate patterns realized with the -i-nth and -nth diffraction separately, the aberration information, and the set of window functions, and determine the overlay value, and / or the overlay value and the alignment value associated with a given direction, by solving the plurality of field dependent image based functions.64. The medium of any of the previous clauses, wherein solving comprises fitting the plurality of determined field dependent image based functions to parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value.65. The medium of any of the previous clauses, wherein the set of window functions for each measured signal is associated with at least two given directions for four pads of the target, with two of the four pads associated with a first given direction, and another two of the four pads associated with a second given direction.66. The medium of any of the previous clauses, the method further comprising: determining, with the one or more processors, for each of the at least two given directions: an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a first pad and an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a second pad, a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the second pad, and a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the first pad, and / or a phase offset due to and linear in an alignment error between diffracted -i-nth and -nth radiation, the phase offset being identical for the second pad and the first pad of the target, based on the intensity modulated fringe pattern and / or based on the at least two second image based metrology signals comprising an intensity modulated pattern for each of the at least two metrology marks of target, and fitting, with the one or more processors, the plurality of determined field dependent image based functions to their parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, using the amplitudes, phases, and / or phase offsets.67. The medium of any of the previous clauses, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted sequentially such that: the alignment value is determined based on the signal from the first radiation sensor using overlay information derived from the signals from the second radiation sensor, after determining the overlay value based on the signals from the second radiation sensor.68. The medium of any of the previous clauses, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted simultaneously such that the alignment value is determined at the same time as the overlay value.69. The medium of any of the previous clauses, wherein a quantity of the plurality of field dependent image based functions corresponds to a number of known variables in the plurality of field dependent image based functions.70. The medium of any of the previous clauses, wherein a number of unknows in the plurality of field dependent image based functions is less than or equal to a quantity of the plurality of field dependent image based functions.71. The medium of any of the previous clauses, wherein the first and second portions of the metrology system are configured such that, in the first portion, the first radiation sensor has a single branch, and, in the second portion, the second radiation sensor has two branches related to the twofold partitioning with the partitioned wedge, the partitioned wedge comprising a starting point of the two branches.72. The medium of any of the previous clauses, wherein the aberration information comprises an aberration function.73. The medium of any of the previous clauses, wherein the aberration information is determined based on an electronic model configured to simulate the imaging lens.74. The medium of any of the previous clauses, wherein the aberration information is four dimensional (4D).75. The medium of any of the previous clauses, wherein the target comprising the first metrology mark in the first layer of the patterned substrate and the second metrology mark in the second layer comprises multiple pads, and wherein each pad comprises a top grating in the second layer and a bottom grating in the first layer.76. The medium of any of the previous clauses, wherein the aberration information is known for the imaging lens, and is obtained by the one or more processors from electronic storage.77. The medium of any of the previous clauses, wherein a radiation source operatively coupled to the one or more processors and the radiation sensors is configured to irradiate the target with radiation.78. The medium of any of the previous clauses, wherein the radiation from the radiation source comprises two incident mutually coherent beams oriented at different angles relative to the target, thetwo incident beams configured to be diffracted by the first and second metrology marks to form the diffracted radiation, wherein the different angles comprise azimuths of 0 and 180 degrees at a same tilt angle.79. The medium of any of the previous clauses, wherein the diffracted radiation comprises two first order diffracted radiation beams, the first radiation sensor configured to generate the intensity modulated fringe pattern based on the two first order diffracted radiation beams.80. The medium of any of the previous clauses, wherein a window function in the set of window functions is determined based on physical edges of the first and second metrology marks.81. The medium of any of the previous clauses, wherein the window function in the set of window functions is determined based on geometry of a pad.82. The medium of any of the previous clauses, wherein the window function is equal to 1 when there are no aberrations associated with the imaging lens and the target is infinite in size.83. The medium of any of the previous clauses, wherein the second metrology mark is above the first metrology mark in the patterned substrate.84. The medium of any of the previous clauses, wherein the target comprises at least one pad that is shifted relative to a different pad by a known bias amount.85. The medium of any of the previous clauses, wherein pads comprise gratings.86. The medium of any of the previous clauses, wherein the target comprises a diffraction-based overlay metrology target.87. The medium of any of the previous clauses, wherein pads of the first and second metrology marks comprise gratings.88. The medium of any of the previous clauses, wherein the target comprises a Micro Diffraction Based Overlay (pDBO) target.89. The medium of any of the previous clauses, wherein the first and / or second radiation sensor comprises an interferometer.90. The medium of any of the previous clauses, wherein the overlay value and / or the alignment value is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.

[0140] 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.

[0141] 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.

[0142] 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

CLAIMS1. A metrology system, comprising: an imaging lens configured to transmit diffracted radiation received from a target comprising 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 imaging lens contributing to aberrations in the diffracted radiation, as the diffracted radiation is subject to interference yielding an image at a detection plane, thereby impacting a quality of the image; a first radiation sensor in a first portion of the metrology system, the first radiation sensor configured to generate a first image based metrology signal based on interference of coherent diffracted radiation for +nth and -nth diffraction orders of higher than 0thorder diffracted radiation, as received from the metrology target through the imaging lens, the first image based metrology signal comprising an intensity modulated fringe pattern for the diffracted radiation superimposed on a background signal; a second radiation sensor in a second portion of the metrology system, the second radiation sensor configured to generate at least two second image based metrology signals based on separate dark field imaging with the -i-nth and -nth diffraction orders received from the metrology target through the imaging lens, wherein separate signals are generated with a partitioned wedge with at least a twofold partitioning, the at least two second image based metrology signals comprising an intensity modulated pattern for each of the metrology marks of target; and one or more processors operatively coupled to the first radiation sensor, and the second radiation sensor, the second radiation sensor associated with the at least twofold partitioned wedge, the one or more processors configured to: obtain aberration information associated with the imaging lens, determine a set of window functions for each measured signal associated with multiple pads of the target, each pad comprising at least portions of the first and second metrology marks, the multiple pads relate to a given direction in a two-dimensional plane of the patterned substrate, the given direction comprising a direction in which measurement is performed; and determine an overlay value, and / or an overlay value and an alignment value in the given direction in the two-dimensional plane of the patterned substrate, based on the intensity modulated fringe pattern, and at least two separate dark field patterns realized with the -i-nth and -nth diffraction orders separately, the aberration information, and the set of window functions.

2. The system of claim 1 , wherein the -i-nth and -nth diffraction orders of higher than 0thorder diffracted radiation comprise +lstand -1stdiffraction orders.

3. The system of any of claims 1 or 2, wherein the one or more processors are configured to determine a plurality of field dependent image based functions based on the intensity modulated fringe pattern, the at least two separate patterns realized with the +nth and -nth diffraction separately, the aberration information, and the set of window functions, and determine the overlay value, and / or the overlay value and the alignment value associated with a given direction, by solving the plurality of field dependent image based functions.

4. The system of claim 3, wherein solving comprises fitting the plurality of determined field dependent image based functions to parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value.

5. The system of claim 4, wherein the set of window functions for each measured signal is associated with at least two given directions for four pads of the target, with two of the four pads associated with a first given direction, and another two of the four pads associated with a second given direction.

6. The system of claim 5, wherein the one or more processors are configured to: determine, for each of the at least two given directions: an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a first pad and an amplitude of each of the at least two diffracted -i-nth and -nth radiation received from a second pad, a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the second pad, and a phase difference between diffracted -i-nth order radiation and diffracted -nth order radiation received from the first pad, and / or a phase offset due to and linear in an alignment error between diffracted -i-nth and -nth radiation, the phase offset being identical for the second pad and the first pad of the target, based on the intensity modulated fringe pattern and / or based on the at least two second image based metrology signals comprising an intensity modulated pattern for each of the at least two metrology marks of target, and fit the plurality of determined field dependent image based functions to their parametrized versions in terms of multiple parameters comprising the overlay value, and / or the overlay value and alignment value, using the amplitudes, phases, and / or phase offsets.

7. The system of claim 6, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted sequentially such that: the alignment value is determined based on the signal from the first radiation sensor using overlay information derived from the signals from the second radiation sensor,after determining the overlay value based on the signals from the second radiation sensor.

8. The system of claim 6, wherein the one or more processors are configured to determine the overlay value and the alignment value, and wherein the plurality of field dependent image based functions are fitted simultaneously such that the alignment value is determined at the same time as the overlay value.

9. The system of any of claims 3-8, wherein a quantity of the plurality of field dependent image based functions corresponds to a number of known variables in the plurality of field dependent image based functions.

10. The system of any of claims 3-9, wherein a number of unknows in the plurality of field dependent image based functions is less than or equal to a quantity of the plurality of field dependent image based functions.

11. The system of any of claims 1-10, further comprising the partitioned wedge with the least a twofold partitioning, wherein the first and second portions of the metrology system are configured such that, in the first portion, the first radiation sensor has a single branch, and, in the second portion, the second radiation sensor has two branches related to the twofold partitioning with the partitioned wedge, the partitioned wedge comprising a starting point of the two branches.

12. The system of any of claims 1-11, wherein the aberration information comprises an aberration function.

13. The system of any of claims 1-12, wherein the aberration information is determined based on an electronic model configured to simulate the imaging lens.

14. The system of any of claims 1-13, wherein the aberration information is four dimensional (4D).

15. The system of any of claims 1-14, wherein the target comprising the first metrology mark in the first layer of the patterned substrate and the second metrology mark in the second layer comprises multiple pads, and wherein each pad comprises a top grating in the second layer and a bottom grating in the first layer.

Images