WO2025201719A1

WO2025201719A1 - Image based metrology based on local signal strength for distorted diffracted radiation

Info

Publication number: WO2025201719A1
Application number: PCT/EP2025/053342
Authority: WO
Inventors: Simon Reinald HUISMAN
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2024-03-27
Filing date: 2025-02-07
Publication date: 2025-10-02
Anticipated expiration: 2026-09-27

Abstract

In a semiconductor structure, metrology marks may be covered by non-planar layers, such as resist layers. A resist layer may have tilted or dished areas that distort radiation diffracted by the metrology marks. This reduces measurement accuracy for interferometer based systems. Advantageously, the present systems and methods use an imaging sensor such as a camera (instead of an interferometer) and local signal strength in the distorted diffracted radiation to generate accurate alignment, overlay, and/or other measurements. For example, a camera may generate a metrology signal in the form of an image, based on diffracted radiation received from a metrology mark in a layer of a patterned substrate. Local signal strength may be determined based on the image; and a position of the metrology mark may be determined based on the local signal strength. The local signal strength can be determined in various manners.

Description

IMAGE BASED METROLOGY BASED ON LOCAL SIGNAL STRENGTH FOR DISTORTED DIFFRACTED RADIATION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63/570,748 which was filed on March 27, 2024 and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] This description relates generally to image based metrology based on local signal strength for distorted diffracted radiation.

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, micro-electro mechanical systems (MEMS) and other devices.

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

[0008] This process in which features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus are printed, is commonly known as low-ki lithography, according to the resolution formula CD = 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). These resolution enhancement techniques often depend on accurate metrology measurements such as alignment and/or overlay of one layer relative to another, for example.

SUMMARY

[0009] In a semiconductor structure, metrology marks may be covered by non-planar layers, such as resist layers. A resist layer may have tilted or dished areas that distort radiation diffracted by the metrology marks. This reduces measurement accuracy for interferometer based systems. Advantageously, the present systems and methods use an imaging sensor such as a camera (instead of an interferometer) and local signal strength in the distorted diffracted radiation to generate accurate alignment, overlay, and/or other measurements. For example, a camera may generate a metrology signal in the form of an image, based on diffracted radiation received from a metrology mark in a layer of a patterned substrate. Local signal strength may be determined based on the image; and a position of the metrology mark may be determined based on the local signal strength. The local signal strength can be determined in various manners.

[0010] According to an embodiment, a metrology system is provided. The metrology system comprises a radiation sensor configured to generate a metrology signal based on diffracted radiation received from a metrology mark in a layer of a patterned substrate. The metrology signal comprises an image. The metrology system comprises one or more processors operatively coupled to the radiation sensor. The one or more processors are configured to determine a local signal strength of the metrology signal based on the image; and determine a position of the metrology mark based on the local signal strength.

[0011] In some embodiments, the radiation sensor comprises an imaging sensor. In some embodiments, the imaging sensor comprises a camera.

[0012] The metrology mark is covered by a non-planar layer of the patterned substrate that distorts the diffracted radiation. In some embodiments, the non-planar layer comprises resist. The non-planar layer comprises localized tilting or dishing. For example, the non-planar layer may comprise a top surface with one or more areas that are not parallel to the layer in the patterned substrate.

[0013] In some embodiments, determining the position of the metrology mark comprises determining a thickness profile of the non-planar layer covering the metrology mark, based on the local signal strength, and determining the position of the metrology mark based on the thickness profile.

[0014] In some embodiments, determining the local signal strength of the metrology signal based on the image comprises: determining a local intensity of one or more pixels in the image and comparing the local intensity to a nominal intensity; determining signal strength for one or more colors and/or polarizations to monitor resonances in a spectrum of the diffracted radiation; determining local contrast changes in the image to determine parts of the image that are in or out of focus; determining a gradient in local intensities and/or a gradient in local resonances in the spectrum of the diffracted and/or a gradient in local image contrast; and/or correlating changes in local signal strength, intensity, and/or contrast with curvature of a non-planar layer covering the metrology mark.

[0015] In some embodiments, the one or more processors are configured to determine alignment and/or overlay of the layer in the patterned substrate and/or a non-planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark. In some embodiments, the one or more processors are configured to facilitate correction of alignment and/or overlay of the layer in the patterned substrate and/or a non-planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark.

[0016] In some embodiments, the one or more processors are configured to determine local phase changes in the diffracted radiation, and facilitate correction of alignment and/or overlay based on the local phase changes and: a local intensity of one or more pixels in the image compared to a nominal intensity; local contrast changes in the image; and/or a gradient in local intensities and/or a gradient in local resonances in a spectrum of the diffracted and/or a gradient in local image contrast. Facilitating correction of alignment and/or overlay based on local phase changes may comprise correcting a magnification error induced by curvature of a non-planar layer covering the mark, for example.

[0017] In some embodiments, the image comprises an intensity modulated pattern. In some embodiments, the radiation sensor is configured such that the intensity modulated pattern for the diffracted radiation comprises a one or more dimensional interference pattern.

[0018] The metrology system may be a dark field or bright field metrology system.

[0019] The mark may be a periodic or non-periodic grating, for example.

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

[0021] According to another embodiment, a metrology method comprising one or more of the operations described above is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.

[0024] Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0025] Fig. 3 schematically depicts an example metrology system, according to an embodiment.

[0026] Fig. 4 schematically depicts an example metrology technique, according to an embodiment.

[0027] Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment. [0028] Fig. 6 illustrates a metrology method, according to an embodiment.

[0029] Fig. 7 illustrates a non-planar (or tilted or dished) layer of resist covering a metrology mark, according to an embodiment.

[0030] Fig. 8 illustrates how distorted diffracted radiation (e.g., caused by the non-planar layer shown in Fig. 7) can reduce measurement accuracy for an interferometer based metrology system and/or prevent such a system from being able to make measurements at all, according to an embodiment.

[0031] Fig. 9 illustrates an image based metrology system configured to interfere diffracted orders by projection, according to an embodiment.

[0032] Fig. 10 illustrates an example image that may be used to determine local signal strength(s) of a metrology signal (such that a position of a metrology mark can be determined based on the local signal strength(s), and alignment and/or overlay may be determined and/or corrected, and/or other operations may be performed based on this position), according to an embodiment.

[0033] Fig. 11 is a block diagram of an example computer system, according to an embodiment.

DETAILED DESCRIPTION

[0034] In semiconductor structures, metrology marks are more and more frequently covered by non- planar layers, such as resist layers. A resist layer may have tilted, dished, and/or other areas that distort radiation diffracted by the metrology marks. This reduces measurement accuracy for interferometer based metrology systems. For example, in interferometer based alignment sensors, resist covered metrology marks cannot be used for alignment if the amount of non-planarity (e.g., tilt, curvature, etc.) in the resist layer becomes too large. Diffracted orders (of radiation diffracted by a metrology mark) may propagate through the resist layer and to the alignment sensor beyond the mode-matching capability of interfered diffracted orders. Diffracted orders are displaced (often non- symmetrically) from the center of a pupil plane in the sensor. As a result, interferometer based alignment sensors cannot form an interferogram, which is needed to determine alignment.

[0035] In contrast, image based metrology sensors are used in the present systems and methods. These are inherently more robust for capturing signals on these types of “deformed” (from the perspective of diffracted radiation that passes through a non-planar layer of the semiconductor structure and impinges non-symmetrically on an interferometer based alignment sensor) metrology marks, since these interfere diffracted orders by projection. Hence, it does not matter if the diffracted orders are shifted in the pupil plane, provided the diffracted orders are re-imaged on the image based metrology sensor. This is because an image of a pattern of diffracted radiation is still formed, from which alignment and/or other metrology determinations may be made. The pattern itself may be non-symmetrical, or shifted by the non-planar layer, and/or may even include a magnification error related component, but the image of the pattern is still able to be analyzed (e.g., as described below) for metrology purposes.

[0036] Advantageously, the present systems and methods use an imaging sensor such as a camera (instead of an interferometer based system) and local signal strength in distorted diffracted radiation to generate accurate alignment, overlay, and/or other measurements. For example, a camera may generate a metrology signal in the form of an image, based on diffracted radiation received from a metrology mark in a layer of a patterned substrate. Local signal strength may be determined based on the image; and a position of the metrology mark may be determined based on the local signal strength. The local signal strength can be determined in various manners, and then used to determine alignment, overlay, and/or other metrics, regardless of any non-planar layer that may cover the mark.

[0037] 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 alignment and/or overlay in a semiconductor device manufacturing process, for example, or for other operations.

[0038] Although specific reference may be made in this text to the measurement of alignment and/or 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.

[0039] 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.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and/or inner radial extent (commonly referred to as o-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. 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.

[0044] 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.

[0045] 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.

[0046] Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0047] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, 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.”

[0048] 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. [0049] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.

[0050] The projection system PS may comprise a plurality of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct for aberrations (phase variations across the pupil plane throughout the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system where its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and/or deform one or more optical elements. Displacement of an optical element may be in any direction (x, y, z, or a combination thereof). Tilting of an optical element is typically out of a plane perpendicular to the optical axis, by rotating about an axis in the x and/or y directions although a rotation about the z axis may be used for a non-rotationally symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and/or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and/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.

[0051] 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.

[0052] In operation of the lithographic apparatus, a radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a shortstroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0053] The depicted apparatus may be used in at least one of the following modes. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). 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. [0054] Combinations and/or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0055] The substrate may be processed, before or after exposure, in for example a back (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multilayer IC, so that the term substrate may also refer to a substrate that already includes multiple processed layers.

[0056] 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. [0057] Various patterns on or provided by a patterning device may have different process windows, i.e., a space of processing variables under which a pattern will be produced within specification. Examples of pattern specifications that relate to potential systematic defects include checks for necking, line pull back, line thinning, CD, edge placement, overlapping, resist top loss, resist undercut and/or bridging. The process window of the patterns on a patterning device or an area thereof may be obtained by merging (e.g., overlapping) process windows of each individual pattern. The boundary of the process window of a group of patterns comprises boundaries of process windows of some of the individual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0058] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and postexposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and/or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input/output port I/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.

[0059] 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)).

[0060] 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.

[0061] 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. Applications of this diffraction-based metrology are in the measurement of alignment and/or overlay, for example.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] To enable metrology, often one or more metrology marks are specifically provided on the substrate. A metrology mark may include an overlay target, for example, an alignment mark, and/or other marks. Typically, the mark is specially designed and may comprise one or more periodic structures. For example, the mark 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 mark 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).

[0066] Fig. 3 depicts an example metrology system 10 that may be used to detect overlay, alignment, and/or perform other metrology operations. It comprises a radiation source 2 which projects or otherwise irradiates radiation onto a substrate W. Substrate W may typically include a metrology mark 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 - e.g., an imaging sensor such as a camera as described below - 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 mark 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.

[0067] As in the lithographic apparatus LA in Fig. 1 , one or more substrate tables (not shown in Fig. 4) may be provided to hold the substrate W during metrology operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where metrology system 10 is integrated with the lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a 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 metrology marks, and in the Z direction to obtain a desired location of the mark 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).

[0068] For typical metrology measurements, a metrology mark 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 mark 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. Mark 30 (e.g., 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, distortion caused by a non-planar resist layer, etc.) such that process variation manifests in variation in mark 30. Accordingly, the measured data from mark 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, mark 30 may represent one or more layers comprising one or more metrology marks.

[0069] For example, the measured data from mark 30 may indicate alignment for a layer of a semiconductor device, overlay, and/or other information. The measured data from mark 30 may be used (e.g., by the one or more processors) for determining one or more semiconductor device manufacturing process parameters based on 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 mark (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. [0070] Fig. 5 illustrates a plan view of a typical mark 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 mark 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 mark 30. The mark 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.

[0071] Fig. 6 illustrates a metrology method 600. In some embodiments, method 600 is performed as part of a semiconductor device manufacturing process. Method 600 is associated with image based metrology sensors, which as described above, are robust for capturing diffracted radiation that passes through a non-planar layer of a semiconductor structure and impinges non-symmetrically on an interferometer based alignment sensor. In some embodiments, one or more operations of method 600 may be implemented in or by system 10 illustrated in Fig. 3, system 900 shown in Fig. 9 , a computer system (e.g., as illustrated in Fig. 11 and described below), and/or in or by other systems, for example. System 10, system 900, system 1000, the computer system, and/or other components may be or form (or form one or more portions of) a bright field metrology system, a dark field metrology system, and/or other metrology systems. In some embodiments, method 600 comprises irradiating (operation 602) a metrology mark in a patterned substrate (such as a semiconductor wafer) with radiation, generating (operation 604) a metrology signal based on diffracted radiation received from the metrology mark, determining (operation 606) a local signal strength of the metrology signal, and determining (operation 608) a position of the metrology mark based on the local signal strength, determining and/or correcting (operation 610) alignment and/or overlay, and/or other operations. Method 600 is described below in the context of alignment and/or overlay, but this is not intended to be limiting. Method 600 may be generally applied to a number of different processes.

[0072] 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.

[0073] 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 in Figs. 3 and 11). The one or more processing devices may include one or more devices executing some or all of the operations of method 600 in response to (machine readable) instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and/or software to be specifically designed for execution of one or more of the operations of method 600 (e.g., see discussion related to Fig. 11 below). [0074] Operation 602 comprises irradiating a metrology mark in a patterned substrate with radiation. In some embodiments, the metrology mark comprises metrology marks in different layers of the patterned substrate, and/or other features. In some embodiments, the metrology mark is associated with an alignment and/or overlay measurement for the patterned substrate. For example, the metrology mark may be or include a dedicated alignment and/or overlay mark comprising one or more diffraction gratings in the same and/or different layers. The radiation may be diffracted by the diffraction grating(s). In some embodiments, the metrology mark comprises one or more structures in the patterned substrate capable of providing a diffraction signal (e.g., a grating or some other structure(s)). In some embodiments, the metrology mark can be any structure in a pattern design layout capable of generating a wide angle diffraction signal.

[0075] In some embodiments, the metrology mark may be included in one or more layers of a substrate in a semiconductor device structure, for example. In some embodiments, the metrology mark 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 mark 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.

[0076] In some embodiments, the metrology mark may be similar to and/or the same as mark 30 shown in Figs. 3 and/or 6-9, and/or other metrology marks. As described above, the metrology mark may be a grating in some embodiments, having a certain pitch and/or other features. The grating may be periodic or non-periodic, for example. 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 (e.g., system 10 shown in Fig. 3, computer system CS shown in Fig. 11) 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 image based metrology.

[0077] The radiation may be generated by a radiation source (e.g., source 2 shown in Fig. 3 and described above) 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 mark, sub-portions (e.g., something less than the whole) of a metrology mark, multiple metrology marks, and/or onto the substrate in other ways. In some embodiments, the metrology mark may be substantially stationary while irradiation occurs, a radiation sensor generates the metrology signal, an image of the metrology mark is generated based on the metrology signal and/or other information, and/or other operations are performed. In some embodiments, the radiation may be scanned across a metrology mark, for example. Scanning may comprise rastering the radiation over a metrology mark such that different portions of the metrology mark are irradiated at different times. 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.

[0078] Operation 604 comprises generating a metrology signal based on diffracted radiation received from a metrology mark, and/or other information. The metrology mark may be covered by a non-planar layer of the patterned substrate that distorts the diffracted radiation. The non-planar layer comprises a top surface with one or more areas that are not parallel to the layer in the patterned substrate. In some embodiments, the non-planar layer comprises localized tilting or dishing, for example. As one possible example, the non-planar layer may be a resist layer, with an uneven or undulating top surface.

[0079] Operation 604 includes detecting reflected and/or transmitted diffracted radiation from the metrology mark through the non-planar layer. Some or all of the diffracted radiation from the metrology mark may be distorted by the non-planar layer, for example. Distorted diffracted radiation comprises radiation that has been moved from an expected position to some alternate position relative to one or more components of the radiation sensor (e.g., as described herein). In some embodiments, the metrology signal comprises alignment and/or overlay position information for the layer(s) in which the metrology mark is formed, the non-planar layer, and/or other layers.

[0080] The metrology signal comprises measurement information pertaining to the metrology mark. For example, the metrology signal may comprise alignment measurement information, overlay measurement information, and/or other metrology signals. The metrology signal may be generated by a radiation sensor (e.g., such as sensor detector 4 shown in Fig. 3, sensor 990 shown in Fig. 9, etc.) and/or other components. The radiation sensor may be operatively coupled to radiation source and/or other components. In some embodiments, the radiation sensor comprises an imaging sensor. In some embodiments, the imaging sensor may comprise a camera, and/or other components, for example. The metrology signal may comprise an image, for example, and/or may take other imaging related forms.

[0081] In operation 604, detecting such radiation comprises detecting phase shifts and/or intensity (amplitude) in (diffracted) radiation received from one or more geometric features of a metrology mark, and forming an image based on this information. The one or more phase shifts and/or amplitude correspond to one or more dimensions of a feature. For example, the phase shift and/or amplitude of diffracted radiation from one side of a feature is different relative to the phase shift and/or amplitude of diffracted radiation from another side of the feature. Detecting the one or more phase shifts and/or amplitude (intensity) in the radiation from the metrology mark comprises imaging 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. Any and/or all of this information may be used to form one or more corresponding images.

[0082] The metrology signal comprises an electronic signal that represents and/or otherwise corresponds to the diffracted radiation from a metrology mark, which can be used to form an image. The metrology signal may indicate an overlay value for one or more layers, for example, an alignment value, and/or other information. Generating the metrology signal comprises sensing the diffracted radiation and converting the sensed radiation into the electronic signal and/or an image. In some embodiments, generating the metrology signal comprises sensing different portions of the radiation from different portions and/or different geometries of the metrology mark (e.g., different parts of a grating, different gratings in different layers, etc.), and combining the different portions of the sensed radiation to form the metrology signal and/or an image. This sensing and converting may be performed by components similar to and/or the same as radiation sensor detector 4 (Fig. 3), sensor 990 (Fig. 9), and/or processors PRO shown in Fig. 3 and Fig. 11, and/or other components.

[0083] In some embodiments, an image comprises an intensity modulated pattern, such as a one or more dimensional interference pattern. The intensity modulated pattern can be used to determine alignment, overlay, and/or other metrics as described herein. The pattern may be generated based on radiation diffracted by a metrology mark (e.g., mark 30 shown in various figures). For example, radiation received by a radiation sensor (e.g., sensor detector 4 shown in Fig. 3, sensor 990 shown in Fig. 9) comprises diffracted radiation. The radiation sensor (and/or one or more processors PRO of the radiation sensor - see Fig. 3, and Fig. 11) is configured to generate a metrology signal, which comprises an intensity modulated pattern. In an intensity modulated pattern, darker and lighter lines may run at an angle (including horizontally or vertically) across an image. Intensity modulation comprises variation in the intensity of radiation reflected by mark 30 and received by sensor detector 4, and/or sensor 990 from across a grating. In an image, intensity modulation may be illustrated by how dark or how light varying darker and lighter lines are. An intensity modulated pattern may comprise a one, two, or more dimensional pattern. In some embodiments, the radiation sensor is configured such that the intensity modulated pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from different portions of one metrology mark, two separate metrology marks, and/or other metrology mark configurations.

[0084] At operation 606, an image, or one or more images, are used to determine local signal strength(s) of the metrology signal. At operation 608, a position of the metrology mark is determined based on the local signal strength(s), and/or other information. At operation 610, alignment and/or overlay may be determined and/or corrected, and/or other operations may be performed. Operations 606, 608, and/or 610 may be performed by one or more processors PRO (see Fig. 3, Fig. 11), which are operatively coupled to the radiation sensor and/or the radiation source, and/or other components.

[0085] In some embodiments, the one or more processors are configured such that determining the local signal strength of the metrology signal based on the image comprises determining a local intensity of one or more pixels in the image and comparing the local intensity to a nominal intensity. In some embodiments, determining the local signal strength of the metrology signal based on the image comprises determining signal strength for one or more colors and/or polarizations to monitor resonances in a spectrum of the diffracted radiation. In some embodiments, the one or more processors are configured such that determining the local signal strength of the metrology signal based on the image comprises determining local contrast changes in the image to determine parts of the image that are in or out of focus. In some embodiments, the one or more processors are configured such that determining the local signal strength of the metrology signal based on the image comprises determining a gradient in local intensities and/or a gradient in local resonances in the spectrum of the diffracted and/or a gradient in local image contrast. In some embodiments, the one or more processors are configured such that determining the local signal strength of the metrology signal based on the image comprises correlating changes in local signal strength, intensity, and/or contrast with curvature of a non-planar layer covering the metrology mark, and/or other operations. In some embodiments, the one or more processors PRO are configured such that determining the position of the metrology mark comprises determining a thickness profile of the non-planar layer covering the metrology mark, based on the local signal strength (e.g., by one of the above operations), and determining the position of the metrology mark based on the thickness profile.

[0086] The one or more processors may be configured to determine alignment and/or overlay of the layer in the patterned substrate and/or a non-planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark, for example. In some embodiments, the one or more processors are configured to facilitate correction of alignment and/or overlay of the layer in the patterned substrate and/or a non-planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark. This may include making a determination about position as described above and then controlling one or more components of system 10 shown in Fig. 3, system 900 shown in Fig. 9, etc., to make changes to one or more semiconductor manufacturing process parameters, machine set points, design changes, etc., to bring alignment and/or overlay within a certain process specification.

[0087] In some embodiments, the one or more processors are configured to determine local phase changes in the diffracted radiation, and facilitate correction of alignment and/or overlay based on the local phase changes. Facilitating correction may also be based on local intensity of one or more pixels in the image compared to a nominal intensity; local contrast changes in the image; a gradient in local intensities and/or a gradient in local resonances in a spectrum of the diffracted and/or a gradient in local image contrast; and/or other information. In some embodiments, facilitating correction of alignment and/or overlay based on local phase changes comprises correcting a magnification error induced by curvature of a non-planar layer (e.g., a resist layer) covering the mark, for example.

[0088] Fig. 7 - Fig. 11 provide several examples of various components and/or operations described above. [0089] Fig. 7 illustrates a non-planar layer 700 covering metrology mark 30 in a layer 702 of a semiconductor structure 704. Non-planar layer 700 may have an uneven or undulating top surface 720. Layer 700 may be a resist layer, for example, and/or other non-planar layers. Non-planar layer 700 comprises top surface 720 with one or more areas 710 that are not parallel to layer 702 in the patterned substrate. In some embodiments, areas 710 comprises localized tilting (e.g., a small segment that is tilted one direction or another relative to layer 702 and/or mark 30) or dishing (e.g., being shaped like a dish or cup, etc.), and/or other non-planar features, for example. As described herein, a metrology signal may be generated based on diffracted radiation received from metrology mark 30, even if non- planar layer 700 distorts the diffracted radiation.

[0090] Fig. 8 illustrates how distorted diffracted radiation 800 (Oth order, + 1 st, and - 1 st order diffracted radiation in this example) can reduce measurement accuracy for an interferometer based metrology system 802 and/or prevent such a system from being able to make measurements at all. For example, as shown in view 801 of Fig. 8, distorted diffracted radiation comprises radiation that has been bent or moved from an expected position to some alternate position relative to one or more components of the radiation sensor. In this example, system 802 comprises an interferometer with axis 803, and a (positive) lens 860, and/or other components. System 802 comprises a radiation source 810 configured to generate radiation 820 that is directed by a spot mirror 830 onto metrology mark 30 in layer 702. Other arrangements and/or components are contemplated. In Fig. 8 (view 801), non-planar layer 700 from Fig. 7 again covers metrology mark 30 in a layer 702 of a semiconductor structure (e.g., structure 704 shown in Fig. 7). Layer 700 may be a resist layer, for example, and/or other non-planar layers. Non-planar layer 700 comprises a top surface (e.g., top surface 720 shown in Fig. 7) with a tilted area 710 that is not parallel to layer 702 in the patterned substrate.

[0091] In interferometer based alignment system 802, resist covered metrology mark 30 cannot be used for alignment and/or other metrology operations if the amount of non-planarity (e.g., tilt in this example) in layer 700 becomes too large. Diffracted orders (Oth, -4-lst, and -1st orders of radiation diffracted by metrology mark 30 in this example) may propagate through layer 700 and to an alignment sensor 850 beyond the mode-matching capability of interfered diffracted orders. Diffracted orders are displaced (often non- symmetrically as shown in Fig. 8) from the center (e.g., axis 803) of a pupil plane in system 802 (see the different bend in the lines of radiation between the resist layer 700 and pupil plane 860. As a result, interferometer based systems cannot form an interferogram, which is needed to determine alignment and/or other metrics, for example. For example, a self-referencing interferometer may not be able to overlap diffracted orders, and/or diffracted orders may be so displaced that they cannot pass through pupil filters of the system. View 851 of system 802 (now shown with lenses 861 and a pupil 862) in Fig. 8 illustrates how the 4-lst and -1st diffracted orders of radiation may be blocked by a pupil 862 block.

[0092] Fig. 9 illustrates an image based metrology system 900 (such as one or more of those described herein) configured to interfere diffracted orders by projection 902. As in Fig. 8, radiation 820 is directed by a spot mirror 830 onto metrology mark 30. Non-planar layer 700 again covers metrology mark 30 in a of a semiconductor structure (e.g., structure 704 shown in Fig. 7). Fig. 9 also illustrates two example lenses 920 and 922, an object plane 950, pupil plane 860, various focal distances f, and an imaged based metrology sensor 990 (e.g., a camera). System 900 interferes diffracted orders by projection. Hence, it does not matter if the diffracted orders are shifted 975 so that they are in a different position in pupil plane 860, provided the diffracted orders are re-imaged on the image based metrology sensor 990. As described above, this is because an image of a pattern of diffracted radiation is still formed, from which alignment and/or other metrology determinations may be made. The pattern itself may be non- symmetrical, or shifted by the non-planar layer, and/or may even include a magnification error related component, but the image of the pattern is still able to be analyzed for metrology purposes.

[0093] In this example, metrology mark 30 (Fig. 8, Fig. 7, etc.) comprises gratings in one or more layers of a patterned substrate. A grating may be formed of solid resist pillars, bars, vias, and/or other features, for example. Metrology mark 30 may be sensitive to changes in processing in a 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 mark 30. Accordingly, the measured data from metrology mark 30 may be used to determine an alignment, overlay, and/or other value, and/or an adjustment (e.g., a correction) based on the alignment, overlay, and/or other value for one or more manufacturing processes, and/or used as a basis for making the actual adjustment. Again note that in this example, metrology mark 30 may represent multiple layers comprising multiple metrology marks.

[0094] In this example, system 900 comprises an imaging sensor such as a camera, one or more processors PRO (see processors PRO illustrated in other figures), and/or other components. The camera and/or some other imaging sensor may be configured to generate a metrology signal comprising an image 951 , for example. The one or more processors PRO may be configured to determine an alignment and/or overlay value based on image 951, and/or other information. In this example, image 951 comprises an intensity modulated pattern 952, such as a one or more dimensional interference pattern. The intensity modulated pattern 952 can be used to determine alignment, overlay, and/or other metrics. Pattern 1052 may be generated based on radiation diffracted by metrology mark 30 and distorted by (tilted) area 710 (Fig. 9, Fig. 8, Fig. 7). In intensity modulated pattern 952, darker and lighter lines run vertically across image 951. Intensity modulation comprises variation in the intensity of radiation reflected by mark 30 and received by sensor 990 from across mark 30 (e.g., a grating). In image 951, intensity modulation is illustrated by how dark or how light varying darker and lighter lines are. Image 951 and/or pattern 952 are representative of phase shifts and/or intensity (amplitude) in (diffracted) radiation received from one or more geometric features of metrology mark 30. The one or more phases and/or amplitudes correspond to one or more dimensions of a feature, but may or may not be symmetrical across pattern 952. For example, tilted area 710 (Fig. 9, Fig. 8, Fig. 7) may cause different amounts of distortion in diffracted radiation. [0095] Image 951, and/or one or more other images, are used by processors PRO to determine local signal strength(s) of the metrology signal. A position of metrology mark 30 is determined based on the local signal strength(s), and/or other information. Alignment and/or overlay may be determined and/or corrected, and/or other operations may be performed based on this position.

[0096] In some embodiments, the one or more processors PRO are configured such that determining local signal strength(a) of the metrology signal based on image 951 comprises determining a local intensity of one or more pixels (defined by grid 980 across a portion of image 951 in this example) in image 951 and comparing the local intensity to a nominal intensity. In some embodiments, determining the local signal strength of the metrology signal based on the image comprises determining signal strength for one or more colors and/or polarizations to monitor resonances in a spectrum of diffracted radiation. In some embodiments, the one or more processors PRO are configured such that determining the local signal strength of the metrology signal based on the image comprises determining local contrast changes in image 951 to determine parts of the image that are in or out of focus. In some embodiments, the one or more processors PRO are configured such that determining the local signal strength of the metrology signal based on image 951 comprises determining a gradient in local intensities and/or a gradient in local resonances in the spectrum of the diffracted and/or a gradient in local image contrast. In some embodiments, the one or more processors PRO are configured such that determining the local signal strength of the metrology signal based on image 951 comprises correlating changes in local signal strength, intensity, and/or contrast with curvature of a non-planar layer covering metrology mark 30, and/or other operations. In some embodiments, the one or more processors PRO are configured such that determining the position of metrology mark 30 comprises determining a thickness profile of the non-planar layer covering metrology mark 30, based on the local signal strength (e.g., determined by one of the above operations), and determining the position of metrology mark 30 based on the thickness profile.

[0097] Phrased another way, system 900 is configured to use local signal strength to determine and/or correct the aligned position of metrology mark 30 when non-planar layers or surfaces are present in a semiconductor structure. The local signal strength can be obtained in various manners (as described above), including monitoring the intensity per (group) of pixels in image 951 and comparing that to the nominal intensity for mark 30. Multiple colors/polarizations can be combined to monitor signal strength resonances to become more robust for other root causes that can lead to intensity changes. Measurements can be combined with local contrast changes to identify parts of the image 951 that are in/out focus. Gradients in the above parameters correlate directly with curvature of the non-planar surface. For example, local phase changes can be used to correct for, e.g., a magnification error induced by the curvature of the resist. This can be applied to bright or dark field microscopy.

[0098] Fig. 10 illustrates an example image 1020 that may be used (e.g., by one or more processors PRO described herein) to determine local signal strength(s) of a metrology signal (such that a position of a metrology mark can be determined based on the local signal strength(s), and alignment and/or overlay may be determined and/or corrected, and/or other operations may be performed based on this position.) This image illustrates systemic variation in local signal strength (show by intensity represented by shading / color in Fig. 10) of various potential indicators that may be used. Image 1020 illustrates local signal strength of -1st order diffracted radiation from a metrology mark (e.g., mark 30 described above). In image 1020, higher local intensity (or signal strength) is illustrated by deeper (e.g., darker) color. Analyzing these local signal strengths using one or more of the techniques described above facilitates determination of the position of the metrology mark. For example, in image 1020, local intensities tend to be higher on the left side of the image, likely suggesting tilted resist covering the metrology mark in this area. The amount of tilt (or a thickness profile of the resist, and/or other characteristics) may be determined based on the signal strength (or color / intensity) differences, and then used to analyze the diffracted radiation from a metrology mark, even if the diffracted radiation is distorted.

[0099] 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 one or more detected phase and/or amplitude variations, an alignment value indicated by the metrology signal, an overlay value indicated by the metrology signal, and/or other information. The one or more parameters may include a parameter of the radiation (the radiation used for determining alignment and/or overlay), an alignment and/or overlay inspection location on a layer of a semiconductor device structure, an alignment value, an overlay value, and/or other parameters. In some embodiments, process parameters can be interpreted broadly to include a stage position, a mask design, a metrology mark 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, and/or other parameters.

[0100] A parameter of the radiation used for determining alignment and/or overlay, 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 of reflected radiation, increase and/or otherwise enhance (e.g., maximize) the phase shifts and/or amplitude 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 the phase shifts and/or amplitude easier to detect, and/or have other advantages.

[0101] 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 alignment and/or overlay value, a lithography exposure may be corrected. As another example, if a determined alignment and/or overlay 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 measurements may breach a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the overlay 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 alignment and/or overlay value to be adjusted back into an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. If there is a difference, that difference may be used to determine an adjustment for an apparatus that is used to produce the devices (e.g., parameter “x” should be increased / decreased / changed so that it matches the new or adjusted version of parameter “x” determined as part of operation 610), for example. In some embodiments, operation 610 may include electronically adjusting an apparatus (e.g., based on the determined process parameters). Electronically adjusting an apparatus may include sending an electronic signal, and/or other communications to the apparatus, for example, that causes a change in the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and/or other adjustments.

[0102] Fig. 11 is a diagram of an example computer system CS that may be used for one or more of the operations described herein. Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0103] 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. [0104] In some embodiments, portions of one or more methods 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.

[0105] 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.

[0106] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a network. Computer system CS can receive the data 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.

[0107] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0108] 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.

[0109] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and/or stored in storage device SD, or other non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0110] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:

1. A metrology system, comprising: a radiation sensor configured to generate a metrology signal based on diffracted radiation received from a metrology mark in a layer of a patterned substrate, the metrology signal comprising an image; and one or more processors operatively coupled to the radiation sensor, the one or more processors configured to: determine a local signal strength of the metrology signal based on the image; and determine a position of the metrology mark based on the local signal strength.

2. The system of clause 1 , wherein the radiation sensor comprises an imaging sensor.

3. The system of any of the previous clauses, wherein the imaging sensor comprises a camera.

4. The system of any of the previous clauses, wherein the metrology mark is covered by a non-planar layer of the patterned substrate that distorts the diffracted radiation.

5. The system of any of the previous clauses, wherein the non-planar layer comprises localized tilting or dishing.

6. The system of any of the previous clauses, wherein determining the position of the metrology mark comprises determining a thickness profile of the non-planar layer covering the metrology mark, based on the local signal strength, and determining the position of the metrology mark based on the thickness profile.

7. The system of any of the previous clauses, wherein the non-planar layer comprises resist. 8. The system of any of the previous clauses, wherein the non-planar layer comprises a top surface with one or more areas that are not parallel to the layer in the patterned substrate.

9. The system of any of the previous clauses, wherein determining the local signal strength of the metrology signal based on the image comprises: determining a local intensity of one or more pixels in the image and comparing the local intensity to a nominal intensity; determining signal strength for one or more colors and/or polarizations to monitor resonances in a spectrum of the diffracted radiation; determining local contrast changes in the image to determine parts of the image that are in or out of focus; determining a gradient in local intensities and/or a gradient in local resonances in the spectrum of the diffracted and/or a gradient in local image contrast; and/or correlating changes in local signal strength, intensity, and/or contrast with curvature of a non-planar layer covering the metrology mark.

10. The system of any of the previous clauses, wherein the one or more processors are further configured to determine alignment and/or overlay of the layer in the patterned substrate and/or a non- planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark.

11. The system of any of the previous clauses, wherein the one or more processors are further configured to facilitate correction of alignment and/or overlay of the layer in the patterned substrate and/or a non-planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark.

12. The system of any of the previous clauses, wherein the one or more processors are further configured to determine local phase changes in the diffracted radiation, and facilitate correction of alignment and/or overlay based on the local phase changes and: a local intensity of one or more pixels in the image compared to a nominal intensity; local contrast changes in the image; and/or a gradient in local intensities and/or a gradient in local resonances in a spectrum of the diffracted and/or a gradient in local image contrast.

13. The system of any of the previous clauses, wherein facilitating correction of alignment and/or overlay based on local phase changes comprises correcting a magnification error induced by curvature of a non-planar layer covering the mark.

14. The system of any of the previous clauses, wherein the image comprises an intensity modulated pattern.

15. The system of any of the previous clauses, wherein the radiation sensor is configured such that the intensity modulated pattern for the diffracted radiation comprises a one or more dimensional interference pattern.

16. The system of any of the previous clauses, wherein the metrology system is a dark field metrology system.

17. The system of any of the previous clauses, wherein the metrology system is a bright field metrology system.

18. The system of any of the previous clauses, wherein the mark is a non-periodic grating. 19. The system of any of the previous clauses, wherein the mark is a periodic grating.

20. The system of any of the previous clauses, further comprising a radiation source operatively coupled to the one or more processors and the radiation sensor, the radiation source configured to irradiate the metrology mark with radiation.

21. A metrology method, comprising: generating, with a radiation sensor, a metrology signal based on diffracted radiation received from a metrology mark in a layer of a patterned substrate, the metrology signal comprising an image; determining, with one or more processors operatively coupled to the radiation sensor, a local signal strength of the metrology signal based on the image; and determining, with the one or more processors, a position of the metrology mark based on the local signal strength.

22. The method of clause 21, wherein the radiation sensor comprises an imaging sensor.

23. The method of any of the previous clauses, wherein the imaging sensor comprises a camera.

24. The method of any of the previous clauses, wherein the metrology mark is covered by a non- planar layer of the patterned substrate that distorts the diffracted radiation.

25. The method of any of the previous clauses, wherein the non-planar layer comprises localized tilting or dishing.

26. The method of any of the previous clauses, wherein determining the position of the metrology mark comprises determining a thickness profile of the non-planar layer covering the metrology mark, based on the local signal strength, and determining the position of the metrology mark based on the thickness profile.

27. The method of any of the previous clauses, wherein the non-planar layer comprises resist.

28. The method of any of the previous clauses, wherein the non-planar layer comprises a top surface with one or more areas that are not parallel to the layer in the patterned substrate.

29. The method of any of the previous clauses, wherein determining the local signal strength of the metrology signal based on the image comprises: determining a local intensity of one or more pixels in the image and comparing the local intensity to a nominal intensity; determining signal strength for one or more colors and/or polarizations to monitor resonances in a spectrum of the diffracted radiation; determining local contrast changes in the image to determine parts of the image that are in or out of focus; determining a gradient in local intensities and/or a gradient in local resonances in the spectrum of the diffracted and/or a gradient in local image contrast; and/or correlating changes in local signal strength, intensity, and/or contrast with curvature of a non-planar layer covering the metrology mark.

30. The method of any of the previous clauses, further comprising determining, with the one or more processors, alignment and/or overlay of the layer in the patterned substrate and/or a non-planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark.

31. The method of any of the previous clauses, further comprising facilitating, with the one or more processors, correction of alignment and/or overlay of the layer in the patterned substrate and/or a non- planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark.

32. The method of any of the previous clauses, further comprising determining, with the one or more processors, local phase changes in the diffracted radiation, and facilitating correction of alignment and/or overlay based on the local phase changes and: a local intensity of one or more pixels in the image compared to a nominal intensity; local contrast changes in the image; and/or a gradient in local intensities and/or a gradient in local resonances in a spectrum of the diffracted and/or a gradient in local image contrast.

33. The method of any of the previous clauses, wherein facilitating correction of alignment and/or overlay based on local phase changes comprises correcting a magnification error induced by curvature of a non-planar layer covering the mark.

34. The method of any of the previous clauses, wherein the image comprises an intensity modulated pattern.

35. The method of any of the previous clauses, wherein the radiation sensor is configured such that the intensity modulated pattern for the diffracted radiation comprises a one or more dimensional interference pattern.

36. The method of any of the previous clauses, wherein the radiation sensor and the one or more processors are part of a dark field metrology system.

37. The method of any of the previous clauses, wherein the radiation sensor and the one or more processors are part of a bright field metrology system.

38. The method of any of the previous clauses, wherein the mark is a non-periodic grating.

39. The method of any of the previous clauses, wherein the mark is a periodic grating.

40. The method of any of the previous clauses, further comprising irradiating, with a radiation source operatively coupled to the one or more processors and the radiation sensor, the metrology mark with radiation. process.

[0111] 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.

[0112] 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.

[0113] 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

2. The system of claim 1 , wherein the radiation sensor comprises an imaging sensor.

3. The system of claim 2, wherein the imaging sensor comprises a camera.

4. The system of any of claims 1-3, wherein the metrology mark is covered by a non-planar layer of the patterned substrate that distorts the diffracted radiation.

5. The system of claim 4, wherein the non-planar layer comprises localized tilting or dishing.

6. The system of claims 4 or 5, wherein determining the position of the metrology mark comprises determining a thickness profile of the non-planar layer covering the metrology mark, based on the local signal strength, and determining the position of the metrology mark based on the thickness profile.

7. The system of any of claims 4-6, wherein the non-planar layer comprises resist.

8. The system of any of claims 4-7, wherein the non-planar layer comprises a top surface with one or more areas that are not parallel to the layer in the patterned substrate.

9. The system of any of claims 1-8, wherein determining the local signal strength of the metrology signal based on the image comprises: determining a local intensity of one or more pixels in the image and comparing the local intensity to a nominal intensity; determining signal strength for one or more colors and/or polarizations to monitor resonances in a spectrum of the diffracted radiation; determining local contrast changes in the image to determine parts of the image that are in or out of focus; determining a gradient in local intensities and/or a gradient in local resonances in the spectrum of the diffracted and/or a gradient in local image contrast; and/or correlating changes in local signal strength, intensity, and/or contrast with curvature of a non-planar layer covering the metrology mark.

10. The system of any of claims 1-9, wherein the one or more processors are further configured to determine alignment and/or overlay of the layer in the patterned substrate and/or a non-planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark.

11. The system of any of claims 1-10, wherein the one or more processors are further configured to facilitate correction of alignment and/or overlay of the layer in the patterned substrate and/or a non- planar layer covering the metrology mark based on the local signal strength and/or the position of the metrology mark.

12. The system of any of claims 1-11, wherein the one or more processors are further configured to determine local phase changes in the diffracted radiation, and facilitate correction of alignment and/or overlay based on the local phase changes and: a local intensity of one or more pixels in the image compared to a nominal intensity; local contrast changes in the image; and/or a gradient in local intensities and/or a gradient in local resonances in a spectrum of the diffracted and/or a gradient in local image contrast.

13. The system of claim 12, wherein facilitating correction of alignment and/or overlay based on local phase changes comprises correcting a magnification error induced by curvature of a non-planar layer covering the mark.

14. The system of any of claims 1-13, wherein the image comprises an intensity modulated pattern.

15. The system of claim 14, wherein the radiation sensor is configured such that the intensity modulated pattern for the diffracted radiation comprises a one or more dimensional interference pattern.