Full plane diffraction based digital holography metrology system and method

Abstract

A metrology system comprising: a first illumination beam, the first illumination beam configured to be diffracted by a target; a second illumination beam, the second illumination beam configured to be dispersed by a dispersive element, wherein the dispersive element is configured to introduce a tilt in the second illumination beam in at least one direction; a detector, the detector configured to detect an interference pattern of the first illumination beam diffracted by the target and the second illumination beam dispersed and tilted by the dispersive element; and a processor operatively connected with the detector, the processor configured to determine a phase and / or amplitude of a waveform of the first illumination beam after it has interacted with the target based on the interference pattern detected by the detector.

Description

FULL PLANE DIFFRACTION BASED DIGITAL HOLOGRAPHY METROLOGY SYSTEM AND METHOD CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 660,795 which was filed on June 17, 2024 and which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0002] The present disclosure relates generally systems and methods for measurement of parameters of interest in semiconductor manufacturing and more specifically to a system and methods for holographic diffraction-based metrology. BACKGROUND

[0003] 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, 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, etc. Patterning can occur in multiple layers, such that a multi-layer stack or device can be constructed from a set of patterned layers which are aligned with one another during patterning and other steps.

[0004] Lithography is a central step in the manufacturing of devices 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- electromechanical systems (MEMS) and other devices.

[0005] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements have continually been reduced. At the same time, the number of functional elements, such as transistors, per device has been steadily increasing, following a trend commonly referred to as “Moore’s law.” At the current state of technology, layers of devices are manufactured using lithographic projection apparatuses that project a design layout onto a substrate using illumination from a deep-ultraviolet illumination source, creating individual functional elements havingdimensions well below 100 nanometers (nm), i.e., less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source).

[0006] 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-k1 lithography, according to the resolution formula CD = k1×λ / NA, where λ is the wavelength of radiation employed (currently in most cases 248nm or 193nm), 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 k1 is an empirical resolution factor. In general, the smaller k1 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, which can include alignment tools, the design layout, or the patterning device.

[0007] Monitoring of device and material features, including CD, and of parameters of interest in a manufacturing process (e.g., fabrication parameters such as overlay offset, position, dose, symmetry, etc.), allows for process monitoring, control, and correction, including control of lithography and other fabrication steps. A metrology apparatus can be used to determine properties of devices and how properties of different devices vary or how properties associated with different layers of the same device vary from layer to layer. The metrology apparatus, which can be a diffraction-based apparatus, an optical apparatus, an electron microscopy apparatus, etc., may alternatively be constructed to identify defects on the device or to align the device and may, for example, be part of the lithographic apparatus or may be a stand-alone device. The metrology apparatus may measure the properties on a latent image (image in a resist layer after the exposure), or on a semi-latent image (image in a resist layer after a post-exposure bake step PEB), or on a developed resist image (in which the exposed or unexposed parts of the resist have been removed), or even on an etched image (after a pattern transfer step such as etching). SUMMARY

[0008] In an embodiment, a metrology system comprising: a first illumination beam, the first illumination beam configured to be diffracted by a target; a second illumination beam, the second illumination beam configured to be dispersed by a dispersive element, wherein the dispersive element is configured to introduce a tilt in the second illumination beam in at least one direction; a detector, the detector configured to detect an interference pattern of the first illumination beam diffracted by the target and the second illumination beam dispersed and tilted by the dispersive element; and a processor operatively connected with the detector, the processor configured to determine a phase and / or amplitude of a waveform of the first illumination beam after it has interacted with the target based on the interference pattern detected by the detector.

[0009] In another embodiment, a method for metrology, comprising: illuminating a diffraction target with a first beam of illumination, the first beam of illumination generating at least one diffraction order; interfering the at least one diffraction order with a second beam of illumination, the second beam of illumination comprising multiple wavelengths; detecting, by a two-dimensional detector, interference of the at least one diffraction order and the second beam of illumination; and determining, by a processor, a phase and / or amplitude of a waveform of the at least one diffraction order after it has interacted with the target based on the interference detected by the two-dimensional detector.

[0010] In an embodiment, a machine-readable medium having instructions thereon, the instructions when executed by a processor being configured to perform the method of another embodiment.

[0011] In a further embodiment, a processor and a machine-readable medium as described in another embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: - Figure 1 depicts a schematic overview of a lithographic apparatus, according to an embodiment. - Figure 2 depicts a schematic overview of a lithographic cell or cluster, according to an embodiment. - Figure 3 depicts a schematic representation of an example metrology system, according to an embodiment. - Figure 4 depicts a schematic representation of an example metrology technique, according to an embodiment. - Figure 5A depicts a schematic representation of an example aberration causing diffraction- based metrology errors, according to an embodiment. - Figure 5B depicts a schematic representation of an effect of an example aberration on detection of diffractions, according to an embodiment. - Figure 6 depicts a schematic representation of an example diffraction-based metrology system, according to an embodiment. - Figure 7A depicts a schematic representation of an example pupil plane holography system for diffraction-based metrology, according to an embodiment. - 7B depicts a schematic representation of another example pupil plane holography system for diffraction-based metrology, according to an embodiment.- Figure 8 depicts a schematic representation of example outputs from an example pupil plane holographic diffraction-based metrology system, according to an embodiment. - Figure 9A depicts a schematic representation of an example pupil plane holography system for diffraction-based metrology including a dispersive element, according to an embodiment. - Figure 9B depicts a schematic representation of another example pupil plane holography system for diffraction-based metrology including a dispersive element, according to an embodiment. - Figure 9C depicts a schematic representation of an example camera field plane holography system for diffraction-based metrology including a dispersive element, according to an embodiment. - Figure 10A depicts a schematic representation of example outputs from an example pupil plane holography diffraction-based metrology system including a dispersive element, according to an embodiment. - Figure 10B depicts a schematic representation of example outputs from an example camera plane holography diffraction-based metrology system including a dispersive element, according to an embodiment. - Figure 11 depicts a schematic representation of an example technique for improvement of diffraction-based metrology with holography, according to an embodiment. - Figure 12 depicts a flowchart illustrating an exemplary method for diffraction-based holography, according to an embodiment. - Figure 13 is a block diagram of an example computer system, according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0013] Embodiments of the present disclosure are described in detail with reference to the drawings, which are provided as illustrative examples of the disclosure so as to enable those skilled in the art to practice the disclosure. Notably, the figures and examples below are not meant to limit the scope of the present disclosure to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present disclosure can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present disclosure will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the disclosure. Embodiments described as being implemented in software should not be limited thereto, but can include embodiments implemented in hardware, or combinations of software and hardware, and vice-versa, as will be apparent to those skilled in the art, unless otherwise specified herein. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the disclosure is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to beascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present disclosure encompasses present and future known equivalents to the known components referred to herein by way of illustration.

[0014] In semiconductor device manufacturing, metrology operations typically include determining the position of a metrology target (or targets) and / or other target in a layer of a semiconductor device structure. This position is typically determined by irradiating a metrology target with radiation, and comparing characteristics of different diffraction orders of radiation reflected from the metrology target. Such techniques are used to measure overlay, alignment, and / or other parameters.

[0015] By way of a brief introduction, the description below relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several components of systems and / or methods for semiconductor device metrology. These systems and methods may be used for measuring overlay, alignment, etc., in a semiconductor device manufacturing process, for example, or for other operations.

[0016] Although specific reference may be made in this text to the manufacture of ICs, it should be explicitly understood that the description herein has many other possible applications. For example, 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.

[0017] In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g., having a wavelength in the range of about 5-100 nm).

[0018] In the present document, the term “wavelength” is used to encompass a wavelength range. For example, an emitted (or diffracted, transmitted, detected, etc.) wavelength may encompass a range of wavelengths, such as with a non-zero bandwidth (or full width half max (FWHM)). A wavelength may have a narrow wavelength range, such as 1 nm, 0.5 nm, 30 femtometers (fm), etc., and may be produced by a coherent source. A wavelength range may be centered on or otherwise include a representative wavelength. A wavelength range may be a closed or open interval.

[0019] A (e.g., semiconductor) patterning device can comprise, or can form, one or more patterns. The pattern can be generated utilizing CAD (computer-aided design) programs, based on a pattern or design layout, this process often being referred to as EDA (electronic design automation). Most CAD programs follow a set of predetermined design rules in order to create functional design layouts / patterning devices. These rules are set by processing and design limitations. For example, design rules define the space tolerance between devices (such as gates, capacitors, etc.) or interconnect lines, so as to ensure that the devices or lines do not interact with one another in anundesirable way. The design rules may include and / or specify specific parameters, limits on and / or ranges for parameters, and / or other information. One or more of the design rule limitations and / or parameters may be referred to as a “critical dimension” (CD). A critical dimension of a device can be defined as the smallest width of a line or hole or the smallest space between two lines or two holes, or other features. Thus, the CD determines the overall size and density of the designed device. One of the goals in device fabrication is to faithfully reproduce the original design intent on the substrate (via the patterning device).

[0020] The term “mask” or “patterning device” as employed in this text may be broadly interpreted as referring to a generic semiconductor patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term “light valve” can also be used in this context. Besides the classic mask (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include a programmable mirror array and a programmable LCD array.

[0021] As used herein, the term “patterning process” generally means a process that creates an etched substrate by the application of specified patterns of light as part of a lithography process. However, “patterning process” can also include (e.g., plasma) etching, as many of the features described herein can provide benefits to forming printed patterns using etch (e.g., plasma) processing.

[0022] As used herein, the term “pattern” means an idealized pattern that is to be etched on a substrate (e.g., wafer) – e.g., based on the design layout described above. A pattern may comprise, for example, various shape(s), arrangement(s) of features, contour(s), etc.

[0023] As used herein, a “printed pattern” means the physical pattern on a substrate that was etched based on a target pattern. The printed pattern can include, for example, troughs, channels, depressions, edges, or other two- and three-dimensional features resulting from a lithography process.

[0024] A patterning system may be a system comprising any or all of the components described above, plus other components configured to performing any or all of the operations associated with these components. A patterning system may include a lithographic projection apparatus, a scanner, systems configured to apply and / or remove resist, etching systems, and / or other systems, for example.

[0025] As used herein, the term “diffraction” refers to the behavior of a beam of light or other electromagnetic radiation when encountering an aperture or series of apertures, including a periodic structure or grating. “Diffraction” can include both constructive and destructive interference, including scattering effects and interferometry. As used herein, a “grating” is a periodic structure, which can be one-dimensional (i.e., comprised of posts of dots), two-dimensional, or three- dimensional, and which causes optical interference, scattering, or diffraction. A “grating” can be a diffraction grating.

[0026] As used throughout this application “or”, unless indicated otherwise, takes a non-exclusive meaning, e.g., encompassing both “and” and “or”. “Each”, “every”, “all”, “corresponding”, “individual” and other relational terms encompass substantially “each”, “every”, “all”, etc., includingcases in which each, every, all, corresponding, individual, etc. may include relationship which are not one-to-one, or do not include every possible item. For example, every may exclude items, such as items determined to be defective during testing, reference items, etc. All may exclude items, such as excess items. Corresponding may not require that items correspond in an exactly one to one manner. For example, a first item may correspond to two of a second item or vice versa. In some cases, individual may refer to multiple of an item, such as each item A has individual item B, where an item A may have two of an item B. Values should further be taken to include ranges, such as ±10%. Ranges should be taken to include endpoints.

[0027] Figure 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).

[0028] 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.

[0029] 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.

[0030] 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 σ-outer and σ-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 wherein 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.

[0031] 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.

[0032] In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0033] 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” herein may be considered synonymous with the more general term “patterning device.”

[0034] The term “patterning device” used herein 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.

[0035] 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.

[0036] The term “projection system” should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system.”

[0037] 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 co- ordinate system wherein 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 opticalelement 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.

[0038] 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 conducted 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.

[0039] In operation of the lithographic apparatus LA, 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 Figure 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short- stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substratealignment marks P1, 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.

[0040] 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.

[0041] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0042] The substrate may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already includes multiple processed layers.

[0043] The terms “radiation” and “beam” used herein 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.

[0044] 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.

[0045] As shown in Figure 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input / output port I / O1, 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.

[0046] 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 (Figure 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 (Figure 1)).

[0047] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, 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 one or more dedicatedmetrology targets 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.

[0048] 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 include the measurement of overlay, alignment, etc. For example, overlay and / or alignment can be measured by comparing parts of the diffraction spectrum (for example, comparing different diffraction orders in the diffraction spectrum of a metrology target such as a periodic grating).

[0049] 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 layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes. Examples of measurement include optical imaging (e.g., optical microscope), non-imaging optical measurement (e.g., measurement based on diffraction such as the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profiling using a stylus, atomic force microscopy (AFM)), and / or non- optical imaging (e.g., scanning electron microscopy (SEM)).

[0050] 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.

[0051] 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.

[0052] To enable the metrology, often one or more metrology targets (or metrology marks) are specifically provided on the substrate. Typically, the target is specially designed and may comprise a periodic structure. For example, the metrology target on a substrate such as a semiconductor wafermay comprise one or more 1-D periodic structures (e.g., geometric features such as gratings), which are printed such that after development, the periodic structural features are formed of solid resist lines. As another example, the metrology target may comprise one or more 2-D periodic structures (e.g., gratings), 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).

[0053] Figure 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 such as a semiconductor wafer (e.g., which may typically include a metrology target). The redirected radiation is passed to a sensor such as a spectrometer detector 4 and / or other sensors, which measures a spectrum (intensity as a function of wavelength) of the specular reflected and / or diffracted radiation, as shown, e.g., in the graph on the left of Figure 4. The detector may generate a metrology detection signal conveying metrology 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 Figure 3.

[0054] As in the lithographic apparatus LA in Figure 1, one or more substrate tables (not shown in Figure 3 or 4) may be provided to hold the substrate W during measurement 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 Figure 1. In an example where metrology system 10 is integrated with the lithographic apparatus, they may 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., a metrology mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at different locations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to the focus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves, including continuously during metrology. 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).

[0055] For typical metrology measurements, a metrology target 30 on substrate W may be a 1-D grating, which is printed such that after development, the bars are formed of solid resist lines (e.g., which may be covered by a deposition layer), and / or other materials. Or the target 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and / or other features in the resist. Surfaces of the features, e.g., bars, resist, fill layers, buried layers, etc., may be uneven (e.g., tilted) with respect to the Z direction.

[0056] 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. Target 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, etc.) such that process variation manifests in variation in target 30, including in layers which support or cover target 30. Accordingly, the measured data from target 30 may be used to determine an adjustment for one or more of the manufacturing processes, and / or used as a basis for making the actual adjustment.

[0057] For example, the measured data from target 30 may indicate overlay for a layer of a semiconductor device. The measured data from target 30 may be used (e.g., by the one or more processors PRO and / or other processors) for determining one or more semiconductor device manufacturing process parameters based the overlay, and determining an adjustment for a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology target 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.

[0058] Figure 5A depicts a schematic representation of an example aberration causing diffraction- based metrology errors. Figure 5A is a schematic cross-sectional view of a resist layer R titled at an angle ^^in the measurement direction (X direction) with respect to the target 30. If the refractive index of the resist is N and the average resist thickness is D, then the angular deviation dθ of the zeroth order reflection light I0 from the perpendicularly incident light is expressed as follows: ^^ = ^ (1)This angular change in the zeroth order diffraction may detected by a detector (such as the spectrometer detector 4 of Figure 3) and produce a deviation in a measurement of the target 30 (e.g., in position, overlay, etc.) in the X-axis direction by dx from the position X0 (including the imaging magnification from the angular deviation dθ on the wafer W surface).

[0059] For the first order (and analogously higher) diffractions, the diffraction angles relative to the incident light (e.g., the light incident normal to the target 30 but refracted by the tilted resist R) are symmetrical and given by: ^^^ = sin^^ ^⁄ ^ (2)where P is the periodicity of the grating, and λ is the wavelength of the light incident on the grating. Then the apparent diffraction angles, after further refraction by the tilted resist R surface, are given by ^^^ = sin^^^^⁄ ^ ^ +^^ = sin^^^^⁄ ^ ^ + sin^^^^ ∗ ^ sin^2^ − ^sin^^ ^⁄ ^ ^^^^ (4)^^^ = sin^^^^⁄ ^ ^ −^^ = sin^^^^⁄ ^ ^ − sin^^^^ ∗ ^ sin^2^ − ^sin^^ ^⁄ ^ ^^^^ (5)However, for first order (and analogously higher) diffractions relative to the target 30, the first order diffractions the diffraction angles normal to the wafer W are given by ^^ ^^The detected locations of the reflection (e.g., zeroth order diffraction), first order diffraction, and higher order diffractions (e.g., second order and higher diffractions) are therefore offset from their expected locations based on the tilt θ, the refractive index of the tilted resist R, and a distance of a detector (such the spectrometer detector of 4 of Figure 3) from the target 30.

[0060] In some embodiments, diffractions may be captured and combined (e.g., through intensity accumulation) with other diffractions, such as through the use of a self-referencing interferometer (SRI). A self-referencing interferometer (SRI) may obtain a reference signal (e.g., optical signal containing diffractions) and generate a transformed signal from at least part of the reference signal, and then combine the reference and transformed signals to generate a signal reflecting a spatial overlap between the reference signal and the transformed signal—from which metrology characteristics (e.g., position, overlay, etc.) may be determined. The transformation may be a reflection, rotation (including an angular rotation), etc. of the reference signal. In some embodiments, the transformation may be a rotation by 180° (e.g., π radians) of the reference signal, such that for an on-axis diffraction, a positive diffraction of order n of a reference signal overlaps with a negative diffraction of order n of a transformed signal, and likewise a negative diffraction of the order n of the reference signal overlaps with a positive diffraction of the order n from the transformed signal. An aberration, such as caused by a tilted resist or any other sample layer or by non-idealities in themetrology system capturing the reference signal and / or generating the transformed signal, may cause deviations in the reference signal and / or transformed signal from the expected value, including deviations may be non-symmetrical. For example, a tilted resist, as depicted in Figure 5A, may shift a positive diffraction and a negative diffraction in the same or different directions, including by the same or different angles and / or distances. In some embodiments, an aberration may cause mismeasurement of a metrology parameter, such as position, overlay, etc. by causing changes to the intensity and / or position of a diffraction, from which metrology parameters are determined.

[0061] Figure 5B depicts a schematic representation of an effect of an example aberration on detection of diffractions. Figure 5B is a plan view of example diffraction spots on a two-dimensional detector 500. Expected positions of a through beam (e.g., 0thorder diffraction, reflected beam, etc.), positive nth order diffraction, and negative nth order diffraction are depicted as hollow circles 510, 512, and 514, respectively. The expected positions of hollow circles 510, 512, and 514, may be determined based on the diffraction order, the wavelength of radiation subject to diffraction, the periodicity of any diffraction grating of the target (e.g., target 30 of Figure 5A), distance from the target to the two-dimensional detector, etc. Measured positions of the through beam (e.g., 0thorder diffraction, reflected beam, etc.), positive nth order diffraction, and negative nth order diffraction are depicted as filled circles 520, 522, and 524, respectively. The measured positions of the filled circles 520, 522, and 524 may differ from their expected positions (e.g., the positions of the hollow circles 510, 512, and 514) due to resist tilt, metrology system aberrations (for example, lens aberrations), and / or due to target non-ideality. For example, the measured positions of the filled circles 520, 522, and 524 may be shifted in both the positive X and positive Y direction, from their expected positions, due to tilt in a resist layer in both the X and Y directions. In another example, the measured positions of the filled circles 520, 522, and 524, may be shifted in different amounts—such as if the periodicity P of the target is different than expected. In such an example, the through beam (e.g., the measure position of the filled circle 520) may coincide with the expected position shown by the hollow circle 510, while the positive nth diffraction shown by filled circle 522 may lie outside (in the positive X direction) of the expected position shown by the hollow circle 512 while the negative nth diffraction shown by filled circle 524 may lie outside (in the negative X direction) of the expected position shown by the hollow circle 514. In cases where target or measurement system non-ideality is present, it may be hard to deconvolve target metrology (e.g., overlay, position, etc.) from non-ideality.

[0062] For systems using SRI, the generation of a transformed signals from the reference signals may increase (for example, double or more) the amount of non-ideality captured by the metrology system which requires correction or compensation in order to obtain accurate metrology measurements. For example, for a system using SRI, transformed signals may be generated by rotating measured signals by 180°. Example transformed signals, which represent transformed measured positions of various diffractions, for the through beam (e.g., 0thorder diffraction, reflected beam, etc.), positive nth order diffraction, and negative nth order diffraction are depicted as filled circles 530, 532, and 534,respectively. In some cases, resist tilt (or other non-idealities) may be enough to cause the reference signals and transformed signals to occur in non-overlapping locations—such as depicted in Figure 5B where the transformed signals are shifted in the negative X and negative Y direction for filled circles 530, 532, and 534. Some systems which use an SRI may determine metrology results based on the overlap, sum, union, etc. of the reference signals and transformed signals. Resist tilt and other non- idealities may separate the reference signals and transformed signals, such as at a detector, which may cause the overlap of such signals to be reduced or even null (e.g., for disjoint signals). This may reduce the ability of the metrology system to determine metrology measurements, and reduce the accuracy of any measurements determined. Additionally, a shift in the location of the through beam—such as shown where filled circle 520 (and filled circle 530) are not coincidental with hollow circle 510—can cause the through beam, which may be of significantly greater intensity—to bleed into a detector field (e.g., to no longer be blocked by a through beam blocker) and cause detector saturation or other effects which may reduce the detected intensity of first or higher order diffractions. For these and other reasons, metrology based on diffraction intensity alone (including intensity summations through SRI) may be less accurate and have a smaller depth of modulation that desired and / or required.

[0063] Figure 6 depicts a schematic representation of an example diffraction-based metrology system. Figure 6 depicts a schematic view of metrology system 600, showing beam paths within the system 600. Note that system 600 is just one representative example of several different possible types of systems (which may or may not have some or all of the same components and / or may function in slightly different ways) that may provide diffraction-based metrology. Examples of such systems include ASML’s SMASH, AURORA, YieldStar system and / or other systems. System 600 is the same as or similar to system 10 described above with respect to Figure 3, with one or more components of system 600 being similar to and / or the same as one or more components of system 10 (and with Figure 6 illustrating several additional possible components of the system). In some embodiments, one or more components of system 600 may replace, be used with, and / or otherwise augment one or more components of system 10. System 600 comprises one or more radiation sources 610A-610D (e.g., similar to and / or the same as source 2 shown in Figure 3), one or more detectors 650A and / or 650B (e.g., similar to and / or the same as detector 4 shown in Figure 3), one or more processors PRO (similar to and / or the same as processor PRO shown in Figure 3), and various lenses (e.g., lenses 620A-620D), beam splitters (e.g., beam splitters 640 and 641), mirrors (e.g., mirrors 630A and 630B), apertures (e.g., aperture AP), interferometers (e.g., interferometer INF), refractive or diffractive components, and / or other components which comprise optical elements of the system 600. One or more processors PRO are operatively connected with detector 650A, detector 650B, and / or other components of system 600.

[0064] Figure 6 illustrates an illumination branch IL of system 600 including radiation sources 610A- 610D, a zeroth order ZO path including a detector 650A, a higher order HO path including a detector650B and one or more processors PRO. As depicted in Figure 6, the higher order HO path may be a path traveled by a first order diffraction as well as diffractions of second or higher order. The use of zeroth order and higher order is provided for descriptive ease for the different paths (e.g., the zeroth order ZO path and higher order path HO) and, in some embodiments, a first order diffraction may travel along the zeroth order ZO path and in other embodiments a first order diffraction may travel along the higher order HO path. The illumination from the illumination branch IL of the system 600 reaches a beam splitter 640 and is directed at the target 30 (such as through the objective lens 620B). When the illumination arrives at the target 30, at least a portion of the illumination is diffracted by the target, such as in region 642. The diffraction may be on-axis (that is, symmetrical about an axis normal to the target 30) diffraction, or off-axis diffraction (that is, asymmetrical about an axis normal to the target 30). The diffraction may be zeroth order diffraction—e.g., reflection. The diffraction may be first order diffraction. The diffraction may be higher order diffraction (e.g., higher order than first order diffraction—that is, second or higher order diffraction). The diffraction may be diffraction of multiple different wavelengths and / or a spectrum of wavelengths simultaneously, sequentially, etc. The diffractions may include positive and negative diffractions of the same order. The diffractions may include diffractions from directionally polarized light (for example, transverse electric (TE), transverse magnetic (TM), etc. polarized light). The diffracted illumination may be passed back through the objective lens 620B (or any other appropriate optical elements) and pass through the beam splitter 640. The beam splitter 640 may selectively pass diffracted light through to the interferometer INF, by reflecting incoming illumination from the illumination branch IL which arrives in region 644 and by transmitting incoming illumination from the target 30 which arrives in region 644. In some embodiments, the region 644 may treat different orders of diffraction differently, such as by blocking a through beam or other operations. The interferometer INF may be an SRI or any other appropriate interferometer. The interferometer may separate various diffraction orders and / or wavelengths or may operate on different diffraction orders and / or wavelengths in the same manner.

[0065] System 600 is a diffraction-based metrology system, where diffraction The system 600 may be configured to determine one or more metrology measurement, such as position, alignment, overlay, etc., based on the target 30. In some embodiments, the components of system 600 may form a portion of an overlay and / or alignment sensor configured to be used in a semiconductor manufacturing process.

[0066] Figure 6 also illustrates a metrology target 30 which may comprise one or more metrology marks, such as diffraction grating targets, formed in a substrate W such as a semiconductor wafer. Target 30 may comprise one or more structures in the patterned substrate capable of providing a diffraction signal. One or more targets 30 may be included in a layer of a substrate in a semiconductor device structure, for example. In some embodiments, target 30 comprises a geometric feature such as a 1D or 2D feature, and / or other geometric features. By way of several non-limitingexamples, the feature may comprise a grating, a line, an edge, a fine-pitched series of lines and / or edges, and / or other features.

[0067] Various lenses (example objective lens 620B is labeled in Figure 6), reflectors, mirrors, refractive or diffractive optical components, and other optical elements are configured to receive, transmit, reflect, focus, and / or perform other operations on the illumination generated by illumination sources 610A-610D, delivered to the target 30, received by the zeroth order ZO and / or higher order HO paths, and / or used by other portions of system 600. These various lenses, reflectors, and / or other optical components may comprise optical elements. The optical elements are configured for directing, shaping, focusing, or otherwise controlling the projection beam of radiation, collectively or singularly. They may include any type of lens, reflector, and / or other optical component configured to allow system 600 to function as described. For example, objective lens 620B may include one or more lenses formed from any transparent material and have curved surfaces configured to concentrate or otherwise focus one or more spots of radiation on target(s) 30. The various lenses, reflectors, optical elements, beam splitters, and other optical elements may be positioned in any location and / or at any angle relative to each other that allows system 600 to function as described herein. This may include positioning at specific relative distances between elements, specific angles between elements, etc. In some embodiments, the various lenses, reflectors, optical elements, beam splitters, and other optical components are positioned relative to each other in system 600 via structural members, clips, clamps, screws, nuts, bolts, adhesive, and / or other mechanical devices. In some embodiments, various ones of the lenses, reflectors, optical elements, beam splitters, and other optical elements are movable relative to each other. Movement may be configured to adjust locations of corresponding spots of illumination on one or more targets 30, for example. In some embodiments, movement comprises tilting, translating or otherwise changing a distance between various lenses, reflectors, and other optical components. In some embodiments, movement may encompass scanning, for example, of the system 600 relative to the wafer W and / or various targets 30 on the surface of the wafer W, such as in the direction 670. Other examples of movement are contemplated.

[0068] In some embodiments, movement may be controlled electronically by a processor, such as processor PRO. Processor PRO may be included in a computing system CS (e.g., as will be described further in relation to Figure11) and may operate based on computer or machine-readable instructions (e.g., as described below related to Figure 11). Electronic communication may occur by transmitting electronic signals between separate components, transmitting data between separate components of system 600, transmitting values between separate components, and / or other communication. The components of system 600 may communicate via wires or wirelessly via a network, such as the Internet or the Internet in combination with various other networks, like local area networks, cellular networks, or personal area networks, internal organizational networks, and / or other networks.

[0069] In some embodiments, one or more actuators (not shown in Figure 6) may be coupled to and configured to move one or more components of system 600 and / or the wafer W. The actuators maybe coupled to one or components of system 600 by adhesive, clips, clamps, screws, a collar, and / or other mechanisms. The actuators may be configured to be controlled electronically. Individual actuators may be configured to convert an electrical signal into mechanical displacement. The mechanical displacement is configured to move a component of system 600. As an example, one or more of the actuators may be piezoelectric. One or more processors PRO may be configured to control the actuators. One or more processors PRO may be configured to individually control each of the one or more actuators.

[0070] The quantity of the various lenses, reflectors, and / or other optical elements shown in Figure 6 is not intended to be limiting. The principles described herein may be extended such that, in some embodiments, system 600 comprises additional or fewer lenses, reflectors, and / or other optical elements.

[0071] Radiation sources 610A-610D are configured to generate radiation. Although four radiation sources are depicted, more or fewer (for example, one radiation source, 12 radiation sources, etc.) may be used. The generated radiation may be in the form of an incident radiation beam (noting that an incident radiation beam described herein may simply be any radiation beam that is incident on some optical element of system 600, for example). The radiation may comprise illumination such as light and / or other radiation. In some embodiments, each individual radiation source may produce a wavelength (or range of wavelengths) or light. In some embodiments, the radiation from radiation sources 610A-610D may comprise a Gaussian radiation beam and / or other radiation. 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 system 600 based on previous measurements, and / or determined in other ways. In some embodiments, the wavelength may be fixed based on characteristics of the radiation source (e.g., by lasing material). In some embodiments, the light comprises visible light, infrared light, near infrared light, and / or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry. The radiation emitted by the radiation sources 610A-610D may be multiplexed by multiplexer MUX, such that the radiation may travel along the same optical fiber, path, etc. The radiation emitted by the radiation sources 610A-610D may be non-interfering with the radiation of other of the sources.

[0072] In operation, system 600 is configured such that an optical element is configured to receive and transmit an incident radiation beam. In this description of Figure 6, an optical element may be any of the elements depicted and described, or any additional instances of such elements. As described above, optical element may comprise a lens, aperture, a beam splitter, a mirror, a refractive or diffractive optical component, and / or other optical elements. The optical element may cause an aberration in the incident radiation beam—in addition to or instead of any aberration caused by variations in the target 30 (such as by tilted resist) as previously described. The aberration may comprise an undesired change in a target characteristic of the incident radiation beam. The targetcharacteristic may be angle, amplitude, phase / wavefront, polarization, focus position, focal spot quality / uniformity, and / or other characteristics.

[0073] Figure 7A depicts a schematic representation of an example pupil plane holography system for diffraction-based metrology. Figure 7A depicts a schematic view of metrology system 700, showing beam paths within the system 700 which is configured for pupil plane holography. The system 700 is depicted and described with reference to at least some of the elements of system 600 of Figure 6, but can instead or additionally be used with any appropriate diffraction based metrology system.

[0074] System 700 comprises an illumination source 710. The illumination source 710 may be any appropriate illumination source, such as a laser, which produces a relatively narrow bandwidth beam of radiation. The illumination source 710 may produce illumination of multiple wavelengths, such as from multiple sources (e.g., laser sources) included in the illumination source 710, by tuning of a source to multiple wavelengths (e.g., by wavelength adjustment of the illumination source 710), including sequentially or concurrently. The illumination source 710 may be connected to one or more optical fiber. Alternatively or additionally, the illumination of the illumination source 710 may be transmitted, such as through atmosphere, by any appropriate optical elements. The illumination source 710 may provide illumination to one or more optical elements, such as lens 720A, which may broaden the illumination to a spot size on the order of an aperture, pupil plane, etc. The beam spot of the illumination emitted by the illumination source may be on the order of the pupil size of the diffraction-based metrology system, where the pupil may be any appropriate aperture, camera pupil, lens pupil, etc. The illumination of the illumination source 710 may be split into at least two beams, such as a reference beam and an illumination beam, by a beam splitter 740. The beam splitter 740 may be any appropriate beam splitter which preserves spatial coherence of at least some of the illumination of path A and path B. Path A and path B are so labeled only for ease of description, and, as such, the labeling does not imply any relative strength, importance, ordering, etc. between the paths of the illumination of the illumination source 710.

[0075] In some embodiments, the illumination of path A is passed through one or more optical elements, which may include a mirror 730A. The illumination of path A may then pass through one or more apertures, which may apertures in an aperture wheel 750. The aperture wheel 750 may be a tunable aperture wheel, from which one or more apertures may be selected. The apertures of the aperture wheel 750 may correspond to one or more diffraction order, such as when illumination is projected through the aperture wheel 750 to illuminate a target 30 on the wafer W. The aperture wheel 750 may be tunable by rotation or any other appropriate movement, such as lateral movement, movement into and out of the beam path, etc. The illumination that passes through the aperture wheel 750 may be reflected by a mirror or any other appropriate element, such as beam splitter 741. Beam splitter 741 may be a selective reflector, in which some illumination is deflected while other illumination is transmitted. The illumination from the beam splitter 741 may pass through lens 720Band be focused on the target 30. The illumination from the lens 720B may be diffracted by the target 30. The positions of the one or more apertures of the aperture wheel 750, as well as the beam splitter 741 and the lens 720B, may determine where and at what incident angle the illumination of path A arrives at the target 30. For example, the aperture wheel 750 may generate two beams of illumination from the illumination of path A, such as beam 751A and beam 751B. The beam 751A and the beam 751B may each generate one or more diffraction from the target 30. In some embodiments, the beam 751A and beam 751B may be symmetric, such as about a central axis of the target 30. In some embodiments, the beam 751A and the beam 751B may be asymmetric or generate non symmetric diffractions. In some embodiments, the beam 751A and beam 751B may be off axis beams, which may generate low angle diffractions, with respect to a central axis of the target 30. For example, the beam 751A may generate a diffraction 752A and the beam 751B may generate a diffraction 752B. Each beam incident on the target 30 may generate one or more diffraction, including a zeroth order diffraction (or reflection), a first order diffraction, a higher order diffraction (e.g., a second order or higher diffraction). In some embodiments, the beams incident on the target 30 may contain multiple wavelengths of illumination, and may generate different diffractions (or a range of diffractions) for each of the multiple wavelengths of illumination. The diffractions generated by the target (e.g., the example diffractions 752A and 752B), in response to illumination from at least part of the illumination of path A, may be captured by the lens 720B and transmitted, including through the beam splitter 741 and / or a beam splitter 742, towards a detector DET.

[0076] In some embodiments, the illumination of path B may bypass the target 30. From the beam splitter 740, the illumination of path B (which may be a reference signal and / or analogous to a reference signal) may not interact with the target 30—either through reflection, diffraction, refraction, etc. The illumination of path B may be dispersed by a dispersive element, which may introduce a dispersion and / or skew into the illumination of path B, such as with respect to the beam splitter 740. In the example depicted in Figure 7A, the skew of path B is generated in the beam splitter 740, but the dispersive element may instead be a separate element from the beam splitter 740. The dispersive element may be any appropriate dispersion element and / or aperture which may cause skewing of the illumination of path B in at least a first direction. In some embodiments, the illumination of path B may be skewed in multiple directions, such as at an angle in the x-direction and at an angle in the y- direction relative to the optical path of the illumination of path B. The illumination of path B may also pass through one or more optical path length adjustors, such as prisms 760A and 760B. The prisms 760A and 760B may adjust the optical path length of the illumination of path B, such as to produce coherence with the illumination of path A and the diffractions 752A and / or 752B. That is, the prisms 760A and 760B and / or any other appropriate optical path length adjustors (including optical path length adjustors (not depicted) in path A or the path of diffractions 752A and 752B) may be operate to match the path length of path B and path B-2 (e.g., the path traveled by some photons from the beam splitter 740 to the detector DET) and the path length of path A and either the path ofthe diffraction 752A or the diffraction 752B (e.g., an alternative path traveled by some photons from the beam splitter 740 to the detector DET). From the beam splitter 740, the illumination of path B may be transmitted to the beam splitter 742 (along path B-2) and redirected at the detector DET. The illumination of path B may travel any appropriate beam path, such that the illumination of path B maintains coherence with at least some diffractions from the target 30 at the detector DET.

[0077] At the detector DET, the illumination of path B and the illumination of the diffractions (e.g., the diffractions 752A and 752B) may be recombined. The detector DET may be a two-dimensional detector. The detector DET may comprise one or more pixels. The detector DET may be a multi- color detector (e.g., may detect wavelength as well as intensity), may have a color filter such as to select for a diffraction wavelength, may be an intensity detector (e.g., may not detect color), or any other appropriate detector. The detector DET may detect a recombination of the illumination of path B and the illumination of the diffractions (e.g., the diffractions 752A and 752B), which may constructively and destructively interfere. At the detector DET, the illumination of path B and the illumination of the diffractions (e.g., the diffractions 752A and 752B) may be spatially coherent, such as to withing a coherence length. Path B, path A, and the path of the diffractions (e.g., the diffractions 752A and 752B) may comprise one or more elements (not depicted) which may adjust path length or any of the paths, such as to cause spatial coherence of the illumination of path B and the path of the diffractions (e.g., the diffractions 752A and 752B). The illumination of path B and the illumination of the diffractions (e.g., the diffractions 752A and 752B) may interfere to generate a hologram on the detector DET. The interference pattern on the detector DET may be recorded by a camera CAM and sent to a processor PRO. In some embodiments, the detector DET may be part of the camera CAM, such as a detector (e.g., pixelated detector) of the camera CAM. In some embodiments, the detector DET may be separate from the camera CAM, such as an interposed detector or detector screen (for example, a fluorescent or phosphorescent material which may be used to down convert high energy photons to a wavelength detectable by the camera CAM). The camera CAM may be a video camera, a still camera, or any other appropriate image recording device. The processor PRO, which may be the same or a different processors PRO that than of system 600, may use the recorded interference pattern (e.g., hologram) to recreate a wavefront of the diffractions (e.g., the diffractions 752A and 752B), which may contain information about the target 30, such as tilt angle, spot size, etc.

[0078] The skew or dispersion introduced into path B may cause the illumination of path B, such as at the detector DET, to be asymmetrical. That is, the angle of the illumination of path B with respect to the detector DET may vary across the surface of the detector DET. As the illumination incident angle varies, the wavenumber (e.g., kxand kyin frequency space) also vary. This asymmetry between the illumination of path B may cause a different periodicity, tilt, location, etc. of the interference pattern of the various diffractions with the illumination of path B. For example, even if the diffractions 752A and 752B are symmetric diffractions (such as a positive first order diffraction and a negative first order diffraction), their constructive and destructive interference with the illumination ofpath B will have difference periodicity in the x and y directions and / or a different tilt, since the illumination of path B is skew and thus different at the various locations of interference. The difference between the periodicity and tilt of the various diffraction patterns may allow additional information about the interference patterns to be obtained. In some embodiments, multiple diffractions may interfere with the illumination of path B, and their different periodicity and / or tilt may allow individual interference patterns to be selected for a given diffraction. In some embodiments, the multiple diffractions may include positive and negative diffractions, diffractions of different orders, diffractions at different wavelengths, etc. Because the multiple diffractions may be separated from one another in the interference pattern, multiple diffraction patterns may be imaged at the same time, from which the wavefunction may be reconstructed (e.g., as in digital holographic microscopy DHM). In some embodiments, the capture, such as by the detector DET, of multiple diffractions in a single interference pattern may increase the speed, accuracy, confidence, etc. of a diffraction-based alignment measurement.

[0079] Figure 7B depicts a schematic representation of another example pupil plane holography system for diffraction-based metrology. Figure 7B depicts a schematic view of metrology system 701, showing beam paths within the system 701 which is configured for pupil plane holography. The system 701 is depicted and described with reference to at least some of the elements of system 600 of Figure 6 and at least some of the elements of system 700 of Figure 7A, but can instead or additionally be used with any appropriate diffraction based metrology system.

[0080] In system 701, path A as depicted in Figure 7A is replaced by a path C. The illumination from the illumination source 710 is split by a beam splitter 743, which may be a beam splitter in an optical fiber or any appropriate beam splitter. The illumination of path B may follow any appropriate path which induces a skew or dispersion, such as the path previously described in relation to Figure 7A. The illumination of path C may follow any appropriate path to produce on-axis illumination of the target 30. For example, the illumination of path C may be redirected towards the target 30 by transmission through a mirror 730C, the beam splitter 741, and the lens 720B. The illumination of path C may arrive at the target 30 as on-axis illumination, which may generate one or more diffraction (e.g., diffraction 753A and 753B). The diffractions may be symmetrical diffraction, such as a positive and negative first order diffraction. In some embodiments, the illumination of path C may be a near- on axis or off-axis illumination of the target 30. In some embodiments, the diffractions collected by the lens 720B may be asymmetric diffractions, for example, a positive first order diffraction and a negative second order diffraction. The diffractions (e.g., the diffractions 753A and 753B) may then interfere with the illumination of path A to generate interference patterns at the detector DET. From the interference pattern, in which the illumination of path B may introduce a skew and / or dispersion, the wavefunction of one or more diffraction produced by the target 30 may be reconstructed and information about the target 30 may be acquired.

[0081] Figure 8 depicts a schematic representation of example outputs from an example pupil plane holographic diffraction-based metrology system. Figure 8 is a plan view of output of a pupil plane holographic diffraction-based metrology system, such as the system 700 of Figure 7A or the system 701 of Figure 7B, at different detection points. Graph 800 depicts multiple diffraction spots on a two- dimensional detector, which may be the detector DET of Figures 7A or 7B or another plane of the metrology system (e.g., the system 700 of Figure 7A or the system 701 of Figure 7B) such as a plane of the lens 720A. The graph 800 shows expected positions of three different detected diffraction spots, where expected positions of a through beam (e.g., 0thorder diffraction, reflected beam, etc.), positive nth order diffraction, and negative nth order diffraction are depicted as hollow circles 810, 812, and 814, respectively. The diffractions of the graph 800 are shown as non-interfered diffractions, such as would arise from the detect illumination diffracted from the target 30 before interference with the illumination of path B. The expected positions of the hollow circles 810, 812, and 814 may be determined based on the diffraction order, the ancle of incident light (e.g., the illumination of path A and / or path C of Figures 7A and 7B, respectively), and the location of the plan at which the diffractions are detected. The positions of the diffractions may be symmetrical or asymmetrical. In some embodiments, there may be no through beam (e.g., 0thorder diffraction), such as if the target 30 is illuminated by off-axis illumination, or if the through beam is blocked, such as at the beam splitter 741 of Figure 7A or 7B.

[0082] Graph 820 depicts multiple diffraction spots on a two-dimensional detector, which may be the detector DET of Figure 7A or 7B or any other appropriate detector, after the diffractions are interfered with the reference illumination (e.g., the illumination of path B of Figure 7A or Figure 7B). The graph 820 shows expected positions and example appearances of two different detected diffraction and reference illumination interference patterns, pattern 822 corresponding to the interference pattern from the positive nth order diffraction of graph 800 and the illumination of path B and pattern 824 corresponding to the interference pattern from the negative nth order diffraction of graph 800 and the illumination of path B. The patterns 822 and 824 may have the same or different periodicity, tilt (e.g., with respect to the x and y directions of the graph 820), relative position to the through beam (e.g., of the hollow circle 810), wavelength, etc. The patterns 822 and 824 may have the same or different intensity (e.g., maximum intensity, minimum intensity, average intensity, etc.). The patterns 822 and 824 may be on a field which has zero background intensity or greater than zero background intensity, such as if the illumination of path B which is not interfered is also detected at the detector DET. Although two interference patterns are depicted, the interference patterns of one or more diffraction pattern and the illumination of path B may overlap. Although two interference patterns are depicted as pattern 822 and 824, more or less interference patterns may be detected (e.g., at the detector DET). For example, multiple diffraction orders may be present, such as at a location corresponding to the graph 800, and may be present as multiple interference patterns in the graph 820. The multiple interference patterns may correspond to positive and negative diffractions of first order diffraction,higher order diffractions (e.g., second order or higher diffractions), for one or more wavelengths. The difference between the periodicity, tilt, location, etc. of the diffraction patterns may allow them to be separated, such as by a fast Fourier transform, and analyzed to determine information about the target 30.

[0083] Graph 830 depicts a spectrum, obtained via a FFT or other transform from at least a portion of the detected interference of the graph 820. From the generated the spectrum of graph 830 in frequency space, a various portions of the real and imaginary wavefunction may be selected and subject to another transform to return from frequency space, such as a Fourier transform, an FFT, etc., to reconstruct the amplitude AMP and phase PH of the wavefront diffracted by the target 30. From the amplitude AMP and phase PH, various metrology parameters may be reconstructed, such as tilt angle, position, overlay, etc. In some embodiments, the amplitude AMP and phase PH may be used to determine parameters and detect non-idealities in the measurement system itself, such as lens aberration, pupil metrology, wafer mark aberrations, etc.

[0084] Figure 9A depicts a schematic representation of an example pupil plane holography system for diffraction-based metrology including a dispersive element. Figure 9A depicts a schematic representation of an example pupil plane holography system for diffraction-based metrology. Figure 9A depicts a schematic view of metrology system 900, showing beam paths within the system 900 which is configured for pupil plane holography. The system 700 is depicted and described with reference to at least some of the elements of system 700 of Figure 7A and 7B, but can instead or additionally be used with any appropriate diffraction based metrology system.

[0085] System 900 comprises an illumination source 710, as previously described in reference to Figure 7A. The illumination source 710 may provide illumination to one or more optical element, such as lens 720A, which may be any appropriate optical element(s) as previously described in reference to Figure 7A. The illumination of the illumination source 710 may be split into at least two beams, such as a reference beam and an illumination beam, by a beam splitter 740, which may be any appropriate beam splitter such as that previously described in relation to Figure 7A. The beam splitter 740 may be any appropriate beam splitter which preserves spatial coherence of at least some of the illumination of path A and path D. Path A and path D are so labeled only for ease of description, and, as such, the labeling does not imply any relative strength, importance, ordering, etc. between the paths of the illumination of the illumination source 710.

[0086] Path A may be any appropriate illumination path which interacts with the target 30, such as the path A previously described in reference to Figure 7A, the path C previously described in reference to Figure 7B, etc. In some embodiments, the illumination of path A is passed through one or more optical elements, which may include a mirror 730B (which may be the same or a different element that the beam splitter 740 described in reference to Figure 7A). The illumination of path A may then pass through one or more apertures, which may apertures in an aperture wheel 750. The aperture wheel 750 may be a tunable aperture wheel, from which one or more apertures may beselected. The apertures of the aperture wheel 750 may correspond to one or more diffraction order, such as when illumination is projected through the aperture wheel 750 to illuminate a target 30 on the wafer W. The aperture wheel 750 may be tunable by rotation or any other appropriate movement, such as lateral movement, movement into and out of the beam path, etc. The illumination that passes through the aperture wheel 750 may be reflected by a mirror or any other appropriate element, such as beam splitter 741. Beam splitter 741 may be a selective reflector, in which some illumination is deflected while other illumination is transmitted. The illumination from the beam splitter 741 may pass through lens 720B and be focused on the target 30. The illumination from the lens 720B may be diffracted by the target 30. The positions of the one or more apertures of the aperture wheel 750, as well as the beam splitter 741 and the lens 720B, may determine where and at what incident angle the illumination of path A arrives at the target 30. For example, the aperture wheel 750 may generate two beams of illumination from the illumination of path A, such as beam 751A and beam 751B. The beam 751A and the beam 751B may each generate one or more diffraction from the target 30. In some embodiments, the beam 751A and beam 751B may be symmetric, such as about a central axis of the target 30. In some embodiments, the beam 751A and the beam 751B may be asymmetric or generate non symmetric diffractions. In some embodiments, the beam 751A and beam 751B may be off axis beams, which may generate low angle diffractions, with respect to a central axis of the target 30. For example, the beam 751A may generate a diffraction 952A and the beam 751B may generate a diffraction 952B. Each beam incident on the target 30 may generate one or more diffraction, including a zeroth order diffraction (or reflection), a first order diffraction, a higher order diffraction (e.g., a second order or higher diffraction). In some embodiments, the beams incident on the target 30 may contain multiple wavelengths of illumination, and may generate different diffractions (or a range of diffractions) for each of the multiple wavelengths of illumination. The diffractions generated by the target (e.g., the example diffractions 952A and 952B), in response to illumination from at least part of the illumination of path A, may be captured by the lens 720B and transmitted, including through the beam splitter 741 and / or a beam splitter 742, towards a detector DET.

[0087] In some embodiments, the illumination of path D may bypass the target 30. From the beam splitter 740, the illumination of path D (which may be a reference signal and / or analogous to a reference signal) may not interact with the target 30—either through reflection, diffraction, refraction, etc. The illumination of path D may be dispersed by a dispersive element DIS, which may introduce a dispersion, such as a wavelength variation, and / or skew into the illumination of path B, such as with respect to the beam splitter 740. The dispersive element DIS may be a diffraction grating, including a one dimensional, two-dimensional, etc. diffraction grating. The dispersive element DIS may be any appropriate dispersive element, such as a metamaterial, prism, etc. The illumination of path D (and the illumination emitted by the illumination source 710) may contain multiple wavelengths of light. The dispersive element DIS may introduce both spatial and wavelength separation into the illumination of the path D. The dispersive element may be any appropriate dispersion elementand / or aperture which may cause dispersion of the illumination of path D in at least a first direction. In some embodiments, the illumination of path D may be dispersed in multiple directions, such as at an angle in the x-direction and at an angle in the y-direction relative to the optical path of the illumination of path D. The illumination of path D may also pass through one or more optical path length adjustors, such as prisms 760A and 760B, either before or after passing through the dispersive element DIS. The prisms 760A and 760B may adjust the optical path length of the illumination of path D and path D-2, such as to produce coherence with the illumination of path A and the diffractions 952A and 952B. That is, the prisms 760A and 760B and / or any other appropriate optical path length adjustors (including optical path length adjustors (not depicted) in path A or the path of diffractions 952A and 952B) may be operate to match the path length of path D and path D-2 (e.g., the path traveled by some photons from the beam splitter 740 to the detector DET) and the path length of path A and either the path of the diffraction 952A or the diffraction 952B (e.g., an alternative path traveled by some photons from the beam splitter 740 to the detector DET). From the beam splitter 740, the illumination of path D may be transmitted to the beam splitter 742 and redirected at the detector DET (e.g., along path D-2), as previously described in reference to Figure 7A. The illumination of path D may travel any appropriate beam path, such that at least some of the illumination of path D maintains coherence with at least some diffractions from the target 30 at the detector DET.

[0088] At the detector DET, the illumination of path D and the illumination of the diffractions (e.g., the diffractions 952A and 952B) may be recombined. The detector DET may be a two-dimensional detector. The detector DET may comprise one or more pixels. The detector DET may be a multi- color detector (e.g., may detect wavelength as well as intensity), may have a color filter such as to select for a diffraction wavelength, may be an intensity detector (e.g., may not detect color), or any other appropriate detector. The detector DET may detect a recombination of the illumination of path D and the illumination of the diffractions (e.g., the diffractions 952A and 952B), which may constructively and destructively interfere. At the detector DET, the illumination of path D and the illumination of the diffractions (e.g., the diffractions 952A and 952B) may be spatially coherent, such as to withing a coherence length. Path D, path A, and the path of the diffractions (e.g., the diffractions 952A and 952B) may comprise one or more elements (not depicted) which may adjust path length or any of the paths, such as to cause spatial coherence of the illumination of path D and the path of the diffractions (e.g., the diffractions 952A and 952B). The illumination of path B and the illumination of the diffractions (e.g., the diffractions 952A and 952B) may interfere to generate a hologram on the detector DET. The interference pattern on the detector DET may be recorded by a camera CAM and sent to a processor PRO. The detector DET may or may not be integrated into the camera CAM. The processor PRO, which may be the same or a different processors PRO that than of system 600, may use the recorded interference pattern (e.g., hologram) to recreate a wavefront of the diffractions (e.g.,the diffractions 952A and 952B), which may contain information about the target 30, such as tilt angle, spot size, etc.

[0089] The skew and / or dispersion introduced into path D may cause the illumination of path D, such as at the detector DET, to be asymmetrical. That is, the angle of the illumination of path B with respect to the detector DET may vary across the surface of the detector DET, as well as the wavelength. As the illumination incident angle and wavelength vary, the wavenumber (e.g., kxand kyin frequency space) also vary. This asymmetry between the illumination of path D may cause a different periodicity, tilt, location, etc. of the interference pattern of the various diffractions with the illumination of path D. For example, even if the diffractions 952A and 952B are symmetric diffractions (such as a positive first order diffraction and a negative first order diffraction), their constructive and destructive interference with the illumination of path D will have difference periodicity in the x and y directions and / or a different tilt, since the illumination of path D is skew and varies in wavelength and thus varies at the different locations of interference. The difference between the periodicity, tilt, and location of the various diffraction patterns may allow additional information about the interference patterns to be obtained. In some embodiments, multiple diffractions may interfere with the illumination of path D, and their different periodicity, tilt, and / or location may allow individual interference patterns to be selected for a given diffraction. In some embodiments, the multiple diffractions may include positive and negative diffractions, diffractions of different orders, diffractions at different wavelengths, etc. Because the multiple diffractions may be separated from one another in the interference pattern, multiple diffraction patterns may be imaged at the same time, from which the wavefunction may be reconstructed (e.g., as in digital holographic microscopy DHM). In some embodiments, the capture, such as by the detector DET, of multiple diffractions in a single interference pattern may increase the speed, accuracy, confidence, etc. of a diffraction-based alignment measurement.

[0090] Figure 9B depicts a schematic representation of another example pupil plane holography system for diffraction-based metrology including a dispersive element. Figure 9B depicts a schematic view of metrology system 901, showing beam paths within the system 901 which is configured for pupil plane holography. The system 901 is depicted and described with reference to at least some of the elements of system 600 of Figure 6, at least some of the elements of system 700 of Figure 7A, at least some of the elements of system 701 of Figure 7B, and at least some of the elements of system 900 of Figure 9A but can instead or additionally be used with any appropriate diffraction based metrology system.

[0091] In system 901, path A as depicted in Figure 9A is replaced by a path C. The illumination from the illumination source 710 is split by a beam splitter 743, which may be a beam splitter in an optical fiber or any appropriate beam splitter. The illumination of path B may follow any appropriate path which induces a skew or dispersion, such as the path previously described in relation to Figure 9A. The illumination of path C may follow any appropriate path to produce on-axis illumination ofthe target 30, such as the path previously described in relation to path C of Figure 7B. For example, the illumination of path C may be redirected towards the target 30 by transmission through a mirror 730C, the beam splitter 741, and the lens 720B. The illumination of path C may arrive at the target 30 as on-axis illumination, which may generate one or more diffraction (e.g., diffraction 953A and 953B). The diffractions may be symmetrical diffraction, such as a positive and negative first order diffraction. In some embodiments, the illumination of path C may be a near-on axis or off-axis illumination of the target 30. In some embodiments, the diffractions collected by the lens 720B may be asymmetric diffractions, for example, a positive first order diffraction and a negative second order diffraction. The diffractions (e.g., the diffractions 953A and 953B) may then interfere with the illumination of path D to generate interference patterns at the detector DET. From the interference pattern, in which the illumination of path D may introduce a wavelength dispersion, the wavefunction of one or more diffraction produced by the target 30 may be reconstructed and information about the target 30 may be acquired.

[0092] Figure 9C depicts a schematic representation of an example camera field plane holography system for diffraction-based metrology including a dispersive element. Figure 9C depicts a schematic view of metrology system 902, showing beam paths within the system 902 which is configured for camera field plane holography. The system 902 is depicted and described with reference to at least some of the elements of system 700 of Figure 7A and system 701 of Figure 7B, but can instead or additionally be used with any appropriate diffraction based metrology system.

[0093] System 902 comprises a first illumination source providing a first reference illumination beam 970A and a second illumination source providing a second reference illumination beam 970B. The illumination of the first reference illumination beam 970A and the second reference illumination beam 970B may be any appropriate illumination, such as previously described. The first illumination source and the second illumination source (not depicted) may be the same or different illumination sources. For example, the first reference illumination beam 970A and the second reference illumination beam 970B may be provided by optical fibers, which are supplied by the same illumination source. The first reference illumination beam 970A and the second reference illumination beam 970B may have the same or different wavelength, polarization, bandwidth, incident angle, etc. Although two reference illumination beams are depicted, more or fewer illumination beams may be used.

[0094] The first reference illumination beam 970A may be dispersed, in any appropriate manner as previously described in reference to Figure 9A, by a first dispersive element DIS. The second reference illumination beam 970B may be dispersed, in any appropriate manner as previously described in reference to Figure 9A, by a second dispersive element DIS-2. DIS-1 and DIS-2 may be the same or different type of dispersive element. In some embodiments, DIS-1 and DIS-2 may be part of the same dispersive element.

[0095] The target 30 may be illuminated by one or more illumination beams, such as a first illumination beam 980A and a second illumination beam 980B. More or fewer illumination beams may be used. The illumination beams may be any appropriate illumination beams, such as previously described in reference to path A of Figure 7A, path C of figure 7B, and path A of Figure 9A. The illumination beams may have the same of different wavelengths, bandwidth, polarization, etc. as each other. Each illumination beam may contain at least a portion of illumination which is spatially coherent with at least a portion of the illumination of one or more of the reference illumination beams, such that each illumination beam may experience interference when passing through the reference beams at the detector DET. Each illumination beam may generate one or more diffraction when interacting with the target 30. One or more diffractions, such as positive diffractions, negative diffractions, first order diffractions, higher order diffractions, etc., may be collected by the lens 720A and directed towards the detector DET for interference with the reference illumination.

[0096] At the detector DET, the reference illumination and the diffracted illumination may be recombined. The detector DET may be a two-dimensional detector. The detector DET may comprise one or more pixels. The detector DET may be a multi-color detector (e.g., may detect wavelength as well as intensity), may have a color filter such as to select for a diffraction wavelength, may be an intensity detector (e.g., may not detect color), or any other appropriate detector. The detector DET may detect a recombination of the reference illumination and the diffracted illumination, which may constructively and destructively interfere. At the detector DET, the reference illumination and the diffracted illumination may be spatially coherent, such as to withing a coherence length. The paths of the reference illumination and the diffracted illumination may comprise one or more elements (not depicted) which may adjust path length or any of the paths, such as to cause spatial coherence of the reference illumination and the diffracted illumination. The reference illumination and the diffracted illumination may interfere to generate a hologram on the detector DET. The interference pattern on the detector DET may be recorded by a camera CAM and sent to a processor PRO. The detector DET may or may not be integrated into the camera CAM. The processor PRO, which may be the same or a different processors PRO that than of system 600, may use the recorded interference pattern (e.g., hologram) to recreate a wavefront of the diffractions (e.g., the diffractions 981A and 981B), which may contain information about the target 30, such as tilt angle, spot size, etc.

[0097] The skew and / or dispersion introduced into reference illumination, such as by dispersive elements DIS-1 and / or DIS-2, may cause the reference illumination, such as at the detector DET, to be asymmetrical. That is, the angle of the reference illumination with respect to the detector DET may vary across the surface of the detector DET, as well as the wavelength and contributing reference illumination beam. As the illumination incident angle and wavelength vary, the wavenumber (e.g., kxand kyin frequency space) also vary. This asymmetry between the reference illumination may cause a different periodicity, tilt, location, etc. of the interference pattern of the various diffractions with the reference illumination. For example, even if the diffractions 981A and 981B are symmetricdiffractions (such as a positive first order diffraction and a negative first order diffraction), their constructive and destructive interference with the reference illumination will have difference periodicity in the x and y directions and / or a different tilt, since the reference illumination varies in wavelength and thus varies at the different locations of interference. The difference between the periodicity, tilt, and location of the various diffraction patterns may allow additional information about the interference patterns to be obtained. In some embodiments, multiple diffractions may interfere with the reference illumination, and their different periodicity, tilt, and / or location may allow individual interference patterns to be selected for a given diffraction. In some embodiments, the multiple diffractions may include positive and negative diffractions, diffractions of different orders, diffractions at different wavelengths, etc. Because the multiple diffractions may be separated from one another in the interference pattern, multiple diffraction patterns may be imaged at the same time, from which the wavefunction may be reconstructed (e.g., as in digital holographic microscopy DHM). In some embodiments, the capture, such as by the detector DET, of multiple diffractions in a single interference pattern may increase the speed, accuracy, confidence, etc. of a diffraction-based alignment measurement.

[0098] Figure 10A depicts a schematic representation of example outputs from an example pupil plane holography diffraction-based metrology system including a dispersive element. Figure 10A is a plan view of output of a pupil plane holographic diffraction-based metrology system, such as the system 900 of Figure 9A. Graph 1020 depicts multiple diffraction spots on a two-dimensional detector, which may be the detector DET of Figure 9A any other appropriate detector, after the diffractions are interfered with the reference illumination (e.g., the illumination of path D of Figure 9A). The graph 1020 shows expected positions and example appearances of ten different detected diffraction and reference illumination interference patterns. The patterns may have the same or different periodicity, tilt (e.g., with respect to the x and y directions of the graph 1020), relative position to the through beam, wavelength, etc. The patterns may have the same or different intensity (e.g., maximum intensity, minimum intensity, average intensity, etc.). The patterns may be on a field which has zero background intensity or greater than zero background intensity, such as if the illumination of path D which is not interfered is also detected at the detector DET. Although ten interference patterns are depicted, the interference patterns of one or more diffraction pattern and the illumination of path D may overlap. Although ten interference patterns are depicted, more or fewer interference patterns may be detected (e.g., at the detector DET). For example, multiple diffraction orders may be present, and may be present as multiple interference patterns in the graph 1020. The multiple interference patterns may correspond to positive and negative diffractions of first order diffraction, higher order diffractions (e.g., second order or higher diffractions), for one or more wavelengths. The difference between the periodicity, tilt, location, etc. of the diffraction patterns may allow them to be separated, such as by a fast Fourier transform, and analyzed to determine information about the target 30.

[0099] Graph 1030 depicts a spectrum, obtained via a FFT or other transform from at least a portion of the detected interference of the graph 1020. From the generated the spectrum of graph 1030 in frequency space, a various portions of the real and imaginary wavefunction may be selected and subject to another transform to return from frequency space, such as a Fourier transform, an FFT, etc., to reconstruct the amplitude AMP and phase PH of the wavefront diffracted by the target 30. From the amplitude AMP and phase PH, various metrology parameters may be reconstructed, such as tilt angle, position, overlay, etc. In some embodiments, the amplitude AMP and phase PH may be used to determine parameters and detect non-idealities in the measurement system itself, such as lens aberration, pupil metrology, wafer mark aberrations, etc.

[0100] Figure 10B depicts a schematic representation of example outputs from an example camera plane holography diffraction-based metrology system including a dispersive element. Figure 10B is a plan view of output of a camera pupil plane holographic diffraction-based metrology system, such as the system 902 of Figure 9C. Graph 1070 depicts multiple overlapping diffraction patterns on a two- dimensional detector, which may be the detector DET of Figure 9C any other appropriate detector, after the diffractions are interfered with the reference illumination (e.g., the first reference illumination beam 970A and the second reference illumination beam 970B of Figure 9A). The graph 1070 shows expected positions and example appearances of different at least partially overlapping detected diffraction and reference illumination interference patterns. The patterns may have the same or different periodicity, tilt (e.g., with respect to the x and y directions of the graph 1070), relative position to the through beam, wavelength, etc. The patterns may have the same or different intensity (e.g., maximum intensity, minimum intensity, average intensity, etc.). The patterns may be on a field which has zero background intensity or greater than zero background intensity, such as if the illumination of the first reference illumination beam 970A and / or the second reference illumination beam 970B which is not interfered is also detected at the detector DET. Although multiple overlapping interference patterns are depicted, the interference patterns of one or more diffraction pattern and the illumination of the first reference illumination beam 970A and the second reference illumination beam 970B may overlap partially, fully, or be non-overlapping, depending on the optical path. Although multiple interference patterns are depicted, more or fewer interference patterns may be detected (e.g., at the detector DET). For example, multiple diffraction orders may be present, and may be present as multiple interference patterns in the graph 1070. The multiple interference patterns may correspond to positive and negative diffractions of first order diffraction, higher order diffractions (e.g., second order or higher diffractions), for one or more wavelengths. The difference between the periodicity, tilt, location, etc. of the diffraction patterns may allow them to be separated, such as by a fast Fourier transform, and analyzed to determine information about the target 30.

[0101] Graph 1080 depicts a spectrum, obtained via a FFT or other transform from at least a portion of the detected interference of the graph 1070. From the generated the spectrum of graph 1080 in frequency space, a various portions of the real and imaginary wavefunction may be selected andsubject to another transform to return from frequency space, such as a Fourier transform, an FFT, etc., to reconstruct the amplitude AMP and phase PH of the wavefront diffracted by the target 30. From the amplitude AMP and phase PH, various metrology parameters may be reconstructed, such as tilt angle, position, overlay, etc. In some embodiments, the amplitude AMP and phase PH may be used to determine parameters and detect non-idealities in the measurement system itself, such as lens aberration, pupil metrology, wafer mark aberrations, etc.

[0102] Figure 11 depicts a schematic representation of an example technique for improvement of diffraction-based metrology with holography. Figure 11 is a schematic representation of digital holographic microscopy (DHM) in conjunction with diffraction-based metrology. A diffraction target 30, which may have one or more tilted layers and / or other non-ideality (as previously described), is subject to illumination which generates one or more diffraction. One or more of the generated diffractions are interfered with one or more known (e.g., reference) signals, which may be a zeroth order diffraction, a reference signal which bypasses the target 30, etc. at an interference operation 910A and / or 910B. The interference generates an interference pattern IFP, which is detected by a two-dimensional detector. The interference pattern IFP is subject to a transform 920 into frequency space, such as a Fourier transform, a fast Fourier transform (FFT), etc. to generate a spectrum 930 in frequency space. From the spectrum 930, various portions of the real and imaginary wavefunction may be selected and subject to another transform 940 to return from frequency space, such as a Fourier transform, an FFT, etc., to reconstruct the amplitude AMP and phase PH of the wavefront diffracted by the target 30. From the amplitude AMP and phase PH, various metrology parameters MET may be reconstructed, such as tilt angle, position, overlay, etc. In some embodiments, the amplitude AMP and phase PH may be used to determine parameters and detect non-idealities in the measurement system itself, such as lens aberration, pupil metrology, wafer mark aberrations, etc.

[0103] Figure 12 depicts a flowchart illustrating an exemplary method 1200 for diffraction-based holography. Each of these operations is described in detail below. The operations of method 1200 presented below are intended to be illustrative. In some embodiments, method 1200 may be accomplished with one or more additional operations not described, and / or without one or more of the operations discussed. Additionally, the order in which the operations of method 1200 are illustrated in Figure 12 and described below is not intended to be limiting. In some embodiments, one or more portions of method 1200 may be implemented (e.g., by simulation, modeling, etc.) in one or more processing devices (e.g., one or more processors). The one or more processing devices may include one or more devices executing some or all of the operations of method 1200 in response to 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 1200, for example.

[0104] At an operation 1202, an illumination beam is diffracted by a target. The illumination beam may be a narrow bandwidth beam of radiation, in any appropriate wavelength regime, such as visible,infrared, ultraviolet, optical, etc. The illumination beam may be emitted by a laser or any other appropriate narrow band source. In some embodiments, the illumination may be emitted by a broadband illumination source and filtered, e.g., spatially, by wavelength filters, etc., to become a more narrow band illumination.

[0105] The illumination may be diffracted by any appropriate target. The target may be a diffraction grating. The target may comprise multiple diffraction gratings. The target may be a point source emitter. The target may be a target designed for position determination. The target may be a multi- layer target and / or a target designed for overlay determination. The target may be etched into a substrate, such as a semiconductor wafer. The target may be fabricated in one or more photoresist layers. The target may be covered by one or more layers or be exposed, at least in part, on the surface of a device. The target may have any appropriate periodicity. The diffraction angles and positions may be dependent on the target’s periodicity.

[0106] The illumination beam may be diffracted in any appropriate manner, such as on-axis (e.g., by illumination normal to the surface of the target), off-axis (e.g., by illumination substantially oblique to the surface of the target), etc. The illumination beam may be polarized and may be diffracted differently based on said polarization. The illumination beam may be diffracted into multiple diffraction orders. The illumination beam may be diffracted into both positive and negative diffraction orders.

[0107] At an operation 1204, the diffracted illumination is combined with a reference beam. The reference beam may be any appropriate reference beam, which is spatially coherent with the diffracted illumination of the illumination beam which produces the diffracted illumination. The reference beam may be emitted by the same source as the illumination beam, and split from the illumination beam by a beam splitter or other optical element. The reference beam may be an undiffracted portion of the illumination beam which produces the diffracted illumination. The reference beam may be made spatially coherent with the diffracted illumination by application of wavelength filtering, spatial filtering, etc.

[0108] The diffracted illumination and the reference beam may be combined through interference, including constructive and destructive interference. The diffracted illumination and the reference beam may be combined by any appropriate method which preserves phase information—e.g., not by intensity summation along. The diffracted illumination and the reference beam may be combined in a hologram. The diffracted illumination and the reference beam may be combined by methods associated with DHM.

[0109] At an operation 1206, the combination of the diffracted illumination and the reference beam is detected, such as by a two-dimensional detector. In some embodiments, the combination may be detected by a one-dimensional detector, such as a scanning one-dimensional detector. The detector may be a camera. The detector may be a screen on which light in incident, where the screen is filmed by a camera. The detector may detect individual photons. The detector may be a time lapse detectorand / or a detector with an accumulation time. The detector may detect the hologram created by the combination of the diffracted illumination and the reference beam. The detector may be focusable or moveable such that the hologram may be focused on the detector. The detector may be a multi-color detector, which may be configured to detect holograms of different wavelengths at substantially the same time.

[0110] At an operation 1208, one or more characteristics of the target may be determined based on the detected combination. The characteristics may include position, overlay, tilt, etc. The characteristics may be determined by a processor based on the detected hologram. The characteristics may be determined by comparing the detected hologram to a library of pre-determined holograms for various arrangements of the target. The characteristics may be determined by calculating target characteristics from the detected hologram, such as through the use of one or more transform. The characteristics may be determined based on the measured intensity of the detected hologram. The characteristics may be determined based on a curve fitting to the measured intensity of the detected hologram. The detected hologram may be used to determine a wavefront for the diffracted illumination of the combination, and the characteristics may be determined based on the determined wavefront. The characteristics may include information about the measurement system, in addition to or instead of information about the target.

[0111] Once the characteristics of the target and / or system are determined, a correction may be applied to diffraction-based metrology. For example, if the resist is known to be tilted at an angle θ, then the overlap between the reference signals and transformed signals of the SRI may be adjusted to correct for the tilt angle (e.g., to increase the signal which is lost due to non-overlapping of the reference and transformed signals generated by the interferometer). In other embodiments, a wafer and / or target may be excluded from metrology, such as if the tilt angle is too large. In another embodiment, a pupil aberration may be determined and then used to correct measured diffraction locations, such as for position and overlay measurements.

[0112] As described above, method 1200 (and / or the other methods and systems described herein) is configured to determine target and / or system characteristics for a diffraction-based metrology system using digital microscopy holography.

[0113] Figure 13 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 instructionsfor 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.

[0114] 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.

[0115] The embodiments may further be described using the following clauses: 1. A metrology system comprising: a first illumination beam, the first illumination beam configured to be diffracted by a target; a second illumination beam, the second illumination beam configured to be dispersed by a dispersive element, wherein the dispersive element is configured to introduce a tilt in the second illumination beam in at least one direction; a detector, the detector configured to detect an interference pattern of the first illumination beam diffracted by the target and the second illumination beam dispersed and tilted by the dispersive element; and a processor operatively connected with the detector, the processor configured to determine a phase and / or amplitude of a waveform of the first illumination beam after it has interacted with the target based on the interference pattern detected by the detector. 2. The system of any preceding clause, the processor further configured to determine a location of the target based on the phase and / or amplitude of the waveform. 3. The system of any preceding clause, the processor further configured to determine an orientation of the target based on the phase and / or amplitude of the waveform. 4. The system of any preceding clause, the processor further configured to determine an overlay of the target based on the phase and / or amplitude of the waveform. 5. The system of any preceding clause, wherein the first illumination beam configured to be diffracted by the target comprises illumination of multiple wavelengths. 6. The system of clause 5, wherein the first illumination beam is further configured to be diffracted by the target into multiple diffractions, at least some of the multiple diffractions corresponding to different of the multiple wavelengths.7. The system of clause 5 or 6, the detector is further configured to detect multiple interference patterns, at least some of the multiple interference patterns corresponding to interaction between different of the multiple diffractions and the second illumination beam dispersed and titled by the dispersive element. 8. The system of clause 7, wherein the multiple interference patterns are detected at different locations. 9. The system of clause 7, wherein at least some of the multiple interference patterns are detected in substantially the same location. 10. The system of clause 8 or 9, wherein the multiple interference patterns are detected in the same and / or different wavelengths. 11. The system of any preceding clause, wherein the first illumination beam comprises significantly on-axis illumination relative to the target. 12. The system of any of clauses 1 to 4, wherein the first illumination beam configured to be diffracted by the target comprises sub-beams, each sub-beam comprising illumination of a corresponding wavelength, wherein at least one of the corresponding wavelengths is different and wherein each-sub beam is configured to be diffracted by the target into one or more corresponding diffraction. 13. The system of clause 12, wherein the sub-beams comprise significantly off-axis illumination relative to the target. 14. The system of clause 12 or 13, wherein at least one of the sub-beams comprises a different illumination angle. 15. The system of any clause 12 to 14, wherein the detector is further configured to detect multiple interference patterns, at least some of the multiple interference patterns corresponding to interaction between different of the diffractions corresponding to the sub- beams and the second illumination beam dispersed and titled by the dispersive element. 16. The system of clause 15, wherein at least some of the multiple interference patterns are detected in substantially the same location. 17. The system of clause 15, wherein the multiple interference patterns are detected at different locations. 18. The system of any clause 1 to 4 or 12 to 15, wherein the first illumination beam comprises significantly off-axis illumination relative to the target. 19. The system of any preceding clause, wherein the second illumination beam dispersed and titled by dispersive element comprises illumination of multiple wavelengths.20. The system of any preceding clause, wherein the second illumination beam further comprises one or more additional illumination beams configured to be dispersed by one or more additional dispersive elements, wherein the one or more additional dispersive elements are configured to introduce a tilt in the one or more additional illumination beams in at least one direction and wherein the detector is configured to detect an interference pattern of the first illumination beam diffracted by the target, the second illumination beam dispersed and tilted by the dispersive element and the one or more one or more additional illumination beams dispersed and titled by the one or more additional dispersive element. 21. The system of clause 20, wherein the tilt in the one or more additional illumination beams is different from the tilt in the second illumination beam. 22. The system of any preceding clause, wherein the dispersive element comprises a diffraction grating. 23. The system of any preceding clause, further comprising one or more optical elements configured to adjust an optical path length of the first illumination beam and / or the second illumination beam. 24. The system of any preceding clause, wherein the detector is configured to detect an interference pattern of one or more first order diffraction of the first illumination beam diffracted by the target and the second illumination beam dispersed and tilted by the dispersive element. 25. The system of clause 24, wherein the detector is configured to detect interference patterns of both a positive and a negative first order diffraction of the first illumination beam diffracted by the target and the second illumination beam dispersed and tilted by the dispersive element. 26. The system of clause 24 or 25, wherein the detector is further configured to detect an interference pattern of at least one higher order diffraction of the first illumination beam diffracted by the target and the second illumination beam dispersed and tilted by the dispersive element. 27. The system of any preceding clause, wherein the first illumination beam and the second illumination beam are significantly spatially coherent, at least in part, at the detector. 28. A method for metrology, comprising: illuminating a diffraction target with a first beam of illumination, the first beam of illumination generating at least one diffraction order; interfering the at least one diffraction order with a second beam of illumination, the second beam of illumination comprising multiple wavelengths;detecting, by a two-dimensional detector, interference of the at least one diffraction order and the second beam of illumination; and determining, by a processor, a phase and / or amplitude of a waveform of the at least one diffraction order after it has interacted with the target based on the interference detected by the two-dimensional detector. 29. The method of clause 28, further comprising determining a location of the target based on the phase and / or amplitude of the waveform. 30. The method of clause 28 or 29, further comprising determining an orientation of the target based on the phase and / or amplitude of the waveform. 31. The method of any clause 28 to 30, further comprising determining an overlay of the target based on the phase and / or amplitude of the waveform. 32. The method of any clause 28 to 30, wherein determining the phase and / or amplitude of the waveform of the at least one diffraction order comprises determining the phase and / or amplitude of the waveform of the at least one diffraction order based on a frequency transform of the detected interference of the at least one diffraction order and the second beam of illumination. 33. The method of clause 32, wherein the frequency transform is a fast Fourier transform (FFT). 34. The method of any clause 28 to 33, wherein determining the phase and / or amplitude of the waveform of the at least one diffraction order comprises: transforming, to frequency space, intensity of the detected interference of the at least one diffraction order and the second beam of illumination; selecting, in the frequency space, at least a region of signal corresponding to the transformed detected interference; and transforming, out of frequency space, the signal of the selected region to generate the phase and / or amplitude of the waveform at the at least one diffraction order. 35. The method of clause 34, wherein transforming comprises transforming intensity of multiple detected interferences corresponding to multiple diffraction orders with the second beam of illumination. 36. The method of clause 35, wherein selecting at least the region of signal corresponding to the transformed detected interference comprises selecting, from multiple regions, the region of signal corresponding to the transformed detected interference of the at least one diffraction order and the second beam of illumination.37. The method of any clause 28 to 36, wherein the first beam of illumination comprises illumination of multiple wavelengths, wherein the first beam of illumination generates at least one diffraction order for two or more of the multiple wavelengths, and wherein detecting the interference comprises detecting, by the two-dimensional detector, interference of each of the at least one diffraction order for two or more of the multiple wavelengths and the second beam of illumination. 38. The method of clause 37, wherein the interference of each of the at least one diffraction order for two or more of the multiple wavelengths and the second beam of illumination are at least partially overlapping on the two-dimensional detector. 39. The method of clause 37, wherein the interference of each of the at least one diffraction order for two or more of the multiple wavelengths and the second beam of illumination are non-overlapping on the two-dimensional detector. 40. The method of any of clauses 28 to 39, wherein the second beam of illumination comprises a beam of illumination with multiple wavelengths in different regions. 41. The method of any of clauses 28 to 40, further comprising generating the second beam of illumination by a dispersive element. 42. The method of clause 41, wherein the dispersive element introduces a tilt into the second beam of illumination. 43. The method of clause 41 or 42, wherein the interference of each of the at least one diffraction order for two or more of the multiple wavelengths and the second beam of illumination are at least partially overlapping in frequency space. 44. The method of clause 41 or 42, wherein the interference of each of the at least one diffraction order for two or more of the multiple wavelengths and the second beam of illumination are non-overlapping in frequency space. 45. The method of any of clauses 28 to 44, wherein locations and / or angles of incidence at which the multiple wavelengths of the second beam of illumination impinge on the two- dimensional detector are known. 46. The method of any clauses 28 to 45, wherein locations and / or angles of regions corresponding to the interference of each of the at least one diffraction order for two or more of the multiple wavelengths and the second beam of illumination occur in frequency space are known. 47. The method of any of clauses 28 to 46, wherein illuminating the diffraction target with the first beam of illumination comprises illuminating the diffraction target on axis with the first beam of illumination.48. The method of any of clauses 28 to 46, illuminating the diffraction target with the first beam of illumination comprises illuminating the diffraction target with at least some off axis illumination from the first beam of illumination. 49. The method of clause 48, wherein the first beam of illumination comprises multiple sub-beams, wherein each sub-beam is configured to be diffracted by the target into one or more corresponding diffractions, wherein at least one of the sub-beams comprises off axis illumination, and wherein detecting interference of the at least one diffraction order and the second beam of illumination comprises detecting interference of at least one of the one or more corresponding diffractions of the multiple sub-beams and the second beam of illumination. 50. The method of clause 49, wherein each sub-beam comprises illumination of a corresponding wavelength and wherein at least one of the corresponding wavelengths is different. 51. The method of any of clauses 28 to 50, wherein the first beam of illumination comprises a portion of the second beam of illumination. 52. The method of any of clauses 28 to 51, wherein the two-dimensional detector comprises a multi-color camera.

[0116] In some embodiments, portions of one or more methods described herein 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) described herein. 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, the description herein is not limited to any specific combination of hardware circuitry and software.

[0117] The term “computer-readable medium” and / or “machine readable medium” as used herein 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-readablemedia 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 herein. Transitory computer-readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[0118] 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 telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0119] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

[0120] 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.

[0121] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CI. 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 CI. 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.

[0122] While the concepts disclosed herein may be used for manufacturing with a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of manufacturing system (e.g., those used for manufacturing on substrates other than silicon wafers).

[0123] In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments. For example, one or more of the operations described above may be included in separate embodiments, or they may be included together in the same embodiment.

[0124] 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

CLAIMS 1. A metrology system comprising: a first illumination beam, the first illumination beam configured to be diffracted by a target; a second illumination beam, the second illumination beam configured to be dispersed by a dispersive element, wherein the dispersive element is configured to introduce a tilt in the second illumination beam in at least one direction; a detector, the detector configured to detect an interference pattern of the first illumination beam diffracted by the target and the second illumination beam dispersed and tilted by the dispersive element; and a processor operatively connected with the detector, the processor configured to determine a phase and / or amplitude of a waveform of the first illumination beam after it has interacted with the target based on the interference pattern detected by the detector.

2. The system of any preceding claim, the processor further configured to determine a location of the target based on the phase and / or amplitude of the waveform.

3. The system of any preceding claim, the processor further configured to determine an orientation of the target based on the phase and / or amplitude of the waveform.

4. The system of any preceding claim, the processor further configured to determine an overlay of the target based on the phase and / or amplitude of the waveform.

5. The system of any preceding claim, wherein the first illumination beam configured to be diffracted by the target comprises illumination of multiple wavelengths.

6. The system of claim 5, wherein the first illumination beam is further configured to be diffracted by the target into multiple diffractions, at least some of the multiple diffractions corresponding to different of the multiple wavelengths.

7. The system of claim 5 or 6, the detector is further configured to detect multiple interference patterns, at least some of the multiple interference patterns corresponding to interaction between different of the multiple diffractions and the second illumination beam dispersed and titled by the dispersive element.

8. The system of claim 7, wherein the multiple interference patterns are detected at different locations.

9. The system of claim 7, wherein at least some of the multiple interference patterns are detected in substantially the same location.

10. The system of claim 8 or 9, wherein the multiple interference patterns are detected in the same and / or different wavelengths.

11. The system of any preceding claim, wherein the first illumination beam comprises significantly on-axis illumination relative to the target.

12. The system of any of claims 1 to 4, wherein the first illumination beam configured to be diffracted by the target comprises sub-beams, each sub-beam comprising illumination of a corresponding wavelength, wherein at least one of the corresponding wavelengths is different and wherein each-sub beam is configured to be diffracted by the target into one or more corresponding diffraction.

13. The system of claim 12, wherein the sub-beams comprise significantly off-axis illumination relative to the target.

14. The system of claim 12 or 13, wherein at least one of the sub-beams comprises a different illumination angle.

15. The system of any claim 12 to 14, wherein the detector is further configured to detect multiple interference patterns, at least some of the multiple interference patterns corresponding to interaction between different of the diffractions corresponding to the sub-beams and the second illumination beam dispersed and titled by the dispersive element.

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