Overlay metrology with enhanced overlay targets

Abstract

Measuring overlay using enhanced overlay targets is described. Multiple dimensional (e.g., x and y components) of an overlay measurement may be acquired in parallel in a digital holographic microscope (for example) system using non-cartesian overlay targets (e.g., overlay targets with structures oriented at angles other than typical ninety degree x and y orientations, but within forty five degrees of a radiation axis). This scheme enables single-shot acquisition of the multiple dimensional components of the overlay measurement (e.g., a full overlay vector). A processor is configured to deconstruct data from the single-shot acquisition (based on the orientation of the overlay targets) into the x and y components of an overlay value. Or the non-cartesian targets may be oriented to correspond to patterned features of interest in a substrate such that the single shot acquisition directly provides an overlay value relative to those features of interest.

Description

OVERLAY METROLOGY WITH ENHANCED OVERLAY TARGETSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 682,537 which was filed on August 13, 2024 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This description relates generally to overlay metrology with enhanced overlay targets.BACKGROUND

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

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

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

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

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

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

[0009] Measuring overlay using enhanced overlay targets is described. Multiple dimensional components (e.g., x and y components, and / or other directional components) of an overlay measurement may be acquired in parallel in a metrology system using non-cartesian overlay targets (e.g., overlay targets with at least some structures oriented at an angle other than typical ninety degree x and y orientations). The metrology system may be a digital holographic microscope, or another metrology apparatus capable of measuring a complex optical field (intensity and phase). This scheme enables single-shot acquisition of the multiple dimensional components of the overlay measurement (e.g., a full overlay vector). A processor is configured to deconstruct data from the single-shot acquisition (based on the orientation of the overlay targets) into the x and y components of an overlay value. Or the noncartesian targets may be oriented to correspond to patterned features of interest in a substrate such that the single shot acquisition directly provides an overlay value relative to those features of interest.

[0010] According to an embodiment, an overlay metrology system is provided. The overlay metrology system comprises a radiation source configured to irradiate a metrology target in a patterned substrate with radiation. The radiation has a radiation axis, and the metrology target comprises structures patterned along first and second target axes. The system comprises a radiation sensor operatively coupled to the radiation source. The radiation sensor is configured to generate a metrology signal based on diffracted radiation received from the structures. The system comprises a holder operatively coupled to the radiation source and the radiation sensor. The holder is configured to hold the patterned substrate such that the target axes are oriented at offset angles with respect to the radiation axis that are within + / - 45 degrees (but which are not zero) of the radiation axis to cause the diffracted radiation from the structures to impinge on the radiation sensor and the radiation sensor to generate the metrology signal. The system comprises one or more processors operatively coupled to the radiation source, the radiation sensor, and the holder. The one or more processors are configured to determine an overlay value for the patterned substrate based on the metrology signal.

[0011] There is a distinction between angles in a substrate plane, and an in-plane angle between the target axes and an out of plane angle with the radiation axis. The offset angles that are within + / - 45 degrees of the radiation axis is with respect to a projection of the radiation axis onto the substrate plane.

[0012] In some embodiments, the metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation, and the one or more processors are configured to determine one or more parameters of fringes in the intensity modulated fringe pattern, and determine the overlay value for the patterned substrate based on the one or more parameters.

[0013] In some embodiments, the structures comprise first structures oriented along the first target axis, and second structures oriented along the second target axis. The radiation source is configured to irradiate the first structures with first radiation oriented along the radiation axis to generate first diffracted radiation, and irradiate the second structures with second radiation oriented in an opposite direction along the radiation axis to generate second diffracted radiation. The radiation sensor isconfigured to detect the first diffracted radiation and the second diffracted radiation. The one or more processors are configured to determine the overlay value using detected first diffracted radiation and detected second diffracted radiation indicated by the metrology signal.

[0014] In some embodiments, the system comprises reference radiation generators configured to generate reference radiation directed toward the radiation sensor configured to interfere with the diffracted radiation from the structures. The overlay value is configured to be determined by the one or more processors based on interference between the reference radiation and the diffracted radiation indicated by the metrology signal.

[0015] In some embodiments, the holder is configured to hold the patterned substrate such that the target axes are oriented at angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the first and second structures to impinge on the radiation sensor simultaneously. The target axes are configured such that the diffracted radiation from structures on the first and second target axes does not fully overlap when impinging on the radiation sensor.

[0016] In some embodiments, the metrology signal comprises non-cartesian overlay components that correspond to the first and second target axes, from which x and y components of the overlay value for the patterned substrate are configured to be determined in parallel. In some embodiments, the first and second target axes are configured to correspond to one or more axes of patterned features in the patterned substrate, such that the non-cartesian overlay components directly correspond to one or more overlay components of interest in the patterned substrate, and are configured to be used to determine overlay with respect to the patterned features.

[0017] In some embodiments, the structures oriented along the first and second target axes have the same pitch. In some embodiments, the structures oriented along the first and second target axes have different pitches.

[0018] In some embodiments, the offset angles of the target axes are the same. In some embodiments, the offset angles of the target axes are different.

[0019] In some embodiments, the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate. Each metrology mark comprises two pads comprising first structures, and two pads comprising second structures, of the structures patterned along the first and second target axes. The radiation sensor is configured such that an intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the first metrology mark and the second metrology mark.

[0020] In some embodiments, the first and second metrology marks comprise non-overlapping gratings.

[0021] In some embodiments, the structures comprise first and second gratings with non-cartesian lines. In some embodiments, the structures comprise one sub-segmented structure patterned along the first and second target axes.

[0022] In some embodiments, the metrology target comprises a diffraction-based overlay metrology target. In some embodiments, the metrology signal and / or the overlay value is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.

[0023] According to another embodiment, an overlay target formed in a patterned substrate is provided. The overlay target comprises the structures configured to be held during overlay metrology such that the first and second target axes are oriented at offset angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the structures to impinge on a radiation sensor.

[0024] According to another embodiment, a metrology method comprising one or more of the operations described above is provided.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above aspects and other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.Fig. 3 schematically depicts an example metrology system, according to an embodiment.Fig. 4 schematically depicts an example metrology technique, according to an embodiment.Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.Fig. 6 illustrates an overlay metrology method, according to an embodiment.Fig. 7 provides another illustration of the metrology system shown in Fig. 3, according to an embodiment.Fig. 8 illustrates a typical cartesian metrology target (e.g., a target with structures oriented at 90 degrees to each other, along x and y axes of the target and / or substrate such as a wafer).Fig. 9 illustrates a pupil space associated with overlay measurement in typical digital holographic microscopy (DHM) systems.Fig. 10 illustrates a pupil space associated with overlay measurement with using radiation oriented at 45 degree angles relative to cartesian structures in a metrology target, according to an embodiment.Fig. 11 illustrates two possible layouts for a non-cartesian metrology target, according to an embodiment.Fig. 12 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0026] In semiconductor device manufacturing, determining overlay typically includes determiningthe (relative) positions of different metrology marks of a metrology target, such as a diffraction based overlay target, in different layers of a semiconductor device structure. In order to meet smaller and smaller node sizes, and / or to make more efficient use of limited substrate real estate, smaller and smaller metrology (overlay, etc.) targets, multi-purpose targets (e.g., one metrology target that can be used for both overlay and alignment), and / or other space saving techniques are needed. Smaller targets and / or targets that can provide information that can be used for multiple purposes facilitate a need for less targets, placement of targets in a field with a limited area, placement of targets closer to the edges of a substrate, and / or other advantages.

[0027] Existing metrology systems often utilize cartesian metrology targets (e.g., targets with structures oriented at 90 degrees to each other, along x and y axes of a target and / or substrate such as a wafer). Typically, x and y components of a metrology value are acquired separately. Radiation oriented along the substrate (and target) x axis is used to provide the x component, and radiation oriented along the substrate (and target) y axis is used to provide the y component. Doubling the number of acquisitions (e.g., one acquisition for x, and one for y) in a photon limited overlay metrology system reduces throughput, among other disadvantages, and is therefore highly undesirable.

[0028] As described above, in contrast to prior systems, the present systems and methods are configured for determining multiple dimensional components (e.g., x and y components, and / or other directional components) of an overlay measurement in parallel in a metrology system using noncartesian overlay targets. The metrology system may be a digital holographic microscope, or another metrology apparatus capable of measuring a complex optical field (intensity and phase). Non -cartesian overlay targets comprise overlay targets with at least some structures oriented at an angle other than typical ninety degree x and y orientations, but within forty five degrees of a radiation axis. This scheme enables single-shot acquisition of the multiple dimensional components of the overlay measurement (e.g., a full overlay vector). A processor is configured to deconstruct data from the single-shot acquisition (based on the orientation of the overlay targets) into the x and y components (and / or any other components) of an overlay value. In addition and / or instead, the non-cartesian targets may be oriented to correspond to patterned features of interest in a substrate such that the single shot acquisition directly provides an overlay value relative to those features of interest.

[0029] The non-cartesian overlay targets need only be irradiated from two directions (instead of four - two for an x axis and two for a y axis), with each direction having its own reference beam. Diffracted radiation from both directions is detected simultaneously, and includes diffracted radiation that may be used to determine both x and y overlay components (without having to perform separate acquisitions). Detected signals corresponding to the two axes (the x and y axes) can be separated in post-processing (e.g., using computational pupil filtering, spatial region of interest selection, via a combination of pupil filtering and spatial selection, and / or using another technique).

[0030] By way of a brief introduction, the following description relates generally to semiconductor device manufacturing and patterning processes. More particularly, the following paragraphs describeseveral components of a system and / or related systems. As described above these systems and methods may be used for measuring overlay in a semiconductor device manufacturing process, for example, or for other operations.

[0031] Although specific reference may be made in this text to the measurement of overlay and the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that the description has many other possible applications. For example, it may be employed in the measurement of other parameters. It may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer” or “die” in this text should be considered as interchangeable with the more general terms “mask”, “substrate” and “target portion”, respectively.

[0032] The term “projection optics” should be broadly interpreted as encompassing various types of optical systems, including refractive optics, reflective optics, apertures and catadioptric optics, for example. The term “projection optics” may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, collectively or singularly. The term “projection optics” may include any optical component in the lithographic projection apparatus, no matter where the optical component is located on an optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, adjusting and / or projecting radiation from the source before the radiation passes the patterning device, and / or optical components for shaping, adjusting and / or projecting the radiation after the radiation passes the patterning device. The projection optics generally exclude the source and the patterning device.

[0033] Fig. 1 schematically depicts an embodiment of a lithographic apparatus LA. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation, or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT (e.g., WTa, WTb or both) configured to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies and often referred to as fields) of the substrate W. The projection system is supported on a reference frame RF. As depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array, or employing a reflective mask).

[0034] 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.

[0035] 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.

[0036] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as o-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator.

[0037] 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.

[0038] 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.

[0039] Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0040] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” may be considered synonymous with the more general term “patterning device.”

[0041] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of the substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in a target portion of the device, such as an integrated circuit.

[0042] 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.

[0043] The term “projection system” should be broadly interpreted as encompassing any type ofprojection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” may be considered as synonymous with the more general term “projection system”.

[0044] The projection system PS may comprise a plurality of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct for aberrations (phase variations across the pupil plane throughout the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system where its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and / or deform one or more optical elements. Displacement of an optical element may be in any direction (x, y, z, or a combination thereof). Tilting of an optical element is typically out of a plane perpendicular to the optical axis, by rotating about an axis in the x and / or y directions although a rotation about the z axis may be used for a non-rotationally symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and / or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and / or by using one or more heating elements to heat one or more selected regions of the optical element. In general, it may not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). The transmission map of a projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithography apparatus LA. Using a computational lithography technique, the patterning device MA may be designed to at least partially correct for apodization.

[0045] The lithographic apparatus may be of atype having two (dual stage) or more tables (e.g., two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system without a substrate that is dedicated to, for example, facilitating measurement, and / or cleaning, etc.). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0046] In operation of the lithographic apparatus, a radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the secondpositioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a shortstroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0047] 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.

[0048] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0049] The substrate may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multilayer IC, so that the term substrate may also refer to a substrate that already includes multiple processed layers.

[0050] The terms “radiation” and “beam” used with respect to lithography encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0051] 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.

[0052] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to as 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 / O 1 , 1 / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0053] 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 thatmeasures some or all of the substrates W (Fig. 1) that have been processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example it may be part of the lithographic apparatus LA (such as alignment sensor AS (Fig. 1)).

[0054] The one or more measured parameters may include, for example, overlay between successive layers formed in or on the patterned substrate, alignment, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. This measurement is often performed on a dedicated metrology target provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and / or at other times.

[0055] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image-based measurement tool and / or various specialized tools. A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this may be termed diffraction-based metrology. One such application of this diffraction- based metrology is in the measurement of overlay (e.g., as described below).

[0056] Thus, in a device fabrication process (e.g., a patterning process or a lithography process), a substrate or other objects may be subjected to various types of measurement during or after the process. The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two or more layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes. Examples of measurement include optical imaging (e.g., optical microscope), non-imaging optical measurement (e.g., measurement based on diffraction such as the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profiling using a stylus, atomic force microscopy (AFM)), and / or non-optical imaging (e.g., scanning electron microscopy (SEM)).

[0057] 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.

[0058] A metrology system may be used to determine one or more properties of the substratestructure, 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.

[0059] To enable the metrology, often one or more targets are specifically provided on the substrate. A target may include an overlay target, for example, an alignment mark, and / or other targets. Typically, the target is specially designed and may comprise one or more periodic structures. For example, the target on a substrate may comprise one or more 1-D periodic structures (e.g., geometric features such as gratings) in one or more layers of the substrate, which are printed such that after development, the periodic structural features are formed of solid resist lines. As another example, the target may comprise one or more 2-D periodic structures (e.g., gratings) in one or more layers, which are printed such that after development, the one or more periodic structures are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0060] Fig. 3 depicts an example inspection (metrology) system 300 that may be used to detect overlay and / or perform other metrology operations. It comprises a radiation source 302 which projects or otherwise irradiates radiation onto a substrate W. Substrate W may typically include a metrology target 310 such as an overlay target, and / or other structures. The redirected radiation is passed to a radiation sensor such as a spectrometer detector (a radiation sensor 304) and / or other sensors, which measures a spectrum (intensity as a function of wavelength) of the specular reflected and / or diffracted radiation, as shown, e.g., in the graph on the left of Fig. 4. The sensor may generate a metrology signal conveying overlay data, alignment data, and / or other data indicative of properties of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in Fig. 4, or by other operations. Note that these are generalized examples. Often, illumination of a target such as overlay target and / or an alignment mark is done orthogonal to the target and / or mark, and not at an angle as shown in Fig. 3.

[0061] As shown in Fig. 3, and in the lithographic apparatus LA in Fig. 1, one or more holders 320 such as substrate tables may be provided to hold the substrate W during metrology operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where inspection system 300 is integrated with the lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest of a structure (e.g., an overlay target and / or an alignment mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at different locations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to thefocus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. Provided the relative position of the substrate and the optical system is correct, it does not matter in principle which one of those is moving, or if both are moving, or a combination of a part of the optical system is moving (e.g., in the Z and / or tilt direction) with the remainder of the optical system being stationary and the substrate is moving (e.g., in the X and Y directions, but also optionally in the Z and / or tilt direction).

[0062] For typical metrology measurements, a target 310 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 310 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and / or other features in the resist. The bars, pillars, vias, and / or other features may be etched into or on the substrate (e.g., into one or more layers on the substrate), deposited on a substrate, covered by a deposition layer, and / or have other properties. Target 310 (e.g., of bars, pillars, vias, etc.) is sensitive to changes in processing in the patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in target 310. Accordingly, the measured data from target 310 may be used to determine an adjustment for one or more of the manufacturing processes, and / or used as a basis for making the actual adjustment. Note that in this example, target 310 may represent one or more layers comprising one or more metrology targets.

[0063] For example, the measured data from target 310 may indicate overlay for layers of a semiconductor device, and / or other information. The measured data from target 310 may be used (e.g., by the one or more processors) for determining one or more semiconductor device manufacturing process parameters based the overlay and / or other information, and / or determining an adjustment for a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology target (e.g., an overlay target) 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.

[0064] Fig. 5 illustrates a plan view of a typical target 310 (e.g., an overlay target), and the extent of a radiation illumination spot S in the system of Fig. 3. Typically, to obtain a diffraction spectrum that is free of interference from surrounding structures, the target 310, in an embodiment, comprises one or more periodic structures (e.g., gratings) larger than the width (e.g., diameter) of the illumination spot S. The width of spot S may be smaller than the width and length of the target 310. The target 310, in other words, is ‘underfilled’ by the illumination, and the diffraction signal is essentially free from any signalsfrom product features and the like outside the target itself. The illumination arrangement may be configured to provide illumination of a uniform intensity across a back focal plane of an objective, for example. Alternatively, by, for example, including an aperture in the illumination path, illumination may be restricted to on axis or off axis directions.

[0065] Fig. 6 illustrates an overlay metrology method 600. In some embodiments, method 600 is performed as part of a semiconductor device manufacturing process. In some embodiments, one or more operations of method 600 may be implemented in or by system 300 illustrated in Fig. 3 (and Fig. 7 described below), a computer system (e.g., as illustrated in Fig. 12 and described below), and / or in or by other systems, for example. In some embodiments, method 600 comprises irradiating (operation 602) a metrology target in a patterned substrate (such as a semiconductor wafer) with radiation, generating (operation 604) a metrology signal based on received radiation from the metrology target, holding (operation 606) the patterned substrate such that target axes of structures of the metrology target are oriented at certain offset angles relative to an axis of the radiation, determining (operation 610) an overlay value, and / or other operations.

[0066] The operations of method 600 presented below are intended to be illustrative. In some embodiments, method 600 may be accomplished with one or more additional operations not described, and / or without one or more of the operations discussed. For example, in some embodiments, method 600 may include an additional operation comprising determining an adjustment for a semiconductor device manufacturing process. Additionally, the order in which the operations of method 600 are illustrated in Fig. 6 and described below is not intended to be limiting.

[0067] In some embodiments, one or more portions of method 600 may be implemented in and / or controlled by one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and / or other mechanisms for electronically processing information - see the description of processors PRO). The one or more processing devices may include one or more devices executing some or all of the operations of method 600 in response to (machine readable) instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software to be specifically designed for execution of one or more of the operations of method 600 (e.g., see discussion related to Fig. 12 below).

[0068] Operation 602 comprises irradiating a metrology target in a patterned substrate with radiation. The metrology target is associated with an overlay measurement for the patterned substrate. The metrology target may be or include a dedicated overlay target. The metrology target comprises one or more structures in the patterned substrate capable of providing a diffraction signal. The metrology target comprises structures patterned along first and second target axes (see additional discussion related to Fig. 11 below). The first and second axes are non-cartesian, oriented at angles other than typical ninety degree x and y orientations for a typical metrology target (although within forty five degrees of a radiation axis as described herein).

[0069] In some embodiments, the metrology target comprises a diffraction-based overlay metrology target. In some embodiments, the metrology target comprises any structure(s) (or repeating series of structures oriented along each of the target axes) capable of generating a wide angle diffraction signal. In some embodiments, the metrology target may be included in one or more layers of a substrate in a semiconductor device structure, for example.

[0070] The structures may comprise one or more geometric features such as ID or 2D features, and / or other geometric features. By way of several non-limiting examples, the structure(s) of a metrology target may comprise a line, an edge, a fine-pitched series of lines and / or edges, a set of multiple fine-pitched series of lines and / or edges, sub-segmented structures (e.g., a line split into smaller rectangles or squares), and / or other features. For example, sub-segmented structures may be gratings in which the repeating feature itself is made up of an arrangement of smaller elements (the smaller elements for instance having the finest size supported by the process).

[0071] These structures are oriented along the first and second target axes. In some embodiments, a same repeating structure is oriented along both of these axes. In some embodiments, different structures are orient along different axes. For example, in some embodiments, the structures comprise first structures oriented along the first target axis, and second structures oriented along the second target axis. The structures may comprise first and second gratings with non-cartesian lines, as one example. As another example, the structures may comprise one sub-segmented structure patterned along the first and second target axes (one structured feature is patterned along both axes). The structures oriented along the first and second target axes may have the same or different pitches.

[0072] In some embodiments, the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate. Each metrology mark may comprise two pads comprising first structures, and two pads comprising second structures, of the structures patterned along the first and second target axes. The metrology marks may or may not overlap. For example, the first and second metrology marks comprise a diffraction-based overlay metrology mark such as a grating and / or other metrology marks. The gratings may have the same pitch, different pitches, and / or other features. In some embodiments, the first and second metrology marks (or any two metrology marks in different layers) may form a Micro Diffraction Based Overlay (pDBO) target, with the first and second metrology marks comprising overlapping gratings in first and second layers of the patterned substrate. The metrology mark in the first layer may be shifted relative to the second metrology mark by a known bias amount. Alternatively, the metrology target may be phase aware, and the top and bottom gratings do not overlap.

[0073] In some embodiments, the radiation source (e.g., source 302 shown in Fig. 3 and in Fig. 7) is configured to irradiate a metrology target (e.g., target 310) in a patterned substrate (e.g., W shown in Fig. 3 and Fig. 7) with radiation. The radiation has a radiation axis (see Fig. 11 below). 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 selectedby a user, determined (e.g. by processor PRO) based on previous metrology measurements, and / or determined in other ways. In some embodiments, the radiation comprises light and / or other radiation. In some embodiments, the light comprises visible light, infrared light, near infrared light, and / or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry.

[0074] In some embodiments, the radiation may be directed by the radiation source (e.g., by way of one or more lenses, a modulator, and / or other components) onto a metrology target, sub-portions (e.g., something less than the whole) of a metrology target, multiple metrology targets, and / or onto the substrate in other ways.

[0075] In some embodiments, the metrology target may be substantially stationary while irradiation occurs, the radiation sensor generates the metrology signal, an image of the metrology target is generated based on the metrology signal and / or other information, and / or other operations are performed. In some embodiments, the radiation may be scanned across a metrology target, for example. Scanning may comprise rastering the radiation over a metrology target such that different portions of the metrology target are irradiated at different times. In some embodiments, characteristics of the radiation (e.g., wavelength, intensity, etc.) may be varied by the radiation source overtime (whether in a stationary or a scanning mode). This may create and / or supplement time varying radiation for analysis. This may also facilitate analysis of individual portions of a feature, comparison of one portion of a feature to another and / or to other features, and / or other analysis.

[0076] Operation 604 comprises generating a metrology signal based on received diffracted radiation from the structures of the metrology target, and / or other information. The metrology signal may be generated by a radiation sensor (e.g., such as radiation sensor 304 shown in 3 and in Fig. 7) operatively coupled to the radiation source, and / or other components. The radiation sensor may comprise an interferometric microscopy detector, such as an interferometric microscope-based sensor. In some embodiments, the radiation sensor may comprise a camera, and / or other components, for example. In some embodiments, the metrology signal comprises overlay information for one or more layers of the substrate conveyed by the diffracted radiation from the metrology target.

[0077] Detecting such radiation comprises detecting intensity shifts in (diffracted) radiation received from one or more geometric features (structures). One or more phase and / or amplitude shifts in diffracted radiation may correspond to one or more dimensions of a structure. For example, the phase and / or amplitude of reflected radiation from one side of a structure is different relative to the phase and / or amplitude of reflected radiation from another side of the structure. Detecting the one or more phase and / or amplitude (intensity) shifts in the radiation from the metrology target comprises measuring local phase shifts (e.g., local phase deltas) and / or amplitude variations that correspond to different portions of a metrology target. For example, the radiation from a specific area of a target may comprise a sinusoidal waveform having a certain phase and / or amplitude. The radiation from a different area of the target may also comprise a sinusoidal waveform, but one with a different phase and / or amplitude. Detecting radiation also comprises measuring a phase and / or amplitude difference in radiation ofdifferent diffraction orders. Detecting the one or more local phase and / or amplitude shifts may be performed using Fourier transformations, Hilbert transformations, for example, and / or other techniques . Interferometry techniques and / or other operations may be used to measure phase and / or amplitude differences in reflected radiation of different diffraction orders.

[0078] The metrology signal comprises an electronic signal that represents and / or otherwise corresponds to the diffracted radiation received from a metrology target. The metrology signal may indicate an overlay value for one or more layers, for example, and / or other information. Generating the metrology signal comprises sensing the radiation and converting the sensed radiation into the electronic signal. In some embodiments, generating the metrology signal comprises sensing different portions of the radiation from different portions and / or different geometries of the metrology target (e.g., different gratings), and combining the different portions of the sensed radiation to form the metrology signal. This sensing and converting may be performed by components similar to and / or the same as radiation sensor 304 and / or processors PRO shown in Fig. 3, Fig. 7, and Fig. 12, and / or other components.

[0079] At operation 606 a holder (e.g., holder 320 shown in Fig. 3 and Fig. 7) operatively coupled to the radiation source and the radiation sensor holds the patterned substrate such that the target axes are oriented at offset angles with respect to the radiation axis that are within + / - 45 degrees of the radiation axis (but which are not zero, see additional discussion below related to Fig. 11). This causes the diffracted radiation from the structures of the metrology target to impinge on the radiation sensor, and the radiation sensor to generate the metrology signal. The holder is configured to hold the patterned substrate such that the target axes are oriented at offset angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the structures oriented along the first and second target axes to impinge on the radiation sensor simultaneously. In some embodiments, the offset angles of the (first and second) target axes are the same. However, in some embodiments, the offset angles may be different. Note there is a distinction between angles in a substrate plane, and an in-plane angle between the target axes and an out of plane angle with the radiation axis, and the offset angles that are within + / - 45 degrees of the radiation axis is with respect to a projection of the radiation axis onto the substrate plane (e.g., as discussed below with respect to Fig. 11).

[0080] At operation 608, an overlay value for the patterned substrate is determined based on the metrology signal and / or other information. Operation 608 may be performed by one or more processors PRO (see Fig. 3, Fig. 7, Fig. 12), and / or other components. The overlay value may be determined using principles of interferometry and / or other principles. As described above, the metrology target is configured to diffract radiation from the radiation source. The metrology signal may comprise an intensity modulated fringe pattern for diffracted radiation received from the metrology target. In some embodiments, the intensity modulated fringe pattern comprises a one or more dimensional interference pattern. In some embodiments, the radiation sensor is configured such that the intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the structures oriented along the first and second target axes. The one or moreprocessors PRO are configured to determine one or more parameters of fringes in the intensity modulated fringe pattern, and determine the overlay value based on the one or more parameters. These parameters may include, for example, one or more amplitudes of fringes, one or more phases of fringes, a difference between amplitudes, a phase difference, a summation of the amplitudes, an average fringe intensity, and / or other parameters. Typically, the overlay value is extracted after several image correction and filtering steps are applied on fringe amplitudes and so on. Similarly, these parameters may be measured as a function of wavelength, polarization, and illumination spatial mode.

[0081] As a practical example of these operations, the structures may comprise first structures oriented along the first (non-cartesian) target axis, and second structures oriented along the second (noncartesian) target axis. The radiation source may irradiate the first structures with first radiation oriented along the radiation axis to generate first diffracted radiation, and irradiate the second structures with second radiation oriented in an opposite direction along the radiation axis to generate second diffracted radiation. The radiation sensor is configured to detect the first diffracted radiation and the second diffracted radiation. The one or more processors are configured to determine the overlay value using detected first diffracted radiation and detected second diffracted radiation indicated by the metrology signal.

[0082] Reference radiation generators may also be utilized. The reference radiation generators may be configured to generate reference radiation directed toward the radiation sensor which is configured to interfere with the diffracted radiation from the structures. The overlay value is configured to be determined by the one or more processors based on interference between the reference radiation and the diffracted radiation indicated by the metrology signal.

[0083] In this example, the metrology signal comprises non-cartesian overlay (e.g., because of the structures oriented along the first and second (non-cartesian) target axes) components that correspond to the first and second target axes, from which x and y components of the overlay value for the patterned substrate are configured to be determined in parallel. The target axes are configured such that the diffracted radiation from structures on the first and second target axes does not fully overlap when impinging on the radiation sensor. In some embodiments, the first and second target axes are configured to correspond to one or more axes of patterned features in the patterned substrate, such that the non- cartesian overlay components directly correspond to one or more overlay components of interest in the patterned substrate, and are configured to be used to determine overlay with respect to the patterned features.

[0084] Fig. 7 - Fig. 11 provide several additional examples (including some contrasting examples) of various components and / or operations described above.

[0085] Fig. 7 provides another illustration of metrology system 300 shown in Fig. 3. System 300 is the same in both figures, with Fig. 7 illustrating additional possible components of the system. In Fig. 7, radiation is generated and directed to metrology target 310 by radiation source 302 (also shown in Fig. 3). Radiation source 302 irradiates metrology target 310 with first radiation 702 oriented along aradiation axis 704 to generate first diffracted radiation 706, and second radiation 708 oriented in an opposite direction along radiation axis 704 to generate second diffracted radiation 710. Reference radiation generators 720 and 722 are configured to generate reference radiation 724 and 726 directed toward radiation sensor 304 which is configured to interfere with the diffracted radiation 706 and 710 from the structures of metrology target 310. The overlay value is configured to be determined by the one or more processors PRO based on interference between reference radiation 724 and 726 and the diffracted radiation 706 and 710 indicated by the metrology signal.

[0086] As shown in Fig. 7, system 300 may include various optical components 750 such as lenses, mirrors, etc., configured to direct (and / or are otherwise associated with directing) radiation 702 and 708 from source 302 to metrology target 310, and direct diffracted radiation 706 and 710 from metrology target 310 toward radiation sensor 304. In this example, sensor 304 comprises a camera, one or more processors, and / or other components. The camera may be configured to generate the metrology signal as described above. The one or more processors may be configured to determine an overlay value based on the metrology signal, also as described above.

[0087] In this example, metrology target 310 on substrate W may comprise gratings, sub-segmented structures, and / or other structures oriented along different target axes. A grating and / or a subsegmented structure may be formed of solid resist pillars, bars, vias, and / or other features, for example. Metrology target 310 may be sensitive to changes in processing in a patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in metrology target 310. Accordingly, the measured data from metrology target 310 may be used to determine an overlay value, and / or an adjustment based on the overlay value for one or more manufacturing processes, and / or used as a basis for making the actual adjustment.

[0088] Substrate W is held by holder 320 such that the target axes are oriented at offset angles with respect to the radiation axis that are within + / - 45 degrees of the radiation axis (see additional discussion below related to Fig. 11). This causes the diffracted radiation from the structures of metrology target 310 to impinge on radiation sensor 304, and radiation sensor 304 to generate the metrology signal. As described above, holder 320 is configured to hold patterned substrate W such that the target axes are oriented at offset angles that are within + / - 45 degrees (in the x - y plane, or substrate plane, as shown in Fig. 11) of radiation axis 704 - i.e., the offset angles are within + / - 45 degrees of radiation axis 704 with respect to a projection of radiation axis 704 onto the substrate plane. This causes diffracted radiation 706 and 710 from the structures oriented along the first and second target axes to impinge on radiation sensor 304 simultaneously.

[0089] In some embodiments, system 300 comprises a digital holographic microscope (DHM). In some embodiments, system 300 may be another metrology apparatus capable of measuring a complex optical field (intensity and phase). As shown in Fig. 7, radiation source 302 may comprise two fiber- coupled illuminators, which project light (radiation 702 and 708) onto overlay metrology target 310.Light (radiation) scattered into + 1st (from one illuminator and structures oriented along a first target axis) radiation 706 and -1st (from the other illuminator and structures oriented along the second target axis) radiation 710 diffraction orders may be captured with an objective lens (e.g., part of optical components 750) and imaged onto a camera (radiation sensor 304), where it interferes with two reference beams (e.g., reference radiation 724 and 726). This creates the sum of two holograms for the +lst and -1st orders. Computational processing of such holograms allows for image correction (e.g., removing aberrations) and enhancement (e.g., introducing apodization), for example. The computationally corrected image reveals overlay and other (scatterometric) information about metrology target 310.

[0090] DHM is compatible with traditional diffraction-based overlay (DBO) metrology targets, prominently uDBO, as well as with new (non-overlapping gratings, or phase-aware) target designs. Such targets typically comprise separate pads configured to enable reconstruction of a full (x, y) overlay vector.

[0091] Fig. 8 illustrates a typical cartesian metrology target 800, such as a conventional uDBO target 800 design. Target 800 comprises structures 802 and 804 (grating lines in this example) oriented at 90 degrees to each other, along x and y axes of target 800 and / or substrate such as a wafer where target 800 is formed. In target 800, there are two orthogonal pairs of pads (e.g., upper left and bottom right, and upper right and bottom left). The grating orientations in target 800 follow cartesian axes x and y, with the x pads typically used for providing an x component of an overlay value, and the y pads providing the y component of the overlay value. In typical DHM systems, these x and y components are acquired in separate operations - illumination along the substrate (and target) x (as shown in Fig. 7) axis provides the x component of the overlay value, and a second subsequent illumination along the substrate (and target) y axis (which is not shown in Fig. 7, but would go into and out of the page) provides the y component of the overlay value.

[0092] Fig. 9 illustrates a pupil space 900 associated with overlay measurement in typical DHM systems. Fig. 9 illustrates typical cartesian metrology target 800, which comprises gratings having a pitch pxconfigured for measurement of the x component of the metrology value, and a pitch py(oriented at 90 degrees) configured for measurement of the y component of the metrology value. Fig. 9 illustrates parameters associated with illuminating along the substrate (and target 800) x axis (from two different oppositely directed illuminators 902 and 904) providing first and second order spots of diffracted radiation 906 and 908 that impinge on an objective 910. These parameters include pupil space 900 kxand kyaxes, an indication that the direction along which light propagates k| | is equal to an intrinsic wave factor, ko, and various distances (in terms of TT and the pitch px) between illuminators 902 and 904 and the spots of diffracted radiation. The notation k|| represents the direction (wavevector) along which light propagates, with respect to the optical axis. The largest possible angle is 90deg, at which k||=kO. It is included in the figure to remind the reader that diffraction that ends up outside this circle cannot be measured (there is no direction for it to go). For a standard acquisition, only one grating (target 800)orientation (x in this example) is captured by objective 910. With this arrangement, a second subsequent illumination along the substrate (and target) y axis would provide the y component of the overlay measurement (see lighter shade y axis related parameters illustrated in Fig. 9).

[0093] Throughput is a key business driver for overlay measurements. Doubling the number of acquisitions (i.e., one in x and one in y) in a photon-limited system necessarily reduces throughput, and so is highly undesirable.

[0094] In some embodiments, system 300 (Fig. 3 and Fig. 7) may be configured for parallel x and y component acquisition using radiation oriented at 45 degree angles relative to the cartesian structures in metrology target 800. However, this may restrict permissible (radiation) wavelength and (target) pitch combinations, thus reducing application space, and reducing an effective imaging aperture of system 300, potentially hurting overlay performance (but is nonetheless possible as an embodiment). For example, Fig. 10 illustrates a pupil space 1000 associated with overlay measurement with using radiation oriented at 45 degree angles relative to the cartesian structures in metrology target 800. Fig. 10 again illustrates typical cartesian metrology target 800, which comprises gratings having a pitch pxconfigured for measurement of the x component of the metrology value, and a pitch py(oriented at 90 degrees) configured for measurement of the y component of the metrology value. However, Fig. 10 illustrates a substrate rotation (of 45 degrees) which permits parallel acquisition of the x and y components of an overlay value. In this example, diffracted radiation from both x and y oriented gratings can be imaged simultaneously (Fig. 10 only illustrates + 1st order diffracted radiation from x and y for simplicity). Imaging performance may be reduced though, because of restricted aperture space 1050 around the beams of + 1st order diffracted radiation, for example.

[0095] The systems (e.g., system 300) and methods (e.g., method 600) describe herein facilitate parallel or simultaneous x and y overlay component acquisition in a system using non-cartesian overlay targets. This measurement scheme enables single-shot acquisition of a full overlay vector. NonCartesian targets may comprise sub-segmented structures, and / or an arrangement of pads with gratings (e.g., as described above), similar to their conventional equivalent, except with differently oriented metrology target axes. Each of these target axes is oriented within 45 degrees of the intended illumination axis.

[0096] Fig. 11 illustrates two possible layouts 1100 and 1102 (other layouts are contemplated) for structures 1104 and 1106 in a non-cartesian metrology target 310. Structures 1104 in layout 1100 comprise non-cartesian (e.g., non-right angle x and y oriented) lines (e.g., gratings). Layout 1102 comprises a sub-segmented structure 1106. The latter, which may be preferred to comply with processing flow design rules, naturally lends itself to two-dimensional gratings. Each layout 1100 and 1102 comprises first and second pitches (pi and P2), which correspond to first and second target axes 1120 and 1122. Note that in some embodiments, one of the axes may be non-cartesian (e.g., 30 degrees), but the other may still be cartesian (e.g., 0 degrees).

[0097] Fig. 11 also illustrates a pupil space 1150 associated with overlay measurement performedwhen a holder (e.g., holder 320 shown in Fig. 7) holds the patterned substrate (see W in Fig. 7) such that the target axes 1120 and 1122 are oriented at offset angles 0 with respect to radiation axis 704 that are (greater than zero but) within + / - 45 degrees of radiation axis 704 to cause the diffracted radiation (1st order pi and 1st order p2 in this example) from structures 1104 or 1106 to impinge on the radiation sensor (via objective 910 in this figure), and the radiation sensor to generate the metrology signal, as described above.

[0098] Radiation source 302 comprises two illuminators, which each have their own reference beam, as shown in Fig. 7. In contrast to standard DHM operation, each illumination beam produces diffraction orders, which are captured by objective 910, and are eventually received by radiation sensor 304 (Fig. 7) for both target axes 1120 and 1122. These diffraction orders follow different paths through system 300 (as shown in Fig. 7) and are thus distinct in pupil space, as indicated in Fig. 11. (Also note that illuminators oriented along the y axis are not needed at all.) Signals corresponding to the two target axes 1120 and 1122 can be separated in post-processing by processor PRO (Fig. 3, Fig. 7, Fig. 12). Computational pupil fdtering may be used to separate such signals. However, depending on metrology target 310 layout (e.g., layout 1100 versus layout 1102), separation may be performed using spatial region of interest selection, via a combination of pupil fdtering and spatial selection, and / or using other techniques.

[0099] The signal for each target axis 1120 and 1122 can be detected using typical techniques for overlay extraction (e.g., as described above), which results in the determination of non-cartesian overlay value components corresponding to target axes 1120 and 1122 for pi and p?. The x and y (cartesian) overlay value components may be determined based on the non-cartesian overlay components and / or other information. Assuming axes 1120 and 1122 are symmetric around the x axis (as shown in this example in Fig. 11), and offset by offset angle 9, the x and y components of an overlay value (OVXand OVyrespectively) may be determined according to the following equations:and similar equations may be derived for arbitrary measurement angles.

[0100] Target optimization for metrology targets according to these principle should ensure that the diffraction orders induced by a given illuminator do not overlap (or at least do not overlap significantly). For a pad (e.g., one quarter of layout 1100) of side length B, there is a pupil space extent of n / B. As may be inferred from Fig. 11, in order for the beams of diffracted radiation to be distinct (significantly non-overlapping), (2n / p) sin 0 should be greater than 2ir / B (or similar for distinct pitches p or angles 0). This constrains the wavelength / pitch ratio, but for suitable overlay targets, a range over 1.5 NA remains feasible, which maintains an increase of 50% over current state of the art overlay measurementsystems.

[0101] For small offset angles (e.g., 9 near zero), measurement uncertainty on the determined OVYcomponent may be higher than that on OVx. During target and recipe design, this factor may influence the selection of illuminator axis (e.g., x or y).

[0102] In some embodiments, an operator may be most interested in the overlay component in some particular (non x or y) direction. For example, for non-cartesian memory or logic arrays, the array axes may represent the quantity of interest. During metrology target optimization, it may be possible to engineer metrology targets that produce the quantity of interest directly, without the added variance from a basis transformation (e.g., to the x or y axes). Phrased another way, first and second target axes 1120 and 1122 may be configured to correspond to one or more axes of patterned features in the patterned substrate, such that the non-cartesian overlay components directly correspond to one or more overlay components of interest in the patterned substrate, and are configured to be used to determine overlay with respect to the patterned features.

[0103] In some embodiments, the two target axes 1120 and 1122 may have the same or different pitches. Overlay measurement may also occur under a different angle than midway between the target axes (such that the offset angles 0 are different, not the same as shown in Fig. 11), as part of a sensitivity trade-off and / or for other reasons.

[0104] These techniques are suitable for all targets known to be compatible with DHM measurement principles, including uDBO, cDBO, IBO, and non-overlapping grating target designs (as described above). Parallel acquisition of a full overlay vector (x and y components at the same time using non- cartesian metrology targets) reduces total acquisition time by half and eliminates one illuminator switch time per target, thus improving throughput. For applications with extremely dark targets and tight requirements, an increasingly prevalent scenario, total measurement time may be dominated by acquisition time, in which case the throughput gain approaches +100%. In a DHM system designed specifically for this mode of operation, there will be a complexity and cost saving, as the additional illuminators (e.g., y illuminators in the example of Fig. 11) can be left out of radiation source 302. In a ‘standard’ four-illuminator DHM system, this mode of operation can be used at no additional cost.

[0105] Returning to Fig. 6, in some embodiments, operation 608 comprises determining an adjustment for a semiconductor device manufacturing process. In some embodiments, operation 608 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on an overlay value indicated by the metrology signal, and / or other information. The one or more parameters may include a parameter of the radiation (the radiation used for determining overlay), an overlay inspection location on a layer of a semiconductor device structure, and / or other parameters. In some embodiments, process parameters can be interpreted broadly to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation (used for exposing resist, etc.), an incident angle of the radiation (used for exposing resist, etc.), a wavelength ofthe radiation (used for exposing resist, etc.), a pupil size and / or shape, a resist material, and / or other parameters.

[0106] A parameter of the radiation used for determining overlay, for example, may include a wavelength, an intensity, an angle of incidence, and / or parameters of the radiation. These parameters may be adjusted to better measure features with specific shapes, enhance the intensity of reflected radiation, increase and / or otherwise enhance (e.g., maximize) phase and / or amplitude shifts (if any) in reflected radiation from one area of a target to the next, and / or for other purposes. This may enable and / or enhance detection of more subtle deviations, make the phase and / or amplitude shifts easier to detect, and / or have other advantages.

[0107] In some embodiments, operation 608 includes determining a process adjustment based on the one or more determined semiconductor device manufacturing process parameters, adjusting a semiconductor device manufacturing apparatus based on the determined adjustment, and / or other operations. For example, based on a measured overlay value, a lithography exposure may be corrected. As another example, if a determined overlay value is not within process tolerances, the misalignment may be caused by one or more manufacturing processes whose process parameters have drifted and / or otherwise changed so that the process is no longer producing acceptable devices (e.g., overlay measurements may breach a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the overlay determination. The new or adjusted process parameters may be configured to cause a manufacturing process to again produce acceptable devices. For example, a new or adjusted process parameter may cause a previously unacceptable overlay value to be adjusted back into an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. If there is a difference, that difference may be used to determine an adjustment for an apparatus that is used to produce the devices (e.g., parameter “x” should be increased / decreased / changed so that it matches the new or adjusted version of parameter “x” determined as part of operation 610), for example. In some embodiments, operation 604 may include electronically adjusting an apparatus (e.g., based on the determined process parameters). Electronically adjusting an apparatus may include sending an electronic signal, and / or other communications to the apparatus, for example, which causes a change in the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and / or other adjustments.

[0108] Fig. 12 is a diagram of an example computer system CS that may be used for one or more of the operations described herein. Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other staticstorage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0109] Computer system CS may be coupled via bus BS to a display DS, such as a flat panel or touch panel display for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[0110] In some embodiments, portions of one or more methods may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions included in main memory MM causes processor PRO to perform the process steps (operations). One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, this description is not limited to any specific combination of hardware circuitry and software.

[0111] The term “computer-readable medium” or “machine-readable medium” refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non- transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the operations described. Transitory computer-readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[0112] 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 instructionsmay initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a network. Computer system CS can receive the data, and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0113] 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. 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.

[0114] 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.

[0115] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0116] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. An overlay metrology system, comprising: a radiation source configured to irradiate a metrology target in a patterned substrate with radiation, wherein the radiation has a radiation axis, and the metrology target comprises structures patterned along first and second target axes; a radiation sensor operatively coupled to the radiation source, the radiation sensor configured to generate a metrology signal based on diffracted radiation received from the structures; a holder operatively coupled to theradiation source and the radiation sensor, the holder configured to hold the patterned substrate such that the target axes are oriented at offset angles with respect to the radiation axis that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the structures to impinge on the radiation sensor and the radiation sensor to generate the metrology signal; and one or more processors operatively coupled to the radiation source, the radiation sensor, and the holder, the one or more processors configured to determine an overlay value for the patterned substrate based on the metrology signal.2. The system of clause 1, wherein the metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation, and the one or more processors are configured to determine one or more parameters of fringes in the intensity modulated fringe pattern, and determine the overlay value for the patterned substrate based on the one or more parameters.3. The system of any of the previous clauses, wherein: the structures comprise first structures oriented along the first target axis, and second structures oriented along the second target axis; the radiation source is configured to irradiate the first structures with first radiation oriented along the radiation axis to generate first diffracted radiation, and irradiate the second structures with second radiation oriented in an opposite direction along the radiation axis to generate second diffracted radiation; the radiation sensor is configured to detect the first diffracted radiation and the second diffracted radiation, and the one or more processors are configured to determine the overlay value using detected first diffracted radiation and detected second diffracted radiation indicated by the metrology signal.4. The system of any of the previous clauses, further comprising reference radiation generators configured to generate reference radiation directed toward the radiation sensor configured to interfere with the diffracted radiation from the structures, wherein the overlay value is configured to be determined by the one or more processors based on interference between the reference radiation and the diffracted radiation indicated by the metrology signal.5. The system of any of the previous clauses, wherein the holder is configured to hold the patterned substrate such that the target axes are oriented at angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the first and second structures to impinge on the radiation sensor simultaneously.6. The system of any of the previous clauses, wherein the metrology signal comprises non-cartesian overlay components that correspond to the first and second target axes, from which x and y components of the overlay value for the patterned substrate are configured to be determined in parallel.7. The system of any of the previous clauses, wherein the first and second target axes are configured to correspond to one or more axes of patterned features in the patterned substrate, such that the noncartesian overlay components directly correspond to one or more overlay components of interest in the patterned substrate, and are configured to be used to determine overlay with respect to the patterned features.8. The system of any of the previous clauses, wherein the target axes are configured such that thediffracted radiation from structures on the first and second target axes does not fully overlap when impinging on the radiation sensor.9. The system of any of the previous clauses, wherein the structures oriented along the first and second target axes have the same pitch.10. The system of any of the previous clauses, wherein the structures oriented along the first and second target axes have different pitches.11. The system of any of the previous clauses, wherein the offset angles of the target axes are the same.12. The system of any of the previous clauses, wherein the offset angles of the target axes are different.13. The system of any of the previous clauses, wherein the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate, each metrology mark comprising two pads comprising first structures, and two pads comprising second structures, of the structures patterned along the first and second target axes.14. The system of any of the previous clauses, wherein the first and second metrology marks comprise non-overlapping gratings.15. The system of any of the previous clauses, wherein the radiation sensor is configured such that an intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the first metrology mark and the second metrology mark.16. The system of any of the previous clauses, wherein the structures comprise first and second gratings with non-cartesian lines.17. The system of any of the previous clauses, wherein the structures comprise one sub-segmented structure patterned along the first and second target axes.18. The system of any of the previous clauses, wherein there is a distinction between angles in a substrate plane, and an in-plane angle between the target axes and an out of plane angle with the radiation axis, and the offset angles that are within + / - 45 degrees of the radiation axis is with respect to a projection of the radiation axis onto the substrate plane.19. The system of any of the previous clauses, wherein the metrology target comprises a diffractionbased overlay metrology target.20. The system of any of the previous clauses, wherein the metrology signal and / or the overlay value is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.21. An overlay metrology target formed in a patterned substrate, the metrology target comprising: structures patterned in the patterned substrate along a first target axis, and along a second target axis; wherein: the structures are configured to diffract radiation received from a radiation source, the radiation has a radiation axis, and the patterned substrate with the structures is configured to be held during overlay metrology such that the first and second target axes are oriented at offset angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the structures to impinge on a radiation sensor.22. The target of clause 21, wherein the target axes are configured such that the diffracted radiation from the first and second structures does not fully overlap when impinging on the radiation sensor.23. The target of any of the previous clauses, wherein the first and second structures oriented along the first and second target axes have the same or different pitches, and wherein the offset angles of the target axes are the same or different.24. The target of any of the previous clauses, wherein the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate, each metrology mark comprising two pads comprising the first structures, and two pads comprising the second structures, wherein the second metrology mark is above the first metrology mark, and wherein the first metrology mark in the first layer is shifted relative to the second metrology mark by a known bias amount.25. The target of any of the previous clauses, wherein the first and second structures comprise gratings with non-cartesian lines, or comprise sub-segmented structures.26. An overlay metrology method, comprising: irradiating, with a radiation source, a metrology target in a patterned substrate with radiation, wherein the radiation has a radiation axis, and the metrology target comprises structures patterned along first and second target axes; generating, with a radiation sensor operatively coupled to the radiation source, a metrology signal based on diffracted radiation received from the structures; holding, with a holder operatively coupled to the radiation source and the radiation sensor, the patterned substrate such that the target axes are oriented at offset angles with respect to the radiation axis that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the structures to impinge on the radiation sensor and the radiation sensor to generate the metrology signal; and determining, with one or more processors operatively coupled to the radiation source, the radiation sensor, and the holder, an overlay value for the patterned substrate based on the metrology signal.27. The method of clause 26, wherein the metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation, and the one or more processors are configured to determine one or more parameters of fringes in the intensity modulated fringe pattern, and determine the overlay value for the patterned substrate based on the one or more parameters.28. The method of any of the previous clauses, wherein: the structures comprise first structures oriented along the first target axis, and second structures oriented along the second target axis; the radiation source is configured to irradiate the first structures with first radiation oriented along the radiation axis to generate first diffracted radiation, and irradiate the second structures with second radiation oriented in an opposite direction along the radiation axis to generate second diffracted radiation; the radiation sensor is configured to detect the first diffracted radiation and the second diffracted radiation, and the one or more processors are configured to determine the overlay value using detected first diffracted radiation and detected second diffracted radiation indicated by the metrology signal.29. The method of any of the previous clauses, further comprising reference radiation generatorsconfigured to generate reference radiation directed toward the radiation sensor configured to interfere with the diffracted radiation from the structures, wherein the overlay value is configured to be determined by the one or more processors based on interference between the reference radiation and the diffracted radiation indicated by the metrology signal.30. The method of any of the previous clauses, wherein the holder is configured to hold the patterned substrate such that the target axes are oriented at angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the first and second structures to impinge on the radiation sensor simultaneously.31. The method of any of the previous clauses, wherein the metrology signal comprises non-cartesian overlay components that correspond to the first and second target axes, from which x and y components of the overlay value for the patterned substrate are configured to be determined in parallel.32. The method of any of the previous clauses, wherein the first and second target axes are configured to correspond to one or more axes of patterned features in the patterned substrate, such that the noncartesian overlay components directly correspond to one or more overlay components of interest in the patterned substrate, and are configured to be used to determine overlay with respect to the patterned features.33. The method of any of the previous clauses, wherein the target axes are configured such that the diffracted radiation from structures on the first and second target axes does not fully overlap when impinging on the radiation sensor.34. The method of any of the previous clauses, wherein the structures oriented along the first and second target axes have the same pitch.35. The method of any of the previous clauses, wherein the structures oriented along the first and second target axes have different pitches.36. The method of any of the previous clauses, wherein the offset angles ofthe target axes are the same.37. The method of any of the previous clauses, wherein the offset angles of the target axes are different. 38. The method of any of the previous clauses, wherein the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate, each metrology mark comprising two pads comprising first structures, and two pads comprising second structures, of the structures patterned along the first and second target axes.39. The method of any of the previous clauses, wherein the first and second metrology marks comprise non-overlapping gratings.40. The method of any of the previous clauses, wherein the radiation sensor is configured such that an intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the first metrology mark and the second metrology mark.41. The method of any of the previous clauses, wherein the structures comprise first and second gratings with non-cartesian lines.42. The method of any of the previous clauses, wherein the structures comprise one sub-segmentedstructure patterned along the first and second target axes.43. The method of any of the previous clauses, wherein there is a distinction between angles in a substrate plane, and an in-plane angle between the target axes and an out of plane angle with the radiation axis, and the offset angles that are within + / - 45 degrees of the radiation axis is with respect to a projection of the radiation axis onto the substrate plane.44. The method of any of the previous clauses, wherein the metrology target comprises a diffractionbased overlay metrology target.45. The method of any of the previous clauses, wherein the metrology signal and / or the overlay value is configured to be used by the one or more processors to adjust a semiconductor device manufacturing process.46. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing patterning radiation from a radiation source of a lithography apparatus to transfer a pattern from a mask onto the photoresist layer; removing a portion the photoresist layer to form the pattern over the substrate; and determining an overlay value associated with the pattern by: irradiating, with a radiation source, a metrology target in the patterned substrate with radiation, wherein the radiation has a radiation axis, and the metrology target comprises structures oriented along first and second target axes; generating, with a radiation sensor operatively coupled to the radiation source, a metrology signal based on diffracted radiation received from the structures; holding, with a holder operatively coupled to the radiation source and the radiation sensor, the patterned substrate such that the target axes are oriented at offset angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the structures to impinge on the radiation sensor and the radiation sensor to generate the metrology signal; and determining, with one or more processors operatively coupled to the radiation source, the radiation sensor, and the holder, the overlay value for the patterned substrate based on the metrology signal.

[0117] The concepts disclosed here may be associated with any generic metrology and / or imaging system for measuring and / or imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths.

[0118] While the concepts disclosed here may be used for metrology and / or imaging on a substrate such as a silicon wafer, it should be understood that the disclosed concepts may be used with any type of metrology and / or imaging systems, e.g., those used for metrology and / or imaging on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments.

[0119] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. An overlay metrology system, comprising: a radiation source configured to irradiate a metrology target in a patterned substrate with radiation, wherein the radiation has a radiation axis, and the metrology target comprises structures patterned along first and second target axes; a radiation sensor operatively coupled to the radiation source, the radiation sensor configured to generate a metrology signal based on diffracted radiation received from the structures; a holder operatively coupled to the radiation source and the radiation sensor, the holder configured to hold the patterned substrate such that the target axes are oriented at offset angles with respect to the radiation axis that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the structures to impinge on the radiation sensor and the radiation sensor to generate the metrology signal; and one or more processors operatively coupled to the radiation source, the radiation sensor, and the holder, the one or more processors configured to determine an overlay value for the patterned substrate based on the metrology signal.

2. The system of claim 1, wherein the metrology signal comprises an intensity modulated fringe pattern for the diffracted radiation, and the one or more processors are configured to determine one or more parameters of fringes in the intensity modulated fringe pattern, and determine the overlay value for the patterned substrate based on the one or more parameters.

3. The system of claims 1 or 2, wherein: the structures comprise first structures oriented along the first target axis, and second structures oriented along the second target axis; the radiation source is configured to irradiate the first structures with first radiation oriented along the radiation axis to generate first diffracted radiation, and irradiate the second structures with second radiation oriented in an opposite direction along the radiation axis to generate second diffracted radiation; the radiation sensor is configured to detect the first diffracted radiation and the second diffracted radiation, and the one or more processors are configured to determine the overlay value using detected first diffracted radiation and detected second diffracted radiation indicated by the metrology signal.

4. The system of any of claims 1-3, further comprising reference radiation generators configured to generate reference radiation directed toward the radiation sensor configured to interfere with the diffracted radiation from the structures, wherein the overlay value is configured to be determined bythe one or more processors based on interference between the reference radiation and the diffracted radiation indicated by the metrology signal.

5. The system of any of claims 1-4, wherein the holder is configured to hold the patterned substrate such that the target axes are oriented at angles that are within + / - 45 degrees of the radiation axis to cause the diffracted radiation from the first and second structures to impinge on the radiation sensor simultaneously.

6. The system of any of claims 1-5, wherein the metrology signal comprises non-cartesian overlay components that correspond to the first and second target axes, from which x and y components of the overlay value for the patterned substrate are configured to be determined in parallel.

7. The system of claim 6, wherein the first and second target axes are configured to correspond to one or more axes of patterned features in the patterned substrate, such that the non-cartesian overlay components directly correspond to one or more overlay components of interest in the patterned substrate, and are configured to be used to determine overlay with respect to the patterned features.

8. The system of any of claims 1-7, wherein the target axes are configured such that the diffracted radiation from structures on the first and second target axes does not fully overlap when impinging on the radiation sensor.

9. The system of any of claims 1-8, wherein the structures oriented along the first and second target axes have the same pitch.

10. The system of any of claims 1-8, wherein the structures oriented along the first and second target axes have different pitches.

11. The system of any of claims 1-10, wherein the offset angles of the target axes are the same.

12. The system of any of claims 1-10, wherein the offset angles of the target axes are different.

13. The system of any of claims 1-12, wherein the metrology target comprises a first metrology mark in a first layer of the patterned substrate and a second metrology mark in a second layer of the patterned substrate, each metrology mark comprising two pads comprising first structures, and two pads comprising second structures, of the structures patterned along the first and second target axes.

14. The system of claim 13, wherein the first and second metrology marks comprise non-overlapping gratings.

15. The system of claim 14, wherein the radiation sensor is configured such that an intensity modulated fringe pattern for the diffracted radiation comprises an interference pattern generated based on diffracted radiation from the first metrology mark and the second metrology mark.

Images