WO2024156452A1

WO2024156452A1 - Wavefront sensor for a metrology system

Info

Publication number: WO2024156452A1
Application number: PCT/EP2023/087474
Authority: WO
Inventors: Fan DENG; Heriniaina RAJAOBERISO; Alexander Kenneth RAUB; Stanislav Smirnov; Adel Joobeur; Richard Carl Zimmerman
Original assignee: Asml Netherlands B.V.
Priority date: 2023-01-23
Filing date: 2023-12-21
Publication date: 2024-08-02

Abstract

Wavefront sensing technology for measuring the wavefront aberrations of an optical field is described. The wavefront sensing technology is lower cost, can be used for measuring on or off axis radiation simultaneously, does not have the same stringent alignment requirements, and does not require the same computational reconstruction of a wavefront compared to prior systems. The 5 wavefront sensing technology utilizes machine learning applied on specular reflection and diffraction images from multiple on and off axis simultaneous pin-hole radiation transmissions to determine wavefront aberrations.

Description

WAVEFRONT SENSOR FOR A METROLOGY SYSTEM

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of US application 63/440,555 which was filed on 23 January 2023 and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] This description relates to a wavefront sensor for a metrology system.

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. Since, in general, the lithographic projection apparatus will have a reduction ratio M (e.g., 4), the speed F at which the substrate is moved will be 1/M times that at which the projection beam scans the patterning device. More information with regard to lithographic devices as described herein can be gleaned, for example, from US 6,046,792, incorporated herein by reference.

[0004] Prior to transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures, such as priming, resist coating, and a soft bake. After exposure, the substrate may be subjected to other procedures (“post-exposure procedures”), such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the transferred pattern. This array of procedures is used as a basis to make an individual layer of a device, e.g., an IC. The substrate may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, deposition, chemo-mechanical polishing, etc., all intended to finish the individual layer of the device. If several layers are required in the device, then the whole procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present in each target portion on the substrate. These devices are then separated from one another by a technique such as dicing or sawing, such that the individual devices can be mounted on a carrier, connected to pins, etc. [0005] Thus, manufacturing devices, such as semiconductor devices, typically involves processing a substrate (e.g., a semiconductor wafer) using a number of fabrication processes to form various features and multiple layers of the devices. Such layers and features are typically manufactured and processed using, e.g., deposition, lithography, etch, deposition, chemical-mechanical polishing, and ion implantation. Multiple devices may be fabricated on a plurality of dies on a substrate and then separated into individual devices. This device manufacturing process may be considered a patterning process. A patterning process involves a patterning step, such as optical and/or nanoimprint lithography using a patterning device in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, deposition, etc.

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

[0007] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements have continually been reduced while the number of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as “Moore’s law.” At the current state of technology, layers of devices are manufactured using lithographic projection apparatuses that project a design layout onto a substrate using illumination from a deep-ultraviolet 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 = ki xk/NA, where Z is the wavelength of radiation employed (currently in most cases 248nm or 193nm), NA is the numerical aperture of projection optics in the lithographic projection apparatus, CD is the “critical dimension”-generally the smallest feature size printed-and 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).

SUMMARY

[0009] Wavefront sensing technology for measuring the wavefront aberrations of an optical field is described. Among other advantages, the wavefront sensing technology is lower cost, can be used for measuring on or off axis radiation simultaneously, does not have the same stringent alignment requirements, and does not require the same computational reconstruction of a wavefront, compared to prior systems. The wavefront sensing technology utilizes machine learning applied on specular reflection and diffraction images from multiple on and off axis simultaneous pin-hole radiation transmissions to determine wavefront aberrations.

[0010] According to an embodiment, a metrology system configured to determine wavefront aberrations for radiation at on and off optical axis positions in an optical field is provided. The system comprises an opaque body. The opaque body comprises transmission regions at a plurality of different locations associated with the on and off optical axis positions. The body is positioned in the optical field and configured to receive and pass radiation through the transmission regions. The system comprises a sensor configured to receive radiation that has passed through the transmission regions and generate images based on the received radiation for the on an off optical axis positions. The system comprises one or more processors operatively connected with the sensor. The one or more processors are configured to use a trained algorithm and the images to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field.

[0011] In some embodiments, the opaque body is a spot size selector.

[0012] In some embodiments, the images comprise images of body transmission regions created by the sensor.

[0013] In some embodiments, the images are point spread function (PSF) images.

[0014] In some embodiments, the sensor comprises a camera and/or a charge coupled device (CCD) array.

[0015] In some embodiments, the sensor comprises a micro diffraction based overlay camera associated with overlay measurement.

[0016] In some embodiments, the one or more processors are configured to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field simultaneously. [0017] In some embodiments, the system further comprises an optical component configured to receive the radiation from each transmission region, and direct portions of the radiation received from each transmission region to different areas of the sensor to form multiple spots of radiation on the sensor for each transmission region. The sensor is configured generate multiple corresponding images for radiation that passes through each transmission region. The one or more processors are configured to determine the wavefront aberrations based on the multiple corresponding images using the trained algorithm. [0018] In some embodiments, the optical component comprises a wedge. In some embodiments, the wedge comprises quadrants. Each quadrant is configured to direct a portion of the radiation received through a transmission region to the different areas of the sensor to form the spots of radiation on the sensor. In some embodiments, the spots of radiation comprise two spots of radiation associated with Oth order diffracted radiation from a substrate, and two spots of radiation associated with 1st order diffracted radiation from the substrate. In some embodiments, the substrate is a semiconductor wafer. [0019] In some embodiments, the system further comprises an illumination mode selector having selectable apertures. The illumination mode selector is positioned in a pupil plane of the system. The illumination mode selector is configured to receive radiation from a radiation source, and transmit portions of the radiation through a selected aperture toward a diffraction grating target on a substrate. Diffracted radiation from the diffraction grating target is directed back toward the optical component in the sensor.

[0020] In some embodiments, determining the wavefront aberrations comprises predicting Zernike coefficients for radiation at the on and off optical axis positions in the optical field.

[0021] In some embodiments, the one or more processors are configured such that the trained algorithm outputs indications of wavefront aberrations based on intensities of spots of radiation in the images. In some embodiments, the trained algorithm is trained by obtaining and providing prior images associated with aberrations to the algorithm. In some embodiments, portions of the prior images associated with the aberrations are labeled as aberrations.

[0022] In some embodiments, the opaque body, the sensor, and the one or more processors are configured to replace a Shack-Hartmann wavefront sensor.

[0023] In some embodiments, the one or more processors are configured to automatically adjust one or more characteristics of the radiation, a deformable mirror inside the sensor, and/or a stage holding a substrate with a target to reduce and/or eliminate wavefront aberrations for the radiation at the on and off optical axis positions in the optical field.

[0024] In some embodiments, radiation that passes through the transmission regions of the opaque body is directed toward a substrate. The substrate comprises a semiconductor wafer having one or more overlay targets configured to reflect the radiation toward the sensor.

[0025] In some embodiments, the system further comprises a radiation source and one or more lenses. The radiation source and the one or more lenses are configured to generate the radiation and direct the radiation toward the opaque body, a substrate, and/or the sensor.

[0026] In some embodiments, the opaque body, the sensor, and the one or more processors are configured for overlay detection. In some embodiments, the metrology system is configured for a semiconductor wafer, and is used in a semiconductor manufacturing process.

[0027] In some embodiments, the trained algorithm comprises a trained machine learning model. In some embodiments, the trained machine learning model comprises a neural network.

[0028] According to another embodiment, there is provided a corresponding metrology method for determining wavefront aberrations for radiation at on and off optical axis positions in the optical field. The method comprises receiving and passing radiation with the opaque body having the transmission regions positioned in the optical field. The body comprises the transmission regions at a plurality of different locations associated with the on and off optical axis positions. The method comprises receiving, with the sensor, the radiation that has passed through the transmission regions. The method comprises generating, with the sensor, the images based on the received radiation for the on an off optical axis positions. The method comprises using, by the one or more processors operatively connected with the sensor, the trained algorithm and the images to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.

[0031] Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0032] Fig. 3 schematically depicts an example inspection system, according to an embodiment. [0033] Fig. 4 schematically depicts an example metrology technique, according to an embodiment. [0034] Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.

[0035] Fig. 6 illustrates a system configured for determining wavefront aberrations for radiation at on and off optical axis positions in an optical field, according to an embodiment.

[0036] Fig. 7 illustrates a simplified schematic view of certain components of the system shown in Fig. 6, according to an embodiment.

[0037] Fig. 8 illustrates a metrology method, according to an embodiment.

[0038] Fig. 9 is a block diagram of an example computer system, according to an embodiment.

DETAILED DESCRIPTION

[0039] In semiconductor device manufacturing, metrology operations typically include determining the position of a metrology mark (or marks) and/or other target in a layer of a semiconductor device structure. This position is typically determined by irradiating a metrology mark with radiation, and comparing characteristics of different diffraction orders of radiation reflected from the metrology mark. Such techniques are used to measure overlay, alignment, and/or other parameters. As part of ensuring accurate mark position determinations, radiation wavefront aberrations are measured and the metrology operations are adjusted based on these measurements.

[0040] A metrology system configured to determine wavefront aberrations for radiation at on and off optical axis positions in an optical field is described below. Compared to prior wavefront aberration measurement systems, the metrology system described below is lower cost because it does not include the complicated elements of a Shack-Hartman sensor such as an array of lenslets measuring local tilts and computational software resources for reconstruction of an entire wavefront, for example. Instead, the metrology system described below relies on trained software algorithms for image based wavefront aberration detection. Among other advantages, the system can be used for measuring on or off axis radiation simultaneously, and does not have the same stringent alignment requirements, compared to prior systems. The wavefront sensing technology described herein utilizes machine learning applied on specular reflection and diffraction images from multiple on and off axis simultaneous pin-hole radiation transmissions to determine wavefront aberrations.

[0041] By way of a brief introduction, the description below relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several components of systems and/or methods for semiconductor device metrology. These systems and methods may be used for measuring overlay, alignment, etc., in a semiconductor device manufacturing process, for example, or for other operations.

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

[0043] The term “projection optics” as used herein 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.

[0044] 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). [0045] 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.

[0046] 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.

[0047] 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 wherein the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator. [0048] 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.

[0049] In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0050] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” [0051] The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of the substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its crosssection 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.

[0052] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phaseshift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.

[0053] The term “projection system” should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system.”

[0054] 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 wherein its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and/or deform one or more optical elements. Displacement of an 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. [0055] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g., two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system without a substrate that is dedicated to, for example, facilitating measurement, and/or cleaning, etc.). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be conducted on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and/or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0056] The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0057] In operation of the lithographic apparatus, a radiation beam B is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies. [0058] 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. [0059] Combinations and/or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0060] The substrate may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already includes multiple processed layers.

[0061] The terms “radiation” and “beam” used herein with respect to lithography encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0062] 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.

[0063] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and/or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input/output port I/Ol, I/O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0064] In order that a substrate that is exposed by the lithographic apparatus is exposed correctly and consistently and/or in order to monitor a part of the patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties such as alignment, overlay (which can be, for example, between structures in overlying layers or between structures in a same layer that have been provided separately to the layer by, for example, a double patterning process), line thickness, critical dimension (CD), focus offset, a material property, etc. Accordingly, a manufacturing facility in which lithocell LC is located also typically includes a metrology system that measures some or all of the substrates W (Fig. 1) that have been processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example it may be part of the lithographic apparatus LA (such as alignment sensor AS (Fig. 1)).

[0065] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. This measurement is often performed on one or more dedicated metrology targets provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and/or at other times.

[0066] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image-based measurement tool and/or various specialized tools. A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted/reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this may be termed diffraction-based metrology. Applications of this diffraction-based metrology include the measurement of overlay, alignment, etc. For example, overlay and/or alignment can be measured by comparing parts of the diffraction spectrum (for example, comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0067] Thus, in a device fabrication process (e.g., a patterning process or a lithography process), a substrate or other objects may be subjected to various types of measurement during or after the process. The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes. Examples of measurement include optical imaging (e.g., optical microscope), non-imaging optical measurement (e.g., measurement based on diffraction such as the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profiling using a stylus, atomic force microscopy (AFM)), and/or non- optical imaging (e.g., scanning electron microscopy (SEM)).

[0068] 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.

[0069] A metrology system may be used to determine one or more properties of the substrate structure, and in particular, how one or more properties of different substrate structures vary, or different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or the lithocell LC, or may be a stand-alone device. [0070] To enable the metrology, often one or more targets are specifically provided on the substrate. Typically, the target is specially designed and may comprise a periodic structure. For example, the target on a substrate may comprise one or more 1-D periodic structures (e.g., geometric features such as gratings), which are printed such that after development, the periodic structural features are formed of solid resist lines. As another example, the target may comprise one or more 2-D periodic structures (e.g., gratings), which are printed such that after development, the one or more periodic structures are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0071] Fig. 3 depicts an example metrology (inspection) system 10 that may be used to detect overlay, alignment, and/or perform other metrology operations. It comprises a radiation or illumination source 2 which projects or otherwise irradiates radiation onto a substrate W (e.g., which may typically include a metrology mark). The redirected radiation is passed to a sensor 4 such as a spectrometer detector 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 metrology data indicative of properties of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in Fig. 4, or by other operations.

[0072] As in the lithographic apparatus LA in Fig. 1, one or more substrate tables (not shown in Fig. 3 or 4) may be provided to hold the substrate W during measurement operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where inspection system 10 is integrated with the lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest of a structure (e.g., a metrology mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at different locations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to the focus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. 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).

[0073] For typical metrology measurements, a target 30 on substrate W may be a 1-D grating, which is printed such that after development, the bars are formed of solid resist lines (e.g., which may be covered by a deposition layer), and/or other materials. Or the target 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and/or other features in the resist.

[0074] The bars, pillars, vias, and/or other features may be etched into or on the substrate (e.g., into one or more layers on the substrate), deposited on a substrate, covered by a deposition layer, and/or have other properties. Target 30 (e.g., of bars, pillars, vias, etc.) is sensitive to changes in processing in the patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in target 30. Accordingly, the measured data from target 30 may be used to determine an adjustment for one or more of the manufacturing processes, and/or used as a basis for making the actual adjustment.

[0075] For example, the measured data from target 30 may indicate overlay for a layer of a semiconductor device. The measured data from target 30 may be used (e.g., by the one or more processors PRO and/or other processors) for determining one or more semiconductor device manufacturing process parameters based the overlay, and determining an adjustment for a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation, an incident angle of the radiation, a wavelength of the radiation, a pupil size and/or shape, a resist material, and/or other process parameters.

[0076] Fig. 5 illustrates a plan view of a typical target 30 (e.g., a metrology mark), and the extent of a typical radiation illumination spot S in the system of Fig. 3. Typically, to obtain a diffraction spectrum that is free of interference from surrounding structures, the target 30, in an embodiment, is a periodic structure (e.g., grating) 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. The target, in other words, is ‘underfilled’ by the illumination, and the diffraction signal is essentially free from any signals from product features and the like outside the target itself. The illumination arrangement may be configured to provide illumination of a uniform intensity across a back focal plane of an objective, for example. Alternatively, for example, by including a spot size selector in the illumination path, illumination may be provided from on axis and off axis directions.

[0077] As described above, ensuring accurate metrology mark position determinations often requires determining wavefront aberrations for incident radiation. Fig. 6 illustrates a system 600 configured for determining wavefront aberrations for radiation at on and off optical axis positions in an optical field. System 600 is the same as or similar to system 10 described above with respect to Fig. 3, with one or more components of system 600 being similar to and/or the same as one or more components of system 10 (and Fig. 6 illustrating several additional possible components of the system). In some embodiments, one or more components of system 600 may replace, be used with, and/or otherwise augment one or more components of system 10. System 600 comprises a radiation source 612 (e.g., similar to and/or the same as source 2 shown in Fig. 3), an opaque body 601 with transmission regions at a plurality of different locations associated with the on and off optical axis positions, an illumination mode selector 607, a sensor 604 (e.g., similar to and/or the same as sensor 4 shown in Fig. 3), an optical component 605 such as a wedge, one or more processors PRO (similar to and/or the same as processor PRO shown in Fig. 3), and various lenses, beam splitters, and/or other components. One or more processors PRO are operatively connected with sensor 604 and/or other components of system 600.

[0078] Fig. 6 illustrates an illumination branch 625 of system 600 including radiation source 612, opaque body 601, and illumination mode selector 607; an overlay detection branch 660 including sensor 604; a focus branch 650; an alignment branch 680; an objective lens 690; and/or other components. In some embodiments, the components of system 600 form a portion of an overlay and/or alignment sensor that is used in a semiconductor manufacturing process.

[0079] Fig. 6 also illustrates a target 30 which may comprise one or more metrology marks, such as diffraction grating targets, formed in a substrate 602 such as a semiconductor wafer, collectively referred to as target 30, for example. Target 30 may comprise one or more structures in the patterned substrate capable of providing a diffraction signal. One or more targets 30 may be included in a layer of a substrate in a semiconductor device structure, for example. In some embodiments, the feature comprises a geometric feature such as a ID or 2D feature, and/or other geometric features. By way of several non-limiting examples, the feature may comprise a grating, a line, an edge, a fine-pitched series of lines and/or edges, and/or other features.

[0080] Sensor 604 is configured to receive radiation from target 30 and generate a signal indicative of a field image position of the radiation. The radiation may be used to determine wavefront aberrations, obtain images of the metrology targets 30, and/or for other uses. The radiation may comprise illumination such as light and/or other radiation. The radiation may have a target wavelength and/or wavelength range, a target intensity, and/or other characteristics. The target wavelength and/or wavelength range, the target intensity, etc., may be entered and/or selected by a user, determined by system 600 based on previous measurements, and/or determined in other ways. In some embodiments, the 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.

[0081] System 600 comprises an optical component 605 configured to receive the radiation reflected from target 30 and substrate 602, change an angle of the radiation, and direct the radiation toward sensor 604. In some embodiments, optical component 605 comprises a wedge and/or other optical components. In some embodiments, optical component 605 comprises a micro diffraction based overlay wedge. The wedge may comprise quadrants, for example. Each quadrant is configured to direct a portion of the radiation to a different region of interest of sensor 604 to form spots of radiation on sensor 604. The spots of radiation may comprise two spots of radiation associated with Oth order diffracted radiation from target 30 on a substrate, and two spots of radiation associated with 1 st order diffracted radiation from target 30, for example. The radiation from optical component 605 (e.g., the wedge) is received with sensor 604, and a signal indicative of a field image position of the radiation is generated. One or more images (e.g., point spread function images and/or other imagaes) may be generated based on the signal. In some embodiments, sensor 604 comprises a camera, a charge coupled device (CCD) array, a complementary metal oxide semiconductor (CMOS), a photodiode array, and/or other sensors. In some embodiments, sensor 604 comprises a micro diffraction based overlay camera associated with overlay measurement. In some embodiments, optical component 605 comprises a micro diffraction based overlay wedge configured to direct the radiation from substrate 602 to the micro diffraction based overlay camera (sensor 604).

[0082] Illumination mode selector 607 is positioned in the pupil plane of system 600. Illumination mode selector 607 is configured to receive radiation from radiation source 612 and opaque body 601 and transmit portions of the radiation through transmissive portions of at least one multi-aperture pattern in the illumination mode selector toward target 30. Each transmissive portion of the multiaperture pattern, for example, can limit radiation propagating through it to the corresponding single quadrant of component 605, for example. Illumination mode selector 607 may help change a shape of the beam at all pupil conjugates (includes 605), and therefore separate Oth order and +/- 1st order beams at optical component 605.

[0083] Alignment branch 680 is configured to receive reflected radiation and generate an alignment signal (e.g., as described above related to Fig. 3-5). This may include generating and/or analyzing one or more images of a target 30, using the radiation described herein. Focus branch 650 is configured to determine a focus position for objective lens 690.

[0084] Various lenses (example objective lens 690 is labeled in Fig. 6), reflectors, and other optical components are configured to receive, transmit, reflect, focus, and/or perform other operations on the illumination generated by illumination source 612, transmitted or reflected by opaque body 601 and /or optical component 605, focused by focus branch 650, received by detection branch 660, received by alignment branch 680, and/or used by other portions of system 600. These various lenses, reflectors, and/or other optical components may comprise any type of lens, reflector, and/or other optical component configured to allow system 600 to function as described. For example, objective lens 690 may be formed from any transparent material and have curved surfaces configured to concentrate or otherwise focus one or more spots of radiation on target(s) 30. The various lenses, reflectors, optical elements, beam splitters, and other optical elements may be positioned in any location and/or at any angle relative to each other that allows system 600 to function as described herein. This may include positioning at specific relative distances between elements, specific angles between elements, etc. In some embodiments, the various lenses, reflectors, optical elements, beam splitters, and other optical components are positioned relative to each other in system 600 via structural members, clips, clamps, screws, nuts, bolts, adhesive, and/or other mechanical devices. In some embodiments, various ones of the lenses, reflectors, optical elements, beam splitters, and other optical elements are movable relative to each other. Movement may be configured to adjust locations of corresponding spots of illumination on one or more targets 30, for example. In some embodiments, movement comprises tilting, translating or otherwise changing a distance between various lenses, reflectors, and other optical components. Other examples of movement are contemplated. [0085] In some embodiments, movement may be controlled electronically by a processor, such as processor PRO. Processor PRO may be included in a computing system CS (Fig. 9) and may operate based on computer or machine readable instructions (e.g., as described below related to Fig. 9). Electronic communication may occur by transmitting electronic signals between separate components, transmitting data between separate components of system 600, transmitting values between separate components, and/or other communication. The components of system 600 may communicate via wires or wirelessly via a network, such as the Internet or the Internet in combination with various other networks, like local area networks, cellular networks, or personal area networks, internal organizational networks, and/or other networks.

[0086] In some embodiments, one or more actuators (not shown in Fig. 6) may be coupled to and configured to move one or more components of system 600. The actuators may be coupled to one or components of system 600 by adhesive, clips, clamps, screws, a collar, and/or other mechanisms. The actuators may be configured to be controlled electronically. Individual actuators may be configured to convert an electrical signal into mechanical displacement. The mechanical displacement is configured to move a component of system 600. As an example, one or more of the actuators may be piezoelectric. One or more processors PRO may be configured to control the actuators. One or more processors PRO may be configured to individually control each of the one or more actuators.

[0087] The quantity of the various lenses, reflectors, and/or other optical components shown in Fig. 6 is not intended to be limiting. The principles described herein may be extended such that, in some embodiments system 600 comprises additional or fewer lenses, reflectors, and/or other optical components.

[0088] Fig. 7 illustrates a simplified schematic view of certain components of system 600 shown in Fig. 6. Fig. 7 illustrates opaque body 601, illumination mode selector 607, target 30 (e.g., a grating), optical component 605 (e.g., a wedge), sensor 604, two spots 708 and 710 (which are representative of four spots of radiation if Fig. 7 was drawn in three dimensions) of radiation 720 incident on sensor 604, and various lenses 702, 704, 706, and 712 that may be included in system 600.

[0089] Radiation 720 is received by, and passed through, opaque body 601. The radiation may be generated by a radiation source similar to and/or the same as source 2 shown in Fig. 3 and source 612 Fig. 6, and/or other radiation sources. Opaque body 601 has transmission regions 750 positioned in the optical field associated with radiation 720. Body 601 comprises transmission regions 750 at a plurality of different locations associated with on and off optical axis positions. For example, in Fig. 7, a transmission region 750 is shown as a dark spot inside a square region 751, which corresponds to the on-axis position, while other dark spots (other transmission regions 750) correspond to different off-axis positions. The example shown in Fig. 7 illustrates radiation 720 that has passed through one particular transmission region 751, but it should be understood that radiation is also passing through other (on and/or off axis) transmission regions 750 in body 601 and being transmitted toward sensor 604 all at the same time. Opaque body 601 may be a spot size selector, for example, and/or other opaque bodies. A spot size selector defines the size and shape of the illuminated area at the substrate 602 (Fig. 6). This area can be smaller or larger than the size of the illuminated target 30.

[0090] Illumination mode selector 607 is positioned in a pupil plane of metrology system 600, such that radiation 720 that passes through transmission regions 750 is received by illumination mode selector 607. Illumination mode selector 607 may have selectable apertures. Illumination mode selector 607 is configured to receive radiation 720 from the radiation source (not shown in Fig. 7) via transmission regions 750 of opaque body 601, and transmit portions of radiation 720 through a selected aperture toward a diffraction grating target 30 on a substrate, for example. Diffracted radiation from diffraction grating target 30 is directed back toward sensor 604. The diffraction grating target may be an overlay target, for example, and/or other targets, as described above. The main function of illumination mode selector 607 is to form several portions of radiation 720 that are not blocked by any components positioned after illumination mode selector 607. Illumination mode selector 607 comprises multiple selectable apertures configured to change a shape of a beam of radiation 720 and diffraction orders at all pupil conjugates, and therefore separate +1 and -1 orders from the Oth order radiation at a uDBO wedge (e.g., optical component 605).

[0091] Optical component 605 is configured to receive the radiation from each transmission region 750 (e.g., after passing through illumination mode selector 607 and reflection off of target 30), and direct portions of radiation 720 received from each transmission region 750 to different areas of sensor 604 to form multiple spots 708, 710 (plus two more spots in three dimensions) of radiation 720 on sensor 604 for each transmission region 750. Sensor 604 is configured to generate multiple corresponding images 760 for radiation 720 that passes through each transmission region 750.

Optical component 605 may comprise a wedge, for example, and/or other optical components. The wedge may have quadrants, with each quadrant configured to direct a portion of radiation 720 received through a transmission region 750 to the different areas of sensor 604 to form spots 708, 710, etc., of radiation 720 on sensor 604. Spots 708, 710, etc., of radiation 720 may comprise two spots of radiation associated with Oth order diffracted radiation from a substrate, two spots of radiation associated with 1st order diffracted radiation from the substrate, and/or other radiation.

[0092] Radiation 720 that has passed through transmission regions 750, through illumination mode selector 607, been reflected off of target 30 such as a diffraction grating, and transmitted through optical component 605, is received with sensor 604. Sensor 604 is configured to generate images 760 based on the received radiation 720 for the on an off optical axis positions. In some embodiments, images 760 comprise images of body transmission regions 750 created by sensor 604. Images 760 may comprise specular reflection and/or diffraction images for wavefront sensing simultaneously, which improves the accuracy of wavefront sensing as described herein. In some embodiments, images 760 may be point spread function (PSF) images, for example, and/or other images. As shown in Fig. 7, an individual image 760 may include four images for four different spots 709, 711, 713, and 715 of radiation 720 (e.g., four images per transmission region 750 instead of only one as in prior systems).

[0093] A trained algorithm and images 760 are used by one or more processors (e.g., PRO shown in Fig. 6) operatively connected with sensor 604 to determine wavefront aberrations for radiation 720 at the on and off optical axis positions in the optical field. In some embodiments, the one or more processors are configured to determine wavefront aberrations for radiation 720 at the on and off optical axis positions in the optical field simultaneously. In some embodiments, the one or more processors are configured to determine the wavefront aberrations based on the multiple corresponding images 760 (e.g., generated based on different portions of the radiation directed to different areas of the sensor using the wedge) using the trained algorithm. The one or more processors may be configured such that the trained algorithm outputs indications of wavefront aberrations based on intensities of spots 709, 711, 713, and 715 of radiation 720 in the images 760, and/or based on other information. In some embodiments, determining the wavefront aberrations comprises predicting Zernike coefficients 790 for radiation 720 at the on and off optical axis positions in the optical field (e.g., a set of Zernike coefficients 790 for each field position).

[0094] In some embodiments, the trained algorithm is trained by obtaining and providing prior images associated with aberrations to the algorithm. Portions of the prior images associated with the aberrations may be labeled as aberrations, for example. In some embodiments, the trained algorithm comprises a trained machine learning algorithm, neural network, and/or other components.

[0095] In some embodiments, the trained algorithm may be and/or include an empirical and/or other simulation model. The empirical model may predict outputs based on correlations between various inputs (e.g., one or more characteristics of a pattern, one or more characteristics of an image, one or more characteristics of the illumination used in the metrology process such as the wavelength and/or illumination fill, etc.).

[0096] The empirical model may be a machine learning model and/or any other parameterized model. In some embodiments, the machine learning model (for example) may be and/or include mathematical equations, algorithms, plots, charts, networks (e.g., neural networks), and/or other tools and machine learning model components. For example, the machine learning model may be and/or include one or more neural networks having an input layer, an output layer, and one or more intermediate or hidden layers. In some embodiments, the one or more neural networks may be and/or include deep neural networks (e.g., neural networks that have one or more intermediate or hidden layers between the input and output layers).

[0097] As an example, the one or more neural networks may be based on a large collection of neural units (or artificial neurons). The one or more neural networks may loosely mimic the manner in which a biological brain works (e.g., via large clusters of biological neurons connected by axons). Each neural unit of a neural network may be connected with many other neural units of the neural network. Such connections can be enforcing or inhibitory in their effect on the activation state of connected neural units. In some embodiments, each individual neural unit may have a summation function that combines the values of all its inputs together. In some embodiments, each connection (or the neural unit itself) may have a threshold function such that a signal must surpass the threshold before it is allowed to propagate to other neural units. These neural network systems may be selflearning and trained, rather than explicitly programmed, and can perform significantly better in certain areas of problem solving, as compared to traditional computer programs. In some embodiments, the one or more neural networks may include multiple layers (e.g., where a signal path traverses from front layers to back layers). In some embodiments, back propagation techniques may be utilized by the neural networks, where forward stimulation is used to reset weights on the “front” neural units. In some embodiments, stimulation and inhibition for the one or more neural networks may be freer flowing, with connections interacting in a more chaotic and complex fashion. In some embodiments, the intermediate layers of the one or more neural networks include one or more convolutional layers, one or more recurrent layers, and/or other layers.

[0098] The one or more neural networks may be trained (i.e., whose parameters are determined) using a set of training data and/or other information. The training data and/or other information may include a set of training samples. Each sample may be a pair comprising an input object (typically a vector, which may be called a feature vector) and a desired output value (also called the supervisory signal). A training algorithm analyzes the training information and adjusts the behavior of the neural network by adjusting the parameters (e.g., weights of one or more layers) of the neural network based on the training data and/or other information. For example, given a set of N training samples of the form {(^xi>Yi)> (^x2,y2)> ■■■ > (^XN>YN)} ^such that ^xi is the feature vector of the i-th example and y; is its supervisory signal, a training algorithm seeks a neural network g: X -> Y, where X is the input space and Y is the output space. A feature vector is an n-dimensional vector of numerical features that represent some object (e.g., an image, a target design, etc.). The vector space associated with these vectors is often called the feature space. After training, the neural network may be used for making predictions using new samples (e.g., new PSF images).

[0099] As another example, an empirical (simulation) model may comprise one or more algorithms. The one or more algorithms may be and/or include mathematical equations, plots, charts, and/or other tools and model components. In some embodiments, an empirical (simulation) model is a physical model comprising one or more algorithms with terms that collectively simulate the physical behavior of reflected radiation, etc.

[00100] Fig. 8 illustrates a metrology method 800 for determining wavefront aberrations for radiation at on and off optical axis positions in an optical field. In some embodiments, method 800 is performed as part of an overlay and/or alignment sensing operation in a semiconductor device manufacturing process, for example. In some embodiments, one or more operations of method 800 may be implemented in or by system 600 illustrated in Fig. 6 and Fig. 7, system 10 illustrated in Fig.

3, a computer system (e.g., as illustrated in Fig. 9 and described below), and/or in or by other systems, for example. In some embodiments, method 800 comprises receiving and passing (operation 802) radiation with an opaque body having transmission regions positioned in the optical field; receiving (operation 804) radiation that has passed through the transmission regions and generating images based on the received radiation for on an off optical axis positions; and using (operation 806) a trained algorithm and the images to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field. The operations of method 800 are intended to be illustrative. In some embodiments, method 800 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 800 may include an additional operation comprising determining an adjustment for a semiconductor device manufacturing process. Additionally, the order in which the operations of method 800 are illustrated in Fig. 8 and described herein is not intended to be limiting.

[00101] In some embodiments, one or more portions of method 800 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). The one or more processing devices may include one or more devices executing some or all of the operations of method 800 in response to instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and/or software to be specifically designed for execution of one or more of the operations of method 800 (e.g., see discussion related to Fig. 9 below).

[00102] At operation 802, radiation is received by, and passed through, an opaque body having transmission regions positioned in the optical field. The body comprises the transmission regions at a plurality of different locations associated with the on and off optical axis positions. The opaque body may be a spot size selector, for example, and/or other opaque bodies. In some embodiments, the opaque body is the same as or similar to opaque body 601 shown in Fig. 6 and Fig. 7, and described above.

[00103] The radiation may be generated by a radiation source similar to and/or the same as source 2 shown in Fig. 3 and source 612 Fig. 6, and/or other radiation sources. Operation 802 may include generating and directing, with the radiation source and one or more lenses, the radiation toward the opaque body, a substrate, and/or the sensor (e.g., as described below).

[00104] In some embodiments, operation 802 comprises positioning an illumination mode selector in a pupil plane of a metrology system, such that radiation that passes through the transmission regions is received by the illumination mode selector. The illumination mode selector may have selectable apertures. The illumination mode selector is configured to receive radiation from the radiation source via the transmission regions of the opaque body, and transmit portions of the radiation through a selected aperture toward a diffraction grating target on a substrate. Diffracted radiation from the diffraction grating target is directed back toward a sensor. The diffraction grating target may be an overlay target, for example, and/or other targets. [00105] At operation 804, radiation that has passed through the transmission regions, through the illumination mode selector, and been reflected off of a target such as a diffraction grating, is received with the sensor. The sensor is configured to generate images based on the received radiation for the on an off optical axis positions. In some embodiments, the images comprise images of body transmission regions created by the sensor. The images may be point spread function (PSF) images, for example, and/or other images. In some embodiments, the sensor comprises a camera and/or a charge coupled device (CCD) array. In some embodiments, the sensor comprises a micro diffraction based overlay camera associated with overlay measurement, for example. In some embodiments, operation 804 is performed by a sensor that is the same as or similar to detector 4 shown in Fig. 3, and sensor 603 shown in Fig. 6 and Fig. 7, and described above.

[00106] In some embodiments, operation 804 includes receiving, with an optical component, the radiation from each transmission region (e.g., after reflection off of a target), and directing, with the optical component, portions of the radiation received from each transmission region to different areas of the sensor to form multiple spots of radiation on the sensor for each transmission region. The sensor is configured generate multiple corresponding images for radiation that passes through each transmission region. The optical component may comprise a wedge, for example, and/or other optical components (e.g., optical component 605 as described above). The wedge may have quadrants, with each quadrant configured to direct a portion of the radiation received through a transmission region to the different areas of the sensor to form the spots of radiation on the sensor. The spots of radiation may comprise two spots of radiation associated with Oth order diffracted radiation from a substrate, two spots of radiation associated with 1st order diffracted radiation from the substrate, and/or other radiation. The substrate may be a semiconductor wafer, for example, and/or other substrates.

[00107] At operation 806, a trained algorithm and the images are used by one or more processors operatively connected with the sensor to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field. In some embodiments, the one or more processors are configured to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field simultaneously. In some embodiments, the one or more processors configured to determine the wavefront aberrations based on the multiple corresponding images (e.g., generated based on different portions of the radiation directed to different areas of the sensor using the wedge) using the trained algorithm. The one or more processors may be configured such that the trained algorithm outputs indications of wavefront aberrations based on intensities of spots of radiation in the images. In some embodiments, determining the wavefront aberrations comprises predicting Zernike coefficients for radiation at the on and off optical axis positions in the optical field.

[00108] In some embodiments, the trained algorithm is trained by obtaining and providing prior images associated with aberrations to the algorithm. Portions of the prior images associated with the aberrations may be labeled as aberrations, for example. In some embodiments, the trained algorithm comprises a trained machine learning model, a neural network, and/or other components. [00109] In some embodiments, as part of operation 806, the one or more processors are configured to automatically adjust one or more characteristics of the radiation, a deformable mirror inside the sensor, a stage holding a substrate with a target, and/or other aspects of a metrology system and/or a metrology operation to reduce and/or eliminate wavefront aberrations for the radiation at the on and off optical axis positions in the optical field. In some embodiments, operation 806 is performed by one or more processors the same as or similar to processor PRO shown in Fig. 3 and Fig. 6, and described above (along with processor PRO shown in Fig. 9 and described below).

[00110] In some embodiments, method 800 is configured for a semiconductor wafer, and is used in a semiconductor manufacturing process. In some embodiments, the opaque body, the sensor, and the one or more processors are configured for overlay detection. In some embodiments, the opaque body, the sensor, the one or more processors, and/or the operations of method 800 are configured to replace the functionality of a Shack-Hartmann wavefront sensor in a metrology system.

[00111] In some embodiments, method 800 comprises detecting reflected radiation from one or more diffraction grating targets. Detecting reflected radiation comprises detecting one or more phase and/or amplitude (intensity) shifts in reflected radiation from one or more geometric features of the target(s). The one or more phase and/or amplitude shifts correspond to one or more dimensions of a target. For example, the phase and/or amplitude of reflected radiation from one side of a target is different relative to the phase and/or amplitude of reflected radiation from another side of the target. [00112] Detecting the one or more phase and/or amplitude (intensity) shifts in the reflected radiation from the target comprises measuring local phase shifts (e.g., local phase deltas) and/or amplitude variations that correspond to different portions of a target. For example, the reflected radiation from a specific area of a target may comprise a sinusoidal waveform having a certain phase and/or amplitude. The reflected radiation from a different area of the target (or a target in a different layer) may also comprise a sinusoidal waveform, but one with a different phase and/or amplitude. Detected reflected radiation also comprises measuring a phase and/or amplitude difference in reflected radiation of different diffraction orders. Detecting the one or more local phase and/or amplitude shifts may be performed using 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.

[00113] In some embodiments, method 800 comprises generating a metrology signal based on the detected reflected radiation from diffraction grating target(s), as described above. The metrology signal is generated by a sensor (such as detector 4 in Fig. 3, sensor 603 in Fig. 6 and Fig. 7, and/or other sensors) based on radiation received by the sensor. The metrology signal comprises measurement information pertaining to the target(s). For example, the metrology signal may be an overlay and/or alignment signal comprising overlay and/or alignment measurement information, and/or other metrology signals. The measurement information (e.g., an overlay value, an alignment value, and/or other information) may be determined using principles of interferometry and/or other principles.

[00114] The metrology signal comprises an electronic signal that represents and/or otherwise corresponds to the radiation reflected from the target(s). The metrology signal may indicate a metrology value associated with a diffraction grating target, for example, and/or other information. Generating the metrology signal comprises sensing the reflected radiation and converting the sensed reflected radiation into the electronic signal. In some embodiments, generating the metrology signal comprises sensing different portions of the reflected radiation from different areas and/or different geometries of the target, and/or multiple targets, and combining the different portions of the reflected radiation to form the metrology signal. This may include generating and/or analyzing one or more images of a target, using the radiation described herein. This sensing and converting may be performed by components similar to and/or the same as detector 4, sensor 603, and/or processors PRO shown in Fig. 3, Fig. 6, and Fig. 9 (described below) and/or other components.

[00115] In some embodiments, method 800 comprises determining an adjustment for a semiconductor device manufacturing process. In some embodiments, method 800 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on one or more detected phase and/or amplitude variations, an overlay and/or alignment value indicated by the metrology signal, and/or other similar systems, and/or other information. The one or more parameters may include a parameter of the radiation (the radiation used for metrology), an overlay value, an alignment value, a metrology inspection location on a layer of a semiconductor device structure, a radiation beam trajectory across a target, and/or other parameters. In some embodiments, process parameters can be interpreted broadly to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation (used for exposing resist, etc.), an incident angle of the radiation (used for exposing resist, etc.), a wavelength of the radiation (used for exposing resist, etc.), a pupil size and/or shape, a resist material, and/or other parameters.

[00116] In some embodiments, method 800 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, if a determined metrology measurement is not within process tolerances, the out of tolerance measurement 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., measurements may breach a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the measurement determination. The new or adjusted process parameters may be configured to cause a manufacturing process to again produce acceptable devices.

[00117] For example, a new or adjusted process parameter may cause a previously unacceptable measurement 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 method 800), for example. In some embodiments, method 800 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.

[00118] Fig. 9 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 similar to and/or the same as processor PRO shown in Fig. 3) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[00119] Computer system CS may be coupled via bus BS to a display DS, such as a flat panel or touch panel display or a cathode ray tube (CRT) 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.

[00120] In some embodiments, all or some of one or more operations described herein may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions included in main memory MM causes processor PRO to perform the process steps (operations) described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[00121] The term “computer-readable medium” or “machine-readable medium” as used herein refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-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 herein. Transitory computer-readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[00122] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[00123] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information. [00124] 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.

[00125] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CI. In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and/or stored in storage device SD, or other nonvolatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[00126] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses. In the following, further features, characteristics, and exemplary technical solutions of the present disclosure will be described in terms of clauses that may be optionally claimed in any combination:

1. A metrology system configured to determine wavefront aberrations for radiation at on and off optical axis positions in an optical field, the system comprising: an opaque body comprising transmission regions at a plurality of different locations associated with the on and off optical axis positions, the body positioned in the optical field and configured to receive and pass radiation through the transmission regions; a sensor configured to receive radiation that has passed through the transmission regions and generate images based on the received radiation for the on an off optical axis positions; and one or more processors operatively connected with the sensor, the one or more processors configured to use a trained algorithm and the images to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field.

2. The system of clause 1, wherein the opaque body is a spot size selector.

3. The system of any of the previous clauses, wherein the images comprise images of body transmission regions created by the sensor.

4. The system of any of the previous clauses, wherein the images are point spread function (PSF) images.

5. The system of any of the previous clauses, wherein the sensor comprises a camera and/or a charge coupled device (CCD) array. 6. The system of any of the previous clauses, wherein the sensor comprises a micro diffraction based overlay camera associated with overlay measurement.

7. The system of any of the previous clauses, wherein the one or more processors are configured to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field simultaneously.

8. The system of any of the previous clauses, further comprising an optical component configured to receive the radiation from each transmission region, and direct portions of the radiation received from each transmission region to different areas of the sensor to form multiple spots of radiation on the sensor for each transmission region, the sensor configured generate multiple corresponding images for radiation that passes through each transmission region, the one or more processors configured to determine the wavefront aberrations based on the multiple corresponding images using the trained algorithm.

9. The system of any of the previous clauses, wherein the optical component comprises a wedge.

10. The system of any of the previous clauses, wherein the wedge comprises quadrants, each quadrant configured to direct a portion of the radiation received through a transmission region to the different areas of the sensor to form the spots of radiation on the sensor.

11. The system of any of the previous clauses, wherein the spots of radiation comprise two spots of radiation associated with 0^th order diffracted radiation from a substrate, and two spots of radiation associated with 1^st order diffracted radiation from the substrate.

12. The system of any of the previous clauses, wherein the substrate is a semiconductor wafer.

13. The system of any of the previous clauses, further comprising an illumination mode selector having selectable apertures, the illumination mode selector positioned in a pupil plane of the system, the illumination mode selector configured to receive radiation from a radiation source, and transmit portions of the radiation through a selected aperture toward a diffraction grating target on a substrate, wherein diffracted radiation from the diffraction grating target is directed back toward the optical component in the sensor.

14. The system of any of the previous clauses, wherein determining the wavefront aberrations comprises predicting Zernike coefficients for radiation at the on and off optical axis positions in the optical field.

15. The system of any of the previous clauses, wherein the one or more processors are configured such that the trained algorithm outputs indications of wavefront aberrations based on intensities of spots of radiation in the images.

16. The system of any of the previous clauses, wherein the trained algorithm is trained by obtaining and providing prior images associated with aberrations to the algorithm.

17. The system of any of the previous clauses, wherein portions of the prior images associated with the aberrations are labeled as aberrations. 18. The system of any of the previous clauses, wherein the opaque body, the sensor, and the one or more processors are configured to replace a Shack-Hartmann wavefront sensor.

19. The system of any of the previous clauses, wherein the one or more processors are further configured to automatically adjust one or more characteristics of the radiation, a deformable mirror inside the sensor, and/or a stage holding a substrate with a target to reduce and/or eliminate wavefront aberrations for the radiation at the on and off optical axis positions in the optical field.

20. The system of any of the previous clauses, wherein radiation that passes through the transmission regions of the opaque body is directed toward a substrate, the substrate comprising a semiconductor wafer having one or more overlay targets configured to reflect the radiation toward the sensor.

21. The system of any of the previous clauses, further comprising a radiation source and one or more lenses, the radiation source and the one or more lenses configured to generate the radiation and direct the radiation toward the opaque body, a substrate, and/or the sensor.

22. The system of any of the previous clauses, wherein the opaque body, the sensor, and the one or more processors are configured for overlay detection.

23. The system of any of the previous clauses, wherein the metrology system is configured for a semiconductor wafer, and is used in a semiconductor manufacturing process.

24. The system of any of the previous clauses, wherein the trained algorithm comprises a trained machine learning model.

25. The system of any of the previous clauses, wherein the trained machine learning model comprises a neural network.

26. A metrology method for determining wavefront aberrations for radiation at on and off optical axis positions in an optical field, the method comprising: receiving and passing radiation with an opaque body having transmission regions positioned in the optical field, the body comprising the transmission regions at a plurality of different locations associated with the on and off optical axis positions; receiving, with a sensor, radiation that has passed through the transmission regions and generating, with the sensor, images based on the received radiation for the on an off optical axis positions; and using, by one or more processors operatively connected with the sensor, a trained algorithm and the images to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field.

27. The method of clause 26, wherein the opaque body is a spot size selector.

28. The method of any of the previous clauses, wherein the images comprise images of body transmission regions created by the sensor.

29. The method of any of the previous clauses, wherein the images are point spread function (PSF) images.

30. The method of any of the previous clauses, wherein the sensor comprises a camera and/or a charge coupled device (CCD) array. 31. The method of any of the previous clauses, wherein the sensor comprises a micro diffraction based overlay camera associated with overlay measurement.

32. The method of any of the previous clauses, wherein the one or more processors are configured to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field simultaneously.

33. The method of any of the previous clauses, further comprising receiving, with an optical component, the radiation from each transmission region, and directing, with the optical component, portions of the radiation received from each transmission region to different areas of the sensor to form multiple spots of radiation on the sensor for each transmission region, the sensor configured generate multiple corresponding images for radiation that passes through each transmission region, the one or more processors configured to determine the wavefront aberrations based on the multiple corresponding images using the trained algorithm.

34. The method of any of the previous clauses, wherein the optical component comprises a wedge.

35. The method of any of the previous clauses, wherein the wedge comprises quadrants, each quadrant configured to direct a portion of the radiation received through a transmission region to the different areas of the sensor to form the spots of radiation on the sensor.

36. The method of any of the previous clauses, wherein the spots of radiation comprise two spots of radiation associated with 0^th order diffracted radiation from a substrate, and two spots of radiation associated with 1^st order diffracted radiation from the substrate.

37. The method of any of the previous clauses, wherein the substrate is a semiconductor wafer.

38. The method of any of any of the previous clauses, further comprising positioning an illumination mode selector in a pupil plane of a metrology system, the illumination mode selector having selectable apertures, the illumination mode selector configured to receive radiation from a radiation source, and transmit portions of the radiation through a selected aperture toward a diffraction grating target on a substrate, wherein diffracted radiation from the diffraction grating target is directed back toward the optical component in the sensor.

39. The method of any of the previous clauses, wherein determining the wavefront aberrations comprises predicting Zernike coefficients for radiation at the on and off optical axis positions in the optical field.

40. The method of any of the previous clauses, wherein the one or more processors are configured such that the trained algorithm outputs indications of wavefront aberrations based on intensities of spots of radiation in the images.

41. The method of any of the previous clauses, wherein the trained algorithm is trained by obtaining and providing prior images associated with aberrations to the algorithm.

42. The method of any of the previous clauses, wherein portions of the prior images associated with the aberrations are labeled as aberrations. 43. The method of any of the previous clauses, wherein the opaque body, the sensor, and the one or more processors are configured to replace a Shack-Hartmann wavefront sensor.

44. The method of any of the previous clauses, wherein the one or more processors are further configured to automatically adjust one or more characteristics of the radiation, a deformable mirror inside the sensor, and/or a stage holding a substrate with a target to reduce and/or eliminate wavefront aberrations for the radiation at the on and off optical axis positions in the optical field.

45. The method of any of the previous clauses, wherein radiation that passes through the transmission regions of the opaque body is directed toward a substrate, the substrate comprising a semiconductor wafer having one or more overlay targets configured to reflect the radiation toward the sensor.

46. The method of any of the previous clauses, further comprising generating and directing, with a radiation source and one or more lenses, the radiation toward the opaque body, a substrate, and/or the sensor.

47. The method of any of the previous clauses, wherein the opaque body, the sensor, and the one or more processors are configured for overlay detection.

48. The method of any of the previous clauses, wherein the method is configured for a semiconductor wafer, and is used in a semiconductor manufacturing process.

49. The method of any of the previous clauses, wherein the trained algorithm comprises a trained machine learning model.

50. The method of any of the previous clauses, wherein the trained machine learning model comprises a neural network.

[00127] The concepts disclosed herein may be associated with any generic imaging system for imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use include EUV (extreme ultra violet), DUV lithography that is capable of producing a 193nm wavelength with the use of an ArF laser, and even a 157nm wavelength with the use of a Fluorine laser. Moreover, EUV lithography is capable of producing wavelengths within a range of 20-5nm by using a synchrotron or by hitting a material (either solid or a plasma) with high energy electrons in order to produce photons within this range.

[00128] While the concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of lithographic imaging systems, e.g., those used for imaging on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments.

[00129] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

2. The system of claim 1, wherein the opaque body is a spot size selector.

3. The system of claims 1 or 2, wherein the images comprise images of body transmission regions created by the sensor.

4. The system of any of claims 1-3, wherein the images are point spread function (PSF) images.

5. The system of any of claims 1-4, wherein the sensor comprises a camera and/or a charge coupled device (CCD) array.

6. The system of claim 5, wherein the sensor comprises a micro diffraction based overlay camera associated with overlay measurement.

7. The system of any of claims 1-6, wherein the one or more processors are configured to determine wavefront aberrations for radiation at the on and off optical axis positions in the optical field simultaneously.

8. The system of any of claims 1-7, further comprising an optical component configured to receive the radiation from each transmission region, and direct portions of the radiation received from each transmission region to different areas of the sensor to form multiple spots of radiation on the sensor for each transmission region, the sensor configured generate multiple corresponding images for radiation that passes through each transmission region, the one or more processors configured to determine the wavefront aberrations based on the multiple corresponding images using the trained algorithm.

9. The system of claim 8, wherein the optical component comprises a wedge.

10. The system of claim 9, wherein the wedge comprises quadrants, each quadrant configured to direct a portion of the radiation received through a transmission region to the different areas of the sensor to form the spots of radiation on the sensor.

11. The system of claim 10, wherein the spots of radiation comprise two spots of radiation associated with 0^th order diffracted radiation from a substrate, and two spots of radiation associated with 1^st order diffracted radiation from the substrate.

12. The system of claim 11, wherein the substrate is a semiconductor wafer.

13. The system of any of claims 8-12, further comprising an illumination mode selector having selectable apertures, the illumination mode selector positioned in a pupil plane of the system, the illumination mode selector configured to receive radiation from a radiation source, and transmit portions of the radiation through a selected aperture toward a diffraction grating target on a substrate, wherein diffracted radiation from the diffraction grating target is directed back toward the optical component in the sensor.

14. The system of any of clams 1-13, wherein determining the wavefront aberrations comprises predicting Zernike coefficients for radiation at the on and off optical axis positions in the optical field.

15. The system of any of claims 1-14, wherein the one or more processors are configured such that the trained algorithm outputs indications of wavefront aberrations based on intensities of spots of radiation in the images.