Wavefront sensors for metrology systems

Abstract

A wavefront sensing technique for measuring wavefront aberrations of an optical field is described. This wavefront sensing technique is lower cost than conventional systems, can be used to measure on-axis or off-axis radiation simultaneously, and does not have the same stringent alignment requirements or require the same computational reconstruction of the wavefront. This wavefront sensing technique utilizes machine learning applied to specular reflection and diffraction images from multiple on-axis and off-axis simultaneous pinhole radiation transmissions to determine wavefront aberrations.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63 / 440,555, filed January 23, 2023, which is incorporated herein by reference in its entirety.

[0002] This specification relates to wavefront sensors for metrology systems. [Background technology]

[0003] Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device (e.g., a mask) may contain or provide a pattern (a "design layout") that corresponds to an individual layer of the IC; this pattern can be transferred onto a target portion (e.g., comprising one or more dies) on a substrate (e.g., a silicon wafer) that is coated with a layer of radiation-sensitive material ("resist"), by, for example, irradiating the target portion through the patterning device. Typically, a single substrate will contain several adjacent target portions, and the pattern is transferred onto these successively by the lithographic projection apparatus, one target portion at a time. In one type of lithographic projection apparatus, the pattern of the entire patterning device is transferred onto one target portion in one go. Such an apparatus is commonly referred to as a stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, the projection beam scans the patterning device in a given reference direction (the "scan" direction) while the substrate is simultaneously moved parallel or anti-parallel to this reference direction. Different portions of the patterning device pattern are progressively transferred onto one target portion. Lithographic projection apparatus typically have a de-magnification factor M (e.g., 4), so that the speed F at which the substrate is moved is 1 / M times the rate at which the projection beam scans the patterning device. More information on the lithographic devices described herein can be gleaned, for example, from U.S. Pat. No. 6,046,792, which is incorporated herein by reference.

[0004] Before 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 series of procedures is used as a basis for fabricating an individual layer of a device, such as an IC. The substrate may then undergo various processes, such as etching, ion implantation (doping), metallization, oxidation, deposition, chemical-mechanical polishing, etc., to finish the individual layers of the device. If several layers are required for a device, the entire procedure, or a variation on it, is repeated for each layer. Eventually, a device will be present on each target portion of the substrate. The devices are then separated from each other by techniques such as dicing or sawing so that the individual devices can be mounted on a carrier or connected to pins.

[0005]

[0005] Thus, manufacturing devices such as semiconductor devices typically involves processing a substrate (e.g., a semiconductor wafer) using several fabrication processes to form various features and multiple layers of the device. Such layers and features are typically produced and processed using, for example, deposition, lithography, etching, chemical-mechanical polishing, and ion implantation. Multiple devices may be fabricated on multiple 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 lithography and / or nanoimprint lithography, in which a patterning device in a lithography apparatus is used to transfer a pattern on the patterning device to the substrate, and typically involves one or more related pattern processing steps, optionally including resist development in a developer, baking the substrate using a bake tool, etching using an etcher using the pattern, deposition, etc.

[0006]

[0006] Lithography is a central step in the fabrication of devices such as integrated circuits, where patterns formed on a substrate define the functional elements of devices such as microprocessors and memory chips. Similar lithographic techniques are also used in the formation of flat panel displays, microelectromechanical systems (MEMS), and other devices.

[0007]

[0007] As semiconductor manufacturing processes continue to improve, the dimensions of functional elements have continually decreased, while the number of functional elements, such as transistors, per device has steadily increased for decades, following a trend colloquially known as "Moore's Law." In the current state of the art, device layers are fabricated using lithographic projection apparatus that project a design layout onto a substrate using illumination from a deep ultraviolet illumination source, creating individual functional elements with 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]

[0008] This process, in which features having dimensions smaller than the classical resolution limit of the lithographic projection apparatus are printed, is commonly known as low k1 lithography, according to the resolution formula CD=k1×λ / NA, where λ is the wavelength of the radiation used (currently most often 248 nm or 193 nm), NA is the numerical aperture of the projection optics in the lithographic projection apparatus, CD is the "critical dimension" (typically the smallest feature size to be printed), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to reproduce a pattern on a substrate similar to the shape and dimensions planned by the designer to achieve a particular electrical functionality and performance. To overcome these difficulties, elaborate fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These steps 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 referred to as "optical and process correction") in the design layout, or other methods commonly defined as "resolution enhancement techniques" (RET). Summary of the Invention

[0009]

[0009] A wavefront sensing technique for measuring wavefront aberrations of an optical field is described. Among other advantages, this wavefront sensing technique is low cost compared to conventional systems, can be used to measure on-axis or off-axis radiation simultaneously, and does not have the same stringent alignment requirements or require the same computational reconstruction of the wavefront. This wavefront sensing technique utilizes machine learning applied to specular reflection and diffraction images from multiple on-axis and off-axis simultaneous pinhole radiation transmissions to determine wavefront aberrations.

[0010] According to one embodiment, there is provided a metrology system configured to determine wavefront aberrations of radiation at on-axis and off-axis locations within an optical field. The system includes an opaque body. The opaque body includes transmissive regions at a plurality of different locations related to the on-axis and off-axis locations. The opaque body is positioned within the optical field and configured to receive radiation and pass it through the transmissive regions. The system includes a sensor configured to receive the radiation that has passed through the transmissive regions and to generate images for the on-axis and off-axis locations based on the received radiation. The system includes one or more processors operably connected to the sensor. The one or more processors are configured to use a trained algorithm and the images to determine wavefront aberrations of the radiation at the on-axis and off-axis locations within the optical field.

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

[0012]

[0012] In some embodiments, the image comprises an image of an opaque medium transmissive area produced by a sensor.

[0013] In some embodiments, the image is a point spread function (PSF) image.

[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 the overlay measurement.

[0016] In some embodiments, the one or more processors are configured to simultaneously determine wavefront aberrations of the radiation at on-axis and off-axis locations within the optical field.

[0017] In some embodiments, the system further includes an optical component configured to receive radiation from each transmissive region and direct a portion of the radiation received from each transmissive region to a different area of ​​the sensor to form multiple spots of radiation on the sensor for each transmissive region. The sensor is configured to generate multiple corresponding images for the radiation passing through each transmissive region. The one or more processors are configured to use a trained algorithm to determine wavefront aberrations based on the multiple corresponding images.

[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 the transmissive region to a different area of ​​the sensor to form a spot of radiation on the sensor. In some embodiments, the spots of radiation comprise two spots of radiation associated with zeroth order diffracted radiation from the substrate and two spots of radiation associated with first order diffracted radiation from the substrate. In some embodiments, the substrate is a semiconductor wafer.

[0019] In some embodiments, the system further includes an illumination mode selector having a selectable aperture. The illumination mode selector is positioned in a pupil plane of the system. The illumination mode selector is configured to receive radiation from the radiation source and transmit a portion of the radiation through a selected aperture toward a diffraction grating target on the substrate. Diffracted radiation from the diffraction grating target is directed back toward an optical component in the sensor.

[0020]

[0020] In some embodiments, determining the wavefront aberration comprises predicting Zernike coefficients of the radiation at on-axis and off-axis positions within the optical field.

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

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

[0024] In some embodiments, radiation passing through the transmissive regions of the opaque body is directed towards a substrate, the substrate comprising a semiconductor wafer having one or more overlay targets configured to reflect the radiation towards a sensor.

[0025] In some embodiments, the system further comprises a radiation source and one or more lenses configured to generate radiation and direct the radiation towards the opaque body, the 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 semiconductor wafers 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 of radiation at on-axis and off-axis locations within an optical field. The method comprises receiving and passing radiation through an opaque body having transmissive regions positioned within the optical field. The opaque body has transmissive regions at a plurality of different locations related to the on-axis and off-axis locations. The method comprises receiving, with a sensor, the radiation that has passed through the transmissive regions. The method comprises generating, with the sensor, images for the on-axis and off-axis locations based on the received radiation. The method comprises determining, by one or more processors operatively connected to the sensor, the wavefront aberrations of the radiation at the on-axis and off-axis locations within the optical field using a trained algorithm and the images. [Brief explanation of the drawings]

[0029]

[0029] The above aspects and other aspects and features will become apparent to those skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying drawings.

[0030] [Figure 1] 1 illustrates a schematic representation of a lithographic apparatus according to an embodiment; [Figure 2]

[0031] 1 illustrates a schematic diagram of an embodiment of a lithographic cell or cluster, according to one embodiment. [Figure 3]

[0032] 1 illustrates a schematic diagram of an exemplary inspection system according to one embodiment. [Figure 4]

[0033] 1 illustrates a schematic diagram of an exemplary metrology technique according to one embodiment. [Figure 5]

[0034] 1 illustrates the relationship between the radiant illumination spot and a metrology target of an inspection system according to one embodiment. [Figure 6]

[0035] 1 illustrates a system configured to determine wavefront aberrations of radiation at on-axis and off-axis positions within an optical field according to one embodiment. [Figure 7]

[0036] 7 shows a simplified schematic diagram of certain components of the system shown in FIG. 6 according to one embodiment. [Figure 8]

[0037] 1 illustrates a metrology method according to one embodiment. [Figure 9]

[0038] FIG. 1 is a block diagram of an exemplary computer system according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031]

[0039] In semiconductor device manufacturing, metrology operations typically involve determining the position of one or more metrology marks and / or other targets in a layer of a semiconductor device structure. This position is typically determined by illuminating the metrology mark with radiation and comparing the characteristics of different diffraction orders of the 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 determination, radiation wavefront aberrations are measured and metrology operations are adjusted based on these measurements.

[0032]

[0040] Described below is a metrology system configured to determine wavefront aberrations of radiation at on-axis and off-axis locations within an optical field. Compared to conventional wavefront aberration measurement systems, the metrology system described below is low-cost because it does not include complex elements of a Shack-Hartmann sensor, such as an array of lenslets to measure local tilt and computational software resources for full wavefront reconstruction. Instead, the metrology system described below relies on trained software algorithms for image-based wavefront aberration detection. Among other advantages, this system can be used to simultaneously measure on-axis or off-axis radiation and does not have the same stringent alignment requirements as conventional systems. The wavefront sensing technology described herein utilizes machine learning applied to specular reflection and diffraction images from multiple simultaneous on-axis and off-axis pinhole radiation transmissions to determine wavefront aberrations.

[0033]

[0041] As a brief introduction, the following description pertains to semiconductor device fabrication and patterning processes. The following paragraphs also describe some components of systems and / or methods for semiconductor device metrology. These systems and methods can be used, for example, to measure overlay, alignment, etc., or for other operations in the semiconductor device fabrication process.

[0034]

[0042] While specific reference may be made herein to measuring 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, the description may be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. Those skilled in the art will recognize that, in the context of such alternative applications, any use of the terms "reticle," "wafer," or "die" herein should be considered interchangeable with the more general terms "mask," "substrate," or "target portion," respectively.

[0035]

[0043] The term "projection optics" as used herein should be interpreted broadly to encompass various types of optical systems, including, for example, refractive optics, reflective optics, apertures, and catadioptric components. The term "projection optics" may also include components that, collectively or individually, operate to direct, shape, or control a projection beam of radiation according to any of these design types. The term "projection optics" may include any optical component of a lithographic projection apparatus, regardless of where the optical component is located in the optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, conditioning, and / or projecting radiation from a radiation source before the radiation passes through a patterning device, and / or optical components for shaping, conditioning, and / or projecting radiation after the radiation has passed through a patterning device. Projection optics generally do not include a radiation source and a patterning device.

[0036]

[0044] Figure 1 schematically depicts an embodiment of a lithographic apparatus LA. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to 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 according to 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 the patterning device MA onto a target portion C (e.g., comprising one or more dies, often referred to as a field) 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 (eg employing a programmable mirror array, or employing a reflective mask).

[0037]

[0045] The illuminator IL receives a radiation beam 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 transmitted from the source SO to the illuminator IL with the aid of a beam delivery system BD, which may comprise, for example, suitable directing mirrors and / or beam expanders. 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.

[0038]

[0046] The illuminator IL may modify 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 within a number of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in the pupil plane of the illuminator IL may be referred to as an illumination mode.

[0039]

[0047] The illuminator IL may include an adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to change the angular distribution of the beam. For example, the illuminator may be operable to vary the number and angular extent of sectors in the pupil plane, where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes can 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 multipole distribution, such as a dipole, quadrupole, or hexapole distribution. A desired illumination mode can be obtained, for example, by inserting an optical element providing that illumination mode into the illuminator IL or by using a spatial light modulator.

[0040]

[0048] The illuminator IL may be operable to change the polarization of the beam or to adjust the polarization using an adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as the 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 the pupil plane of the illuminator IL. The polarization direction of the radiation may be different in different regions of the pupil plane of the illuminator IL. The polarization state of the radiation may be selected depending on the illumination mode. In a multipole illumination mode, the polarization of each pole of the radiation beam may be approximately perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, in a dipole illumination mode, the radiation may be linearly polarized in a direction approximately perpendicular to a line bisecting 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 the X and Y polarization states. In the case of a quadrupole illumination mode, the radiation in each pole sector may be linearly polarized in a direction approximately perpendicular to the line bisecting that sector. This polarization mode may be referred to as XY polarization. Similarly, in the case of a hexapole illumination mode, the radiation in each pole sector may be linearly polarized in a direction approximately perpendicular to the line bisecting that sector. This polarization mode may be referred to as TE polarization.

[0041]

[0049] The illuminator IL will generally also include various other components, such as an integrator IN and a condenser CO. Illumination systems 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 radiation beam B having a desired uniformity and intensity distribution in its cross-section.

[0042]

[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 as synonymous with the more general term "patterning device".

[0043]

[0051] The term "patterning device", as used herein, should be interpreted broadly as referring to any device that can be used to impart a pattern to a target portion of a substrate. In an embodiment, the patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in the 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 if, for example, the pattern includes phase-shifting features or so-called assist features. Generally, the pattern imparted to the radiation beam corresponds to a particular functional layer in a device, such as an integrated circuit, that is to be created in the target portion of the device.

[0044]

[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 phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam that is reflected by the mirror matrix.

[0045]

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

[0046]

[0054] The projection system PS may include multiple optical (e.g., lens) elements and may further include an adjustment mechanism configured to adjust one or more of the optical elements to correct aberrations (phase variations across the pupil plane across the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements in the projection system PS in one or more different ways. The projection system may have a coordinate system, the optical axis of which extends in the z-direction. The adjustment mechanism may be operable to perform any combination of the following: displacing one or more optical elements, tilting one or more optical elements, and / or deforming one or more optical elements. The displacement of the optical elements may be in any direction (x, y, z, or a combination thereof). The tilt of an optical element is typically achieved by rotating it about an axis in the x- and / or y-direction out of a plane perpendicular to the optical axis, although rotation about the z-axis may be used in the case of non-rotationally symmetric aspherical optical elements. The deformation of the optical element may include low-frequency shapes (e.g., astigmatism) and / or high-frequency shapes (e.g., freeform aspheric surfaces). The deformation of the optical element may be performed, for example, by applying a force to one or more sides of the optical element using one or more actuators and / or by heating one or more selected regions of the optical element using one or more heating elements. Generally, it would not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). A transmission map of the projection system PS may be used when designing a patterning device (e.g., a mask) MA of the lithographic apparatus LA. Using computational lithography techniques, the patterning device MA may be designed to at least partially correct for apodization.

[0047]

[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, e.g. substrate tables WTa and tables WTb below the projection system without substrates dedicated to facilitating measurement and / or cleaning etc.). In such a "multi-stage" machine, the additional tables may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements may be made using alignment sensors AS and / or level (height, tilt etc.) measurements using level sensors LS.

[0048]

[0056] The lithographic apparatus may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. Immersion liquids 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. As used herein, the term "immersion" does not mean that a structure such as the substrate has to be submerged in the liquid, but rather that a liquid is located between the projection system and the substrate during exposure.

[0049]

[0057] During operation of the lithographic apparatus, a radiation beam B is conditioned and provided by an illumination system IL. The radiation beam B is incident on a patterning device (e.g., a mask) MA, which is held on a support structure (e.g., a mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF (e.g., an interferometer device, a linear encoder, a 2D encoder, or a capacitive sensor), the substrate table WT can be accurately moved, for example, to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (not explicitly shown in FIG. 1 ) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, for example after a mechanical search of 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. The patterning device MA and the substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks occupy dedicated target portions, the substrate alignment marks 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.

[0050]

[0058] The depicted apparatus can 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 the target portion C in one go (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 during 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 the 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-scan direction) of the target portion during a single dynamic exposure, while the length of the scanning motion determines the height (in the scan direction) of the target portion. In another mode, the support structure MT holds the programmable patterning device and is kept essentially stationary, while the substrate table WT is moved or scanned simultaneously with a pattern imparted to the radiation beam being projected onto the target portion C. In this mode, a pulsed radiation source is typically used, with the programmable patterning device being updated as required after each movement of the substrate table WT, or between successive pulses of radiation during a scan. This mode of operation is readily adaptable to maskless lithography employing a programmable patterning device such as a programmable mirror array of the type referred to above.

[0051]

[0059] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0052]

[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 tool or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Also, a substrate may be processed multiple times, for example to create a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0053]

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

[0054]

[0062] Various patterns on or provided by a patterning device may have different process windows, i.e., the space of processing variables under which the patterns are generated within specifications. Examples of pattern specifications related to potential systematic defects include checks for necking, line pullback, line thinning, CD, edge placement, overlap, resist top loss, resist undercut, and / or bridging. The process window of a patterning device or an area thereof may be obtained by merging (e.g., overlapping) the process windows of the individual patterns. The boundary of the process window of a group of patterns comprises the boundaries of the process windows of some of the individual patterns. In other words, these individual patterns define the process window of the group of patterns.

[0055]

[0063] As shown in FIG. 2, the lithography apparatus LA may form part of a lithographic cell LC, sometimes referred to as a lithocell or cluster, which also includes equipment for performing pre-exposure and post-exposure processes on a substrate. Conventionally, this includes one or more spin coaters SC for depositing one or more resist layers, one or more developers for developing exposed resist, one or more chill plates CH, and / or one or more bake plates BK. A substrate handler, or robot RO, retrieves one or more substrates from input / output ports I / O1, I / O2, moves them between various process tools, and delivers them to the loading bay LB of the lithography apparatus. These tools, often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. In this way, the various tools can be operated to maximize throughput and processing efficiency.

[0056]

[0064] To ensure that substrates exposed by a lithographic apparatus are accurately and consistently exposed, and / or to monitor portions of a 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 substrates or other objects to measure or determine one or more properties, such as alignment, overlay (e.g., between structures of overlying layers, or between structures in the same layer that are provided separately, e.g., by a double patterning process), line thickness, critical dimension (CD), focus offset, material properties, etc. Accordingly, a manufacturing facility in which a lithocell LC is located typically also includes a metrology system that measures some or all of the substrates W ( FIG. 1 ) processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithographic apparatus LA, for example, as an alignment sensor AS ( FIG. 1 ).

[0057]

[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 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. The measurements are often performed on one or more dedicated metrology targets provided on the substrate. Measurements can be performed after resist development but before etching, after etching, after deposition, and / or at other times.

[0058]

[0066] Various techniques exist for making measurements of structures formed in patterning processes, including the use of scanning electron microscopes, image-based metrology tools, and / or various specialized tools. One rapid, 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. Conventionally, this can be referred to as diffraction-based metrology. Applications of this diffraction-based metrology include measuring overlay, alignment, etc. For example, overlay and / or alignment can be measured by comparing portions of the diffraction spectra (e.g., comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0059]

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

[0060]

[0068] Metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, adjustments may be made to the exposure of a subsequent substrate and / or to subsequent exposures of an exposed substrate (especially if inspection can be performed soon enough and quickly enough that one or more other substrates of the same batch can still be exposed). Also, already exposed substrates may be removed and reprocessed to improve yield, or discarded, thereby avoiding further processing of substrates known to be defective. If only some target portions of a substrate are defective, further exposures may be performed only on those target portions that meet specifications. Other manufacturing process adjustments are also possible.

[0061]

[0069] A metrology system may be used to determine one or more properties of a substrate structure, and in particular how one or more properties vary between different substrate structures or between different layers of the same substrate structure. The metrology system may be integrated into the lithographic apparatus LA or lithocell LC, or may be a stand-alone device.

[0062]

[0070] To enable metrology, one or more targets are often specially provided on the substrate. Typically, the target is specially designed and may include a periodic structure. For example, the target on the substrate may include one or more 1D periodic structures (e.g., geometric features such as gratings) that are printed such that, after development, the periodic structural features are formed of solid resist lines. As another example, the target may include one or more 2D periodic structures (e.g., gratings) that 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).

[0063]

[0071] FIG. 3 illustrates an exemplary metrology (inspection) system 10 that may be used to detect overlay, alignment, and / or perform other metrology operations. It includes a radiation or illumination source 2 that projects or otherwise illuminates radiation onto a substrate W (which may, for example, typically include metrology marks). The redirected radiation is passed to a sensor 4, such as a spectrometer detector and / or other sensor that measures the spectrum (intensity as a function of wavelength) of the specularly reflected and / or diffracted radiation, as shown in the left graph of FIG. 4. The sensor may generate metrology signals that convey metrology data characteristic 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.

[0064]

[0072] Similar to the lithographic apparatus LA of FIG. 1, one or more substrate tables (not shown in FIG. 3 or FIG. 4) may be provided to hold the substrate W during measurement operations. The one or more substrate tables may be similar in configuration to or identical to the substrate table WT (WTa and / or WTb) of FIG. 1. In examples where the 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 relative to the measurement optical system. For example, various sensors and actuators are provided to acquire the position of a target portion of interest of the structure (e.g., a metrology mark) and move it into position under the objective lens. Typically, many measurements will be made of the target portion of the structure at various locations across the substrate W. The substrate support can be moved in the X and Y directions to acquire various targets, and in the Z direction to obtain the desired location of the target portion relative to the focus of the optical system. For example, it is convenient to consider and describe operation as if the objective lens were brought to a different location relative to the substrate, when in fact the optical system remains substantially stationary (typically in the X and Y directions, but possibly also in the Z direction) and the substrate moves. Provided the relative positions of the substrate and the optical system are correct, it does not matter in principle which of them is moving, or whether both are moving, or a combination of part of the optical system moving (e.g. in the Z direction and / or tilt direction) and the substrate moving (e.g. in the X and Y directions, but optionally also in the Z direction and / or tilt direction) while the rest of the optical system is stationary.

[0065]

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

[0066]

[0074] The bars, pillars, vias, and / or other features may be etched into or on a substrate (e.g., in one or more layers on the substrate), may be deposited on a substrate, may be covered by a deposited layer, and / or may have other properties. Targets 30 (e.g., bars, pillars, vias, etc.) are sensitive to processing variations in the patterning process (e.g., optical aberrations, focus changes, dose changes, etc. in a lithographic projection apparatus such as a projection system), and as a result, process variations manifest as fluctuations in target 30. Accordingly, measurement data from target 30 can be used to determine and / or serve as a basis for making adjustments to one or more of the manufacturing processes.

[0067]

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

[0068]

[0076] FIG. 5 shows a plan view of a typical target 30 (e.g., a metrology mark) and the extent of a typical emitted illumination spot S in the system of FIG. 3. To obtain a diffraction spectrum free of interference from surrounding structures, the target 30 is typically a periodic structure (e.g., a grating) that is larger than the width (e.g., diameter) of the illumination spot S in one embodiment. The width of the spot S may be smaller than the width and length of the target. In other words, the target is "underfilled" by the illumination, and the diffraction signal is essentially free of any signal from product features outside the target itself. The illumination array may be configured to provide uniform-intensity illumination across the back focal plane of the objective, for example. Alternatively, illumination may be provided from both on-axis and off-axis directions, for example, by including a spot size selector in the illumination path.

[0069]

[0077] As mentioned above, ensuring accurate metrology mark position determination often requires determining wavefront aberrations of incident radiation. Figure 6 shows a system 600 configured to determine wavefront aberrations of radiation at on-axis and off-axis locations within an optical field. System 600 may be the same as or similar to system 10 described above with respect to Figure 3, with one or more components of system 600 being similar and / or the same as one or more components of system 10 (and Figure 6 shows some possible additional components of the system). In some embodiments, one or more components of system 600 may replace, be used in conjunction with, and / or otherwise augment one or more components of system 10. System 600 includes a radiation source 612 (e.g., similar and / or the same as radiation source 2 shown in FIG. 3), an opaque body 601 having transmissive regions at multiple different locations related to on-axis and off-axis positions, an illumination mode selector 607, a sensor 604 (e.g., similar 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 and / or the same as processor PRO shown in FIG. 3), and various lenses, beam splitters, and / or other components. The one or more processors PRO are operatively connected to sensor 604 and / or other components of system 600.

[0070]

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

[0071]

[0079] 6 also shows a target 30, which may comprise one or more metrology marks, such as, for example, a diffraction grating target formed in a substrate 602, such as a semiconductor wafer, collectively referred to as target 30. The target 30 may comprise one or more structures in a patterned substrate capable of providing a diffraction signal. One or more targets 30 may be included in a layer of a substrate, for example, in a semiconductor device structure. In some embodiments, the features comprise geometric features, such as 1D or 2D features, and / or other geometric features. As some non-limiting examples, the features may comprise gratings, lines, edges, a series of fine-pitch lines and / or edges, and / or other features.

[0072]

[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, to obtain an image of metrology target 30, and / or for other applications. 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, target intensity, etc. may be input 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 suitable for interferometry.

[0073]

[0081] The system 600 includes an optical component 605 configured to receive radiation reflected from the target 30 and the substrate 602, change the angle of the radiation, and direct the radiation toward a sensor 604. In some embodiments, the optical component 605 includes a wedge and / or other optical components. In some embodiments, the optical component 605 includes a micro-diffraction-based overlay wedge. The wedge may include, for example, quadrants. Each quadrant is configured to direct a portion of the radiation to a different region of interest on the sensor 604 to form a spot of radiation on the sensor 604. The spots of radiation may include, for example, two spots of radiation associated with zeroth-order diffracted radiation from the target 30 on the substrate and two spots of radiation associated with first-order diffracted radiation from the target 30. The radiation from the optical component 605 (e.g., the wedge) is received by the 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 images) 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 sensor. In some embodiments, sensor 604 comprises a micro-diffraction-based overlay camera associated with overlay measurements. In some embodiments, optical component 605 comprises a micro-diffraction-based overlay wedge configured to direct radiation from substrate 602 to the micro-diffraction-based overlay camera (sensor 604).

[0074]

[0082] The illumination mode selector 607 is positioned in a pupil plane of the system 600. The illumination mode selector 607 is configured to receive radiation from the radiation source 612 and the opaque body 601 and transmit a portion of the radiation through a transparent portion of at least one multi-aperture pattern of the illumination mode selector towards the target 30. For example, each transparent portion of the multi-aperture pattern may confine the radiation propagating therethrough to, for example, a corresponding single quadrant of the component 605. The illumination mode selector 607 may help to change the shape of the beam at all pupil conjugates (including 605) and thus help to separate the 0th and + / -1st order beams in the optical component 605.

[0075]

[0083] The alignment branch 680 is configured to receive the reflected radiation and generate an alignment signal (e.g., as described above in connection with Figures 3-5), which may include generating and / or analyzing one or more images of the target 30 using the radiation as described herein. The focus branch 650 is configured to determine the focus position of the objective lens 690.

[0076]

[0084] Various lenses (an exemplary 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 produced by the illumination source 612, transmitted or reflected by the opaque body 601 and / or optical components 605, focused by the focusing branch 650, received by the detection branch 660, received by the alignment branch 680, and / or used by other portions of the 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 enable the system 600 to function as described. For example, the objective lens 690 may be formed from any transparent material and may have a curved surface configured to concentrate or otherwise focus one or more spots of radiation onto one or more targets 30. The various lenses, reflectors, optical elements, beam splitters, and other optical elements may be positioned at any location and / or angle relative to one another that enables 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 one another in system 600 via structural members, clips, clamps, screws, nuts, bolts, adhesives, and / or other mechanical devices. In some embodiments, various of the lenses, reflectors, optical elements, beam splitters, and other optical elements are movable relative to one another. The movement may be configured, for example, to adjust the location of corresponding spots of illumination on one or more targets 30. In some embodiments, the movement comprises tilting, translating, or otherwise changing the distance between the various lenses, reflectors, and other optical components. Other examples of movement are also contemplated.

[0077]

[0085] In some embodiments, movement may be controlled electronically by a processor, such as processor PRO. Processor PRO may be included in computing system CS (FIG. 9) and may operate based on computer- or machine-readable instructions (e.g., as described below in connection with FIG. 9). Electronic communication may occur by transmitting electronic signals between different components, transmitting data between different components of system 600, transmitting values ​​between different components, and / or other communications. Components of system 600 may communicate wired or wirelessly over a network, such as the Internet, or a local area network, a cellular network, or a personal area network, the Internet in combination with an internal organizational network, and / or other network.

[0078]

[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 more components of system 600 by adhesives, clips, clamps, screws, collars, and / or other mechanisms. The actuators may be configured to be electronically controlled. Individual actuators may be configured to convert electrical signals into mechanical displacements. The mechanical displacements are configured to move components 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.

[0079]

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

[0080]

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

[0081]

[0089] Radiation 720 is received by and passes through opaque body 601. The radiation may be generated by a radiation source similar and / or the same as radiation source 2 shown in FIG. 3 and radiation source 612 shown in FIG. 6, and / or by other radiation sources. Opaque body 601 has transmissive regions 750 positioned within an optical field associated with radiation 720. Opaque body 601 includes transmissive regions 750 at multiple different locations associated with on-axis and off-axis positions. For example, in FIG. 7, one transmissive region 750 is shown as a dark spot inside square region 751 corresponding to an on-axis position, while other dark spots (other transmissive regions 750) correspond to different off-axis positions. While the example shown in FIG. 7 shows radiation 720 passing through one particular transmissive region 751, it should be understood that radiation also passes through other (on-axis and / or off-axis) transmissive regions 750 within opaque body 601, all being transmitted simultaneously toward sensor 604. The opaque body 601 may be, for example, a spot size selector and / or another opaque body. The spot size selector defines the size and shape of the area to be illuminated on the substrate 602 (FIG. 6). This area may be smaller or larger than the size of the illuminated target 30.

[0082]

[0090] The illumination mode selector 607 is positioned in a pupil plane of the metrology system 600 such that radiation 720 passing through the transmissive region 750 is received by the illumination mode selector 607. The illumination mode selector 607 may have a selectable aperture. The illumination mode selector 607 is configured, for example, to receive radiation 720 from a radiation source (not shown in FIG. 7 ) through the transmissive region 750 of the opaque body 601 and transmit a portion of the radiation 720 through a selected aperture toward a grating target 30 on the substrate. Diffracted radiation from the grating target 30 is directed back toward the sensor 604. The grating target may be, for example, an overlay target and / or other target as described above. The primary function of the illumination mode selector 607 is to form some portion of the radiation 720 that is not blocked by any components positioned after the illumination mode selector 607. The illumination mode selector 607 has a plurality of selectable apertures configured to vary the shape and diffraction orders of the radiation beam 720 at all pupil conjugates and thus separate the +1st and -1st orders from the 0th order radiation in the uDBO wedge (e.g., optical component 605).

[0083]

[0091] The optical component 605 is configured to receive radiation from each transparent region 750 (e.g., after passing through the illumination mode selector 607 and reflecting off the target 30) and to direct a portion of the radiation 720 received from each transparent region 750 to a different area of ​​the sensor 604 to form multiple spots 708, 710 (plus two more spots in three dimensions) of radiation 720 on the sensor 604 for each transparent region 750. The sensor 604 is configured to generate multiple corresponding images 760 for the radiation 720 passing through each transparent region 750. The optical component 605 may comprise, for example, a wedge and / or other optical components. The wedge may have quadrants, each configured to direct a portion of the radiation 720 received through a transparent region 750 to a different area of ​​the sensor 604 to form spots 708, 710, etc. of radiation 720 on the sensor 604. The spots 708, 710 etc. of radiation 720 may comprise two spots of radiation associated with zeroth order diffracted radiation from the substrate, two spots of radiation associated with first order diffracted radiation from the substrate, and / or other radiation.

[0084]

[0092] Radiation 720 passing through the transmissive region 750, passing through the illumination mode selector 607, reflected from the target 30, such as a diffraction grating, and transmitted through the optical component 605 is received by the sensor 604. The sensor 604 is configured to generate an image 760 for on-axis and off-axis locations based on the received radiation 720. In some embodiments, the image 760 comprises an image of the opaque transmissive region 750 produced by the sensor 604. The image 760 may also comprise a specular reflection and / or diffraction image for wavefront sensing, which improves the accuracy of the wavefront sensing described herein. In some embodiments, the image 760 may be, for example, a point spread function (PSF) image and / or other image. As shown in FIG. 7 , each image 760 may include four images of four different spots 709, 711, 713, and 715 of radiation 720 (e.g., four images per transmissive region 750, rather than just one as in conventional systems).

[0085]

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

[0086]

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

[0087]

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

[0088]

[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 a mathematical equation, an algorithm, a plot, a chart, a network (e.g., a neural network), 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 a deep neural network (e.g., a neural network having one or more intermediate or hidden layers between the input layer and the output layer).

[0089]

[0097] As an example, 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 roughly mimic the way 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 to many other neural units of the neural network. Such connections may be constraining or inhibitory in terms of their influence on the activation states of the connected neural units. In some embodiments, each individual neural unit may have a summation function that adds together the values ​​of all of its inputs. In some embodiments, each connection (or the neural unit itself) may have a threshold function, whereby a signal must exceed that threshold before being allowed to propagate to other neural units. These neural network systems may be self-learning or trained rather than explicitly programmed, and may perform significantly better in certain areas of problem solving compared to traditional computer programs. In some embodiments, one or more neural networks may include multiple layers (e.g., signal paths traverse from previous layers to subsequent layers). In some embodiments, a backpropagation technique may be utilized by a neural network, in which a forward stimulus is used to reset weights for a "previous" neural unit. In some embodiments, the stimuli and inhibitions for one or more neural networks may flow more freely, with connections interacting in a more chaotic and complex manner. In some embodiments, the intermediate layers of one or more neural networks include one or more convolutional layers, one or more recurrent layers, and / or other layers.

[0090]

[0098] One or more neural networks may be trained (i.e., their parameters may be 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, sometimes called a feature vector) and a desired output value (also called a supervisory signal). A training algorithm analyzes the training information and adjusts the behavior of the neural network by adjusting the parameters of the neural network (e.g., the weights of one or more layers) based on the training data and / or other information. For example, x i is the feature vector of the i-th example, and y i is its monitoring signal. N ,y N Given a set of N training samples of the form {\displaystyle \mathbb {N}}, the training algorithm searches for 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 can be used to make predictions using new samples (e.g., new PSF images).

[0091]

[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, the empirical (simulation) model is a physical model comprising one or more algorithms with terms that collectively simulate physical behavior such as reflected radiation.

[0092]

[0100] FIG. 8 illustrates a metrology method 800 for determining wavefront aberrations of radiation at on-axis and off-axis locations within an optical field. In some embodiments, method 800 is performed, for example, as part of an overlay and / or alignment sensing operation in a semiconductor device manufacturing process. In some embodiments, one or more operations of method 800 may be implemented in or by, for example, system 600 shown in FIGS. 6 and 7 , system 10 shown in FIG. 3 , a computer system (e.g., as shown in FIG. 9 and described below), and / or other systems. In some embodiments, method 800 comprises receiving and passing radiation through an opaque body having a transmissive region positioned within the optical field (operation 802); receiving the radiation that has passed through the transmissive region and generating images for the on-axis and off-axis locations based on the received radiation (operation 804); and determining wavefront aberrations of the radiation at the on-axis and off-axis locations within the optical field using the trained algorithm and the images (operation 806). 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 described. For example, in some embodiments, method 800 may include an additional operation comprising determining adjustments for a semiconductor device manufacturing process. Also, the order of operations of method 800 shown in FIG. 8 and described herein is not intended to be limiting.

[0093]

[0101] 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., digital processors, analog processors, digital circuits designed to process information, analog circuits designed to process information, state machines, and / or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices that perform some or all of the operations of method 800 in response to instructions electronically stored 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 to perform one or more of the operations of method 800 (see, e.g., the discussion related to FIG. 9 below).

[0094]

[0102] In operation 802, radiation is received by and passes through an opaque body having transmissive regions positioned within the optical field. The opaque body has transmissive regions at multiple different locations related to on-axis and off-axis locations. The opaque body may be, for example, a spot size selector and / or another opaque body. In some embodiments, the opaque body is the same as or similar to the opaque body 601 shown in Figures 6 and 7 and described above.

[0095]

[0103] The radiation may be generated by a radiation source similar to and / or the same as radiation source 2 shown in Figure 3 and radiation source 612 shown in Figure 6, and / or by other radiation sources. Operation 802 may include generating radiation using a radiation source and one or more lenses (e.g., as described below) and directing the radiation toward the opaque body, the substrate, and / or the sensor.

[0096]

[0104] In some embodiments, operation 802 comprises positioning an illumination mode selector in a pupil plane of the metrology system such that radiation passing through the transmissive region is received by the illumination mode selector. The illumination mode selector may have a selectable aperture. The illumination mode selector is configured to receive radiation from a radiation source through the transmissive region of the opaque body and transmit a portion of the radiation through a selected aperture toward a grating target on the substrate. Diffracted radiation from the grating target is directed back toward a sensor. The grating target may be, for example, an overlay target and / or another target.

[0097]

[0105] In operation 804, radiation passing through the transmissive region, passing through the illumination mode selector, and reflected from a target, such as a diffraction grating, is received by a sensor. The sensor is configured to generate images for on-axis and off-axis locations based on the received radiation. In some embodiments, the images comprise images of the opaque body transmissive region produced by the sensor. The images may be, for example, point spread function (PSF) images 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, for example, a micro-diffraction-based overlay camera associated with overlay measurements. In some embodiments, operation 804 is performed by a sensor the same as or similar to detector 4 shown in FIG. 3 and sensor 603 shown in FIGS. 6 and 7 and described above.

[0098]

[0106] In some embodiments, operation 804 includes receiving radiation from each transparent region (e.g., after reflection from a target) using an optical component and directing a portion of the received radiation from each transparent region to a different area of ​​a sensor using the optical component to form multiple spots of radiation on the sensor for each transparent region. The sensor is configured to generate multiple corresponding images for radiation passing through each transparent region. The optical component may comprise, for example, a wedge and / or other optical component (e.g., optical component 605 described above). The wedge may comprise quadrants, each configured to direct a portion of the radiation received through the transparent region to a different area of ​​the sensor to form a spot of radiation on the sensor. The spots of radiation may comprise two spots of radiation associated with zeroth-order diffracted radiation from the substrate, two spots of radiation associated with first-order diffracted radiation from the substrate, and / or other radiation. The substrate may be, for example, a semiconductor wafer and / or other substrate.

[0099]

[0107] In operation 806, the trained algorithm and the images are used by one or more processors operatively connected to the sensor to determine wavefront aberrations of the radiation at on-axis and off-axis locations within the optical field. In some embodiments, the one or more processors are configured to simultaneously determine wavefront aberrations of the radiation at on-axis and off-axis locations within the optical field. In some embodiments, the one or more processors are configured to use the trained algorithm to determine wavefront aberrations based on multiple corresponding images (e.g., generated based on different portions of the radiation directed to different areas of the sensor using a wedge). The one or more processors may be configured to use the trained algorithm to output an indication of the wavefront aberrations based on the intensity of spots of radiation in the images. In some embodiments, determining the wavefront aberrations comprises predicting Zernike coefficients of the radiation at on-axis and off-axis locations within the optical field.

[0100]

[0108] In some embodiments, the trained algorithm is trained by obtaining and providing to the algorithm prior images associated with aberrations. For example, a portion of the prior images associated with aberrations may be labeled as aberrations. In some embodiments, the trained algorithm comprises a trained machine learning model, a neural network, and / or other components.

[0101]

[0109] 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 within the sensor, a stage holding the substrate with the target, and / or other aspects of the metrology system and / or metrology operation to reduce and / or eliminate wavefront aberrations of the radiation at on-axis and off-axis locations within the optical field. In some embodiments, operation 806 is performed by one or more processors the same as or similar to the processor PRO shown in Figures 3 and 6 and described above (together with processor PRO shown in Figure 9 and described below).

[0102]

[0110] In some embodiments, method 800 is configured for use with semiconductor wafers and 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.

[0103]

[0111] In some embodiments, method 800 comprises detecting reflected radiation from one or more diffraction grating targets. Detecting the reflected radiation comprises detecting one or more phase and / or amplitude (intensity) shifts in the reflected radiation from one or more geometric features of the one or more targets. The one or more phase and / or amplitude shifts correspond to one or more dimensions of the target. For example, the phase and / or amplitude of the reflected radiation from one side of a target is different from the phase and / or amplitude of the reflected radiation from another side of the target.

[0104]

[0112] Detecting one or more phase and / or amplitude (intensity) shifts in reflected radiation from a target comprises measuring local phase shifts (e.g., local phase delta) and / or amplitude variations corresponding to different portions of the target. For example, reflected radiation from a particular area of ​​the target may comprise a sinusoidal waveform having a particular phase and / or amplitude. Reflected radiation from different areas of the target (or targets on different layers) may also comprise a sinusoidal waveform, but with different phases and / or amplitudes. Detecting the reflected radiation may also comprise measuring phase and / or amplitude differences in different diffraction orders of reflected radiation. Detecting one or more local phase and / or amplitude shifts may be performed using, for example, a Hilbert transform and / or other techniques. Interferometry techniques and / or other operations may be used to measure phase and / or amplitude differences in different diffraction orders of reflected radiation.

[0105]

[0113] In some embodiments, method 800 comprises generating a metrology signal based on detected reflected radiation from one or more diffraction grating targets, as described above. The metrology signal is generated by a sensor (such as detector 4 in FIG. 3 , sensor 603 in FIGS. 6 and 7 , and / or other sensors) based on radiation received by the sensor. The metrology signal comprises measurement information about the one or more targets. 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., overlay values, alignment values, and / or other information) may be determined using principles of interferometry and / or other principles.

[0106]

[0114] The metrology signal comprises an electronic signal representative of and / or otherwise corresponding to radiation reflected from one or more targets. The metrology signal may indicate, for example, metrology values ​​and / or other information associated with a diffraction grating target. Generating the metrology signal comprises detecting the reflected radiation and converting the detected reflected radiation into an electronic signal. In some embodiments, generating the metrology signal comprises detecting different portions of the reflected radiation from different areas and / or different geometries of the target and / or from 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 the target using the radiation described herein. This detecting and converting may be performed by components similar to and / or the same as the detector 4, sensor 603, and / or processor PRO shown in FIGS. 3, 6, and 9 (described below), and / or other components.

[0107]

[0115] In some embodiments, method 800 comprises determining adjustments 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, overlay and / or alignment values ​​indicated by metrology signals, and / or other similar systems and / or other information. The one or more parameters may include parameters of the radiation (radiation used for metrology), overlay values, alignment values, locations of metrology inspections on layers of semiconductor device structures, radiation beam trajectories across targets, and / or other parameters. In some embodiments, the process parameters may be broadly interpreted to include stage position, mask design, metrology target design, semiconductor device design, intensity of radiation (e.g., used to expose resist), angle of incidence of radiation (e.g., used to expose resist), wavelength of radiation (e.g., used to expose resist), pupil size and / or shape, resist material, and / or other parameters.

[0108]

[0116] In some embodiments, method 800 includes determining process adjustments based on the one or more determined semiconductor device manufacturing process parameters, adjusting semiconductor device manufacturing equipment based on the determined adjustments, and / or other operations. For example, if the determined metrology measurements are not within process tolerances, the out-of-tolerance measurements may be caused by one or more manufacturing process parameters drifting and / or otherwise changing, such that the process no longer produces acceptable devices (e.g., the measurements may breach a threshold of acceptability). One or more new or adjusted process parameters may be determined based on the determination of the measurements. The new or adjusted process parameters may be configured to cause the manufacturing process to again produce acceptable devices.

[0109]

[0117] For example, new or adjusted process parameters may cause a previously unacceptable measurement 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 are differences, the differences may be used, for example, to determine adjustments to equipment used to produce the device (e.g., parameter "x" should be increased / decreased / changed to match the new or adjusted version of parameter "x" determined as part of method 800). In some embodiments, method 800 may include electronically adjusting the equipment (e.g., based on the determined process parameters). Electronically adjusting the equipment may include, for example, sending an electronic signal and / or other communication to the equipment, which causes a change in the equipment. The electronic adjustment may include, for example, changing settings and / or other adjustments to the equipment.

[0110]

[0118] 9 is a diagram of an exemplary computer system CS that may be used for one or more of the operations described herein. The computer system CS includes a bus BS or other communication mechanism for communicating information and a processor PRO (or multiple processors similar and / or identical to the processor PRO shown in FIG. 3) coupled to the bus BS for processing information. The computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus BS for storing information and instructions to be executed by the processor PRO. The main memory MM may also be used to store temporary variables or other intermediate information during execution of instructions by the processor PRO. The computer system CS further includes a read-only memory (ROM) or other static storage device coupled to the bus BS for storing static information and instructions for the processor PRO. A storage device SD, such as a magnetic or optical disk, for storing information and instructions is provided and coupled to the bus BS.

[0111]

[0119] The computer system CS may be coupled via a 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. Input devices ID, including alphanumeric and other keys, are coupled to the bus BS for communicating information and command selections to the processor PRO. Another type of user input device is a cursor control CC, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor PRO and for controlling cursor movement on the 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), which allows the device to specify a position in a plane. A touch-panel (screen) display may also be used as an input device.

[0112]

[0120] 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 stored 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 contained in main memory MM causes processor PRO to perform the process steps (operations) described herein. One or more processors in a multiprocessing arrangement may be employed to execute the sequences of instructions stored in main memory MM. In some embodiments, hardwired 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.

[0113]

[0121] As used herein, the terms "computer-readable medium" or "machine-readable medium" refer to any medium that participates in providing instructions to a processor PRO for execution. Such media 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 a storage device SD. Volatile media include dynamic memory, such as a main memory MM. Transmission media include coaxial cables, copper wire, and optical fibers, including the wires that comprise a bus BS. Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. The computer-readable medium may be non-transitory, such as a floppy disk, a flexible disk, a hard disk, magnetic tape, any other magnetic medium, a CD-ROM, a DVD, any other optical medium, a punched card, paper tape, any other physical medium with a pattern of holes, a RAM, a PROM, an EPROM, a FLASH-EPROM, or any other memory chip or cartridge. Non-transitory computer-readable media may have instructions recorded on them. The instructions, when executed by a computer, may implement any of the operations described herein. The transitory computer-readable medium may include, for example, a carrier wave or other propagating electromagnetic signal.

[0114]

[0122] 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 reside on a magnetic disk of a remote computer. The remote computer may 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 may receive the data on the telephone line and convert the data to an infrared signal using an infrared transmitter. An infrared detector coupled to bus BS may 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.

[0115]

[0123] The computer system CS may also include a communications interface CI coupled to the bus BS. The communications interface CI provides a two-way data communication coupling to a network link NDL, which is connected to a local network LAN. For example, the communications interface CI may be an Integrated Services Digital Network (ISDN) card or a modem for providing a data communication connection to a corresponding type of telephone line. As another example, the communications interface CI may be a LAN card for providing a data communication connection to a compatible local area network (LAN). A wireless link may also be implemented. In any such implementation, the communications interface CI sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

[0116]

[0124] The network link NDL provides data communication to other data devices, typically through one or more networks. For example, the network link NDL may provide a connection to a host computer HC through a local network LAN. This may include data communication services provided through the worldwide packet data communication network now commonly referred to as the "Internet" INT. The 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 the network data link NDL and through the communication interface CI that carry digital data to and from the computer system CS are exemplary forms of carrier waves conveying information.

[0117]

[0125] The computer system CS can send messages and receive data, including program code, through one or more networks, the network data link NDL, and the communication interface CI. In the Internet example, a host computer HC may transmit requested code for an application program through the Internet INT, the network data link NDL, the local network LAN, and the communication interface CI. One such downloaded application may, for example, provide all or part of the methods described herein. The received code may be executed by the processor PRO upon receipt and / or stored in the storage device SD or other non-volatile storage device for later execution. In this manner, the computer system CS may obtain application code in the form of a carrier wave.

[0118]

[0126] Various embodiments of the systems and methods of the present invention are disclosed in the following numbered clause list. Further features, characteristics, and exemplary technical solutions of the present disclosure are described below with respect to clauses that may optionally be claimed in any combination.

[0119] 1. A metrology system configured to determine wavefront aberrations of radiation at on-axis and off-axis locations within an optical field, the system comprising: an opaque body having transparent regions at a plurality of different locations related to the on-axis and off-axis locations, the opaque body positioned within the optical field and configured to receive radiation and pass it through the transparent regions; a sensor configured to receive radiation that has passed through the transparent regions and generate images for the on-axis and off-axis locations based on the received radiation; and one or more processors operably connected to the sensor, the one or more processors configured to use trained algorithms and the images to determine wavefront aberrations of the radiation at the on-axis and off-axis locations within the optical field. 2. The system of clause 1, wherein the opaque body is a spot size selector. 3. The system of any of clauses 1 to 2, wherein the image comprises an image of a transparent area of ​​an opaque medium produced by a sensor. 4. The system of any of clauses 1 to 3, wherein the image is a point spread function (PSF) image. 5. The system of any of clauses 1 to 4, wherein the sensor comprises a camera and / or a charge-coupled device (CCD) array. 6. The system of any of clauses 1 to 5, wherein the sensor comprises a micro-diffraction-based overlay camera associated with the overlay measurement. 7. The system of any of clauses 1 to 6, wherein the one or more processors are configured to simultaneously determine wavefront aberrations of the radiation at on-axis and off-axis locations within the optical field. 8. The system of any of clauses 1 to 7, further comprising an optical component configured to receive radiation from each transmissive region and direct a portion of the radiation received from each transmissive region to a different area of ​​the sensor to form multiple spots of system radiation on the sensor for each transmissive region, the sensor configured to generate multiple corresponding images for radiation passing through each transmissive region, and the one or more processors configured to use a trained algorithm to determine wavefront aberrations based on the multiple corresponding images. 9. The system of any of clauses 1 to 8, wherein the optical component comprises a wedge. 10. The system of any of clauses 1 to 9, wherein the wedge comprises quadrants, each quadrant configured to direct a portion of the radiation received through the transparent region to a different area of ​​the sensor to form a spot of radiation on the sensor. 11. The system of any of clauses 1 to 10, wherein the spots of radiation comprise two spots of radiation associated with zeroth order diffracted radiation from the substrate and two spots of radiation associated with first order diffracted radiation from the substrate. 12. The system of any of clauses 1 to 11, wherein the substrate is a semiconductor wafer. 13. The system of any of clauses 1 to 12, further comprising an illumination mode selector having a selectable aperture, the illumination mode selector positioned in a pupil plane of the system, the illumination mode selector configured to receive radiation from the radiation source and transmit a portion of the radiation through a selected aperture towards a diffraction grating target on the substrate, and wherein diffracted radiation from the diffraction grating target is directed back towards an optical component in the sensor. 14. The system of any of clauses 1 to 13, wherein determining the wavefront aberration comprises predicting Zernike coefficients of the radiation at on-axis and off-axis positions within the optical field. 15. The system of any of clauses 1 to 14, wherein the one or more processors are configured to output an indication of wavefront aberration based on the intensity of spots of radiation in the image using a trained algorithm. 16. The system of any of clauses 1 to 15, wherein the trained algorithm is trained by obtaining and providing to the algorithm previous images related to the aberration. 17. The system of any of clauses 1 to 16, wherein a portion of the previous image that is associated with an aberration is labeled as an aberration. 18. The system of any of clauses 1 to 17, 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 clauses 1 to 18, wherein the one or more processors are further configured to automatically adjust one or more characteristics of the radiation, a deformable mirror within the sensor, and / or a stage holding a substrate with a target to reduce and / or eliminate wavefront aberrations of the radiation at on-axis and off-axis positions within the optical field. 20. The system of any of clauses 1 to 19, wherein radiation passing through the transmissive region of the opaque body is directed towards a substrate, the substrate comprising a semiconductor wafer having one or more overlay targets configured to reflect radiation towards the sensor. 21. The system of any of clauses 1 to 20, further comprising a radiation source and one or more lenses configured to generate radiation and direct the radiation towards the opaque body, the substrate and / or the sensor. 22. The system of any of clauses 1 to 21, wherein the opaque body, the sensor, and the one or more processors are configured for overlay detection. 23. A metrology system is a system according to any of clauses 1 to 22 configured for semiconductor wafers and used in a semiconductor manufacturing process. 24. The system of any of clauses 1 to 23, wherein the trained algorithm comprises a trained machine learning model. 25. The system of any of clauses 1 to 24, wherein the trained machine learning model comprises a neural network. 26. A metrology method for determining wavefront aberrations of radiation at on-axis and off-axis locations within an optical field, the method comprising: receiving and passing radiation through an opaque body having transmissive regions positioned within the optical field, the opaque body having transmissive regions at a plurality of different locations related to the on-axis and off-axis locations; receiving the radiation that has passed through the transmissive regions using a sensor; generating images for the on-axis and off-axis locations based on the received radiation using the sensor; and determining, by one or more processors operatively connected to the sensor, the wavefront aberrations of the radiation at the on-axis and off-axis locations within the optical field using trained algorithms and the images. 27. The method of clause 26, wherein the opaque body is a spot size selector. 28. The method of any of clauses 26 to 27, wherein the image comprises an image of a region of opaque material transmitted by a sensor. 29. The method of any of clauses 26 to 28, wherein the image is a point spread function (PSF) image. 30. The method of any of clauses 26 to 29, wherein the sensor comprises a camera and / or a charge-coupled device (CCD) array. 31. The method of any of clauses 26 to 30, wherein the sensor comprises a micro-diffraction-based overlay camera associated with the overlay measurement. 32. The method of any of clauses 26 to 31, wherein the one or more processors are configured to simultaneously determine wavefront aberrations of the radiation at on-axis and off-axis locations within the optical field. 33. The method of any of clauses 26 to 32, further comprising: receiving radiation from each transmissive region using an optical component; and directing a portion of the received radiation from each transmissive region to a different area of ​​the sensor using the optical component to form a plurality of spots of system radiation on the sensor for each transmissive region; the sensor configured to generate a plurality of corresponding images for radiation passing through each transmissive region; and the one or more processors configured to use a trained algorithm to determine wavefront aberrations based on the plurality of corresponding images. 34. The method of any of clauses 26 to 33, wherein the optical component comprises a wedge. 35. The method of any of clauses 26 to 34, wherein the wedge comprises quadrants, each quadrant configured to direct a portion of the radiation received through the transparent region to a different area of ​​the sensor to form a spot of radiation on the sensor. 36. The method of any of clauses 26 to 35, wherein the spots of radiation comprise two spots of radiation associated with zeroth order diffracted radiation from the substrate and two spots of radiation associated with first order diffracted radiation from the substrate. 37. The method of any of clauses 26 to 36, wherein the substrate is a semiconductor wafer. 38. The method of any of clauses 26 to 37, further comprising positioning an illumination mode selector in a pupil plane of the metrology system, the illumination mode selector having a selectable aperture, the illumination mode selector configured to receive radiation from the radiation source and transmit a portion of the radiation through the selected aperture towards a diffraction grating target on the substrate, and wherein diffracted radiation from the diffraction grating target is directed back towards an optical component in the sensor. 39. The method of any of clauses 26 to 38, wherein determining the wavefront aberration comprises predicting Zernike coefficients of the radiation at on-axis and off-axis positions within the optical field. 40. The method of any of clauses 26 to 39, wherein the one or more processors are configured to output an indication of wavefront aberration based on the intensity of the spots of radiation in the image by a trained algorithm. 41. Any of the methods of clauses 26 to 40, wherein the trained algorithm is trained by obtaining and providing to the algorithm previous images related to the aberration. 42. The method of any of clauses 26 to 41, wherein a portion of the previous image that is associated with an aberration is labeled as an aberration. 43. The method of any of clauses 26 to 42, 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 clauses 26 to 43, wherein the one or more processors are further configured to automatically adjust one or more characteristics of the radiation, a deformable mirror within the sensor, and / or a stage holding a substrate with the target to reduce and / or eliminate wavefront aberrations of the radiation at on-axis and off-axis positions within the optical field. 45. The method of any of clauses 26 to 44, wherein radiation passing through the transmissive region of the opaque body is directed towards a substrate, the substrate comprising a semiconductor wafer having one or more overlay targets configured to reflect radiation towards the sensor. 46. ​​The method of any of clauses 26 to 45, further comprising using a radiation source and one or more lenses to generate radiation and direct the radiation towards the opaque body, the substrate, and / or the sensor. 47. The method of any of clauses 26 to 46, wherein the opaque body, the sensor, and the one or more processors are configured for overlay detection. 48. The method of any of clauses 26 to 47, wherein the method is configured for use with semiconductor wafers and is used in a semiconductor manufacturing process. 49. Any of the methods of clauses 26 to 48, wherein the trained algorithm comprises a trained machine learning model. 50. Any of the methods of clauses 26 to 49, wherein the trained machine learning model comprises a neural network.

[0120]

[0127] The concepts disclosed herein may be associated with any general-purpose imaging system for imaging subwavelength features and may be particularly useful with emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use include EUV (extreme ultraviolet), DUV lithography, which can produce wavelengths of 193 nm using ArF lasers and even 157 nm using fluorine lasers. EUV lithography can also produce wavelengths within this range by using synchrotrons or by bombarding materials (either solids or plasmas) with high-energy electrons to generate photons in the 20-5 nm range.

[0121]

[0128] Although the concepts disclosed herein may be used for imaging on substrates such as silicon wafers, it should be understood that the disclosed concepts may be used in any type of lithographic imaging system, for example, one used for imaging on substrates other than silicon wafers. Furthermore, combinations and subcombinations of the disclosed elements may comprise separate embodiments.

[0122]

[0129] The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to one skilled in the art that modifications can be made as described without departing from the scope of the claims below.

Claims

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

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

3. The system of claim 1 or 2, wherein the image comprises an image of an area of ​​opaque material transmitted by the sensor.

4. The system of claim 1 , wherein the image is a point spread function (PSF) image.

5. The system of claim 1 , 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 an overlay measurement.

7. The system of claim 1 , wherein the one or more processors are configured to simultaneously determine wavefront aberrations of radiation at on-axis and off-axis locations within the optical field.

8. an optical component configured to receive the radiation from each transparent region and direct a portion of the radiation received from each transparent region to a different area of ​​the sensor to form multiple spots of radiation on the sensor for each transparent region; the sensor is configured to generate a plurality of corresponding images for radiation passing through each transmissive region; The system of claim 1 , wherein the one or more processors are configured to use the trained algorithm to determine the wavefront aberrations based on the plurality of corresponding images.

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

10. the wedge comprises a quadrant; 10. The system of claim 9, wherein each quadrant is configured to direct a portion of the radiation received through a transmissive region to a different area of ​​the sensor to form a spot of the radiation on the sensor.

11. The system of claim 10 , wherein the spots of radiation comprise two spots of radiation associated with zeroth order diffracted radiation from the substrate and two spots of radiation associated with first order diffracted radiation from the substrate.

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

13. an illumination mode selector having a selectable aperture; 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 a portion of the radiation through a selected aperture toward a grating target on a substrate; 13. The system of claim 8, wherein diffracted radiation from the grating target is directed back towards the optical component within the sensor.

14. 14. The system of claim 1, wherein determining the wavefront aberrations comprises predicting Zernike coefficients of radiation at on-axis and off-axis positions within the optical field.

15. 15. The system of claim 1 , wherein the one or more processors are configured such that the trained algorithm outputs an indication of wavefront aberrations based on the intensity of spots of radiation in the image.

Images