WO2025078100A2

WO2025078100A2 - Wavefront measurement for multi core optical fiber in semiconductor metrology systems and methods

Info

Publication number: WO2025078100A2
Application number: PCT/EP2024/075578
Authority: WO
Inventors: Arjan Johannes Anton BEUKMAN; Sebastianus Adrianus GOORDEN; Sergei SOKOLOV
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2023-10-12
Filing date: 2024-09-12
Publication date: 2025-04-17
Anticipated expiration: 2026-04-12
Also published as: TW202540782A; WO2025078100A3

Abstract

Wavefront measurement for multi core optical fibers is described. A multi core optical fiber is configured to conduct radiation from a radiation source to a structure such as a metrology target in one or more layers of a patterned substrate, and diffracted and/or reflected radiation from the metrology target to a radiation sensor. The multi core optical fiber has a length configured to facilitate placement of the radiation source and/or the radiation sensor in a spaced location relative to the patterned substrate. Optical path length differences between a subset of cores in the multi core optical fiber with reflectors are determined for different wavelengths of radiation from the radiation source. The optical path length differences are determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores. The optical path length differences indicate wavefront distortion.

Description

WAVEFRONT MEASUREMENT FOR MULTI CORE OPTICAL FIBER IN SEMICONDUCTOR METROLOGY SYSTEMS AND METHODS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63/543,891 which was filed on October 12, 2023 and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] This description relates to wavefront measurement for multi core optical fibers in semiconductor metrology systems and methods.

BACKGROUND

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

[0004] Prior to transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures, such as priming, resist coating, and a soft bake. After exposure, the substrate may be subjected to other procedures (“post-exposure procedures”), such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the transferred pattern. This array of procedures is used as a basis to make an individual layer of a device, e.g., an IC. The substrate may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, deposition, chemo-mechanical polishing, etc., all intended to finish the individual layer of the device. If several layers are required in the device, then the whole procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present in each target portion on the substrate. These devices are then separated from one another by a technique such as dicing or sawing, such that the individual devices can be mounted on a carrier, connected to pins, etc. [0005] This device manufacturing process may be considered a patterning process. A patterning process involves a patterning step, such as optical and/or nanoimprint lithography using a patterning device in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, deposition, etc. Lithography is a central step in the manufacturing of device such as ICs, where patterns formed on substrates define functional elements of the devices, such as microprocessors, memory chips, etc. Similar lithographic techniques are also used in the formation of flat panel displays, micro-electro mechanical systems (MEMS) and other devices.

[0006] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements have continually been reduced while the number of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as “Moore’s law.” At the current state of technology, layers of devices are manufactured using lithographic projection apparatuses that project a design layout onto a substrate using illumination from a deep-ultraviolet illumination source, creating individual functional elements having dimensions well below 100 nm, i.e. less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source).

[0007] This process in which features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus are printed, is commonly known as low-ki lithography, according to the resolution formula CD = kjxk/NA, where I is the wavelength of radiation employed (currently in most cases 248nm or 193nm), NA is the numerical aperture of projection optics in the lithographic projection apparatus, CD is the “critical dimension”-generally the smallest feature size printed-and ki is an empirical resolution factor. In general, the smaller ki the more difficult it becomes to reproduce a pattern on the substrate that resembles the shape and dimensions planned by a designer in order to achieve particular electrical functionality and performance. To overcome these difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase shifting patterning devices, optical proximity correction (OPC, sometimes also referred to as “optical and process correction”) in the design layout, or other methods generally defined as “resolution enhancement techniques” (RET). Metrology is an integral part of these fine-tuning steps.

SUMMARY

[0008] Multi core optical fiber based metrology systems are susceptible to (dynamic) wavefront distortions during operation. In the present systems and methods, wavefront distortion in a multi core optical fiber is probed by measuring optical path lengths of a small number of the cores of the multi core optical fiber. As described below, a multi core optical fiber may be configured to conduct radiation from a radiation source to a structure such as a metrology target in one or more layers of a patterned substrate, and diffracted and/or reflected radiation from the metrology target to a radiation sensor. The multi core optical fiber has a length configured to facilitate placement of the radiation source and/or the radiation sensor in a spaced location relative to the patterned substrate. Optical path length differences between a subset of cores in the multi core optical fiber with reflectors (which in some embodiments simply comprise reflective air glass interfaces) are determined for different wavelengths of radiation from the radiation source. The optical path length differences are determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores. The optical path length differences indicate wavefront distortion. The wavefront distortion can be used to correct and/or prevent measurement error in multi core optical fiber based metrology systems and/or other systems.

[0009] According to an embodiment, a semiconductor metrology system is provided. The system comprises a radiation source configured to generate radiation comprising different wavelengths. The system comprises a multi core optical fiber, operatively coupled to the radiation source, configured to receive and conduct the radiation from the radiation source toward a structure in a layer of a patterned substrate. The multi core optical fiber has a length configured to facilitate placement of the radiation source in a spaced location relative to the patterned substrate. The system comprises reflectors coupled to a subset of cores of the multi core optical fiber at or near a substrate side end of the multi core optical fiber. The reflectors are configured to reflect the radiation from the radiation source back through the subset of cores. The system comprises a radiation sensor, operatively coupled to the multi core optical fiber and the radiation source. The radiation sensor is configured to determine optical path length differences between the subset of cores with the reflectors for the different wavelengths of radiation. The optical path length differences are determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores. The optical path length differences indicate wavefront distortion in the multi core optical fiber for the different wavelengths.

[0010] In some embodiments, the radiation sensor is configured to detect phase information of the reflected radiation, and determine the optical path length differences between cores for the different wavelengths of radiation based on the phase information. In some embodiments, the phase information comprises absolute phases for reflected radiation from different cores, relative phase differences for reflected radiation from different cores, and/or an interference pattern for reflected radiation from different cores.

[0011] In some embodiments, the radiation sensor comprises an interferometer, a photodiode, and/or a camera.

[0012] In some embodiments, the different wavelengths are associated with different channels.

[0013] In some embodiments, the radiation source is configured to sequentially generate radiation comprising different wavelengths such that optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined sequentially by the radiation sensor.

[0014] In some embodiments, the system comprises a multiplexer and a demultiplexer with dichroic beam splitters configured to cooperate with the radiation source to generate the radiation comprising different wavelengths in parallel such that the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined in parallel by the radiation sensor.

[0015] In some embodiments, the wavefront distortion in the multi core optical fiber is caused by bending of the multi core optical fiber, vibration of the multi core fiber, and/or dynamic temperature variation over the multi core fiber.

[0016] In some embodiments, the reflectors are evaporated onto their respective cores, comprise mirrors, comprise narrow band dielectric coatings configured to reflect only one or few of the wavelengths of radiation from the radiation source, and/or comprise an air glass interface.

[0017] In some embodiments, the reflectors comprise air glass interfaces and a coherence length of the reflected radiation is shorter than an extra optical path length associated with a second reflection such that only reflected radiation from the air glass interfaces contribute to a signal from the radiation sensor. In these embodiments, the reflection from an air/gas interface is a partial reflection, and the second reflection is from the patterned substrate such that the extra optical path length between the partial reflection and the second reflection is large enough to ensure that the second reflection does not interfere with the reflections from the air glass interfaces.

[0018] In some embodiments, the system comprises a stop configured to absorb remaining radiation such that no reflection is caused by other cores.

[0019] In some embodiments, the radiation sensor comprises a camera, and the reflected radiation forms a phase interference pattern on the camera configured to be used to determine the optical path length differences. The wavefront distortion in the multi core optical fiber is determined by fitting the phase of the interference pattern on the camera, and the phase is determined with respect to a center pixel of the camera.

[0020] In some embodiments, the reflectors are coupled to all cores of the multi core optical fiber at or near the substrate side end of the multi core optical fiber; and the radiation sensor is configured to determine optical path length differences for all of the cores based on reflected radiation that impinges on the radiation sensor after passing back through the cores.

[0021] In some embodiments, the radiation source is configured to generate spatially incoherent radiation.

[0022] In some embodiments, the radiation source comprises a laser.

[0023] In some embodiments, the radiation sensor comprises a camera, and radiation from the radiation source is coherent radiation through all cores or a large subset of cores, such that distortion in the multi core optical fiber presents as a displaced and/or distorted focus on the camera; a complex field of the focus is measured interferomically with an off axis reference beam; and by Fourier transforming an associated field, a phase in a pupil plane is obtained, which equals a path length change per fiber core.

[0024] In some embodiments, the system comprises a phase compensating element configured to correct a path length for each core. The phase compensating element is configured to be adjusted based on the optical path length differences.

[0025] In some embodiments, the length of the multi core optical fiber is up to about 0.1 meters, 0.25 meters, 0.5 meters, 1 meter, or 10 meters.

[0026] In some embodiments, the subset of cores comprises at least two cores. In some embodiments, the subset of cores comprises two cores, and the two cores are located on opposite outer edges of the multi core optical fiber such that radiation reflected through the two cores is configured to be used by the radiation sensor to determine a linear x or y tilt term of the wavefront distortion. In some embodiments, the subset of cores comprises four cores, and the four cores comprise pairs of cores located on opposite outer edges of the multi core optical fiber such that radiation reflected through the pairs of cores is configured to be used by the radiation sensor to determine linear x and y tilt terms of the wavefront distortion. In some embodiments, the linear x or y tilt term comprises alignment error for an alignment measurement made by the metrology system for the layer of the patterned substrate. [0027] In some embodiments, the structure comprises a metrology mark. The multi core optical fiber is configured to conduct the radiation from the radiation source to the structure, and diffracted radiation from the structure to the radiation sensor, through cores of the multi core optical fiber without reflectors. The radiation sensor is configured to generate a metrology signal based on diffracted radiation received from the structure through the cores of the multi core optical fiber without reflectors. [0028] In some embodiments, the system comprises one or more processors operatively coupled to the radiation source and the radiation sensor. The one or more processors are configured to determine an alignment of the layer based on the metrology signal and the alignment error. In some embodiments, the alignment is configured to be used by one or more processors to adjust a semiconductor device manufacturing process.

[0029] According to another embodiment, a metrology method is provided. The metrology method comprises one or more of the operations performed by the system(s) described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above aspects and other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

[0031] Fig. 1 schematically depicts a lithography apparatus, according to an embodiment.

[0032] Fig. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0033] Fig. 3 schematically depicts an example inspection system, according to an embodiment. [0034] Fig. 4 schematically depicts an example metrology technique, according to an embodiment. [0035] Fig. 5 illustrates the relationship between a radiation illumination spot of an inspection system and a metrology target, according to an embodiment.

[0036] Fig. 6 illustrates a metrology system configured to determine wavefront distortion in a multi core optical fiber used for metrology applications, according to an embodiment.

[0037] Fig. 7 illustrates end views of three different possible examples of multi core optical fibers, according to an embodiment.

[0038] Fig. 8 illustrates another example metrology system that utilizes a multi core optical fiber, according to an embodiment.

[0039] Fig. 9 illustrates a multi core optical fiber with reflectors configured to be used to measure optical path length differences between cores, and in turn wavefront distortion in the optical fiber, according to an embodiment.

[0040] Fig. 10 illustrates detecting phase information comprising relative phase differences for reflected radiation from different cores, and determining optical path length differences between cores for different wavelengths of radiation based on the relative phase differences, according to an embodiment.

[0041] Fig. 11 illustrates a metrology method for determining wavefront distortion in one or more multi core optical fibers, according to an embodiment.

[0042] Fig. 12 is a block diagram of an example computer system, according to an embodiment.

DETAILED DESCRIPTION

[0043] In semiconductor device manufacturing, metrology operations typically include determining an aligned position of a structure such as a metrology mark (or marks) and/or other structures in one or more layers of a semiconductor device structure (e.g., a patterned substrate). This alignment position is typically determined by irradiating a metrology mark with radiation, and comparing characteristics of different diffraction orders of radiation reflected from the metrology mark. Such techniques are also used to measure overlay and/or other parameters.

[0044] The present systems and methods utilize a multi core optical fiber configured to conduct radiation from a radiation source to a metrology mark and/or other structures, and conduct diffracted and/or reflected radiation back to a radiation sensor. The multi core optical fiber has a length configured to facilitate placement of a radiation source, the radiation sensor, actuated elements, processors, associated electronics, and/or other components of a metrology system in a spaced location relative to a patterned substrate. This provides increased functional space for other components of the metrology system to be located proximate to the patterned substrate, which may reduce or eliminate some of the engineering constraints for a system configured to measure increased numbers of marks, and/or have other advantages.

[0045] However, multi core optical fiber based systems are susceptible to (dynamic) wavefront distortions during operation. Wavefront distortion in a multi core fiber may be caused by bending of the multi core fiber, vibration of the multi core fiber, temperature variation over the multi core fiber, and/or may have other causes. For example, bending can occur if the radiation sensor is moving, which causes the multi core optical fiber to move. The multi core optical fiber may not be in the same position for each measurement in a series of measurements. Multi core optical fiber vibrations may also occur during movement, and/or may be caused by other functional elements of a metrology system. A multi core optical fiber may vary in temperature if a heat generating component of the metrology system is located nearby (e.g., a camera or a power source which produces heat). Varying temperature can also occur through heating by the small internal absorption of radiation passing through a multi core fiber. In alignment metrology systems (as one example application) a linear term of the wavefront distortion (e.g., tilt) is directly related to alignment error, and therefore should be measured and corrected.

[0046] Advantageously, the present systems and methods are configured to perform such measurements and corrections. In the present systems and methods, wavefront distortion in a multi core optical fiber is determined by measuring optical path lengths of a small number of the cores of the multi core optical fiber. Optical path length differences between a subset of cores in the multi core optical fiber are determined for different wavelengths of radiation from a radiation source. The optical path length differences indicate wavefront distortion. The wavefront distortion can be used to correct and/or prevent measurement error in multi core optical fiber based metrology systems and/or other systems.

[0047] By way of a brief introduction, the description below relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several components of systems and/or methods for semiconductor device metrology. These systems and methods may be used for measuring alignment, overlay, focus, dose, etc., in a semiconductor device manufacturing process, for example, or for other operations.

[0048] Although specific reference may be made to the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that the description has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle,” “wafer” or “die” in this text should be considered as interchangeable with the more general terms “mask,” “substrate” and “target portion,” respectively.

[0049] The term “projection optics” should be broadly interpreted as encompassing various types of optical systems, including refractive optics, reflective optics, apertures and catadioptric optics, for example. The term “projection optics” may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, collectively or singularly. The term “projection optics” may include any optical component in the lithographic projection apparatus, no matter where the optical component is located on an optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, adjusting and/or projecting radiation from the source before the radiation passes the patterning device, and/or optical components for shaping, adjusting and/or projecting the radiation after the radiation passes the patterning device. The projection optics generally exclude the source and the patterning device.

[0050] Fig. 1 schematically depicts an embodiment of a lithographic apparatus LA. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation, or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT (e.g., WTa, WTb or both) configured to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies and often referred to as fields) of the substrate W. The projection system is supported on a reference frame RF. In this example, the apparatus is transmissive (e.g. employs a transmissive mask). Alternatively, the apparatus may be reflective (e.g. employing a programmable mirror array, or employing a reflective mask).

[0051] The illuminator IL receives a beam of radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising for example suitable directing mirrors and/or a beam expander. In other cases, the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system or source.

[0052] The illuminator IL may alter the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non-zero within an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a plurality of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in a pupil plane of the illuminator IL may be referred to as an illumination mode.

[0053] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and/or inner radial extent (commonly referred to as o-outer and o-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane wherein the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator.

[0054] The illuminator IL may be operable to alter the polarization of the beam and may be operable to adjust the polarization using adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as a polarization mode. The use of different polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across a pupil plane of the illuminator IL. The polarization direction of radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen in dependence on the illumination mode. For multi-pole illumination modes, the polarization of each pole of the radiation beam may be generally perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, for a dipole illumination mode, the radiation may be linearly polarized in a direction that is substantially perpendicular to a line that bisects the two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as X-polarized and Y-polarized states. For a quadrupole illumination mode, the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as XY polarization. Similarly, for a hexapole illumination mode the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as TE polarization.

[0055] In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0056] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

[0057] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of the substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in a target portion of the device, such as an integrated circuit.

[0058] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.

[0059] The term “projection system” should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system.”

[0060] The projection system PS may comprise a plurality of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct for aberrations (phase variations across the pupil plane throughout the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system wherein its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and/or deform one or more optical elements. Displacement of an optical element may be in any direction (x, y, z, or a combination thereof). Tilting of an optical element is typically out of a plane perpendicular to the optical axis, by rotating about an axis in the x and/or y directions although a rotation about the z axis may be used for a non-rotationally symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and/or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and/or by using one or more heating elements to heat one or more selected regions of the optical element. In general, it may not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). The transmission map of a projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithography apparatus LA. Using a computational lithography technique, the patterning device MA may be designed to at least partially correct for apodization.

[0061] The lithographic apparatus may have two (dual stage) or more tables (e.g., two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system without a substrate that is dedicated to, for example, facilitating measurement, and/or cleaning, etc.). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be conducted on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and/or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0062] The lithographic apparatus may also be configured such that at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

[0063] In operation, a radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies. [0064] Lithography apparatus LA may be used in a step mode or a scan mode. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the abovedescribed modes of use or entirely different modes of use may also be employed.

[0065] The substrate may be processed, before or after exposure, in a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. In addition, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already includes multiple processed layers.

[0066] The terms “radiation” and “beam” used herein with respect to lithography encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0067] Various patterns on or provided by a patterning device may have different process windows. i.e., a space of processing variables under which a pattern will be produced within specification. Examples of pattern specifications that relate to potential systematic defects include checks for necking, line pull back, line thinning, CD, edge placement, overlapping, resist top loss, resist undercut and/or bridging. The process window of the patterns on a patterning device or an area thereof may be obtained by merging (e.g., overlapping) process windows of each individual pattern. The boundary of the process window of a group of patterns comprises boundaries of process windows of some of the individual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0068] As shown in Fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and/or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input/output port I/Ol, I/O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0069] To ensure that a substrate that is exposed by the lithographic apparatus is exposed correctly and consistently and/or in order to monitor a part of the patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties such as alignment, overlay (which can be, for example, between structures in overlying layers or between structures in a same layer that have been provided separately to the layer by, for example, a double patterning process), line thickness, critical dimension (CD), focus offset, a material property, a proper exposure dose, etc. Accordingly, a manufacturing facility in which lithocell LC is located also typically includes a metrology system that measures some or all of the substrates W (Fig. 1) that have been processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example it may be part of the lithographic apparatus LA (such as alignment sensor AS (Fig. 1)).

[0070] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. This measurement is often performed on one or more dedicated metrology targets provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and/or at other times.

[0071] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image -based measurement tool and/or various specialized tools. A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted/reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this may be termed diffraction-based metrology. Applications of this diffraction-based metrology include the measurement of alignment, overlay, etc. For example, alignment and/or overlay can be measured by comparing parts of the diffraction spectrum (for example, comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0072] In a device fabrication process (e.g., a patterning process or a lithography process), a substrate such as a wafer or other objects may be subjected to various types of measurement during or after the process. The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes. Examples of measurement include optical imaging (e.g., optical microscope), non-imaging optical measurement (e.g., measurement based on diffraction such as the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profiling using a stylus, atomic force microscopy (AFM)), and/or non-optical imaging (e.g., scanning electron microscopy (SEM)).

[0073] Metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, an adjustment may be made to exposure of a subsequent substrate (especially if the inspection can be done soon and fast enough that one or more other substrates of the batch are still to be exposed) and/or to subsequent exposure of the exposed substrate. Also, an already exposed substrate may be stripped and reworked to improve yield, or discarded, thereby avoiding performing further processing on a substrate known to be faulty. In a case where only some target portions of a substrate are faulty, further exposures may be performed only on those target portions which meet specifications. Other manufacturing process adjustments are contemplated.

[0074] A metrology system may be used to determine one or more properties of the substrate structure, and in particular, how one or more properties of different substrate structures vary, or different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or the lithocell LC, or may be a stand-alone device.

[0075] To enable the metrology, often one or more targets and/or other structures are specifically provided on the substrate. Typically, the structure (e.g., metrology target) is specially designed and may comprise a periodic structure. For example, the target on a substrate may comprise one or more 1- D periodic structures (e.g., geometric features such as gratings), which are printed such that after development, the periodic structural features are formed of solid resist lines. As another example, the target may comprise one or more 2-D periodic structures (e.g., gratings), which are printed such that after development, the one or more periodic structures are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0076] Fig. 3 depicts an example metrology system 10 that may be used to detect alignment, overlay, and/or perform other metrology operations. It comprises a radiation or illumination source 2 which projects or otherwise irradiates radiation toward and/or onto a substrate W (e.g., which may typically include a metrology mark). Redirected radiation is passed to a radiation sensor such as a spectrometer detector 4 and/or other sensors, which measures a spectrum (intensity as a function of wavelength) of the specular reflected and/or diffracted radiation, as shown, e.g., in the graph on the left of Fig. 4. The sensor may generate a metrology signal conveying metrology data indicative of properties of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in Fig. 4, or by other operations.

[0077] As in the lithographic apparatus LA in Fig. 1 , one or more substrate tables (not shown in Fig. 4) may be provided to hold the substrate W during measurement operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Fig. 1. In an example where system 10 is integrated with the lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest of a structure (e.g., a metrology mark), and to bring it into position under an objective lens. Typically, many measurements will be made on target portions of a structure at different locations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the target portion relative to the focus of the optical system. It is convenient to think and describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. Provided the relative position of the substrate and the optical system is correct, it does not matter in principle which one of those is moving, or if both are moving, or a combination of a part of the optical system is moving (e.g., in the Z and/or tilt direction) with the remainder of the optical system being stationary and the substrate is moving (e.g., in the X and Y directions, but also optionally in the Z and/or tilt direction).

[0078] For typical metrology measurements, a structure such as a target 30 on substrate W may be a 1-D grating, which is printed such that after development, the bars are formed of solid resist lines (e.g., which may be covered by a deposition layer), and/or other materials. Or the target 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and/or other features in the resist. [0079] The bars, pillars, vias, and/or other features may be etched into or on the substrate (e.g., into one or more layers on the substrate), deposited on a substrate, covered by a deposition layer, and/or have other properties. Target (portion) 30 (e.g., of bars, pillars, vias, etc.) is sensitive to changes in processing in the patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in target 30. Accordingly, the measured data from target 30 may be used to determine an adjustment for one or more of the manufacturing processes, and/or used as a basis for making the actual adjustment.

[0080] For example, the measured data from target 30 may indicate alignment for a layer of a semiconductor device. The measured data from target 30 may be used (e.g., by the one or more processors PRO and/or other processors) for determining one or more semiconductor device manufacturing process parameters based the overlay, and determining an adjustment for a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation, an incident angle of the radiation, a wavelength of the radiation, a pupil size and/or shape, a resist material, and/or other process parameters.

[0081] Fig. 5 illustrates a plan view of a typical structure such as a metrology target (e.g., a metrology mark) 30, and the extent of a typical radiation illumination spot S in the system of Fig. 3. Typically, to obtain a diffraction spectrum that is free of interference from surrounding structures, the target 30, in an embodiment, is a periodic structure (e.g., grating) larger than the width (e.g., diameter) of the illumination spot S. The width of spot S may be smaller than the width and length of the target. The target, in other words, is ‘underfilled’ by the illumination, and the diffraction signal is essentially free from any signals from product features and the like outside the target itself. The illumination arrangement may be configured to provide illumination of a uniform intensity across a back focal plane of an objective, for example. Alternatively, by, for example, including an aperture in the illumination path, illumination may be restricted to on axis or off axis directions.

[0082] Fig. 6 illustrates a metrology system 600 configured to determine wavefront distortion in a multi core optical fiber 602 used for metrology applications. System 600 may be similar to and/or the same as system 10 described above with respect to Fig. 3. In some embodiments, one or more components of system 600 may be similar to and/or the same as one or more components of system 10. In some embodiments, one or more components of system 600 may replace, be used with, and/or otherwise augment one or more components of system 10. System 600 includes a radiation source 604, a radiation sensor 606, and/or other components.

[0083] Radiation source 604 (e.g., which is similar to and/or the same as source 2 in Fig. 3) is configured to irradiate a structure (e.g., such as a target 30 shown in Fig. 3) in one or more layers of a patterned substrate 608 with radiation 610. Radiation 610 may comprise different wavelengths. The different wavelengths may be associated with different channels of system 600, for example. Different colors of light can be split into different channels for different detectors, for example.

[0084] The radiation may be used to obtain measurements from such a structure, and/or for other uses. The radiation may comprise illumination such as visible light, infrared radiation, and/or other radiation. A structure may comprise one or more metrology targets and/or marks, such as diffraction grating targets, formed in a substrate such as a semiconductor wafer, for example, and/or other structures.

[0085] In some embodiments, the structure comprises an alignment metrology mark, a diffraction based overlay metrology mark including a first grating in an underlayer of the patterned substrate, and a second grating in an upper layer of the patterned substrate, and/or other structures. The second grating may be directly above the first grating in the patterned substrate, for example. The radiation comprises different wavelengths. The radiation may have target wavelengths and/or wavelength ranges, a target intensity, and/or other characteristics. The target wavelengths and/or wavelength ranges, the target intensity, etc., may be entered and/or selected by a user, determined by the system (e.g., system 10 shown in Fig. 3 and/or system 600 shown in Fig. 6) based on previous measurements, and/or determined in other ways. In some embodiments, the radiation comprises light and/or other radiation. In some embodiments, the light comprises visible light, infrared light, near infrared light, and/or other light. In some embodiments, the radiation may be any radiation appropriate for interferometry.

[0086] In some embodiments, radiation source 604 is configured to generate spatially coherent radiation. In some embodiments, radiation source 604 is configured to generate spatially incoherent and/or partially incoherent radiation. In some embodiments, radiation source 604 may be a laser, a lamp and/or light emitting diode (LED) and/or other incoherent sources, and/or other radiation sources. [0087] Radiation sensor 606 (e.g., which is similar to and/or the same as detector 4 shown in Fig. 3) is configured to generate a metrology signal based on diffracted and/or reflected radiation received from the structure. The metrology signal comprises metrology information for the one or more layers. The metrology information may comprise optical metrology information, for example, and/or other information. In some embodiments, the metrology information comprises alignment position information, overlay information, focus metrology information, exposure dose metrology information, and/or other information. In some embodiments, radiation sensor 606 may comprise an interferometer, a photodiode, a camera, and/or other detectors.

[0088] In some embodiments, radiation sensor 606 is configured to generate a metrology signal based on the detected reflected radiation from structures such as diffraction grating target(s), as described above. For example, the metrology signal may be an alignment signal comprising alignment measurement information, and/or other metrology signals. The measurement information (e.g., an alignment value, and/or other information) may be determined using principles of interferometry and/or other principles. [0089] Multi core optical fiber 602 is configured to conduct radiation 610 from radiation source 604 to the structure, and the diffracted and/or reflected radiation 610 from the structure to radiation sensor 606. Multi core optical fiber 602 is passive, having no moving parts or electrically controlled components. Multi core optical fiber 602 has a length (e.g., the length of the line forming multi core optical fiber 602 in this this example) configured to facilitate placement of radiation source 604, radiation sensor 606, and/or other components in a spaced location relative to patterned substrate 608. Multi core optical fiber 602 has the length configured to facilitate placement of radiation source 604 and/or radiation sensor 606 (and/or other components) in a spaced location relative to patterned substrate 608 to provide increased functional space for other components of metrology system 600 located proximate to patterned substrate 608. In embodiments, a variety of optical elements can be used to guide the light from and to specific cores of multi core optical fiber 602. These elements can include non-polarizing beam splitters, polarizing beam splitters, dichroic mirrors, partial mirrors (e.g. mirrors with holes in them and placed under 45 degrees with respect to propagation direction of light), combinations of the above, etc.

[0090] These components may include a substrate side microlens array 620, for example, individual lenses, and/or other various components. For example, on the wafer side in typical embodiments there may be only passive elements such as microlenses, lenses, micromirrors, mirrors, polarization selecting and/or tuning elements, beam splitters, spatial filters / beam blocks, etc. On a far side (e.g., in a spaced location) there may be a larger variety of elements, potentially including scanning mirrors, spatial light modulators (for example digital-micromirror-devices or liquid crystal based modulators), filter wheels, tunable color filters, large numbers of dichroic mirrors to separate colors onto separate (areas of) detectors (such as separate camera chips), etc. Elements such as scanning mirrors, spatial light modulators, etc., can be used to tune parameters of the illumination radiation (before reaching a wafer) and/or the detection radiation (before reaching the sensor), for example.

[0091] There may be multiple multi core optical fibers 602 to measure multiple different / spaced metrology marks on the wafer at the same time. These multiple multi core optical fibers may be connected each to their own individual source 604 and/or sensor 606, or they may share a common sensor 606 and/or source 604, for example. In some embodiments, there may be multiple multi core optical fibers 602 used to measure one structure (e.g., metrology mark), for example, separate multi core optical fibers for illumination and detection, or for measuring different polarizations, etc.

[0092] For comparison, Fig. 6 also illustrates a metrology system 650 that does not include multi core optical fiber 602. In metrology system 650, the (location) options for radiation source (tunability) and detectors (e.g. ability to use cameras) are greatly restricted. System 600 provides a new metrology system design architecture compared to system 650. As described above, system 600 utilizes multi core optical fiber 602 to provide increased functional space for other components of system 600 to be located proximate to patterned substrate 608, which may reduce or eliminate some of the engineering constraints for a system configured to measure increased numbers of marks, and/or have other advantages.

[0093] In some embodiments, more multi core optical fiber 602 comprises a super directional etching in a crystalline material, an optical ablation structure, a structure formed by step by step deposition of layers, printed waveguides in many layers on top of each other on a substrate, and/or other structures. In some embodiments, multi core optical fiber 602 may be manufactured by starting from a macroscopic stack of glass rods / (hollow) tubes which is then heated up and pulled into a multi core fiber with microscopic (transverse) length scales, for example.

[0094] In some embodiments, the spaced location comprises a location away from a side of the patterned substrate 608 that includes the structure and the one or more layers. In some embodiments, the length of multi core optical fiber 602 (e.g., to reach a spaced location such as an opposite side of patterned substrate 608) is up to about 0.1 meters, 0.25 meters, 0.5 meters, 1 meter, or 10 meters (or even more if needed).

[0095] As an example, Fig. 7 illustrates end views of three different possible examples of multi core optical fibers 700, 702, and 704. Each multi core optical fiber 700, 702, and 704 has a plurality of different individual cores 701, 703, and 705, respectively. Each multi core optical fiber 700, 702, and 704 may have up to 10, 100, 500, 1000, or more individual cores. The length of the multi core optical fibers 700, 702, and/or 704 may be up to about 0.1 meters, 0.25 meters, 0.5 meters, 1 meter, or 10 meters, or even more if needed to reach a spaced location such as an opposite side of a patterned substrate. Radiation in different cores of multi core optical fibers 700, 702, and/or 704 may be spatially coherent or incoherent relative to each other. Spatial coherence plays an important role in image formation. In some embodiments coherence is required to generate the image, i.e., image generation would not work without spatial coherence. In some embodiments, incoherence helps to reduce crosstalk and coherent / scattering artefacts, (i.e., it helps to improve the image formation and consequently improves the metrology accuracy).

[0096] In some embodiments, radiation source 604 (Fig. 6) and multi core optical fibers 700, 702, 704 are configured such that a sub-set of cores 701, 703, 705 is used to conduct the radiation from radiation source 604 to the structure, and such that diffracted light from the structure is captured by a different sub-set of cores. In some embodiments, multi core optical fibers 700, 702, 704 are configured to support different wavelength ranges, different diffraction orders, and/or radiation having other characteristics. (Note that these are just examples, and that an actual embodiment of the system may be different. For example, the various properties of low-cross talk, polarization-maintaining, single- spatial-mode of a large wavelength range, high core density (i.e. not too large core spacing), high number of cores (e.g. 1000), not too difficult/expensive to manufacture, etc., may be provided in a combined manner by a given multi core optical fiber.)

[0097] Fig. 8 illustrates another example metrology system 800 that utilizes a multi core optical fiber 802. System 800 may be similar to and/or the same as system 600 shown in Fig. 6, and/or system 10 described above with respect to Fig. 3. In some embodiments, one or more components of system 800 may be similar to and/or the same as one or more components of system 600 and/or system 10. In some embodiments, one or more components of system 800 may replace, be used with, and/or otherwise augment one or more components of system 600 and/or system 10. System 800 includes a radiation source 804, a radiation sensor 806, and/or other components.

[0098] Fig. 8 illustrates a first view 801 with multi core optical fiber 802 positioned directly above, but still remote from, a target structure 803 (e.g., a metrology mark) in a substrate 805 such as a semiconductor wafer. View 801 illustrates how (considering the additional details described below), in the detection path, a complex field at a sensor side plane 850 resembles the complex field at a wafer side plane 850. This means that a radiation sensor 806 image may be obtained as if multi core optical fiber 802 is not present at all (though advantageously multi core optical fiber 802 is present and used to space source 804, sensor 806, etc., from substrate 805).

[0099] In some embodiments, system 800 comprises one or more substrate side optical elements configured for focusing radiation 810 (which is similar to and/or the same as radiation 610 shown in Fig. 6) from radiation source 804 on structure 803, and guiding diffracted and/or reflected radiation from structure 803 into multi core optical fiber 802. In this example, the one or more substrate side optical elements include a microlens array 820, a lens 822, and/or other components. In some embodiments, 820 and/or 830 may be a ‘standard’ microlens array placed at some distance from the multi core optical fiber. Every microlens may be (nominally) identical and/or may be optimized to fit a respective core. In some embodiments, 820 and/or 830 maybe 3D-printed with, e.g., laser lithography, and/or manufactured with other methods. Each microlens may be a doublet, triplet, etc., for example, to minimize aberrations over a broad wavelength range and/or for other purposes. Microlenses may be shaped or optimized with something like a focused ion beam, for example. In some embodiments, there may be be an imaging system between a multi core fiber and a microlens array. In some embodiments, the function of the microlenses may be provided with a spatial light modulator, and/or other components. In some embodiments, micromirrors and/or other components may be used instead of and/or in addition to microlenses. In some embodiments, the micro lenses may be adjusted (or an additional segmented element may be added closely spaced with respect to the microlens) that adjusts the angle of the beams. In some embodiments, the angles of the beams may be such that each beam illuminates the same spot on the wafer. This may effectively replace the function of the lens 822, so that 822 can be removed, which would save space and cost, for example.

[00100] In some embodiments, system 800 comprises one or more source and/or sensor side optical elements configured for guiding radiation 810 from radiation source 804 into one or more multi core optical fibers 802 and guiding diffracted and/or reflected radiation from substrate 805 and conducted through one or more multi core optical fibers 802 toward radiation sensor 806. The one or more source and sensor side optical elements may comprise a source and sensor side microlens array 830, a lens 832, an optical cube 834, a pathlength matching element 836, for example, and/or other components. In some embodiments, a number of lenses in the source and sensor side microlens array 830 also corresponds to a number of cores in the one or more multi core optical fibers 802.

[00101] Fig. 8 also illustrates a second view 807 of system 800 with the length of multi core optical fiber 802 exaggerated compared to view 801 to show that radiation source 804, radiation sensor 806, and/or other components of system 800 may be located even more remotely from target structure 803 (e.g., a metrology mark) in substrate 805 than what is shown in view 801. Note that not every element from view 801 is repeated in view 807. In this example, the length of multi core optical fiber 802 in view 807 is about one meter (Im) to about 10 meters (10m).

[00102] In some embodiments, system 800 comprises one or more optical elements 870 configured for blocking, or separating onto a different radiation sensor, Oth order light from patterned substrate 805 with respect to 1st or higher order diffracted light. For example, this may be accomplished using a configuration with wedges (e.g., with different wedge angles at different parts of the pupil causing the light of different parts of the pupil to be collected in different images on different locations on the sensor). A partially reflecting mirror may instead and/or also be used, which could be placed under 45 degree angle with respect to the beam. For example, the black areas in 870 could be reflected sideways (90 degree angle with respect to the rest of the beam), whereas the white area could propagate straight through.

[00103] In some embodiments, multi core optical fiber 802 has a subset of cores on one side, which guides the +lst order radiation, and another subset of cores on the other side, which guides the -1st order radiation, for example. In some embodiments, multi core optical fiber 802 comprises two or more multi core optical fibers 802 per radiation sensor 806. The shaded bars within multi core optical fiber 802 shown in Fig. 8 represent the cores 899 of a (single) multi core optical fiber 802. For example, multi core optical fiber 802 comprises a collection of cores 899.

[00104] As described above, system 600 (Fig. 6) and/or system 800 (Fig. 8) may include a pathlength matching element 836. This may include a phase compensating/ correcting element. The phase compensating element may compensate for the fact that, in a realistic multi core optical fiber, each core may have a (slightly) different optical pathlength. For example due to a variation in core diameter. This can be compensated for with e.g. a thin piece of glass per core. The material could be dispersion- matched to the multi core optical fiber, so the phase compensation works for a broad wavelength range - e.g., certain crystals or custom engineered materials may be useful. The material may be electrooptic, liquid crystal based (e.g., a spatial light modulator), static or fast-switchable (e.g., switching when switching colors), polarization-dependent (i.e., phase compensating two polarization components separately, which can be done with any birefringent active or passive solution, etc. This may be performed by post-processing the multi core fiber itself. For example, adding or removing material from individual cores to compensate for the pathlength/phase differences with other cores may be performed. Adding material may be done by e.g. adding liquid, curing it where material needs to be added with a nanoscribe like system (or shorter wavelengths), removing the remaining liquid, etc. (removing material may be optical ablation or FIB like, for example). [00105] In some embodiments of system 600 and/or system 800, movement of a stage (e.g., WTa, WTb described above), a radiation sensor (such as detector 4 in Fig. 3, sensor 606 in Fig. 6, sensor 806 in Fig. 8, and/or other sensors), and/or a multi core optical fiber described herein may be synchronized to scan a metrology target structure, with one or more actuators and/or other components. The radiation sensor is configured to generate an image based on diffracted radiation received during a scan. In some embodiments, the scan is continuous such that the radiation sensor receives a uninterrupted stream of diffracted radiation, which is used to generate the image. In some embodiments, the radiation sensor comprises a camera or a scan mirror, for example. In some embodiments, the radiation sensor comprises a camera having a shutter, and the shutter remains open during an entirety of the scan.

[00106] System 800 (and/or system 600, system 10, etc.) may include one or more actuators configured to synchronize movement of the stage, the radiation sensor, the multi core optical fiber, and/or other components to scan the target structure. The actuator(s) may be provided, for example, to acquire the position of the target structure, and/or a target portion of interest of a target structure (e.g., a portion of a metrology mark), and to bring it into position under an objective. In some embodiments, these actuators may move the stage relative to other components of the system. However, in some embodiments, these actuators may move one or more of the other components of the system (e.g., the one or more multi core optical fibers, the radiation sensor, etc.) relative to the stage (and the patterned substrate) and/or other components of the system. For example, the system may include a scanning mirror configured to be actuated in combination with the stage during a scan. This may include synchronized movement and/or other actuation, for example.

[00107] In some embodiments, the one or more actuators and/or other components of the system are operatively coupled to one or more processors (e.g., such as processors PRO described herein). The one or more processors may be configured (e.g., by programmed instructions and/or based on other information) to control the actuators and/or other components to function as described herein.

[00108] As described above, multi core optical fiber based metrology systems are susceptible to (dynamic) wavefront distortions during operation. In systems 10 (Fig. 3), 600 (Fig. 6), and 800 (Fig. 8), wavefront distortion in a multi core optical fiber (e.g., multi core optical fiber 602 shown in Fig. 2, multi core optical fiber 802 shown in Fig. 8) is determined by measuring optical path lengths of a small number of the cores of the multi core optical fiber. Optical path length differences between a subset of cores in the multi core optical fiber with reflectors are determined for different wavelengths of radiation from the radiation source. The optical path length differences are determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores. The optical path length differences indicate wavefront distortion. The wavefront distortion can be used to correct and/or prevent measurement error in multi core optical fiber based metrology systems and/or other systems.

[00109] Fig. 9 illustrates a multi core optical fiber 900 (e.g., similar to and/or the same as the various multi core optical fibers shown in Fig. 6-8) with reflectors 902 configured to be used to measure optical path length differences between cores 904, and in turn wavefront distortion, in optical fiber 900. The linear term of the wavefront distortion (tilt) is directly (or directly related to) alignment error, and therefore should be measured and corrected for an alignment application, for example. Fig. 9 illustrates probing the wavefront distortion in multi core optical fiber 900 by measuring optical path lengths of a small number of the fibers or cores 904. It is beneficial to probe the wavefront distortion for each wavelength of radiation 901 (which is similar to and/or the same as radiation 610 shown in Fig. 6 and/or radiation 810 shown in Fig. 8) used for metrology. This can be done by scanning the wavelength of a radiation source 918 (e.g., a laser in this example), and measuring optical path length differences in time (i.e., measure colors sequentially), and/or using other techniques, as described below.

[00110] Radiation 901 from a radiation source 918 (e.g., which is similar to and/or the same as source 2 shown in Fig. 3, source 604 shown in Fig. 6, or source 804 shown in Fig. 8) is received and conducted with multi core optical fiber 900. This may be thought of as being toward a (e.g., metrology target) structure (e.g., target 30 shown in Fig. 3 or target structure 803 shown in Fig. 8) in a layer (or one or more layers) of a patterned substrate (e.g., patterned substrate W shown in Fig. 3, substrate 608 shown in Fig. 6, or substrate 805 shown in Fig. 8), but optical fiber 900 may be oriented in any direction or position. Radiation 901 comprises different wavelengths. Reflectors 902 are configured to reflect radiation 901 from radiation source 918 back through a subset of cores - the subset of cores formed by cores 904 in Fig. 9 - of multi core optical fiber 900 to a sensor 920 (which is similar to and/or the same as detector 4 shown in Fig. 3, sensor 606 shown in Fig. 6, or sensor 806 shown in Fig. 8). Radiation 901 may be directed to and/or from source 918 and/or sensor 920 by a beam splitter 922, a reference surface 924, and/or other components. In some embodiments, sensor 920, beam splitter 922, reference surface 924, and/or other components may form an interferometer, may be and/or include a camera, and/or form other types of sensors, for example. Importantly, the optical paths of radiation 901 associated with reference surface 924 and radiation 901 used to probe multi core optical fiber 900 are similar within the coherence length of radiation 901. This can be ensured by using a fiber-based reference with the same length, for example.

[00111] In some embodiments, sensor 920 comprises a photodiode and splitter 922, source 918, surface 924, and end 910 are all fiber coupled elements. Such a configuration may comprise a displacement interferometer (for a single fiber), for example. In some embodiments, all elements may be free-space elements as well as fiber elements.

[00112] Reflectors 902 may be coupled to and/or otherwise formed by the subset of cores at or near a substrate side end 910 of multi core optical fiber 900. In some embodiments, the subset of cores comprises at least two cores. In Fig. 7, this may be two cores 904 on opposite sides of multi core optical fiber 900 (i.e., either left and right core 904, or top and bottom core 904, in Fig. 9). In some embodiments, the subset of cores comprises two cores, and the two cores are located on opposite outer edges of the multi core optical fiber such that radiation reflected through the two cores is configured to be used by radiation sensor 920 to determine a linear x or y tilt term of any wavefront distortion. In some embodiments, the subset of cores comprises four cores (i.e., all four cores 904 shown in Fig. 9), and the four cores comprise pairs of cores located on opposite outer edges of multi core optical fiber 900 such that radiation reflected through the pairs of cores is configured to be used by radiation sensor 920 to determine linear x and y tilt terms of the wavefront distortion. The linear x or y tilt term may comprise alignment error for an alignment measurement made by a metrology system (e.g., system 10 shown in Fig. 3, system 600 shown in Fig. 6, system 800 shown in Fig. 8) for the layer of the patterned substrate, for example.

[00113] In some embodiments, coupling reflectors 902 to cores 904 comprises evaporating reflectors 902 onto their respective cores 904. This may comprise using a hard mask (e.g., blocking other cores) and evaporating a metallic material onto cores 904, for example. In some embodiments, reflectors 902 comprise mirrors coupled to cores 904 by machining, additive manufacturing, adhesive, clips, clamps, coating, and/or other components and/or processes. In some embodiments, reflectors 902 comprise narrow band dielectric coatings configured to reflect only one or few of the wavelengths of radiation from radiation source 918. In some embodiments, reflectors 902 comprise an air glass interface at or near end 910 of multi core optical fiber 900, and/or other structures.

[00114] For example, a narrow-band dielectric coating may be applied at or near the end (e.g., end 910) of a core 904 of multi core optical fiber 900, that only reflects one (or a few) wavelengths (of radiation 901) that are used to measure wavefront distortion. Wavelengths that are not used for a substrate (e.g., wafer) alignment measurement, for example, may be selected. The narrow-band dielectric coating may be applied by various deposition techniques, including, for example, plasma- assisted deposition.

[00115] As another example, reflectors 902 may comprise air glass interfaces (e.g., the ends of cores 904). Without evaporating and/or otherwise applying a reflective material at the end of various cores, there will be a (small) reflection due to the air-glass interfaces at the end of the cores, which can be detected by sensor 920 (e.g., an interferometer). In this way, no extra fabrication is required on multi core optical fiber 900. A reflection from an glass-air interface can be distinguished from other reflections in several ways. For example, one way is a coherence length of the reflected radiation may be shorter than an extra optical path length associated with a second reflection such that only reflected radiation from air glass interfaces contribute to a signal from the radiation sensor. A reflection from an air/gas interface may be a partial reflection, for example, and the second reflection may be from the patterned substrate such that the extra optical path length between the partial reflection and the second reflection is large enough to ensure that the second reflection does not interfere with the reflections from the air glass interfaces.

[00116] In some embodiments, remaining radiation is absorbed with a stop 980, such that no reflection is caused by other cores. Stop 980 in Fig. 9 is illustrated merely as a placeholder example, and may or may not be similar to and/or the same as a real world version of stop 980. Stop 980 may be formed from one or more light absorbing materials, formed with one or more light absorbing surface structures, and/or be formed in other ways. In Fig. 9 stop 980 is illustrated in side view as a single surface at or near end 910 of multi core optical fiber 900. This illustration is not intended to be limiting. Stop 980 may comprise an absorbing stop which covers only cores 904 such that light which escapes through a reflector 902 is absorbed in the stop. Stop 980 may be configured to ensure that measurements are performed in between an alignment mark measurement and ensuring that there is no wafer under the sensor (no wafer is imaged) or it is facing an absorbing pad. Stop 980 may be located directly at the end(s) of core(s) 904, or spaced some distance away. Stop 980 may be formed with one or more openings so that some radiation is blocked and some radiation reaches a nearby substrate, for example. Stop 980 may be formed from a plurality of individual surfaces (e.g., coupled to open ends of different cores), and/or a different structure all together. Stop 980 may be located at an opposite end of multi core optical fiber 900.

[00117] Note that in Fig. 9, a single source 918 is shown directing radiation into a single core 904, which is reflected by a single reflector 902, and directed to a single sensor 920. This is not intended to be limiting. Fig. 9 is a simplified example intended to demonstrate the principles described herein. In some embodiments, radiation from source 918 may be directed into multiple cores 904, or all of the cores, as described. More than one source may be used. More than one sensor may be used. More than one beam splitter may be used. Combinations of one or more of each of these components may be used, etc.

[00118] Optical path length differences between the subset of cores (e.g., cores 904) with reflectors 902 are determined for the different wavelengths of radiation 901 from radiation source 918. The determining is performed with radiation sensor 920, which is operatively coupled to multi core optical fiber 900 and radiation source 918 (e.g., by splitter 922 in this example). The sensor may include one or more processor(s) PRO (Fig. 3, Fig. 12) configured to make these determinations, for example. If the optical path lengths of the subset of cores (e.g., cores 904) are the same, there is no wavefront distortion. Deviations indicate optical path length differences, and wavefront distortion(s). Low order wavefront distortions may be dominant, because these are caused by temperature gradients, bending stress, etc., such that only a limited number of cores (e.g., 904) need be coupled with reflectors 902. However, higher order wavefront distortions can be measured by coupling more cores with reflectors. For example, adding a reflector on a central core of multi core optical fiber 900 may facilitate correcting for parabolic distortions.

[00119] Optical path length differences are determined based on path lengths of reflected radiation 901 that impinges on radiation sensor 920 after passing back through the subset of cores 904. The optical path length differences indicate wavefront distortion in multi core optical fiber 900 for the different wavelengths in radiation 901. As described above, the wavefront distortion in multi core optical fiber 900 may be caused by bending of the multi core optical fiber, vibration of the multi core fiber, dynamic temperature variation over the multi core fiber, and/or may have other causes. In some embodiments, a path length for each core may be corrected with a phase compensating element. The phase compensating element may be configured to be adjusted based on the optical path length differences and/or other information. The phase compensating element may be similar to and/or the same as pathlength matching element 836 shown in Fig. 8 and described above. The phase compensating element may be manually controlled, controlled by one or more processors PRO, and/or controlled in other ways. In some embodiments, the phase compensating element may comprise a spatial light modulator and/or other components. A setting of the phase compensating element (per core) may be adjusted based on the wavefront distortion measurements performed as described herein. [00120] In some embodiments, radiation sensor 920 is configured to detect phase information of the reflected radiation 901, and determine the optical path length differences between cores 904 for the different wavelengths of radiation 901 based on the phase information. The phase information may comprise absolute phases for reflected radiation 901 from different cores 904, relative phase differences for reflected radiation 901 from different cores 904, an interference pattern for reflected radiation 901 from different cores 904, and/or other phase information.

[00121] For example, radiation sensor 920 may comprise a camera, and the reflected radiation 901 may form a phase interference pattern on the camera configured to be used to determine the optical path length differences. The wavefront distortion in multi core optical fiber 900 may be determined by fitting the phase of the interference pattern on the camera. The phase may be determined with respect to a center pixel of the camera, for example. In this example, the wavefront distortion may be caused by bending or temperature change of multi core optical fiber 900, for example. The camera may be the same detection camera that is also used for alignment measurements, instead of using additional detectors. The fitting may be performed using a fitting algorithm that is the same as or similar to a fitting algorithm used for alignment. In this example, wavefront distortion associated with the bending and/or temperature change may be determined when the metrology system is not performing an alignment measurement, for example while moving a stage to a next metrology mark.

[00122] As another example, Fig. 10 illustrates detecting phase information comprising relative phase differences for reflected radiation 1001 (which is similar to and/or the same as radiation 610 shown in Fig. 6, radiation 810 shown in Fig. 8, and/or radiation 901 shown in Fig. 9) from different cores 1004, and determining optical path length differences between cores 1004 for the different wavelengths of radiation 1001 based on the relative phase differences. These operations are performed with a sensor 1020 (which is similar to and/or the same as sensor 920 shown in Fig. 9, and/or the other sensors described above) based on radiation generated by a radiation source 1018 (which is similar to and/or the same as source 918 shown in Fig. 9, and/or the other sources described above), and reflected by reflectors 1002 (which are similar to and/or the same as reflectors 902 shown in Fig. 9). Fig. 10 also illustrates a splitter 1022 (which is similar to and/or the same as splitter 922 shown in Fig. 9), mirrors 1050 (and/or other similar components configured to direct radiation 1001 to and/or from cores 1004. A relative difference may be enough to correct for alignment errors. Change in relative difference compared to the original state may be used for correction, for example. [00123] Returning to Fig. 9, in some embodiments, radiation source 918 is configured to sequentially generate radiation 901 comprising different wavelengths such that optical path length differences indicating wavefront distortion in multi core optical fiber 900 for the different wavelengths are also determined sequentially by radiation sensor 920. For example, wavefront distortion may be probed sequentially for each wavelength used. This can be done by scanning the wavelength of source 918 (e.g., a laser in this example), and measuring optical path length differences in time (i.e., measuring colors sequentially).

[00124] In some embodiments, one or more components 990 (e.g., comprising a multiplexer and a demultiplexer with dichroic beam splitters, and/or other components) are configured to cooperate with radiation source 918 to generate radiation 901 comprising different wavelengths in parallel such that the optical path length differences indicating wavefront distortion in multi core optical fiber 900 for the different wavelengths are also determined in parallel by radiation sensor 920. (Again note that Fig. 9 illustrates a single example pathway for radiation 901. This is easily extendable to one or more of the parallel radiation generation embodiments described above.) In some embodiments, various optics (e.g., lenses, etc.) - even though not shown in Fig. 9 (or Fig. 10) may be used to couple the light into and from cores 904 for free space configurations. Beam splitter 922, elements 990 and 918, 920 can also be fiber coupled, for example.

[00125] In some embodiments, reflectors 902 may be coupled to all cores of multi core optical fiber 900 at or near the substrate side end 910 of multi core optical fiber 900. In these embodiments, reflectors 902 may be air/glass interfaces, for example, and/or other reflectors. Radiation sensor 920 is configured to determine optical path length differences for all of the cores based on reflected radiation that impinges on the radiation sensor after passing back through the cores. This approach may be used to determine path length differences and/or wavefront distortion for (e.g., fully calibrate) all cores, instead of only a small number of cores, for example by scanning the radiation over all cores (e.g., one by one).

[00126] In a practical implementation of multi core optical fiber 900, sensor 920, and source 918, radiation sensor 920 may comprise a camera. Radiation 901 from radiation source 918 may be coherent radiation, such that wavefront distortion in multi core optical fiber 900 presents as a displaced and/or distorted focus on the camera. A complex field of the focus may be measured interferomically with an off axis reference beam (e.g., essentially like 924); and by Fourier transforming an associated field, a phase in a pupil plane is obtained, which equals a path length change per fiber core. For example, coherent radiation may be provided through all cores, or a large subset of cores. This may lead to a sharp focus on the camera if there is no wavefront distortion in multi core optical fiber 900, and to a displaced and/or higher-order distorted focus if there is a wavefront distortion in multi core optical fiber 900. One needs to illuminate many or all cores at once coherently (using spatially coherent light) such that on a detection camera and/or other sensor all coherent contributions add up to a focus (similar to principles associated with a Shack-Hartmann sensor). That focus might be distorted but in the first order approximation the focus will shift according to the phase tilt. The complex field of this (distorted) focus may be measured interferometrically, with the off-axis reference beam, for example. By Fourier transforming this field, the phase in the pupil plane may be obtained, which approximately equals the path length change per fiber core.

[00127] Fig. 11 illustrates a metrology method 1100 for determining wavefront distortion in one or more multi core optical fibers. In some embodiments, one or more operations of method 1100 may be implemented in or by system 600 illustrated in Fig. 6 (and/or other systems and/or components shown in Fig. 7-10), system 10 illustrated in Fig. 3, system 800 shown in Fig. 8 (and/or other components shown in Fig. 9-10), a computer system (e.g., as illustrated in Fig. 12 and described below), and/or in or by other systems, for example. In some embodiments, method 1100 comprises generating (operation 1102) radiation comprising different wavelengths, receiving and conducting (operation 1104) the radiation toward a (e.g., metrology target) structure in a layer (or one or more layers) of a patterned substrate with a multi core optical fiber, reflecting (operation 1106) the radiation with reflectors coupled to a subset of cores of the multi core optical fiber at or near a substrate side end of the multi core optical fiber, determining (operation 1108) optical path length differences between the subset of cores with the reflectors for the different wavelengths of radiation from the radiation source, and/or other operations. [00128] The operations of method 1100 are intended to be illustrative. In some embodiments, method 1100 may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. For example, in some embodiments, method 1100 may include additional operations related to determining an adjustment for a semiconductor device manufacturing process. Additionally, the order in which the operations of method 1100 are illustrated in Fig. 11 and described herein is not intended to be limiting.

[00129] In some embodiments, one or more portions of method 1100 may be implemented in and/or controlled by one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices executing some or all of the operations of method 1100 in response to instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and/or software to be specifically designed for execution of one or more of the operations of method 1100 (e.g., see discussion of processors PRO related to Fig. 12 below).

[00130] At operation 1102, radiation comprising different wavelengths is generated. The different wavelengths may be associated with different channels of a metrology system, for example. The radiation may have a target wavelength and/or wavelength ranges, a target intensity, and/or other characteristics. The radiation may be spatially incoherent, for example. The target wavelength and/or wavelength ranges, the target intensity, etc., may be entered and/or selected by a user, determined by the system (e.g., system 10 shown in Fig. 3, system 600 shown in Fig. 6, and/or system 800 shown in Fig. 8) based on previous measurements, and/or determined in other ways. In some embodiments, the radiation comprises light and/or other radiation. In some embodiments, the light comprises visible light, infrared light, near infrared light, and/or other light. In some embodiments, the radiation may be any radiation appropriate for metrology. In some embodiments, operation 1102 is performed by a radiation source similar to and/or the same as source 2 shown in Fig. 3, source 604 shown in Fig. 6, and/or source 804 shown in Fig. 8. As one example, the radiation source may be a laser.

[00131] At operation 1104, the radiation from the radiation source is received and conducted, with a multi core optical fiber operatively coupled to the radiation source, toward a (e.g., metrology target) structure in a layer (or one or more layers) of a patterned substrate. The patterned substrate may be a semiconductor wafer, as one representative example. The multi core optical fiber has a length configured to facilitate placement of the radiation source in a spaced location relative to the patterned substrate. In some embodiments, the spaced location comprises a location away from a side of the patterned substrate that includes the structure and the one or more layers. In some embodiments, the length of the one or more multi core waveguides is up to about 0.1 meters, 0.25 meters, 0.5 meters, 1 meter, or 10 meters (or even more if needed). In some embodiments, operation 1104 is performed by a multi core optical fiber similar to and/or the same as multi core optical fiber 602 shown in Fig. 6, one or more of the multi core optical fibers shown in Fig. 7, multi core optical fiber 802 shown in Fig. 8, and/or multi core optical fiber 900 shown in Fig. 9.

[00132] At operation 1106, the radiation from the radiation source is reflected back through a subset of cores of the multi core optical fiber. The reflecting is performed by reflectors coupled to the subset of cores of the multi core optical fiber at or near a substrate side end of the multi core optical fiber. In some embodiments, the subset of cores comprises at least two cores. In some embodiments, the subset of cores comprises two cores, and the two cores are located on opposite outer edges of the multi core optical fiber such that radiation reflected through the two cores is configured to be used by the radiation sensor to determine a linear x or y tilt term of the wavefront distortion. In some embodiments, the subset of cores comprises four cores, and the four cores comprise pairs of cores located on opposite outer edges of the multi core optical fiber such that radiation reflected through the pairs of cores is configured to be used by the radiation sensor to determine linear x and y tilt terms of the wavefront distortion. The linear x or y tilt term may comprise alignment error for an alignment measurement made by a metrology system (e.g., system 10 shown in Fig. 3, system 600 shown in Fig. 6, system 800 shown in Fig. 8) for the layer of the patterned substrate, for example.

[00133] The reflectors may be similar to and/or the same as reflectors 902 shown in Fig. 9, for example. In some embodiments, the reflectors are evaporated onto their respective cores, comprise mirrors, comprise narrow band dielectric coatings configured to reflect only one or few of the wavelengths of radiation from the radiation source, comprise an air glass interface, and/or comprise other structures. In some embodiments, operation 1106 comprises absorbing, with a stop, remaining radiation such that no reflection is caused by other cores.

[00134] In some embodiments, the reflectors comprise air glass interfaces. A coherence length of the reflected radiation may be shorter than an extra optical path length associated with a second reflection such that only reflected radiation from air glass interfaces contribute to a signal from the radiation sensor (see description of operation 1108 below). A reflection from an air/gas interface may be a partial reflection, for example, and the second reflection may be from the patterned substrate such that the extra optical path length between the partial reflection and the second reflection is large enough to ensure that the second reflection does not interfere with the reflections from the air glass interfaces.

[00135] At operation 1108, optical path length differences between the subset of cores with the reflectors are determined for the different wavelengths of radiation from the radiation source. The determining is performed with a radiation sensor operatively coupled to the multi core optical fiber and the radiation source. The sensor may be similar to and/or the same as detector 4 in Fig. 3, sensor 606 in Fig. 6, sensor 806 in Fig. 8, processor(s) PRO (Fig. 3, Fig. 12), and/or other sensors. For example, the sensor may comprise an interferometer, a camera, and/or other sensors. The optical path length differences are determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores. The optical path length differences indicate wavefront distortion in the multi core optical fiber for the different wavelengths. The wavefront distortion in the multi core optical fiber may be caused by bending of the multi core optical fiber, vibration of the multi core fiber, dynamic temperature variation over the multi core fiber, and/or may have other causes. Operation 1108 may comprise correcting, with a phase compensating element, a path length for each core. The phase compensating element may be configured to be adjusted based on the optical path length differences and/or other information.

[00136] In some embodiments, the radiation sensor is configured to detect phase information of the reflected radiation, and determine the optical path length differences between cores for the different wavelengths of radiation based on the phase information. The phase information may comprise absolute phases for reflected radiation from different cores, relative phase differences for reflected radiation from different cores, an interference pattern for reflected radiation from different cores, and/or other phase information. For example, the radiation sensor may comprise a camera, and the reflected radiation may form a phase interference pattern on the camera configured to be used to determine the optical path length differences. The wavefront distortion in the multi core optical fiber may be determined by fitting the phase of the interference pattern on the camera. The phase may be determined with respect to a center pixel of the camera, for example.

[00137] In some embodiments, method 1100 comprises sequentially generating, with the radiation source, radiation comprising different wavelengths such that optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined sequentially by the radiation sensor. In some embodiments, method 1100 comprises generating, with a multiplexer and a demultiplexer with dichroic beam splitters configured to cooperate with the radiation source, the radiation comprising different wavelengths in parallel such that the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined in parallel by the radiation sensor.

[00138] In some embodiments, the reflectors are coupled to all cores of the multi core optical fiber at or near the substrate side end of the multi core optical fiber. In these embodiments, the reflectors may be air/glass interfaces, for example, and/or other reflectors. The radiation sensor is configured to determine optical path length differences for all of the cores based on reflected radiation that impinges on the radiation sensor after passing back through the cores.

[00139] In a practical implementation of method 1100, the radiation source comprises a camera, and radiation from the radiation source is coherent radiation, such that distortion in the multi core optical fiber presents as a displaced and/or distorted focus on the camera. A complex field of the focus is measured interferomically with an off axis reference beam; and by Fourier transforming an associated field, a phase in a pupil plane is obtained, which equals a path length change per fiber core.

[00140] In some embodiments, the structure (in the patterned substrate) comprises a metrology mark. The multi core optical fiber is configured to conduct the radiation from the radiation source to the structure, and diffracted radiation from the structure to the radiation sensor, through cores of the multi core optical fiber without reflectors; and the radiation sensor is configured to generate a metrology signal based on diffracted radiation received from the structure through the cores of the multi core optical fiber without reflectors. The metrology signal comprises metrology information for one or more layers of the structure. Method 1100 may comprise determining, with one or more processors (e.g., processors PRO described herein) operatively coupled to the radiation source and the radiation sensor, an alignment of the layer based on the metrology signal and the alignment error. The alignment may be used by the one or more processors to adjust a semiconductor device manufacturing process, for example.

[00141] In some embodiments, alignment and/or other measurements may be determined at operation 1108. For example, one or more processors (such as processors PRO described herein) may be configured to determine an alignment position for one or more layers of the structure based on the metrology signal. The one or more processors may be configured to determine the alignment position by determining a phase difference between 4-lst and -1st diffraction orders of the diffracted radiation from the structure (e.g., conducted by different cores of the multi core optical fiber). For example, a first core may be configured to conduct -4-lst order diffracted radiation from the structure toward the sensor, and a second core is configured to conduct -1st order diffracted radiation from the structure toward the sensor. In typical embodiments, some cores will conduct the 4-lst order radiation for a first wavelength while at the same time other cores will conduct the 4-lst order radiation for another wavelength (etc.).

[00142] Alignment may be determined based on diffracted radiation from a structure such as a diffraction grating target and/or other information. In some embodiments, the radiation may be directed onto multiple targets, a single target, sub-portions (e.g., something less than the whole) of a target, and/or onto a substrate in other ways. In some embodiments, the radiation may be directed onto a target in a time varying manner. For example, the radiation may be rastered over a target (e.g., by moving the target under the radiation) such that different portions of the target are irradiated at different times. As another example, characteristics of the radiation (e.g., wavelength, intensity, etc.) may be varied. This may create time varying data envelopes, or windows, for analysis. The data envelopes may facilitate analysis of individual sub-portions of a target, comparison of one portion of a target to another and/or to other targets (e.g., in other layers), and/or other analysis.

[00143] The metrology signal comprises an electronic signal that represents and/or otherwise corresponds to the radiation reflected from the structure (e.g., a diffraction grating target). The metrology signal may indicate a metrology value associated with a diffraction grating target, for example, and/or other information. Generating the metrology signal comprises sensing the reflected radiation and converting the sensed reflected radiation into the electronic signal. In some embodiments, generating the metrology signal comprises sensing different portions of the reflected radiation from different areas and/or different geometries of the target, and/or multiple targets, and combining the different portions of the reflected radiation to form the metrology signal. This may include generating and/or analyzing one or more images of a target, using the radiation described herein.

[00144] In some embodiments, method 1100 comprises determining an adjustment for a semiconductor device manufacturing process. In some embodiments, method 1100 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on one or more detected phase and/or amplitude variations, an alignment value indicated by the metrology signal, and/or other similar systems, and/or other information. The one or more parameters may include a parameter of the radiation (the radiation used for metrology), an alignment value, a metrology inspection location on a layer of a semiconductor device structure, a radiation beam trajectory across a target structure, and/or other parameters. In some embodiments, process parameters can be interpreted broadly to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of the radiation (used for exposing resist, etc.), an incident angle of the radiation (used for exposing resist, etc.), a wavelength of the radiation (used for exposing resist, etc.), a pupil size and/or shape, a resist material, and/or other parameters. Exposure lens parameters can also be very important to control - e.g., to adjust the shape of the currently exposed layer/field to match the measured alignment/overlay (on one or more previous layers)

[00145] In some embodiments, method 1100 includes determining a process adjustment based on the one or more determined semiconductor device manufacturing process parameters, adjusting a semiconductor device manufacturing apparatus based on the determined adjustment, and/or other operations. For example, if a determined metrology measurement is not within process tolerances, the out of tolerance measurement may be caused by one or more manufacturing processes whose process parameters have drifted and/or otherwise changed so that the process is no longer producing acceptable devices (e.g., measurements may breach a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the measurement determination. The new or adjusted process parameters may be configured to cause a manufacturing process to again produce acceptable devices.

[00146] For example, a new or adjusted process parameter may cause a previously unacceptable measurement value to be adjusted back into an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. If there is a difference, that difference may be used to determine an adjustment for an apparatus that is used to produce the devices (e.g., parameter “x” should be increased / decreased / changed so that it matches the new or adjusted version of parameter “x” determined as part of method 1100), for example. In some embodiments, method 1100 may include electronically adjusting an apparatus (e.g., based on the determined process parameters). Electronically adjusting an apparatus may include sending an electronic signal, and/or other communications to the apparatus, for example, which causes a change in the apparatus. The electronic adjustment may include changing a setting on the apparatus, for example, and/or other adjustments.

[00147] Fig. 12 is a diagram of an example computer system CS that may be used for one or more of the operations described herein. Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors similar to and/or the same as processor PRO shown in Fig. 3) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[00148] Computer system CS may be coupled via bus BS to a display DS, such as a flat panel or touch panel display or a cathode ray tube (CRT) for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[00149] In some embodiments, all or some of one or more operations described herein may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions included in main memory MM causes processor PRO to perform the process steps (operations) described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[00150] The term “computer-readable medium” or “machine -readable medium” as used herein refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non- transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non-transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the operations described herein. Transitory computer-readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[00151] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[00152] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[00153] Network link NDL typically provides data communication through one or more networks to other data devices. For example, network link NDL may provide a connection through local network LAN to a host computer HC. This can include data communication services provided through the worldwide packet data communication network, now commonly referred to as the “Internet” INT. Local network LAN (Internet) may use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network data link NDL and through communication interface CI, which carry the digital data to and from computer system CS, are exemplary forms of carrier waves transporting the information.

[00154] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example, host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN, and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and/or stored in storage device SD, or other non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[00155] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses. In the following, further features, characteristics, and exemplary technical solutions of the present disclosure will be described in terms of clauses that may be optionally claimed in any combination:

1. A semiconductor metrology system, comprising: a radiation source configured to generate radiation comprising different wavelengths; a multi core optical fiber, operatively coupled to the radiation source, configured to receive and conduct the radiation from the radiation source toward a structure in a layer of a patterned substrate, the multi core optical fiber having a length configured to facilitate placement of the radiation source in a spaced location relative to the patterned substrate; reflectors coupled to a subset of cores of the multi core optical fiber at or near a substrate side end of the multi core optical fiber, the reflectors configured to reflect the radiation from the radiation source back through the subset of cores; and a radiation sensor, operatively coupled to the multi core optical fiber and the radiation source, configured to determine optical path length differences between the subset of cores with the reflectors for the different wavelengths of radiation from the radiation source, the optical path length differences determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores, the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths. 2. The system of clause 1 , wherein the radiation sensor is configured to detect phase information of the reflected radiation, and determine the optical path length differences between cores for the different wavelengths of radiation based on the phase information.

3. The system of any of the previous clauses, wherein the phase information comprises absolute phases for reflected radiation from different cores, relative phase differences for reflected radiation from different cores, and/or an interference pattern for reflected radiation from different cores.

4. The system of any of the previous clauses, wherein the radiation sensor comprises an interferometer, a photodiode, and/or a camera.

5. The system of any of the previous clauses, wherein the different wavelengths are associated with different channels.

6. The system of any of the previous clauses, wherein the radiation source is configured to sequentially generate radiation comprising different wavelengths such that optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined sequentially by the radiation sensor.

7. The system of any of the previous clauses, further comprising a multiplexer and a demultiplexer with dichroic beam splitters configured to cooperate with the radiation source to generate the radiation comprising different wavelengths in parallel such that the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined in parallel by the radiation sensor.

8. The system of any of the previous clauses, wherein the wavefront distortion in the multi core optical fiber is caused by bending of the multi core optical fiber, vibration of the multi core fiber, and/or dynamic temperature variation over the multi core fiber.

9. The system of any of the previous clauses, wherein the reflectors are evaporated onto their respective cores, comprise mirrors, comprise narrow band dielectric coatings configured to reflect only one or few of the wavelengths of radiation from the radiation source, and/or comprise an air glass interface.

10. The system of any of the previous clauses, wherein: the reflectors comprise air glass interfaces and a coherence length of the reflected radiation is shorter than an extra optical path length associated with a second reflection such that only reflected radiation from the air glass interfaces contribute to a signal from the radiation sensor; and a reflection from an air/gas interface is a partial reflection, and the second reflection is from the patterned substrate such that the extra optical path length between the partial reflection and the second reflection is large enough to ensure that the second reflection does not interfere with the reflections from the air glass interfaces.

11. The system of any of the previous clauses, further comprising a stop configured to absorb remaining radiation such that no reflection is caused by other cores.

12. The system of any of the previous clauses, wherein the radiation sensor comprises a camera, and the reflected radiation forms a phase interference pattern on the camera configured to be used to determine the optical path length differences, wherein the wavefront distortion in the multi core optical fiber is determined by fitting the phase of the interference pattern on the camera, and wherein the phase is determined with respect to a center pixel of the camera.

13. The system of any of the previous clauses, wherein the reflectors are coupled to all cores of the multi core optical fiber at or near the substrate side end of the multi core optical fiber; and the radiation sensor is configured to determine optical path length differences for all of the cores based on reflected radiation that impinges on the radiation sensor after passing back through the cores.

14. The system of any of the previous clauses, wherein the radiation source is configured to generate spatially incoherent radiation.

15. The system of any of the previous clauses, wherein the radiation source comprises a laser.

16. The system of any of the previous clauses, wherein: the radiation sensor comprises a camera, and radiation from the radiation source is coherent radiation through all cores or a large subset of cores, such that distortion in the multi core optical fiber presents as a displaced and/or distorted focus on the camera; a complex field of the focus is measured interferomically with an off axis reference beam; and by Fourier transforming an associated field, a phase in a pupil plane is obtained, which equals a path length change per fiber core.

17. The system of any of the previous clauses, further comprising a phase compensating element configured to correct a path length for each core; wherein the phase compensating element is configured to be adjusted based on the optical path length differences.

18. The system of any of the previous clauses, wherein the length of the multi core optical fiber is up to about 0.1 meters, 0.25 meters, 0.5 meters, 1 meter, or 10 meters.

19. The system of any of the previous clauses, wherein the subset of cores comprises at least two cores.

20. The system of any of the previous clauses, wherein the subset of cores comprises two cores, and wherein the two cores are located on opposite outer edges of the multi core optical fiber such that radiation reflected through the two cores is configured to be used by the radiation sensor to determine a linear x or y tilt term of the wavefront distortion.

21. The system of any of the previous clauses, wherein the subset of cores comprises four cores, and wherein the four cores comprise pairs of cores located on opposite outer edges of the multi core optical fiber such that radiation reflected through the pairs of cores is configured to be used by the radiation sensor to determine linear x and y tilt terms of the wavefront distortion.

22. The system of any of the previous clauses, wherein the linear x or y tilt term comprises alignment error for an alignment measurement made by the metrology system for the layer of the patterned substrate.

23. The system of any of the previous clauses, wherein: the structure comprises a metrology mark, the multi core optical fiber is further configured to conduct the radiation from the radiation source to the structure, and diffracted radiation from the structure to the radiation sensor, through cores of the multi core optical fiber without reflectors; and the radiation sensor is further configured to generate a metrology signal based on diffracted radiation received from the structure through the cores of the multi core optical fiber without reflectors.

24. The system of any of the previous clauses, further comprising one or more processors operatively coupled to the radiation source and the radiation sensor, the one or more processors configured to determine an alignment of the layer based on the metrology signal and the alignment error.

25. The system of any of the previous clauses, wherein the alignment is configured to be used by one or more processors to adjust a semiconductor device manufacturing process.

26. A semiconductor metrology method, comprising: generating, with a radiation source, radiation comprising different wavelengths; receiving and conducting, with a multi core optical fiber operatively coupled to the radiation source, the radiation from the radiation source toward a structure in a layer of a patterned substrate, the multi core optical fiber having a length configured to facilitate placement of the radiation source in a spaced location relative to the patterned substrate; reflecting, with reflectors coupled to a subset of cores of the multi core optical fiber at or near a substrate side end of the multi core optical fiber, the radiation from the radiation source back through the subset of cores; and determining, with a radiation sensor operatively coupled to the multi core optical fiber and the radiation source, optical path length differences between the subset of cores with the reflectors for the different wavelengths of radiation from the radiation source, the optical path length differences determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores, the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths.

27. The method of clause 26, wherein the radiation sensor is configured to detect phase information of the reflected radiation, and determine the optical path length differences between cores for the different wavelengths of radiation based on the phase information.

28. The method of any of the previous clauses, wherein the phase information comprises absolute phases for reflected radiation from different cores, relative phase differences for reflected radiation from different cores, and/or an interference pattern for reflected radiation from different cores.

29. The method of any of the previous clauses, wherein the radiation sensor comprises an interferometer, a photodiode, and/or a camera.

30. The method of any of the previous clauses, wherein the different wavelengths are associated with different channels.

31. The method of any of the previous clauses, further comprising sequentially generating, with the radiation source, radiation comprising different wavelengths such that optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined sequentially by the radiation sensor.

32. The method of any of the previous clauses, further comprising generating, with a multiplexer and a demultiplexer with dichroic beam splitters configured to cooperate with the radiation source, the radiation comprising different wavelengths in parallel such that the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined in parallel by the radiation sensor.

33. The method of any of the previous clauses, wherein the wavefront distortion in the multi core optical fiber is caused by bending of the multi core optical fiber, vibration of the multi core fiber, and/or dynamic temperature variation over the multi core fiber.

34. The method of any of the previous clauses, wherein the reflectors are evaporated onto their respective cores, comprise mirrors, comprise narrow band dielectric coatings configured to reflect only one or few of the wavelengths of radiation from the radiation source, and/or comprise an air glass interface.

35. The method of any of the previous clauses, wherein: the reflectors comprise air glass interfaces and a coherence length of the reflected radiation is shorter than an extra optical path length associated with a second reflection such that only reflected radiation from the air glass interfaces contribute to a signal from the radiation sensor; and a reflection from an air/gas interface is a partial reflection, and the second reflection is from the patterned substrate such that the extra optical path length between the partial reflection and the second reflection is large enough to ensure that the second reflection does not interfere with the reflections from the air glass interfaces.

36. The method of any of the previous clauses, further comprising absorbing, with a stop, remaining radiation such that no reflection is caused by other cores.

37. The method of any of the previous clauses, wherein the radiation sensor comprises a camera, and the reflected radiation forms a phase interference pattern on the camera configured to be used to determine the optical path length differences, wherein the wavefront distortion in the multi core optical fiber is determined by fitting the phase of the interference pattern on the camera, and wherein the phase is determined with respect to a center pixel of the camera.

38. The method of any of the previous clauses, wherein the reflectors are coupled to all cores of the multi core optical fiber at or near the substrate side end of the multi core optical fiber; and the radiation sensor is configured to determine optical path length differences for all of the cores based on reflected radiation that impinges on the radiation sensor after passing back through the cores.

39. The method of any of the previous clauses, wherein the radiation source is configured to generate spatially incoherent radiation.

40. The method of any of the previous clauses, wherein the radiation source comprises a laser.

41. The method of any of the previous clauses, wherein: the radiation sensor comprises a camera, and radiation from the radiation source is coherent radiation through all cores or a large subset of cores, such that distortion in the multi core optical fiber presents as a displaced and/or distorted focus on the camera; a complex field of the focus is measured interferomically with an off axis reference beam; and by Fourier transforming an associated field, a phase in a pupil plane is obtained, which equals a path length change per fiber core. 42. The method of any of the previous clauses, further comprising correcting, with a phase compensating element, a path length for each core; wherein the phase compensating element is configured to be adjusted based on the optical path length differences.

43. The method of any of the previous clauses, wherein the length of the multi core optical fiber is up to about 0.1 meters, 0.25 meters, 0.5 meters, 1 meter, or 10 meters.

44. The method of any of the previous clauses, wherein the subset of cores comprises at least two cores.

45. The method of any of the previous clauses, wherein the subset of cores comprises two cores, and wherein the two cores are located on opposite outer edges of the multi core optical fiber such that radiation reflected through the two cores is configured to be used by the radiation sensor to determine a linear x or y tilt term of the wavefront distortion.

46. The method of any of the previous clauses, wherein the subset of cores comprises four cores, and wherein the four cores comprise pairs of cores located on opposite outer edges of the multi core optical fiber such that radiation reflected through the pairs of cores is configured to be used by the radiation sensor to determine linear x and y tilt terms of the wavefront distortion.

47. The method of any of the previous clauses, wherein the linear x or y tilt term comprises alignment error for an alignment measurement made by a metrology system for the layer of the patterned substrate.

48. The method of any of the previous clauses, wherein: the structure comprises a metrology mark, the multi core optical fiber is further configured to conduct the radiation from the radiation source to the structure, and diffracted radiation from the structure to the radiation sensor, through cores of the multi core optical fiber without reflectors; and the radiation sensor is further configured to generate a metrology signal based on diffracted radiation received from the structure through the cores of the multi core optical fiber without reflectors.

49. The method of any of the previous clauses, further comprising determining, with one or more processors operatively coupled to the radiation source and the radiation sensor, an alignment of the layer based on the metrology signal and the alignment error.

50. The method of any of the previous clauses, wherein the alignment is configured to be used by one or more processors to adjust a semiconductor device manufacturing process.

[00156] The concepts disclosed herein may be associated with any generic imaging system for imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use include EUV (extreme ultra violet), DUV lithography that is capable of producing a 193nm wavelength with the use of an ArF laser, and even a 157nm wavelength with the use of a Fluorine laser. Moreover, EUV lithography is capable of producing wavelengths within a range of 20-5nm by using a synchrotron or by hitting a material (either solid or a plasma) with high energy electrons in order to produce photons within this range.

[00157] While the concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of lithographic imaging systems, e.g., those used for imaging on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments.

[00158] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

1. A semiconductor metrology system, comprising: a radiation source configured to generate radiation comprising different wavelengths; a multi core optical fiber, operatively coupled to the radiation source, configured to receive and conduct the radiation from the radiation source toward a structure in a layer of a patterned substrate, the multi core optical fiber having a length configured to facilitate placement of the radiation source in a spaced location relative to the patterned substrate; reflectors coupled to a subset of cores of the multi core optical fiber at or near a substrate side end of the multi core optical fiber, the reflectors configured to reflect the radiation from the radiation source back through the subset of cores; and a radiation sensor, operatively coupled to the multi core optical fiber and the radiation source, configured to determine optical path length differences between the subset of cores with the reflectors for the different wavelengths of radiation from the radiation source, the optical path length differences determined based on path lengths of reflected radiation that impinges on the radiation sensor after passing back through the subset of cores, the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths.

2. The system of claim 1 , wherein the radiation sensor is configured to detect phase information of the reflected radiation, and determine the optical path length differences between cores for the different wavelengths of radiation based on the phase information.

3. The system of claim 2, wherein the phase information comprises absolute phases for reflected radiation from different cores, relative phase differences for reflected radiation from different cores, and/or an interference pattern for reflected radiation from different cores.

4. The system of any of claims 1-3, wherein the radiation sensor comprises an interferometer, a photodiode, and/or a camera.

5. The system of any of claims 1-4, wherein the different wavelengths are associated with different channels.

6. The system of any of claims 1-5, wherein the radiation source is configured to sequentially generate radiation comprising different wavelengths such that optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined sequentially by the radiation sensor.

7. The system of any of claims 1-5, further comprising a multiplexer and a demultiplexer with dichroic beam splitters configured to cooperate with the radiation source to generate the radiation comprising different wavelengths in parallel such that the optical path length differences indicating wavefront distortion in the multi core optical fiber for the different wavelengths are also determined in parallel by the radiation sensor.

8. The system of any of claims 1-7, wherein the wavefront distortion in the multi core optical fiber is caused by bending of the multi core optical fiber, vibration of the multi core fiber, and/or dynamic temperature variation over the multi core fiber.

9. The system of any of claims 1-8, wherein the reflectors are evaporated onto their respective cores, comprise mirrors, comprise narrow band dielectric coatings configured to reflect only one or few of the wavelengths of radiation from the radiation source, and/or comprise an air glass interface.

10. The system of any of claims 1-9, wherein: the reflectors comprise air glass interfaces and a coherence length of the reflected radiation is shorter than an extra optical path length associated with a second reflection such that only reflected radiation from the air glass interfaces contribute to a signal from the radiation sensor; and a reflection from an air/gas interface is a partial reflection, and the second reflection is from the patterned substrate such that the extra optical path length between the partial reflection and the second reflection is large enough to ensure that the second reflection does not interfere with the reflections from the air glass interfaces.

11. The system of claim 10, further comprising a stop configured to absorb remaining radiation such that no reflection is caused by other cores.

12. The system of any of claims 1-11, wherein the radiation sensor comprises a camera, and the reflected radiation forms a phase interference pattern on the camera configured to be used to determine the optical path length differences, wherein the wavefront distortion in the multi core optical fiber is determined by fitting the phase of the interference pattern on the camera, and wherein the phase is determined with respect to a center pixel of the camera.

13. The system of any of claims 1-12, wherein the reflectors are coupled to all cores of the multi core optical fiber at or near the substrate side end of the multi core optical fiber; and the radiation sensor is configured to determine optical path length differences for all of the cores based on reflected radiation that impinges on the radiation sensor after passing back through the cores.

14. The system of any of claims 1-13, wherein the radiation source is configured to generate spatially incoherent radiation.

15. The system of any of claims 1-13, wherein the radiation source comprises a laser.