Lithographic apparatus, metrology systems, phased array illumination sources and methods thereof

A system includes a radiation source, first and second phased arrays, and a detector. The first and second phased arrays include optical elements, a plurality of ports, waveguides, and phase modulators. The optical elements radiate radiation waves. The waveguides guide radiation from a port of the plurality of ports to the optical elements. Phase modulators adjust phases of the radiation waves. One or both of the first and second phased arrays form a first beam and/or a second beam of radiation directed toward a target structure based on the port coupled to the radiation source. The detector receives radiation scattered by the target structure and generates a measurement signal based on the received radiation.

FIELD

The present disclosure relates to metrology systems with integrated optics, for example, illumination systems with integrated phased arrays used in metrology systems for inspecting lithographic processes and wafer alignment.

BACKGROUND

Another lithographic system is an interferometric lithographic system where there is no patterning device, but rather a light beam is split into two beams, and the two beams are caused to interfere at a target portion of the substrate through the use of a reflection system. The interference causes lines to be formed at the target portion of the substrate.

During lithographic operation, different processing steps may require different layers to be sequentially formed on the substrate. Accordingly, it can be necessary to position the substrate relative to prior patterns formed thereon with a high degree of accuracy. Generally, alignment marks are placed on the substrate to be aligned and are located with reference to a second object. A lithographic apparatus may use an inspection apparatus (e.g., alignment apparatus) for detecting positions of the alignment marks and for aligning the substrate using the alignment marks to ensure accurate exposure from a mask. Misalignment between the alignment marks at two different layers is measured as overlay error.

In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate and critical linewidth of developed photosensitive resist. This measurement can be performed on a product substrate and/or on a dedicated metrology target. There are various techniques for making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. A fast and non-invasive form of a specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range. By contrast, angularly resolved scatterometers may use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

Such optical scatterometers can be used to measure parameters, such as critical dimensions of developed photosensitive resist or overlay error (OV) between two layers formed in or on the patterned substrate. Properties of the substrate can be determined by comparing the properties of an illumination beam before and after the beam has been reflected or scattered by the substrate.

As ICs become smaller and more densely packed, so too increases the number of features that must be inspected per wafer. It is desirable to improve the capabilities of metrology systems in order to keep pace with current high-volume manufacturing rates and improve production speeds beyond what is currently available. Accordingly, there is a need to provide metrology tools capable of quickly and accurately measuring a large number of lithographic features. Metrology solutions may include, e.g., increasing the number of simultaneous measurements and/or increasing the speed of a measurement.

SUMMARY

In some embodiments, a system includes a radiation source, first and second phased arrays, and a detector. The first and second phased arrays include optical elements, a plurality of ports, waveguides, and phase modulators. The optical elements radiate radiation waves. The waveguides guide radiation from a port of the plurality of ports to the optical elements. Phase modulators adjust phases of the radiation waves. One or both of the first and second phased arrays form a first beam and/or a second beam of radiation directed toward a target structure based on the port coupled to the radiation source. The detector receives radiation scattered by the target structure and generates a measurement signal based on the received radiation.

In some embodiments, a system includes a radiation source, a phased array, a detector, and a controller. The phased array generates a beam of radiation and directs the beam toward a target structure on a substrate. The detector receives radiation scattered by the target structure and generates a measurement signal based on the received radiation. A controller controls a phase offset of each respective optical element to control a direction of the beam. The phased array includes optical elements, waveguides, and phase modulators. The optical elements radiate radiation waves. The waveguides guide radiation from the radiation source to the optical elements. The phase modulators adjust phases of the radiation waves such that the radiation waves accumulate to form the beam.

In some embodiments, a system includes a phased array. The phased array includes optical elements, waveguides, phase modulators, and one or metal elements. The optical elements radiate or detect radiation waves. The waveguides guide radiation from the radiation source to the optical elements or from the optical elements to a detector. The phase modulators adjust phases of the radiation waves. The one or more metal elements are interposed between the waveguides configured to reduce coupling between optical elements.

The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.

DETAILED DESCRIPTION

The term “about” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term “about” may indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present disclosure can be implemented.

Example Lithographic Systems

FIGS.1A and1Bshow schematic illustrations of a lithographic apparatus100and lithographic apparatus100′, respectively, in which embodiments of the present disclosure may be implemented. Lithographic apparatus100and lithographic apparatus100′ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus100and100′ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus100′, the patterning device MA and the projection system PS are transmissive.

The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus100and100′, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which may be fixed or movable, as required. By using sensors, the support structure MT may ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

The term “patterning device” MA should be broadly interpreted as referring to any device that may be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

The terms “inspection apparatus,” “metrology apparatus,” and the like may be used herein to refer to, e.g., a device or system used for measuring a property of a structure (e.g., overlay error, critical dimension parameters) or used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment apparatus).

The term “projection system” PS may encompass 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 on the substrate W or the use of a vacuum. A vacuum environment may be used for EUV or electron beam radiation since other gases may absorb too much radiation or electrons. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus100and/or lithographic apparatus100′ may be of a type having two (dual stage) or more substrate tables WT (and/or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

Referring toFIGS.1A and1B, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus100,100′ can may be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus100or100′, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (inFIG.1B) including, for example, suitable directing mirrors and/or a beam expander. In other cases, the source SO may be an integral part of the lithographic apparatus100,100′, for example, when the source SO 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.

The illuminator IL may include an adjuster AD (inFIG.1B) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as “σ-outer” and “σ-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may comprise various other components (inFIG.1B), such as an integrator IN and a condenser CO. The illuminator IL may be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

Referring toFIG.1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2(for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT may be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1may be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W may be aligned using mask alignment marks M1, M2and substrate alignment marks P1, P2.

Referring toFIG.1B, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

The projection system PS projects an image MP′ of the mask pattern MP, where image MP′ is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP may include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

The projection system PS is arranged to capture, by means of a lens or lens group L, not only the zeroth order diffracted beams, but also first-order or first- and higher-order diffracted beams (not shown). In some embodiments, dipole illumination for imaging line patterns extending in a direction perpendicular to a line may be used to utilize the resolution enhancement effect of dipole illumination. For example, first-order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some embodiments, astigmatism aberration may be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some embodiments, astigmatism aberration may be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in U.S. Pat. No. 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

With the aid of the second positioner PW and position sensor IF (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT may be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown inFIG.1B) may be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

In general, movement of the mask table 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 mask table MT may be connected to a short-stroke actuator only or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2, and substrate alignment marks P1, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they may be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

Mask table MT and patterning device MA may be in a vacuum chamber V, where an in-vacuum robot IVR may be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot may be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

The lithographic apparatus100and100′ may be used in at least one of the following modes:1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B 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 may be exposed.2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B 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 (for example, mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO may be 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 may be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

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

In a further embodiment, lithographic apparatus100includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

Subsequently the radiation traverses the illumination system IL, which may include a faceted field mirror device222and a faceted pupil mirror device224arranged to provide a desired angular distribution of the radiation beam221, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation221at the patterning device MA, held by the support structure MT, a patterned beam226is formed and the patterned beam226is imaged by the projection system PS via reflective elements228,229onto a substrate W held by the wafer stage or substrate table WT.

More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter240may optionally be present, depending upon the type of lithographic apparatus. Further, there may be more mirrors present than those shown in theFIG.2, for example there may be one to six additional reflective elements present in the projection system PS than shown inFIG.2.

Collector optic CO, as illustrated inFIG.2, is depicted as a nested collector with grazing incidence reflectors253,254, and255, just as an example of a collector (or collector mirror). The grazing incidence reflectors253,254, and255are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

Exemplary Lithographic Cell

FIG.3shows a lithographic cell300, also sometimes referred to a lithocell or cluster, according to some embodiments. Lithographic apparatus100or100′ may form part of lithographic cell300. Lithographic cell300may also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input/output ports I/O1, I/O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus100or100′. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses may be operated to maximize throughput and processing efficiency.

Exemplary Inspection Apparatuses

In order to control the lithographic process to place device features accurately on the substrate, alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more alignment apparatuses and/or systems by which positions of marks on a substrate must be measured accurately. These alignment apparatuses are effectively position measuring apparatuses. Different types of marks and different types of alignment apparatuses and/or systems are known from different times and different manufacturers. A type of system widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Pat. No. 6,961,116 (den Boef et al.). Generally marks are measured separately to obtain X- and Y-positions. A combined X- and Y-measurement may be performed using the techniques described in U.S. Publication No. 2009/195768 A (Bijnen et al.), however. The full contents of both of these disclosures are incorporated herein by reference.

FIG.4Ashows a schematic of a cross-sectional view of an inspection apparatus400, according to some embodiments. In some embodiments, inspection apparatus400may be implemented as part of lithographic apparatus100or100′. Inspection apparatus400may be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Inspection apparatus400may be further configured to detect positions of alignment marks on the substrate and to align the substrate with respect to the patterning device or other components of lithographic apparatus100or100′ using the detected positions of the alignment marks. Such alignment of the substrate may ensure accurate exposure of one or more patterns on the substrate.

In some embodiments, inspection apparatus400may include an illumination system412, a beam splitter414, an interferometer426, a detector428, a beam analyzer430, and an overlay calculation processor432. Illumination system412may be configured to provide an electromagnetic narrow band radiation beam413having one or more passbands. In an example, the one or more passbands may be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system412may be further configured to provide one or more passbands having substantially constant center wavelength (CWL) values over a long period of time (e.g., over a lifetime of illumination system412). Such configuration of illumination system412may help to prevent the shift of the actual CWL values from the desired CWL values, as discussed above, in current alignment systems. And, as a result, the use of constant CWL values may improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus400) compared to the current alignment apparatuses.

In some embodiments, beam splitter414may be configured to receive radiation beam413and split radiation beam413into at least two radiation sub-beams. For example, radiation beam413may be split into radiation sub-beams415and417, as shown inFIG.4A. Beam splitter414may be further configured to direct radiation sub-beam415onto a substrate420placed on a stage422. In one example, the stage422is movable along direction424. Radiation sub-beam415may be configured to illuminate an alignment mark or a target418located on substrate420. Alignment mark or target418may be coated with a radiation sensitive film. In some embodiments, alignment mark or target418may have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target418is rotated 180° about an axis of symmetry perpendicular to a plane of alignment mark or target418, rotated alignment mark or target418may be substantially identical to an unrotated alignment mark or target418. The target418on substrate420may be (a) a resist layer grating comprising bars that are formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure comprising a resist grating overlaid or interleaved on a product layer grating. The bars may alternatively be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberrations will manifest themselves in a variation in the printed grating. One in-line method used in device manufacturing for measurements of line width, pitch, and critical dimension makes use of a technique known as “scatterometry”. Methods of scatterometry are described in Raymond et al., “Multiparameter Grating Metrology Using Optical Scatterometry”, J. Vac. Sci. Tech. B, Vol. 15, no. 2, pp. 361-368 (1997) and Niu et al., “Specular Spectroscopic Scatterometry in DUV Lithography”, SPIE, Vol. 3677 (1999), which are both incorporated by reference herein in their entireties. In scatterometry, light is reflected by periodic structures in the target, and the resulting reflection spectrum at a given angle is detected. The structure giving rise to the reflection spectrum is reconstructed, e.g. using Rigorous Coupled-Wave Analysis (RCWA) or by comparison to a library of patterns derived by simulation. Accordingly, the scatterometry data of the printed gratings is used to reconstruct the gratings. The parameters of the grating, such as line widths and shapes, may be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and/or other scatterometry processes.

In some embodiments, beam splitter414may be further configured to receive diffraction radiation beam419and split diffraction radiation beam419into at least two radiation sub-beams, according to an embodiment. Diffraction radiation beam419may be split into diffraction radiation sub-beams429and439, as shown inFIG.4A.

It should be noted that even though beam splitter414is shown to direct radiation sub-beam415towards alignment mark or target418and to direct diffracted radiation sub-beam429towards interferometer426, the disclosure is not so limiting. It would be apparent to a person skilled in the relevant art that other optical arrangements may be used to obtain the similar result of illuminating alignment mark or target418on substrate420and detecting an image of alignment mark or target418.

As illustrated inFIG.4A, interferometer426may be configured to receive radiation sub-beam417and diffracted radiation sub-beam429through beam splitter414. In an example embodiment, diffracted radiation sub-beam429may be at least a portion of radiation sub-beam415that may be reflected from alignment mark or target418. In an example of this embodiment, interferometer426comprises any appropriate set of optical-elements, for example, a combination of prisms that may be configured to form two images of alignment mark or target418based on the received diffracted radiation sub-beam429. It should be appreciated that a good quality image need not be formed, but that the features of alignment mark418should be resolved. Interferometer426may be further configured to rotate one of the two images with respect to the other of the two images 180° and recombine the rotated and unrotated images interferometrically.

In some embodiments, detector428may be configured to receive the recombined image via interferometer signal427and detect interference as a result of the recombined image when alignment axis421of inspection apparatus400passes through a center of symmetry (not shown) of alignment mark or target418. Such interference may be due to alignment mark or target418being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example embodiment. Based on the detected interference, detector428may be further configured to determine a position of the center of symmetry of alignment mark or target418and consequently, detect a position of substrate420. According to an example, alignment axis421may be aligned with an optical beam perpendicular to substrate420and passing through a center of image rotation interferometer426. Detector428may be further configured to estimate the positions of alignment mark or target418by implementing sensor characteristics and interacting with wafer mark process variations.

In a further embodiment, detector428determines the position of the center of symmetry of alignment mark or target418by performing one or more of the following measurements:1. measuring position variations for various wavelengths (position shift between colors);2. measuring position variations for various orders (position shift between diffraction orders); and3. measuring position variations for various polarizations (position shift between polarizations).
This data may for example be obtained with any type of alignment sensor, for example a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Pat. No. 6,961,116 that employs a self-referencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software, or Athena (Advanced Technology using High order ENhancement of Alignment), as described in U.S. Pat. No. 6,297,876, which directs each of seven diffraction orders to a dedicated detector, which are both incorporated by reference herein in their entireties.

In some embodiments, beam analyzer430may be configured to receive and determine an optical state of diffracted radiation sub-beam439. The optical state may be a measure of beam wavelength, polarization, or beam profile. Beam analyzer430may be further configured to determine a position of stage422and correlate the position of stage422with the position of the center of symmetry of alignment mark or target418. As such, the position of alignment mark or target418and, consequently, the position of substrate420can be accurately known with reference to stage422. Alternatively, beam analyzer430may be configured to determine a position of inspection apparatus400or any other reference element such that the center of symmetry of alignment mark or target418can be known with reference to inspection apparatus400or any other reference element. Beam analyzer430may be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some embodiments, beam analyzer430may be directly integrated into inspection apparatus400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments.

In some embodiments, beam analyzer430may be further configured to determine the overlay data between two patterns on substrate420. One of these patterns may be a reference pattern on a reference layer. The other pattern may be an exposed pattern on an exposed layer. The reference layer may be an etched layer already present on substrate420. The reference layer may be generated by a reference pattern exposed on the substrate by lithographic apparatus100and/or100′. The exposed layer may be a resist layer exposed adjacent to the reference layer. The exposed layer may be generated by an exposure pattern exposed on substrate420by lithographic apparatus100or100′. The exposed pattern on substrate420may correspond to a movement of substrate420by stage422. In some embodiments, the measured overlay data may also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data may be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus100or100′, such that after the calibration, the offset between the exposed layer and the reference layer may be minimized.

In some embodiments, beam analyzer430may be further configured to determine a model of the product stack profile of substrate420, and may be configured to measure overlay, critical dimension, and focus of target418in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target418, or substrate420, and may include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile may also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer430may be found in the metrology apparatus known as Yieldstar™, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Pat. No. 8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer430may be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer430may process an overlay parameter (an indication of the positioning accuracy of the layer with respect to a previous layer on the substrate or the positioning accuracy of the first layer with respective to marks on the substrate), a focus parameter, and/or a critical dimension parameter (e.g., line width and its variations) of the depicted image in the layer. Other parameters are image parameters relating to the quality of the depicted image of the exposed pattern.

In some embodiments, an array of detectors (not shown) may be connected to beam analyzer430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector428may be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range but each need separate pre-amps. The number of elements is therefore limited. CCD linear arrays offer many elements that may be read-out at high speed and are especially of interest if phase-stepping detection is used.

In some embodiments, a second beam analyzer430′ may be configured to receive and determine an optical state of diffracted radiation sub-beam429, as shown inFIG.4B. The optical state may be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer430′ may be identical to beam analyzer430. Alternatively, second beam analyzer430′ may be configured to perform at least all the functions of beam analyzer430, such as determining a position of stage422and correlating the position of stage422with the position of the center of symmetry of alignment mark or target418. As such, the position of alignment mark or target418and, consequently, the position of substrate420, can be accurately known with reference to stage422. Second beam analyzer430′ may also be configured to determine a position of inspection apparatus400, or any other reference element, such that the center of symmetry of alignment mark or target418may be known with reference to inspection apparatus400, or any other reference element. Second beam analyzer430′ may be further configured to determine the overlay data between two patterns and a model of the product stack profile of substrate420. Second beam analyzer430′ may also be configured to measure overlay, critical dimension, and focus of target418in a single measurement.

In some embodiments, second beam analyzer430′ may be directly integrated into inspection apparatus400, or it may be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other embodiments. Alternatively, second beam analyzer430′ and beam analyzer430may be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams429and439.

In some embodiments, processor432receives information from detector428and beam analyzer430. For example, processor432may be an overlay calculation processor. The information may comprise a model of the product stack profile constructed by beam analyzer430. Alternatively, processor432may construct a model of the product mark profile using the received information about the product mark. In either case, processor432constructs a model of the stacked product and overlay mark profile using or incorporating a model of the product mark profile. The stack model is then used to determine the overlay offset and minimizes the spectral effect on the overlay offset measurement. Processor432may create a basic correction algorithm based on the information received from detector428and beam analyzer430, including but not limited to the optical state of the illumination beam, the alignment signals, associated position estimates, and the optical state in the pupil, image, and additional planes. The pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor432may utilize the basic correction algorithm to characterize the inspection apparatus400with reference to wafer marks and/or alignment marks418.

In some embodiments, processor432may be further configured to determine printed pattern position offset error with respect to the sensor estimate for each mark based on the information received from detector428and beam analyzer430. The information includes but is not limited to the product stack profile, measurements of overlay, critical dimension, and focus of each alignment marks or target418on substrate420. Processor432may utilize a clustering algorithm to group the marks into sets of similar constant offset error, and create an alignment error offset correction table based on the information. The clustering algorithm may be based on overlay measurement, the position estimates, and additional optical stack process information associated with each set of offset errors. The overlay is calculated for a number of different marks, for example, overlay targets having a positive and a negative bias around a programmed overlay offset. The target that measures the smallest overlay is taken as reference (as it is measured with the best accuracy). From this measured small overlay, and the known programmed overlay of its corresponding target, the overlay error may be deduced. Table 1 illustrates how this may be performed. The smallest measured overlay in the example shown is −1 nm. However this is in relation to a target with a programmed overlay of −30 nm. Consequently the process must have introduced an overlay error of 29 nm.

TABLE 1Programmed overlay−70−50−30−10103050Measured overlay−38−19−121436690Difference between32312931333640measured andprogrammed overlayOverlay error32—24711
The smallest value may be taken to be the reference point and, relative to this, the offset may be calculated between measured overlay and that expected due to the programmed overlay. This offset determines the overlay error for each mark or the sets of marks with similar offsets. Therefore, in the Table 1 example, the smallest measured overlay was −1 nm, at the target position with programmed overlay of 30 nm. The difference between the expected and measured overlay at the other targets is compared to this reference. A table such as Table 1 may also be obtained from marks and target418under different illumination settings, the illumination setting, which results in the smallest overlay error, and its corresponding calibration factor, may be determined and selected. Following this, processor432may group marks into sets of similar overlay error. The criteria for grouping marks may be adjusted based on different process controls, for example, different error tolerances for different processes.

In some embodiments, processor432may confirm that all or most members of the group have similar offset errors, and apply an individual offset correction from the clustering algorithm to each mark, based on its additional optical stack metrology. Processor432may determine corrections for each mark and feed the corrections back to lithographic apparatus100or100′ for correcting errors in the overlay, for example, by feeding corrections into the inspection apparatus400.

Exemplary Inspection Apparatuses Using Phased Arrays

Until now, the discussion has focused on inspection apparatuses that use optical hardware (e.g., beam splitter414, interferometer426) to collect and direct light scattered by the target structure toward a detector. The optical hardware is also often needed for correcting aberrations or otherwise adjusting radiation that has been scattered by a target structure. In some example, size requirements of light-directing optical hardware may mean large sensor footprints, e.g., in the order of approximately 20 mm×20 mm or greater. In these examples, due to large sensor footprints, inspection apparatuses may include only one or a few sensing components for inspecting a wafer, which may impact the ability to inspect large numbers of wafers in a given time frame. The speed of wafer inspection can be increased by, for example, decreasing the time per measurement (e.g., by collecting more photons) and/or increasing the number of independent sensing components (e.g., by reducing the footprint). Embodiments of the present disclosure provide structures and functions to more quickly and efficiently perform inspection of structures on a substrate.

FIG.5shows a schematic of an inspection apparatus550, according to some embodiments. In some embodiments, inspection apparatus550comprises an illumination system500and a detector546. Inspection apparatus550may comprise an optical element544and more iterations of illumination system500. Optical element544may comprise a lens or a system of lens elements. Inspection apparatus550may comprise a photonic integrated circuit (PIC) on which illumination system500is disposed. Optical element544and/or detector546may also be disposed on the PIC.

In some embodiments, illumination system500is configured to generate a beam of radiation516. Illumination system500may adjust the direction beam of radiation516. It should be appreciated that directions of beam of radiation516depicted inFIG.5are not limiting. For example, directions of beam of radiation516may be adjusted into or out of the page. Illumination system500may comprise one or more phased arrays. The phased arrays allow adjusting the direction of beam of radiation516.

In some embodiments, a measurement comprises directing beam of radiation516toward a target structure536. Target structure536is disposed on a substrate538. Target structure536scatters (e.g., diffracts) radiation to generate scattered radiation542. The measurement further comprises receiving scattered radiation542at detector546. Optical element544may be used to focus scattered radiation542onto detector546.

In some embodiments, inspection apparatus550may be implemented as part of lithographic apparatus100or100′ (FIGS.1A and1B). Inspection apparatus550may be implemented as an alignment apparatus for aligning a substrate with respect to a reticle.

In some embodiments, inspection apparatus550is configured to measure a result of a lithographic process (e.g., overlay error) performed on a substrate. Measuring the result of the lithographic process may be performed outside of a lithographic apparatus (e.g., in a detached metrology apparatus or dedicated overlay inspection tool).

FIG.6shows a schematic of an illumination system600, according to some embodiments. In some embodiments, illumination system600may be implemented as part of an inspection apparatus, e.g., as illumination system500in inspection apparatus550(FIG.5).

In some embodiments, phase modulators602are disposed along waveguides604(e.g., intersecting or adjacent to waveguides). In some embodiments, optical elements606are disposed downstream of phase modulators602along waveguides604. In some embodiments the number of phase modulators602, waveguides604, and optical elements606are equal (e.g., there is a one-to-one-to-one correspondence in a set of a phase modulator, waveguide, and optical element). In some embodiments, phase modulators602, waveguides604, and optical elements606are arranged as a so-called phased array (e.g., an array of radiation elements for generating radiation having given phases).

In some embodiments, waveguides604are configured to guide radiation. The radiation may be supplied by radiation source608and received at inputs of the phased array. Merely as an example, line612indicates the inputs. Waveguides604may be configured to guide radiation (e.g., from radiation source608) to optical elements606. Optical elements606may be configured to radiate radiation waves614(e.g., by outcoupling the radiation from waveguides604). Optical elements606may be referred to herein as “emitters,” “emission elements,” and the like, referencing their function of emitting radiation. Phase modulators602are configured to adjust phases of radiation waves614.

In some embodiments, the phases of radiation waves614are adjusted such that radiation waves614accumulate to form a beam of radiation616. The direction of beam616is based on the phases of radiation waves614. The phased array of illumination system600may generate of radiation616and to direct beam of radiation616(e.g., toward a target structure). Phase modulation may comprise adjusting phase delays of radiation waves614. Phase modulation may comprise staggering phase delays of radiation waves614. InFIG.6, the direction angle θ of beam of radiation616is provided as an example and is not limiting. It should also be appreciated that illumination system600may comprise a 2-dimensional phased array. A 2-dimensional arrangement allows adjusting the direction of beam of radiation616in two dimensions (e.g., out of the page;FIG.6shows a 1-dimensional array for simplicity).

In some embodiments, illumination system600comprises a PIC. In other words, illumination system600and components therein (e.g., radiation sources, phase modulators, etc.) may be part of a PIC. The PIC allows illumination system600to be built extremely small (e.g., sub-millimeter). In some embodiments, illumination system600may reduce the number of optical components in a metrology tool. For example, it is possible to reduce or eliminate the need for optical hardware traditionally used to direct light (e.g., lens, mirror, beam splitter, micro-electro-mechanical system (MEMS), and the like). Illumination system600may adjust the direction beam of radiation616without using optical hardware or moving elements (e.g., mechanical elements). Consequently, a metrology system (e.g., an alignment sensor) may be substantially miniaturized compared to traditional metrology systems that rely on bulky optical hardware.

In some embodiments, controller610is configured to control phase modulators602to control the direction of beam of radiation616. It should be appreciated that controller610may be external to illumination system600.

In some embodiments, radiation source608is configured to generate broadband wavelengths or two or more narrowband wavelengths. In some embodiments, radiation source608comprises two or more source elements618. Each source element of source elements618is configured to generate a subset of the broadband wavelengths and/or the two or more narrowband wavelengths. The radiation generated by radiation source608may be coherent radiation. When generating multiple wavelengths with a single source element, each wavelength component may be coherent. Multi-wavelength coherent radiation sources are commercially available. Source elements618may be, e.g., laser diodes.

For ease of discussion, a first phased array622is designated by a dotted outline. In some embodiments, illumination system600comprises a second phased array624. For simplicity, phased array has been drawn with simplified inputs from source radiation source608and controller610. However, it should be appreciated that elements and arrangements within second phased array624are substantially similar (e.g., symmetrized) to first phased array622. In some embodiments, illumination system comprises more phased arrays.

In some embodiments, one or more spectral filters620may be used to select one or more wavelengths from radiation source608to enter first and second phased arrays622and624. For example, first and second spectral filters may be used to select respective first and second wavelengths from radiation source608. A first wavelength may enter first phased array622and the second wavelength may enter a second phased array624. First phased array624may generate beam of radiation616having the first wavelength and phased array622may be used to generate another beam of radiation having the second wavelength. The first and second wavelengths may be substantially different or similar. A direction of the beam from phased array at622may be adjusted independently from beam of radiation616(e.g., toward a target structure). In some embodiments, beams from first phased array622and second phased array624have substantially similar wavelengths.

FIG.7shows a schematic of an illumination system700, according to some embodiments. Particularly,FIG.7shows a non-limiting example of an arrangement of phased arrays (e.g., illumination system600ofFIG.6may be so altered). Therefore, elements ofFIG.7may be considered to have similar structures and functions as similarly numbered elements inFIG.6(e.g., elements sharing the two right-most numeric digits).

In some embodiments, illumination system700comprises phased arrays722a,722b,724a, and724b. Illumination system700may further comprise one or more additional phased arrays726.

In some embodiment, phased array722acomprises phase modulators702, waveguides704, and optical elements706(substantially similar to phase modulators602, waveguides604, and optical elements606inFIG.6). In some embodiments, phased arrays722b,724a,724b, and one or more additional phased arrays726comprise structures and functions that may be substantially similar to those of phased array722a. Illumination system700may further comprise optical filters720, a major waveguide728, waveguides730, a radiation source708, a controller710, and/or a multiplexer732. In some embodiments, illumination system700comprises a PIC. Furthermore, any phased arrays may be omitted, for example, to simplify PIC designs by having single phased array(s) instead of phased array pairs.

In some embodiments, radiation source708is configured to generate radiation. Radiation generated by radiation source708may have one wavelength, multiple wavelengths, or a continuum of wavelengths. In some embodiments, radiation source708comprises two or more source elements718. Each source element718is configured to generate a subset of the broadband wavelengths and/or the two or more narrowband wavelengths. Major waveguide728may be a multi-mode waveguide for allowing multiple wavelengths. In embodiments in which two or more wavelengths are generated by distinct source elements, multiplexer732may be used to combine radiation of different wavelengths into a single channel (e.g., major waveguide728).

In some embodiments, radiation generated by radiation source708may be received at inputs of phased arrays722a,722b,724a,724b, and/or one or more additional phased arrays726. Major waveguide728and waveguides730may be used to guide the radiation from radiation source708to phased arrays722a,722b,724a,724b, and/or one or more additional phased arrays726. For example, major waveguide728guides radiation from radiation source708to a first optical filter of optical filters720. In some embodiments, the first optical filter of optical filters720selects a first wavelength to send to phased arrays722aand722bvia corresponding waveguides of waveguides730. Thus optical filters720may perform demultiplexing. It should be appreciated that other demultiplexing solutions may be envisioned. For example, optical filters720may be replaced with a single demultiplexer for selecting and sending given wavelengths to waveguides730and the phased arrays.

A depiction of a single major waveguide728should not be construed as limiting (current depiction is merely for simplification of the drawing). It should be appreciated that alternative arrangements can be envisioned for major waveguide728, radiation source708, and/or waveguides730. For example, in some embodiments, illumination system700may comprise a major waveguide per pair of phased arrays. In some embodiments, illumination system700may omit major waveguide728and directly couple waveguides730to corresponding source elements718(correspondence may be based on desired wavelength for each phased array). In this scenario, optical filters720may be omitted since waveguides730would be configured to directly receive a single narrowband wavelength from corresponding source elements718.

It was mentioned that in some embodiments illumination system600(FIG.6) could be used to generate beams of radiation, each beam having a distinct wavelength. Similarly, in some embodiments, phased arrays722aand/or722bare configured to generate a beam of radiation having a first wavelength. And phased arrays724aand/or724bare configured to generate another beam of radiation having a second wavelength. Corresponding optical filters of optical filters720may be used to select the first and second wavelengths. Similarly, one or more additional phased arrays726may be used to generate other wavelengths. In some embodiments, illumination system700may generate beams of a number of wavelengths A from the phased arrays (e.g., λ1, λ2, . . . λN).

Therefore, in some embodiments illumination system700is capable of generating one or more beams of radiation, some beams having distinct wavelengths and/or some having substantially similar wavelengths. Similar to discussions in reference toFIG.6, the phased arrays of illumination system700allow adjusting directions of the beams. For example, controller710is configured to control phase modulators (e.g., phase modulators702) to control the directions of the beams generated by each phased array. It should be appreciated that controller710may be external to illumination system700.

A polarization state of the beams generated phased arrays may be determined by the orientation of the phased arrays. Therefore, it may be advantageous to introduce a set of phased arrays rotated by 90 degrees. In some embodiments, illumination system700may comprise a set of phased arrays734that are substantially similar to phased arrays722a,722b,724a,724b, and one or more additional phased arrays726. The line of phased arrays734may be rotated by 90 degrees with respect to phased arrays722a,722b,724a,724b, and one or more additional phased arrays726(shown by the dotted outlines of phased arrays734). For simplicity, only half of phased arrays734are shown as the other half would be disposed approximately at the locations of optical filters720. It should be appreciated that all of the phased arrays in illumination system700may be disposed on a single PIC substrate (e.g., multi-layered and/or rerouting waveguides) or may be distributed over two or more PICs in order to allow accommodation of all of the phased arrays in illumination system700.

FIG.8shows a perspective view of an illumination system800, according to some embodiments. Elements ofFIG.8may have similar structures and functions as similarly numbered elements inFIGS.6and7(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.8in order to enhance clarity (e.g., an analog to radiation source708ofFIG.7). Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.8may also comprise elements analogous to those shown inFIGS.6and7.

In some embodiments, illumination system800comprises phased arrays822a,822b,824a, and824b. Illumination system800may further comprise one or more additional phased arrays826. Phased arrays822a,822b,824a,824b, and one or more additional phased arrays826, may comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, phased arrays822aand822bare configured to generate beams of radiation816. Beams of radiation816may have a first wavelength. Beams of radiation816may be directed at a target structure836. Target structure836is disposed on a substrate838. Phased arrays824aand824bare configured to generate beams of radiation840. Beams of radiation840may be directed at a target structure836. Beams of radiation840may have a second wavelength. The first and second wavelengths are generated as described in reference toFIG.7. In some embodiments, illumination system800may generate beams of a number of wavelengths A from the phased arrays (e.g., λ1, λ2. . . λN).

In some embodiments, phased arrays822a,822b,824a,822b, and one or more additional phased arrays826, are configured to direct and steer the beams they generate. For example, beams of radiation816may be adjusted to illuminate a location on target structure836(e.g., beam spots overlap). In some embodiments, target structure836scatters (e.g., diffracts) beams of radiation816and840, shown as scattered radiation842. Beams of radiation840may also be adjusted to illuminate the same, or substantially similar, location as illuminated by beams of radiation816. In some embodiments, steering the beams allows the angle of incidence of the beams on target structure836to be adjusted. To change the angle of incidence, substrate838may be moved in the Z-direction (toward or away from illumination system800) and beams of radiation816and/or840are steered to illuminate target structure836at a different angle of incidence. Thus, it is possible to adjust the angle of incidence through a continuum of off-axis angles (e.g., angles of incidence different from zero). An advantage is that a direction of scattered radiation842may be adjusted.

FIG.9shows a schematic of a metrology system950, according to some embodiments. Elements ofFIG.9may have similar structures and functions as similarly numbered elements inFIGS.5-8(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.9in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.9may also comprise elements analogous to those shown in, e.g.,FIGS.6-8.

In some embodiments, metrology system950comprises an illumination system900, an optical element944, and a detector946. Illumination system900comprises phased arrays924a,924b, and one or more additional phased arrays926. Phased arrays924a,924b, and/or one or more additional phased arrays926comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6). Optical element944may comprise a lens or a system of lens elements.

In some embodiments, phased arrays924aand924bare configured to generate beams of radiation940. Beams of radiation940may be directed at a target structure936. Target structure836is disposed on a substrate938. In some embodiments, illumination system900may generate beams of a number of wavelengths λ from the phased arrays (e.g., λ1, λ2. . . λN) as described in reference to, e.g.,FIGS.6,7, and8.

In some embodiments, phased arrays924a,924b, and one or more additional phased arrays926are configured to direct and steer the beams they generate. For example, beams of radiation940may be adjusted to illuminate a location on target structure936. Target structure936scatters beams of radiation940, shown as scattered radiation942. Scattered radiation942may be incident on detector946. That is, detector946may receive scattered radiation942. Detector946may generate a measurement signal based on the receipt of scattered radiation942. In one embodiment, to enhance the optical signal or image, optical element944may focus scattered radiation942onto detector946.

FIG.10shows a schematic of a metrology system1050, according to some embodiments. Earlier it was mentioned that a direction of radiation scattered by a target may be adjusted. Controlling the direction of scattered radiation is shown by example inFIG.10. Elements ofFIG.10may have similar structures and functions as similarly numbered elements inFIGS.5-9(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.10in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.10may also comprise elements analogous to those shown in, e.g.,FIGS.6-9.

In some embodiments, metrology system1050comprises an illumination system1000, an optical element1044, and a detector1046. Illumination system1000comprises phased arrays1024a,1024b, and one or more additional phased arrays1026. Phased arrays1024a,1024b, and/or one or more additional phased arrays1026comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, phased arrays1024aand1024bare configured to generate beams of radiation1040. Beams of radiation1040may be directed at a target structure1036. Target structure1036may be disposed on a substrate1038. Substrate1038may be disposed on a substrate table1048. Substrate table1048may be configured to move in any of axes X, Y, and Z, where the Z-axis is defined inFIG.10as being perpendicular to the surface of substrate1038. Coordinate axes are provided for clarity of description and are not limiting. In some embodiments, illumination system1000may generate beams of a number of wavelengths λ from the phased arrays (e.g., λ1, λ2. . . λN) as described in reference to, e.g.,FIGS.6,7, and8.

In some embodiments, phased arrays1024a,1024b, and one or more additional phased arrays1026are configured to direct and steer the beams they generate. For example, beams of radiation1040may be adjusted to illuminate a location on target structure1036. Target structure1036scatters beams of radiation1040, shown as scattered radiation1042.

In some embodiments, the structures, functions, and interactions of optical element1044, detector1046and scattered radiation1042may be as described previously for optical element944, detector946, and scattered radiation942ofFIG.9.

Earlier it was mentioned that embodiments perform, among others things, adjusting directions of both radiation incident on a target and radiation scattered by the target.FIG.10illustrates how it may be accomplished. Directions of beams of radiation1040may be adjusted by phased arrays1024aand1024b(shown via respective angles θaand θb, which may or may not be equal). Depending on parameters (e.g., Z distance, geometry of target), scattered radiation1042may or may not be directed at detector1046(see scattered radiation942inFIG.9). This may be remedied by moving substrate table1048(e.g., in the Z direction) so that scattered radiation1042(being a diffraction order) is directed substantially perpendicular to the surface of substrate1038. Consequently, the aspherity requirements of optical element1044may be relaxed (e.g., can use lenses with low numerical aperture (NA)) and the overall X-Y footprint of the lens/detector stack can be reduced. In contrast, traditional optical measurements collect radiation over a large range of scattering angles, often requiring collection optics having high NA.

Metrology systems employing optical hardware tend to have large X-Y footprints. For example, it may be difficult to engineer metrology system400, with all its optical hardware, to fit in a footprint less than 400 mm2(e.g., 20 mm×20 mm). Since the illumination systems having phased arrays can also be miniaturized via PICs, it is possible to reduce their footprint. The term “footprint” may be used herein to refer to a cross section of a metrology system that is substantially perpendicular to the scattered radiation it receives from a target. For example, the Z-axis inFIG.10is perpendicular to the footprint of metrology system1050.

In some embodiments, a PIC-based metrology system (e.g., having at least a light source and a detector) may comprise a footprint having an area less than approximately 100 mm2, 50 mm2, 25 mm2, or 16 mm2. The PIC-based metrology system may comprise a footprint having a width less than approximately 10 mm, 7 mm, 5 mm, or 4 mm. By transitive property, these dimensions also apply to footprints of individual elements within the PIC-based metrology system.

FIG.11shows a schematic of a metrology system1150, according to some embodiments. Embodiments referring toFIG.11show, for example, how fewer phased arrays may be employed to further reduce a footprint of a metrology system. Elements ofFIG.11may have similar structures and functions as similarly numbered elements inFIGS.5-10(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.10in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.11may also comprise elements analogous to those shown in, e.g.,FIGS.6-10.

In some embodiments, metrology system1150comprises an illumination system1100, an optical element1144, and a detector1146. Metrology system1150further comprises a time multiplexer1152and a phase shifter1154. Illumination system1100comprises phased arrays1122aand1122b. Time multiplexer1152and phase shifter1154may be comprised within illumination system1100as they are components related to beam generation. For example, time multiplexer1152and phase shifter1154may be disposed on a PIC substrate of metrology system1150. Phased arrays1122aand1122bcomprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, phased arrays1122aand1122bare configured to generate beams of radiation1116. Beams of radiation1116may be directed at a target structure1136. Target structure1136is disposed on a substrate1138. Substrate1138may be disposed on a substrate table1148. In some embodiments, phased arrays1122aand1122bare configured to direct and steer the beams they generate. For example, beams of radiation1116may be adjusted to illuminate a location on target structure1136. Target structure1136scatters beams of radiation1116, shown as scattered radiation1142.

In some embodiments, the structures, functions, and interactions of optical element1144, detector1146and scattered radiation1142may be as described previously for optical element944, detector946, and scattered radiation942ofFIG.9.

In some embodiments, illumination system1100may generate beams of a number of wavelengths λ from the phased arrays (e.g., λ1, λ2. . . λN) as described in reference to, e.g.,FIGS.6,7, and8. However, in some embodiments, time multiplexer1152and phase shifter1154may be used to modify the wavelength generation as described in reference toFIGS.6,7, and8, for example, by allowing phased arrays1122aand1122bto output radiation having a wavelength that is selectable from a plurality of wavelengths. That is, phased arrays are not dedicated to a particular wavelength. In contrast,FIG.7showed the use of optical filters720, which would potentially commit a phased array to a particular wavelength if the optical filters are not adjustable.

In some embodiments, multi-wavelength radiation may be passed through time multiplexer1152. Time multiplexer1152is configured to allow through one wavelength at any given time. The multi-wavelength radiation may be generated by a radiation source as described in reference toFIG.6(e.g., radiation source608). The radiation source may be disposed within illumination system1100. The radiation passed through time multiplexer1152may then be passed through phase shifter1154. The function of phase shifter1154is to adjust phases to account for certain changes in beams of radiation1116arising from changing their wavelength. In one example, the directions θaand θbof beams of radiation1116are sensitive to the wavelength of the radiation. Switching the wavelength (e.g., using a multiplexer) can appreciably shift the beam directions even when other parameters of beam generation are kept the same. Therefore, phase shifter1154may further adjust the phases of the radiation in illumination system1100(in addition to phase modulators) to account for the changes introduced by going from one wavelength to another, so as to preserve a directional response of beams of radiation1116. Phase shifter1154may be in communication with detector1146. The phase adjustments made by phase shifter1154may be based on the measurement signal generated by detector1146.

An advantage of using time multiplexer1152and/or phase shifter1154is that they can be implemented via integrated optics, allowing for size reduction of metrology system1150and relying on fewer or no moving parts.

Regarding phased arrays, they are also advantageous because they allow manipulation of more than just a beam direction. For example, the intensity distribution of a beam spot may be adjusted, which as advantageous for metrology systems. For example, an optical measurement can be made more accurately if the beam spot fills only the intended target and avoids illuminating structures outside of the target.FIGS.12-15will further illustrate an example of beam spot control.

FIG.12shows a graph1255of a “top-hat” intensity profile1256(or top-hat profile or beam cross section) of a beam of radiation, according to some embodiment. Top-hat intensity profile1256departs from a traditional Gaussian intensity distribution of typical coherent beams (e.g., a laser). The vertical axis of graph1255represents a relative intensity of a beam of radiation, given in arbitrary units (a. u.). The horizontal axis of graph1255represents a distance or displacement, along the X-axis, from the center of the beam at a slice corresponding to Y=0 (beam center is positioned at (X,Y)=(0,0)). Units of mm are provided on the horizontal axis as example only, and should not be construed as limiting. Top-hat intensity profile1256was generated by numerical simulation, to be further clarified in reference toFIG.13. Inset1257is a two-dimensional intensity map representation of the data in graph1255.

In some embodiments, top-hat intensity profile1256comprises a constant intensity region1258and an outer region1260. Constant intensity region1258has substantially constant or flat illumination intensity, e.g., over most of the cross section of the beam of radiation. Outer region1260shows a small crest of the intensity, which is a residual from the numerical simulation. In some embodiments, the crest in outer region1260may be reduced to the same magnitude as constant intensity region1258, whether in simulation or in actual beam generation. Therefore, in some embodiments, outer region1260may be absent and the intensity drops off immediately at the edge of constant intensity region1258.

Top-hat intensity profile1256is a trait of a beam spot that may allow for a more uniform illumination of a target structure, while preventing or reducing illumination of features outside of the target structure. Illuminating features outside of the target structure may lead to undesirable scattered radiation being detected (cross-talk).

FIG.13shows an exemplary wavefront of a beam of radiation1316, according to some embodiments.FIG.13shows how a numerical simulation may be setup to arrive at top-hat intensity profile1256(FIG.12). In some embodiments, the wavefront of beam of radiation1316may be modeled via a superposition of radiation waves1314. Radiation waves1314may be beamlets (e.g., Gaussian beamlets). Each radiation wave1314may have a wavefront surface normal1362that indicates a propagation direction of the beamlet. Parameters of radiation waves1314(e.g., phases, amplitudes, position, and the like) may be adjusted to arrive at a wavefront intensity distribution that is substantially similar to top-hat intensity profile1256(FIG.6). Embodiments described hearing provide structures and functions for generating beams of radiation having a top-hat intensity profile.

FIG.14shows an illumination branch of a metrology system1450, according to some embodiments. In some embodiments, metrology system1450comprises an illumination system1400and an optical element1462. Optical element1462may comprise a lens element1462a, an aperture1462band/or a lens element1462c. Lens element1462amay be a beam shaper (e.g., a bi-asphere lens). Lens element1462cmay be a re-image lens or an achromatic mirror.

In some embodiments, illumination system1400is configured to generate beam of radiation1416. Beam of radiation1416may comprise beamlets of radiation1414. Upstream of optical element1462, beam of radiation1416may have a substantially non-flat (e.g., Gaussian) intensity profile1464. Illumination system1400may be of a type that has difficulty generating a top-hat intensity profile (e.g., a typical laser). Therefore, optical element1462may be configured to shape an intensity distribution of beam of radiation1416so as to generate a top-hat intensity profile1456(see top-hat intensity profile1256,FIG.12). Beam of radiation1416, having a top-hat intensity profile1456may then be directed at a substrate1438.

FIG.15shows an illumination branch of a metrology system1550, according to some embodiments. In some embodiments, metrology system1550comprises an illumination system1500and optical elements1562. However, different fromFIG.14, optical elements1562may comprise a freeform reflective beam shapers.

In some embodiments, illumination system1500is configured to generate beam of radiation1516. Beam of radiation1516may comprise beamlets of radiation1514. Upstream of optical elements1562, beam of radiation1516may have a substantially non-flat (e.g., Gaussian) intensity profile1564. Illumination system1500may be of a type that has difficulty generating a top-hat intensity profile (e.g., a typical laser). Therefore, optical elements1562may be configured to shape an intensity distribution of beam of radiation1516so as to generate a top-hat intensity profile1556(see top-hat intensity profile1256,FIG.12). Beam of radiation1516, having a top-hat intensity profile1556may then be directed at a substrate1538.

Embodiments referencingFIGS.14and15use optical hardware (e.g., optical elements1462and1562) that can increase the volume requirements of a metrology system. However, in embodiments involving phased arrays, the illumination sources may allow for beam shaping without using additional optical hardware.

In reference toFIG.6, in some embodiments, the wavefront of beam of radiation616may be approximately modeled by superimposing radiation waves614. One example approximation may be, for example, approximating radiation waves614as Gaussian beamlets (e.g., instead of spherical waves). Based on the numerical simulation, parameters of beam generation may be determined (e.g., phases and amplitudes of radiation waves614) that allow beam of radiation616to achieve an intensity profile that is substantially similar to top-hat intensity profile1256(FIG.12). Thus, in some embodiments, beams generated by phased arrays comprise beam profiles that are adjustable based on adjusted phases and amplitudes.

In some embodiments, phased arrays may generate a beam with a top hat-intensity profile having full-width at half-maximum less than approximately 2 microns. In some embodiments, the top hat-intensity profile has a full-width at half-maximum less than approximately 500 nm.

Example Methods for Inspecting Results of a Lithographic Process

In some embodiments, an optical measurement performed on a substrate may comprise capturing a high definition image (e.g., using a camera detector) of a target structure on a substrate. One commercially available example is the previously mentioned Yieldstar™ of ASML. Embodiments of the present disclosure (e.g.,FIGS.5,9,10, and11) may also be used to perform image capture measurements.

In some embodiments (usingFIG.10as an example), detector1046comprises an image capture device (e.g., a camera). Detector1046may generate a measurement signal based on the received radiation or detected image (e.g., scattered radiation1042from target structure1036). The measurement signal may comprise information of the received radiation, for example, intensity, phases, and the like.

Metrology system1050may divide the detected image into subregions (e.g., image pixels). The subregions may result directly from individual detector elements of a camera (hardware-based) or may be determined by a processor or controller (software-based, e.g., interpolation). Furthermore, known computational enhancement techniques may be used for enhancing image clarity/focus of the detected image and/or reducing aberrations arising from the optics of metrology system1050. From the measurement signal, a lithographic properties of substrate1038may be determined (e.g., overlay error, critical dimension parameters, and the like).

Phase information is different than imaging techniques that illuminate targets with incoherent radiation. For example, using a phased-array based metrology system, a target measured at different Z-positions may result in detected images having different phases. In some embodiments, a first optical measurement comprises illuminating target structure1036(e.g., using beam of radiation1040) and detecting scattered radiation1042, all at a first Z-position Z1of target structure1036. A second optical measurement comprises the steps of the first optical measurement performed at a Z-position Z2of target structure1036. The difference in Z-positions may be between approximately 0 to one wavelength of scattered radiation1042. Metrology system1050, using a processor or controller, may then compare measurement signals from the first and second optical measurements, for example, phase differences. Aberrations in metrology system1050(e.g., from optical element1044) may be determined based on the phase differences. The aberrations may then be compensated computationally without using additional optical hardware (e.g., more lenses). Thus, metrology systems in embodiments of the present disclosure are capable of making accurate optical measurements while footprints much smaller than dictated by additional optical hardware.

In some embodiments, detecting an image of target structure1036comprises moving substrate1038in the X-Y plane (e.g., scanning beams of radiation1040across target structure1036by moving substrate table1048). However, scanning may cause beams of radiation1040to fall on structures outside of target structure1036and may cause undesirable interference in the detected image of target structure1036. Therefore, in some embodiments, detecting an image of target structure1036comprises performing the measurement while target structure1036is motionless relative to detector1046(i.e., substrate1038and substrate table1048are motionless). In this scenario, the illumination spot generated by beams of radiation1040are adjusted such that the spot size of the illumination spot just fills target structure1036while minimizing illumination of structures surrounding target structure1036. The illumination spot may comprise an intensity profile that is substantially similar to top-hat intensity profile1256(FIG.12).

In some embodiments, the term cross-talk is used to describe the phenomena of interference resulting from illuminating structures outside of the target (e.g., cross-talk between desirable and undesirable scattered radiation arriving at the detector). Structures and functions of the present disclosure can be used to reduce cross-talk.

FIGS.16A and16Billustrate example illumination techniques for compensating for the effects of cross-talk in a metrology system, according to some embodiments. Particularly,FIG.16Arelates to a stationary beam spot measurement whileFIG.16Brelates to a scanning measurement to move the beam spot in an annular path.

ReferencingFIG.16, in some embodiments, a target structure1636is illuminated by beam of radiation1616. Beam of radiation1616may be generated using embodiments of metrology and illumination systems of the present disclosure. Beam of radiation1616may have a beam spot that just nearly envelops the entirety of target structure1636(e.g., just barely overfilled). In some embodiments, beam of radiation1616has an intensity profile that is substantially similar to top-hat intensity profile1256(FIG.12). Top-hat intensity profile1256provides a steep drop in the illumination intensity near the edge of constant intensity region1258(FIG.12). Therefore, illumination of structures outside of target structure1636may be reduced or avoided. A beam spot having a Gaussian-like intensity profile would have an intensity that does not drop off as rapidly, and would therefore result in increased illumination of structures outside of target structure1636, which in turn increases cross-talk.

There may be instances where structures are printed very close to target structure1636, for example, for efficient use of substrate surface area. Therefore, it may be difficult to avoid illuminating structures printed closely to target structure1636.FIG.16Billustrates an example measurement technique to gather information about how structures nearby target structure1636can interfere with measurements. In some embodiments, a beam spot of beam of radiation1616is reduced to underfill target structure1636. The beam manipulation capabilities of phased arrays may be used to achieve the reduced size of the beam spot. Using the beam steering capabilities of phased arrays, beam of radiation1616may be scanned around target structure1636(e.g., in a circle, a ring path) so as to illuminate structures outside of target structure1636(of particular interest are the structures outside of target structure1636that would be illuminated by the beam spot illustrated inFIG.16A). The radiation scattered by the structures outside of target structure1636is detected and a measurement signal is generated.

In some embodiments, the measurement information gathered in reference toFIG.16B(e.g., background measurement) may be used to enhance the clarity of the measurement in reference toFIG.16A(e.g., signal-of-interest). Thus, the effects of cross-talk may be compensated or reduced by removing, from the signal-of-interest, the influence of the structures outside of target structure1636.

In some embodiments, using phased arrays as described herein allows selectable wavelength. Different wavelengths may have differing cross-talk contributions. Embodiments in reference toFIG.16may be performed at different wavelength selections in order to treat the different cross-talk contributions.

In some embodiments, the structures and functions described herein for inspecting results of a lithographic process may be combined with other inspection techniques, for example, diffraction-based overlay as described in U.S. Pat. No. 8,339,595, which is incorporated by reference herein in its entirety.

Example Methods for Inspecting Alignment of a Substrate

When performing a lithographic process on a substrate, it is important for the substrate to be in precise alignment within the lithographic apparatus such that the newly applied layer lays on top of existing layers on the substrate with precise positioning (overlay). Therefore, lithographic apparatuses rely on metrology systems to measure the position of the substrate relative to the position of the projected illumination pattern of the new layer (e.g., alignment sensors, position sensors IF1and IF2inFIG.1A). Commercially available examples of alignment sensors are the previously mentioned SMASH and ATHENA sensor by ASML of Netherlands. Structures and functions of alignment sensors have been discussed in reference toFIG.4and in U.S. Pat. No. 6,961,116 and U.S. Pub. Appl. No. 2009/195768, which are all incorporated by reference herein in their entireties.

Before describing embodiments of alignment metrology systems in more detail, however, it is instructive to describe some of the optical phenomena employed in alignment and position sensing techniques.

In some embodiments, an alignment mark comprises a periodic structure, for example, a grating. The alignment mark may be the target structure to be scanned by an alignment metrology system. The alignment mark may comprise a given pitch, line width, and total width of the entire structure. The pitch of the alignment mark is particularly relevant to positioning accuracy. In some embodiments, a structured illumination may be incident on the alignment mark. The structured illumination may comprise a fringe pattern or periodic structure having parameters that are substantially similar to the alignment mark (e.g., pitch). The structured illumination may be achieved by placing a suitable reference plate (e.g., a grating) in the path of the illumination. When the alignment mark is scanned with a structured illumination, a Moiré effect may be produced, and radiation reflected by the alignment mark may experience periodic intensity variations during the scan. The radiation reflected by the alignment mark is directed at a detector. The detector may output a signal that is based on a property of the detected radiation (e.g., intensity, power, and the like). It should be appreciated that the reference plate may be placed downstream of the alignment mark, i.e., in the detection branch of the metrology system. In this scenario, the alignment mark may produce the structured illumination (e.g., by reflection), which is then passed through the reference plate and then to the detector. The detected intensity may have a similar periodic variation during a scan. The previously mentioned Athena sensor employs a reference plate technique.

In some embodiments, the Moiré effect may be achieved without using a reference plate. For example, an alignment mark is illuminated with a beam having a standard spot (non-structured). The alignment mark, having a periodic structure, may scatter radiation along different diffraction order directions (e.g., −1 and +1). The diffracted radiation may comprise the periodic structure of the alignment mark. Using suitable routing optics, the separated diffraction orders may be brought together to achieve the Moiré effect. Since the alignment mark serves as both the target and the reference, the technique is often referred to as self-referencing. The previously mentioned SMASH sensor employs a self-referencing alignment technique.

FIG.17shows a graph1700of integrated irradiance as a function of beam position on an alignment mark (e.g., a scanning measurement), according to some embodiments. The vertical axis may represent a normalized intensity of radiation at a detector of a metrology system, given in arbitrary units (a. u.). The detected radiation may comprise a Moiré pattern as discussed above. The horizontal axis may represent a relative position of the beam that illuminates the alignment mark, given in microns as an example and not limiting. As the beam moves across the alignment mark, the radiation incident on the detector may undergo a series of peaks1702and valleys1704. Inset1706may represent the intensity distribution on the detector at peaks1702, where dark is low intensity and bright is high intensity. Inset1708may represent the intensity distribution at valleys1704. In an embodiment where a reference plate is used, so long as the pitch of the structured illumination and the reference plate are substantially matched, the peaks and valleys may be used to accurately determine a position of the alignment mark, for example, by considering the known pitch, the number of peaks and valleys of the detected radiation, and the total width of the alignment mark. Conversely, in an embodiment where there is a pitch mismatch between the reference plate and the alignment mark may reduce accuracy of position determination. In some embodiments, self-referencing technique allows for the pitch to be matched since the reference and the target are based on a same alignment mark.

In some embodiments, devices features follow trends in the IC technology space to shrink device features and achieve an efficient use of wafer surface area. In some embodiments, smaller alignment marks with a continuous range of pitch options may be chosen for the reference structure. A reference plate technique may present difficulties for following such market trends. For example, a reference plate technique forces a user to include, in their wafer products, alignment marks that conform to one of the reference plates, even if the alignment marks adversely impact production performance. Reference plates may not be easily interchangeable. Even if interchangeable reference plates were used, the alignment marks may be limited based on available reference plate options.

In some embodiments, both the reference plate and self-referencing techniques depend on optical hardware that increase the footprint of the metrology system. It can be envisioned that multiple metrology systems may be closely packed together to inspect more targets on a substrate, simultaneously or nearly simultaneously (e.g., to increase inspection throughput and reduce production times). However, metrology systems having large footprints limit the number of metrology systems that can be closely packed. Embodiments of the present disclosure provide structures and functions for overcoming the above-mentioned issues of metrology systems.

FIG.18shows an illumination system1800, according to some embodiments. Elements ofFIG.18may have similar structures and functions as similarly numbered elements inFIGS.5-11(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.11in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.18may also comprise elements analogous to those shown in, e.g.,FIGS.6-11.

In some embodiments, illumination system1800comprises phased arrays1822aand1822b. In some embodiments, phased arrays1822aand1822bare configured to generate beams of radiation1816. Beams of radiation1816may be directed at a target structure1836. Target structure1836may be disposed on a substrate1838. Substrate1838may be disposed on a substrate table1848. In some embodiments, phased arrays1822aand1822bare configured to direct and steer the beams they generate. For example, beams of radiation1816may be adjusted to illuminate a location on target structure1836.

In some embodiments, illumination system1800may generate beams of a number of wavelengths λ from the phased arrays (e.g., λ1, λ2. . . λN) as described in reference to, e.g.,FIGS.6,7, and8. Phased arrays1822aand1822bmay output radiation having a wavelength that is selectable from a plurality of wavelengths (e.g., see time multiplexer1152ofFIG.11).

Coherent light sources may be interfered to create structured illumination (e.g., fringe pattern). For example, a fringe pattern is created in a laser-sourced interferometer. Similarly, in some embodiments, beams of radiation1816may be directed to overlap at a location on target structure1836. By exploiting the coherence nature of the beams, the beams may be interfered at the location. Consequently, the beam spot may comprise a fringe intensity profile1866. The position of the beam spot (relative to substrate1838) may be adjusted. Adjusting the beam spot's position may be achieved by controlling the directions of beams of radiation1816and/or moving substrate1838using substrate table1848. The adjustment function of the beam spot may be used for scanning across target structure1836, during a measurement for example.

In some embodiments, the pitch of fringe intensity profile may depend on the wavelength of radiation used and the angles of incidence of beams of radiation1816. The spatial distribution of fringe intensity profile1866may be approximated with the following equation:
I(x,t)=I1(t)+I2(t)+2√{square root over (I1(t)I2(t))} cos(2πx/Λ).  Eq. 1

In equation 1, I1and I2represent intensities of beams from respective phased arrays (e.g., from phased arrays1822aand1822b). The cosine term determines the periodic nature of fringe intensity profile1866. The pitch of fringe intensity profile1866is determined by the modulation period Λ, which is given by the following equation:

In equation 2, λ represents the wavelength of beams of radiation1816. In some embodiments, λ1is the angle of incidence (with respect to the surface of substrate1838) of beam of radiation1816coming from phased array1822awhile θ2regards phased array1822b. Thus, phased arrays1822aand1822bmay allow controlling the pitch of fringe-structured illumination in a continuous range. In some embodiments, a user of a metrology system employing illumination system1800has the freedom to design alignment marks with any pitch within the range afforded by modulation period Λ. Also, the overall size of alignment marks may be made much smaller than allowed by currently available metrology systems. As described previously in reference toFIG.10, the Z distance of substrate table1048may be adjusted to accommodate a range of values for angles of incidence θ1and θ2.

In some embodiments, a calibration structure1868(e.g., a reference plate) may be provided on substrate table1848or on some other fiducial of an apparatus that substrate table1848may belong to (e.g., a lithographic apparatus). Calibration structure1868may comprise a plurality of reference structures for a plurality of pitch settings. A reference structure on calibration structure1868may be illuminated with fringe intensity profile1866. The detection of radiation scattered by calibration structure1868may be used to determine whether fringe intensity profile1866truly has the selected pitch based on selected parameters of phased arrays1822aand1822b. Any detector of a metrology system may be used to receive radiation scattered by calibration structure1868(e.g., detector1046ofFIG.10or a dedicated calibration detector (not shown)).

In some embodiments, a controller (e.g.,710inFIG.7) may receive a pitch and/or wavelength selections as an input from a user. The controller may then determine phased array parameters (e.g., phase delays for adjusting angles of incidence) to achieve the selected pitch parameters based on the selected wavelength.

In some embodiments, phased arrays, such as1822aand1822b, allow metrology systems to avoid the need for reference plates or optical hardware employed in self-referencing techniques. Using compact metrology systems closely packed together may allow alignment marks, which are distributed on a substrate, to be closer to a metrology system. In some embodiments, even if the alignment mark is not perfectly parallel to the closest metrology system, only a short movement will allow the alignment mark to be moved into a measurement position. In some embodiments, the more densely packed the metrology systems are made, the shorter and fewer the movements of alignment marks may get, which may allow many more alignment marks to be inspected in a given time. For example, a size reduction of a metrology system from 400 mm2to 16 mm2allows 25 times more metrology systems to be fit for the same amount of area. And so the number of simultaneous or near simultaneous inspections can be greatly enhanced.

In some embodiments, metrology systems, phased arrays, and associated optical elements of the present disclosure are configured to work in wavelength ranges spanning UV, visible, and IR (e.g., approximately 400-2000 nm).

In some embodiments, a receiving system and the illumination system may be included on a single PIC. The receiver system receives scattered radiation by the target structure and redirect the scattered radiation to a detector. The receiver system may also be implemented on a separate PIC.

FIG.19shows a perspective view of an inspection system1950, according to some embodiments. Elements ofFIG.19may have similar structures and functions as similarly numbered elements inFIGS.6and7(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.19in order to enhance clarity (e.g., an analog to radiation source708ofFIG.7). Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.19may also comprise elements analogous to those shown inFIGS.6and7.

In some embodiments, inspection system1950includes an illumination system1900, a receiver system1970, and a detector (not shown).

In some embodiments, illumination system1900comprises phased arrays1922aand1922b. Phased arrays1922aand1922bmay comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, phased arrays1922aand1922bare configured to generate beams of radiation1916. Beams of radiation1916may have a first wavelength. Beams of radiation1916may be directed at a target structure1936. Target structure1936is disposed on a substrate1938. In some embodiments, illumination system1900may generate beams of a number of wavelengths λ from the phased arrays (e.g., λ1, λ2. . . λN).

In some embodiments, phased arrays1922aand1922b, are configured to direct and steer the beams they generate. For example, beams of radiation1916may be adjusted to illuminate a location on target structure1936(e.g., beam spots overlap). In some embodiments, target structure1936scatters (e.g., diffracts) beams of radiation1916, shown as scattered radiation1942. In some embodiments, steering the beams allows the angle of incidence of the beams on target structure1936to be adjusted. To change the angle of incidence, substrate1938may be moved in the Z-direction (toward or away from illumination system1900) and beams of radiation1916is steered to illuminate target structure1936at a different angle of incidence. Thus, it is possible to adjust the angle of incidence through a continuum of off-axis angles (e.g., angles of incidence different from zero). An advantage is that a direction of scattered radiation1942may be adjusted.

Receiver system1970detects scattered radiation1942. In one embodiment, scattered radiation1942may be perpendicularly incident on receiver system1970(i.e., normal incidence). Detection system1970may redirect the scattered radiation to a detector and/or generate a measurement signal based on the received radiation or detected image (e.g., scattered radiation1942from target structure1936). The measurement signal may comprise information of the received radiation, for example, intensity, phases, and the like.

Receiver system1970includes a receiver array including one or more phased arrays1972. Phased array1972includes optical elements and waveguides. Phased array1972is substantially similar to phased arrays1922aand1922bbut is operating in a receiving mode. For example, optical elements of the phased array1972(e.g., optical elements606ofFIG.6) are configured to receive radiation1942. Optical elements may couple the received radiation to waveguides of the phased array (e.g., waveguide604ofFIG.6).

FIG.20shows an inspection system2050, according to some embodiments. Elements ofFIG.20may have similar structures and functions as similarly numbered elements inFIGS.6and7(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.20in order to enhance clarity (e.g., an analog to radiation source708ofFIG.7). Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.20may also comprise elements analogous to those shown inFIGS.6and7.

Inspection system2050includes an illumination system2000, a receiving system2070. In some embodiments, illumination system2000comprises phased arrays2022a,2022b. Illumination system2000may further comprise one or more additional phased arrays (not shown). Phased arrays2022a,2022bmay comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, phased arrays2022aand2022bare configured to generate beams of radiation2016a,2016b. Beams of radiation2016a,2016bmay have a first wavelength. Beams of radiation2016a,2016bmay be directed at a target structure2036. Target structure2036is disposed on a substrate2038. In some embodiments, phased arrays2022a,2022b, are configured to direct and steer the beams they generate. For example, beams of radiation2016a,2016bmay be adjusted to illuminate a location on target structure2036(e.g., beam spots overlap). In some embodiments, target structure2036scatters (e.g., diffracts) beams of radiation2016, shown as scattered radiation2042. In some embodiments, steering the beams allows the angle of incidence of the beams on target structure2036to be adjusted. To change the angle of incidence, substrate2038may be moved in the Z-direction (toward or away from illumination system2000) and beams of radiation2016a,2016bare steered to illuminate target structure2036at a different angle of incidence. Thus, it is possible to adjust the angle of incidence through a continuum of off-axis angles (e.g., angles of incidence different from zero). An advantage is that a direction of scattered radiation2042may be adjusted.

In some embodiments, receiver system2070also includes phased array2048a,2048b, a reflecting element2052, and one or more detectors. Reflecting element2052may be configured to receive scattered radiation from the target structure2036. Reflecting element2052may be a mirror formed by a reflective material. For example, reflecting element2052may be formed using a silver layer, a gold layer, a copper layer, an aluminum layer, or the like as would be understood by one of ordinary skill in the art. Reflecting element2052, illumination system2044, and phased arrays2048a,2048bmay be formed on a single PIC.

Phased arrays2048a,2048bmay be configured to receive scattered radiation by the target structure2036. Phased arrays2048a,2048bmay be substantially similar to phased arrays2022aand2022bbut are operating in a receiving mode. For example, optical elements of phased arrays2048a,2048bare configured to receive scattered radiation and couple the scattered radiation to waveguides of the phased arrays.

In some embodiments, beams of radiation2016a,2016bare scattered by the target structure2036forming scattered radiation2042a,2042b. Reflecting element2050receives scattered radiation2042a,2042band reflects scattered radiation2042a,2042bback towards target structure2036forming reflected radiation2054a,2054b. Reflected radiation2054a,2054bincident on target structure2036is scattered toward each of the phased arrays2048a,2048b. For example, radiation2054ais scattered towards phased array2048aand phased array2048bforming two scattered radiation2056a,2056b. Similarly, radiation2052bis scattered towards phased array2048aand phased array2048bforming scattered radiation2058a,2058b. That is, two copies of the radiation are received by each of the phased arrays2048a,2048b. Phased arrays2048a,2048bmay be coupled to one or more detectors. Measurement signals from the two phased arrays2048a,2048bcan be used for calibration (i.e., by using a reference signal) and to check the reliability of measurement. For example, a difference between the two measurement signals may be used to monitor asymmetry, imbalance, and phased array angle mismatch.

FIG.21shows an inspection system2150, according to some embodiments. Elements ofFIG.21may have similar structures and functions as similarly numbered elements inFIGS.6and7(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.21in order to enhance clarity (e.g., an analog to radiation source708ofFIG.7). Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.21may also comprise elements analogous to those shown inFIGS.6and7.

In some embodiments, inspection system2150includes an illumination system2100and a receiver system2170. Illumination system2100and receiver system2170may be formed on separate photonic integrated circuits.

In some embodiments, illumination system2100is configured to generate a beam of radiation2116. Illumination system2100may adjust the direction beam of radiation2116. It should be appreciated that directions of beam of radiation2116depicted inFIG.21are not limiting. Beams of radiation2116may be directed to a target structure2036. Illumination system2100is tilted with respect to a normal of target structure2036. In other words, a small angle α exists between a plane of detection system2128and a plane of illumination system2100. Thus, the beams of radiation2116are incident at an angle on target structure2136(i.e., oblique incidence). Target structure2136scatters (e.g., diffracts) radiation to generate scattered radiation2142. Scattered radiation2142is at an angle with respect to a normal to target structure2136and is scattered towards the receiver system2170.

Illumination system2100may comprise one or more phased arrays. The phased arrays allow adjusting the direction of beam of radiation2116.

Receiver system2170may include one or more receiving elements such as an optical coupler2160. Optical coupler2160is configured to couple scattered radiation2142into a detector of receiver system2170. Optical coupler2160may be a phased array, a grating, or the like as would be understood by one of ordinary skill in the art.

In one embodiment, receiver system2170includes a fiber configured to collect the radiation and focus the radiation into a detector.

In one embodiment, the detector may be an array of detectors. For the detector array, a number of options are possible: a bundle of multimode fibers, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of a bundle of multimode fibers enables any dissipating elements to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range but each need separate pre-amps. The number of elements is therefore limited. CCD linear arrays offer many elements that may be read-out at high speed and are especially of interest if phase-stepping detection is used.

In some embodiments, inspection apparatus2150may be implemented as part of lithographic apparatus100or100′ (FIGS.1A and1B). Inspection apparatus2150may be implemented as an alignment apparatus for aligning a substrate with respect to a reticle.

In some embodiments, inspection apparatus2150is configured to measure a result of a lithographic process (e.g., overlay error) performed on a substrate. Measuring the result of the lithographic process may be performed outside of a lithographic apparatus (e.g., in a detached metrology apparatus or dedicated overlay inspection tool).

FIG.22shows a schematic of an illumination system2200, according to some embodiments. In some embodiments, illumination system2200may be implemented as part of an inspection apparatus, e.g., as illumination system500in inspection apparatus550(FIG.5). Elements ofFIG.22may have similar structures and functions as similarly numbered elements inFIG.6(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.22in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.22may also comprise elements analogous to those shown in, e.g.,FIG.6.

In some embodiments, phase modulators2202are disposed along waveguides2204(e.g., intersecting or adjacent to waveguides). In some embodiments, optical elements2206are disposed downstream of phase modulators2202along waveguides2204. In some embodiments the number of phase modulators2202, waveguides2204, and optical elements2206are equal (e.g., there is a one-to-one-to-one correspondence in a set of a phase modulator, waveguide, and optical element). In some embodiments, phase modulators2202, waveguides2204, and optical elements2206are arranged as a so-called phased array (e.g., an array of radiation elements for generating radiation having given phases).

For ease of discussion, a first phased array2222ais designated by a dotted outline. In some embodiments, illumination system2200comprises a second phased array2222b(also designated by a dotted outline). In some embodiments, illumination system comprises more phased arrays.

In some embodiments, light is coupled to phased arrays2222aand2222busing two or more input ports2272. For example, light may be coupled to phased arrays2222aand2222busing a first port2272a, a second port2272b, and a third port2272c.

In some aspects, illumination system2200further comprises a first coupler2274aand a second coupler2272b. First coupler2274acan couple light from first input port2272aand second input port2272b. Second coupler2274bcan couple light from second input port2272band third input port2272c. In some aspects, first coupler2274aand second coupler2274bcomprise two by two couplers.

In some embodiments, illumination system2200comprises a first splitter tree2276aand a second splitter tree2276b. In some aspects, first splitter tree2276acan extend from the first coupler2274ato optical elements2206of first phased array2222a. And, e.g., second splitter tree2276bcan extend from the second coupler2274bto optical elements2206of second phased array2222b. In some aspects, first splitter tree2276aand second splitter tree2276bcan include a plurality of splitters2280. The plurality of splitters2280comprise one to two splitters. In some aspects, each optical element2206of phased arrays2222aand2222bcan be located at a leaf of respective first splitter tree2276aand second splitter tree2276b.

In some embodiments, waveguides2204are configured to guide radiation. The radiation may be supplied by a radiation source2208and received at one or more ports of the phased arrays. Waveguides2204may be configured to guide radiation (e.g., from the input ports2272a,2272b, or2227c) to optical elements2206. Optical elements2206may be configured to radiate radiation waves. Optical elements2206may be referred to herein as “emitters,” “emission elements,” and the like, referencing their function of emitting radiation. Optical element2206may comprise waveguide gratings or antenna emitters.

In some embodiments, phase modulators2202are configured to adjust phases of radiation waves. In some embodiments, the phases of radiation waves2214are adjusted such that radiation waves2214accumulate to form a beam of radiation2216. For example, the radiation waves2214may form a first beam of radiation2216aand a second beam or radiation2216b. The direction of beams2216aand2216bis based on the phases of radiation waves2214. The phased arrays of illumination system2200may generate first and second beams of radiation2216aand2216band direct first and second beams of radiation2216aand2216b(e.g., toward a target structure). Phase modulation may comprise adjusting phase delays of radiation waves2214.

In some embodiments, light may be emitted from phased array2222aand/or phased array2222bby selecting an input port. For example, light may be emitted from phased array2222aand phased array2222bwhen second input port2272bis used. Light can be emitted from phased array2222awhen first input port2272ais used. Light can be emitted from phased array2222bwhen third input port2272cis used. In other words, first beam of radiation2216amay form when the radiation source2208is coupled to first input port2272a. Second beam of radiation2216bmay form when the radiation source2208is coupled to third input port2272c. In some aspects, first beam of radiation2216aand second beam of radiation2216bmay simultaneously form when the radiation source2208is coupled to second input port2272b.

In some embodiments, first input port2272aand third input port2272ccan be used during spot size characterization. In some aspects, second input port2272bcan be used during alignment measurements. Thus, an alignment mark (not shown, example alignment mark418inFIG.4A) is illuminated by both optical phase arrays2222aand2222bsimultaneously while performing alignment measurements. For example, alignment measurements may include measuring a result of a lithographic process (e.g., overlay error) performed on a substrate. During spot size characterization, first input port2272aor third input port2272cmay be used to illuminate structures outside of the target structure as described inFIGS.16A and16B.

In some embodiments, controller2210is configured to receive from a user a selection of a measurement mode (i.e., alignment measurement, spot size characterization). In some aspects, controller2210can identify the port based on the selection. Further, controller2210may control a connection between radiation source2208and the identified port. For example, controller2210can couple radiation source2208to second input port2272bwhen alignment measurement mode is inputted by the user. In some embodiments, radiation source2208may include multiple radiation sources. Each input port (e.g., first input port2272a, second input port2272b, third input port2272c) may be coupled to a different radiation source.

In some embodiments, illumination system2200comprises a photonic integrated circuit (PIC). In other words, illumination system2200and components therein (e.g., radiation sources, phase modulators, etc.) may be part of the PIC. The PIC allows illumination system2200to be built extremely small (e.g., sub-millimeter).

FIG.23shows a schematic of an illumination system2300, according to some embodiments. In some embodiments, illumination system2300may be implemented as part of an inspection apparatus, e.g., as illumination system500in inspection apparatus550(FIG.5). Elements ofFIG.23may have similar structures and functions as similarly numbered elements inFIG.22(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.23in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.23may also comprise elements analogous to those shown in, e.g.,FIG.22. For example, illumination system2300may comprise a radiation source and a controller.

In some embodiments, illumination system2300comprises phase modulators2302, waveguides2304, and optical elements2306. Phase modulators2302may comprise electro-optic modulators, thermo-optic modulators, and the like. Radiation from a radiation source (not shown) may be coupled to the phased arrays2322aand2322bvia input port2372. Phased arrays2322aand2322bmay comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, phase modulators2302are disposed along waveguides2304(e.g., intersecting or adjacent to waveguides). In some embodiments, optical elements2306are disposed downstream of phase modulators2302along waveguides2304.

In some embodiments, the phases of radiation waves (not shown) are adjusted such that radiation waves accumulate to form a beam of radiation2316. For example, the radiation waves may form a first beam of radiation2316aand a second beam of radiation2316b. The direction of beams2316aand2316bis based on the phases of radiation waves.

In some embodiments, phase modulation may comprise staggering phase delays of radiation waves. In some embodiments, a phase offset may be applied to each emitter (i.e., optical element2306) to steer the emitted beam. In some aspects, the beams of radiation2316a,2316bmay be steered in two directions θ and φ. In some embodiments, a controller (not shown inFIG.23, e.g., controller610ofFIG.6) is configured to control phase modulators2302to control the direction of beam of radiation2316. In some aspects, phase modulators2302can comprise multi-pass phase shifters.

In some embodiments, the controller may control the direction of the beam of radiation2316to scan the substrate (e.g., substrate538ofFIG.5). Thus, in some aspects, the substrate may be fixed with respect to the inspection apparatus. A target structure may be scanned by steering the emitted beam in the horizontal or vertical direction.

FIG.24shows a schematic of an illumination system2400, according to some embodiments. In some embodiments, illumination system2400may be implemented as part of an inspection apparatus, e.g., as illumination system500in inspection apparatus550(FIG.5). Elements ofFIG.24may have similar structures and functions as similarly numbered elements inFIG.22(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.24in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.24may also comprise elements analogous to those shown in, e.g.,FIG.22.

Illumination system2400may include a first phased array2422aand a second phased array2422b. Phased arrays2422aand2422bmay comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, the illumination system2400may include a first input port2472a, a second input port2472b, and a third input port2472c. First input port2472amay couple radiation from a radiation source (e.g., radiation source608ofFIG.6) to first phased array2422a. Second input port2472bmay simultaneously couple light to first phased array2422aand second phased array2422b. Third input port2472cmay couple light to second phased array2422b.

In some embodiments, illumination system2400further comprises a controller (e.g.,2210ofFIG.22). The controller may be configured to apply amplitude weighting to each of the optical elements. Thus, the controller may vary the amplitude weight of each element. The controller may be coupled to an attenuator2482coupled to the optical element. For example, the attenuator2482may be coupled to phase modulator2402(i.e., positioned downstream from phase modulator2402). Amplitude weighting (via attenuator2482) may be used for modifying beam of radiation.

In some embodiments, amplitude weighting may be used in transmit and/or receiver mode. For example, attenuators2482may be included in receiver system2170ofFIG.21. Thus, amplitude weighting may be applied to receiver arrays. In some aspects, a receiver array can be substantially similar to a phased array, e.g., first phased array2422abut operating in a receiver mode.

FIG.25shows a schematic of an illumination system2500, according to some embodiments. In some embodiments, illumination system2500may be implemented as part of an inspection apparatus, e.g., as illumination system500in inspection apparatus550(FIG.5). Elements ofFIG.25may have similar structures and functions as similarly numbered elements inFIG.22(e.g., elements sharing the two right-most numeric digits). It should be appreciated that certain structures have been omitted fromFIG.25in order to enhance clarity. Therefore, unless otherwise specified, it should be appreciated that embodiments referencingFIG.25may also comprise elements analogous to those shown in, e.g.,FIG.22.

Illumination system2500may include a first phased array2522aand a second phased array2522b. Phased arrays2522aand2522bmay comprise structures and functions that may be substantially similar to those of, e.g., phased array622(FIG.6).

In some embodiments, the illumination system2500may include a first input port2572a, a second input port2572b, a third input port2572c, waveguides2504, and optical elements2506.

In some embodiments, metal elements2578(i.e., conducting elements) may be positioned between optical elements2506to reduce coupling (e.g., mutual coupling) between adjacent optical elements2506. In some aspects, the approaches described herein can improve the performance of the illumination system2500. In some aspects, metal elements2578may be interposed between waveguides2504. In some aspects, metal elements2578may be from copper or other conductive materials. In some aspects, metal elements2578are approximately co-planar with optical elements2506. In some embodiments, metal elements2578can bisect a distance between an optical element2506and a corresponding adjacent optical element2506. In some embodiments, metal elements2578can be parallel to waveguides2504and co-planar with the waveguides2504.

In some embodiments, metal elements2578may be formed on the photonic integrated circuit (PIC).

In some embodiments, metal elements2578may be interposed in a receiver system, e.g., receiver system2170ofFIG.21. In some aspects, metal elements may be interposed between optical elements and waveguides in a receiver array. In some aspects, a receiver array is substantially similar to a phased array, e.g., phased array2522abut is operating in a receiving mode.

The embodiments may further be described using the following clauses:1. A system comprising:a radiation source;a phased array configured to generate a beam of radiation and to direct the beam toward a target structure on a substrate, the phased array comprising:optical elements configured to radiate radiation waves,waveguides configured to guide radiation from the radiation source to the optical elements, andphase modulators configured to adjust phases of the radiation waves such that the radiation waves accumulate to form the beam; anda detector configured to receive radiation scattered by the target structure and to generate a measurement signal based on the received radiation.2. The system of clause 1, wherein a direction of the beam is based on the phases.3. The system of clause 2, further comprising a controller configured to control the phase modulators to control the direction of the beam.4. The system of clause 1, wherein the phased array is configured to adjust the direction of the beam without moving elements.5. The system of clause 1, wherein the phased array further comprises a photonic integrated circuit.6. The system of clause 1, wherein each of the phase modulator comprises an electro-optic phase modulator.7. The system of clause 1, further comprising a lens configured to focus the radiation scattered by the target structure onto the detector.8. The system of clause 1, wherein the radiation source is configured to generate broadband wavelengths or two or more narrowband wavelengths.9. The system of clause 8, wherein:the radiation source comprises source elements; andeach of the source elements is configured to generate a subset of the broadband wavelengths or the two or more narrowband wavelengths.10. The system of clause 1, further comprising a spectral filter configured to select a wavelength from the radiation source to enter the phased array, wherein the beam has the wavelength.11. The system of clause 1, further comprising a time multiplexer configured to select a sequence of wavelengths from the radiation source to enter the phased array, wherein the beam has the sequence of wavelengths one wavelength at a time.12. The system of clause 1, further comprising a phase shifter configured to compensate a directional shift of a beam resulting from a selection of a wavelength from the radiation source to enter the phased array.13. The system of clause 1, wherein:the phased array is further configured to adjust amplitudes of the radiation waves; andthe beam comprises a beam profile that is based on the amplitudes and phases.14. The system of clause 13, wherein the beam profile comprises a substantially flat intensity distribution.15. The system of clause 13, wherein a full-width at half-maximum of the flat intensity distribution is less than approximately 2 microns.16. The system of clause 12, wherein a full-width at half-maximum of the beam profile is less than approximately 500 nm.17. The system of clause 1, wherein the system has a footprint area less than approximately 100 mm2, 50 mm2, 25 mm2, or 16 mm2.18. The system of clause 1, wherein the detector comprises an image capture device.19. The system of clause 1, wherein the system is configured to selectively illuminate structures near the target structure and to use radiation detected by the detector resulting from the illumination to reduce interference of the received radiation.20. The system of clause 1, wherein the system is configured to determine at least one of overlay error and critical dimension of the target structure based on the measurement signal.21. The system of clause 1, further comprising another phased array configured to generate another beam of radiation and to direct the beam toward the target structure.22. The system of clause 21, further comprising:a first spectral filter configured to select a first wavelength from the radiation source to enter the phased array, wherein the beam has the first wavelength; anda second spectral filter configured to select a second wavelength from the radiation source to enter the another phased array, wherein the another beam has the second wavelength.23. The system of clause 21, wherein the beam and the another beam have substantially similar wavelengths.24. The system of clause 21, wherein the beam and the another beam are directed to overlap at the target structure and to form a beam profile having a fringe pattern.25. The system of clause 24, wherein a pitch of the fringe pattern is adjustable based on a selection of phases of radiation waves radiated by the phased array and the another phased array and a selection of wavelength of the beam and the another beam.26. The system of clause 24, further comprising a controller configured to receive, from a user, input comprising selections of at least one of pitch and wavelength of the fringe pattern and to determine adjustments to the phases based on the input so as to set a pitch of the fringe pattern according to the selections.27. The system of clause 24, wherein the measurement signal is further based on scattered radiation resulting from the fringe pattern and the system is configured to scan the fringe pattern across the target structure and to determine a position of the target structure based on the measurement signal.28. A lithographic apparatus comprising:an illumination system configured to illuminate a pattern of a patterning device;a support configured to support the patterning device;a substrate table configured to support a substrate;a projection system configured to project an image of the pattern onto the substrate; anda metrology system comprising:a radiation source;a phased array configured to generate a beam of radiation and to direct the beam toward a target structure on the substrate, the phased array comprising:optical elements configured to radiate radiation waves,waveguides configured to guide radiation from the radiation source to the optical elements, andphase modulators configured to adjust phases of the radiation waves such that the radiation waves accumulate to form the beam; anda detector configured to receive radiation scattered by the target structure and to generate a measurement signal based on the received radiation.29. An illumination system comprising:first and second phased arrays configured to generate first and second beams of radiation respectively, each of the first and second phased arrays comprising:optical elements configured to radiate radiation waves;waveguides configured to guide source radiation to the optical elements; andphase modulators configured to adjust phases of the radiation waves,wherein the phases of the radiation waves from the first and second phased arrays are adjusted such that the radiation waves from the first and second phased arrays respectively accumulate to form the first and second beams, andwherein the first and second beams are directed to overlap and interfere to form a beam profile having a fringe pattern.30. The illumination system of clause 29, wherein directions of the first and second beams are respectively based on the phases in the first and second phased arrays.31. The illumination system of clause 29, wherein the illumination system is configured to adjust a property of at least one of the first and second beams to adjust a property of the fringe pattern.32. The illumination system of clause 31, wherein a property of the fringe pattern is pitch.33. The illumination system of clause 31, wherein the property of the at least one of the first and second beams comprises phase delays of the radiation waves from the first and second phased arrays, respectively.34. The illumination system of clause 31, wherein the property of the at least one of the first and second beams is wavelength.35. The system of clause 29, wherein a pitch of the fringe pattern is adjustable based on a selection of phases of radiation waves radiated by the phased array and the another phased array and a selection of wavelength of the beam and the another beam.36. The illumination system of clause 29, further comprising a controller configured to receive, from a user, input comprising selections of at least one of pitch and wavelength of the fringe pattern and to determine adjustments to the phases in the first and second phased arrays based on the input so as to set a pitch of the fringe pattern according to the selections.37. The illumination system of clause 29, further comprising a radiation source configured to generate the source radiation that is received at the first and second phased arrays.38. The illumination system of clause 37, wherein the radiation source is further configured to generate broadband wavelengths or two or more narrowband wavelengths.39. The illumination system of clause 38, wherein:the radiation source comprises source elements; andeach of the source elements is configured to generate a subset of the broadband wavelengths or the two or more narrowband wavelengths.40. The illumination system of clause 37, further comprising:a first spectral filter configured to select a first wavelength from the radiation source to enter the first phased array, wherein the first beam has the first wavelength; anda second spectral filter configured to select a second wavelength from the radiation source to enter the second phased array, wherein the second beam has the second wavelength.41. A lithographic apparatus comprising:an illumination system configured to illuminate a pattern of a patterning device;a support configured to support the patterning device;a substrate table configured to support a substrate;a projection system configured to project an image of the pattern onto the substrate; anda metrology system comprising:first and second phased arrays configured to generate first and second beams of radiation and respectively and to direct the first and second beams respectively toward a target structure on the substrate, each of the first and second phased arrays comprising:optical elements configured to radiate radiation waves;waveguides configured to guide source radiation to the optical elements; andphase modulators configured to adjust phases of the radiation waves,wherein the phases of the radiation waves from the first and second phased arrays are adjusted such that the radiation waves from the first and second phased arrays respectively accumulate to form the first and second beams, andwherein the first and second beams are directed to overlap at the target structure to form a beam profile having a fringe pattern; anda detector configured to receive radiation scattered by the target structure and to generate a measurement signal based on the received radiation.42. A method comprising:generating a beam of radiation using a phased array, the generating comprising:generating source radiation;guiding the source radiation to optical elements using waveguides;radiating radiation waves using the optical elements; andsetting phases of the radiation waves using phase modulators such that the radiation waves accumulate to form the beam;directing the beam toward a target structure on a substrate, wherein the direction of the beam is based on the phases;receiving, at a detector, radiation scattered by the target structure; andgenerating a measurement signal based on the received radiation.43. A system comprising:a radiation source;first and second phased arrays comprising optical elements configured to radiate radiation waves, waveguides configured to guide radiation from the radiation source to the optical elements, and phase modulators configured to adjust phases of the radiation waves, wherein the first and second phased arrays are respectively configured to form first and second beams of radiation directed toward a target structure to form an illumination profile having a fringe pattern based on the adjusting;a receiver array configured to receive radiation scattered by the target structure; anda detector configured to generate a measurement signal based on the received radiation.44. The system of clause 43, wherein the receiver array comprises: waveguides configured to guide the received radiation to the detector; and optical elements configured to couple the received radiation into the waveguides.45. The system of clause 43, wherein the receiver array is disposed between the first and second phased arrays.46. The system of clause 43, further comprising a second receiver array.47. The system of clause 46, wherein the receiver array is disposed adjacent to the first phased array and the second receiver array is disposed adjacent to the second phased array.48. The system of clause 46, wherein the receiver array receives the scattered radiation via a reflecting element.49. The system of clause 48, wherein the reflecting element is a mirror made of silver, gold, aluminum, or copper.50. The system of clause 49, wherein the reflecting element reflects the scattered radiation back to the target structure.51. The system of clause 50, wherein both of the receiver array and the second receiver array receives the scattered radiation.52. The system of clause 43, wherein the first and second phased arrays and are parts of a photonic integrated circuit and the receiver array is a part of the integrated circuit or a separate photonic integrated circuit.53. The system of clause 52, wherein the photonic integrated circuit and the separate photonic integrated circuit are tilted with respect to a perpendicular of the target structure.54. A lithographic apparatus comprising:an illumination system configured to illuminate a pattern of a patterning device;a support configured to support the patterning device;a substrate table configured to support a substrate;a projection system configured to project an image of the pattern onto the substrate; anda metrology system comprising:first and second phased arrays configured to generate first and second beams of radiation respectively and to direct the first and second beams respectively toward a target structure on the substrate, each of the first and second phased arrays comprising:optical elements configured to radiate radiation waves;waveguides configured to guide source radiation to the optical elements; andphase modulators configured to adjust phases of the radiation waves,wherein the phases of the radiation waves from the first and second phased arrays are adjusted such that the radiation waves from the first and second phased arrays respectively accumulate to form the first and second beams, andwherein the first and second beams are directed to overlap at the target structure to form a beam profile having a fringe pattern;a receiver array configured to receive radiation scattered by the target structure; anda detector configured to generate a measurement signal based on the received radiation.55. A method comprising:generating a beam of radiation using a phased array, the generating comprising:generating source radiation;guiding the source radiation to optical elements using waveguides;radiating radiation waves using the optical elements; andsetting phases of the radiation waves using phase modulators such that the radiation waves accumulate to form the beam;directing the beam toward a target structure on a substrate, wherein the direction of the beam is based on the phases;receiving, at a receiver array, radiation scattered by the target structure; and generating, at a detector, a measurement signal based on the received radiation.56. The method of clause 55, further comprising:receiving at a second receiver array, the radiation scattered by the target structure;generating a second measurement signal based on the received radiation at the second receiver array; andanalyzing the measurement signal and the second measurement signal to perform a reliability measurement.57. A system comprising:a radiation source;first and second phased arrays comprising optical elements configured to radiate radiation waves, a plurality of ports, waveguides configured to guide radiation from a port of the plurality of ports to the optical elements, and phase modulators configured to adjust phases of the radiation waves, wherein one or both of the first and second phased arrays are respectively configured to form a first beam and/or a second beam of radiation directed toward a target structure based on the port coupled to the radiation source; anda detector configured to receive radiation scattered by the target structure and to generate a measurement signal based on the received radiation.58. The system of clause 57, wherein the plurality of ports comprise:a first input port coupled to the first phased array;a second input port coupled to the first and second phased arrays; anda third input port coupled to the second phased array.59. The system of clause 58, wherein:the first beam is formed when the radiation source is coupled to the first input port,the second beam is formed when the radiation source is coupled to the third port, andthe first beam and the second beam are simultaneously formed when the radiation source is coupled to the second input port.60. The system of clause 58, wherein the radiation source is coupled to the second input port during alignment measurements.61. The system of clause 58, wherein the radiation source is coupled to the first input port or the third input port during spot size characterization of the respective first or second beams.62. The system of clause 57, further comprising:a first tree extending from a first coupler to the optical elements of the first phased array; anda second tree extending from a second coupler to the optical elements of the second phased array,wherein each optical element of the optical elements is located at a leaf of the first tree or the second tree.63. The system of clause 62, wherein:the first coupler comprises a two by two coupler connecting a first input port and a second input port to the first tree; andthe second coupler comprises a two by two coupler connecting the second input port and a third input port to the second tree.64. The system of clause 62, wherein the first and second trees comprises a plurality of splitters.65. The system of clause 57, wherein the first beam and the second beam have the same direction.66. The system of clause 57, further comprising one or more metal elements interposed between the waveguides.67. The system of clause 57, further comprising:a controller configured to receive from a user, to input a selection of a measurement mode, to identify the port from the plurality of ports according to the selection, and to control a connection between the radiation source and the identified port.68. A system comprising:a radiation source;a phased array configured to generate a beam of radiation and to direct the beam toward a target structure on a substrate, the phased array comprising:optical elements configured to radiate radiation waves,waveguides configured to guide radiation from the radiation source to the optical elements, andphase modulators configured to adjust phases of the radiation waves such that the radiation waves accumulate to form the beam;a detector configured to receive radiation scattered by the target structure and to generate a measurement signal based on the received radiation; anda controller configured to control a phase offset of each respective optical element to control a direction of the beam.69. The system of clause 68, wherein the controller is further configured to control the direction of the beam to scan the substrate.70. The system of clause 69, wherein the beam is configured to scan the substrate without moving elements.71. The system of clause 68, wherein the phased array comprises a splitter tree from the radiation source to the optical elements.72. The system of clause 68, further comprising one or more metal elements interposed between the waveguides.73. The system of clause 68, wherein the controller is further configured to apply amplitude weighting to each optical element of the optical elements.74. A system comprising:a phased array comprising:optical elements configured to radiate or detect radiation waves;waveguides configured to guide radiation from the radiation source to the optical elements or from the optical elements to a detector;phase modulators configured to adjust phases of the radiation waves; andone or more metal elements interposed between the waveguides configured to reduce coupling between optical elements.75. The system of clause 74, wherein the phased array further comprises a photonic integrated circuit.76. The system of clause 75, wherein the one or metal elements are formed on the photonic integrated circuit.

Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein can be processed, before or after exposure, in for example a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit and/or an inspection unit. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrate can 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 contains multiple processed layers.

It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present disclosure is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

The term “substrate” as used herein describes a material onto which material layers are added. In some embodiments, the substrate itself can be patterned and materials added on top of it may also be patterned, or may remain without patterning.

Although specific reference can be made in this text to the use of the apparatus and/or system according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus and/or system has many other possible applications. For example, it can be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD 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 being replaced by the more general terms “mask,” “substrate,” and “target portion,” respectively.

While specific embodiments of the invention have been described above, it will be appreciated that the invention can be practiced otherwise than as described. The description is not intended to limit the invention.