Alignment system and lithographic apparatus

Abstract

Disclosed is a photonic integrated circuit metrology sensor comprising: a first interference device being operable to receive at least a pair of corresponding diffraction orders having been scattered from a target and generate at least a first signal and a second signal; an imbalanced delay arrangement arranged to impose an imbalanced delay on a portion of said first signal and a portion of said second signal to obtain a first delayed signal and a second delayed signal; a second interference device being operable to receive at least said second first delayed signal and a second delayed signal and generate a third signal and a fourth signal; and a waveguide device arrangement being configured at least to guide said first signal, second signal, third signal and fourth signal for detection.

Description

ALIGNMENT SYSTEM AND LITHOGRAPHIC APPARATUS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 683,990 which was filed on August 16, 2024 and which is incorporated herein in its entirety by reference. FIELD

[0002] The present disclosure relates to metrology systems, for example, an alignment system for measuring alignment mark positions in lithographic apparatuses and systems. BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation- sensitive material (photoresist or simply “resist”) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During lithographic operation, different processing steps can entail different layers to be sequentially formed on the substrate. Accordingly, it may 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 can use an 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.

[0005] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters can 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 Confidentialuse 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 use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0006] 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.

[0007] Production speed and throughput is of great importance in lithographic fabrication of ICs and electronic devices. It is desirable for metrology systems used in fabrication to acquire measurements quickly for increasing wafer throughput. Typically, alignment systems will measure an alignment mark by scanning a measurement beam with respect to an alignment mark to generate an alignment signal. This scanning takes a finite time.

[0008] Accordingly, it is desirable to improve metrology apparatuses such as alignment sensors for supporting shorter measurement times in conjunction with lithographic processes. Additionally it is desirable for such metrology apparatuses or alignment sensors to support smaller and more densely packed metrology targets (e.g., alignment marks). SUMMARY

[0009] In a first aspect of the invention there is provided a a photonic integrated circuit metrology sensor comprising: a first interference device being operable to receive at least a pair of corresponding diffraction orders having been scattered from a target and generate at least a first signal and a second signal; an imbalanced delay arrangement arranged to impose an imbalanced delay on a portion of said first signal and a portion of said second signal to obtain a first delayed signal and a second delayed signal; a second interference device being operable to receive at least said second first delayed signal and a second delayed signal and generate a third signal and a fourth signal; and a waveguide device arrangement being configured at least to guide said first signal, second signal, third signal and fourth signal for detection.

[0010] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. ConfidentialAdditional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein. BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0011] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein. - Figure 1A shows a reflective lithographic apparatus, according to some aspects - Figure 1B shows a transmissive lithographic apparatus, according to some aspects; - Figure 2 shows more details of a reflective lithographic apparatus, according to some aspects; - Figure 3 shows a lithographic cell, according to some aspects; - Figures 4A and 4B are schematic illustrations of metrology apparatuses. - Figure 5 is a schematic illustration of an integrated optic metrology apparatus; - Figure 6 is a photonic circuit diagram for the integrated optic metrology apparatus of Figure 5; - Figure 7 is a photonic circuit diagram for an integrated optic metrology apparatus according to concepts disclosed herein; and - Figure 8 show signal traces for alignment signals obtained using the metrology apparatus of Figure 5 / 6 (top) and the metrology apparatus of Figure 7 (bottom).

[0012] The features of the present disclosure 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

[0013] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0014] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to Confidentialanother element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0015] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can 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).

[0016] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine-readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0017] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0018] Example Lithographic Systems

[0019] FIGS. 1A and 1B show a lithographic apparatus 100 and a lithographic apparatus 100’, respectively, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ 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 apparatus 100 and 100’ 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 Confidentialsubstrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0020] The illumination system IL can 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.

[0021] 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 apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0022] The term “patterning device” MA should be broadly interpreted as referring to any device that can 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 can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0023] The patterning device MA can be transmissive (as in lithographic apparatus 100’ of Figure 1B) or reflective (as in lithographic apparatus 100 of Figure 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0024] The term “projection system” PS can 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 can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0025] Lithographic apparatus 100 and / or lithographic apparatus 100’ can 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 can be used in parallel, or preparatory steps can be carried Confidentialout 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.

[0026] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be located between the projection system and the substrate during exposure.

[0027] Referring to FIGS. 1A and 1B, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100’ can 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 apparatus 100 or 100’, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in Figure 1B) including, for example, suitable directing mirrors and / or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100’, for example, when the source SO is a mercury lamp. A radiation system can comprise the source SO, the illuminator IL, and / or the beam delivery system BD.

[0028] The illuminator IL can include an adjuster AD (in Figure 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 can be adjusted. In addition, the illuminator IL can comprise various other components (in Figure 1B), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0029] Referring to Figure 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 apparatus 100, 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 can 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 IF1 can 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 can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Confidential

[0030] Referring to Figure 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.

[0031] The projection system PS projects an image of the mask pattern MP, where the image 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 can 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.

[0032] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zeroth order diffracted beams, first order diffracted beams, and / or higher order diffracted beams (not shown). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can 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 aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, astigmatism aberration can 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 US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0033] With the aid of the second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can 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 in Figure 1B) can be used Confidentialto 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).

[0034] In general, movement of the mask table MT can 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 can 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 can be connected to a short-stroke actuator or can be fixed. Mask MA and substrate W can 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 can 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 can be located between the dies.

[0035] Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can 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 can be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0036] The lithographic apparatus 100 and 100’ can 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 can 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 can 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 can be employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0037] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed. Confidential

[0038] In some aspects, lithographic apparatus 100 includes 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.

[0039] In some aspects, lithographic apparatus 100’ includes a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.

[0040] Figure 2 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 can be formed by a discharge produced plasma source. EUV radiation can be produced by a gas or vapor, for example Xe gas, Li vapor, or Sn vapor in which EUV radiation emitting plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The EUV radiation emitting plasma 210 is created by, for example, an electrical discharge causing at least a partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor can be used for efficient generation of the radiation. In some aspects, a plasma of excited tin (Sn) (e.g., excited via a laser) is provided to produce EUV radiation.

[0041] The radiation emitted by the EUV radiation emitting plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 can include a channel structure. Contamination trap 230 can also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure.

[0042] The collector chamber 212 can include a radiation collector CO, which can be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point INTF. The virtual source point INTF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus INTF is located at or near an opening 219 in the enclosing structure 220. The virtual source point INTF is an image of the EUV radiation emitting plasma 210. Grating spectral filter 240 is used in particular for suppressing infra-red (IR) radiation.

[0043] Subsequently the radiation traverses the illumination system IL, which can include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221, at the patterning device MA, as well as a desired uniformity of Confidentialradiation intensity at the patterning device MA. Upon reflection of the beam of radiation 221 at the patterning device MA, held by the support structure MT, a patterned beam 226 is formed and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by the wafer stage or substrate table WT.

[0044] More elements than shown can generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 can optionally be present, depending upon the type of lithographic apparatus. Further, there can be more mirrors present than those shown in the Figure 2, for example there can be one to six additional reflective elements present in the projection system PS than shown in Figure 2.

[0045] Collector optic CO, as illustrated in Figure 2, is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are 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.

[0046] Example Lithographic Cell

[0047] Figure 3 shows a lithographic cell 300, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatus 100 or 100’ can form part of lithographic cell 300. Lithographic cell 300 can 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 apparatus 100 or 100’. 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 can be operated to maximize throughput and processing efficiency.

[0048] Example Inspection Apparatus

[0049] 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 inspection apparatuses for accurate positioning of marks on a substrate. 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. Patent 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 can 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. Confidential

[0050] Figure 4A shows a cross-sectional view of an inspection apparatus 400 that can be implemented as a part of lithographic apparatus 100 or 100’, according to some aspects. In some aspects, inspection apparatus 400 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Inspection apparatus 400 can 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 apparatus 100 or 100’ using the detected positions of the alignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0051] The terms “inspection apparatus,” “metrology system,” or the like can be used herein to refer to, e.g., a device used for measuring a property of a structure (e.g., overlay sensor, critical dimension sensor, or the like), a device or system used in a lithographic apparatus to inspect an alignment of a wafer (e.g., alignment sensor), or the like.

[0052] In some aspects, inspection apparatus 400 can include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a processor 432. Illumination system 412 can be configured to provide an electromagnetic narrow band radiation beam 413 having one or more passbands. In an example, the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm. In another example, the one or more passbands can be discrete narrow passbands within a spectrum of wavelengths between about 500 nm to about 900 nm. Illumination system 412 can 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 system 412). Such configuration of illumination system 412 can 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 can improve long-term stability and accuracy of alignment systems (e.g., inspection apparatus 400) compared to the current alignment apparatuses.

[0053] In some aspects, beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 can be split into radiation sub-beams 415 and 417, as shown in Figure 4A. Beam splitter 414 can be further configured to direct radiation sub-beam 415 onto a substrate 420 placed on a stage 422. In one example, the stage 422 is movable along direction 424. Radiation sub-beam 415 can be configured to illuminate an alignment mark or a target 418 located on substrate 420. Alignment mark or target 418 can be coated with a radiation sensitive film. In some aspects, alignment mark or target 418 can have one hundred and eighty degrees (i.e., 180°) symmetry. That is, when alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to a plane of alignment mark or target 418, rotated alignment mark or target 418 can be substantially identical to an unrotated alignment mark or target 418. The target 418 on substrate 420 can 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 can alternatively Confidentialbe 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, can be input to the reconstruction process, performed by processing unit PU, from knowledge of the printing step and / or other scatterometry processes.

[0054] In some aspects, beam splitter 414 can be further configured to receive diffraction radiation beam 419 and split diffraction radiation beam 419 into at least two radiation sub-beams, according to an aspect. Diffraction radiation beam 419 can be split into diffraction radiation sub-beams 429 and 439, as shown in Figure 4A.

[0055] It should be noted that even though beam splitter 414 is shown to direct radiation sub-beam 415 towards alignment mark or target 418 and to direct diffracted radiation sub-beam 429 towards interferometer 426, the disclosure is not so limiting. Other optical arrangements can be used to obtain the similar result of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0056] As illustrated in Figure 4A, interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example aspect, diffracted radiation sub-beam 429 can be at least a portion of radiation sub-beam 415 that can be reflected from alignment mark or target 418. In an example of this aspect, interferometer 426 comprises any appropriate set of optical-elements, for example, a combination of prisms that can be configured to form two images of alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be appreciated that a good quality image need not be formed. It can be enough to have the features of alignment mark 418 resolved. Interferometer 426 can 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.

[0057] In some aspects, detector 428 can be configured to receive the recombined image via interferometer signal 427 and detect interference as a result of the recombined image when alignment axis 421 of inspection apparatus 400 passes through a center of symmetry (not shown) of alignment Confidentialmark or target 418. Such interference can be due to alignment mark or target 418 being 180° symmetrical, and the recombined image interfering constructively or destructively, according to an example aspect. Based on the detected interference, detector 428 can be further configured to determine a position of the center of symmetry of alignment mark or target 418 and consequently, detect a position of substrate 420. According to an example, alignment axis 421 can be aligned with an optical beam perpendicular to substrate 420 and passing through a center of image rotation interferometer 426. Detector 428 can be further configured to estimate the positions of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

[0058] In a further aspect, detector 428 determines the position of the center of symmetry of alignment mark or target 418 by 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); 3. measuring position variations for various polarizations (position shift between polarizations); and 4. measuring intensity difference between opposite orders of a diffraction order pair (e.g., to characterize and correct for asymmetry).

[0059] This data can be obtained using any type of alignment sensor, for example, a SMASH (SMart Alignment Sensor Hybrid) sensor, as described in U.S. Patent 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. Patent 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.

[0060] In some aspects, beam analyzer 430 can be configured to receive and determine an optical state of diffracted radiation sub-beam 439. The optical state can be a measure of beam wavelength, polarization, or beam profile. Beam analyzer 430 can be further configured to determine a position of stage 422 and correlate the position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420 can be accurately known with reference to stage 422. Alternatively, beam analyzer 430 can be configured to determine a position of inspection apparatus 400 or any other reference element such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400 or any other reference element. Beam analyzer 430 can be a point or an imaging polarimeter with some form of wavelength-band selectivity. In some aspects, beam analyzer 430 can be directly integrated into inspection apparatus 400, or connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects.

[0061] In some aspects, beam analyzer 430 can be further configured to determine the overlay data between two patterns on substrate 420. One of these patterns can be a reference pattern on a reference layer. The other pattern can be an exposed pattern on an exposed layer. The reference layer can be an Confidentialetched layer already present on substrate 420. The reference layer can be generated by a reference pattern exposed on the substrate by lithographic apparatus 100 and / or 100’. The exposed layer can be a resist layer exposed adjacent to the reference layer. The exposed layer can be generated by an exposure pattern exposed on substrate 420 by lithographic apparatus 100 or 100’. The exposed pattern on substrate 420 can correspond to a movement of substrate 420 by stage 422. In some aspects, the measured overlay data can also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data can be used as calibration data to calibrate the exposure pattern exposed by lithographic apparatus 100 or 100’, such that after the calibration, the offset between the exposed layer and the reference layer can be minimized.

[0062] In some aspects, beam analyzer 430 can be further configured to determine a model of the product stack profile of substrate 420, and can be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement. The product stack profile contains information on the stacked product such as alignment mark, target 418, or substrate 420, and can include mark process variation-induced optical signature metrology that is a function of illumination variation. The product stack profile can also include product grating profile, mark stack profile, and mark asymmetry information. An example of beam analyzer 430 is YieldstarTM, manufactured by ASML, Veldhoven, The Netherlands, as described in U.S. Patent No.8,706,442, which is incorporated by reference herein in its entirety. Beam analyzer 430 can be further configured to process information related to a particular property of an exposed pattern in that layer. For example, beam analyzer 430 can 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.

[0063] In some aspects, an array of detectors (not shown) can be connected to beam analyzer 430, and allows the possibility of accurate stack profile detection as discussed below. For example, detector 428 can 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 can be read-out at high speed and are especially of interest if phase-stepping detection is used.

[0064] In some aspects, a second beam analyzer 430’ can be configured to receive and determine an optical state of diffracted radiation sub-beam 429, as shown in Figure 4B. The optical state can be a measure of beam wavelength, polarization, or beam profile. Second beam analyzer 430’ can be identical to beam analyzer 430. Alternatively, second beam analyzer 430’ can be configured to perform one or more of the functions of beam analyzer 430, such as determining a position of stage 422 and correlating Confidentialthe position of stage 422 with the position of the center of symmetry of alignment mark or target 418. As such, the position of alignment mark or target 418 and, consequently, the position of substrate 420, can be accurately known with reference to stage 422. Second beam analyzer 430’ can also be configured to determine a position of inspection apparatus 400, or any other reference element, such that the center of symmetry of alignment mark or target 418 can be known with reference to inspection apparatus 400, or any other reference element.

[0065] In some aspects, second beam analyzer 430’ can be directly integrated into inspection apparatus 400, or it can be connected via fiber optics of several types: polarization preserving single mode, multimode, or imaging, according to other aspects. Alternatively, second beam analyzer 430’ and beam analyzer 430 can be combined to form a single analyzer (not shown) configured to receive and determine the optical states of both diffracted radiation sub-beams 429 and 439.

[0066] In some aspects, processor 432 receives information from detector 428 and beam analyzer 430. Processor 432 can create a basic correction algorithm based on the information received from detector 428 and beam analyzer 430, 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. Processor 432 can utilize the basic correction algorithm to characterize the inspection apparatus 400 with reference to wafer marks and / or alignment marks 418.

[0067] As ICs continue to shrink, demand is increasing for lithographic tools capable of processing smaller and more densely packed metrology targets (e.g., alignment marks). A single wafer can include numerous targets for measurements (e.g., alignment, overlay, or the like). In turn, the large number of targets on the wafer can introduce delays in production due to the additional measurements, reducing production throughput. Therefore, it is desirable for metrology systems to measure targets faster for increasing wafer throughput.

[0068] A solution can be to reduce the time spent measuring each target. However, such an implementation can be challenging. For example, in an attempt to quickly move from target to target, a detection time (e.g., photon collection time or integration time) of a metrology system can be reduced. But in this scenario, the measurements can suffer signal-to-noise issues that degrade the reliability of the measurements. It is analogous to setting a very high shutter speed on a camera used in photography (e.g., a few milliseconds of exposure), resulting in the capture of a poorly resolved image due to the lack of sufficient illumination.

[0069] An on-chip metrology system is described in WO2022258275A1, incorporated herein by reference. Such an on-chip metrology system can be (or include) an on-chip alignment sensor designed using integrated optics.

[0070] FIG. 5 shows a schematic of such an on-chip metrology system 500 that can be implemented as a part of lithographic apparatus 100 or 100’. Additionally, or alternatively, metrology system 500 Confidentialthat can be implemented as a dedicated metrology system. For example, the integrated optical alignment sensor of this disclosure can be implemented as part of lithographic apparatus 100 or 100’ or can be implemented as a dedicated metrology system.

[0071] In some embodiments, metrology system 500 can be configured to align a substrate (e.g., substrate W) with respect to a patterning device (e.g., patterning device MA). Metrology system 500 can 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 apparatus 100 or 100’ using the detected positions of the alignment marks. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate. According to some embodiments, metrology system 500 can be part of metrology system 400 of FIG.4A and / or FIG.4B.

[0072] Metrology system 500 can include illumination system 501 configured to generate beam of radiation 503 for illuminating target 505. In some embodiments, and as discussed in more detail below, illumination system 501 can include one or more radiation sources and one or more illumination gratings. Alternatively, illumination system 501 can include one or more illumination gratings coupled to one or more external radiation sources.

[0073] For example (as with all embodiments disclosed herein), target 505 can include, but is not limited to, an alignment mark on a substrate. After illuminating target 505 using beam of radiation 503, diffraction beam of radiations 507, 509a, and 509b are diffracted from target 505. Diffracted beam of radiation 507 can include a 0 diffraction order beam of radiation. Diffracted beam of radiation 509a can include a +1 diffraction order beam of radiation. Diffracted beam of radiation 509b can include a -1 diffraction order beam of radiation. Although FIG. 5 illustrates 0 and ±1 diffraction orders, the embodiments of this disclosure are not limited to these diffraction orders and other diffraction orders (e.g., ±2, ±3, ±4, ±5, etc.) can also be used.

[0074] The diffracted beam of radiation 507 may be blocked by illumination system 501. However, diffracted beam of radiation 509a is received by capturing system 511a and diffracted beam of radiation 509b is received by capturing system 511b. As an example, capturing systems 511a and 511b can include one or more capturing gratings.

[0075] In some embodiments, capturing system 511a can be coupled to waveguide device 513a and capturing system 511b can be coupled to waveguide device 513b. Capturing systems 511a and 511b can generate guided modes of radiation from the received diffracted radiation, according to some embodiments. Waveguide devices 513a and 513b can propagate the guided modes of radiation from capturing systems 511a and 511b to interference device 515. In some examples, waveguide devices 513a and 513b can include a single-mode fiber. In some examples, waveguide devices 513a and 513b can include a multimode fiber. The term “waveguide device” or the like can be used herein to refer to a device that can propagate radiation by directing the radiation along a guide and / or medium. An example of a waveguide device is an optical fiber. Another example of a waveguide device is a Confidentialmicrowave cavity. Yet another example of a waveguide device is a strip of light-transmissive material affixed on a substrate (e.g., as can be found in photonic circuits).

[0076] In an embodiment, interference device 515 can include an interferometer. For example, interference device 515 can include any appropriate set of optical-elements to interfere (e.g., combine) the received diffracted beams of radiation (e.g., 509a and 509b) to measure a phase difference between the received diffracted beams of radiation. In some examples, the phase difference can be a measure of the position of the alignment mark on the substrate. In some examples, interference device 515 can include a wide waveguide device configured to interfere (e.g., combine) the received diffracted beams of radiation (e.g., 509a and 509b). In some examples, interference device 515 can include directional couplers, Mach-Zehnder interferometers, multimode interferometer (MMI), or the like. The embodiments of this disclosure are not limited to these examples and interference device 515 can include any set of optical elements for interfering / combining the diffracted beams of radiation received from capturing systems 511a and 511b.

[0077] According to some embodiments, the combined (e.g., interfered) guided modes of radiation from interference device 515 is sent to detectors 517a and 517b. Detectors 517a and 517b can be configured to generate a measurement signal(s) based on the combined guided modes of radiation (e.g., a linear combination of the guided modes of radiation.) In some examples, detectors 517a and 517b can detect an interference as a result of the combined guided modes of radiation (e.g., interfered guided mode of radiations.) In some examples, based on the detected interference, detectors 517a and 517b can be configured to determine a position of the center of symmetry of alignment mark or target 505 and consequently, detect a position of a substrate.

[0078] In some embodiments, the generated measurement signal(s) (generated by detectors 517a and 517b) can be sent to a processor (not shown - e.g., processor 432 of FIGS. 4A and 4B) for further analysis. The processor can analyze the measurement signal(s) to determine a characteristic of target 505. For example, the processor can be an overlay calculation processor. Additionally, or alternatively, the processor can create a basic correction algorithm based on the information received from detectors 517a and 517b, 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 embodiments of this disclosure are not limited to these examples and the processor can determine other characteristic(s) of target 505 based on the measurement signal(s) generated by detectors 517a and 517b.

[0079] According to some embodiments, illumination system 501 and grating capture system 511 can be located on the same chip (on-chip alignment sensor.) In some examples, illumination system 501 can include one or more radiation sources that are external to on-chip alignment sensor and can include one or more illumination gratings that are on the on-chip alignment sensor. In some examples, waveguide devices 513, interference device 515, and detector 517 are on the same chip (on-chip alignment sensor) as illumination system 501 and grating capture system 511. In these examples, Confidentialwaveguide devices 513, interference device 515, and detector 517 are on the same plane as illumination system 501 and grating capture system 511. Alternatively, one or more of waveguide devices 513, interference device 515, and detector 517 can be external to the on-chip alignment sensor. Similarly, the processor can be on the on-chip alignment sensor or be external to the on-chip alignment sensor.

[0080] As discussed in more detail below, illumination system 501 can generate a plurality of beams of radiation with different wavelengths. Additionally, or alternatively, capturing system 511 can include a plurality of pairs of capturing gratings, where each pair of capturing gratings corresponds to a wavelength. In a non-limiting example, the wavelengths for the illumination system 501 and capturing system 511 can include, but are not limited to, 532 nm, 633 nm, 780 nm, and 850 nm. In another non limiting example, the wavelengths can include, but are not limited to, wavelengths between about 1540 nm and about 1580 nm. The embodiments of this disclosure are not limited to these examples and can include other wavelength values. In some examples, beam of radiation 503 can include a beam of radiation with predetermined amplitude and phase profile. In a non-limiting example, beam of radiation 503 can include a Gaussian beam of radiation with a Gaussian spot size of about 40 pm at a distance 519 of about 10 mm. In some examples, distance 519 is the distance (e.g., in Z axis) from the on-chip alignment sensor from target 505. The embodiments of this disclosure are not limited to these examples and can include different spot sizes and distances.

[0081] Although some examples of this disclosure are discussed with respect to one on-chip alignment sensor, the embodiments of this disclosure are not limited to these examples. For example, a metrology system of this disclosure can include a plurality of the disclosed on-chip alignment sensors configured to perform alignment in parallel on a plurality of alignment marks. Each on-chip alignment sensor of the plurality of the on-chip alignment sensors can perform an alignment process on a corresponding alignment mark. The alignment processes can be performed in parallel. One or more processors can be configured to assist with the alignment processes (e.g., determine one or more characteristics of the alignment marks in parallel.)

[0082] Figure 6 is a photonic circuit diagram for the alignment sensor of Figure 5, for one color. There is an aperture ILL in the center to allow the illumination to pass through the integrated optic sensor. The scattered radiation, e.g., a pair of corresponding diffraction orders (e.g., the +1 and -1 orders) from the alignment mark are captured by capturing systems or capture gratings CG1, CG2 (i.e., each of the +1 and -1 orders are captured by a respective capture grating). Respective waveguide devices WG propagate the guided modes of radiation from capture gratings CG1, CG2 to interference device or multimode interferometer MMI. The multimode interferometer measures the sum signal (e.g., sumsignal power ^^^^1 ):= |^^^^+|2 + |^^^^−|2 + 2|^^^^+||^^^^−| cos(^^^^+ − ^^^^−) and difference signal (e.g.,difference signal power ^^^^2 ): ^^^^2 = |^^^^+|2 + |^^^^−|2 − 2|^^^^+||^^^^−| cos(^^^^+ − ^^^^−) , where the complexamplitude of the electric field of the positive and negative diffraction orders are respectively ^^^^+^^^^^^^^^^^^+Confidentialand ^^^^−^^^^^^^^^^^^−. As has already been described, to extract the phase difference between the two diffraction orders, the mark needs to be scanned.

[0083] The metrology sensors or alignment sensors described above, and in particular the integrated optic (on-chip) metrology sensors (alignment sensors) depicted in Figure 5, require a scanning over the alignment mark to obtain an alignment signal. This scanning takes a finite time per alignment mark. The need to scan also means that the marks have to be sufficiently large to facilitate the scanning.

[0084] Speed is important in alignment metrology, as alignment is performed for each substrate and therefore the faster alignment can be performed, the better the productivity (throughput). As such, it can be appreciated that faster alignment metrology directly results in more substrates being produced (exposed) per hour. In addition, alignment marks take up important space (real estate) on the reticle and substrate. Reducing the size of the alignment marks means that less space is used.

[0085] To address these issues, a metrology sensor, e.g., an integrated optic (on-chip) metrology sensor or alignment sensor is proposed which does not require the measurement beam to be scanned over the alignment mark (i.e., it can measure the marks statically without relative movement between beam and mark).

[0086] Figure 7 is a photonic circuit design for a metrology sensor, e.g., an integrated optic (on-chip) metrology sensor which enables extraction of the phase difference between the two diffraction orders without scanning the phase. As such, an integrated optics based alignment sensor is described which measures the alignment position directly without the need of scanning the alignment mark. This sensor measures not only a first signal (the aforementioned sum signal or more specifically the summation interference of the positive and negative diffraction orders) and a second signal (the aforementioned difference signal summation or more specifically the difference interference of the positive and negative diffraction orders) but also a third signal and a fourth signal, where the third signal and fourth signal comprise phase shifted versions of the first signal and second signal respectively.

[0087] In an embodiment, the third signal and fourth signal may be obtained by interfering a first delayed signal and a second delayed signal, where the first delayed signal and second delayed signal comprise differently delayed versions of the first signal and second signal respectively. The first delayed signal and a second delayed signal are combined (e.g., interfered) to obtain the third signal and fourth signal. The phase difference imposed between the first delayed signal and second delayed signal may optionally be ^^^^ / 2 as this provides the strongest signal, although other delay magnitudes are possible.

[0088] As with the example of Figure 6, a first 2x2 interference device or multimode interferometer MMI1 receives the diffracted fields as collected by capturing systems or capture gratings CG1, CG2 and generates a first signal ^^^^1or sum signal and a second signal ^^^^2or difference signal. A respective third and fourth interference device or multimode interferometer MMI3, MMI4 splits each of the first signal and second signal into two branches. In each case, one branch is propagated to a detection arrangement (not shown), so as to detect first signal ^^^^1and second signal ^^^^2(i.e., conventional sum and difference signals). The respective signals in the other branch from each of the third and fourth Confidentialmultimode interferometers MMI3, MMI4 are propagated to a second interferometer device or 2x2 multimode interferometer MMI2 via imbalanced delay lines, having lengths ^^^^1,^^^^2 respectively, to obtain the first delayed signal and second delayed signal. This interferometer MMI2 generates the third signal ^^^^3and fourth signal ^^^^4from the first delayed signal and second delayed signal for detection via the detection arrangement.

[0089] As has been mentioned, phase imbalance imposed to obtain the first delayed signal and seconddelayed signal may be an approximately ^^^^ / 2 phase difference: ^^^^^^^^ = ^^^^0^^^^^^^^^^^^^^^^(L1 − L2) ≈ π / 2, whereL1 − L2 = ^^^^and where ^^^^^^^^^^^^^^^^is the effective refractive index of the delay lines, ^^^^ is the radiationwavelength and ^^^^0 is the wavenumber: ^^^^0 = 2^^^^ / ^^^^. By way of a specific example, the length differencebetween the two delay lines may be approximately 100 nm for an operating wavelength of around 600 nm in a SiN integrated photonic platform. While a ^^^^ / 2 delay provides the strongest signal, the concept works for any non-zero phase difference (or more generally for any phase difference Δ^^^^≠^^^^^^^^, where ^^^^ is an integer).

[0090] The power of the first signalsecond signal ^^^^2, third signal ^^^^3and fourth signal ^^^^4may be written as:

[0091] As before, the complex amplitude of the electric field of the positive and negative diffraction orders are respectively ^^^^+^^^^^^^^^^^^+and ^^^^−^^^^^^^^^^^^−.

[0092] Combining these equations, it can therefore be shown that: ^^^^^^^^ = ^^^^ − ^^^^ =4^^^^^^^^ =^^^^4 − ^^^^3+ −^^^^arctan^^^^1 − ^^^^2where ^^^^ is the pitch of the alignment mark and ^^^^ is the distance from the center of the mark (alignment position). It can be seen that for an ideal case, with a single measurement and without using any fitting algorithm, the alignment position ^^^^ can be extracted.

[0093] Figure 8 shows a plot of alignment position ^^^^ against signal power S for a conventional alignment sensor (top) and for a non-scanning alignment sensor (bottom) according to concepts Confidentialdisclosed herein. For conventional sensor, the alignment signals comprise a sum alignment signal ^^^^1and difference alignment signal ^^^^2. The mark needs to be scanned so as to fit a sine function on the alignment signals to extract the alignment position. In the non-scanning case, the alignment signals additionally comprise third signal ^^^^3and fourth signal ^^^^4, and the alignment position at each point (e.g., point ^^^^ illustrated) is directl^^^^4−^^^^31y derived from the equation: ^^^^=

[0094] It can be appreciated that there are negligible errors for realistic cases. One source of error is the change in the effective length due to the temperature variation. The refractive index of glass and SiN approximately varies around 2x10-5per 1K. Hence, the alignment position changes as a function of temperature as:

[0095] Considering^^^^^^^^^^^^^^^^^^^^^^^^^^^^ =2×10−5K-1and assuming that the temperature changes 1K during the measurement, the alignment position deviation is in the order of 50 pm, which is negligible. However, for a shorter time, the temperature variation is less, so the delay line (the phase difference between the two arms) can be calibrated during the wafer swapping. For example, such a delay line calibration may be performed by scanning a reference mark and using a fitting algorithm to fit a curve to the scanned signal to compare the phase difference between the first signal ^^^^1and its delayed version i.e., fourth signal ^^^^4(or equally by comparing the third signal ^^^^3and second signal ^^^^2). Such a calibration may be performed when the temperature drift is high and / or may be performed per lot.

[0096] Another source of error is a local alignment error or local alignment position deviation (APD) due to mark asymmetry and / or critical dimension (CD) variations. Local APD is the local error in the alignment position measurement due to the local mark deformation. To address this, a measurement may comprise a (e.g., short) scanning over the mark (a smaller scan than presently performed). An averaging of the signal over the scan length can then be performed, e.g., to improve the repro. Note that no fitting on the alignment signal is required to extract the alignment position, as is the case with conventional scanned alignment metrology.

[0097] The accuracy of the proposed metrology sensor is mostly dominated by the stage vibration and drift. Therefore, the methods described herein may also be used to measure this stage vibration and drift. If the relative position of the mark and the sensor is shifted due to the vibration, it is an equivalent of a change in the alignment position. If the mark is not scanned during a measurement, as is proposed in many examples herein, any change in the alignment signal ^^^^^^^^ is due only to the vibration and / or drift. As such, this change in alignment signal may be measured and used to determine a measure of the vibration and / or drift.

[0098] The embodiments may further be described using the following clauses: Confidential1. A photonic integrated circuit metrology sensor comprising: a first interference device being operable to receive at least a pair of corresponding diffraction orders having been scattered from a target and generate at least a first signal and a second signal; an imbalanced delay arrangement arranged to impose an imbalanced delay on a portion of said first signal and a portion of said second signal to obtain a first delayed signal and a second delayed signal; a second interference device being operable to receive at least said second first delayed signal and a second delayed signal and generate a third signal and a fourth signal; and a waveguide device arrangement being configured at least to guide said first signal, second signal, third signal and fourth signal for detection. 2. A photonic integrated circuit metrology sensor as claimed in clause 1, further comprising at least one detector for detecting said first signal, second signal, third signal and fourth signal. 3. A photonic integrated circuit metrology sensor as claimed in clause 1 or clause 2, wherein said first signal comprises a sum interference signal of said pair of corresponding diffraction orders and said second signal comprises a difference interference signal of said pair of corresponding diffraction orders. 4. A photonic integrated circuit metrology sensor as claimed in any preceding clause, wherein the first signal and second signal are each a function of the cosine of a phase difference between the diffraction orders of said pair of corresponding diffraction orders, and said third signal and fourth signal are each a function of the sine of the phase difference between the diffraction orders of said pair of corresponding diffraction orders. 5. A photonic integrated circuit metrology sensor as claimed in any preceding clause, further comprising a third interference device for splitting said first signal and a fourth interference device for splitting said second signal, said waveguide arrangement being further configured such that a first portion of said first signal and a first portion of the second signal is each guided for detection and a second portion of said first signal and a second portion of the second signal is guided to said imbalanced delay arrangement. 6. A photonic integrated circuit metrology sensor as claimed in clause 5, wherein said third interference device and said fourth interference device each comprise a 1x2 multimode interferometer. 7. A photonic integrated circuit metrology sensor as claimed in any preceding clause, wherein said first interference device and said second interference device each comprise a 2x2 multimode interferometer. 8. A photonic integrated circuit metrology sensor as claimed in any preceding clause, further comprising at least a first capturing system and a second capturing system for capturing respectively each diffraction order of said pair of corresponding diffraction orders. 9. A photonic integrated circuit metrology sensor as claimed in clause 8, wherein said first capturing system and second capturing system each comprise a respective capture grating. Confidential10. A photonic integrated circuit metrology sensor as claimed in any preceding clause, further comprising a processor being operable to determine a position value from said first signal, second signal, third signal and fourth signal. 11. A photonic integrated circuit metrology sensor as claimed in clause 10, wherein said processor is operable to determine the position value without a fitting of a curve to any of said first signal, second signal, third signal and fourth signal. 12. A photonic integrated circuit metrology sensor as claimed in clause 10 or 11, wherein said processor is operable to determine the position value without a scanning of measurement radiation with respect to the target. 13. A photonic integrated circuit metrology sensor as claimed in clause 12, wherein said processor is further operable to determine a change in said position value; and determine a measure of vibration and / or drift of an associated lithographic apparatus or component thereof from said determined change in said position value. 14. A photonic integrated circuit metrology sensor as claimed in clause 10 or 11, being operable to scan the measurement radiation with respect to the target; wherein said processor is operable to average the first signal, second signal, third signal and fourth signal and / or the position value over said scan. 15. A photonic integrated circuit metrology sensor as claimed in any of clauses 10 to 14, wherein said processor is operable to extract the position value directly from a ratio of a first difference and a second difference, said first difference comprising a difference of the fourth signal and third signal and said second difference comprising a difference of the first signal and second signal. 16. A photonic integrated circuit metrology sensor as claimed in any preceding clause, wherein said imbalanced delay arrangement is operable to impose a phase difference of substantially ^^^^ / 2 between said first delayed signal and said second delayed signal. 17. A photonic integrated circuit metrology sensor being operable as an alignment sensor. 18. A lithographic apparatus comprising: a patterning device support for supporting a patterning device; a substrate support for supporting a substrate; a projection system being operable to project a patterned beam onto the substrate, subsequent to the beam being patterned by the patterning device; and a photonic integrated circuit metrology sensor of any preceding clause, being operable to measure positional information relating to a position of said substrate.

[0099] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength λ of 365, 248, 193, 157 or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-100 nm such as, for example, 13.5 nm), Confidentialor hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G- line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiation used within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0100] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate 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) and / or a metrology unit. Where applicable, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0101] Furthermore, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0102] 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 specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0103] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are Confidentialappropriately performed. The foregoing description of specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0104] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above-described aspects, but should be defined in accordance with the following claims and their equivalents. Confidential

Claims

CLAIMS 1. A photonic integrated circuit metrology sensor comprising: a first interference device being operable to receive at least a pair of corresponding diffraction orders having been scattered from a target and generate at least a first signal and a second signal; an imbalanced delay arrangement arranged to impose an imbalanced delay on a portion of said first signal and a portion of said second signal to obtain a first delayed signal and a second delayed signal; a second interference device being operable to receive at least said second first delayed signal and a second delayed signal and generate a third signal and a fourth signal; and a waveguide device arrangement being configured at least to guide said first signal, second signal, third signal and fourth signal for detection.

2. A photonic integrated circuit metrology sensor as claimed in claim 1, further comprising at least one detector for detecting said first signal, second signal, third signal and fourth signal.

3. A photonic integrated circuit metrology sensor as claimed in claim 1 or claim 2, wherein said first signal comprises a sum interference signal of said pair of corresponding diffraction orders and said second signal comprises a difference interference signal of said pair of corresponding diffraction orders.

4. A photonic integrated circuit metrology sensor as claimed in any preceding claim, wherein the first signal and second signal are each a function of the cosine of a phase difference between the diffraction orders of said pair of corresponding diffraction orders, and said third signal and fourth signal are each a function of the sine of the phase difference between the diffraction orders of said pair of corresponding diffraction orders.

5. A photonic integrated circuit metrology sensor as claimed in any preceding claim, further comprising a third interference device for splitting said first signal and a fourth interference device for splitting said second signal, said waveguide arrangement being further configured such that a first portion of said first signal and a first portion of the second signal is each guided for detection and a second portion of said first signal and a second portion of the second signal is guided to said imbalanced delay arrangement.

6. A photonic integrated circuit metrology sensor as claimed in claim 5, wherein said third interference device and said fourth interference device each comprise a 1x2 multimode interferometer. Confidential7. A photonic integrated circuit metrology sensor as claimed in any preceding claim, wherein said first interference device and said second interference device each comprise a 2x2 multimode interferometer.

8. A photonic integrated circuit metrology sensor as claimed in any preceding claim, further comprising at least a first capturing system and a second capturing system for capturing respectively each diffraction order of said pair of corresponding diffraction orders.

9. A photonic integrated circuit metrology sensor as claimed in claim 8, wherein said first capturing system and second capturing system each comprise a respective capture grating.

10. A photonic integrated circuit metrology sensor as claimed in any preceding claim, further comprising a processor being operable to determine a position value from said first signal, second signal, third signal and fourth signal.

11. A photonic integrated circuit metrology sensor as claimed in claim 10, wherein said processor is operable to determine the position value without a fitting of a curve to any of said first signal, second signal, third signal and fourth signal.

12. A photonic integrated circuit metrology sensor as claimed in claim 10 or 11, wherein said processor is operable to determine the position value without a scanning of measurement radiation with respect to the target.

13. A photonic integrated circuit metrology sensor as claimed in claim 12, wherein said processor is further operable to determine a change in said position value; and determine a measure of vibration and / or drift of an associated lithographic apparatus or component thereof from said determined change in said position value.

14. A photonic integrated circuit metrology sensor as claimed in claim 10 or 11, being operable to scan the measurement radiation with respect to the target; wherein said processor is operable to average the first signal, second signal, third signal and fourth signal and / or the position value over said scan.

15. A photonic integrated circuit metrology sensor as claimed in any of claims 10 to 14, wherein said processor is operable to extract the position value directly from a ratio of a first difference and a second difference, said first difference comprising a difference of the fourth signal and third signal and said second difference comprising a difference of the first signal and second signal. Confidential

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