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WO2024188592A1 - Métrologie d'alignement utilisant un oscillateur local - Google Patents

Métrologie d'alignement utilisant un oscillateur local Download PDF

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Publication number
WO2024188592A1
WO2024188592A1 PCT/EP2024/054088 EP2024054088W WO2024188592A1 WO 2024188592 A1 WO2024188592 A1 WO 2024188592A1 EP 2024054088 W EP2024054088 W EP 2024054088W WO 2024188592 A1 WO2024188592 A1 WO 2024188592A1
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WO
WIPO (PCT)
Prior art keywords
signal
radiation
detection module
substrate
target
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
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PCT/EP2024/054088
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English (en)
Inventor
Saman Jahani
Roxana REZVANI NARAGHI
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ASML Netherlands BV
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ASML Netherlands BV
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Publication date
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Priority to CN202480018105.1A priority Critical patent/CN120883146A/zh
Publication of WO2024188592A1 publication Critical patent/WO2024188592A1/fr
Anticipated expiration legal-status Critical
Pending legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
    • G03F9/7088—Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/355—Non-linear optics characterised by the materials used
    • G02F1/3551—Crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/39—Non-linear optics for parametric generation or amplification of light, infrared or ultraviolet waves
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/0014—Monitoring arrangements not otherwise provided for
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0092—Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity

Definitions

  • the present disclosure relates to alignment metrology, for example, a detection module for a metrology apparatus and a method for detecting an alignment of a substrate in lithographic apparatuses and systems.
  • 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).
  • 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.
  • photoresist radiation-sensitive material
  • a single substrate will contain a network of adjacent target portions that are successively patterned.
  • 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.
  • lithographic operation During lithographic operation, different processing steps can entail 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • angularly resolved scatterometers 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.
  • Substrate alignment for lithographic processes is measured using alignment sensors.
  • an alignment sensor measures an interference signal of the positive and negative diffraction orders of radiation that is diffracted from an alignment mark. As the alignment mark is moved, the phase of the diffracted radiation for the positive and negative diffraction orders is shifted, causing a change in the intensity of the interfered signal.
  • Some alignment sensors have difficulty detecting low intensity signals.
  • amplifying the signals through conventional means also increases the noise figure (NF).
  • SNR signal to noise ratio
  • SNR signal to noise ratio
  • a metrology apparatus having a detection module capable of detecting low intensity signals without requiring the capture of both the positive and negative diffraction orders.
  • exemplary aspects of this disclosure relate to a detection module that can increase the intensity of a detected signal without increasing the phase noise and can eliminate the need for capturing more than diffraction order.
  • a beam of radiation may be diffracted from a target and coupled to a single mode waveguide or fiber, so that the phase (and consequently the alignment position) can be retrieved from the interaction of the signal and a local oscillator.
  • Using a phase sensitive amplifier (PSA) can allow the output amplified signal to be squeezed, suppressing the uncertainty in a desired quadrature (e.g., phase) while enhancing the uncertainty in a related but undesirable quadrature (e.g., intensity).
  • PSA phase sensitive amplifier
  • a detection module can comprise a PSA and a detector.
  • the PSA can be configured to receive a source signal diffracted from a target on a surface of a substrate, receive a pump signal, and transmit an amplified signal based on a phase between the pump signal and the source signal.
  • the detector can be configured to receive the amplified signal and determine an alignment position of the target based on the amplified signal.
  • a metrology apparatus can comprise a light source, an optical system, a PSA, a detector, and a controller.
  • the light source can be configured to generate a beam of radiation.
  • the optical system can be configured to illuminate a target on a surface of a substrate with the beam of radiation to generate a source signal.
  • the PSA can be configured to receive a pump signal or a local oscillator, receive the source signal from the target, and transmit an amplified signal or interfered signal based on a phase between the pump signal or local oscillator and the source signal.
  • the detector can be configured to receive the amplified signal.
  • the controller can be coupled to the detector and configured to determine an alignment position of the target based on the amplified signal.
  • a method for detecting an alignment of a substrate can comprise receiving a pump signal.
  • a source signal diffracted from a target on a surface of the substrate can be received.
  • the pump signal and the source signal can be nonlinearly interacted in a PSA to generate an amplified signal.
  • An alignment position of the target can be determined based on the amplified signal.
  • FIG. 1A shows a reflective lithographic apparatus, according to some aspects.
  • FIG. IB shows a transmissive lithographic apparatus, according to some aspects.
  • FIG. 2 shows more details of a reflective lithographic apparatus, according to some aspects.
  • FIG. 3 shows a lithographic cell, according to some aspects.
  • FIGS. 4A and 4B show inspection apparatuses, according to some aspects.
  • FIG. 5 shows a detector module according to some aspects.
  • FIG. 6 shows a method for detecting an alignment of a substrate according to some aspects.
  • FIG. 7 shows a detector module according to other aspects.
  • FIG. 8 shows a method for detecting an alignment of a substrate according to other aspects.
  • FIG. 9 shows a detector module according to another aspect.
  • FIG. 10 shows a method for detecting an alignment of a substrate according to another aspect.
  • 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 another 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.
  • 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).
  • 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).
  • 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.
  • 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.
  • non-transitory can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.
  • FIGS. 1A and IB 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.
  • an illumination system illumination system
  • IL for example, deep ultra violet or extreme ultra violet radiation
  • a support structure for example, a mask table
  • MT configured to support a pattern
  • 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.
  • 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 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.
  • the patterning device MA can be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 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.
  • 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.
  • 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).
  • the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure.
  • the additional table may not be a substrate table WT.
  • 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.
  • a liquid having a relatively high refractive index e.g., water
  • 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.
  • immersion as used herein does not mean that a structure, such as a substrate, must be submerged in liquid.
  • a liquid can be located between the projection system and the substrate during exposure.
  • the illuminator IL can include an adjuster AD (in FIG. IB) for adjusting the angular intensity distribution of the radiation beam.
  • AD adjuster
  • the illuminator IL can comprise various other components (in FIG. IB), 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.
  • 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.
  • the radiation beam B is 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.
  • 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).
  • 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 Ml, M2 and substrate alignment marks Pl, P2.
  • 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 of the mask pattern MP, where the image is formed by diffracted beams produced from the mask pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W.
  • 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.
  • 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).
  • 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.
  • 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).
  • 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.
  • 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).
  • the first positioner PM and another position sensor can 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).
  • 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.
  • movement of the substrate table WT can be realized using a long-stroke module and a shortstroke module, which form part of the second positioner PW.
  • 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 Ml, M2, and substrate alignment marks Pl, P2.
  • 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).
  • the mask alignment marks can be located between the dies.
  • 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.
  • 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.
  • the lithographic apparatus 100 and 100’ can be used in at least one of the following modes:
  • 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.
  • 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.
  • 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.
  • lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography.
  • EUV extreme ultraviolet
  • 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.
  • lithographic apparatus 100’ includes a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography.
  • DUV deep ultraviolet
  • 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.
  • FIG. 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.
  • a plasma of excited tin (Sn) (e.g., excited via a laser) is provided to produce EUV radiation.
  • 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.
  • 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.
  • 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 radiation intensity at the patterning device MA.
  • the illumination system IL 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 radiation intensity at the patterning device MA.
  • 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 FIG. 2, for example there can be one to six additional reflective elements present in the projection system PS than shown in FIG. 2.
  • Collector optic CO 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.
  • FIG. 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/Ol, I/O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 100’.
  • alignment marks are generally provided on the substrate, and the lithographic apparatus includes one or more 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.
  • FIG. 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.
  • 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.
  • 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.
  • 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
  • inspection apparatus 400 can include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and an overlay calculation processor 432.
  • Illumination system 412 can be configured to provide an electromagnetic narrow band radiation beam 413 having one or more passbands.
  • the one or more passbands can be within a spectrum of wavelengths between about 500 nm to about 900 nm.
  • 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).
  • CWL center wavelength
  • 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.
  • beam splitter 414 can be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams.
  • radiation beam 413 can be split into radiation sub-beams 415 and 417, as shown in FIG. 4A.
  • Beam splitter 414 can be further configured to direct radiation sub-beam 415 onto a substrate 420 placed on a stage 422.
  • 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.
  • 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 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.
  • 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 FIG. 4A.
  • 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.
  • interferometer 426 can be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414.
  • 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.
  • 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.
  • 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 mark 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.
  • 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.
  • 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.
  • 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:
  • 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.
  • SMASH SMart Alignment Sensor Hybrid
  • 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.
  • 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.
  • 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 etched 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.
  • 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.
  • 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.
  • 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.
  • an array of detectors can be connected to beam analyzer 430, and allows the possibility of accurate stack profile detection as discussed below.
  • detector 428 can be an array of detectors.
  • 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.
  • 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.
  • a second beam analyzer 430’ can be configured to receive and determine an optical state of diffracted radiation sub-beam 429, as shown in FIG. 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.
  • 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 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.
  • 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. Second beam analyzer 430’ can be further configured to determine the overlay data between two patterns and a model of the product stack profile of substrate 420. Second beam analyzer 430’ can also be configured to measure overlay, critical dimension, and focus of target 418 in a single measurement.
  • 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.
  • 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.
  • processor 432 receives information from detector 428 and beam analyzer 430.
  • processor 432 can be an overlay calculation processor.
  • the information can comprise a model of the product stack profile constructed by beam analyzer 430.
  • processor 432 can construct a model of the product mark profile using the received information about the product mark.
  • processor 432 constructs 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.
  • 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.
  • processor 432 can 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 detector 428 and beam analyzer 430.
  • the information includes but is not limited to the product stack profile, measurements of overlay, critical dimension, and focus of each alignment marks or target 418 on substrate 420.
  • Processor 432 can 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 can 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 can be deduced. Table 1 illustrates how this can 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. The process may have introduced an overlay error of 29 nm.
  • the smallest value can be taken to be the reference point and, relative to this, the offset can 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 can also be obtained from marks and target 418 under different illumination settings, the illumination setting, which results in the smallest overlay error, and its corresponding calibration factor, can be determined and selected. Following this, processor 432 can group marks into sets of similar overlay error. The criteria for grouping marks can be adjusted based on different process controls, for example, different error tolerances for different processes.
  • processor 432 can 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. Processor 432 can determine corrections for each mark and feed the corrections back to lithographic apparatus 100 or 100’ for correcting errors in the overlay, for example, by feeding corrections into the inspection apparatus 400.
  • FIG. 5 shows a detection module 500 according to some embodiments.
  • a beam of radiation 502 can be generated by a light source (not shown; see, e.g., source SO in FIGS. 1 and 2 and illumination system 412 in FIGS. 4A and 4B).
  • the beam of radiation 502 can be used to illuminate a target 504 on a surface of a substrate, so that light is diffracted from target 504 to form source signal 506.
  • source signal 506 is received at one end of phase sensitive amplifier (PSA) 510.
  • PSA phase sensitive amplifier
  • a pump signal 508 can also be received at the same end of PSA 510 as source signal 506.
  • pump signal 508 and source signal 506 interact with each other in PSA 510 to produce amplified signal 512 based on a phase difference between pump signal 508 and source signal 508.
  • Amplified signal 512 can be transmitted from PSA 510 to detector 514.
  • the interaction between pump signal 508 and 512 can be nonlinear.
  • Detector 514 can receive amplified signal 512 from PSA 510 and, based on amplified signal 512, can determine an alignment position of target 504, and thus an alignment position of the substrate.
  • light used for beam of radiation 502 can have essentially any wavelength.
  • the wavelength for beam of radiation 502 can be guided by practical considerations, such as the availability of light sources of different frequencies, the materials forming the substrate and/or target being measured, optical properties of the target such as the diffraction order pattern of light diffracted from the target, or other practical considerations that would immediately be apparent to one of ordinary skill in the art.
  • Commonly used wavelengths for beam of radiation 502 can include 500 nm up to 2000 nm.
  • pump signal 508 can be supplied by the same light source that generates beam of radiation 502, or by a separate light source.
  • Pump signal 508 can be chosen to be a harmonic frequency of beam of radiation 502 and source signal 506.
  • pump signal 508 can constitute a beam of radiation having a frequency that is a second harmonic of the frequency of the beam of radiation 502.
  • beam of radiation 502 is comprised of light having a wavelength of 2090 nm
  • pump signal 508 can be chosen to have a wavelength of 1045 nm.
  • pump signal 508 could constitute light having two frequencies that are detuned from the frequency of beam of radiation 502 in equal but opposite ways. For example, in some embodiments using materials with higher order nonlinearities, two pump beams can be provided.
  • one of the pump beams can be detuned from a central frequency by addition of a specific value to the central frequency, while the other pump beam can be detuned from the central frequency by subtraction of the same specific value from the central frequency.
  • PSA 510 can comprise a waveguide or fiber that receives pump signal 508 and source signal 506 and guides the signals to detector 514.
  • PSA 510 can comprise a single mode waveguide or fiber.
  • PSA 510 can constitute a local oscillator configured to interfere and mix pump signal 508 and source signal 506 to generate amplified signal 512.
  • an intensity of amplified signal 512 will be determined by a phase difference between pump signal 508 and source signal 506. When the phase of pump signal 508 and source signal 506 align, the intensity of amplified signal 512 will increase, creating a boosted or amplified signal.
  • the phase of pump signal 508 and source signal 506 anti-align when the phase of pump signal 508 and source signal 506 anti-align, the intensity of amplified signal 512 will decrease, creating a diminished or deamplified signal.
  • the phase of pump signal 508 will remain constant while the phase of source signal 506 will change as beam of radiation 502 is scanned across target 504.
  • the phase of the signal 506 is changed, and as a result, the intensity of amplified signal 512 will increase and decrease with the scanning of target 504.
  • this combination of amplified and deamplified signals is referred to herein as the “amplified signal.”
  • the above discussion relates to the amplification of a phase measurement.
  • the mixing of the phases of the pump signal and the source signal optically amplifies the phase measurement.
  • Such optical amplification is highly sensitive to the phases of the pump signal and the source signal, and thus reduces an overall uncertainty in the resulting phase measurement (also called “squeezing”).
  • the uncertainty in the amplitude measurement will increase proportionally since phase and amplitude are related by the uncertainty principle.
  • the PSA suppresses a phase noise while enhancing an intensity noise of the amplified signal.
  • PSA 510 can constitute a nonlinear waveguide.
  • PSA 510 can comprise a nonlinear crystal, such as a nonlinear crystal of second order or higher.
  • a nonlinear crystal may comprise a material having a Pockels nonlinearity.
  • Non-limiting examples of such materials include, but not limited to, lithium nitrate, lithium tantalate, aluminum nitrate, gallium arsenide, barium borate (BBO), and the like, although one of ordinary skill in the art will appreciate that a range of materials could suitably be used to form PSA 510 to have a nonlinear character.
  • PSA 510 can constitute a material having a Kerr nonlinearity.
  • Non-limiting examples of such materials include, but not limited to, silicon, silicon nitride, silicon carbide, aluminum oxide, silicon dioxide.
  • detector 514 can be configured to receive amplified signal 512 and determine an alignment position of target 504 based on amplified signal 512.
  • an intensity of amplified signal 512 can be at a maximum when target 504 is properly aligned, so that detector 514 can determine when target 504 is aligned by measuring the intensity of amplified signal 512.
  • Detector 514 can constitute a photodiode, a single photon detector, an optical spectrum analyzer, a CCD camera, or any optical detector that can suitably measure the intensity of amplified signal 512.
  • FIG. 6 shows a method 600 for measuring an alignment of a target on a substrate according to some aspects.
  • the steps of method 600 can be performed by detector module 500 in FIG. 5.
  • method 600 is also applicable to embodiments of a detector module other than detector module 500.
  • method 600 begins by receiving a pump signal from a light source at step 602.
  • the pump signal may be similar in some respects to pump signal 508.
  • a source signal is received after being diffracted from a target on a substrate.
  • the source signal may be similar in some respects to source signal 506.
  • the pump signal and the source signal are interacted in a PSA to generate an amplified signal.
  • the PSA and the amplified signal may be similar in some respects to PSA 510 and amplified signal 512, respectively.
  • the interaction between the source signal and the pump signal may be nonlinear.
  • an alignment position of the target is determined based on the amplified signal.
  • the determination may be performed by a detector that is similar in some respects to detector 514. However, the determination can also be performed by, for example, a processor coupled to a memory that is separate from a detector, or a controller that is coupled to the detector to determine the position of the target.
  • FIG. 7 shows an embodiment of a detector module 700 according to another aspect of the disclosure.
  • Many of the elements of detector module 700 function similar to the elements of detector module 500 shown in FIG. 5.
  • target 704, source signal 706, pump signal 708, PSA 710, amplified signal 712, and detector 714 can each function similar to target 504, source signal 506, pump signal 508, PSA 510, amplified signal 512, and detector 514 in detector module 500.
  • detector module 700 differs from detector module 500 at least in the way in which pump signal 708 is generated.
  • detector module 700 can comprise a nonlinear medium 703.
  • a beam of radiation 701 can be generated by a light source and directed towards nonlinear medium 703.
  • nonlinear medium 703 can generate light 705 based on a frequency of beam of radiation 701 while also transmitting beam of radiation 702 having the frequency of beam of radiation 701 to target 704.
  • nonlinear medium 703 can generate light 705 that is a second harmonic of beam of radiation 701, although nonlinear medium 703 could be chosen to generate a higher harmonic of beam of radiation 701.
  • light 705 can be used as pump signal 708.
  • optical element 707 for example a beam splitter, a mirror, or the like, can be used to transmit light 705 to PSA 710 as pump signal 708 while allowing beam of radiation 702 to illuminate target 704.
  • detector module 700 does not require a separate source for pump signal 708.
  • the inclusion of nonlinear medium 703 upstream of target 704 can decrease the intensity of source signal 706.
  • FIG. 8 shows a method 800 for measuring an alignment of a target on a substrate according to some aspects.
  • the steps of method 800 can be performed by detector module 700 in FIG. 7.
  • method 800 is also applicable to embodiments of a detector module other than detector module 700.
  • method 800 begins at step 801 by transmitting a beam of radiation from a light source through a nonlinear medium to generate light having a frequency that is a harmonic of the beam of radiation.
  • the beam of radiation, the nonlinear medium, and the light may be similar in some respects to beam of radiation 701, nonlinear medium 703, and light 705, respectively.
  • the light is received by a PSA as a pump signal.
  • the PSA and pump signal may be similar in some respects to PSA 710 and pump signal 708, respectively.
  • FIG. 9 shows an embodiment of a detector module 900 according to a further aspect of the disclosure.
  • Many of the elements of detector module 900 function similar to the elements of detector module 500 shown in FIG. 5.
  • target 904, source signal 906, pump signal 908, PSA 910, amplified signal 912, and detector 914 can each function similarly to target 504, source signal 506, pump signal 508, PSA 510, amplified signal 512, and detector 514 in detector module 500.
  • detector module 900 differs from detector module 500 at least in the use of an idler signal 913, as described herein.
  • a beam of radiation 901 can be transmitted through an optical element 907, for example, a beam splitter, mirror, or the like, to produce beam of radiation 902 to illuminate target 904 on a substrate and to produce beam of radiation 909.
  • a difference-frequency generator (DFG) 911 can be positioned between optical element 907 to receive pump signal 908 and beam of radiation 909. DFG 911 can nonlinearly interact pump signal 908 and beam of radiation 909 to generate idler signal 913.
  • pump signal 908 and beam of radiation 909 can interact via three-wave mixing or four-wave mixing to generate idler signal 913.
  • idler signal 913 can be transmitted to PSA 910.
  • remaining light 915 can be directed away from PSA 910.
  • light 915 can be directed away from PSA 910.
  • DFG 911 can be a nonlinear medium.
  • DFG 911 can be chosen to generate an idler signal 913 having a frequency that is a difference between a frequency of pump signal 908 and beam of radiation 909.
  • DFG 911 can generate idler signal 913 by annihilating photons of pump signal 908.
  • pump signal 908 can excite a transition in DFG 911 to a different energy state such that the sum of the photon energy of the signal and idler is equal to the photon energy of the pump.
  • PSA 910 can interfere the remaining of the pump signal 908 and source signal 906 with idler signal 913 to generate amplified signal 912.
  • detector 914 can use amplified signal 912 to determine an alignment position of target 904.
  • FIG. 10 shows a method 1000 for measuring an alignment of a target on a substrate according to some aspects.
  • the steps of method 1000 can be performed by detector module 900 in FIG. 9.
  • method 1000 is also applicable to embodiments of a detector module other than detector module 900.
  • method 1000 begins at step 1001 by a DFG receiving a beam of radiation from a light source and receiving a pump signal.
  • the DFG, the beam of radiation, and the pump signal may be similar in some respects to DFG 911, beam of radiation 909, and pump signal 908.
  • DFG 911 can generate an idler signal based on the beam of radiation and the pump signal.
  • the idler signal may be similar in some respects to idler signal 913.
  • a PSA can receive the pump signal, the idler signal, and a source signal.
  • the PSA and source signal may be similar in some respects to PSA 910 and source signal 906.
  • the PSA can generate an amplified signal by interacting the source signal, the pump signal, and the idler signal.
  • the amplified signal may be similar in some respects to amplified signal 912.
  • an alignment of a position of the target may be made based on the amplified signal.
  • the determination may be performed by a detector that is similar in some respects to detector 914. However, the determination can also be performed by, for example, a processor coupled to a memory that is separate from a detector, or a controller that is coupled to the detector to determine the position of the target.
  • a detection module comprising: a phase sensitive amplifier configured to receive a source signal diffracted from a target on a surface of a substrate; receive a pump signal; and transmit an amplified signal based on a phase between the pump signal and the source signal; and a detector configured to receive the amplified signal and determine an alignment position of the target based on the amplified signal.
  • nonlinear crystal comprises lithium nitride, aluminum nitride, gallium arsenide, and/or barium borate.
  • phase sensitive amplifier is further configured to receive an idler signal.
  • the detection module of clause 10 further comprising a difference-frequency generator (DFG) configured to receive the input signal and the pump signal.
  • DFG difference-frequency generator
  • a metrology apparatus comprising: a light source configured to generate a beam of radiation; an optical system configured to illuminate a target on a surface of a substrate with the beam of radiation to generate a source signal; a phase sensitive amplifier configured to receive a pump signal; receive the source signal from the target; and transmit an amplified signal based on a phase between the pump signal and the source signal; a detector configured to receive the amplified signal; and a controller coupled to the detector and configured to determine an alignment position of the target based on the amplified signal.
  • a method for detecting an alignment of a substrate comprising: receiving a pump signal; receiving a source signal diffracted from a target on a surface of the substrate; nonlinearly interacting the pump signal and the source signal to generate an amplified signal based on a phase difference between the source signal and the pump signal; and determining an alignment position of the target based on the amplified signal.

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Abstract

Un module de détection comprend un amplificateur sensible à la phase (PSA) et un détecteur. Le PSA reçoit un signal source diffracté à partir d'une cible sur une surface d'un substrat. Le PSA reçoit également un signal de pompe. Le PSA transmet un signal amplifié sur la base d'une phase entre le signal de pompe et le signal source. Le détecteur reçoit le signal amplifié et détermine une position d'alignement de la cible sur la base du signal amplifié.
PCT/EP2024/054088 2023-03-14 2024-02-16 Métrologie d'alignement utilisant un oscillateur local Pending WO2024188592A1 (fr)

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