EP4630880A1 - Source de rayonnement supercontinuum - Google Patents

Source de rayonnement supercontinuum

Info

Publication number
EP4630880A1
EP4630880A1 EP23798967.8A EP23798967A EP4630880A1 EP 4630880 A1 EP4630880 A1 EP 4630880A1 EP 23798967 A EP23798967 A EP 23798967A EP 4630880 A1 EP4630880 A1 EP 4630880A1
Authority
EP
European Patent Office
Prior art keywords
supercontinuum
radiation
radiation source
generation stage
nonlinear
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
Application number
EP23798967.8A
Other languages
German (de)
English (en)
Inventor
Amir Abdolvand
John Colin TRAVERS
Yongfeng Ni
Mohsen SAJADI HEZAVEH
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ASML Netherlands BV
Original Assignee
ASML Netherlands BV
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by ASML Netherlands BV filed Critical ASML Netherlands BV
Publication of EP4630880A1 publication Critical patent/EP4630880A1/fr
Pending legal-status Critical Current

Links

Classifications

    • 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
    • G02F1/3528—Non-linear optics for producing a supercontinuum
    • 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
    • G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
    • 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
    • G02F1/365—Non-linear optics in an optical waveguide structure
    • 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
    • G02F2202/00—Materials and properties
    • G02F2202/32—Photonic crystals

Definitions

  • the present invention relates to a supercontinuum or broadband radiation source, and in particular such a broadband radiation source in relation to metrology applications in the manufacture of integrated circuits.
  • a lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate.
  • a lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
  • a lithographic apparatus may, for example, project a pattern (also often referred to as “design layout” or “design”) at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).
  • a lithographic apparatus may use electromagnetic radiation.
  • the wavelength of this radiation determines the minimum size of features which can be formed on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm.
  • a lithographic apparatus which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.
  • EUV extreme ultraviolet
  • Low-ki lithography may be used to process features with dimensions smaller than the classical resolution limit of a lithographic apparatus.
  • CD kix /NA
  • X the wavelength of radiation employed
  • NA the numerical aperture of the projection optics in the lithographic apparatus
  • CD is the “critical dimension” (generally the smallest feature size printed, but in this case half-pitch)
  • ki is an empirical resolution factor.
  • sophisticated fine-tuning steps may be applied to the lithographic projection apparatus and/or design layout.
  • RET resolution enhancement techniques
  • Metrology tools are used in many aspects of the IC manufacturing process, for example as alignment tools for proper positioning of a substrate prior to an exposure, leveling tools to measure a surface topology of the substrate, for e.g., focus control and scatterometry based tools for inspecting/measuring the exposed and/or etched product in process control.
  • a radiation source is required.
  • broadband or white light radiation sources are increasingly used for such metrology applications. It would be desirable to improve on present devices for broadband radiation generation.
  • a broadband radiation source for generating output broadband radiation comprising a plurality of supercontinuum generation stages arranged in series, each said supercontinuum generation stage comprising a respective nonlinear generation element; wherein said plurality of supercontinuum generation stages comprises at least a first supercontinuum generation stage and a second supercontinuum generation stage, said second supercontinuum generation stage succeeding said first supercontinuum generation stage in said series; and wherein a damage tolerance of a first nonlinear generation element comprised within the first supercontinuum generation stage is greater than a damage tolerance of at least a second nonlinear generation element comprised within the second supercontinuum generation stage.
  • a broadband radiation source for generating output broadband radiation comprising a plurality of supercontinuum generation stages arranged in series, each said supercontinuum generation stage comprising a respective nonlinear generation element; wherein said plurality of supercontinuum generation stages comprises at least a first supercontinuum generation stage and a second supercontinuum generation stage, said second supercontinuum generation stage succeeding said first supercontinuum generation stage in said series; and wherein an optical nonlinearity of a first nonlinear generation element comprised within the first supercontinuum generation stage is lower than an optical nonlinearity of at least a second nonlinear generation element comprised within the second supercontinuum generation stage
  • Other aspects of the invention comprise metrology device comprising the broadband radiation source device of the first aspect or second aspects.
  • Figure 1 depicts a schematic overview of a lithographic apparatus
  • Figure 2 depicts a schematic overview of a lithographic cell
  • Figure 3 depicts a schematic representation of holistic lithography, representing a cooperation between three key technologies to optimize semiconductor manufacturing
  • Figure 4 depicts a schematic overview of a scatterometry apparatus used as a metrology device, which may comprise a radiation source according to embodiments of the invention
  • Figure 5 depicts a schematic overview of a level sensor apparatus which may comprise a radiation source according to embodiments of the invention
  • Figure 6 depicts a schematic overview of an alignment sensor apparatus which may comprise a radiation source according to embodiments of the invention
  • Figure 7 is a schematic cross sectional view of a hollow-core optical fiber that may form part of a radiation source according to an embodiment, in a transverse plane (i.e. perpendicular to an axis of the optical fiber);
  • Figure 8 depicts a schematic representation of a known radiation source for providing broadband output radiation
  • FIGS 9 (a) and (b) schematically depict the transverse cross-sections of examples of hollow-core photonic crystal fiber (HC-PCF) designs for supercontinuum generation;
  • Figure 10 schematically illustrates a broadband radiation source according to a first embodiment
  • Figure 11 schematically illustrates a broadband radiation source according to a first embodiment
  • Figure 12 schematically illustrates a broadband radiation source according to a second embodiment
  • Figure 13 schematically illustrates a broadband radiation source according to a third embodiment
  • Figure 14 schematically illustrates a broadband radiation source according to a fourth embodiment
  • Figure 15 schematically illustrates a broadband radiation source according to a fifth embodiment
  • Figure 16 depicts a block diagram of a computer system for controlling a broadband radiation source.
  • the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range of about 5-100 nm).
  • reticle may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate.
  • the term “light valve” can also be used in this context.
  • examples of other such patterning devices include a programmable mirror array and a programmable LCD array.
  • FIG. 1 schematically depicts a lithographic apparatus LA.
  • the lithographic apparatus LA includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation or EUV radiation), a mask support (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA in accordance with certain parameters, a substrate support (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support in accordance with certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.
  • the illumination system IL receives a radiation beam from a radiation source SO, e.g. via a beam delivery system BD.
  • the illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and/or other types of optical components, or any combination thereof, for directing, shaping, and/or controlling radiation.
  • the illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.
  • projection system PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and/or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system” PS.
  • the lithographic apparatus LA may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system PS and the substrate W - which is also referred to as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.
  • the lithographic apparatus LA may also be of a type having two or more substrate supports WT (also named “dual stage”). In such “multiple stage” machine, the substrate supports WT may be used in parallel, and/or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W.
  • the lithographic apparatus LA may comprise a measurement stage.
  • the measurement stage is arranged to hold a sensor and/or a cleaning device.
  • the sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B.
  • the measurement stage may hold multiple sensors.
  • the cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid.
  • the measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS.
  • the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. 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. With the aid of the second positioner PW and a position measurement system IF, the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position.
  • the patterning device e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA.
  • the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W.
  • the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused
  • first positioner PM and possibly another position sensor may be used to accurately position the patterning device MA with respect to the path of the radiation beam B.
  • Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.
  • substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions.
  • Substrate alignment marks Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C.
  • the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to as a lithocell or (litho)cluster, which often also includes apparatus to perform pre- and post-exposure processes on a substrate W.
  • a lithographic cell LC also sometimes referred to as a lithocell or (litho)cluster
  • these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH and bake plates BK, e.g. for conditioning the temperature of substrates W e.g. for conditioning solvents in the resist layers.
  • a substrate handler, or robot, RO picks up substrates W from input/output ports I/Ol, I/O2, moves them between the different process apparatus and delivers the substrates W to the loading bay LB of the lithographic apparatus LA.
  • the devices in the lithocell which are often also collectively referred to as the track, are typically under the control of a track control unit TCU that in itself may be controlled by a supervisory control system SCS, which may also control the lithographic apparatus LA, e.g. via lithography control unit LACU.
  • a supervisory control system SCS which may also control the lithographic apparatus LA, e.g. via lithography control unit LACU.
  • inspection tools may be included in the lithocell LC. If errors are detected, adjustments, for example, may be made to exposures of subsequent substrates or to other processing steps that are to be performed on the substrates W, especially if the inspection is done before other substrates W of the same batch or lot are still to be exposed or processed.
  • An inspection apparatus which may also be referred to as a metrology apparatus, is used to determine properties of the substrates W, and in particular, how properties of different substrates W vary or how properties associated with different layers of the same substrate W vary from layer to layer.
  • the inspection apparatus may alternatively be constructed to identify defects on the substrate W and may, for example, be part of the lithocell LC, or may be integrated into the lithographic apparatus LA, or may even be a stand-alone device.
  • the inspection apparatus may measure the properties on a latent image (image in a resist layer after the exposure), or on a semi-latent image (image in a resist layer after a post-exposure bake step PEB), or on a developed resist image (in which the exposed or unexposed parts of the resist have been removed), or even on an etched image (after a pattern transfer step such as etching).
  • the patterning process in a lithographic apparatus LA is one of the most critical steps in the processing which requires high accuracy of dimensioning and placement of structures on the substrate W.
  • three systems may be combined in a so called “holistic” control environment as schematically depicted in Fig. 3.
  • One of these systems is the lithographic apparatus LA which is (virtually) connected to a metrology tool MT (a second system) and to a computer system CL (a third system).
  • the key of such “holistic” environment is to optimize the cooperation between these three systems to enhance the overall process window and provide tight control loops to ensure that the patterning performed by the lithographic apparatus LA stays within a process window.
  • the process window defines a range of process parameters (e.g. dose, focus, overlay) within which a specific manufacturing process yields a defined result (e.g. a functional semiconductor device) - typically within which the process parameters in the lithographic process or patterning process are allowed to vary.
  • the computer system CL may use (part of) the design layout to be patterned to predict which resolution enhancement techniques to use and to perform computational lithography simulations and calculations to determine which mask layout and lithographic apparatus settings achieve the largest overall process window of the patterning process (depicted in Fig. 3 by the double arrow in the first scale SCI).
  • the resolution enhancement techniques are arranged to match the patterning possibilities of the lithographic apparatus LA.
  • the computer system CL may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g. using input from the metrology tool MT) to predict whether defects may be present due to e.g. sub-optimal processing (depicted in Fig. 3 by the arrow pointing “0” in the second scale SC2).
  • the metrology tool MT may provide input to the computer system CL to enable accurate simulations and predictions, and may provide feedback to the lithographic apparatus LA to identify possible drifts, e.g. in a calibration status of the lithographic apparatus LA (depicted in Fig. 3 by the multiple arrows in the third scale SC3).
  • a calibration status of the lithographic apparatus LA depicted in Fig. 3 by the multiple arrows in the third scale SC3.
  • tools to make such measurement are typically called metrology tools MT.
  • Different types of metrology tools MT for making such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools MT.
  • Scatterometers are versatile instruments which allow measurements of the parameters of a lithographic process by having a sensor in the pupil or a conjugate plane with the pupil of the objective of the scatterometer, measurements usually referred as pupil based measurements, or by having the sensor in the image plane or a plane conjugate with the image plane, in which case the measurements are usually referred as image or field based measurements.
  • Such scatterometers and the associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, incorporated herein by reference in their entirety.
  • Aforementioned scatterometers may measure gratings using light from soft x-ray and visible to near-IR wavelength range.
  • the scatterometer MT is an angular resolved scatterometer.
  • reconstruction methods may be applied to the measured signal to reconstruct or calculate properties of the grating.
  • Such reconstruction may, for example, result from simulating interaction of scattered radiation with a mathematical model of the target structure and comparing the simulation results with those of a measurement. Parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the real target.
  • the scatterometer MT is a spectroscopic scatterometer MT.
  • the radiation emitted by a radiation source is directed onto the target and the reflected or scattered radiation from the target is directed to a spectrometer detector, which measures a spectrum (i.e. a measurement of intensity as a function of wavelength) of the specular reflected radiation. From this data, the structure or profile of the target giving rise to the detected spectrum may be reconstructed, e.g. by Rigorous Coupled Wave Analysis and non-linear regression or by comparison with a library of simulated spectra.
  • the scatterometer MT is an ellipsometric scatterometer.
  • the ellipsometric scatterometer allows for determining parameters of a lithographic process by measuring scattered radiation for each polarization states.
  • Such metrology apparatus emits polarized light (such as linear, circular, or elliptic) by using, for example, appropriate polarization filters in the illumination section of the metrology apparatus.
  • a source suitable for the metrology apparatus may provide polarized radiation as well.
  • the scatterometer MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring asymmetry in the reflected spectrum and/or the detection configuration, the asymmetry being related to the extent of the overlay.
  • the two (typically overlapping) grating structures may be applied in two different layers (not necessarily consecutive layers), and may be formed substantially at the same position on the wafer.
  • the scatterometer may have a symmetrical detection configuration as described e.g. in co-owned patent application EP1,628,164A, such that any asymmetry is clearly distinguishable. This provides a straightforward way to measure misalignment in gratings. Further examples for measuring overlay error between the two layers containing periodic structures as target is measured through asymmetry of the periodic structures may be found in PCT patent application publication no. WO 2011/012624 or US patent application US 20160161863, incorporated herein by reference in its entirety.
  • Focus and dose may be determined simultaneously by scatterometry (or alternatively by scanning electron microscopy) as described in US patent application US2011-0249244, incorporated herein by reference in its entirety.
  • a single structure may be used which has a unique combination of critical dimension and sidewall angle measurements for each point in a focus energy matrix (FEM - also referred to as Focus Exposure Matrix). If these unique combinations of critical dimension and sidewall angle are available, the focus and dose values may be uniquely determined from these measurements.
  • FEM focus energy matrix
  • a metrology target may be an ensemble of composite gratings, formed by a lithographic process, mostly in resist, but also after etch process for example.
  • the pitch and line-width of the structures in the gratings strongly depend on the measurement optics (in particular the NA of the optics) to be able to capture diffraction orders coming from the metrology targets.
  • the diffracted signal may be used to determine shifts between two layers (also referred to ‘overlay’) or may be used to reconstruct at least part of the original grating as produced by the lithographic process. This reconstruction may be used to provide guidance of the quality of the lithographic process and may be used to control at least part of the lithographic process.
  • Targets may have smaller sub-segmentation which are configured to mimic dimensions of the functional part of the design layout in a target. Due to this sub-segmentation, the targets will behave more similar to the functional part of the design layout such that the overall process parameter measurements resembles the functional part of the design layout better.
  • the targets may be measured in an underfilled mode or in an overfilled mode. In the underfilled mode, the measurement beam generates a spot that is smaller than the overall target. In the overfilled mode, the measurement beam generates a spot that is larger than the overall target. In such overfilled mode, it may also be possible to measure different targets simultaneously, thus determining different processing parameters at the same time.
  • substrate measurement recipe may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns measured, or both.
  • the measurement used in a substrate measurement recipe is a diffraction-based optical measurement
  • one or more of the parameters of the measurement may include the wavelength of the radiation, the polarization of the radiation, the incident angle of radiation relative to the substrate, the orientation of radiation relative to a pattern on the substrate, etc.
  • One of the criteria to select a measurement recipe may, for example, be a sensitivity of one of the measurement parameters to processing variations. More examples are described in US patent application US2016-0161863 and published US patent application US 2016/0370717 Al incorporated herein by reference in its entirety.
  • a metrology apparatus such as a scatterometer, is depicted in Figure 4. It comprises a broadband (white light) radiation projector 2 which projects radiation onto a substrate 6. The reflected or scattered radiation is passed to a spectrometer detector 4, which measures a spectrum 10 (i.e. a measurement of intensity as a function of wavelength) of the specular reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by processing unit PU, e.g. by Rigorous Coupled Wave Analysis and non-linear regression or by comparison with a library of simulated spectra as shown at the bottom of Figure 3.
  • processing unit PU e.g. by Rigorous Coupled Wave Analysis and non-linear regression or by comparison with a library of simulated spectra as shown at the bottom of Figure 3.
  • a scatterometer may be configured as a normalincidence scatterometer or an oblique-incidence scatterometer.
  • substrate measurement recipe may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns measured, or both.
  • the measurement used in a substrate measurement recipe is a diffraction-based optical measurement
  • one or more of the parameters of the measurement may include the wavelength of the radiation, the polarization of the radiation, the incident angle of radiation relative to the substrate, the orientation of radiation relative to a pattern on the substrate, etc.
  • One of the criteria to select a measurement recipe may, for example, be a sensitivity of one of the measurement parameters to processing variations.
  • FIG. 1 Another type of metrology tool used in IC manufacture is a topography measurement system, level sensor or height sensor.
  • a topography measurement system level sensor or height sensor.
  • Such a tool may be integrated in the lithographic apparatus, for measuring a topography of a top surface of a substrate (or wafer).
  • a map of the topography of the substrate also referred to as height map, may be generated from these measurements indicating a height of the substrate as a function of the position on the substrate.
  • This height map may subsequently be used to correct the position of the substrate during transfer of the pattern on the substrate, in order to provide an aerial image of the patterning device in a properly focus position on the substrate.
  • the level or height sensor performs measurements at a fixed location (relative to its own optical system) and a relative movement between the substrate and the optical system of the level or height sensor results in height measurements at locations across the substrate.
  • the level sensor comprises an optical system, which includes a projection unit LSP and a detection unit LSD.
  • the projection unit LSP comprises a radiation source LSO providing a beam of radiation LSB which is imparted by a projection grating PGR of the projection unit LSP.
  • the radiation source LSO may be, for example, a narrowband or broadband light source, such as a supercontinuum light source, polarized or nonpolarized, pulsed or continuous, such as a polarized or non-polarized laser beam.
  • the radiation source LSO may include a plurality of radiation sources having different colors, or wavelength ranges, such as a plurality of LEDs.
  • the radiation source LSO of the level sensor LS is not restricted to visible radiation, but may additionally or alternatively encompass UV and/or IR radiation and any range of wavelengths suitable to reflect from a surface of a substrate.
  • the projection grating PGR is a periodic grating comprising a periodic structure resulting in a beam of radiation BE1 having a periodically varying intensity.
  • the beam of radiation BE1 with the periodically varying intensity is directed towards a measurement location MLO on a substrate W having an angle of incidence ANG with respect to an axis perpendicular (Z-axis) to the incident substrate surface between 0 degrees and 90 degrees, typically between 70 degrees and 80 degrees.
  • the patterned beam of radiation BE1 is reflected by the substrate W (indicated by arrows BE2) and directed towards the detection unit LSD.
  • the level sensor further comprises a detection system comprising a detection grating DGR, a detector DET and a processing unit (not shown) for processing an output signal of the detector DET.
  • the detection grating DGR may be identical to the projection grating PGR.
  • the detector DET produces a detector output signal indicative of the light received, for example indicative of the intensity of the light received, such as a photodetector, or representative of a spatial distribution of the intensity received, such as a camera.
  • the detector DET may comprise any combination of one or more detector types.
  • the height level at the measurement location MLO can be determined.
  • the detected height level is typically related to the signal strength as measured by the detector DET, the signal strength having a periodicity that depends, amongst others, on the design of the projection grating PGR and the (oblique) angle of incidence ANG.
  • the projection unit LSP and/or the detection unit LSD may include further optical elements, such as lenses and/or mirrors, along the path of the patterned beam of radiation between the projection grating PGR and the detection grating DGR (not shown).
  • the detection grating DGR may be omitted, and the detector DET may be placed at the position where the detection grating DGR is located. Such a configuration provides a more direct detection of the image of the projection grating PGR.
  • a level sensor LS may be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of measurement areas MLO or spots covering a larger measurement range.
  • a critical aspect of performance of the lithographic apparatus is therefore the ability to place the applied pattern correctly and accurately in relation to features laid down in previous layers (by the same apparatus or a different lithographic apparatus).
  • the substrate is provided with one or more sets of marks or targets.
  • Each mark is a structure whose position can be measured at a later time using a position sensor, typically an optical position sensor.
  • the position sensor may be referred to as “alignment sensor” and marks may be referred to as “alignment marks”.
  • a lithographic apparatus may include one or more (e.g. a plurality of) alignment sensors by which positions of alignment marks provided on a substrate can be measured accurately.
  • Alignment (or position) sensors may use optical phenomena such as diffraction and interference to obtain position information from alignment marks formed on the substrate.
  • An example of an alignment sensor used in current lithographic apparatus is based on a self-referencing interferometer as described in US6961116.
  • Various enhancements and modifications of the position sensor have been developed, for example as disclosed in US2015261097A1. The contents of all of these publications are incorporated herein by reference.
  • FIG. 6 is a schematic block diagram of an embodiment of a known alignment sensor AS, such as is described, for example, in US6961116, and which is incorporated by reference.
  • Radiation source RSO provides a beam RB of radiation of one or more wavelengths, which is diverted by diverting optics onto a mark, such as mark AM located on substrate W, as an illumination spot SP.
  • the diverting optics comprises a spot mirror SM and an objective lens OL.
  • the illumination spot SP, by which the mark AM is illuminated, may be slightly smaller in diameter than the width of the mark itself.
  • Radiation diffracted by the alignment mark AM is collimated (in this example via the objective lens OL) into an information-carrying beam IB.
  • the term “diffracted” is intended to include zero-order diffraction from the mark (which may be referred to as reflection).
  • a self-referencing interferometer SRI e.g. of the type disclosed in US6961116 mentioned above, interferes the beam IB with itself after which the beam is received by a photodetector PD. Additional optics (not shown) may be included to provide separate beams in case more than one wavelength is created by the radiation source RSO.
  • the photodetector may be a single element, or it may comprise a number of pixels, if desired.
  • the photodetector may comprise a sensor array.
  • the diverting optics which in this example comprises the spot mirror SM, may also serve to block zero order radiation reflected from the mark, so that the information-carrying beam IB comprises only higher order diffracted radiation from the mark AM (this is not essential to the measurement, but improves signal to noise ratios).
  • Intensity signals SI are supplied to a processing unit PU.
  • a processing unit PU By a combination of optical processing in the block SRI and computational processing in the unit PU, values for X- and Y- position on the substrate relative to a reference frame are output.
  • a single measurement of the type illustrated only fixes the position of the mark within a certain range corresponding to one pitch of the mark.
  • Coarser measurement techniques are used in conjunction with this to identify which period of a sine wave is the one containing the marked position.
  • the same process at coarser and/or finer levels may be repeated at different wavelengths for increased accuracy and/or for robust detection of the mark irrespective of the materials from which the mark is made, and materials on and/or below which the mark is provided.
  • the wavelengths may be multiplexed and de-multiplexed optically so as to be processed simultaneously, and/or they may be multiplexed by time division or frequency division.
  • the alignment sensor and spot SP remain stationary, while it is the substrate W that moves.
  • the alignment sensor can thus be mounted rigidly and accurately to a reference frame, while effectively scanning the mark AM in a direction opposite to the direction of movement of substrate W.
  • the substrate W is controlled in this movement by its mounting on a substrate support and a substrate positioning system controlling the movement of the substrate support.
  • a substrate support position sensor e.g. an interferometer
  • one or more (alignment) marks are provided on the substrate support.
  • a measurement of the position of the marks provided on the substrate support allows the position of the substrate support as determined by the position sensor to be calibrated (e.g. relative to a frame to which the alignment system is connected).
  • a measurement of the position of the alignment marks provided on the substrate allows the position of the substrate relative to the substrate support to be determined.
  • Metrology tools MT such as a scatterometer, topography measurement system, or position measurement system mentioned above may use radiation originating from a radiation source to perform a measurement.
  • the properties of the radiation used by a metrology tool may affect the type and quality of measurements that may be performed.
  • it may be advantageous to use multiple radiation frequencies to measure a substrate for example broadband radiation may be used. Multiple different frequencies may be able to propagate, irradiate, and scatter off a metrology target with no or minimal interference with other frequencies. Therefore different frequencies may for example be used to obtain more metrology data simultaneously. Different radiation frequencies may also be able to interrogate and discover different properties of a metrology target.
  • Broadband radiation may be useful in metrology systems MT such as for example level sensors, alignment mark measurement systems, scatterometry tools, or inspection tools.
  • a broadband radiation source may be a supercontinuum source.
  • High-quality broadband radiation for example supercontinuum radiation
  • One method for generating broadband radiation may be to broaden high-power narrow band or single frequency input radiation or pump radiation, for example making use of non-linear, higher order effects.
  • the input radiation (which may be produced using a laser) may be referred to as pump radiation.
  • the input radiation may be referred to as seed radiation.
  • radiation may be confined into a small area so that strongly localized high intensity radiation is achieved. In those areas, the radiation may interact with broadening structures and/or materials forming a non-linear medium so as to create broadband output radiation. In the high intensity radiation areas, different materials and/or structures may be used to enable and/or improve radiation broadening by providing a suitable non-linear medium.
  • the broadband output radiation is created in a photonic crystal fiber (PCF).
  • a photonic crystal fiber has microstructures around its fiber core assisting in confining radiation that travels through the fiber in the fiber core.
  • the fiber core can be made of a solid material that has non-linear properties and that is capable of generating broadband radiation when high intensity pump radiation is transmitted through the fiber core.
  • it is feasible to generate broadband radiation in solid-core photonic crystal fibers there may be a few disadvantages of using a solid material. For example, if UV radiation is generated in the solid-core, this radiation might not be present in the output spectrum of the fiber because the radiation is absorbed by most solid material and causes permanent damage.
  • methods and apparatus for broadening input radiation may use a fiber for confining input radiation, and for broadening the input radiation to output broadband radiation.
  • the fiber may be a hollow-core fiber, and may comprise internal structures to achieve effective guiding and confinement of radiation in the fiber.
  • the fiber may be a hollow-core photonic crystal fiber (HC-PCF), which is particularly suitable for strong radiation confinement, predominantly inside the hollow-core of the fiber, achieving high radiation intensities.
  • the hollow-core of the fiber may be filled with a gas acting as a broadening medium for broadening input radiation.
  • a fiber and gas arrangement may be used to create a supercontinuum radiation source.
  • Radiation input to the fiber may be electromagnetic radiation, for example radiation in one or more of the infrared, visible, UV, and extreme UV spectra.
  • the output radiation may consist of or comprise broadband radiation, which may be referred to herein as white light.
  • the optical fiber is a hollow-core, photonic crystal fiber (HC-PCF).
  • the optical fiber may be a hollow-core, photonic crystal fiber of a type comprising anti-resonant structures for confinement of radiation.
  • Such fibers comprising anti-resonant structures are known in the art as anti-resonant fibers, tubular fibers, single-ring fibers, negative curvature fibers or inhibited coupling fibers.
  • the optical fiber may be photonic bandgap fibers (HC-PBFs, for example a Kagome fiber).
  • HC-PCFs hollow-core photonic bandgap fibers
  • HC-ARFs hollow-core anti -resonant reflecting fibers
  • Figure 7 is a schematic cross sectional view of the optical fiber OF in a transverse plane. Further embodiments similar to the practical example of the fiber of Figure 7 are disclosed in WO2017/032454A1.
  • the optical fiber OF comprises an elongate body, which is longer in one dimension compared to the other two dimensions of the fiber OF. This longer dimension may be referred to as an axial direction and may define an axis of the optical fiber OF. The two other dimensions define a plane which may be referred to as a transverse plane.
  • Figure 7 shows a cross-section of the optical fiber OF in this transverse plane (i.e. perpendicular to the axis), which is labelled as the x-y plane.
  • the transverse cross-section of the optical fiber OF may be substantially constant along the fiber axis.
  • the optical fiber OF has some degree of flexibility and therefore the direction of the axis will not, in general, be uniform along the length of the optical fiber OF.
  • the terms such as the optical axis, the transverse cross-section and the like will be understood to mean the local optical axis, the local transverse cross-section and so on.
  • components are described as being cylindrical or tubular these terms will be understood to encompass such shapes that may have been distorted as the optical fiber OF is flexed.
  • the optical fiber OF may have any length and it will be appreciated that the length of the optical fiber OF may be dependent on the application.
  • the optical fiber OF may have a length between 1 cm and 10 m, for example, the optical fiber OF may have a length between 10 cm and 100 cm.
  • the optical fiber OF comprises: a hollow-core HC; a cladding portion surrounding the hollow-core HC; and a support portion SP surrounding and supporting the cladding portion.
  • the optical fiber OF may be considered to comprise a body (comprising the cladding portion and the support portion SP) having a hollow-core HC.
  • the cladding portion comprises a plurality of antiresonance elements for guiding radiation through the hollow-core HC.
  • the plurality of anti-resonance elements are arranged to confine radiation that propagates through the optical fiber OF predominantly inside the hollow-core HC and to guide the radiation along the optical fiber OF.
  • the hollow-core HC of the optical fiber OF may be disposed substantially in a central region of the optical fiber OF, so that the axis of the optical fiber OF may also define an axis of the hollow-core HC of the optical fiber OF.
  • the cladding portion comprises a plurality of anti-resonance elements for guiding radiation propagating through the optical fiber OF.
  • the cladding portion comprises a single ring of six tubular capillaries CAP.
  • Each of the tubular capillaries CAP acts as an anti-resonance element.
  • these anti-resonance element may come in different cross-sections, e.g. an elliptical cross-section or a nested circular cross-section in which there is a circular tube of a smaller diameter resides in a circular tube of a larger diameter.
  • the capillaries CAP may also be referred to as tubes.
  • the capillaries CAP may be circular in cross section, or may have another shape.
  • Each capillary CAP comprises a generally cylindrical wall portion WP that at least partially defines the hollow-core HC of the optical fiber OF and separates the hollow-core HC from a capillary cavity CC. It will be appreciated that the wall portion WP may act as an anti-reflecting Fabry-Perot resonator for radiation that propagates through the hollow-core HC (and which may be incident on the wall portion WP at a grazing incidence angle).
  • the thickness of the wall portion WP may be suitable so as to ensure that reflection back into the hollow-core HC is generally enhanced whereas transmission into the capillary cavity CC is generally suppressed.
  • the capillary wall portion WP may have a thickness between 0.01 - 10.0 pm.
  • the term cladding portion is intended to mean a portion of the optical fiber OF for guiding radiation propagating through the optical fiber OF (i.e. the capillaries CAP which confine said radiation within the hollow-core HC).
  • the radiation may be confined in the form of transverse modes, propagating along the fiber axis.
  • the support portion is generally tubular and supports the six capillaries CAP of the cladding portion.
  • the six capillaries CAP are distributed evenly around an inner surface if the inner support portion SP.
  • the six capillaries CAP may be described as being disposed in a generally hexagonal formation.
  • the capillaries CAP are arranged so that each capillary is not in contact with any of the other capillaries CAP.
  • Each of the capillaries CAP is in contact with the inner support portion SP and spaced apart from adjacent capillaries CAP in the ring structure.
  • Such an arrangement may be beneficial since it may increase a transmission bandwidth of the optical fiber OF (relative, for example, to an arrangement wherein the capillaries are in contact with each other).
  • each of the capillaries CAP may be in contact with adjacent capillaries CAP in the ring structure.
  • the six capillaries CAP of the cladding portion are disposed in a ring structure around the hollow-core HC.
  • An inner surface of the ring structure of capillaries CAP at least partially defines the hollow-core HC of the optical fiber OF.
  • the diameter d of the hollow-core HC (which may be defined as the smallest dimension between opposed capillaries, indicated by arrow d) may be between 10 and 1000 pm.
  • the diameter d of the hollow-core HC may affect the mode field diameter, impact loss, dispersion, modal plurality, and non-linearity properties of the hollow-core HC optical fiber OF.
  • the cladding portion comprises a single ring arrangement of capillaries CAP (which act as anti-resonance elements). Therefore, a line in any radial direction from a center of the hollow-core HC to an exterior of the optical fiber OF passes through no more than one capillary CAP.
  • FIG. 9(a) shows an embodiment of HC-PCFs with three rings of capillaries CAP stacking on top of each other along the radial direction.
  • each capillary CAP is in contact with other capillaries both in the same ring and in a different ring.
  • the embodiment shown in Figure 7 comprises a ring of six capillaries, in other embodiments, one or more rings comprising any number of antiresonance elements (for example 4, 5, 6, 7, 8, 9, 10, 11 or 12 capillaries) may be provided in the cladding portion.
  • Figure 9(b) shows a modified embodiment of the above discussed HC-PCFs with a single ring of tubular capillaries.
  • a support tube ST may be included in the HC-PCF.
  • the support tube may be made of silica.
  • the tubular capillaries of the examples of Figure 7 and Figures 9 (a) and (b) may have a circular cross-sectional shape. Other shapes are also possible for the tubular capillaries, like elliptical or polygonal cross-sections. Additionally, the solid material of the tubular capillaries of the examples of Figure 7 and Figures 9 (a) and (b) may comprise plastic material, like PMA, glass, like silica, or soft glass.
  • FIG 8 depicts a known radiation source RDS for providing broadband output radiation.
  • the radiation source RDS may comprise a pulsed pump radiation source PRS, a continuous wave source or any type of source that is capable of generating short pulses of a desired length and energy level; an optical fiber OF (for example of the type shown in Figure 7) with a hollow-core HC; and a working medium WM (for example a gas) disposed within the hollow-core HC.
  • the radiation source RDS comprises the optical fiber OF shown in Figure 7, in alternative embodiments other types of hollow-core HC optical fiber OF may be used.
  • the pulsed pump radiation source PRS is configured to provide input radiation IRD.
  • the hollow-core HC of the optical fiber OF is arranged to receive the input radiation IRD from the pulsed pump radiation source PRS, and broaden it to provide output radiation ORD.
  • the working medium WM enables the broadening of the frequency range of the received input radiation IRD so as to provide broadband output radiation ORD.
  • the radiation source RDS further comprises a reservoir RSV.
  • the optical fiber OF is disposed inside the reservoir RSV.
  • the reservoir RSV may also be referred to as a housing, container or gas cell.
  • the reservoir RSV is configured to contain the working medium WM.
  • the reservoir RSV may comprise one or more features, known in the art, for controlling, regulating, and/or monitoring the composition of the working medium WM (which may be a gas or a liquid) inside the reservoir RSV.
  • the reservoir RSV may comprise a first transparent window TW1.
  • the optical fiber OF is disposed inside the reservoir RSV such that the first transparent window TW1 is located proximate to an input end IE of the optical fiber OF.
  • the first transparent window TW 1 may form part of a wall of the reservoir RSV.
  • the first transparent window TW 1 may be transparent for at least the received input radiation frequencies, so that received input radiation IRD (or at least a large portion thereof) may be coupled into the optical fiber OF located inside reservoir RSV. It will be appreciated that optics (not shown) may be provided for coupling the input radiation IRD into the optical fiber OF.
  • the reservoir RSV comprises a second transparent window TW2, forming part of a wall of the reservoir RSV.
  • the second transparent window TW2 is located proximate to an output end OE of the optical fiber OF.
  • the second transparent window TW2 may be transparent for at least the frequencies of the broadband output radiation ORD of the apparatus 120.
  • the two opposed ends of the optical fiber OF may be placed inside different reservoirs.
  • the optical fiber OF may comprise a first end section configured to receive input radiation IRD, and a second end section for outputting broadband output radiation ORD.
  • the first end section may be placed inside a first reservoir, comprising a working medium WM.
  • the second end section may be placed inside a second reservoir, wherein the second reservoir may also comprise a working medium WM.
  • the functioning of the reservoirs may be as described in relation to Figure 8 above.
  • the first reservoir may comprise a first transparent window, configured to be transparent for input radiation IRD.
  • the second reservoir may comprise a second transparent window configured to be transparent for broadband output broadband radiation ORD.
  • the first and second reservoirs may also comprise a sealable opening to permit the optical fiber OF to be placed partially inside and partially outside the reservoir, so that a gas can be sealed inside the reservoir.
  • the optical fiber OF may further comprise a middle section not contained inside a reservoir.
  • Such an arrangement using two separate gas reservoirs may be particularly convenient for embodiments wherein the optical fiber OF is relatively long (for example when the length is more than 1 m). It will be appreciated that for such arrangements which use two separate gas reservoirs, the two reservoirs (which may comprise one or more features, known in the art, for controlling, regulating, and/or monitoring the composition of a gas inside the two reservoirs) may be considered to provide an apparatus for providing the working medium WM within the hollow-core HC of the optical fiber OF.
  • a window may be transparent for a frequency if at least 50%, 75%, 85%, 90%, 95%, or 99% of incident radiation of that frequency on the window is transmitted through the window.
  • Both the first TW1 and the second TW2 transparent windows may form an airtight seal within the walls of the reservoir RSV so that the working medium WM (which may be a gas) may be contained within the reservoir RSV. It will be appreciated that the gas WM may be contained within the reservoir RSV at a pressure different to the ambient pressure of the reservoir RSV.
  • the working medium WM which may be a gas
  • the working medium WM may comprise a noble gas such as Argon, Krypton, and Xenon, a Raman active gas such as Hydrogen, Deuterium and Nitrogen, a gas mixture such as an Argon/Hydrogen mixture, a Xenon/Deuterium mixture, a Krypton/Nitrogen mixture, a mixture of molecular gases, e.g. Nitrogen/Hydrogen mixture, a mixture of atomic gases, e.g. Argon/Helium, Krypton/Helium, Xenon/Helium, or a trinary gas mixture such as Argon/Helium/Hydrogen, or Krypton/Helium/Hydrogen.
  • a noble gas such as Argon, Krypton, and Xenon
  • a Raman active gas such as Hydrogen, Deuterium and Nitrogen
  • a gas mixture such as an Argon/Hydrogen mixture, a Xenon/Deuterium mixture,
  • the nonlinear optical processes can include modulational instability (MI), soliton selfcompression, soliton fission, Kerr effect, Raman effect and dispersive wave generation (DWG), details of which are described in WO2018/127266A1 and US9160137B1 (both of which are hereby incorporated by reference). Since the aforementioned parameters can be tuned, the generated broadband pulse dynamics and the associated spectral broadening characteristics can be adjusted so as to optimize the frequency conversion. For example, dispersion of a gas-filled hollow core fiber, as a key element defining the interaction regime of a laser pulse with the WM, can be tuned by varying the working medium WM pressure in the reservoir RSV (i.e. gas cell pressure).
  • WM pressure in the reservoir RSV i.e. gas cell pressure
  • the working medium WM may be disposed within the hollow-core HC at least during receipt of input radiation IRD for producing broadband output radiation ORD. It will be appreciated that, while the optical fiber OF is not receiving input radiation IRD for producing broadband output radiation, the gas WM may be wholly or partially absent from the hollow-core HC. [00083] In order to achieve frequency broadening high intensity radiation may be desirable.
  • An advantage of having a hollow-core HC optical fiber OF is that it may achieve high intensity radiation through strong spatial confinement of radiation propagating through the optical fiber OF, achieving high localized radiation intensities.
  • the radiation intensity inside the optical fiber OF may be high, for example due to high received input radiation intensity and/or due to strong spatial confinement of the radiation inside the optical fiber OF.
  • hollow-core optical fibers can guide radiation having a broader wavelength range that solid-core fibers and, in particular, hollowcore optical fibers can guide radiation in both the ultraviolet and infrared ranges in spectral regions that fused silica (typical glass used in optical fibers) is absorbing.
  • An advantage of using a hollow-core HC optical fiber OF may be that the majority of the radiation guided inside the optical fiber OF is confined to the hollow-core HC. Therefore, the majority of the interaction of the radiation inside the optical fiber OF is with the working medium WM, which is provided inside the hollow-core HC of the optical fiber OF. As a result, the broadening effects of the working medium WM on the radiation may be increased.
  • the received input radiation IRD may be electromagnetic radiation.
  • the input radiation IRD may be received as pulsed radiation.
  • the input radiation IRD may comprise ultrafast pulses, for example, generated by a laser.
  • the input radiation IRD may be temporally and/or spatially coherent radiation.
  • the input radiation IRD may be collimated radiation, an advantage of which may be to facilitate and improve the efficiency of coupling the input radiation IRD into the optical fiber OF.
  • the input radiation IRD may comprise a single frequency, or a narrow range of frequencies.
  • the input radiation IRD may be generated by a laser.
  • the output radiation ORD may be collimated and/or may be temporally and/or spatially coherent.
  • the broadband range of the output radiation ORD may be a continuous range, comprising a continuous range of radiation frequencies.
  • the output radiation ORD may comprise supercontinuum radiation.
  • Continuous radiation may be beneficial for use in a number of applications, for example in metrology applications.
  • the continuous range of frequencies may be used to interrogate a large number of properties.
  • the continuous range of frequencies may for example be used to determine and/or eliminate a frequency dependency of a measured property and/or to enable fast selection and/or switching among different frequencies with a spectral filtering device.
  • Supercontinuum output radiation ORD may comprise for example electromagnetic radiation over a wavelength range of 100 nm - 4000 nm.
  • the broadband output radiation ORD frequency range may be for example 400 nm - 900 nm, 500 nm - 900 nm, or 200 nm - 2000 nm.
  • the supercontinuum output radiation ORD may comprise white light.
  • the input radiation IRD provided by the pulsed pump radiation source PRS may be pulsed.
  • the input radiation IRD may comprise electromagnetic radiation of one or more frequencies between 200 nm and 3 pm.
  • the input radiation IRD may for example comprise electromagnetic radiation with a wavelength of 1.03 pm.
  • the repetition rate of the pulsed radiation IRD may be of an order of magnitude of 1 kHz to 100 MHz.
  • the pulse energies may have an order of magnitude of 1 nJ to 100 pJ, for example 1 - 10 pJ.
  • a pulse duration for the input radiation IRD may be between 1 fs and 10 ps, for example 300 fs.
  • the average power of input radiation IRD may be between 100 mW to several 100 W.
  • the average power of input radiation IRD may for example be 20 - 50 W.
  • the pulsed pump radiation source PRS may be a laser.
  • the spatio-temporal transmission characteristics of such a laser pulse, e.g. its spectral amplitude and phase, transmitted along the optical fiber OF can be varied and tuned through adjustment of (pump) laser parameters, tuned thermodynamic properties of the working medium WM, and/or optical fiber OF parameters, for example its core diameter and/or length.
  • Said spatio-temporal transmission characteristics may include one or more of: output power, output mode profile, output temporal profile, width of the output temporal profile (or output pulse width), output spectral profile, and bandwidth of the output spectral profile (or output spectral bandwidth).
  • Said input radiation source IRS parameters may include one or more of: pump wavelength, pump pulse energy, pump pulse width, pump pulse repetition rate.
  • Said optical fiber OF parameters may include one or more of: optical fiber length, size and shape of the hollow-core HC, size and shape of the capillaries, thickness of the walls of the capillaries surrounding the hollow-core HC.
  • Said working component WM e.g. filling gas, parameters may include one or more of: gas type, gas pressure and gas temperature, or gas composition and/or partial pressures in the case where the WM is a mixture of different gases.
  • the broadband output radiation ORD provided by the radiation source RDS may have an average output power of at least 100 mW.
  • the average output power may be at least 1 W.
  • the average output power may be at least 5 W.
  • the average output power may be at least 10 W.
  • the broadband output radiation ORD may be pulsed broadband output radiation ORD.
  • the broadband output radiation ORD may be continuous wave CW broadband output radiation ORD.
  • the broadband output radiation ORD may have a power spectral density in the entire wavelength band of the output radiation of at least 0.01 mW/nm.
  • the power spectral density in the entire wavelength band of the broadband output radiation may be at least 3 mW/nm.
  • nonlinear optical processes involved in generation of broadband output radiation ORD (e.g., supercontinuum or white light). Which nonlinear optical process has a more pronounced spectral broadening effect over the others will depend on how the operating parameters are set. For example, by selecting a pump wavelength and/or an optical fiber OF such that the pump pulse propagates through the fiber in a normal dispersion region (positive group velocity dispersion (GVD)), self-phase modulation is the dominant nonlinear optical process and is responsible for spectral expansion of the pump pulse.
  • ORD broadband output radiation
  • spectral broadening of input radiation IRD provided by the pulsed pump radiation source PRS is driven by soliton dynamics which require a pump pulse to propagate in an optical fiber OF in the anomalous dispersion region (negative GVD).
  • the effects of Kerr nonlinearity and dispersion act in opposition to each other so that the pulse preserves and/or enhances its peak intensity.
  • the pulse parameters of a pump pulse which is launched into an optical fiber OF (e.g., HC-PCF) with anomalous chromatic dispersion, do not exactly match those of a soliton, the pump pulse will evolve into a soliton pulse with a certain soliton order and a dispersive wave.
  • soliton self-compression and modulation instability are the two primary mechanisms for spectral broadening in soliton driven broadband radiation generation.
  • the distinction between the two mechanisms is that the soliton self-compression process is associated with low soliton orders whereas the modulation instability process is associated with high soliton orders.
  • the soliton order N of the pulsed input radiation IRD is a convenient parameter that can be used to distinguish conditions under which spectral broadening is dominated by modulation instability and conditions under which spectral broadening is dominated by soliton self-compression.
  • the soliton order N of the pulsed input radiation IRD is given by: where y is a nonlinear phase (or nonlinear parameter); P p is a pump peak power of the pulsed input radiation IRD; T is a pump pulse duration of the pulsed input radiation IRD; and ? 2 i s the group- velocity dispersion of the nonlinear element, e.g., fiber and the working medium WM.
  • Spectral broadening is typically dominated by modulation instability when N » 20 whereas spectral broadening is typically dominated by soliton self-compression when N « 20.
  • Some known broadband radiation sources use arrangements which produce spectral broadening of pulsed pump radiation but wherein parameters of the pulsed pump radiation, the optical fiber and the working medium are configured to allow modulation instability to produce the spectral broadening.
  • modulation instability is used to produce the spectral broadening.
  • modulation instability is known to produce broadband radiation having a relatively flat intensity-wavelength distribution, provided a sufficient number of pulses are averaged.
  • Such a broadband radiation source may be referred to as a white light radiation source (due to the relatively flat spectral intensity distribution).
  • modulation instability can be achieved using relatively economical laser sources as the pump radiation source.
  • a present technology for supercontinuum (SC) generation relies on the interaction of a drive laser radiation with a nonlinear element in order to increase the spectral bandwidth.
  • the peak intensity of the laser radiation is sufficiently high such that it undergoes a multitude of optical nonlinear effects thereby broadening its spectrum.
  • the wavelength of the laser pulse is chosen so that it falls either under the normal or anomalous dispersion regime of the nonlinear element.
  • the broadening is governed by self-phase modulation (SPM), while in the latter case the spectral broadening is governed by soliton dynamics.
  • the nonlinear element may be designed to provide purely normal dispersion, such as All-Normal-Dispersion (ANDi) fibers. In this case, broadening is governed by SPM and optical wave breaking.
  • PSD power spectral density
  • a typical arrangement may comprise pumping the nonlinear element with a pump laser fundamental and its (e.g., second) harmonic.
  • a pump laser fundamental and its (e.g., second) harmonic e.g., second
  • the fundamental and its harmonic(s) are in different dispersion regimes of the nonlinear medium. This results in the laser radiation in the normal dispersion to broaden quickly in time, thus losing its peak intensity which in turn results in less spectral broadening.
  • the nonlinear medium is pumped with a laser pulse is to achieve a sufficiently high peak intensity, so as to initiate a nonlinear optical process such as SSC or MI.
  • a nonlinear optical process such as SSC or MI.
  • recent advances in supercontinuum generation and nonlinear optical media enable generation of supercontinua with high peak intensities, which may also be sufficient for initiating a nonlinear optical process in subsequent nonlinear elements/media.
  • high-energy, high peak intensity supercontinua may be generated in a gas-filled hollow-core fiber (e.g., a HC-PCF) via MI or SSC processes.
  • a supercontinuum comprises radiation (e.g., originating from a laser) which has subsequently undergone at least one spectral broadening step via (or within) a nonlinear medium.
  • the level of intensity required may be relative to the optical nonlinearity and optical damage of the subsequent nonlinear element stages.
  • a proposed radiation source comprises two or more successive supercontinuum generation stages, each said supercontinuum generation stage comprising a respective nonlinear generation element, and wherein a damage tolerance of a first nonlinear generation element comprised within a first supercontinuum generation stage is greater than a damage tolerance of at least a second nonlinear generation element comprised within a second supercontinuum generation stage, and wherein said second supercontinuum generation stage immediately succeeds said first supercontinuum generation stage.
  • the first supercontinuum generation stage may be arranged to generate a first supercontinuum and provide said first supercontinuum to said second supercontinuum generation stage to generate a second supercontinuum.
  • the second supercontinuum generation stage may be the final supercontinuum generation stage, and the second supercontinuum used as the output broadband radiation.
  • the second supercontinuum generation stage is not the final supercontinuum generation stage, the second supercontinuum may be provided to the immediately successive supercontinuum generation stage. As such each successive supercontinuum generation stage before a final supercontinuum generation stage may generate a supercontinnum for the next supercontinuum generation stage.
  • the radiation source may comprise a radiation source arranged to provide laser radiation for said first supercontinuum generation stage, so as to generate said first supercontinuum.
  • each successive supercontinuum generation stage may have a lower damage tolerance than its preceding supercontinuum generation stage (i.e., the stages may be arranged in order of their damage tolerance: from higher tolerance to lower tolerance).
  • the second supercontinuum generation stage may have a lower damage tolerance than the first supercontinuum generation stage, while successive supercontinuum generation stages after the second stage may have any damage tolerance; e.g., the damage tolerance may remain constant or become larger for successive supercontinuum generation stages after the second stage.
  • Damage tolerance may be assessed according to a damage threshold for each respective nonlinear generation element comprised within each supercontinuum generation stage.
  • a radiation source wherein an optical nonlinearity of a first nonlinear generation element comprised within the first supercontinuum generation stage is lower than an optical nonlinearity of at least a second nonlinear generation element comprised within the second supercontinuum generation stage.
  • the first nonlinear generation element may comprise a hollow-core fiber (e.g., a HC-PCF).
  • the second nonlinear generation element may comprise a solid nonlinear generation medium.
  • the solid nonlinear generation medium may comprise a solid-core fiber (e.g., a SC-PCF), or a (synthetic) crystal (e.g., a BBO crystal or PPLN crystal).
  • a nonlinear generation element may comprise a nonlinear generation medium (e.g., where the nonlinear generation medium is a solid element), or a nonlinear generation element may comprise an element for confining a nonlinear generation medium (e.g., where the nonlinear generation medium is a gas, e.g., the nonlinear generation element may be a hollow-core fiber). It can be appreciated that, in either case, any nonlinear generation medium may also be a liquid.
  • FIG. 10 schematically illustrates the concept according to a general embodiment.
  • a drive laser DL generates drive radiation DR which is received by a first supercontinuum generation stage SCGS 1.
  • the first supercontinuum generation stage comprises a first nonlinear generation element having a first damage threshold.
  • the first supercontinuum generation stage generates a first supercontinuum SCi which is received by the next successive supercontinuum generation stage or second supercontinuum generation stage, the second supercontinuum generation stage comprising a second nonlinear generation element having a second damage threshold smaller than the first damage threshold.
  • there may be any number of intervening supercontinuum generation stages i.e., n>2) between first supercontinuum generation stage SCG1 and final supercontinuum generation stage SCGSn, each one receiving a supercontinuum from an immediately preceding supercontinuum generation stage and generating a supercontinuum for an immediately succeeding supercontinuum generation stage, the penultimate stage generating a supercontinuum SC n -i for pumping the final supercontinuum generation stage.
  • the damage thresholds of the nonlinear generation elements of each supercontinuum generation stage also decrease (or at least not increase) for each successive supercontinuum generation stage after the second supercontinuum generation stage, i.e., from input to output of the radiation source.
  • each supercontinuum generated (at least before the final stage) is intense enough, with respect to the optical nonlinearity of the relevant stage, to drive further nonlinear optical phenomena, e.g., frequency mixing and spectral broadening, in the next supercontinuum generation stage thus producing a new enhanced supercontinuum radiation at the output of the each successive supercontinuum generation stage.
  • Enhanced in this context may describe having an improved PSD flatness (e.g., a flatter PSD) and increased spectral coverage, particularly in a supercontinuum region of interest, and/or improved PSD values.
  • FIG. 11 shows an arrangement where (at least) the first supercontinuum generation stage comprises a gas-filled hollow-core fiber HCF (e.g., a HC-PCF).
  • HCF gas-filled hollow-core fiber
  • a hollow-core fiber HCF may generate a supercontinuum from drive radiation DR (e.g., emitted by drive laser DE) via MI and/or SSC.
  • drive radiation DR e.g., emitted by drive laser DE
  • MI the generated first supercontinuum radiation SCi has a fine temporal structure consisting of sharp (e.g., ⁇ 10 femtosecond) temporal structures.
  • the supercontinuum radiation SCi may be received by a next supercontinuum generation stage comprising a solid-core fiber SCF (or other solid nonlinear medium) such as a SC-PCF.
  • the solid-core fiber SCF may generate output supercontinuum SCout (as depicted) or a further supercontinuum for a further supercontinuum generation stage (as before there may be any number of such stages). Since the damage threshold of a gas-filled hollow-core fiber is higher than a solid-core PCF, the peak intensities of the spikes of supercontinuum SCi are sufficiently high to drive a nonlinear broadening in a second nonlinear element, such as a solid-core PCF.
  • the first supercontinuum radiation SCi may be coupled via free space optics into the solid-core fiber SCF.
  • the hollow-core fiber HCF may be spliced to the solid-core fiber SCF, making free-space optics redundant.
  • the MI- or SSC-based supercontinuum may drive further nonlinear effects in another gas.
  • the following stage benefits from the fine temporal structure of MI- based supercontinuum, or short pulses of the SSC supercontinuum in order to drive further nonlinear processes.
  • the dispersive wave is red-shifted, filling the PSD dip.
  • the remaining part of the SPM- broadened pump goes through four-wave mixing (FWM) and converts its energy to other wavelengths, both on the short- and long-wavelengths sides, resulting in further smoothening of the spectrum.
  • Figures 12 and 13 each illustrate an arrangement where the first supercontinuum SCi is generated via filamentation in a transparent solid or filamentation element FE.
  • Supercontinuum generation in solids via filamentation is a good way for making compact, alignment-free, robust solid- state broadband light sources at low cost. As has been described, it is desired to improve the spectral flatness and? increase the spectral coverage of the output supercontinuum SCout.
  • the damage threshold for proposed bulk media e.g., first nonlinear medium
  • the filamentation element FE e.g., sapphire, fused silica, or laser crystals such as KGW or YAG
  • these media can be used for (at least) the first supercontinuum generation stage, followed by one or more additional supercontinuum generation stages comprising respective nonlinear elements with lower damage thresholds.
  • these nonlinear elements may comprise one or more of a solid-core fiber SCF (as depicted in Figure 12) or a frequency mixing stage FMS (as depicted in Figure 13) in order to increase the bandwidth of the supercontinuum and smoothen its PSD.
  • a solid-core fiber SCF as depicted in Figure 12
  • FMS frequency mixing stage
  • the frequency mixing stage FMS may comprise a synthetic crystal such as periodically poled lithium niobate (PPLN).
  • PPLN periodically poled lithium niobate
  • the frequency mixing stage may support broadband phase-matching. For example, this could be via quasi-phase-matched, broadband second harmonic generation.
  • Other techniques for broadband phase-matching such as an angularly dispersed supercontinuum can also be used.
  • Figure 14 illustrates another embodiment where the supercontinuum generation occurs via stage-wise broadening in a series of two or more (e.g., solid-core) fibers having a core diameter which decreases for each successive stage.
  • three such stages are provided comprising a first solid-core fiber SCF1 having a first diameter, a second solid-core fiber SCF2 having a second diameter smaller than the first diameter and a third solid-core fiber SCF3 having a third diameter smaller than the second diameter.
  • the damage threshold reduces for each successive nonlinear element or solid-core fiber SCF1, SCF2, SCF3.
  • the materials of which the solid-core fibers are comprised may differ for one or more of the fibers, therefore also taking advantage of various dispersion profiles provided by different core matrerials.
  • the coupling between the different fibers may be all via free-space optics, may be all spliced or a combination of the two (i.e., a first pair SCF1, SCF2 free-space coupled and a second pair SCF2, SCF3 spliced or vice versa).
  • adaptors may be provided between the fibers for mode-filling the diameters of each successive fiber.
  • Figure 15 shows a further embodiment, wherein at least one supercontinuum generation stage after the first supercontinuum stage SCGS 1 comprises a crystal such as a barium borate (BBO) crystal BBO as the nonlinear medium.
  • BBO barium borate
  • Such a BBO crystal enhances the output broadband radiation characteristics in the visible frequency range.
  • the first supercontinuum stage SCGS1 may comprise a hollow-core fiber (e.g., a HC- PCF), for example.
  • Figures 11 to 15 show a non-exhaustive number of different arrangements possible within the context of the disclosure herein and the general arrangement of Figure 10. Other arrangements are possible within the scope of the disclosure.
  • a feedback loop may be configured to control (e.g., adjust) the input radiation (e.g., in terms of power) based upon a performance metric, e.g., a measured PSD, of each supercontinuum stage; for example this may be done to prevent optical damage.
  • a performance metric e.g., a measured PSD
  • FIG 16 is a block diagram that illustrates a computer system 1600 that may assist in implementing the methods and flows disclosed herein.
  • Computer system 1600 includes a bus 1602 or other communication mechanism for communicating information, and a processor 1604 (or multiple processors 1604 and 1605) coupled with bus 1602 for processing information.
  • Computer system 1600 also includes a main memory 1606, such as a random access memory (RAM) or other dynamic storage device, coupled to bus 1602 for storing information and instructions to be executed by processor 1604.
  • Main memory 1606 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 1604.
  • Computer system 1600 further includes a read only memory (ROM) 1608 or other static storage device coupled to bus 1602 for storing static information and instructions for processor 1604.
  • ROM read only memory
  • a storage device 1610 such as a magnetic disk or optical disk, is provided and coupled to bus 1602 for storing information and instructions.
  • Computer system 1600 may be coupled via bus 1602 to a display 1612, such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user.
  • a display 1612 such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user.
  • An input device 1614 is coupled to bus 1602 for communicating information and command selections to processor 1604.
  • cursor control 1616 such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor 1604 and for controlling cursor movement on display 1612.
  • This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane.
  • a touch panel (screen) display may also be used as an input device.
  • One or more of the methods as described herein may be performed by computer system 1600 in response to processor 1604 executing one or more sequences of one or more instructions contained in main memory 1606. Such instructions may be read into main memory 1606 from another computer-readable medium, such as storage device 1610. Execution of the sequences of instructions contained in main memory 1606 causes processor 1604 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory 1606. In an alternative embodiment, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.
  • Nonvolatile media include, for example, optical or magnetic disks, such as storage device 1610.
  • Volatile media include dynamic memory, such as main memory 1606.
  • Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus 1602. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications.
  • RF radio frequency
  • IR infrared
  • Computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD- ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.
  • Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor 1604 for execution.
  • the instructions may initially be borne on a magnetic disk of a remote computer.
  • the remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem.
  • a modem local to computer system 1600 can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal.
  • An infrared detector coupled to bus 1602 can receive the data carried in the infrared signal and place the data on bus 1602.
  • Bus 1602 carries the data to main memory 1606, from which processor 1604 retrieves and executes the instructions.
  • the instructions received by main memory 1606 may optionally be stored on storage device 1610 either before or after execution by processor 1604.
  • Computer system 1600 also preferably includes a communication interface 1618 coupled to bus 1602.
  • Communication interface 1618 provides a two-way data communication coupling to a network link 1620 that is connected to a local network 1622.
  • communication interface 1618 may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line.
  • ISDN integrated services digital network
  • communication interface 1618 may be a local area network (LAN) card to provide a data communication connection to a compatible LAN.
  • LAN local area network
  • Wireless links may also be implemented.
  • communication interface 1618 sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.
  • Network link 1620 typically provides data communication through one or more networks to other data devices.
  • network link 1620 may provide a connection through local network 1622 to a host computer 1624 or to data equipment operated by an Internet Service Provider (ISP) 1626.
  • ISP 1626 provides data communication services through the worldwide packet data communication network, now commonly referred to as the “Internet” 1628.
  • Internet 1628 uses electrical, electromagnetic or optical signals that carry digital data streams.
  • the signals through the various networks and the signals on network link 1620 and through communication interface 1618, which carry the digital data to and from computer system 1600, are exemplary forms of carrier waves transporting the information.
  • Computer system 1600 may send messages and receive data, including program code, through the network(s), network link 1620, and communication interface 1618.
  • a server 1630 might transmit a requested code for an application program through Internet 1628, ISP 1626, local network 1622 and communication interface 1618.
  • One such downloaded application may provide for one or more of the techniques described herein, for example.
  • the received code may be executed by processor 1604 as it is received, and/or stored in storage device 1610, or other non-volatile storage for later execution. In this manner, computer system 1600 may obtain application code in the form of a carrier wave.
  • a broadband radiation source for generating output broadband radiation comprising a plurality of supercontinuum generation stages arranged in series, each said supercontinuum generation stage comprising a respective nonlinear generation element; wherein said plurality of supercontinuum generation stages comprises at least a first supercontinuum generation stage and a second supercontinuum generation stage, said second supercontinuum generation stage succeeding said first supercontinuum generation stage in said series; and wherein a damage tolerance of a first nonlinear generation element comprised within the first supercontinuum generation stage is greater than a damage tolerance of at least a second nonlinear generation element comprised within the second supercontinuum generation stage.
  • a broadband radiation source according to clause 1, wherein said first supercontinuum generation stage is arranged to generate a first supercontinuum and provide said first supercontinuum to said second supercontinuum generation stage, so as to generate a second supercontinuum.
  • a broadband radiation source according to clause 2, further comprising a laser radiation source arranged to provide laser radiation for said first supercontinuum generation stage, so as to generate said first supercontinuum.
  • a broadband radiation source according to any preceding clause, wherein said second supercontinuum generation stage is a final supercontinuum generation stage, such that said output broadband radiation comprises said second supercontinuum.
  • a broadband radiation source comprising one or more further supercontinuum generation stages, wherein said second supercontinuum is provided to the next sequential supercontinuum generation stage of said one or more further supercontinuum generation stages, such that each successive supercontinuum generation stage before a final supercontinuum generation stage generates a supercontinuum for the next supercontinuum generation stage in said series, said output broadband radiation comprising a supercontinuum from said final supercontinuum generation stage.
  • each successive supercontinuum generation stage after said second supercontinuum generation stage comprises a respective nonlinear generation element having a lower or equal damage tolerance than the nonlinear generation element of the immediately preceding supercontinuum generation stage.
  • each successive supercontinuum generation stage comprises a respective nonlinear generation element having a lower damage tolerance than the nonlinear generation element of the immediately preceding supercontinuum generation stage.
  • a broadband radiation source comprising free-space coupling between at least said first supercontinuum generation stage and said second supercontinuum generation stage.
  • a broadband radiation source comprising free-space coupling between all of said plurality of supercontinuum generation stages.
  • a broadband radiation source according to any of clauses 1 to 8, comprising fiber-based coupling between all of said plurality of supercontinuum generation stages.
  • a broadband radiation source according to any of clauses 1 to 8, wherein said first nonlinear element and second nonlinear element are spliced together.
  • a broadband radiation source according to clause 11, wherein all of said respective nonlinear generation elements are spliced together.
  • a broadband radiation source according to any preceding clause, wherein at least said first nonlinear generation element comprises a hollow-core fiber.
  • a broadband radiation source according to any of clauses 1 to 12, wherein at least said first nonlinear generation element comprises a solid-core fiber.
  • a broadband radiation source according to any of clauses 1 to 12, wherein at least said first nonlinear generation element comprises a filamentation element operable to generate a supercontinuum via filamentation.
  • said solid nonlinear generation element comprises a solid-core fiber.
  • a broadband radiation source according to clause 17, wherein said solid nonlinear generation element comprises a crystal.
  • a broadband radiation source according to clause 19, wherein said solid nonlinear generation element comprises a BBO crystal.
  • a broadband radiation source according to any of clauses 1 to 17, wherein at least said second supercontinuum generation stage comprises a frequency mixing stage.
  • a broadband radiation source according to any of clauses 1 to 12, wherein said plurality of supercontinuum generation stages each comprise a respective optical fiber, each optical fiber having a diameter which decreases for each successive supercontinuum generation stage.
  • a broadband radiation source according to any preceding clause, wherein said output broadband radiation comprises at least wavelengths between 100 nm and 1200 nm.
  • a broadband radiation source according to any preceding clause, wherein said output broadband radiation comprises at least wavelengths in a range between 400 nm and 900 nm.
  • a broadband radiation source for generating output broadband radiation comprising a plurality of supercontinuum generation stages arranged in series, each said supercontinuum generation stage comprising a respective nonlinear generation element; wherein said plurality of supercontinuum generation stages comprises at least a first supercontinuum generation stage and a second supercontinuum generation stage, said second supercontinuum generation stage succeeding said first supercontinuum generation stage in said series; and wherein an optical nonlinearity of a first nonlinear generation element comprised within the first supercontinuum generation stage is lower than an optical nonlinearity of at least a second nonlinear generation element comprised within the second supercontinuum generation stage.
  • a metrology device comprising a radiation source according to any preceding clause.
  • a metrology device comprising a scatterometer metrology apparatus, a level sensor or an alignment sensor.
  • Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

Est divulguée une source de rayonnement à large bande pour générer un rayonnement à large bande de sortie, comprenant une pluralité d'étages de génération de supercontinuum agencés en série, chaque étage de génération de supercontinuum comprenant un élément de génération non linéaire respectif. La pluralité d'étages de génération de supercontinuum comprend au moins un premier étage de génération de supercontinuum et un second étage de génération de supercontinuum, le second étage de génération de supercontinuum succédant au premier étage de génération de supercontinuum dans la série. Une tolérance aux dommages d'un premier élément de génération non linéaire compris dans le premier étage de génération de supercontinuum est supérieure à une tolérance aux dommages d'au moins un second élément de génération non linéaire compris dans le second étage de génération de supercontinuum.
EP23798967.8A 2022-12-07 2023-11-06 Source de rayonnement supercontinuum Pending EP4630880A1 (fr)

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PCT/EP2023/080777 WO2024120709A1 (fr) 2022-12-07 2023-11-06 Source de rayonnement supercontinuum

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JP2025541764A (ja) 2025-12-23
CN120303615A (zh) 2025-07-11

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