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WO2025233062A1 - Procédé de conception d'un composant optique pour coupler un rayonnement à large bande dans une fibre optique - Google Patents

Procédé de conception d'un composant optique pour coupler un rayonnement à large bande dans une fibre optique

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Publication number
WO2025233062A1
WO2025233062A1 PCT/EP2025/058958 EP2025058958W WO2025233062A1 WO 2025233062 A1 WO2025233062 A1 WO 2025233062A1 EP 2025058958 W EP2025058958 W EP 2025058958W WO 2025233062 A1 WO2025233062 A1 WO 2025233062A1
Authority
WO
WIPO (PCT)
Prior art keywords
wavelength
optical component
optical
radiation
wavelength range
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
PCT/EP2025/058958
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English (en)
Inventor
David Alejandro VILLEGAS LOPEZ
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ASML Netherlands BV
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ASML Netherlands BV
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Filing date
Publication date
Application filed by ASML Netherlands BV filed Critical ASML Netherlands BV
Publication of WO2025233062A1 publication Critical patent/WO2025233062A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/32—Optical coupling means having lens focusing means positioned between opposed fibre ends
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/0004—Microscopes specially adapted for specific applications
    • G02B21/0016—Technical microscopes, e.g. for inspection or measuring in industrial production processes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/06—Means for illuminating specimens
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/16—Microscopes adapted for ultraviolet illumination ; Fluorescence microscopes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
    • G02B27/005—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration for correction of secondary colour or higher-order chromatic aberrations
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/1006—Beam splitting or combining systems for splitting or combining different wavelengths
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/12—Beam splitting or combining systems operating by refraction only
    • G02B27/123—The splitting element being a lens or a system of lenses, including arrays and surfaces with refractive power
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/0087—Simple or compound lenses with index gradient
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/262—Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements

Definitions

  • the present invention relates to a method of designing an optical component for coupling a broadband optical beam into an optical fiber, a method of manufacturing such an optical component and an optical component designed by the proposed design method, in particular such an optical component 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
  • 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 better control (e.g., multiple wavelength or wavelength band selection, wavelength-based intensity control) of broadband radiation.
  • a method of designing an optical component for coupling a broadband radiation into a first optical fiber comprising obtaining a radiuswavelength relationship between a collimated beam radius and a wavelength of the broadband radiation in a wavelength range of the broadband radiation; determining a plurality of light-transmitting zones in a transversal plane of the optical component based on the radius-wavelength relationship, wherein the transversal plane is perpendicular to an optical axis of the optical component, and wherein each of the plurality of light-transmitting zones is configured to transmit a different respective wavelength range either overlapping with or falling within the wavelength range of the broadband radiation; and optimizing an efficiency of coupling of the broadband radiation into the optical fiber for each of the different wavelength ranges by varying one or more parameters associated with the optical component.
  • an optical component for coupling a broadband radiation into an optical fiber comprising: a plurality of light-transmitting zones in a transversal plane perpendicular to an optical axis of the optical component, wherein each of the plurality of light-transmitting zones is configured to transmit a different respective wavelength range either overlapping with or falling within a wavelength range of the broadband radiation; and wherein one or more parameters of the optical component are configured to provide an optimal efficiency of coupling of the broadband radiation into the optical fiber for each of the different wavelength ranges.
  • a method of manufacturing an optical component comprising: designing an optical component by performing the method of the first aspect; and manufacturing the optical component in accordance with the design.
  • an optical arrangement comprising: an optical fiber and an optical component according to the second aspect for coupling a broadband radiation into the optical fiber.
  • aspects of the invention comprise metrology device comprising an optical arrangement according the fourth aspect.
  • 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 7A depicts schematically transmission of a broadband optical beam through a singlet lens resulting in a large amount of lateral chromatic aberration
  • Figure 7B depicts schematically transmission of a broadband optical beam through a singlet lens resulting in a large amount of axial chromatic aberration
  • Figure 7C depicts schematically transmission of a broadband optical beam through an achromatic lens resulting in a significantly lower amount of chromatic aberration
  • Figure 8A depicts schematically an example scatterometry-based metrology system
  • Figure 8B depicts schematically an example dark-field digital holographic microscope (df- DHM) for use in the metrology system of Figure 8A;
  • df- DHM dark-field digital holographic microscope
  • Figure 9 shows an example plot of mode field diameter (MFD) and numerical aperture (NA) of an optical fiber (e.g., a large mode area fiber or photonic crystal fiber) as a function of wavelength;
  • MFD mode field diameter
  • NA numerical aperture
  • Figures 10 shows a workflow of the proposed design method in accordance with an embodiment
  • Figures 11A-11C schematically depict a first example implementation of the proposed design method
  • Figures 12A-12C schematically depict a second example implementation of the proposed design method
  • Figure 13 shows an example plot of three radial refractive index profiles (or radial refractive index gradients) respectively for three different light-emitting zones of a singlet gradient refractive index (GRIN) lens (e.g., as shown in Figures 12A-12C);
  • GRIN gradient refractive index
  • Figure 14 shows an example plot of three axial refractive index profiles (or axial refractive index gradients) respectively for three different light-emitting zones of the same singlet GRIN lens; and
  • Figure 15 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 US6952253B2, 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”).
  • 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/O I , 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).
  • metrology tools MT In lithographic processes, it is desirable to make frequently measurements of the structures created, e.g., for process control and verification. 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 US2010/0328655A1, US2011/102753A1, US2012/0044470A1, US2011/0249244A1, US2011/0026032 Al or EP1628164A2, which are 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.
  • Various embodiments of existing ellipsometric scatterometers are described in US patents US7791724B2, US7701577B2, US8115926B2, US8553227B2, US8681312B2,
  • 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 EP1628164A2, such that any asymmetry is clearly distinguishable. This provides a straightforward way to measure misalignment in gratings.
  • Focus and dose may be determined simultaneously by scatterometry (or alternatively by scanning electron microscopy) as described in US patent application US2011/0249244A1, which is 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 US2016/0161863A1 and published US patent application US2016/0370717A1, which are 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 normal-incidence 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. 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.
  • “height” in this context refers to a dimension broadly out of the plane to the substrate (also referred to as Z-axis).
  • 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.
  • the detector DET may be placed at the position where the detection grating DGR is located.
  • 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 US6961116B2.
  • Various enhancements and modifications of the position sensor have been developed, for example as disclosed in US2015/261097A1. 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 US6961116B2, 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 US6961116B2 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).
  • 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.
  • 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.
  • a broadband optical system is often used to transfer a broadband output radiation from a broadband radiation source to an application plane (e.g., a wafer plane).
  • such an optical system may be further configured to control or adjust one or more characteristics of the broadband output radiation so as to obtain, for example, a desired transverse beam profile, a desired temporal profile, and/or a desired spectral profile.
  • the broadband optical system may comprise various different reflective (e.g., optical mirrors) and/or transmissive (e.g., optical lenses) optical elements which are typically optimized for reflecting or transmitting the broadband output radiation.
  • each optical element may comprise one or more optical coatings that are either highly transmissive (in the case of a transmissive optical element) or highly reflective (in the case of a reflective optical element) at least in the wavelength range of the broadband output radiation.
  • optical elements, in particular transmissive optical elements may become incapable of maintaining their designed performance when the spectral coverage of the broadband output radiation becomes sufficiently wide.
  • material dispersion means the refractive index of the transmissive optical element varies with the wavelength of light.
  • chromatic aberration which occurs when an optical lens is used to focus a broadband optical beam.
  • chromatic aberration There are two types of chromatic aberration: lateral (or transverse) chromatic aberration and axial chromatic aberration, which are respectively illustrated in Figures 7A and 7B.
  • lateral aberration occurs when different wavelengths i, X 2 , (e.g., blue, green, and red wavelengths) are focused at different transverse positions in the focal plane FP of an optical lens LEN.
  • Wavelength z. 2 may correspond to the designed (or nominal) wavelength at which the lens LEN is designed and manufactured.
  • wavelength z. 2 is focused at an on-axis (i.e.
  • axial aberration occurs when different wavelengths Xi’, X 2 ’, X3’ are focused at different axial positions LI’, L2’, L3’ along the optical axis OA’ of an optical lens LEN’.
  • a focal length is defined as the distance between the lens and the focus position.
  • wavelength X 2 ’ may correspond to the designed (or nominal) wavelength at which the lens LEN’ is designed and manufactured.
  • the focus position L2’ of wavelength 2’ is sufficiently close the designed focus position, whereas the focus positions of other wavelengths , X 3 ’ are more deviated from the designed focus position due to the impact of material dispersion of the lens LEN’ .
  • optical lenses LEN, LEN’ shown in Figures 7A and 7B are both singlet lenses made of one type of optical glass.
  • apochromatic lenses have been developed and are now widely used in optical systems.
  • An apochromatic lens is a compound lens in which two or more materials with different refractive indices and different dispersions are assembled together.
  • Figure 7C schematically illustrates focusing of a broadband optical beam by an example apochromatic lens ALEN.
  • the example apochromatic lens ALEN is formed by assembling (e.g., optical bonding) two lens elements L-A, L-B together.
  • Such a two-element apochromatic lens ALEN is also known as apochromatic doublet.
  • the two lens elements L-A, L-B may be made of for example crown glass and flint glass, respectively.
  • the combination of two lens elements L-A, L-B is capable of reducing or minimizing both lateral and axial chromatic aberration and consequently the focus positions LI”, L2”, L3” of the respective wavelengths Xi”, X 2 ”, 3” are much closer to each other as well as to the designed (or nominal) position.
  • a three-element apochromatic lens may be preferred.
  • Such an apochromatic lens is also known as apochromatic triplet (see below).
  • FIG 8A schematically an example scatterometry-based metrology system.
  • the metrology system comprises a broadband radiation source BRS, a broadband optical system (BOS) and a dark field holographic digital microscope (df-DHM).
  • BRS broadband radiation source
  • BOS broadband optical system
  • df-DHM dark field holographic digital microscope
  • the broadband radiation source BRS is configured to emit broadband output radiation ORD.
  • the broadband radiation source BRS may be a fiber-based supercontinuum light source.
  • the broadband output radiation ORD may be produced in a large mode area (LMA) fiber or a photonic crystal fiber (PCF).
  • the broadband output radiation ORD may span a wavelength range e.g., from 400 nm to 1600 nm.
  • the broadband optical system BOS is configured to split the broadband output radiation ORD into multiple (e.g., two) pairs of beamlets IL1 & RF1 and IL2 & RF2 before transporting them to the df-DHM via optical fibers (e.g., polarization maintaining fibers (PMF)).
  • the two beamlets IL1 & RF1, IL2 & RF2 of each beamlet pair are at least partially coherent to each other and each beamlet pair corresponds to a different sub-range of wavelengths of the broadband output radiation ORD.
  • a first beamlet pair may correspond to a first wavelength range spanning from 400 nm to 600 nm
  • a the second beamlet pair may correspond to a second wavelength range spanning from 600 nm to 800 nm, and so on.
  • the broadband optical system BOS comprises a beam splitting unit BSU for splitting the broadband output radiation ORD into multiple beamlets, multiple optical fibers PMF1, PMF2 for transporting the respective beamlets to the df-DHM, and multiple optical components (or coupling optics) CL for coupling the beamlets IL1, RF1, IL2, RF2 into respective optical fibers PMF1, PMF2.
  • the beam splitting unit BSU may comprise an acousto-optic tunable filter AOTF (not shown) configured to split the broadband output radiation into e.g., two beamlets.
  • the beam splitting unit BSU may comprise additional beam splitters (e.g., beam splitting cubes) (not shown) configured to split each of the beamlets from the AOTF into another two beamlets, thus providing beamlet pairs, e.g., IL1 & RF1, IL2 & RF2.
  • the beam splitting unit BSU may further comprise optical delay lines (e.g., one for each beamlet pair) to control the coherence between the two beamlets of each beamlet pair.
  • FIG 8B schematically depicts an example dark field digital holographic microscope (df- DHM) for use in the metrology system shown in Figure 8A.
  • a metrology target 1060 comprising a structure on a substrate 1050 is illuminated by two illumination beams of radiation, i.e., a first illumination beam of radiation 1010 and a second illumination beam of radiation 1020.
  • Such two illumination beams 1010, 1020 may simultaneously illuminate the metrology target 1060.
  • the first illumination beam 1010 may be incident on the metrology target 1060 at a first angle of incidence in a first direction with respect to the optical axis OA.
  • the second illumination beam 1020 may be incident on the metrology target 1060 at a second angle of incidence in a second direction with respect to the optical axis OA.
  • the first angle of incidence of the first illumination beam 1010 and the second angle of incidence of the second illumination beam 1020 may be substantially the same.
  • the angle of incidence of each illumination beam may be, for example in the range of 70 degrees to 90 degrees, in the range of 50 degrees to 90 degrees, in the range of 30 degrees to 90 degrees, in the range of 10 degrees to 90 degrees.
  • the illumination of the metrology target 1060 may result in radiation being scattered from the target.
  • the first illumination beam 1010 may be incident on the metrology target 1060 at a first azimuthal angle, corresponding to the first direction.
  • the second illumination beam 1020 may be incident on the metrology target 1060 at a second azimuthal angle, corresponding to the second direction.
  • the first azimuthal angle of the first illumination beam 1010 and the second azimuthal angle of the second illumination beam 1020 may be different; e.g., opposing angles 180 degrees apart.
  • the scattered radiation may comprise reflected radiation, diffracted radiation or transmitted radiation.
  • the metrology target may be a diffraction-based overlay target; and each illumination beam may correspond to a scattered beam comprising at least one non-zeroth diffraction order.
  • Each scattered beam carries information of the illuminated metrology target.
  • the first illumination beam 1010 may correspond to the first scattered beam 1011 comprising the positive first diffraction order +l st DF;
  • the second illumination beam 1020 may correspond to the second scattered beam 1021 comprising the negative first diffraction order -1 st DF.
  • the zeroth diffraction order and other undesired diffraction orders may either be blocked by a beam blocking element (not shown) or configured to completely fall outside the NA of the objective lens 1070.
  • the df-DHM may be operated in a dark field mode.
  • one or more optical elements e.g., a lens combination, may be used to achieve same optical effect of the objective lens 1070.
  • Both scattered beams 1011, 1021 may be collected by objective lens 1070 and subsequently re-focused onto an image sensor 1080.
  • Objective lens 1070 may comprise multiple lenses, and/or df- DHM may comprise a lens system having two or more lenses, e.g., an objective lens and an imaging lens, thereby defining a pupil plane of the objective lens between the two lenses and an image plane at the focus of the imaging lens.
  • a portion 1012 of the first scattered beam 1011 and a portion 1022 of the second scattered beam 1021 are simultaneously incident at a common position of the image sensor 1080.
  • two reference beams of radiation i.e.
  • a first reference beam 1030 and a second reference beam 1040 are incident on the same position of the image sensor 1080.
  • Such four beams may be grouped into two pairs of scattered radiation and reference radiation.
  • the first scattered-reference beam pair may comprise the portion 1012 of the first scattered beam 1011 and the first reference beam 1040.
  • the second scattered-reference beam pair may comprise the portion 1022 of the second scattered beam 1021 and the second reference beam 1030.
  • These two scattered-reference beam pairs may subsequently form two interference patterns (holographic images) which at least partially overlap in spatial domain.
  • the first pair of beamlets IL1 & RF1 emitted from the first optical fibers PMF1 may be used to provide the first illumination beam 1010 and the first reference beam 1040, respectively; and the second pair of beamlets IL2 & RF2 emitted from the second optical fibers PMF2 may be used to provide the second illumination beam 1020 and the second reference beam 1030, respectively.
  • the metrology target 1060 can be simultaneously illuminated by two illumination beams 1010, 1020 of different wavelengths. Such a configuration allows for parallel sensing which results in a higher wafer throughput.
  • each optical component CE may either comprise a microscope objective or an off-axis parabolic mirror.
  • microscope objectives often contain a large number of lens elements which can cause significant transmission loss and lead to a lower throughput.
  • aberration corrections are applied over the complete field of view and aperture of a microscope objective.
  • Most of existing microscope objectives are corrected for aberration in a visible wavelength range, e.g., between 400 and 700 nm with only a few being corrected in an extended wavelength range, e.g., between 400 and 1000 nm.
  • existing microscope objectives are typically designed for incoherent or partially coherent illumination light and often comprise cemented lens elements configured for chromatic corrections (e.g., doublets).
  • coherent illumination light e.g., the broadband output radiation ORD in the metrology system shown in Figure 8A
  • the small spatial separations between lens elements of a microscope objective can act as optical resonators and thus cause ghost effect and transmission loss.
  • FIG. 9 is a plot comparing the variations of the MFD and the NA of an example PCF as a function of wavelength in the wavelength range between 600 nm and 1600 nm. As shown in Figure 9, the MFD of this particular fiber is about 8.2 pm at 600 nm and about 9.32 pm at 1600 nm. This corresponds to a variation of 13.6%.
  • the NA of the fiber is about 0.08 at 600 nm and about 0.15 at 1600. This corresponds to a variation of 87.5%, thus significantly higher than the variation of MFD in the same wavelength range. Since the NA of the fiber determines the divergence of the broadband output radiation ORD at any given wavelength, a linearly varying NA of the fiber leads to a linearly varying divergence of the broadband output radiation ORD.
  • the broadband output radiation ORD is collimated, e.g., by a collimation lens, the linear dependance of the divergence of the broadband output radiation ORD with the wavelength will translate into a linear dependence of the beam size (e.g., beam radius or beam diameter) of the collimated broadband output radiation ORD with the wavelength.
  • the beam size e.g., beam radius or beam diameter
  • Such a relationship between the collimated beam size and the wavelength can be utilized to better design an optical component (e.g., the optical components CL shown in Figure 8A) such that aberration corrections are no longer applied over the
  • the present disclosure provides a method of designing an optical component (e.g., the optical components CL shown in Figure 8 A) for coupling a broadband radiation (e.g., the broadband output radiation ORD emitted from the broadband radiation source BRS) into an optical fiber.
  • the optical component may be for example a triplet comprising three lens elements (e.g., the triplet shown in Figures 11A-11C) or a singlet (e.g., the singlet gradient- index “GRIN” lens shown in Figures 12A-12C). It will be appreciated that the proposed design method may also be applicable to other different optical components.
  • the broadband radiation may span for example from 400 nm to 1600 nm, from 400 nm to 1200 nm, or from 400 nm to 1000 nm.
  • the optical fiber for receiving the broadband radiation may be for example a PMF (e.g., PMF1 or PMF2 shown in Figure 8A) configured to transport the broadband radiation e.g., to a downstream system such as the df-DHM system shown in Figure 8B.
  • the full aperture of the optical component may be divided into a plurality of different zones, each of which transmits a different respective range of wavelengths.
  • the fiber coupling efficiency is then optimized on a zone-by-zone basis - that is to say, for each of the plurality of different zones, the fiber coupling efficiency is optimized only for the wavelengths that transmit through the corresponding zone.
  • the fiber coupling efficiency is a field function of the far- field distributions of the light source and the receiving fiber.
  • Figure 10 shows a workflow of the proposed design method in accordance with an embodiment.
  • the proposed method comprises the following three main steps.
  • the proposed design method comprises obtaining a radius-wavelength relationship between a collimated beam radius and a wavelength of the broadband radiation in a wavelength range of the broadband radiation.
  • the broadband radiation may be emitted from a broadband radiation source and may be substantially collimated before entering the optical component.
  • the collimated beam radius of the broadband radiation may vary proportionally with the wavelength of the broadband radiation.
  • the collimated beam radius of the broadband radiation may increase linearly with the wavelength of the broadband radiation. This may correspond to the situation where the broadband radiation is emitted from a LMA fiber or a PCF, wherein the NA of the fiber increases linearly with the wavelength while the MFD stays relatively constant (e.g., as shown in Figure 9).
  • the radius-wavelength relationship between the collimated beam radius and the wavelength of the broadband radiation in the wavelength range of the broadband radiation may be obtained by direct measurement of the collimated beam size as a function of the wavelength e.g., at a position immediately before the optical component.
  • the radius-wavelength relationship may be obtained by simulation of the collimated beam size based on characteristics (e.g., a refractive index profile) of the optical fiber (e.g., a LMA fiber or a PCF) within which the broadband radiation is generated.
  • the radius-wavelength relationship may be obtained by (1) obtaining a refractive index profile of the optical fiber (e.g., a LMA fiber or a PCF); (2) determining one or more NA values of the optical fiber (e.g., as shown in Figure 9) for one or more respective wavelengths in the wavelength range of the broadband radiation; and (3) for each of the one or more wavelengths, determining, via simulation, a collimated beam radius of the broadband radiation using the NA value determined for the corresponding wavelength.
  • a refractive index profile of the optical fiber e.g., a LMA fiber or a PCF
  • NA values of the optical fiber e.g., as shown in Figure 9
  • the proposed design method may comprise determining a plurality of lighttransmitting zones in a transversal plane of the optical component based on the obtained radiuswavelength relationship.
  • the transversal plane may be perpendicular to an optical axis of the optical component.
  • Each of the plurality of light-transmitting zones may be configured to transmit a different respective wavelength range either overlapping with or falling within the wavelength range of the broadband radiation.
  • each of the different wavelength ranges may comprise a different respective minimum wavelength and a common maximum wavelength.
  • the different minimum wavelengths may spread across the wavelength range of the broadband radiation and the common maximum wavelength is equal to a maximum wavelength of the wavelength range of the broadband radiation.
  • the maximum wavelength of the wavelength range of the broadband radiation may form one of the different wavelength range on its own.
  • step 1020 may comprise: defining the different minimum wavelengths and the common maximum wavelength so as to define the different wavelength ranges. As such, each of the different ranges may span from a respective one of the different minimum wavelengths to the common maximum wavelength.
  • Step 1020 may comprise determining a size of each of the plurality of light-transmitting zones using the respective one of the different minimum wavelengths. The size of each light-transmitting zone is defined as a radial distance from the optical axis in the transversal plane of the optical component which may be equal to the beam radius of the collimated broadband radiation at the respective one of the different minimum wavelengths.
  • FIGs 11 A-l 1C schematically depict a first example implementation of the proposed design method.
  • a triplet TLA comprising three lens elements LE1-LE3 is designed to optimally couple a broadband radiation ORD into an optical fiber F, which may be for example a PMF (e.g., PMF1 or PMF2 shown in Figure 8A).
  • the triplet TLA may comprise a focal length FL which may be defined by a user.
  • the end facet of the optical fiber F may be located in the focal plane of the triplet TLA.
  • the broadband radiation ORD may comprise a wavelength range between 400 nm and 1600 nm.
  • the broadband radiation ORD may be substantially collimated before entering the triplet TLA.
  • the collimated beam radius Rl, R2, R3 may increase linearly with the wavelength.
  • the collimated beam radius Rl, R2, R3 may be directly measured at a fixed wavelength interval. For example, the collimated beam radius may be measured every 100 nm from 400 nm to 1600 nm.
  • the minimum wavelengths of the different wavelength ranges may be flexibly defined.
  • the wavelength range of the broadband radiation ORD may be equally divided into three (or any other number of) sub-ranges.
  • the minimum wavelengths that are used to determine the different wavelength ranges (and thus the plurality of light-transmitting zones) may be defined as the minimum wavelengths of the equally spaced sub-ranges.
  • the wavelength range between 400 nm and 1600 nm is divided into three equally spaced sub-ranges, i.e.
  • the minimum wavelengths will be 400 nm, 800 nm and 1200 nm, and 1200 nm - 1600 nm
  • the minimum wavelengths will be 400 nm, 800 nm and 1200 nm
  • the common maximum wavelength will be 1600 nm.
  • the three minimum wavelengths and the common maximum wavelength define three different wavelength ranges, namely a first wavelength range WB1 being between 400 nm and 1600 nm, a second wavelength range WB2 being between 800 nm and 1600 nm, and a third wavelength range WB3 being between 1200 nm and 1600 nm.
  • the first wavelength range WB1 overlaps completely with the wavelength range of the broadband radiation ORD while each of the second wavelength range WB2 and the third wavelength range WB3 overlaps only a portion of the wavelength range of the broadband radiation ORD.
  • the beam radii Rl, R2, R3 at respective minimum wavelengths may then be determined based on the linear relationship between the collimated beam radius and the wavelength of the broadband radiation (which provides a one-to-one correspondence between the beam radius and wavelength).
  • each light-transmitting zone LTZ1, LTZ2, LTZ3 may be defined by a radial distance from the optical axis OA of the triplet TLA, which is equal to the beam radius Rl, R2, R3 of the collimated broadband radiation ORD determined at the respective one of the different minimum wavelengths.
  • FIGS 12A-12C schematically depict a second example implementation of the proposed design method.
  • a singlet GRIN lens SGRIN is designed to optimally couple a broadband radiation ORD into an optical fiber F, which may be for example a PMF (e.g., PMF1 or PMF2 shown in Figure 8A).
  • the singlet GRIN lens SGRIN may comprise a focal length FL which may be defined by a user.
  • the end facet of the optical fiber F may be located in the focal plane of the triplet TLA.
  • the broadband radiation ORD may comprise a wavelength range between 400 nm and 1600 nm.
  • the broadband radiation ORD may be substantially collimated before entering the singlet GRIN lens SGRIN.
  • the collimated beam radius Rl, R2, R3 may increase linearly with the wavelength.
  • the collimated beam radius Rl, R2, R3 may be directly measured at a fixed wavelength interval. For example, the collimated beam radius may be measured every 100 nm from 400 nm to 1600 nm.
  • the minimum wavelengths of the different wavelength ranges may be defined as 400 nm, 800 nm and 1200 nm and the common maximum wavelength may be defined as 1600 nm.
  • the three minimum wavelengths and the common maximum wavelength may define three different wavelength ranges, namely a first wavelength range WB1 being between 400 nm and 1600 nm, a second wavelength range WB2 being between 800 nm and 1600 nm, and a third wavelength range WB3 being between 1200 nm and 1600 nm.
  • the first wavelength range WB 1 overlaps completely with the wavelength range of the broadband radiation ORD while each of the second wavelength range WB2 and the third wavelength range WB3 overlaps only a portion of the wavelength range of the broadband radiation ORD.
  • there may be a fourth wavelength range (not shown) which may comprise only the common maximum wavelength, i.e. 1600 nm.
  • each light-transmitting zone LTZ1, LTZ2, LTZ3 may be defined by a radial distance from the optical axis OA of the singlet GRIN lens SGRIN, which is equal to the beam radius Rl, R2, or R3 of the collimated broadband radiation ORD determined at the respective one of the different minimum wavelengths.
  • the proposed design may comprise optimizing an efficiency of coupling of the broadband radiation into the optical fiber for each of the different wavelength ranges.
  • said optimizing step may comprise optimizing, for the narrowest wavelength range of said different wavelength ranges, the efficiency of coupling of the broadband radiation into the optical fiber for at least one wavelength within said narrowest wavelength range; and for each respective non-narrowest wavelength range of said different wavelength ranges, optimizing the efficiency of coupling of the broadband radiation into the optical fiber for at least one wavelength comprised within said respective non-narrowest wavelength range but not comprised within the next narrowest wavelength range of said different wavelength ranges.
  • the efficiency of coupling of the broadband radiation into the optical fiber may be optimized for at least one wavelength within a range defined by the minimum wavelength of said respective non-narrowest wavelength range and a minimum wavelength of the next narrowest wavelength range of said different wavelength ranges.
  • the fiber coupling efficiency may be optimized for e.g., 1400 nm; for the second wavelength range WB2 (between 800 nm and 1600 nm), the fiber coupling efficiency may be optimized for e.g., 1000 nm (which is comprised within the range between 800 nm and 1200 nm); for the first wavelength range WB1 (between 400 nm and 1600 nm), the fiber coupling efficiency may be optimized for e.g., 600 nm (which is comprised within the range between 400 nm and 800 nm).
  • the second wavelength range WB2 is the next narrowest range for the first wavelength range WB1 and the third wavelength range WB3 is the next narrowest range for the second wavelength range WB2, i.e., the next narrowest is the successive next narrowest.
  • the optimization of the fiber coupling efficiency may be achieved by varying one or more parameters associated with the optical component. Such an optimization may be based on physical optics propagation. Step 1030 may be carried out in a software program configured for designing and simulating optical systems, such as Ansys Zemax OpticStudio marketed by Ansys Incorporation, Code V marketed by Synopsys Incorporation, or VirtualLab Fusion marketed by LightTrans International GmbH.
  • one or more merit functions may be used to optimize the total power coupling efficiency on a zone-by-zone basis, i.e. the total power coupling efficiency is optimized only for the wavelengths (e.g., wavelengths in the first wavelength range WB1) that transmit through the corresponding light-transmitting zone (e.g., the first light-transmitting zone LTZ1) of the optical component.
  • the total power coupling efficiency may be defined as:
  • the fiber coupling receiver efficiency may be expressed as: where F r (x,y) is the function describing the receiving fiber complex amplitude, W(x,y) is the function describing the complex amplitude of the beam coupling into the fiber, F (x, y) and W'(x, y) are the complex conjugates of F r (x,y) and W(x,y), respectively. Note that these functions are all complex valued, so this is a coherent overlap integral.
  • the fiber coupling receiver efficiency is calculated individually for both the x- and y-polarized portions of the beam, using only the x- or y- components of the complex-valued electric field, respectively.
  • the overall fiber coupling receiver efficiency is then calculated via a weighted average between the x- and y-polarized fiber coupling receiver efficiencies, based on the powers of the x- and y-polarized portions of the beam.
  • the maximum value of the fiber coupling receiver efficiency T(x,y) is 1.0 which may be achieved when the mode of the beam perfectly matches the mode of the fiber in both amplitude and phase at all points. Any deviation in mode shape, or phase, will reduce the value of the fiber coupling receiver efficiency T(x,y) to less than 1.0.
  • Optical aberrations typically introduce phase deviations which reduce receiver efficiency.
  • the total power coupling efficiency may be optimized for each of the different wavelength ranges WB1, WB2, WB3 which correspond to the light-transmitting zones ETZ1, ETZ2, ETZ3, respectively.
  • the total power coupling efficiency may be optimized for each of the different wavelength ranges WB1, WB2, WB3 which correspond to the light-transmitting zones LTZ1, LTZ2, LTZ3, respectively.
  • This may be achieved by varying one or more parameters associated with the singlet GRIN lens which may include: a radial refractive index profile (or a radial refractive index gradient) for each of the light-transmitting zones LTZ1, LTZ2, LTZ3 of the singlet GRIN lens, each radial profile representing spatially varying refractive indices along a radial direction of the singlet GRIN lens, which may be perpendicular to the optical axis OA’ of the singlet GRIN lens; and/or an axial refractive index profile (or an axial refractive index gradient) for each of the light-transmitting zones LTZ1, LTZ2, LTZ3 of the singlet GRIN lens, each axial profile representing spatially varying refractive indices along the optical axis OA of the singlet GRIN lens.
  • Figure 13 shows an example plot of three radial refractive index profiles (or radial refractive index gradients) RP1, RP2, RP3 respectively for three different light-emitting zones LTZ1, LTZ2, LTZ3 of the singlet GRIN lens (e.g., singlet GRIN lens SGRIN shown in Figures 12A-12C).
  • Each of the three radial refractive index profiles RP1, RP2, RP3 represents spatially varying refractive indices RIN along a radial direction R, which may be perpendicular to the optical axis of the singlet GRIN lens (e.g., as shown in Figures 12A-12C).
  • the “0” position on the horizontal axis (or R axis) corresponds to the position of the optical axis in a transversal plane of the singlet GRIN lens.
  • Each of the three radial refractive index profiles RP1, RP2, RP3 may be determined using the minimum wavelength of the corresponding wavelength range WB 1 , WB2, WB3.
  • the first radial refractive index profile RP1 may be determined using the minimum wavelength (i.e. 400 nm) of the first wavelength range WB1 (i.e. between 400 nm and 1600 nm)
  • the second radial refractive index profile RP2 may be determined using the minimum wavelength (i.e. 800 nm) of the first wavelength range WB2 (i.e.
  • the third radial refractive index profile RP3 may be determined using the minimum wavelength (i.e. 1200 nm) of the first wavelength range WB3 (i.e. between 1200 nm and 1600 nm),
  • Figure 14 shows an example plot of three axial refractive index profiles (or axial refractive index gradients) API, AP2, AP3 respectively for three different light-emitting zones LTZ1, LTZ2, LTZ3 of the same singlet GRIN lens.
  • Each of the three axial refractive index profiles RP1, RP2, RP3 represents spatially varying refractive indices RIN along an axial direction of the singlet GRIN lens (e.g., as shown in Figures 12A-12C).
  • the “0” position on the horizontal axis (or L axis) corresponds to the position of the input surface (via which the broadband radiation enters the singlet GRIN lens) on the optical axis of the singlet GRIN lens.
  • Each of the three axial refractive index profiles RP1, RP2, RP3 may be determined using the minimum wavelength of the corresponding wavelength range WB1, WB2, WB3.
  • the first axial refractive index profile API may be determined using the minimum wavelength (i.e. 400 nm) of the first wavelength range WB1 (i.e. between 400 nm and 1600 nm)
  • the second axial refractive index profile AP2 may be determined using the minimum wavelength (i.e. 800 nm) of the first wavelength range WB2 (i.e. between 800 nm and 1600 nm)
  • the third axial refractive index profile AP3 may be determined using the minimum wavelength (i.e.
  • the total power coupling efficiency may be optimized for each of the different wavelength ranges. This may be achieved by varying one or more parameters of the optical component which may include: one or more surface curvatures of the optical component, and/or one or more thicknesses of one or more elements of the optical component, and/or one or more spatial distances between one or more elements of the optical component, and/or one or more aperture sizes of one or more elements of the optical component; and/or one or more refractive indices of one or more elements of the optical component, and/or a radial refractive index profile (or a radial refractive index gradient) for each of the light-transmitting zones of the optical component; and/or an axial refractive index profile (or a radial refractive index gradient) for each of the light-transmitting zones of the optical component.
  • a method of manufacturing an optical component comprising: designing an optical component by performing the method of design as outlined above; and manufacturing the optical component in accordance with the design.
  • the designing step may comprises obtaining one or more radial refractive index profiles respectively for one or more different light-emitting zones of the optical component; and obtaining one or more axial refractive index profiles respectively for one or more different light-emitting zones of the optical component.
  • the manufacturing step may comprise 3D printing the optical component using the one or more radial refractive index profiles and the one or more axial refractive index profiles.
  • the singlet GRIN lens may be 3D printed using drop on demand inkjet printing techniques. Further information about manufacturing singlet GRIN lens via inkjet printing can be found in the scientific publication “Freeform gradient- index media: a new frontier in freeform optics”, by David H. Lippman, Nicholas S. Kochan, Tianyi Yang, Greg R. Schmidt, Julie L. Bentley, and Duncan T. Moore, Optics Express, p. 36997, Vol. 29, No. 22/25 Oct 2021, and the US patent US9447299B2, which are incorporated herein by reference.
  • FIG. 15 is a block diagram that illustrates a computer system 1500 that may assist in implementing the methods and flows disclosed herein.
  • Computer system 1500 includes a bus 1502 or other communication mechanism for communicating information, and a processor 1504 (or multiple processors 1504 and 1505) coupled with bus 1502 for processing information.
  • Computer system 1500 also includes a main memory 1506, such as a random access memory (RAM) or other dynamic storage device, coupled to bus 1502 for storing information and instructions to be executed by processor 1504.
  • Main memory 1506 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 1504.
  • Computer system 1500 further includes a read only memory (ROM) 1508 or other static storage device coupled to bus 1502 for storing static information and instructions for processor 1504.
  • ROM read only memory
  • a storage device 1510 such as a magnetic disk or optical disk, is provided and coupled to bus 1502 for storing information and instructions.
  • Computer system 1500 may be coupled via bus 1502 to a display 1512, such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user.
  • a display 1512 such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user.
  • An input device 1514 is coupled to bus 1502 for communicating information and command selections to processor 1504.
  • cursor control 1516 such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor 1504 and for controlling cursor movement on display 1512.
  • 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 1500 in response to processor 1504 executing one or more sequences of one or more instructions contained in main memory 1506. Such instructions may be read into main memory 1506 from another computer-readable medium, such as storage device 1510. Execution of the sequences of instructions contained in main memory 1506 causes processor 1504 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 1506. 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 1510.
  • Volatile media include dynamic memory, such as main memory 1506.
  • Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus 1502. 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 1504 for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer.
  • the remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem.
  • a modem local to computer system 1500 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 1502 can receive the data carried in the infrared signal and place the data on bus 1502.
  • Bus 1502 carries the data to main memory 1506, from which processor 1504 retrieves and executes the instructions.
  • the instructions received by main memory 1506 may optionally be stored on storage device 1510 either before or after execution by processor 1504.
  • Computer system 1500 also preferably includes a communication interface 1518 coupled to bus 1502.
  • Communication interface 1518 provides a two-way data communication coupling to a network link 1520 that is connected to a local network 1522.
  • communication interface 1518 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 1518 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 1518 sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.
  • Network link 1520 typically provides data communication through one or more networks to other data devices.
  • network link 1520 may provide a connection through local network 1522 to a host computer 1524 or to data equipment operated by an Internet Service Provider (ISP) 1526.
  • ISP 1526 in turn provides data communication services through the worldwide packet data communication network, now commonly referred to as the “Internet” 1528.
  • Internet 1528 uses electrical, electromagnetic or optical signals that carry digital data streams.
  • the signals through the various networks and the signals on network link 1520 and through communication interface 1518, which carry the digital data to and from computer system 1500, are exemplary forms of carrier waves transporting the information.
  • Computer system 1500 may send messages and receive data, including program code, through the network(s), network link 1520, and communication interface 1518.
  • a server 1530 might transmit a requested code for an application program through Internet 1528, ISP 1526, local network 1522 and communication interface 1518.
  • 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 1504 as it is received, and/or stored in storage device 1510, or other non-volatile storage for later execution. In this manner, computer system 1500 may obtain application code in the form of a carrier wave.
  • a method of designing an optical component for coupling a broadband radiation into a first optical fiber comprising obtaining a radius-wavelength relationship between a collimated beam radius and a wavelength of the broadband radiation in a wavelength range of the broadband radiation; determining a plurality of light-transmitting zones in a transversal plane of the optical component based on the radius-wavelength relationship, wherein the transversal plane is perpendicular to an optical axis of the optical component, and wherein each of the plurality of light-transmitting zones is configured to transmit a respective different wavelength range either overlapping with or comprised within the wavelength range of the broadband radiation; and optimizing an efficiency of coupling of the broadband radiation into the optical fiber for each of the different wavelength ranges by varying one or more parameters associated with the optical component.
  • said optimizing step comprises optimizing, for the narrowest wavelength range of said different wavelength ranges, the efficiency of coupling of the broadband radiation into the optical fiber for at least one wavelength within said narrowest wavelength range; and for each respective non-narrowest wavelength range of said different wavelength ranges, optimizing the efficiency of coupling of the broadband radiation into the optical fiber for at least one wavelength comprised within said respective non-narrowest wavelength range but not comprised within the next narrowest wavelength range of said different wavelength ranges.
  • said optimizing step comprises optimizing an efficiency of the coupling for collimated broadband radiation, said collimated broadband radiation comprising said broadband radiation having been collimated.
  • said optimizing step comprises optimizing an efficiency of the coupling for said broadband radiation emitted from a second optical fiber.
  • the second optical fiber comprises a large mode area “LMA” fiber or a photonic crystal fiber “PCF”.
  • the obtaining step comprises: obtaining a refractive index profile of the second optical fiber; determining one or more numerical aperture “NA” values of the second optical fiber for one or more respective wavelengths in the wavelength range of the broadband radiation; and determining, for each of the one or more wavelengths, a collimated beam radius of the broadband radiation using the NA value determined for the corresponding wavelength.
  • each of the different wavelength ranges comprises a different respective minimum wavelength and a common maximum wavelength.
  • each of the different minimum wavelengths comprises a different respective wavelength within the wavelength range of the broadband radiation and the common maximum wavelength is equal to a maximum wavelength of the wavelength range of the broadband radiation.
  • the determining step comprises: defining the different minimum wavelengths and the common maximum wavelength so as to define the different wavelength ranges; and determining a size of each of the plurality of light-transmitting zones using the respective one of the different minimum wavelengths, the size of each light-transmitting aperture being a radial distance from the optical axis in the transversal plane of the optical component.
  • the one or more parameters associated with the optical component comprise: one or more surface curvatures of the optical component; and/or one or more thicknesses of one or more elements of the optical component; and/or one or more spatial distances between one or more elements of the optical component; and/or one or more aperture sizes of one or more elements of the optical component; and/or one or more refractive indices of one or more elements of the optical component; and/or a radial refractive index profile for each of the plurality of light-transmitting zones of the optical component; and/or an axial refractive index profile for each of the plurality of light-transmitting zones of the optical component.
  • optical component comprises a triplet lens.
  • wavelength range of the broadband radiation spans from 400 nm to 1600 nm.
  • a method of manufacturing an optical component comprising: designing an optical component by performing the method of any preceding clause; and manufacturing the optical component in accordance with the design.
  • the optical component is a singlet GRIN lens and wherein the designing step comprises obtaining one or more radial refractive index profiles respectively for one or more different light-emitting zones of the optical component; and obtaining one or more axial refractive index profiles respectively for one or more different light-emitting zones of the optical component.
  • An optical component for coupling a broadband radiation into an optical fiber comprising: a plurality of light-transmitting zones in a transversal plane perpendicular to an optical axis of the optical component, wherein each of the plurality of light-transmitting zones is configured to transmit a different respective wavelength range either overlapping with or falling within a wavelength range of the broadband radiation; and wherein one or more parameters of the optical component are configured to provide an optimal efficiency of coupling of the broadband radiation into the optical fiber for each of the different wavelength ranges.
  • each of the different wavelength ranges comprises a different respective minimum wavelength and a common maximum wavelength.
  • each of the different minimum wavelengths comprises a different respective wavelength within the wavelength range of the broadband radiation and the common maximum wavelength is equal to a maximum wavelength of the wavelength range of the broadband radiation.
  • an optical component according to any of clauses 25 to 30, wherein the one or more parameters associated with the optical component comprise: one or more surface curvatures of the optical component; and/or one or more thicknesses of one or more elements of the optical component; and/or one or more spatial distances between one or more elements of the optical component; and/or one or more aperture sizes of one or more elements of the optical component; and/or one or more refractive indices of one or more elements of the optical component; and/or a radial refractive index profile for each of the plurality of light-transmitting zones of the optical component; and/or an axial refractive index profile for each of the plurality of light-transmitting zones of the optical component.
  • An optical arrangement comprising: an optical fiber; and an optical component for coupling a broadband radiation into the optical fiber according to any of clauses 25 to 33.
  • 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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Abstract

L'invention concerne un procédé de conception d'un composant optique pour coupler un rayonnement à large bande dans une première fibre optique, comprenant l'obtention d'une relation rayon-longueur d'onde entre un rayon de faisceau collimaté et une longueur d'onde du rayonnement à large bande dans une plage de longueurs d'onde du rayonnement à large bande ; déterminer une pluralité de zones de transmission de lumière dans un plan transversal du composant optique sur la base de la relation rayon-longueur d'onde, le plan transversal étant perpendiculaire à un axe optique du composant optique, et chacune de la pluralité de zones de transmission de lumière étant configurée pour transmettre une plage de longueurs d'onde respective différente soit chevauchant soit tombant dans la plage de longueurs d'onde du rayonnement à large bande ; et optimiser une efficacité de couplage du rayonnement à large bande dans la fibre optique pour chacune des différentes plages de longueurs d'onde en faisant varier un ou plusieurs paramètres associés au composant optique.
PCT/EP2025/058958 2024-05-06 2025-04-02 Procédé de conception d'un composant optique pour coupler un rayonnement à large bande dans une fibre optique Pending WO2025233062A1 (fr)

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