Mounted Hollow Core Fiber Arrangements

Abstract

A mounted hollow core optical fiber arrangement includes: a hollow core optical fiber having a microstructure; and a mounting arrangement including a plurality of mounting contacts, the mounting contacts being configured to apply a force to an outer layer of the hollow core optical fiber. A portion of the hollow core optical fiber is located in a receiving area of ​​the mounting arrangement. The plurality of mounting contacts are positioned around the receiving area. The mounting contacts are distributed around the receiving area, the distribution of the mounting contacts corresponding to the distribution of features of the microstructure of the hollow core optical fiber. The mounted hollow core optical fiber can be used in a radiation source device to provide broadband radiation.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 19181578.6 filed on June 21, 2019 and EP application 19186702.7 filed on July 17, 2019, which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to mounted optical fiber arrangements for hollow core optical fibers. In particular, it relates to the distribution of forces applied by mounting to hollow core optical fibers including internal microstructures. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern (also commonly referred to as a "design layout" or "design") at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0005] In order to project a pattern onto a substrate, a lithographic apparatus can use electromagnetic radiation. The wavelength of the radiation determines the minimum size of a feature that can be formed on a substrate. Typical wavelengths currently used are 365nm (i-line), 248nm, 193nm, and 13.5nm. Compared to a lithographic apparatus using, for example, radiation with a wavelength of 193nm, a lithographic apparatus using extreme ultraviolet (EUV) radiation with a wavelength in the range of 4 to 20nm (e.g., 6.7nm or 13.5nm) can be used to form smaller features on a substrate.

[0006] Low k1 lithography can be used to process features with dimensions smaller than the typical resolution limit of the lithographic apparatus. In such a process, the resolution formula can be expressed as CD=k1×λ / NA, where λ is the wavelength of radiation employed, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the "critical dimension" (the minimum feature size typically printed, but in this case the half pitch), and k1 is an empirical resolution factor. In general, the smaller the k1, the more difficult it is to reproduce a pattern on a substrate that is similar in shape and size to that planned by the circuit designer to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. For example, these include, but are not limited to, optimization of NA, customized illumination schemes, use of phase-shifted patterning devices, various optimizations of the design layout such as optical proximity correction (OPC, sometimes also referred to as "optical and process correction") in the design layout, or other methods generally defined as "resolution enhancement technology" (RET). Alternatively, a tight control loop for controlling the stability of the lithographic apparatus can be used to improve the reproduction of patterns at low k1.

[0007] In connection with lithographic applications, many different types of measurements can be performed within and outside of a lithographic apparatus. Typically, such measurements can be performed by the apparatus using a radiation source for illuminating a measurement target and a detection system operable to measure at least one property of a portion of the incident radiation scattered from the target. Examples of measurement equipment external to a lithographic apparatus include metrology equipment and inspection equipment. A metrology equipment can return data related to one or more properties of a substrate, where the data can be quantitative data. Inspection equipment can detect defects or imperfections on a substrate. Examples of measurement systems within a lithographic apparatus include topography measurements, position measurements, and alignment measurements to measure properties of a pattern on a substrate.

[0008] The quality of a measurement may affect the quality of the lithography process with which it is associated. One of the elements that may affect the quality of a measurement is the quality of the radiation used in the measurement.

[0009] Different types of radiation can be used to interrogate different properties of the substrate. Summary of the invention

[0010] According to a first aspect of the present disclosure, there is provided a mounting type hollow core optical fiber arrangement, comprising: a hollow core optical fiber having a microstructure; and a mounting arrangement comprising a plurality of mounting contacts, the mounting contacts being configured to apply a force to an outer layer of the hollow core optical fiber. A portion of the hollow core optical fiber is located in a receiving area of ​​the mounting arrangement. The plurality of mounting contacts are positioned around the receiving area. The mounting contacts are distributed around the receiving area, the distribution of the mounting contacts corresponding to the distribution of features of the microstructure of the hollow core optical fiber.

[0011] Optionally, each mounting contact of the plurality of mounting contacts may be configured to apply a substantially equal force to an outer layer of the hollow-core optical fiber.

[0012] Optionally, the locations of the plurality of mounting contacts may be equally spaced around the receiving area.

[0013] Optionally, the distribution of features of the microstructure may include symmetry. The symmetry of the positions of the plurality of mounting contacts may correspond to the symmetry of the microstructure.

[0014] Alternatively, the hollow core optical fiber may be a hollow core photonic crystal fiber comprising a single ring structure having a plurality of capillaries surrounding the hollow core.

[0015] Optionally, the capillary distribution in the single ring structure may have multiple rotational symmetries. The number of mounting contacts is an integer multiple of the number of rotational symmetries, or the number of rotational symmetries is an integer multiple of the number of mounting contacts.

[0016] Alternatively, the number of mounting contacts may be equal to the number of capillaries surrounding the hollow core.

[0017] Alternatively, the portion of the hollow-core optical fiber mounted within the receiving area of ​​the mounting arrangement may be an end portion of the hollow-core optical fiber.

[0018] Optionally, the force applied by the mounting contacts may be adjustable.

[0019] Optionally, the mounting arrangement may include a spring loaded screw configured to adjust the force applied by the mounting contacts.

[0020] Optionally, the mounting arrangement may comprise an electrical arrangement configured to adjust the force applied by the mounting contacts by applying an electric field.

[0021] Optionally, the electrical arrangement may include a first plate at a first side of the mounting arrangement and a second plate at a second side of the mounting arrangement, wherein the receiving area is located between the first side and the second side. The force may be configured to be adjusted by adjusting an electric field applied between the first plate and the second plate.

[0022] Optionally, the mounting arrangement may comprise a magnetic arrangement configured to adjust the force applied by the mounting contacts by applying a magnetic field.

[0023] Optionally, the magnetic arrangement may include a first magnet on a first side of the mounting arrangement and a second magnet on a second side of the mounting arrangement, wherein the receiving area is located between the first side and the second side. The force may be configured to be adjusted by adjusting a magnetic field applied between the first magnet and the second magnet.

[0024] Optionally, the force may be configured to be adjusted to optimize the performance of the hollow core optical fiber for a predetermined narrow wavelength range.

[0025] Alternatively, the predetermined narrow wavelength range may include wavelengths of a source for providing input radiation to be coupled into the hollow core optical fiber.

[0026] Optionally, the predetermined wavelength range may include at least a portion of an operating wavelength range of the hollow core optical fiber.

[0027] Optionally, the hollow core optical fiber may be configured to operate over a broadband wavelength range.

[0028] Alternatively, the broadband wavelength range may include wavelengths from 200 nm to 2000 nm.

[0029] Alternatively, the broadband wavelength range may include wavelengths from 400 nm to 1000 nm.

[0030] Alternatively, the mounting arrangement may include a base having a recess forming part of the receiving area and a top cover configured to cover the base.

[0031] Optionally, the top cover may include a groove for receiving the hollow core optical fiber, wherein the top cover groove may be aligned with the base groove to form a receiving area.

[0032] Alternatively, the base recess and the top cover may be configured to form a polygonal form when the top cover covers the base.

[0033] Optionally, each side of the polygonal form may include mounting contacts.

[0034] Alternatively, the polygonal form may be a regular polygonal form.

[0035] Optionally, the mounted hollow core optical fiber arrangement may further include a reservoir configured to provide a resealable gas seal between an interior of the reservoir and an exterior of the reservoir. The mounted hollow core optical fiber may be located within the reservoir. The reservoir may be configured to contain a controlled gas mixture.

[0036] Optionally, the mounted hollow core optical fiber arrangement may include a second mounting arrangement, wherein the second portion of the hollow core optical fiber may be located within a receiving area of ​​the second mounting arrangement.

[0037] According to another aspect of the present disclosure, there is provided a mounted hollow core optical fiber arrangement, comprising: a hollow core optical fiber having a microstructure; and a mounting arrangement comprising a plurality of mounting contacts, the mounting contacts being configured to apply a force to an outer layer of the hollow core optical fiber at a plurality of contact points. The hollow core optical fiber may be located in a receiving area of ​​the mounting arrangement. The plurality of mounting contacts may be uniformly positioned around the receiving area of ​​the mounting arrangement. The plurality of mounting contacts may be configured to apply a substantially equal force to an outer layer of the hollow core optical fiber at each of the plurality of contact points.

[0038] Alternatively, the hollow core optical fiber may be a hollow core photonic crystal fiber comprising a single ring including a plurality of capillaries surrounding the hollow core.

[0039] According to another aspect of the present disclosure, a radiation source device for providing output radiation is provided. The radiation source device may include the above-mentioned mounted hollow core optical fiber arrangement. The hollow core optical fiber may include an input end configured to receive input radiation and an output end configured to provide output radiation. The output end of the hollow core optical fiber may be located within the accommodation area of ​​the first mounting arrangement.

[0040] Optionally, the output radiation may be broadband output radiation.The hollow core optical fiber may be configured to receive input radiation at an input end, broaden the wavelength range of the input radiation as the radiation propagates through the hollow core optical fiber, and provide broadband output radiation at an output end of the hollow core optical fiber.

[0041] Optionally, the input end of the hollow core optical fiber may be located in a receiving area of ​​the second mounting arrangement, the receiving area being configured to receive the input end of the hollow core optical fiber.The second mounting arrangement and the input end may be located within the interior of the reservoir.

[0042] Optionally, the first mounting arrangement can be configured to apply a first force to the output end, and the second mounting arrangement can be configured to apply a second force to the input end. The first force can be optimized to reduce stress-induced losses or mode scrambling within a narrow range of wavelengths included in the output radiation. The second force can be optimized to reduce stress-induced losses or mode scrambling within the input wavelength.

[0043] According to another aspect of the present disclosure, a method of installing a hollow core optical fiber into an installation arrangement is provided. The method may include: providing the above-mentioned hollow core optical fiber and installation arrangement; installing a portion of the hollow core optical fiber into the installation arrangement; providing input radiation into an end section of the hollow core optical fiber; measuring radiation output by the hollow core optical fiber to determine stress-induced losses or mode scrambling; and when measuring radiation output by the optical fiber, adjusting the force applied by a plurality of installation contacts of the installation arrangement so that stress-induced losses or mode scrambling within the hollow core optical fiber are reduced.

[0044] According to another aspect of the present disclosure, a measurement arrangement is provided, comprising the above-mentioned radiation source device.

[0045] According to another aspect of the present disclosure, a measurement device is provided, comprising the above-mentioned measurement arrangement.

[0046] According to another aspect of the present disclosure, there is provided an inspection device comprising the above-mentioned metrology arrangement.

[0047] According to another aspect of the present disclosure, there is provided a lithographic apparatus comprising the above-mentioned metrology arrangement. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0049] - Figure 1 depicts a schematic overview of a lithography apparatus;

[0050] - Figure 2 A schematic overview of a lithography unit is depicted;

[0051] - Figure 3 Depicted is a schematic representation of overall lithography showing the collaboration between three key technologies to optimize semiconductor manufacturing;

[0052] - Figure 4 depicts a schematic overview of a level sensor;

[0053] - Figure 5 depicts a schematic overview of an alignment sensor;

[0054] - Figure 6 depicts a known setup of an optical fiber installed in a mounting arrangement;

[0055] - Figure 7 depicts the unevenly distributed forces applied to a hollow core optical fiber by an adhesive;

[0056] - Figure 8 Example bundle profiles of hollow core optical fibers depicting uniform force distribution (left) and non-uniform force distribution (right);

[0057] - Fig. 9 depicts a schematic representation of a mounted hollow core optical fiber arrangement including a hollow core optical fiber having a microstructure surrounding the hollow core;

[0058] - Fig.10 depicts a schematic representation of a hollow core optical fiber held by a plurality of mounting contacts, the distribution of the plurality of mounting contacts corresponding to the distribution of a microstructure of the hollow core optical fiber;

[0059] - Fig.11 depicts a schematic representation of a mounted hollow core optical fiber arrangement;

[0060] - Fig.12 depicts a schematic representation of a mounted hollow core optical fiber arrangement wherein the accommodation area has a regular polygonal form;

[0061] - Fig.13 depicts an installed hollow core optical fiber arrangement configured to apply an adjustable force to an installed hollow core optical fiber; and

[0062] - Fig.14 Depicted is a schematic representation of an installed hollow core optical fiber arrangement within a resealable reservoir.

[0063] - Fig.15 is a schematic cross-sectional view in a transverse plane (ie, perpendicular to the axis of the optical fiber) of a hollow core optical fiber that may form part of a radiation source according to an embodiment;

[0064] - Fig.16 depicts a schematic representation of a radiation source according to an embodiment for providing broadband output radiation; and

[0065] - Fig.17 (a) and (b) schematically depict transverse cross-sections of examples of hollow core photonic crystal fiber (HC-PCF) designs for supercontinuum generation. DETAILED DESCRIPTION

[0066] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., wavelengths in the range of about 5 to 100 nm).

[0067] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart to an incident radiation beam a patterned cross-section corresponding to the pattern to be created in a target portion of a substrate. In this context, the term "light valve" can also be used. In addition to classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), other examples of such patterning devices may include programmable mirror arrays and programmable LCD arrays.

[0068] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an 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) T 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 according to certain parameters, a substrate support (e.g. a wafer stage) WT constructed to hold a substrate W, e.g. a resist-coated wafer, and connected to a second positioner PW configured to accurately position the substrate support according to 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 the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0069] In operation, 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 the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0070] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof, as appropriate for the exposure radiation used and / or other factors (such as the use of immersion liquid or the use of a vacuum). Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0071] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, to fill the space between the projection system PS and the substrate W, which is also known as immersion lithography. More information on immersion technology is given in US6952253, which is incorporated herein by reference.

[0072] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps for preparing a substrate W for subsequent exposure may be performed on a substrate W located on one of the substrate supports WT, while another substrate W on another substrate support WT is used to expose a pattern on another substrate W.

[0073] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measuring table. The measuring table is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measuring table may hold a plurality of sensors. The cleaning means may be arranged to clean a part of the lithographic apparatus, e.g. a part of the projection system PS or a part of a system for providing immersion liquid. The measuring table may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0074] In operation, a radiation beam B is incident on a patterning device, such as a mask MA, which is held on a mask support T and is patterned by a pattern (design layout) present on the patterning device MA. After traversing the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, the first positioner PM and possibly another position sensor (in Figure 1 The patterning device MA (not explicitly depicted in the figure) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, they can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, these are called scribe line alignment marks.

[0075] like Figure 2 As shown, the lithography apparatus LA may form part of a lithography cell LC, which is sometimes also referred to as a lithography cell or (lithography cell) cluster, which typically also includes equipment for performing pre-exposure and post-exposure processes on a substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH and a bake plate BK, for example, for regulating the temperature of the substrate W (e.g. for regulating the solvent in the resist layer). A substrate handler or robot RO picks up substrates W from input / output ports I / O1, I / O2, moves them between the different process equipment, and delivers the substrates W to a feed station LB of the lithography apparatus LA. The devices in the lithography cell (also often collectively referred to as tracks) are typically controlled by a track control unit TCU, which itself may be controlled by a supervisory control system SCS, which may also control the lithography apparatus LA, for example via a lithography control unit LACU.

[0076] In order for a substrate W exposed by the lithographic apparatus LA to be correctly and consistently exposed, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), etc. For this purpose, an inspection tool (not shown) may be included in the lithography cell LC. If an error is detected, for example, adjustments may be made to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, particularly if the inspection is done before other substrates W of the same batch or lot are still to be exposed or processed.

[0077] An inspection apparatus (which may also be referred to as a metrology apparatus) is used to determine properties of a substrate W, in particular how properties vary from one substrate W to another, or how properties associated with different layers of the same substrate W vary from layer to layer. The inspection apparatus may alternatively be configured to identify defects on the substrate W, and may for example be part of the lithography cell LC, or may be integrated into the lithography apparatus LA, or may even be a stand-alone device. The inspection apparatus may measure properties on a latent image (the image in the resist layer after exposure) or a semi-latent image (the image in the resist layer after a post-exposure bake step PEB), or on a developed resist image (where exposed or unexposed parts of the resist have been removed), or even on an etched image (after a pattern transfer step such as etching).

[0078] Typically, the patterning process in the lithography apparatus LA is one of the most critical steps in the process, which requires high accuracy in dimensioning and placement of structures on the substrate W. To ensure this high accuracy, the three systems can be combined into a so-called "holistic" control environment, such as Figure 3 Schematically depicted in . One of these systems is the lithography apparatus LA, which is (in practice) connected to a metrology tool MT (a second system) and a computer system CL (a third system). The key to this "holistic" environment is to optimize the cooperation between these three systems to enhance the overall process window, and to provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA stays within the process window. The process window defines the range of process parameters (e.g. dose, focus, overlay) within which a specific manufacturing process will produce a defined result (e.g. a functional semiconductor device), and typically within which process parameters of a lithography process or patterning process are allowed to vary.

[0079] The computer system CL can use (a portion of) the design layout to be patterned to predict which resolution enhancement techniques to use, and perform computational lithography simulations and calculations to determine which mask layouts and lithography equipment settings achieve the maximum overall process window (in Figure 3 Typically, the resolution enhancement technique is 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 a metrology tool MET) to predict whether defects may be present (e.g. due to suboptimal processing). Figure 3 0 in the figure).

[0080] 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, such as in the calibration state of the lithographic apparatus LA (in Figure 3 (depicted by multiple arrows in the third scale SC3).

[0081] During the lithographic process, it is desirable to frequently measure the structures created, for example for process control and verification. The tool that performs such measurements is typically referred to as a measurement tool MT. Different types of measurement tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer measurement tools MT. Scatterometers are versatile instruments that allow measurement of parameters of the lithographic process by placing a sensor in the pupil of a scatterometer objective or in a plane conjugate to the pupil (these measurements are generally referred to as pupil-based measurements) or by placing a sensor in an image plane or in a plane conjugate to the image plane (in this case, these measurements are generally referred to as image-based or field-based measurements). Such scatterometers and associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, which are incorporated herein by reference in their entirety. The scatterometer described above can measure the grating using light from soft x-rays and visible to the near IR wavelength range.

[0082] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, reconstruction methods can be applied to the measured signals to reconstruct or calculate the properties of the grating. For example, such a reconstruction can be performed by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measured results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from an actual target.

[0083] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer MT, radiation emitted by a radiation source is directed onto a target and reflected or scattered radiation from the target is directed to a spectrometer detector which measures the spectrum of the specularly reflected radiation (i.e. measures the intensity as a function of wavelength). From this data, the structure or profile of the target which produced the detected spectrum can be reconstructed, for example by rigorous coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra.

[0084] In a third embodiment, the scatterometer MT is an ellipsometer. An ellipsometer allows the parameters of a lithography process to be determined by measuring the scattered radiation for each polarization state. Such a metrology device emits polarized light (such as linear, circular or elliptical) by using, for example, appropriate polarization filters in the illumination section of the metrology device. A source suitable for the metrology device may also provide polarized radiation. Various embodiments of existing ellipsometers are described in U.S. patent applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110 and 13 / 891,410, which are incorporated herein by reference in their entirety.

[0085] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring a reflection spectrum and / or an asymmetry in the detection configuration, the asymmetry being related to the degree of the overlap. The two (usually overlapping) grating structures may be applied in two different layers (not necessarily continuous layers) and may be formed at substantially the same position on the wafer. The scatterometer may have a symmetrical detection configuration such as described in co-owned patent application EP1,628,164A, so that any asymmetry is clearly distinguishable. This provides a direct way of measuring misalignment in the gratings. Other examples for measuring the overlay error between two layers comprising a periodic structure when the target passes through the asymmetry measurement of the periodic structure may be found in PCT patent application publication number WO 2011 / 012624 or in US patent application US 20160161863, which are incorporated herein by reference in their entirety.

[0086] Other parameters of interest may be focus and dose. Focus and dose may be determined simultaneously by scatterometry (or alternatively by scanning electron microscopy), as described in U.S. Patent Application US2011-0249244, which is incorporated herein by reference in its entirety. A single structure may be used that has a unique combination of critical dimension and sidewall angle measurements for each point in the focus energy matrix (FEM, also called focus exposure matrix). If these unique combinations of critical dimension and sidewall angle are available, then focus and dose values ​​may be uniquely determined from these measurements.

[0087] The metrology target may be the entirety of a composite grating, which is formed by a lithography process, primarily in a resist, but may also be formed after, for example, an etching process. Typically, the pitch and line width of the structures in the grating are largely determined by the measurement optics (particularly the NA of the optics) in order to be able to capture the diffraction orders from the metrology target. As indicated earlier, the diffraction signal may be used to determine the offset (also referred to as 'overlap') between two layers, or may be used to reconstruct at least part of the original grating produced by the lithography process. This reconstruction may be used to provide guidance on the quality of the lithography process, and may be used to control at least part of the lithography process. The target may have smaller sub-segments, which are configured to mimic the size of a functional part of the design layout in the target. Due to the sub-segments, the behavior of the target will be more similar to the functional part of the design layout, so that the overall process parameter measurement better resembles the functional part of the design layout. The target may be measured in an underfill mode or an overfill mode. In the underfill mode, the measurement beam generates a spot that is smaller than the overall target. In the overfill mode, the measurement beam generates a spot that is larger than the overall target. In this overfill mode, it is also possible to measure different targets simultaneously and thus determine different processing parameters simultaneously.

[0088] The overall measurement quality of the lithography parameters using a specific target is at least partially determined by the measurement scheme used to measure the lithography parameters. The term "substrate measurement scheme" may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement scheme is an optical measurement based on diffraction, the one or more parameters measured may include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the radiation orientation relative to the pattern on the substrate, etc. One of the criteria for selecting the measurement scheme may be, for example, the sensitivity of one of the measurement parameters to process variations. More examples are described in U.S. patent application US2016-0161863 and published U.S. patent application US 2016 / 0370717A1, which are incorporated herein by reference in their entirety.

[0089] A topography measurement system, a level sensor or a height sensor that can be integrated in a lithographic apparatus is arranged to measure the topography of a substrate (or wafer). A map of the topography of the substrate (also referred to as a height map) can be generated from these measurements, which indicates the height of the substrate according to the position on the substrate. The height map can then be used to correct the position of the substrate during the transfer of the pattern onto the substrate so as to provide an aerial image of the pattern forming device in an appropriate focus position on the substrate. It is to be understood that in this context, "height" refers to a dimension (also referred to as the Z axis) that is clearly outside the plane for the substrate. Typically, the level or height sensor performs measurements at a fixed position (relative to its own optical system), and the relative movement between the substrate and the optical system of the level or height sensor results in height measurements at positions across the substrate.

[0090] Examples of level or height sensors LS known in the art are Figure 4 , which only illustrates the operating principle. In this example, the level sensor comprises an optical system comprising a projection unit LSP and a detection unit LSD. The projection unit LSP comprises a radiation source LSO, which provides a radiation beam LSB imparted by a projection grating PGR of the projection unit LSP. The radiation source LSO can be, for example, a narrowband or broadband radiation source (such as a supercontinuum light source), polarized or unpolarized, pulsed or continuous, such as a polarized or unpolarized laser beam. The radiation source LSO can include a plurality of radiation sources with different colors or wavelength ranges, such as a plurality of LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation, but can additionally or alternatively cover UV and / or IR radiation and any wavelength range suitable for reflection from the substrate surface.

[0091] The projection grating PGR is a periodic grating including a periodic structure, which causes the radiation beam BE1 to have a periodically varying intensity. The radiation beam BE1 with periodically varying intensity is directed to a measurement position MLO on a substrate W having an incident angle ANG with respect to an axis (Z axis) perpendicular to the incident substrate surface, the incident angle ANG being between 0 and 90 degrees, typically between 70 and 80 degrees. At the measurement position MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and directed to a detection unit LSD.

[0092] In order to determine the height level at the measuring position MLO, 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 generates a detector output signal which is indicative of the received light, for example indicating the intensity of the received light (such as a photodetector), or representing the spatial distribution of the received intensity (such as a camera). The detector DET may comprise any combination of one or more detector types.

[0093] By means of triangulation techniques the height level at the measurement position MLO can be determined.The detected height level is typically related to the signal intensity measured by the detector DET, which has a periodicity that depends inter alia on the design of the projection grating PGR and the (oblique) angle of incidence ANG.

[0094] The projection unit LSP and / or the detection unit LSD may comprise further optical elements such as lenses and / or mirrors along the path (not shown) of the patterned radiation beam between the projection grating PGR and the detection grating DGR.

[0095] In an embodiment, the detection grating DGR may be omitted and the detector DET may be placed where the detection grating DGR is located. This configuration provides a more direct detection of the image of the projection grating PGR.

[0096] In order to effectively cover the surface of the substrate W, the 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.

[0097] For example, various height sensors of the general type are disclosed in US7265364 and US7646471, both of which are incorporated herein by reference. A height sensor using UV radiation rather than visible or infrared radiation is disclosed in US2010233600A1, which is incorporated herein by reference. In WO2016102127A1 (which is incorporated herein by reference), a compact height sensor is described that uses a multi-element detector to detect and identify the position of a grating image without the need for a detection grating.

[0098] In the manufacture of complex devices, typically many lithographic patterning steps are performed to form functional features in successive layers on a substrate. Therefore, a key aspect of the performance of a lithographic apparatus is the ability to correctly and accurately place the applied pattern with respect to features laid down in a previous layer (either by the same apparatus or by a different lithographic apparatus). For this purpose, a substrate is provided with one or more sets of marks. Each mark is a structure whose position can be measured later using a position sensor (typically an optical position sensor). The position sensor may be referred to as an "alignment sensor" and the mark may be referred to as an "alignment mark".

[0099] The lithographic apparatus may include one or more (e.g., multiple) alignment sensors, by which the positions of alignment marks disposed on the substrate can be accurately measured. The alignment (or position) sensor 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 a current lithographic apparatus is based on a self-referencing interferometer described in US6961116. For example, as disclosed in US2015261097A1, various enhancements and modifications of position sensors have been developed. The contents of all of these publications are incorporated herein by reference.

[0100] Figure 5 is a schematic block diagram of an embodiment of a known alignment sensor AS, such as described, for example, in US6961116, which is incorporated herein by reference. A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is steered by steering optics onto a mark, such as a mark AM located on a substrate W, as an illumination spot SP. In this example, the steering optics comprise a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP, at which the mark AM is illuminated, may be slightly smaller than the width of the mark itself.

[0101] Radiation diffracted by the mark AM is collimated (in this example, via the objective lens OL) into an information-carrying beam IB. The term "diffraction" 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) causes the beam IB to interfere with itself, after which the beam is received by a photodetector PD. In the event that more than one wavelength is created by the radiation source RSO, additional optics (not shown) may be included to provide separate beams. If desired, the photodetector may be a single element, or it may comprise several pixels. The photodetector may comprise an array of sensors.

[0102] The steering optics comprising a spot mirror SM in this example may also be used 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 (which is not essential for the measurement but improves the signal-to-noise ratio).

[0103] The intensity signal SI is supplied to the processing unit PU. By a combination of optical processing in block SRI and computational processing in unit PU, values ​​of the X and Y position on the substrate relative to the reference system are output.

[0104] A single measurement of the type illustrated only fixes the position of the mark within a specific range corresponding to one pitch of the mark. Coarse measurement techniques are used in conjunction with this to identify which period of the sine wave is the period that contains the marked position. The same process can be repeated at different wavelengths at coarser and / or finer levels to increase accuracy and / or robustly detect the mark regardless of the material the mark is made of and the material on and / or below the location where the mark is set. The wavelengths can be optically multiplexed and demultiplexed so as to be processed simultaneously, and / or they can be multiplexed by time or frequency division.

[0105] In this example, the alignment sensor and the spot SP remain stationary while the substrate W is moving. The alignment sensor can therefore be rigidly and accurately mounted to the reference system while effectively scanning the mark AM in a direction opposite to the direction of movement of the 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) measures the position of a substrate support (not shown). In an embodiment, one or more (alignment) marks are provided on the substrate support. Measuring the position of the mark provided on the substrate support allows the position of the substrate support determined by the position sensor to be calibrated (e.g., relative to a frame to which the alignment system is connected). Measuring the position of the alignment mark provided on the substrate allows the position of the substrate relative to the substrate support to be determined.

[0106] The measurement tool MT (such as the scatterometer, position measurement system or topography measurement system mentioned above) can use the radiation origin from the radiation source to perform the measurement. The radiation properties used by the measurement tool MT may affect the type and quality of the measurement that may be performed. The radiation frequency used for measurement may affect the size of the feature that may be interrogated by the radiation, and may affect the way different materials interact with the radiation. For some applications, it may be advantageous to use multiple radiation frequencies to measure the substrate. For example, broadband radiation can be used, which may be supercontinuum radiation. Multiple different frequencies may be able to propagate, illuminate and / or scatter the measurement target without interfering with other frequencies or with minimal interference. Therefore, for example, different frequencies can be used to obtain more and more various measurement data at the same time. Different radiation frequencies may also be able to interrogate and discover different properties of the measurement target. Broadband radiation can also be used for measurement tools MT, such as, for example, level sensors, alignment mark measurement systems, scattering measurement tools or inspection tools. The broadband radiation source may be a supercontinuum source. In some instances, the broadband output radiation can be selectively filtered to substantially remove one or more frequencies and / or frequency bands from the output radiation. This may be done, for example, to obtain filtered output radiation comprising one or more narrowband radiation regions of interest. Selective filtering may provide an adjustable radiation source. The radiation may be electromagnetic radiation.

[0107] Generating high-quality broadband radiation may be difficult. One option for generating broadband radiation (such as broadband electromagnetic radiation) is to use a nonlinear frequency broadening effect. In order to obtain a significant nonlinear effect, a high radiation intensity may be required. High radiation can be achieved in an optical fiber. The optical fiber may have an elongated dimension including an optical axis, and the cross-section may be substantially constant along the optical axis. Radiation may be coupled into the optical fiber. The radiation may propagate through the optical fiber along the elongated dimension. The radiation may be confined to a small space inside the optical fiber, for example, mainly in the core of the optical fiber. Due to its ability to confine radiation to a small area, the optical fiber may be suitable for creating a localized high radiation intensity in a portion of the optical fiber. However, the high radiation intensity may damage the optical fiber material and / or the optical fiber structure. Damage to the optical fiber may cause the optical performance of the optical fiber to degrade, which may result in a reduction in the life of the optical fiber.

[0108] To address the issue of radiation-induced damage, hollow core optical fibers can be used to generate broadband radiation. Hollow core optical fibers can be designed so that most of the radiation coupled into the optical fiber is confined within the hollow core. Thus, the interaction of radiation with the optical fiber material is reduced, which may result in reduced damage to the optical fiber material.

[0109] Microstructures can be included in hollow core optical fibers, such as hollow cores surrounding optical fibers. Microstructures can control and optimize radiation confinement and guiding properties within optical fibers. Microstructures can form photonic crystal structures to create photonic crystal fibers. For example, the microstructures can include multiple thin-walled features, such as periodic lattices or capillaries, for controlling the confinement and guiding properties of radiation within the hollow core. The thin-walled features can have, for example, a wall thickness ranging between 100 nm and 1000 nm, between 500 nm and 1000 nm, between 100 nm and 500 nm. Specifically, the thin-walled features can have a wall thickness between 100 nm and 300 nm.

[0110] Hollow core photonic crystal fibers (HC-PCFs) can confine radiation primarily within the hollow core. HC-PCFs can guide radiation as transverse modes along the fiber axis, which can be located in a central region along the elongated dimension of the fiber. The hollow core can be filled with a gas mixture that, when interacting with the high intensity radiation coupled into the fiber, undergoes a nonlinear broadening effect to generate broadband output radiation.

[0111] An example microstructure includes a single ring structure in which a hollow core is surrounded by a single ring of capillaries. The capillaries can be thin-walled tubes parallel to the optical axis of the optical fiber. The thin walls of the capillaries can cause interference effects that can be used to control mode confinement within the optical fiber, thereby creating a photonic crystal fiber.

[0112] Radiation guidance within a hollow core optical fiber may be sensitive to changes in the internal microstructure of the optical fiber. Unwanted or unexpected changes in radiation confinement and guidance in a hollow core optical fiber may have a negative impact on the properties of the output radiation. Changes in radiation confinement and guidance may produce one or more of damage to the optical fiber, reduced performance of the optical fiber, and reduced life of the optical fiber. One type of feature that may affect the radiation behavior within the optical fiber is the force applied to the optical fiber. The force applied to the optical fiber may introduce stress into the optical fiber. Stress within the optical fiber (e.g., stress in the microstructure) may in turn lead to increased sensitivity to damage and / or change the radiation confinement within the optical fiber. An example of a force that may be applied to the optical fiber is a situation where the optical fiber is mounted in a mounting arrangement. The mounting arrangement may apply a clamping force to keep the optical fiber in a desired position. The desired position may, for example, involve a coupling element for coupling radiation into and / or from the optical fiber. The mounting arrangement may be in physical contact with a portion of the optical fiber, for example, for controlling the position of the portion of the optical fiber. The mounting arrangement may, for example, be used to promote efficient coupling of radiation into and / or out of the optical fiber. Therefore, the mounting arrangement may be found at one or both ends of the optical fiber.

[0113] Forces applied to the optical fiber by the installation arrangement may introduce stresses in the optical fiber material, which may affect the optical fiber performance. Greater applied forces may introduce greater stresses and may have a greater negative impact on the optical fiber performance. After the magnitude of the force, the hollow core optical fiber may be sensitive to the distribution of the force. Specifically, asymmetric stresses introduced in the optical fiber may have a negative impact on the optical fiber performance. Asymmetric stresses may be introduced by an asymmetric installation arrangement, such as an arrangement that uses a sleeve or adhesive to position the optical fiber. Asymmetric forces may also be applied by an installation arrangement in which the optical fiber is contacted by sharp edges and / or twisted parts. Asymmetric stress distribution may result in one or more of the following: reduced optional transmission through the optical fiber, mode scrambling of the guided modes in the optical fiber, and increased damage and reduced life of the optical fiber. The effects of mode scrambling may be stronger for higher radiation frequencies. Therefore, it is desirable to obtain a symmetrical stress distribution to reduce the negative impact of the installation arrangement on the hollow core optical fiber.

[0114] Figure 6 A known example arrangement of an optical fiber 102 positioned in a mounting arrangement 104 is depicted. The illustrated optical fiber has a protective coating 106 applied around the outer layer of the optical fiber. The coating 106 may be stripped from a first portion of the optical fiber positioned in the mounting arrangement, for example to enable better coupling of radiation into the optical fiber. A second portion of the mounting arrangement retains the polymer coating 106. Adhesive 108 has been inserted into the area where the optical fiber 102 is received by the mounting arrangement to attach the optical fiber and secure it in place in the mounting arrangement 104. The adhesive 108 may apply an asymmetric force distribution to the optical fiber 102. Example asymmetric force distribution in Figure 7 , which depicts forces F1 to F6 applied to the hollow core optical fiber 102. The forces F1 to F6 are shown as being applied by the adhesive 108. The forces F1 to F6 have an uneven distribution around the optical fiber 102 and are unequal in magnitude, resulting in an overall asymmetry in the total force applied to the optical fiber 102.

[0115] An example of the effects of uneven force distribution is Figure 8 , which depict example beam profiles for two different force distributions. The left figure shows the beam profile of the collimated output radiation of the optical fiber for a mounting arrangement with a uniformly distributed force applied to the optical fiber. The right figure shows the beam profile of the collimated output radiation of the optical fiber for a mounting arrangement with an uneven force distribution applied.

[0116] In order to make the force application around the optical fiber 102 uniform, a protective coating 106 can be applied around the outer layer of the hollow core optical fiber. The protective coating 106 can be, for example, a polymer coating. However, in some instances, the use of a polymer or other material coating is not suitable for the application. For example, when the optical fiber 102 is used, organic components in the adhesive, polymer or other material may be out-gased. This may cause gaseous residues to be released into the immediate environment of the optical fiber. The gaseous residues may be irradiated, which may cause impurities to be added to the material surrounding the hollow core of the optical fiber 102. These impurities can be located on or near the inner surface of the optical fiber material and can reduce the damage threshold of the optical fiber.

[0117] Methods and apparatus are described herein for mounting optical fibers with uniform force distribution to reduce stress-induced losses and / or mode scrambling within hollow core optical fibers. To mitigate the potential negative outgassing effects described above, the methods and apparatus are configured for use with bare optical fibers, that is, optical fibers without a protective coating 106. The inventors have recognized that the presence of microstructures within an optical fiber may affect the fiber's response to the force distribution. Therefore, it is proposed to provide a force distribution that matches the distribution of elements in the microstructure.

[0118] Fig. 9 A schematic diagram of a mounting hollow core optical fiber arrangement 200 is depicted, including a hollow core optical fiber 202 having a microstructure 203 of a hollow core 201 surrounding the optical fiber 202. For the sake of brevity, the hollow core optical fiber 202 may be referred to as the optical fiber 202 throughout the text. A portion of the hollow core optical fiber 202 is located in a receiving area 205 of a mounting arrangement 204 having a plurality of mounting contacts MC. The receiving area is an area around the optical fiber, where the optical fiber is to be placed. Optionally, the cross-section of the receiving area is in a plane perpendicular to the direction of the optical fiber. The mounting contacts MC are located in the receiving area and distributed around the receiving area. The mounting contacts MC may be configured to apply a force 206 to the outer layer of the hollow core optical fiber 202. The mounting contacts MC are positioned around the receiving portion 205 of the mounting arrangement 204 so that they can contact the optical fiber 202. The mounting contacts MC may be distributed around the receiving area 205, wherein the distribution may be designed to correspond to the distribution of features of the microstructure 203 of the optical fiber 202.

[0119] When the distribution of the mounting contacts MC is designed to correspond to the distribution of the microstructure of the optical fiber, this means that the position of the contact point between the mounting contacts and the outer layer of the hollow core optical fiber is based on the position of the microstructure of the optical fiber. In one embodiment, at least one contact point is positioned to align with the position of one of the capillaries, which means that the line from the center to the contact point substantially coincides with the line from the center to the capillary, as seen in the radial direction from the center of the optical fiber. In another embodiment, at least one contact point is positioned between two capillaries of the single ring structure, optionally centered, which means that the line from the center to the contact point is substantially between two lines from the centers of the two capillaries, optionally substantially centered, as seen in the radial direction from the center of the optical fiber.

[0120] Optionally, all contact points are positioned to align with the position of at least part of the capillaries, or are positioned in the center between two capillaries of a single ring structure.

[0121] Optionally, the symmetry of the distribution of the mounting contacts corresponds to the distribution of the microstructure of the optical fiber, which means that the symmetry of the distribution of the mounting contacts is based on at least one symmetry of the microstructure. In one example, the microstructure includes a 60 degree rotational symmetry and a 120 degree rotational symmetry, and the mounting contacts MD may include one of the 60 degree rotational symmetry and the 120 degree rotational symmetry.

[0122] Optionally, the symmetry is reflection symmetry. Optionally, the symmetry is rotational symmetry.

[0123] Optionally, the number of mounting contacts is an integer multiple of the number of rotational symmetries, or the number of rotational symmetries is an integer multiple of the number of mounting contacts. It should be noted that the integer multiple herein refers to one of one, two, three, four, five, etc.

[0124] The inventors have recognised that the performance of the optical fibre 202 may be improved by matching the distribution of mounting contacts MC to the distribution of features of the microstructure 203. This correspondence may result in a correspondence between the locations where the force 206 is applied and the resulting stress introduced into the optical fibre 202. The stress distribution in the optical fibre may then correspond to the features of the microstructure, meaning that a more uniform stress distribution may be achieved compared to a situation where the mounting contacts MC do not correspond to the distribution of features of the microstructure 203. Thus, an advantage of the corresponding distribution of mounting contacts MC and microstructure features 203 may be a reduction in stress-induced losses and / or mode scrambling within the hollow core optical fibre 202. The losses may be losses in optical output power from the optical fibre 202 in part or all of the output frequency range. Mode scrambling may result in a reduction in the quality of the shape and power distribution of the output radiation of the optical fibre 202. This in turn may result in a reduction in the performance of the mounted hollow core optical fibre arrangement 200, for example when used in metrology applications.

[0125] Each of the plurality of mounting contacts MC may apply substantially equal force to the outer layer of the hollow core optical fiber 202. The three arrows indicating applied forces 206 are shown to have the same magnitude, indicating that they apply forces 206 having the same magnitude.

[0126] The locations where the contacts MC are mounted may be equally spaced around the accommodation area 205. Fig. 9 204, where three mounting contacts MC apply force 206 spaced 120 degrees around the circumference of an optical fiber 202 located in a mounting arrangement 204. The equal spacing of the mounting contacts CM can reflect the corresponding equal spacing of features of the microstructure. For example, N equally spaced mounting contacts can correspond to an equally spaced distribution of N features. A feature can include a repeating single element or a cluster of elements, where the cluster is repeated. In another example, N equally spaced mounting contacts CM can correspond to 2N equally spaced features of the microstructure 203. This Fig. 9 , where three mounting contacts CM apply a force 206 to an optical fiber 202 having six microstructure features 203 .

[0127] In one example, a hollow core optical fiber 202 including a microstructure is disposed within a receiving area of ​​a mounting arrangement 204 to form a mounted hollow core optical fiber arrangement 200. The mounting arrangement may have a plurality of mounting contacts configured to apply a force to an outer layer of the hollow core optical fiber 202 at a plurality of contact points. The plurality of mounting contacts may be evenly positioned around the receiving area of ​​the mounting arrangement. The plurality of mounting contacts MC may be configured to apply substantially equal force to an outer layer of the hollow core optical fiber 202 at each of the plurality of contact points.

[0128] The distribution of features of microstructure 230 may include one or more symmetries. The symmetry of the locations of mounting contacts CM may correspond to at least one of the one or more symmetries of microstructure 230. Fig. 9 The depicted microstructure 203 includes 120 degrees of rotational symmetry, and Fig. 9 The mounting contact MD also includes 120 degree rotational symmetry. It should be noted that Fig. 9 The depicted microstructure 203 also includes 60 degree rotational symmetry.

[0129] The microstructure of the hollow core optical fiber 202 may include a photonic crystal structure. The optical fiber 202 may be a hollow core photonic crystal fiber (HC-PCF). The microstructure 203 may include a single ring structure 208. The single ring may have a plurality of capillaries surrounding the hollow core 201. Fig.10An example hollow core optical fiber 202 is depicted, including a single ring structure 208 having a plurality of capillaries 210. Surrounding the single ring structure 208 may be a cladding material 212, which may be a matrix material (eg, a glass material).

[0130] The distribution of the capillaries 210 around the hollow core 201 may have a variety of rotational symmetries. In the case where the capillaries are equally spaced around the hollow core, the number of rotational symmetries may be equal to the number of capillaries. Fig.10 (a) depicts a hollow core optical fiber 202 having 6 equally spaced capillaries 210 surrounding the hollow core 201. The equally spaced capillaries may be placed at 60 degree intervals. The mounting contacts MC apply a force 206 at 6 similar substantially equidistant locations. Fig.10 (b) depicts a hollow core optical fiber 202 having five equally spaced capillaries 210 surrounding the hollow core 201. The equally spaced capillaries may be placed at 72 degree intervals.

[0131] In some embodiments, the location of features of microstructure 203 may be aligned with the location of mounting contacts MC of the mounting arrangement. Fig.10 , the mounting contact MC is depicted as being aligned to be positioned in the center between the two capillaries 210 of the single ring structure 208. Another example arrangement may be to align the position of the capillary 210 with the position of the mounting contact MC. This may be optimized to obtain further reductions in stress-induced losses or mode scrambling in the hollow core optical fiber 202. However, alignment of the microstructure 203 with the position of the mounting contact MC is not required. It may be sufficient to have a corresponding distribution of features of the microstructure 203 compared to the mounting contact MC.

[0132] The portion of the hollow core optical fiber 202 that is located within the mounting arrangement 204 can be an end of the optical fiber. The mounted hollow core optical fiber arrangement 200 can include two separate mounting arrangements 204. The first mounting arrangement 204 can hold a first end of the optical fiber 202. The second mounting arrangement 204 can hold a second end of the optical fiber 202. The first end and the second end can be opposite ends of the same hollow core optical fiber 202.

[0133] Fig.11 An example embodiment of a mounted hollow core optical fiber arrangement 200 is depicted. A hollow core optical fiber 202 can be located within a receiving area 205 of a mounting arrangement 204. The mounting arrangement 204 can include a base 214 and a top cover 216. A force 218 can be applied to the top cover 216 of the mounting arrangement 204. The force 218 can be converted by the mounting arrangement into a force applied to the outer layer of the optical fiber 202. The base 214 can include a groove. The space available in the groove can form a portion of the receiving space 205. The groove can be a V-shaped groove, such as Fig.11In alternative embodiments, the grooves may have a polygonal shape, a curved shape, and / or an irregular shape.

[0134] The top cover 216 may also include a groove (not shown) Fig.11 214). The groove can be located on the side of the top cover facing the base so that when the top cover 216 is placed on top of the base 214 in its intended position, the groove in the base 214 can be aligned with the groove in the top cover 216. When the grooves in the top cover 216 and the base 214 are aligned, they can form a receiving area 205 for the hollow core optical fiber 202.

[0135] The receiving area may have a polygonal shape. The polygonal shape may be formed, for example, by a polygonal groove in the base in combination with the top cover. If the top cover includes a groove, the polygonal receiving area may be formed by the aligned grooves of the top cover 216 and the base 214. The polygonal form may be a regular polygonal form, that is, a polygon in which the size of each angle between two adjacent sides is substantially the same. Fig.11 In the embodiment, the grooves in the base and the top cover can be combined to form a regular triangle. Fig.12 Two other example mounting arrangements (a) and (b) are depicted. Fig.12 The mounting arrangements of the present invention each include a top cover 216 having grooves and a base 214 having grooves, wherein the grooves form a substantially regular polygon. In mounting arrangement (a), the grooves are combined to form a substantially regular hexagon. In mounting arrangement (b), the grooves are combined to form a substantially regular pentagon. The regular polygon can accommodate the hollow core optical fiber 202.

[0136] In the above-mentioned accommodation area 205, the mounting contacts may be formed by points or areas on the border of the accommodation area. In the case where the accommodation area has a polygonal shape, each side may include a mounting contact. In the case where the accommodation area has a regular polygonal shape, the mounting contacts may be substantially positioned in the center of each side of the polygon.

[0137] The mounting arrangement 204 can be formed of a material that can be mechanically processed to form at least a portion of the accommodation area 205. The mounting arrangement may include a metal, such as aluminum, brass, or stainless steel. The mounting arrangement 204 may include quartz glass (SiO2). For example, a groove may be etched in the quartz glass to form a portion of the accommodation area 205 of the mounting arrangement 204. The mounting arrangement 204 may include silicon (Si). The mounting arrangement 204 may be formed of a variety of materials. The length of the hollow core optical fiber 202 may be in the range of tens of centimeters to tens of meters. For example, the length of the hollow core optical fiber 202 may be between 10cm and 100m. The hollow core optical fiber length may be between 10cm and 1m. The length of the hollow core optical fiber 202 may be determined based on the application for which the mounted hollow core optical fiber arrangement 200 is used. Specifically, the length may be determined by the spectral requirements of the application for which the hollow core optical fiber 202 is intended to be used.

[0138] Adjustable force

[0139] The mounting arrangement may be configured to apply an adjustable force to the hollow core optical fiber 202 . Fig.13 A mounting arrangement 204 is shown that includes a base 214 and a top cover 216, as described above. When the top cover 216 and the base 214 are aligned, an adjustable force 220 can be applied by pressing them toward each other. The magnitude of the force applied to the mounting arrangement 204 to push the top cover 216 and the base 214 together can be proportional to the strength of the force applied by the mounting contacts on the outer layer of the hollow core optical fiber 202. The force applied to the mounting arrangement can, for example, range between tens of mN to several N. An example range of the force applied to the mounting arrangement 204 can be 10 mN to 10 N.

[0140] An advantage of having a mounting arrangement 204 capable of applying an adjustable force 220 to the outer layer of the installed optical fiber is that the force can be adjusted to improve the optical performance of the hollow core optical fiber 202. If the magnitude of the force applied to the outer layer of the hollow core optical fiber 202 is too high, this may result in stress-induced losses or increased mode scrambling. This in turn may result in a reduced quality output radiation beam. If the force applied to the outer layer of the hollow core optical fiber 202 is too low, the optical fiber 202 may not be properly secured by the mounting arrangement 204. If the optical fiber 202 is not securely mounted in a stable manner, this may result in reduced coupling efficiency of radiation into and / or out of the optical fiber 202. Low clamping force may result in slippage of the optical fiber 202, which in turn may result in radiation coupling losses. It may be possible to determine and operate the installed optical fiber arrangement 200 using a maximum allowable force. This maximum allowable force may be determined as a force with the highest magnitude that can achieve low-loss, high modal purity radiation transmission. The maximum tolerable force may be a balance between the risk of the optical fiber 202 slipping or moving in the mounting arrangement 204 at too low a force and degradation of optical performance at too high a force. Both low losses and high modal purity may be determined to perform better than a predetermined threshold. The maximum tolerable force may depend on the system and / or application in which the optical fiber 202 is used. For example, the maximum tolerable force may be determined based on one or more of modal quality, average power spectrum variation, polarization, etc.

[0141] The force may be applied to the mounting arrangement 204 by a structure including a spring loaded screw. The spring in the structure may be adjusted to control the amount of force applied by the structure to the mounting arrangement 204. The force applied by the spring loaded screw may be adjusted manually, or may be set electronically. Electronic setting of the force may include setting a target magnitude of the force, and causing the control system to adjust the spring loaded screw until the target magnitude is achieved. To achieve the target force magnitude, the control system may, for example, include a sensor, or may be calibrated to correlate the screw position with the corresponding force.

[0142] The force may be applied to the mounting arrangement 204 by the electrical arrangement. The electrical arrangement may be configured to adjust the force applied by the mounting contacts MC to the outer layer of the hollow core optical fiber 202. The force may be adjusted by adjusting the electric field. In an example embodiment, the electrical arrangement may include a first plate located on a first side of the mounting arrangement 204. The electrical arrangement may also include a second plate located on a second side of the mounting arrangement 204. The first plate and the second plate may be formed of conductive materials so that when a field is applied between the first plate and the second plate, the plates attract each other. This may be achieved by the accumulation of opposite charges on the opposing plates.

[0143] The second plate can be opposite to the first plate such that at least a portion of the mounting arrangement 204 is located between the first plate and the second plate. The portion located between the first plate and the second plate may include a receiving area. The first side and the second side of the mounting arrangement 204 may correspond to the sides of the base 214 and the top cover 216 of the mounting arrangement 204, respectively, such that when the first plate and the second plate are pulled toward each other, the base 214 and the top cover 216 are pressed together.

[0144] The force may be applied to the mounting arrangement 204 by a magnetic arrangement. The magnetic arrangement may be configured to adjust the force applied by the mounting arrangement 204 by applying a magnetic field. The magnetic arrangement may include a first magnet on a first side of the mounting arrangement 204, and may include a second magnet on a second side of the mounting arrangement. In some instances, both magnets may be magnets with adjustable magnetic fields. In other instances, one of the magnets may have an adjustable magnetic field, while the other magnet may be a magnet with a constant magnetic field. The magnets may be, for example, electromagnets or permanent magnets. The magnetic arrangement may apply an adjustable force by applying opposite magnetic charges to the first plate and the second plate so that they are attracted toward each other. This may pull the first side of the mounting arrangement toward the second side of the mounting arrangement, where the magnet is located. The first side and the second side may be on opposite sides of the mounting arrangement. A portion of the mounting arrangement including the accommodation area may be located between the first side and the second side. The first side and the second side may be located on the base 214 and the top cover 216 of the mounting arrangement, respectively. When the magnets are attracted together, the base 214 can be pulled toward the top cover 216, thereby exerting a force on the hollow core optical fiber 202 located in the receiving area 205. Adjusting the attractive force between the two magnets can adjust the force applied to the outer layer of the hollow core optical fiber 202.

[0145] The force applied by the base 214 to the top cover 216 can be equal and opposite to the force applied by the top cover 216 to the base 214 of the mounting arrangement. The manner in which the force applied by the top cover is converted to the force applied by the mounting contacts depends on the shape and size of the accommodation area. The shape of the accommodation area can be designed in such a way that the preferred force application is achieved. For example, the length and / or angle of the polygon can be changed to change the ratio of the force applied to the top cover 216 or the base 214 that is converted to the mounting contacts MC.

[0146] As described above, the forces applied by the mounting arrangement 204 to the outer layer of the hollow core optical fiber 202 can be adjusted to reduce stress-induced losses or mode scrambling. The amount of losses and / or mode scrambling within the hollow core optical fiber 202 may be wavelength dependent. This may be particularly relevant in embodiments where the hollow core optical fiber 202 is configured to operate over a broadband wavelength range. The range over which the hollow core optical fiber is configured to function may be referred to as the operating wavelength range of the optical fiber. The operating wavelength range may include radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum. The broadband wavelength range may, for example, include wavelengths from 200 nm to 2000 nm or from 400 nm to 1000 nm.

[0147] The force applied by the mounting contacts can be configured to be adjusted to optimize the performance of at least a portion of the operating wavelength range of the hollow core optical fiber 202. As described above, optimizing performance can refer to adjusting the force applied to the hollow core optical fiber to reduce stress-induced losses and / or mode scrambling. The portion of the operating wavelength that the force adjustment can optimize can be a narrowband wavelength range. The portion can include one or more discrete wavelengths and / or one or more narrow wavelength ranges. The portion can be, for example, an output wavelength of interest for an application in which the hollow core optical fiber 202 is used. In some examples, the portion can include the wavelength of the input radiation coupled into the hollow core optical fiber 202.

[0148] Hollow core fiber 202 can be used for broadband radiation source, as described above. Hollow core fiber 202 can be used, for example, to broaden input radiation to provide broadband output radiation. The broadband output radiation can include input radiation. The input radiation can include a single wavelength, multiple discrete wavelengths, or a narrowband wavelength range. The output radiation can be supercontinuum radiation.

[0149] Fig.14 A schematic overview of a mounted hollow core optical fiber arrangement 200 located within a reservoir 222 is depicted. In order to broaden the input radiation to obtain broadband output radiation, the hollow core of the optical fiber 202 can be filled with a gas mixture 224. In order to provide and control the gas mixture 224 within the hollow core of the optical fiber 202, the optical fiber can be placed in a resealable reservoir 222. The reservoir 222 can have a gas mixture control unit 226 to provide suitable gas conditions within the interior of the reservoir so that broadband radiation is generated. The reservoir 222 can include all or one or more portions of the hollow core optical fiber 202. One or more portions of the hollow core optical fiber 202 can include at least an end of the hollow core optical fiber 202, wherein the gas mixture can enter and / or leave the hollow core of the optical fiber 202.

[0150] A radiation source device for providing output radiation is described herein. The radiation source device can receive input radiation from an input radiation source. The radiation source device can include a mounted hollow core fiber arrangement described herein. The input radiation can be coupled into the hollow core fiber 202, the radiation can propagate through the fiber, and the output radiation can be coupled out of the hollow core fiber 202. In order to be able to couple into and out of the hollow core fiber 202, the end of the hollow core fiber can be mounted in a mounting arrangement 204. The radiation source device coupled to a source (coupling the input radiation into the hollow core fiber 202) can form a radiation source.

[0151] The output radiation can be broadband radiation. In order to broaden the input radiation to generate broadband output radiation, the mounted hollow core optical fiber arrangement 200 can be placed in a reservoir for providing a controllable gas mixture. The gas mixture provided in the optical fiber can include a hydrogen component and an additional component. The additional component can be an inert gas. The additional component can include one or more of argon, krypton, neon, helium and xenon. Alternatively or additionally, the additional component can include a molecular gas (e.g., H2, N2, O2, CH4, SF6).

[0152] The hollow core optical fiber 202 may be formed of a glass material. For example, the hollow core optical fiber 202 may be composed of or include any of the following: high purity silica (SiO2) (e.g., F300 material sold by Heraeus Holding AG, Germany); soft glass, such as, for example, lead silicate glass (e.g., SF6 glass sold by SCHOTT AG, Germany); or other special glasses, such as, for example, chalcogenide glass or heavy metal fluoride glass (also known as ZBLAN glass). Other materials having properties suitable for optical fiber functionality (e.g., substantially transparent to frequencies in the operating range of the optical fiber) may also be used.

[0153] The hollow core optical fiber 202 can be mounted to both the input end and the output end of the hollow core optical fiber 202. The force applied by the mounting arrangement 204 can be adjusted to optimize the performance of different wavelengths (multiple) at the input end and the output end of the optical fiber. For example, the force applied by the mounting arrangement 204 at the input end can be adjusted to optimize the performance of one or more input radiation wavelengths. The force applied by the mounting arrangement 204 at the output end can be adjusted to optimize the performance of one or more wavelengths of output radiation.

[0154] In order to determine the optimal force applied by the mounting arrangement 204 to the mounted optical fiber portion, the adjustable force applied by the mounting arrangement can be adjusted. In order to adjust the adjustable force according to the specific requirements of a particular installed hollow core optical fiber arrangement 200, the adjustment can be performed in use. In use may mean used as part of a radiation source. The output radiation coupled from the hollow core optical fiber 202 can be measured and the quality of the radiation beam can be evaluated in order to adjust the force and determine the optimal force setting.

[0155] A method for installing the hollow core optical fiber 202 into the mounting arrangement 204 will now be described. A portion (e.g., an end) of the hollow core optical fiber 202 can be installed in the receiving area 205 of the mounting arrangement 204. The optical fiber 202 can be installed on both ends by two separate mounting arrangements 204. The mounted hollow core optical fiber arrangement can be placed in a resealable reservoir. The reservoir can be configured to provide a controllable gas mixture to achieve spectral broadening of the input radiation within the hollow core optical fiber 202. The force applied by the mounting contact MC can be adjustable and can be adjusted to obtain optimized performance of the hollow core optical fiber 202. Adjusting the adjustable force can include spectral filtering of the broadband output radiation from the hollow core optical fiber 202. Spectral filtering can select a narrow band of filtered output radiation wavelengths. When the filtered output radiation beam is monitored, the force applied by the mounting arrangement through the mounting contact MC can then be adjusted.

[0156] Adjustment of the force of the filtered portion of the output radiation may be performed for a mounting arrangement that secures the output end of the hollow core fiber 202. The input end of the hollow core fiber 202 may be secured in an adjustable force-adjusted mounting arrangement to optimize performance for input wavelength radiation.

[0157] Due to the remote adjustment possibility, it may be possible to adjust the adjustable force while the hollow core optical fiber 202 is in use within the reservoir.The force may be adjusted within the reservoir, for example by remote control and operation of an electrical arrangement, a magnetic arrangement or a mechanical force arrangement for adjusting the force.

[0158] When the mounted hollow core optical fiber arrangement 200 is in use, the adjustable force can be readjusted. For example, the optical fiber can form part of a broadband radiation source that is configured to operate in an apparatus that sequentially uses different parts of the broadband wavelength range. This can be achieved, for example, by filtering different parts of the output wavelength range in sequence. As the wavelength(s) of interest to the application change, the adjustable force can be readjusted to optimize the performance of those wavelength(s), as described above.

[0159] The mounted hollow core optical fiber arrangement 200 described herein may be used for a broadband radiation source. The broadband radiation source may be used in a metrology arrangement, for example in a metrology tool MT, such as the metrology equipment and / or inspection equipment described above. The radiation source may be used in a lithography apparatus LA. The radiation source may, for example, be used in a metrology arrangement within a lithography apparatus LA. An example of a metrology arrangement within a lithography apparatus LA is Figure 5 Alignment sensor shown.

[0160] A measurement tool MT (such as the scatterometer, topography measurement system or position measurement system mentioned above) may perform measurements using radiation originating from a radiation source. The properties of the radiation used by the measurement tool may affect the type and quality of the measurements that can be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure the substrate, for example broadband radiation may be used. Multiple different frequencies may be able to propagate, illuminate and scatter the measurement target without interfering or with minimal interference to other frequencies. Thus, for example, different frequencies may be used to obtain more measurement data at the same time. Different radiation frequencies may also be able to interrogate and discover different properties of the measurement target. Broadband radiation may be used for a measurement system MT, such as, for example, a level sensor, an alignment mark measurement system, a scattering measurement tool or an inspection tool. The broadband radiation source may be a supercontinuum source.

[0161] Generating high quality broadband radiation (e.g., supercontinuum radiation) may be difficult. One method for generating broadband radiation may be to broaden high power narrowband or single frequency input radiation, for example by utilizing nonlinear high-order effects. The input radiation (which may be generated using a laser) may be referred to as pump radiation. Alternatively, the input radiation may be referred to as seed radiation. In order to obtain high power radiation for the broadening effect, the radiation may be confined to a small region so that strongly localized high intensity radiation is achieved. In these regions, the radiation may interact with the broadening structure and / or material forming the nonlinear medium, thereby creating broadband output radiation. In the high intensity radiation region, different materials and / or structures may be used to achieve and / or improve radiation broadening by providing a suitable nonlinear medium.

[0162] In some embodiments, broadband output radiation is created in a photonic crystal fiber (PCF). In many embodiments, such a photonic crystal fiber has a microstructure around its fiber core that helps confine the radiation traveling through the fiber in the fiber core. The fiber core can be made of a solid material that has nonlinear properties and is capable of generating broadband radiation when high-intensity pump radiation is transmitted through the fiber core. Although it is feasible to generate broadband radiation in a solid core photonic crystal fiber, there may be some disadvantages to using solid materials. For example, if UV radiation is generated in a solid core, the radiation may not appear in the output spectrum of the fiber because the radiation is absorbed by most solid materials.

[0163] In some embodiments, as described below Fig.16 As further discussed, methods and apparatus for broadening input radiation may use an optical fiber to confine the input radiation, and to broaden the input radiation to output broadband radiation. The optical fiber may be a hollow core optical fiber, and may include internal structures to enable efficient guiding and confinement of radiation in the optical fiber. The optical fiber may be a hollow core photonic crystal fiber (HC-PCF), which is particularly suitable for strong radiation confinement, primarily within the hollow core of the optical fiber, thereby achieving high radiation intensity. The hollow core of the optical fiber may be filled with a gas that acts as a broadening medium for broadening the input radiation. Such an optical fiber and gas arrangement may be used to create a supercontinuum radiation source. The radiation input to the optical fiber may be electromagnetic radiation, such as radiation in one or more of the infrared, visible, UV, and extreme UV spectra. The output radiation may consist of or include broadband radiation, which may be referred to herein as white light. The output radiation may be

[0164] Some embodiments relate to new designs of such broadband radiation sources including optical fibers. The optical fiber is a hollow core photonic crystal fiber (HC-PCF). Specifically, the optical fiber can be a hollow core photonic crystal fiber, a type of which includes an antiresonant structure for limiting radiation. Such optical fibers including antiresonant structures are referred to in the art as antiresonant fibers, tubular fibers, single ring fibers, negative curvature fibers, or suppressed coupling fibers. Various different designs of such optical fibers are known in the art. Alternatively, the optical fiber can be a photonic bandgap fiber (HC-PBF, such as a Kagome fiber).

[0165] Various types of HC-PCFs can be designed, each based on a different physical guidance mechanism. Two such HC-PCFs include: hollow core photonic bandgap fiber (HC-PBF) and hollow core antiresonant reflective fiber (HC-ARF). The design and manufacturing details of HC-PCFs can be found in U.S. Patent US2004 / 015085A1 (for HC-PBF) and International PCT Patent Application WO2017 / 032454A1 (for hollow core antiresonant reflective fiber), which are incorporated herein by reference. Fig.17 (a) shows a Kagome optical fiber, including a Kagome lattice structure.

[0166] Examples of optical fibers used as radiation sources are now referred to Fig.15 describe, Fig.15 is a schematic cross-sectional view of an optical fiber OF in a transverse plane. Fig.15 Similar other embodiments of practical examples of optical fibers are disclosed in WO 2017 / 032454 A1.

[0167] The optical fiber OF comprises an elongated body which is longer in one dimension compared to the other two dimensions of the optical fiber OF. This longer dimension may be referred to as the axial direction and may define the axis of the optical fiber OF. The two other dimensions define a plane which may be referred to as a transverse plane. Fig.15 A cross section of the optical fiber OF is shown in this transverse plane (ie perpendicular to the axis), which is labeled xy plane.The transverse cross section of the optical fiber OF may be substantially constant along the fiber axis.

[0168] It will be appreciated that the optical fiber OF has a degree of flexibility and therefore the direction of the axis will not generally be consistent along the length of the optical fiber OF. Terms such as optical axis, transverse cross section, etc. will be understood to refer to a local optical axis, a local transverse cross section, etc. Furthermore, where a component is described as cylindrical or tubular, these terms will be understood to encompass such shapes that may have deformed as the optical fiber OF is flexed.

[0169] The optical fiber OF may have any length, and it is understood that the length of the optical fiber OF may depend on the application. The length of the optical fiber OF may be between 1 cm and 10 m, for example the length of the optical fiber OF may be between 10 cm and 100 cm.

[0170] The optical fiber OF includes: a hollow core COR; a cladding portion surrounding the hollow core COR; and a support portion SP surrounding and supporting the cladding portion. The optical fiber OF can be considered to include a body (including a cladding portion and a support portion SP) having a hollow core COR. The cladding portion includes a plurality of anti-resonance elements for guiding radiation through the hollow core COR. Specifically, the plurality of anti-resonance elements are arranged to limit radiation propagating through the optical fiber OF mainly within the hollow core HC, and to guide the radiation along the optical fiber OF. The hollow core HC of the optical fiber OF can be substantially disposed in a central region of the optical fiber OF, so that the axis of the optical fiber OF can also define the axis of the hollow core HC of the optical fiber OF.

[0171] The cladding portion comprises a plurality of anti-resonance elements for guiding radiation propagating through the optical fiber OF. Specifically, in this embodiment, the cladding portion comprises a single ring of six tubular capillaries CAP. Each of the tubular capillaries CAP acts as an anti-resonance element.

[0172] The capillary CAP may also be referred to as a tube. The cross section of the capillary CAP may be circular, or may have another shape. Each capillary CAP includes a generally cylindrical wall WP, which at least partially defines the hollow core HC of the optical fiber OF and separates the hollow core HC from the capillary cavity CC. It is to be understood that the wall WP may act as an anti-reflection Fabry-Perot resonator for radiation propagating through the hollow core HC (and which may be incident on the wall WP at a grazing angle of incidence). The thickness of the wall WP may be suitable to ensure that the reflection returned to the hollow core HC is generally enhanced, while the transmission into the capillary cavity CC is generally suppressed. In some embodiments, the capillary wall WP may have a thickness between 0.01 and 10.0 μm.

[0173] It is to be understood that as used herein, the term cladding portion is intended to denote the portion of an optical fiber OF used to guide radiation propagating through the optical fiber OF (i.e. the capillary CAP confining said radiation within the hollow core COR). The radiation may be confined in the form of a transverse mode, propagating along the fiber axis.

[0174] The support portion is generally tubular and supports the six capillaries CAP of the cladding portion. The six capillaries CAP are evenly distributed around the inner surface of the inner support portion SP. The six capillaries CAP can be described as being arranged in a generally hexagonal formation.

[0175] The capillary CAPs are arranged so that each capillary does not contact any other capillary CAP. Each of the capillary CAPs is in contact with the inner support portion SP and is spaced apart from adjacent capillary CAPs in the annular structure. This arrangement may be beneficial because it may increase the transmission bandwidth of the optical fiber OF (e.g., relative to an arrangement in which the capillaries are in contact with each other). Alternatively, in some embodiments, each of the capillary CAPs may be in contact with adjacent capillary CAPs in the annular structure.

[0176] The six capillaries CAP of the cladding part are arranged in an annular structure around the hollow core COR. The inner surface of the annular structure of the capillaries CAP at least partially defines the hollow core HC of the optical fiber OF. The diameter d of the hollow core HC (which can be defined as the smallest dimension between the relative capillaries, as indicated by the arrow d) can be between 10 and 1000 μm. The diameter d of the hollow core HC may affect the mode field parameters, impact loss, dispersion, modal diversity and nonlinear properties of the hollow core optical fiber OF.

[0177] In this embodiment, the cladding portion comprises a single ring arrangement of capillaries CAP (acting as anti-resonance elements).Thus, a line in any radial direction from the center of the hollow core HC to the outside of the optical fiber OF passes through no more than one capillary CAP.

[0178] It is to be understood that other embodiments may be provided with different arrangements of anti-resonant elements. These arrangements may include arrangements with multiple anti-resonant element rings and arrangements with nested anti-resonant elements. Fig.15 The illustrated embodiment includes a ring of six capillaries, but in other embodiments, one or more rings including any number of antiresonant elements (e.g., 4, 5, 6, 7, 8, 9, 10, 11, or 12 capillaries) may be disposed in the cladding portion.

[0179] Fig.17 (b) shows a modified embodiment of the HC-PCF discussed above with a single loop of tubular capillaries. Fig.17 In the example of (b), there are two coaxial rings of tubular capillary 21. In order to hold the inner and outer rings of tubular capillary 21, a support tube ST may be included in the HC-PCF. The support tube may be made of silica.

[0180] Fig.15 and Fig.17 The tubular capillaries of the examples of (a) and (b) may have a circular cross-sectional shape. Other shapes are also possible for the tubular capillaries, such as an elliptical or polygonal cross-section. Additionally, Fig.15 and Fig.17 The solid material of the exemplary tubular capillaries of (a) and (b) may include plastic materials such as PMA, glass (such as silica), or soft glass.

[0181] Fig.16 A radiation source RDS for providing broadband output radiation is depicted. The radiation source RDS comprises a pulsed pump radiation source PRS or any other type of source capable of generating short pulses of a desired length and energy level; an optical fiber OF with a hollow core COR (e.g. Fig.15 and a working medium WM (e.g., gas) disposed within the hollow core COR. Fig.16 Medium radiation sources RDS include Fig.15 An optical fiber OF is shown, but in alternative embodiments other types of hollow core optical fibers may be used.

[0182] 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 to broaden it to provide output radiation ORD. The working medium WM is capable of broadening the frequency range of the received input radiation IRD, thereby providing broadband output radiation ORD.

[0183] The radiation source RDS also includes a reservoir RSV. The optical fiber OF is disposed in the reservoir RSV. The reservoir RSV may also be referred to as a housing, a container or an air chamber. The reservoir RSV is configured to contain a working medium WM. The reservoir RSV may include one or more features known in the art for controlling, adjusting and / or monitoring the composition of the working medium WM (which may be a gas) in the reservoir RSV. The reservoir RSV may include a first transparent window TW1. In use, the optical fiber OF is disposed in the reservoir RSV so that the first transparent window TW1 is located near the input end IE of the optical fiber OF. The first transparent window TW1 may form a portion of the wall of the reservoir RSV. The first transparent window TW1 may be transparent at least to the received input radiation frequency, so that the received input radiation IRD (or at least most of it) may be coupled to the optical fiber OF located in the reservoir RSV. It is to be understood that an optical device (not shown) may be provided for coupling the input radiation IRD into the optical fiber OF.

[0184] The reservoir RSV comprises a second transparent window TW2 forming part of a wall of the reservoir RSV. In use, when the optical fiber OF is arranged in the reservoir RSV, the second transparent window TW2 is located near the output end OE of the optical fiber OF. The second transparent window TW2 may be transparent at least to the frequency of the broadband output radiation ORD of the device 120.

[0185] Alternatively, in another embodiment, the two opposite ends of the optical fiber OF may be placed in different reservoirs. The optical fiber OF may include a first end configured to receive input radiation IRD and a second end for outputting broadband output radiation ORD. The first end may be placed in a first reservoir including a working medium WM. The second end section may be placed in a second reservoir, wherein the second reservoir may also include a working medium WM. The operation of the reservoir may be as described above with respect to Fig.16As described. The first reservoir may include a first transparent window configured to be transparent to the input radiation IRD. The second reservoir may include a second transparent window configured to be transparent to the broadband output broadband radiation ORD. The first reservoir and the second reservoir may also include a sealable opening to allow the optical fiber OF to be partially placed in the reservoir and partially placed outside the reservoir so that the gas can be sealed in the reservoir. The optical fiber OF may also include an intermediate section that is not contained in the reservoir. This arrangement using two separate gas reservoirs may be particularly convenient for embodiments in which the optical fiber OF is relatively long (for example, when the length is greater than 1m). It is to be understood that for this arrangement using two separate gas reservoirs, the two reservoirs (which may include one or more features known in the art for controlling, adjusting and / or monitoring the composition of the gas in the two reservoirs) can be considered to provide a device for providing a working medium WM in the hollow core HC of the optical fiber OF.

[0186] In this context, a window may be transparent to 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.

[0187] Both the first TW1 transparent window and the second TW2 transparent window may form a gas seal within the wall of the reservoir RSV so that a working medium WM (which may be a gas) may be contained within the reservoir RSV. It is understood that the gas WM may be contained within the reservoir RSV at a pressure different from the ambient pressure of the reservoir RSV.

[0188] The working medium WM may include: inert gases such as argon, krypton and xenon; Raman active gases such as hydrogen, deuterium and nitrogen; or gas mixtures such as argon / hydrogen mixtures, xenon / deuterium mixtures, krypton / nitrogen mixtures or nitrogen / hydrogen mixtures. Depending on the type of filling gas, nonlinear optical processes can include modulation instability (MI), soliton self-compression, soliton fission, Kerr effect, Raman effect and dispersive wave generation, details of which are described in WO2018 / 127266A1 and US9160137B1 (both incorporated herein by reference). Since the dispersion of the filling gas can be adjusted by changing the working medium WM pressure (i.e., the gas chamber pressure) in the reservoir RSR, the generated broadband pulse dynamics and the associated spectral broadening properties can be adjusted to optimize frequency conversion.

[0189] In one embodiment, the working medium WM may be disposed within the hollow core HC at least during reception of input radiation IRD to generate broadband output radiation ORD. It is to be understood that the gas WM may be completely or partially absent from the hollow core COR while the optical fiber OF does not receive input radiation IRD to generate broadband output radiation.

[0190] In order to achieve frequency broadening, high intensity radiation may be desirable. An advantage of having a hollow core optical fiber OF is that it may achieve high intensity radiation by strong spatial confinement of the radiation propagating through the optical fiber OF, thereby achieving a high localized radiation intensity. The radiation intensity within the optical fiber OF may be high, for example due to a high intensity of the received input radiation and / or due to the strong spatial confinement of the radiation within the optical fiber OF. An advantage of hollow core optical fibers is that they are able to guide radiation over a wider wavelength range than solid core optical fibers, in particular hollow core optical fibers are able to guide radiation in the ultraviolet and infrared ranges.

[0191] An advantage of using a hollow core optical fiber OF may be that most of the radiation guided within the optical fiber OF is confined within the hollow core COR. Therefore, most of the interactions of the radiation within the optical fiber OF occur with the working medium WM, which is arranged within the hollow core HC of the optical fiber OF. Therefore, the broadening effect of the working medium WM on the radiation may be increased.

[0192] The received input radiation IRD may be electromagnetic radiation. The input radiation IRD may be received as pulsed radiation. For example, the input radiation IRD may comprise ultrafast pulses, for example generated by a laser.

[0193] The input radiation IRD may be coherent radiation. The input radiation IRD may be collimated radiation, which may have the advantage of facilitating and improving the efficiency of coupling the input radiation IRD into the optical fiber OF. The input radiation IRD may include a single frequency or a narrow range of frequencies. The input radiation IRD may be generated by a laser. Similarly, the output radiation ORD may be collimated and / or may be coherent.

[0194] The broadband range of the output radiation ORD may be a continuous range, including a continuous range of radiation frequencies. The output radiation ORD may include supercontinuum radiation. Continuous radiation may be useful for use in many applications, such as in measurement applications. For example, a continuous range of frequencies may be used to interrogate a large number of properties. A continuous range of frequencies may, for example, be used to determine and / or eliminate the frequency dependence of the measured properties. The supercontinuum output radiation ORD may include, for example, electromagnetic radiation in the wavelength range of 100 nm to 4000 nm. The broadband output radiation ORD frequency range may be, for example, 400 nm to 900 nm, 500 nm to 900 nm, or 200 nm to 2000 nm. The supercontinuum output radiation ORD may include white light.

[0195] The input radiation IRD provided by the pulsed pump radiation source PRS may be pulsed. The input radiation IRD may include electromagnetic radiation of one or more frequencies between 200nm and 2μm. The input radiation IRD may, for example, include electromagnetic radiation with a wavelength of 1.03μm. The repetition rate of the pulsed radiation IRD may be of the order of 1kHz to 100MHz. The pulse energy may be of the order of 0.1μJ to 100μJ, for example 1 to 10μJ. The pulse duration of the input radiation IRD may be between 10fs and 10ps, for example 300fs. The average power of the input radiation IRD may be between 100mW and several 100W. The average power of the input radiation IRD may, for example, be 20 to 50W.

[0196] The pulsed pump radiation source PRS may be a laser. The spatiotemporal transmission characteristics of such laser pulses transmitted along the optical fiber OF (e.g., their spectral amplitude and phase) can be changed and adjusted by adjusting (pumping) laser parameters, working part WM changes, and optical fiber OF parameters. The spatiotemporal transmission characteristics may include one or more of the following: output power, output mode profile, output time profile, width of the output time profile (or output pulse width), output spectral profile, and bandwidth of the output spectral profile (or output spectral bandwidth). The pulsed pump radiation source PRS parameters may include one or more of the following: pump wavelength, pump pulse energy, pump pulse width, pump pulse repetition rate. The optical fiber OF parameters may include one or more of the following: optical fiber length, size and shape of the hollow core 101, size and shape of the capillary, thickness of the capillary wall surrounding the hollow core. The working part WM (e.g., filling gas) parameters may include one or more of the following: gas type, gas pressure, and gas temperature.

[0197] The broadband output radiation ORD provided by the radiation source RDS may have an average output power of 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 a pulsed broadband output radiation ORD. The broadband output radiation ORD may have a power spectral density of at least 0.1 mW / nm in the entire wavelength band of the output radiation. The power spectral density of the broadband output radiation in the entire wavelength band may be at least 3 mW / nm.

[0198] Further embodiments are disclosed in the subsequent numbered clauses:

[0199] 1. A mounted hollow core optical fiber arrangement comprising:

[0200] A hollow core optical fiber having a microstructure; and

[0201] a mounting arrangement including a plurality of mounting contacts configured to apply a force to an outer layer of a hollow core optical fiber;

[0202] in

[0203] A portion of the hollow core optical fiber is located in a receiving area of ​​the mounting arrangement;

[0204] A plurality of mounting contacts are positioned around the receiving area; and

[0205] The mounting contacts are distributed around the receiving area, the distribution of the mounting contacts corresponding to the distribution of features of the microstructure of the hollow core optical fiber.

[0206] 2. The mounted hollow core optical fiber arrangement of clause 1, wherein each mounting contact of the plurality of mounting contacts is configured to apply substantially equal force to an outer layer of the hollow core optical fiber.

[0207] 3. A mounted hollow core optical fibre arrangement according to any of the preceding clauses, wherein the positions of the plurality of mounting contacts are equally spaced around the receiving area.

[0208] 4. A mounted hollow core optical fibre arrangement according to any preceding clause, wherein the distribution of features of the microstructure comprises a symmetry, and wherein the symmetry of the positions of the plurality of mounting contacts corresponds to the symmetry of the microstructure.

[0209] 5. A mounted hollow core optical fibre arrangement according to any preceding clause, wherein the hollow core optical fibre is a hollow core photonic crystal fibre comprising a single ring structure having a plurality of capillaries surrounding the hollow core.

[0210] 6. A mounted hollow core optical fiber arrangement according to item 5, wherein the capillary distribution in the single ring structure has multiple rotational symmetries, and wherein the number of mounting contacts is an integer multiple of the number of rotational symmetries, or the number of rotational symmetries is an integer multiple of the number of mounting contacts.

[0211] 7. A mounted hollow core optical fibre arrangement according to any of clauses 5 to 6, wherein the number of mounting contacts is equal to the number of capillaries surrounding the hollow core.

[0212] 8. A mounted hollow core optical fibre arrangement according to any preceding clause, wherein the portion of the hollow core optical fibre mounted within the receiving area of ​​the mounting arrangement is an end portion of the hollow core optical fibre.

[0213] 9. A mounted hollow core optical fibre arrangement according to any preceding clause, wherein the force applied by the mounting contacts is adjustable.

[0214] 10. A mounted hollow core optical fiber arrangement according to clause 9, wherein the mounting arrangement comprises a spring loaded screw configured to adjust the force applied by the mounting contact.

[0215] 11. A mounted hollow core optical fiber arrangement according to clause 9, wherein the mounting arrangement comprises an electrical arrangement configured to adjust the force applied by the mounting contacts by applying an electric field.

[0216] 12. A mounted hollow core optical fiber arrangement according to clause 11, wherein the electrical arrangement comprises a first plate on a first side of the mounting arrangement and a second plate on a second side of the mounting arrangement, wherein the receiving area is located between the first side and the second side;

[0217] And wherein the force is configured to be adjusted by adjusting an electric field applied between the first plate and the second plate.

[0218] 13. A mounted hollow core optical fiber arrangement according to clause 9, wherein the mounting arrangement comprises a magnetic arrangement configured to adjust the force applied by the mounting contacts by applying a magnetic field.

[0219] 14. A mounted hollow core optical fiber arrangement according to clause 13, wherein the magnetic arrangement comprises a first magnet on a first side of the mounting arrangement and a second magnet on a second side of the mounting arrangement, wherein the receiving area is located between the first side and the second side;

[0220] And wherein the force is configured to be adjusted by adjusting a magnetic field applied between the first magnet and the second magnet.

[0221] 15. A mounted hollow core optical fibre arrangement according to any of clauses 9 to 14, wherein the force is configured to be adjusted to optimise the performance of the hollow core optical fibre for a predetermined narrow wavelength range.

[0222] 16. A mounted hollow core optical fiber arrangement according to clause 15, wherein the predetermined narrow wavelength range includes the wavelength of a source for providing input radiation to be coupled into the hollow core optical fiber.

[0223] 17. An installed hollow core optical fiber arrangement according to clause 15, wherein the predetermined wavelength range includes at least a portion of an operating wavelength range of the hollow core optical fiber.

[0224] 18. An installed hollow core optical fibre arrangement according to any preceding clause, wherein the hollow core optical fibre is configured to operate over a broadband wavelength range.

[0225] 19. An installed hollow core optical fiber arrangement according to clause 18, wherein the broadband wavelength range includes wavelengths from 200 nm to 2000 nm.

[0226] 20. An installed hollow core optical fibre arrangement according to any of clauses 18 or 19, wherein the broadband wavelength range comprises wavelengths from 400 nm to 1000 nm.

[0227] 21. A mounted hollow core optical fibre arrangement according to any preceding clause, wherein the mounting arrangement comprises a base having a groove forming part of the accommodation area and a top cover configured to cover the base.

[0228] 22. A mounted hollow core optical fiber arrangement according to clause 21, wherein the top cover includes a groove for receiving the hollow core optical fiber, and wherein the top cover groove is aligned with the base groove to form a receiving area.

[0229] 23. A mounted hollow core optical fibre arrangement according to any of clauses 21 or 22, wherein the base groove and the top cover are configured to form a polygonal form when the top cover covers the base.

[0230] 24. A mounted hollow core optical fiber arrangement according to clause 23, wherein each side of the polygonal form comprises a mounting contact.

[0231] 25. A mounted hollow core optical fibre arrangement according to any one of clauses 23 to 24, wherein the polygonal form is a regular polygonal form.

[0232] 26. A mounted hollow core optical fiber arrangement according to any of the preceding clauses, further comprising a reservoir configured to provide a resealable gas seal between an interior of the reservoir and an exterior of the reservoir;

[0233] Wherein the mounted hollow core optical fiber is located within a reservoir; and wherein the reservoir is configured to contain a controlled gas mixture.

[0234] 27. A mounted hollow core optical fibre arrangement according to any preceding clause, comprising a second mounting arrangement, wherein a second portion of the hollow core optical fibre is located within a receiving area of ​​the second mounting arrangement.

[0235] 28. A mounted hollow core optical fiber arrangement comprising:

[0236] A hollow core optical fiber having a microstructure; and

[0237] a mounting arrangement including a plurality of mounting contacts configured to apply a force to an outer layer of the hollow core optical fiber at a plurality of contact points;

[0238] in:

[0239] The hollow core optical fiber is located in a receiving area of ​​the mounting arrangement;

[0240] The plurality of mounting contacts are evenly positioned around a receiving area of ​​the mounting arrangement; and

[0241] The plurality of mounting contacts are configured to apply a substantially equal force to the outer layer of the hollow core optical fiber at each of the plurality of contact points.

[0242] 29. A mounted hollow core optical fiber arrangement according to clause 28, wherein the hollow core optical fiber is a hollow core photonic crystal fiber comprising a single ring including a plurality of capillaries surrounding the hollow core.

[0243] 30. A radiation source device for providing output radiation, comprising:

[0244] A mounted hollow core optical fiber arrangement according to any of clauses 26 to 27, wherein the hollow core optical fiber comprises an input end configured to receive input radiation and an output end configured to provide output radiation;

[0245] The output end of the hollow core optical fiber is located in the accommodating area of ​​the first installation arrangement.

[0246] 31. A radiation source device according to item 30, wherein the output radiation is broadband output radiation, and wherein the hollow core optical fiber is configured to receive the input radiation at an input end, broaden the wavelength range of the input radiation as the radiation propagates through the hollow core optical fiber, and provide broadband output radiation at the output end of the hollow core optical fiber.

[0247] 32. A radiation source apparatus according to any of clauses 30 to 31, wherein the input end of the hollow core optical fiber is located in a receiving area of ​​the second mounting arrangement, the receiving area being configured to receive the input end of the hollow core optical fiber;

[0248] The second mounting arrangement and the input end are located within the interior of the reservoir.

[0249] 33. The radiation source apparatus of clause 32, wherein the first mounting arrangement is configured to apply a first force to the output end, and the second mounting arrangement is configured to apply a second force to the input end;

[0250] wherein the first force is optimized to reduce stress-induced losses or mode scrambling within a narrow range of wavelengths included in the output radiation; and

[0251] The second force is optimized to reduce stress-induced losses or mode scrambling within the input wavelength.

[0252] 34. A method of installing a hollow core optical fiber into an installation arrangement, the method comprising:

[0253] When dependent upon clause 9, there is provided the hollow core optical fiber and mounting arrangement of clauses 9 to 27;

[0254] installing a portion of the hollow core optical fiber into a mounting arrangement;

[0255] providing input radiation into an end section of the hollow core optical fiber;

[0256] Measuring the radiation output from a hollow core fiber to determine stress-induced losses or mode scrambling;

[0257] When measuring radiation output by the optical fiber, the forces applied by the plurality of mounting contacts of the mounting arrangement are adjusted such that stress-induced losses or mode scrambling within the hollow core optical fiber are reduced.

[0258] 35. A metrology arrangement comprising a radiation source device according to any of clauses 30 to 33.

[0259] 36. A metrology device comprising a metrology arrangement according to clause 35.

[0260] 37. An inspection device comprising a metrology arrangement according to clause 35.

[0261] 38. A lithographic apparatus comprising a metrology arrangement according to clause 35.

[0262] Although specific reference is made to "measurement equipment / tool / system" or "inspection equipment / tool / system," these terms may refer to the same or similar types of tools, equipment, or systems. For example, an inspection or measurement equipment including embodiments of the present invention may be used to determine characteristics of structures on a substrate or wafer. For example, an inspection equipment or measurement equipment including embodiments of the present invention may be used to detect defects in a substrate or defects in a structure on a substrate or wafer. In such embodiments, the characteristics of a structure of interest on a substrate may be related to a defect in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate or wafer.

[0263] Although the use of lithographic equipment in the manufacture of ICs may be specifically cited herein, it should be understood that the lithographic equipment described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0264] Although embodiments of the present invention may be specifically referenced herein in the context of lithographic equipment, embodiments of the present invention may be used in other equipment. Embodiments of the present invention may form part of a mask inspection equipment, a metrology equipment, or any equipment that measures or processes objects such as a wafer (or other substrate) or a mask (or other pattern forming device). These equipment may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0265] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0266] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in a manner other than as described. The above description is intended to be illustrative, not restrictive. Therefore, it will be apparent to those skilled in the art that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A mounted hollow core optical fiber arrangement comprising: Hollow core optical fiber with microstructure; as well as a mounting arrangement including a plurality of mounting contacts configured to apply a force to an outer layer of a hollow core optical fiber; in A portion of the hollow core optical fiber is located in a receiving area of ​​the mounting arrangement; A plurality of mounting contacts are positioned around the receiving area; and The mounting contacts are distributed around the receiving area, the distribution of the mounting contacts corresponding to the distribution of features of the microstructure of the hollow core optical fiber such that: The number of the plurality of mounting contacts is an integer multiple of the number of rotational symmetries of the distribution of features of the microstructure of the hollow core optical fiber, or the number of rotational symmetries is an integer multiple of the number of mounting contacts, or at least one of the mounting contacts is positioned to align with the position of one of the features, or At least one of the mounting contacts is positioned substantially equidistantly between two of the features.

2. The mounted hollow core optical fiber arrangement of claim 1, wherein each of the plurality of mounting contacts is configured to apply substantially equal force to an outer layer of the hollow core optical fiber.

3. A mounted hollow core optical fiber arrangement according to claim 1 or 2, wherein the positions of the plurality of mounting contacts are equally spaced around the receiving area.

4. A mounted hollow core optical fiber arrangement according to claim 1 or 2, wherein the distribution of features of the microstructure includes symmetry, and wherein the symmetry of the positions of the plurality of mounting contacts corresponds to the symmetry of the microstructure.

5. A mounted hollow core optical fiber arrangement according to claim 1 or 2, wherein the hollow core optical fiber is a hollow core photonic crystal fiber comprising a single ring structure having a plurality of capillaries surrounding the hollow core.

6. The mounted hollow core optical fiber arrangement of claim 5, wherein the capillary distribution in the single ring structure has multiple rotational symmetries.

7. The mounted hollow core optical fiber arrangement of claim 5, wherein the number of mounting contacts is equal to the number of capillaries surrounding the hollow core.

8. A mounted hollow core optical fiber arrangement according to claim 1 or 2, wherein the portion of the hollow core optical fiber mounted within the receiving area of ​​the mounting arrangement is an end portion of the hollow core optical fiber.

9. A mounted hollow core optical fiber arrangement according to claim 1 or 2, wherein the force applied by the mounting contacts is adjustable.

10. The mounted hollow core optical fiber arrangement of claim 9, wherein the mounting arrangement comprises a spring loaded screw configured to adjust the force applied by the mounting contact.

11. The mounted hollow core optical fiber arrangement of claim 9, wherein the mounting arrangement comprises an electrical arrangement configured to adjust the force applied by the mounting contacts by applying an electric field.

12. The mounted hollow core optical fiber arrangement of claim 11, wherein the electrical arrangement comprises a first plate on a first side of the mounting arrangement and a second plate on a second side of the mounting arrangement, wherein the receiving area is located between the first side and the second side; And wherein the force is configured to be adjusted by adjusting an electric field applied between the first plate and the second plate.

13. The mounted hollow core optical fiber arrangement of claim 9, wherein the mounting arrangement comprises a magnetic arrangement configured to adjust the force applied by the mounting contacts by applying a magnetic field.

14. The mounted hollow core optical fiber arrangement of claim 13, wherein the magnetic arrangement comprises a first magnet on a first side of the mounting arrangement and a second magnet on a second side of the mounting arrangement, wherein the receiving area is located between the first side and the second side; And wherein the force is configured to be adjusted by adjusting a magnetic field applied between the first magnet and the second magnet.

15. The mounted hollow core optical fiber arrangement of claim 9, wherein the force is configured to be adjusted to optimize the performance of the hollow core optical fiber for a predetermined narrow wavelength range.

16. A mounted hollow core optical fibre arrangement according to claim 15, wherein the predetermined narrow wavelength range includes the wavelength of a source for providing input radiation to be coupled into the hollow core optical fibre.

17. The installed hollow core optical fiber arrangement of claim 15, wherein the predetermined wavelength range comprises at least a portion of an operating wavelength range of the hollow core optical fiber.

18. The mounted hollow core optical fiber arrangement of claim 1 or 2, wherein the hollow core optical fiber is configured to operate over a broadband wavelength range.

19. An installed hollow core optical fiber arrangement according to claim 18, wherein the broadband wavelength range comprises wavelengths from 200 nm to 2000 nm.

20. The mounted hollow core optical fiber arrangement of claim 18, wherein the broadband wavelength range includes wavelengths from 400 nm to 1000 nm.

21. A mounted hollow core optical fibre arrangement according to claim 1 or 2, wherein the mounting arrangement comprises a base having a groove forming a part of the accommodation area and a top cover configured to cover the base.

22. The mounted hollow core optical fiber arrangement of claim 21, wherein the top cover comprises a groove for receiving the hollow core optical fiber, and wherein the top cover groove is aligned with the base groove to form a receiving area.

23. The mounted hollow core optical fiber arrangement of claim 21, wherein the base groove and the top cover are configured to form a polygonal form when the top cover covers the base.

24. A mounted hollow core optical fiber arrangement according to claim 23, wherein each side of the polygonal form comprises a mounting contact.

25. The mounted hollow core optical fiber arrangement of claim 23, wherein the polygonal form is a regular polygonal form.

26. The mounted hollow core optical fiber arrangement of claim 1 or 2, further comprising a reservoir configured to provide a resealable gas seal between an interior of the reservoir and an exterior of the reservoir; Wherein the mounted hollow core optical fiber is located within a reservoir; and wherein the reservoir is configured to contain a controlled gas mixture.

27. The mounted hollow core optical fiber arrangement of claim 1 or 2, comprising a second mounting arrangement, wherein a second portion of the hollow core optical fiber is located within a receiving area of ​​the second mounting arrangement.

28. A mounted hollow core optical fiber arrangement comprising: Hollow core optical fiber with microstructure; as well as a mounting arrangement including a plurality of mounting contacts configured to apply a force to an outer layer of the hollow core optical fiber at a plurality of contact points; in: The hollow core optical fiber is located in a receiving area of ​​the mounting arrangement; The plurality of mounting contacts are evenly positioned around a receiving area of ​​the mounting arrangement; and The plurality of mounting contacts are configured to apply a substantially equal force to the outer layer of the hollow core optical fiber at each of the plurality of contact points.

29. A mounted hollow core optical fiber arrangement according to claim 28, wherein the hollow core optical fiber is a hollow core photonic crystal fiber comprising a single ring including a plurality of capillaries surrounding the hollow core.

30. A radiation source device for providing output radiation, comprising: A mounted hollow core optical fiber arrangement according to any one of claims 26 to 27, wherein the hollow core optical fiber comprises an input end configured to receive input radiation and an output end configured to provide output radiation; The output end of the hollow core optical fiber is located in the accommodating area of ​​the first installation arrangement.

31. A radiation source device according to claim 30, wherein the output radiation is broadband output radiation, and wherein the hollow core optical fiber is configured to receive the input radiation at an input end, broaden the wavelength range of the input radiation as the radiation propagates through the hollow core optical fiber, and provide broadband output radiation at the output end of the hollow core optical fiber.

32. The radiation source apparatus of claim 30, wherein the input end of the hollow core optical fiber is located in a receiving area of ​​the second mounting arrangement, the receiving area being configured to receive the input end of the hollow core optical fiber; The second mounting arrangement and the input end are located within the interior of the reservoir.

33. The radiation source apparatus of claim 32, wherein the first mounting arrangement is configured to apply a first force to the output end, and the second mounting arrangement is configured to apply a second force to the input end; wherein the first force is optimized to reduce stress-induced losses or mode scrambling within a narrow range of wavelengths included in the output radiation; and The second force is optimized to reduce stress-induced losses or mode scrambling within the input wavelength.

34. A method of installing a hollow core optical fiber into an installation arrangement, the method comprising: Providing a hollow core optical fiber and mounting arrangement as claimed in any one of claims 9-17, 19-20, 22-25, or providing a hollow core optical fiber and mounting arrangement as claimed in any one of claims 18, 21, 26-27, and wherein the force applied by the mounting contact is adjustable; installing a portion of the hollow core optical fiber into a mounting arrangement; providing input radiation into an end section of the hollow core optical fiber; Measuring the radiation output from a hollow core fiber to determine stress-induced losses or mode scrambling; When measuring radiation output by the optical fiber, the forces applied by the plurality of mounting contacts of the mounting arrangement are adjusted such that stress-induced losses or mode scrambling within the hollow core optical fiber are reduced.

35. A metrology arrangement comprising a radiation source device according to any one of claims 30 to 33.

36. A metrology device comprising a metrology arrangement according to claim 35.

37. An inspection device comprising a metrology arrangement according to claim 35.

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