Radiation source assembly for generating broadband radiation

Abstract

A radiation source assembly for generating broadband radiation. The radiation source assembly includes a gas cell containing a hollow core fiber, the gas cell including an input port configured to receive pump radiation and an output port configured to output broadband radiation, and the hollow core of the gas cell and the hollow core fiber are filled with a gas composition. The radiation source assembly further includes at least one getter provided within the gas cell and at least partially surrounded by the gas composition, the hollow core fiber being configured to receive pump radiation at the input end of the hollow core fiber and to output broadband radiation at the output end of the hollow core fiber.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the priority of European Patent Application Publication No. 23178125.3 filed on June 7, 2023, which is hereby incorporated by reference in its entirety into this specification.

[0002]

[0002] The present invention relates to a radiation source assembly for generating broadband radiation. In particular, the present invention relates to a radiation source assembly including a gas cell enclosing a hollow - core fiber, wherein at least one getter is provided within the gas cell and is at least partially surrounded by a gas composition within the gas cell.

Background Art

[0003]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can project, for example, a pattern (often also referred to as a “design layout” or “design”) in a patterning device (e.g., a mask) onto a layer of radiation - sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004]

[0004] To project a pattern onto a substrate, a lithographic apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that can be formed on the substrate. Typical wavelengths currently in use are 365 nm (i - line), 248 nm, 193 nm, and 13.5 nm. Lithographic apparatuses using extreme ultraviolet (EUV) radiation with wavelengths in the range of 4 - 20 nm, for example 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate compared to, for example, lithographic apparatuses using radiation with a wavelength of 193 nm.

[0005]

[0005] Low k1 lithography may be used to process features having dimensions smaller than the conventional resolution limit of a lithography apparatus. In such a process, the resolution formula may be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optical system of the lithography apparatus, CD is the "critical dimension" (generally the smallest feature size printed, but in this case it is the half-pitch), and k1 is an empirical resolution coefficient. Generally, the smaller k1, the more difficult it becomes to reproduce a pattern on the substrate that resembles the shape and dimensions planned by the circuit designer in order to achieve a particular electrical function and performance. To overcome these difficulties, elaborate fine-tuning steps may be applied to the lithography projection apparatus and / or the design layout. These include, but are not limited to, optimization of NA, customized illumination schemes, use of phase-shift patterning devices, various optimizations of the design layout, such as optical proximity correction (OPC, sometimes called "optical and process correction") or other methods generally defined as "resolution enhancement techniques" (RET) in the design layout. Alternatively, a strict control loop may be used to control the stability of the lithography equipment in order to improve pattern reproducibility at low k1.

[0006]

[0006] In the field of lithography, many measurement systems can be used both inside and outside the lithography apparatus. Generally, such measurement systems may use a radiation source that irradiates a target with radiation and a detection system that is capable of measuring at least one characteristic of a portion of the incident radiation scattered from the target. An example of a measurement system outside the lithography apparatus is an inspection or measuring device that can be used to determine the characteristics of a pattern previously projected onto a substrate by the lithography apparatus. Such an external inspection device may include, for example, a scatterometer. Examples of measurement systems that may be provided inside the lithography apparatus include a topography measuring system (also known as a level sensor), a position measuring system (e.g., an interference device) that determines the position of the reticle or wafer stage, and an alignment sensor that determines the position of alignment marks. These measuring devices can perform measurements using electromagnetic radiation.

[0007]

[0007] Some measurement systems may perform one or more measurements using radiation with a variety of wavelength ranges. This may be made possible, for example, by providing a broadband radiation source such as a supercontinium radiation source. A supercontinium radiation source may include a hollow core fiber, in which broadband radiation is generated through spectral broadening of the received input radiation, which may often be called pump radiation. The spectral broadening process may depend on nonlinear effects, such as the interaction of confined pump radiation with a gas composition / gas mixture that exhibits a substantially nonlinear response.

[0008]

[0008] Assemblies, apparatus and methods for providing broadband radiation with improved output and / or lifetime are described herein. [Overview of the project]

[0009]

[0009] According to one aspect of the present disclosure, a radiation source assembly is provided for generating broadband radiation, the radiation source assembly comprising a gas cell containing a hollow core fiber, the gas cell comprising an input port arranged to receive pump radiation and an output port arranged to output broadband radiation, wherein the gas cell and the hollow core of the hollow core fiber comprise the gas cell and at least one getter provided within the gas cell and at least partially surrounded by the gas composition, the hollow core fiber comprising the gas cell comprising at least one getter comprising at least one getter comprising at least one getter comprising at least one input end of the hollow core fiber and at least partially surrounded by the output end of the hollow core fiber.

[0010]

[0010] At least one getter favorably absorbs moisture and other undesirable compounds (e.g., undesirable residual gases) to provide a clean environment within the gas cell, thereby extending the lifespan of the radiation source assembly.

[0011]

[0011] At least one of the getters may be located in the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the input port, and / or at a distance of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the input end of the hollow core fiber. At least one of the getters may be located in the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the output port, and / or at a distance of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the output end of the hollow core fiber. By selecting the geometric position of the getters to match the maximum flow rate at the input and / or output ends of the hollow core fiber, the capture of unwanted compounds is improved, thereby extending the life of the radiation source assembly.

[0012]

[0012] At least one of the getters may be positioned in the gas cell at a distance of less than 5 mm, preferably less than 2 mm, more preferably less than 1.5 mm from the section of the hollow core fiber where broadband radiation is generated during use. By selecting the geometric position of the getter to coincide with the location in the hollow core fiber where white light is generated, the capture of unwanted compounds is improved, thereby extending the life of the radiation source assembly.

[0013]

[0013] Multiple getters may be provided within the gas cell and at least partially surrounded by the gas composition.

[0014]

[0014] Multiple getters are dispersed at different locations along the hollow core fibers within the gas cell. Dispersing the getter material at multiple locations along the fibers improves the efficiency of maintaining the gas composition (particularly the working gas) in an optimal state throughout the entire life of the gas cell.

[0015]

[0015] The radiation source assembly may include a particle filter provided within the gas cell and at least partially surrounded by the gas composition. The particle filter advantageously collects any suspended silica nanoparticles that may form in the gas cell. Since these silica nanoparticles cause glassy growth and limit the lifespan of the radiation source assembly, the particle filter advantageously extends the lifespan of the radiation source assembly.

[0016]

[0016] The gas cell includes a first channel containing a hollow core fiber and a second channel coupled to the first channel, which provides a feedback path for the gas composition to circulate within the gas cell, with at least one of the getters located within the second channel. This geometric shape of the gas cell advantageously results in an optimized gas flow for purifying the working gas in the gas composition.

[0017]

[0017] A particle filter may be provided in the second channel.

[0018]

[0018] Of at least one getter, the getter may include a zirconium vanadium iron alloy.

[0019]

[0019] Of at least one getter, the getter may include Ca3O4 and / or BaLi4.

[0020]

[0020] Of at least one getter, the getter may include at least one of manganese oxide, silver oxide, and cobalt oxide.

[0021]

[0021] Of at least one getter, the getter may include one or more getter elements, and each of the one or more getter elements includes a porous material and a zeolite crystal. The getter material is embedded in a highly porous medium and also has the function of capturing particles. Thereby, it is not necessary to have a dedicated particle filter for capturing silica nanoparticles.

[0022]

[0022] The pressure of the gas composition may be at least 5 bar, optionally at least 30 bar, optionally at least 60 bar.

[0023]

[0023] The gas composition includes at least one noble gas.

[0024]

[0024] The gas composition may include an operating gas.

[0025]

[0025] The operating gas may include at least one of argon, krypton, neon, and xenon.

[0026]

[0026] The gas composition may include a cooling gas. The cooling gas may include helium and / or neon.

[0027]

[0027] The gas composition may contain a gas component that is less than 4% of the entire gas composition within the hollow core fiber. By providing a getter within the gas cell, this proportion of the gas component can advantageously be maintained without problems of contamination.

[0028]

[0028] The gas component may include hydrogen, at least one isotope of hydrogen (e.g., deuterium and / or tritium), or nitrogen.

[0029]

[0029] The hollow core fiber may be a hollow core photonic crystal fiber. The hollow core photonic crystal fiber may include a single ring of a plurality of capillaries around the hollow core.

[0030]

[0030] The broadband radiation may include supercontinuum radiation.

[0031]

[0031] The broadband radiation may include radiation having wavelengths within the range of 200 nm to 2000 nm.

[0032]

[0032] The radiation source assembly may further include a pump input assembly configured to provide pump radiation to the hollow core fiber.

[0033]

[0033] The pump input assembly may include a pulsed pump laser.

[0034]

[0034] According to another aspect of the present disclosure, a measuring device for determining a characteristic of interest of a structure on a substrate is provided, the measuring device including a radiation source assembly according to any of the embodiments described herein.

[0035]

[0035] According to another aspect of the present disclosure, an inspection device for inspecting a structure on a substrate is provided, the inspection device including a radiation source assembly according to any of the embodiments described herein.

[0036]

[0036] In another aspect of the present disclosure, a lithography apparatus is provided which includes a radiation source assembly according to any embodiment described herein.

[0037]

[0037] According to another aspect of this disclosure, a lithocell is provided which includes a measuring device, an inspection device, or a lithography device as described herein.

[0038]

[0038] Another aspect of the present disclosure provides a method for generating broadband radiation, comprising providing a radiation source assembly according to any embodiment described herein, and providing pump radiation to the input end of a hollow core fiber to generate broadband radiation.

[0039]

[0039] In embodiments in which the gas composition comprises less than 4% of the total gas components in the hollow core fiber, providing may include evacuating the gas cell to a pressure below a predetermined pressure value, saturating the getter with the gas corresponding to the gas components in the gas composition after evacuating, evacuating the gas cell to a pressure below a predetermined pressure value after saturating, and filling the gas cell with the gas composition.

[0040]

[0040] Hereinafter, embodiments of the present invention will be described merely as examples with reference to the attached schematic drawings. [Brief explanation of the drawing]

[0041] [Figure 1] A schematic diagram of a lithography apparatus is shown. [Figure 2] A schematic diagram of a lithographic cell is shown. [Figure 3] This diagram illustrates the coordination between three key technologies for optimizing semiconductor manufacturing, representing holistic lithography. [Figure 4] A schematic diagram of the scantrometer measurement tool is shown. [Figure 5] A schematic diagram of the level sensor measurement tool is shown. [Figure 6]A schematic diagram of the alignment sensor measurement tool is shown. [Figure 7] This shows a schematic example of contamination growth at the output end face of a hollow core fiber after long-term operation. [Figure 8(a)] A schematic diagram of a cross-section of an exemplary hollow core fiber that can be used for broadband generation is shown. [Figure 8(b)] A schematic diagram of the hollow core fiber within the radiation source assembly is shown. [Figure 9] A schematic diagram of the getter placed within the radiation source assembly is shown. [Figure 10] A schematic diagram of multiple getters arranged within the radiation source assembly is shown. [Figure 11] A schematic diagram of a getter placed within the radiation source assembly near the section of the hollow core fiber where broadband radiation is generated is shown. [Figure 12] A schematic diagram of a getter placed within a radiation source assembly, including a gas cell having first and second channels, is shown. [Figure 13] A flowchart of the steps in the method for generating broadband signals is shown. [Figure 14a] This waveform shows the hydrogen pressure inside a gas cell while the gas cell is filled with a hydrogen-containing gas composition, after saturating the getter inside the gas cell with hydrogen. [Figure 14b] This waveform shows the absorption capacity of hydrogen in a gas cell while the gas cell is filled with a hydrogen-containing gas composition, after the getter inside the gas cell has been saturated with hydrogen. [Modes for carrying out the invention]

[0042]

[0041] In this specification, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 to 100 nm).

[0043]

[0042] The terms “reticle,” “mask,” or “patterning device” as used herein may be broadly interpreted to refer to general patterning devices that can be used to provide an incident radiation beam with a patterned cross section corresponding to a pattern to be formed on a target portion of a substrate. In this context, the term “light bulb” may also be used. In addition to conventional masks (transmissive or reflective, binary, phase-shifted, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0044]

[0043] Figure 1 schematically shows a lithography apparatus LA. The lithography apparatus LA includes an illumination system (also called an illuminator) IL configured to adjust a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to precisely position the patterning device MA according to specific parameters, a substrate support (e.g., a wafer table) WT constructed to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to precisely position the substrate support according to specific parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project the pattern applied to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (e.g., including one or more dies).

[0045]

[0044] During operation, the illumination system IL receives the radiant beam from the radiation source SO, for example, via the 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, to guide, shape and / or control the radiation. The illuminator IL may be used to adjust the radiant beam B so that the beam cross-section has a desired spatial distribution and angular intensity distribution in the plane of the patterning device MA.

[0046]

[0045] The term “projection system” PS as used herein should be interpreted broadly to encompass a variety of projection systems, including refractive, reflective, reflective-refracting, anamorphic, magnetic, electromagnetic, and / or electrostatic-optical systems or any combination thereof, as appropriate, due to the exposure radiation used and / or other factors such as the use of immersion liquid or vacuum. When the term “projection lens” is used herein, it may be considered synonymous with the more general term “projection system” PS.

[0047]

[0046] The lithography apparatus LA may be of a type, also known as immersion lithography, in which at least a portion of the substrate may be covered with a liquid with a relatively high refractive index, such as water, to fill the gap between the projection system PS and the substrate W. Further information relating to immersion technology is described in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0048]

[0047] The lithography apparatus LA may be of a type having two or more substrate support WTs (also called a “dual stage”). In such a “multistage” machine, the substrate support WTs may be used in parallel, and / or while a step is being performed to prepare a substrate W located on one substrate support WT for subsequent exposure of the substrate W, another substrate W located on the other substrate support WT may be used to expose a pattern onto the other substrate W.

[0049]

[0048] In addition to the substrate support WT, the lithography apparatus LA may include a measurement stage. The measurement stage is configured to hold sensors and / or cleaning devices. The sensors may be configured to measure the characteristics of the projection system PS or the characteristics of the radiated beam B. The measurement stage may hold multiple sensors. The cleaning devices may be configured to clean parts of the lithography apparatus, such as parts of the projection system PS or parts of the system that supplies the immersion fluid. The measurement stage may move under the projection system PS when the substrate support WT is away from the projection system PS.

[0050]

[0049] During operation, the radiating beam B is incident on a patterning device, for example, a mask MA held on a mask support MT, and is patterned by the pattern (design layout) present on the patterning device MA. After crossing the mask MA, the radiating beam B passes through a projection system PS that focuses the beam onto a target portion C of the substrate W. A second positioner PW and a position measuring system IF can be used to precisely move the substrate support WT to position different target portions C at focused and aligned positions within the path of the radiating beam B, for example. Similarly, a first positioner PM and optionally (not explicitly shown in Figure 1) another position sensor may be used to precisely position the patterning device MA relative to the path of the radiating beam B. The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The illustrated substrate alignment marks P1, P2 occupy dedicated target portions but may be located in the space between target portions. When substrate alignment marks P1 and P2 are located between target portions C, they are known as scribe line alignment marks.

[0051]

[0050] As shown in Figure 2, the lithography apparatus LA may form part of a lithographic cell LC, sometimes called a lithocell or (litho)cluster, which often also includes apparatus for performing pre-exposure and post-exposure processes on the substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, and cooling plates CH and bake plates BK for adjusting the temperature of the substrate W, for example, to adjust the solvent in the resist layer. A substrate handler or robot RO picks up the substrate W from input / output ports I / O1 and I / O2 and moves it between various process apparatuses to deliver the substrate W to the loading bay LB of the lithography apparatus LA. The devices within the lithocell, often collectively called a track, are typically under the control of a track control unit TCU, which itself can be controlled by a monitoring and control system SCS, which can also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0052]

[0051] To ensure that the substrate W exposed by the lithography apparatus LA is exposed accurately and consistently, it is desirable to inspect the substrate to measure the characteristics of the patterned structure, such as overlay errors between subsequent layers, line thickness, and critical dimension (CD). For this purpose, inspection tools (not shown) may be included in the lithocell LC. If errors are detected, especially if the inspection is performed before other substrates W of the same batch or lot are exposed or processed, adjustments may be made to the exposure of subsequent substrates or other process steps to be performed on the substrate W.

[0053]

[0052] An inspection device, which may also be called a measuring device, is used to determine the properties of a substrate W, in particular how the properties of different substrates W change, or how the properties related to different layers of the same substrate W change layer by layer. Alternatively, the inspection device may be constructed to identify defects on the substrate W and may be, for example, part of a lithocell LC, or incorporated into a lithography apparatus LA, or may be a standalone device. The inspection device may measure the properties of a latent image (an image in the resist layer after exposure), or a semi-latent image (an image in the resist layer after a post-exposure bake step PEB), or a developed resist image (with the exposed or unexposed parts of the resist removed), or even an etched image (after a pattern transfer step such as etching).

[0054]

[0053] Typically, the patterning process in a lithography apparatus LA is one of the most critical steps in the process, requiring high precision in dimensionalizing and positioning structures on a substrate W. To ensure this high precision, three systems can be combined as a so-called "holistic" control environment, as schematically shown in Figure 3. One of these systems is the lithography apparatus LA (virtually) connected to a measurement tool MT (second system) and a computer system CL (third system). The essence of such a "holistic" environment is to optimize the coordination between these three systems to strengthen the entire process window and establish a strict control loop to ensure that the patterning performed by the lithography apparatus LA stays within the process window. The process window defines a range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process yields a defined result (e.g., a functional semiconductor device), and typically, within this range, changes in process parameters in the lithography or patterning process are permitted.

[0055]

[0054] The computer system CL can use (part of) the design layout to be patterned to predict which resolution enhancement techniques should be used, and can perform computer lithography simulations and calculations to determine the mask layout and lithography apparatus settings that achieve maximization of the entire process window of the patterning process (indicated by the double-headed arrows on the first scale SC1 in Figure 3). Typically, the resolution enhancement techniques are configured to match the patterning capabilities of the lithography apparatus LA. The computer system CL can also be used to predict whether defects may exist (for example, due to suboptimal processing) by detecting where in the process window the lithography apparatus LA is currently operating (for example, using input from the measurement tool MT) (indicated by the arrow pointing to "0" on the second scale SC2 in Figure 3).

[0056]

[0055] The measurement tool MT can provide input to the computer system CL that enables accurate simulation and prediction, and can provide feedback to the lithography apparatus LA that identifies possible drifts (for example, in the calibration status of the lithography apparatus LA) (indicated by multiple arrows in the third scale SC3 in Figure 3). Different types of measurement tools MT for measuring one or more characteristics related to the lithography apparatus and / or the substrate to be patterned are described below.

[0057]

[0056] In lithography processes, it is desirable to frequently measure the formed structures, for example, for process control and verification. Tools used to perform such measurements are typically called measuring tools (MT). Different types of measuring tools (MT) are known for performing such measurements, including scanning electron microscopes or various forms of scaltrometer measuring tools (MT). A scaltrometer is a general-purpose instrument that enables the measurement of parameters in a lithography process, and by having a sensor on the pupil or conjugate plane of the pupil of the scaltrometer's objective system, measurements are usually performed which are called pupil-based measurements, or by having a sensor on the image plane or conjugate plane of the image plane, measurements are usually performed which are called image or field-based measurements. Such scattrometers and related measurement techniques are further described in U.S. Patent Publication No. 20100328655, U.S. Patent Publication No. 2011102753A1, U.S. Patent Publication No. 20120044470A, U.S. Patent Publication No. 20110249244, U.S. Patent Publication No. 20110026032, or European Patent Publication No. 1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned scattrometers can measure gratings using soft X-rays and light in the visible to near-infrared wavelength range.

[0058]

[0057] In the first embodiment, the scatometer MT is an angle-resolved scatometer. In such a scatometer, a reconstruction method may be applied to the measured signal in order to reconstruct or calculate the properties of the lattice. Such reconstruction may result from, for example, simulating the interaction between scattered radiation and 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 the actual target.

[0059]

[0058] In a second embodiment, the scatorometer MT is a spectrometer MT. In such a spectrometer MT, radiation emitted from a radiation source is guided onto a target, and reflected or scattered radiation from the target is guided to a spectrometer detector to measure the spectrum of specular reflection (i.e., a measurement of intensity as a function of wavelength). From this data, the structure or profile of the target that yields the detected spectrum can be reconstructed, for example, by exact coupled wave analysis and nonlinear regression or comparison with a library of simulated spectra.

[0060]

[0059] In a third embodiment, the scattermeter MT is an elliptic polarizing scattermeter. The elliptic polarizing scattermeter makes it possible to determine the parameters of the lithography process by measuring the scattered radiation for each polarization state. Such a measuring device emits polarized light (such as a straight line, circle, or ellipse) by using a suitable polarizing filter in the illumination section of the measuring device, for example. A radiation source suitable for the measuring device may also provide polarized radiation. Various embodiments of existing elliptic polarization scatromometers are described in U.S. Patent Applications Nos. 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.

[0061]

[0060] In one embodiment of the scatrometer MT, the scatrometer MT is adapted to measure the overlay of two misaligned grids or periodic structures by measuring the asymmetry in the reflectance spectrum and / or the detection configuration, the asymmetry relating to the degree of overlay. The two (typically overlapping) grid structures may be applied to two different layers (not necessarily consecutive layers) and may be formed at substantially the same location on the wafer. The scatrometer may have a symmetric detection configuration such that any asymmetry is clearly distinguishable, as described, for example, in the jointly owned European Patent Application Publication 1,628,164A. This provides a simple method for measuring grid misalignment. Further examples of measuring overlay errors between two layers containing periodic structures, such that the target is measured by the asymmetry of the periodic structure, can be found in the PCT Patent Application International Publication 2011 / 012624 or the U.S. Patent Application Publication 20160161863, which are incorporated herein by reference in their entirety.

[0062]

[0061] Other parameters of interest may be focus and dose. Focus and dose can be determined simultaneously by scantometry (or alternatively by scanning electron microscopy), as described in U.S. Patent Application Publication 2011 / 0249244, which is incorporated herein by reference in whole. A single structure may be used having a unique combination of sidewall angle measurements and critical dimensions for each point of the focus energy matrix (FEM, also called the focus exposure matrix). If these unique combinations of sidewall angles and critical dimensions are available, the values ​​of focus and dose can be uniquely determined from these measurements.

[0063]

[0062] The measurement target may be an assembly of composite gratings, which are mostly formed within the resist by the lithography process, but also formed, for example, after the etching process. Typically, the pitch and linewidth of the grating structure depend heavily on the measurement optics (especially the NA of the optics) so that the diffraction order from the measurement target can be captured. As previously shown, the diffraction signal may be used to determine the shift between two layers (also called "overlay") or to reconstruct at least a portion of the original grating produced by the lithography process. This reconstruction may be used to provide an indication of the quality of the lithography process and may be used to control at least a portion of the lithography process. The target may have smaller subdivisions configured to mimic the dimensions of the functional parts of the design layout within the target. Due to these subdivisions, the target behaves more similarly to the functional parts of the design layout, and as a result, the measurements of the overall process parameters more closely resemble those of the functional parts of the design layout. The target may be measured in unfilled mode or overfilled mode. In unfilled mode, the measurement beam produces a spot smaller than the entire target. In overfill mode, the measurement beam generates a spot larger than the entire target. In such overfill mode, it may be possible to measure different targets simultaneously, thereby determining different processing parameters at the same time.

[0064]

[0063] The overall measurement quality of lithography parameters using a particular target is determined at least in part by the measurement recipe used to measure these lithography parameters. The term “substrate measurement recipe” may include one or more parameters of the measurement itself, one or more parameters of one or more patterns measured, or both. For example, if the measurement used in a substrate measurement recipe is an optical measurement based on diffraction, one or more parameters of the measurement may include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation on the substrate, and the direction of the radiation on the pattern on the substrate. One criterion for selecting a measurement recipe may be, for example, the sensitivity of one of the measurement parameters to process variations. More examples are described in U.S. Patent Application Publication 2016 / 0161863 and U.S. Patent Application Publication 2016 / 0370717A1, which are incorporated herein by reference in their entirety.

[0065]

[0064] A measuring device such as a scatromometer SM1 is shown in Figure 4. The measuring device includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate 6. The reflected or scattered radiation is passed to a spectrometer detector 4, which measures the spectrum 10 of the specularly reflected radiation (i.e., a measurement of intensity In1 as a function of wavelength λ). From this data, the structure or profile that gives rise to the detected spectrum can be reconstructed by a processing unit (PU), for example, by exact coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra as shown at the bottom of Figure 4. Generally, for reconstruction, the general form of the structure is known, some parameters are estimated from knowledge of the process in which the structure was fabricated, and only a few parameters of the structure remain that will be determined from the scatromometer data. Such a scatromometer may be configured as a normal incidence scatromometer or an oblique incidence scatromometer.

[0066]

[0065] In lithography processes, it is desirable to frequently measure the formed structure, for example, for process control and verification. Various tools are known for performing such measurements, including various types of measuring devices such as scanning electron microscopes or scatorometers. Known examples of scatorometers often rely on providing dedicated measurement targets, such as unfilled targets (targets in the form of simple or overlapping gratings in different layers, large enough for the measurement beam to produce a spot smaller than the grating) or overfilled targets (where the illumination spot partially or completely encloses the target). Furthermore, the use of an angle-resolved scatorometer to irradiate an unfilled target, such as a grating, allows for the use of a so-called reconstruction method, in which the interaction between scattered radiation and a mathematical model of the target structure can be simulated, and the properties of the grating can be calculated by comparing the simulation results with the measurement results. The model parameters are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from an actual target.

[0067]

[0066] A scatrometer is a general-purpose instrument that enables the measurement of parameters in a lithography process, and by having a sensor on the pupil or conjugate plane of the pupil of the objective system of the scatrometer, measurements are usually performed which are called pupil-based measurements, or by having a sensor on the image plane or conjugate plane of the image plane, measurements are usually performed which are called image or field-based measurements. Such scatrometers and related measurement techniques are further described in U.S. Patent Application Publication No. 20100328655, U.S. Patent Application Publication No. 2011102753A1, U.S. Patent Application Publication No. 20120044470A, U.S. Patent Application Publication No. 20110249244, U.S. Patent Application Publication No. 20110026032 or European Patent Application Publication No. 1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned scattometer can measure multiple targets from multiple gratings in a single image using soft X-rays and light in the visible to near-infrared wavelength range.

[0068]

[0067] A topography measurement system, level sensor, or height sensor, which may be integrated with a lithography apparatus, is configured to measure the topography of the top surface of a substrate (or wafer). A topographic map of the substrate, also called a height map, can be generated from these measurements, showing the height of the substrate as a function of its position on the substrate. This height map can then be used to correct the position of the substrate during the transfer of a pattern on the substrate in order to provide a spatial image of the patterning device at the appropriate focus position on the substrate. In this context, it will be understood that “height” broadly refers to the out-of-plane dimension relative to the substrate (also called the Z-axis). Typically, a level or height sensor performs measurements at a fixed position (relative to its own optics), and as a result of relative movement between the substrate and the optics of the level or height sensor, height measurements are obtained at multiple locations across the substrate.

[0069]

[0068] An example of a level sensor or height sensor LS known in the art is schematically shown in Figure 5, but this figure only shows the operating principle. In this example, the level sensor includes an optical system, which includes a projection unit LSP and a detection unit LSD. The projection unit LSP includes a radiation source LSO that provides a radiation beam LSB divided by the projection grating PGR of the projection unit LSP. The radiation source LSO may be a narrowband or broadband radiation source such as a polarized or unpolarized pulsed or continuous supercontinuum light source, such as a polarized or unpolarized laser beam. The radiation source LSO may include multiple radiation sources having different color or wavelength ranges, such as multiple LEDs. The radiation source LSO of the level sensor LS is not limited to visible light radiation and may additionally or alternatively include UV and / or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

[0070]

[0069] The projection grating PGR is a periodic grating containing a periodic structure, thereby causing the radiation beam BE1 to have a periodically changing intensity. The radiation beam BE1, whose intensity fluctuates periodically, is guided toward the measurement position MLO on the substrate W with an incident angle ANG of 0 to 90 degrees, typically 70 to 80 degrees, with respect to an axis perpendicular to the incident substrate surface (Z axis). At the measurement position MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and guided toward the detection unit LSD.

[0071]

[0070] To determine the height level at the measurement position MLO, the level sensor further includes a detection system comprising a detection grid DGR, a detector DET, and a processing unit (not shown) for processing the output signal of the detector DET. The detection grid DGR may be identical to the projection grid PGR. The detector DET generates a detector output signal that indicates the received light, for example, the intensity of the received light, like a photodetector, or the spatial distribution of the received intensity, like a camera. The detector DET may include any combination of one or more types of detectors.

[0072]

[0071] The height level at the measurement position MLO can be determined by triangulation techniques. The detected height level is typically related to the signal intensity measured by the detector DET, which has a periodicity that depends particularly on the design of the projection grid PGR and the (oblique) incidence angle ANG.

[0073]

[0072] The projection unit LSP and / or detection unit LSD may include further optical elements such as lenses and / or mirrors along the path of the patterned radiation beam between the projection grid PGR and the detection grid DGR (not shown).

[0074]

[0073] In one embodiment, the detection grid DGR may be omitted, and the detector DET may be placed where the detection grid DGR is located. Such a configuration results in more direct detection of the image of the projection grid PGR.

[0075]

[0074] 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 a measurement area MLO or an array of spots that cover a wider measurement range.

[0076]

[0075] Various types of height sensors are disclosed, for example, in U.S. Patent No. 7,265364 and U.S. Patent No. 7,646471, both of which are incorporated herein by reference. A height sensor that uses UV radiation as an alternative to visible light radiation or infrared radiation is disclosed in U.S. Patent Application Publication No. 2010233600A1, which is incorporated herein by reference. International Publication No. 2016102127A1, which is incorporated by reference, describes a small height sensor that uses a multi-element detector to detect and recognize the position of a grid image without requiring a detection grid.

[0077]

[0076] The position measurement system PMS may include any type of sensor suitable for determining the position of the substrate support WT. The position measurement system PMS may include any type of sensor suitable for determining the position of the mask support MT. The sensor may be an optical sensor such as an interferometer or encoder. The position measurement system PMS may include a combined system of an interferometer and an encoder. The sensor may be another type of sensor such as a magnetic sensor, a capacitive sensor or an inductive sensor. The position measurement system PMS may determine the position relative to a reference, such as a measuring frame MF or a projection system PS. The position measurement system PMS may determine the position of the substrate table WT and / or mask support MT by measuring the position or by measuring the time derivative of the position, such as velocity or acceleration.

[0078]

[0077] A position measurement system (PMS) may include an encoder system. Encoder systems are known, for example, from U.S. Patent Application Publication No. 2007 / 0058173A1, filed September 7, 2006, which is incorporated herein by reference. An encoder system includes an encoder head, a grating, and a sensor. The encoder system can receive a primary radiation beam and a secondary radiation beam. Both the primary and secondary radiation beams originate from the same radiation beam, i.e., the original radiation beam. At least one of the primary and secondary radiation beams is produced by diffracting the original radiation beam through a grating. If both the primary and secondary radiation beams are produced by diffracting the original radiation beam through a grating, the diffraction order of the primary radiation beam must be different from that of the secondary radiation beam. Different diffraction orders are, for example, +1st, -1st, +2nd, and -2nd. The encoder system optically combines the primary and secondary radiation beams into a combined radiation beam. A sensor in the encoder head determines the phase or phase difference of the combined radiation beam. The sensor generates a signal based on phase or phase difference. The signal represents the position of the encoder head relative to the grid. One of the encoder heads and the grid may be located on a substrate structure WT. The other of the encoder heads and the grid may be located on a measurement frame MF or a base frame BF. For example, multiple encoder heads may be located on the measurement frame MF, while the grid is located on the top surface of the substrate support WT. In another example, the grid may be located on the bottom surface of the substrate support WT, and the encoder head may be located below the substrate support WT.

[0079]

[0078] The position measurement system (PMS) may include an interferometer system. Interferometer systems are known, for example, from U.S. Patent No. 6,020,964, filed July 13, 1998, which is incorporated herein by reference. An interferometer system may include a beam splitter, mirrors, a reference mirror, and a sensor. The radiating beam is split by the beam splitter into a reference beam and a measurement beam. The measurement beam propagates to the mirrors, is reflected by the mirrors and returns to the beam splitter. The reference beam propagates to the reference mirrors, is reflected by the reference mirrors and returns to the beam splitter. At the beam splitter, the measurement beam and the reference beam are coupled into a combined radiating beam. The combined radiating beam is incident on a sensor. The sensor determines the phase or frequency of the combined radiating beam. The sensor generates a signal based on the phase or frequency. The signal represents the displacement of the mirror. In one embodiment, the mirror is connected to a substrate support WT. The reference mirror may be connected to a measurement frame MF. In one embodiment, the measurement beam and the reference beam are coupled into a combined emission beam by an additional optical component, rather than by a beam splitter.

[0080]

[0079] In the manufacture of complex devices, typically many lithography patterning steps are performed, thereby forming functional features in continuous layers on a substrate. Therefore, a critical aspect of the performance of a lithography apparatus is its ability to accurately and precisely position the pattern to be applied with respect to features defined in preceding layers (by the same or different lithography apparatus). For this purpose, one or more sets of marks are provided on the substrate. Each mark is a structure whose position can be measured at a later point in time using a position sensor, typically an optical position sensor. The position sensor may be called an “alignment sensor”, and the marks may be called “alignment marks”. The marks may also be called measurement targets.

[0081]

[0080] A lithography apparatus may include one or more alignment sensors capable of accurately measuring the position of alignment marks provided on a substrate. Alignment (or position) sensors can acquire positional information from alignment marks formed on a substrate using optical phenomena such as diffraction and interference. An example of an alignment sensor used in current lithography apparatus is based on a self-referencing interferometer, as described in U.S. Patent No. 6,961,116. Various developments and modifications of position sensors have been developed, for example, as disclosed in U.S. Patent Application Publication No. 2015261097A1. All of the contents of these publications are incorporated herein by reference.

[0082]

[0081] The marks or alignment marks may include a series of bars formed on or inside a layer provided on the substrate, or formed (directly) within the substrate. The bars may be spaced at regular intervals and may function as grid lines so that the marks may be considered as diffraction gratings having a known spatial period (pitch). Depending on the orientation of these grid lines, the marks may be designed to allow measurements of positions along the X axis or along the Y axis (in a substantially perpendicular orientation to the X axis). Marks including bars positioned at +45 degrees and / or -45 degrees with respect to both the X and Y axes may allow combined X and Y measurements to be performed using the technique described in U.S. Patent Application Publication 2009 / 195768A, which is incorporated by reference.

[0083]

[0082] The alignment sensor optically scans each mark with a radiation spot to acquire a periodically fluctuating signal such as a sine wave. The phase of this signal is analyzed to determine the position of the mark, and therefore the position of the substrate relative to the alignment sensor, which is then fixed relative to the reference frame of the lithography apparatus. So-called coarse marks and fine marks relating to different (coarse and fine) mark dimensions may be provided so that the alignment sensor can distinguish different cycles of the periodic signal and distinguish the precise position (phase) within the cycle. Marks of different pitches may also be used for this purpose.

[0084]

[0083] Measuring the position of the marks can also provide information about the deformation of the substrate, for example, if those marks are provided in the form of a wafer grid. Substrate deformation can occur, for example, due to electrostatic clamping of the substrate to a substrate table and / or heating of the substrate when the substrate is exposed to radiation.

[0085]

[0084] Figure 6 is a schematic block diagram of one embodiment of a known alignment sensor AS, such as that described in U.S. Patent No. 6,961,116, which is incorporated by reference. The radiation source RSO provides a radiation beam RB of one or more wavelengths, which is redirected by a redirection optical system, as an illumination spot SP to a mark such as a mark AM located on a substrate W. In this example, the redirection optical system includes a spot mirror SM and an objective lens OL. The illumination spot SP that illuminates the mark AM may have a diameter slightly smaller than the width of the mark itself.

[0086]

[0085] The radiation diffracted by the mark AM is collimated to the information transmission beam IB (through the objective lens OL in this example). The term “diffracted” is intended to include zero-order diffraction (which may be called reflection) from the mark. For example, a self-referencing interferometer SRI of the type disclosed in U.S. Patent No. 6,961,116 above interferes with the beam IB by itself, and the beam is then received by a photodetector PD. If the radiation source RSO produces two or more wavelengths, additional optics (not shown) may be included to provide separate beams. The photodetector may be a single element or may include multiple pixels as needed. The photodetector may include a sensor array.

[0087]

[0086] In this example, the redirection optical system, including the spot mirror SM, can also block the zero-order radiation reflected from the mark, so that the information transmission beam IB contains only the higher-order diffracted radiation from the mark AM (this is not essential for the measurement, but improves the signal-to-noise ratio).

[0088]

[0087] The intensity signal SI is supplied to the processing unit PU. By combining the optical processing in block SRI and the computational processing in unit PU, the X and Y position values ​​on the substrate with respect to the reference frame are output.

[0089]

[0088] A single measurement of the type shown in the illustration only determines the position of the mark within a specific range corresponding to one pitch of the mark. In conjunction with this, a coarser measurement technique is used to identify which period of the sine wave contains the marked position. Regardless of the material on which the mark is made and the material on which the mark is placed above and / or below, the same process may be repeated at coarser and / or finer levels with different wavelengths for improved accuracy and / or robust detection of the mark. Wavelengths may be optically multiplexed and demultiplexed so as to be processed simultaneously, and / or wavelengths may be multiplexed by time division or frequency division.

[0090]

[0089] In this example, the alignment sensor and spot SP remain stationary, while the substrate W moves. Therefore, the alignment sensor can be firmly and accurately mounted to a reference frame while scanning the mark AM in substantially the opposite direction to the movement of the substrate W. The substrate W is controlled in this movement by the mounting of the substrate W to the substrate support and by a substrate positioning system that controls the movement of the substrate support. A substrate support position sensor (e.g., an interferometer) measures the position of the substrate support (not shown). In one embodiment, one or more (alignment) marks are provided on the substrate support. By measuring the position of the marks provided on the substrate support, it is possible to calibrate the position of the substrate support determined by the position sensor (e.g., with respect to the frame to which the alignment system is connected). By measuring the position of the alignment marks provided on the substrate, it is possible to determine the position of the substrate relative to the substrate support.

[0091]

[0090] Measurement and / or inspection tools (also called measuring tools) such as those described above often use radiation to acquire measurement data. Different types of radiation may be used depending on the measurement target and the characteristics to be measured. One of the various characteristics of radiation is the wavelength used to acquire the measurement, because different wavelengths can provide different information about the measurement target. Some measuring tools may use broadband radiation, such as supercontinuum radiation, to allow adjustment and selection of the measurement wavelength that will be measured or used with broadband radiation. Depending on the range of output wavelengths and the characteristics of the broadband source, a finite difference method may be used to obtain broadband radiation. In some implementations for generating broadband radiation, a nonlinear effect can be used to broaden an input radiation (also called pump radiation) over a narrow wavelength range. Various known devices and methods exist for achieving nonlinear broadening. Often, these methods rely on confining the pump radiation to achieve the high intensity required to receive a significant nonlinear effect.

[0092]

[0091] Known methods for confining radiation for nonlinear broadening include confining laser pump radiation within an optical fiber to generate broadband radiation. The laser may be an ultrashort pulse laser (e.g., pico-femtosecond pulses). The nonlinear propagation dynamics of this radiation within the fiber can result in the generation of broadband radiation as a result of soliton self-compression and / or modulation instability. This can be used, for example, to generate supercontinuous radiation spanning the IR-UV wavelength range.

[0093]

[0092] The above method may be used to generate broadband radiation using the nonlinear broadening of a laser pulse (e.g., a femtosecond laser pulse) propagating along a gas-filled hollow core fiber, such as a hollow core photonic crystal fiber (HC-PCF). The gas mixture (also called a gas composition) filling the fiber may contain one or more components, at least one of which is a working gas. The working gas may be a gas that exhibits significant nonlinear effects when interacting with high-intensity radiation. The performance and lifetime of the light source may depend on the composition of the gas mixture filling the fiber.

[0094]

[0093] In this disclosure, two cases of gas compositions are referred to.

[0095]

[0094] In the first case, the radiation source assembly may use a gas cell containing a gas composition of only one or more noble gases, i.e., a gas cell that does not use hydrogen (or any other molecular gas). For example, the working gas may include at least one of argon AR, krypton KR, neon NE, and xenon XE. Such a configuration does not exhibit plasma-related instability and allows the working gas to be used without hydrogen (or any other molecular gas) as a plasma quencher. Here, it is necessary to keep residual reactive gas to a minimum. Examples of impurity concentrations c when argon Ar is used are as follows: cO2 ≤ 2 ppm, cH2O ≤ 3 ppm, no trace hydrogen, cC n H m ≤0.2 ppm, cN2 ≤5 ppm. These values ​​do not take into account gas release from gas cell components, and their levels should be equal to or less than the impurity concentration in the filling working gas.

[0096]

[0095] In the second case, the radiation source assembly may use a gas cell containing a gas composition of one or more noble gases mixed with a plasma quenching gas such as hydrogen (e.g., a mixture of argon, helium, and hydrogen). Such implementations exhibit plasma-related instability and therefore depend on a very specific and carefully adjusted gas mixture of the working gas, cooling gas, and further gas components (plasma quenching gas). A stable plasma can be formed inside the hollow core fiber. Due to the high intensity of the pump input pulses inside the hollow core fiber, each pulse can ionize a small portion of the gas mixture and form a plasma. This ionization can occur as a result of tunnel ionization. The plasma can be ionized while the laser pulse is present. Between laser pulses, the plasma can decay / recombine between pulses. If the plasma mass decays / recombines fast enough between subsequent pulses, no plasma accumulation occurs. However, if the plasma decay / recombination is too slow, some plasma remains when the subsequent laser pulse arrives. The remaining free electrons can be accelerated by subsequent laser pulses, potentially ionizing further neutral atoms. This can lead to exponential growth in plasma density within the fiber. This plasma formation can ultimately lead to strong absorption of the pump laser radiation and the generated broadband radiation. In this case, a molecular gas such as hydrogen is added to the gas composition to quench the plasma accumulation in the gas.

[0097]

[0096] The working gas may include at least one of argon AR, krypton KR, neon NE, and xenon XE. Depending on the type of working gas in the gas composition, the nonlinear optical processes may include modulation instability (MI), soliton self-compression, soliton splitting, Kerr effect, Raman effect, and dispersion wave generation, details of which are described in International Publication No. 2018 / 127266A1 and U.S. Patent No. 9160137B1 (both incorporated herein by reference). Other properties, such as the pressure of the gas mixture inside the fiber, may affect the nonlinear broadening effect. The working gas may be an atomic gas with sufficiently high optical nonlinearity and ionization potential to (1) produce spectral broadening and (2) reduce the overall ionization level to extend the lifetime.

[0098]

[0097] The cooling gas may be a light gas configured to increase the thermal conductivity of the gas composition. The cooling gas may be an atomic gas having sufficiently high thermal conductivity to improve the operation of the radiator assembly at high repetition rates by reducing the thermal effects associated with the white light generation process.

[0099]

[0098] Further gaseous components such as hydrogen or nitrogen (plasma quenching gas) are added to quench the plasma accumulation at the start of the white light phase, thereby solving the observed instability problem described above.

[0100]

[0099] In both the first and second cases described above, the inventors observed that in a closed gas cell, (i) silicon-supported molecules, (ii) H2O, i.e., water remaining in the gas cell as an adsorbed molecule, for example on a metal surface, and (iii) residual gases such as O2, CO2, and H2 in the presence of a photogenerated plasma shorten the lifespan of the radiation source assembly due to the glassy growth phenomenon. Adding hydrogen to the gas composition also results in two undesirable effects: (1) Hydrogen itself plays a significant role in the formation of volatile molecules such as SiH4 or molecules with high surface mobility such as SiHx (where x < 4). These create nucleation centers for glassy growth. (2) Diffusion of hydrogen into certain metal components of the cell can cause changes in material properties and lead to embrittlement.

[0101] [000100] Instead of using hydrogen to solve the instability problem, nitrogen can be added to the gas cell environment. Nitrogen, if used, can result in low-temperature deposition of Si3N4 depending on the availability of reactive species specific to its growth.

[0102] [000101] The inventors observed that increased contamination can occur at the end faces of hollow core fibers and / or at the optical ports of the radiation source assemblies. The inventors observed that clusters of silica nanoparticles form in the early stages of glassy growth. These nanoparticles float within the gas cell until they accumulate at the end faces of the hollow core fibers. The increased contamination appears to occur where the light intensity is highest. In particular, the increased contamination is greater at the output surface of the hollow core fiber than at the output optical ports. The increased contamination also appears to occur where the light is spectrally spread, and in particular, the contamination does not increase significantly on the input surface. Furthermore, the contamination is observed primarily at the output surface of the hollow core fiber and, to a much lower degree, inside the hollow core fiber itself.

[0103] [000102] Contaminants may be generated by the abrasion of silica particles from the windows of the gas cell or the hollow core fiber. The contaminants may undergo a photo-induced process by the broadened and output light from the hollow core fiber, altering their chemical structure and / or crystallizing on the output surface. After a certain period of time during operation (e.g., after a certain dose (J) of laser energy has been transmitted), this contamination results in a degradation of the fiber's performance. This degradation can be caused by glassy growth (GGP): for example, SiO2 growth at the output end of the fiber. x It could be called a structure.

[0104] [000103] The accumulation of these contaminants leads to a reduction in the lifespan of the light source. Increased contamination of GGP and the resulting output surface can protrude into the optical path of the divergent beam. This causes scattering of the output light and therefore leads to a decrease in the output power of the light source. GGP shortens the lifespan of the light source. Because GGP causes light scattering, the performance of the fiber is lost. This can result in, for example, the photon budget required for the sensor not being met after about 200 hours. GGP also causes drift in the light source output / spectral density and mode profile, which, if not resolved, will require frequent recalibration. Therefore, a short fiber lifespan means that the fiber will need to be replaced frequently in the field, which can cause very large machine downtime (several days) per year. This is unacceptable for industrial products.

[0105] [000104] To date, known methods for reducing the concentration of contaminants and preventing their formation have focused on (i) thorough cleaning of the gas cell and the components of the pump input assembly configured to pump radiation into the gas cell, (ii) techniques for manufacturing the hollow core fiber itself, such as techniques for tapering the ends of the hollow core fiber, and (iii) the specific gases used in the gas cell and the concentration of each of those gases.

[0106] [000105] Figure 7 shows a schematic example of increased contamination at the output end face of the HC-PCF after long-term operation.

[0107] [000106] Herein we describe a radiation source assembly that has an improved lifetime when operating as part of a broadband radiation source.

[0108] [000107] This specification provides hollow core fibers for broadband generation. Figure 8(a) shows a cross-section of an exemplary hollow core fiber 800 that can be used for generating broadband radiation. Figure 8(b) shows the hollow core fiber 800 in a radiation source assembly 850. The hollow core fiber 800 may be a photonic crystal fiber of a hollow core (HC-PCF). The hollow core fiber 800 has a hollow core 802 filled with a gas composition. The hollow core fiber 800 is configured to receive pump radiation 810 (e.g., pulsed pump radiation) at the input end 812 of the hollow core fiber 800. The hollow core fiber 800 is further configured to confine and guide the pump radiation through the fiber so that the pump radiation interacts with the gas composition (particularly a working gas) to generate broadband radiation by nonlinear broadening of the pump radiation. The broadened radiation may be provided as broadband output radiation 820 at the output end 814 of the hollow core fiber 800. During propagation, radiation can be confined within the hollow core 802 of the hollow core fiber 800.

[0109] [000108] Now, the elements of the radiation source assembly 850 shown in Figure 8(b) will be described in more detail. The radiation source assembly 850 may include a pump input assembly 830 (e.g., a pulse pump input assembly) for providing pump radiation to the radiation source assembly 850. The pump input assembly 830 may be configured to provide input radiation 810, also called pump radiation, to the hollow core fiber 800. The hollow core 802 of the hollow core fiber 800 may be configured to receive the input radiation 810 from the pump input assembly 830 and broaden it to provide output radiation 820. A gas mixture may enable broadening the frequency range of the received input radiation 810 to provide broadband output radiation 820. The pump input assembly 830 may be configured to receive radiation from an external radiation source or may include a pump radiation source such as a laser or any other type of radiation source that can generate short pulses of radiation having a desired length and energy level.

[0110] [000109] Broadband radiation may include supercontinuum radiation. Supercontinuum radiation may include radiation in the range from ultraviolet (UV) to infrared (IR) radiation. This may be, for example, in the range of 100 nm to 2000 nm, 200 nm to 2000 nm, 200 nm to 1600 nm, or 400 nm to 1600 nm.

[0111] [000110] The input / pump radiation may be pulsed pump radiation. The pump radiation may be a single (pulsed) radiation beam supplied to the optical input. The radiation may be in the range of 400 nm to 2000 nm or in the range of 800 nm to 1600 nm. The pulsed radiation may include radiation of one or more specific wavelengths, e.g., 400 nm, 515 nm, 532 nm, 800 nm, 1030 nm, 1064 nm, 1550 nm and / or 2000 nm. The repetition rate of the pulsed radiation may be in the range of approximately 1 kHz to 100 MHz. The pulse energy may be in the range of approximately 0.1 μJ to 100 μJ, e.g., 1 to 10 μJ. The pulse length of the input radiation may be 10 fs to 10 ps, ​​e.g., 300 fs. The average power of the input radiation may be 100 mW to several hundred watts. The average power of the input radiation may be, e.g., 20 to 50 watts. The pulse pump output may have a pulse output that exceeds the ionization threshold of the gas composition.

[0112] [000111] The hollow core 802 of the hollow core fiber 800 is filled with a gas composition. The hollow core fiber 800 is housed in a gas cell 840 (also called a housing, container, or reservoir). The gas cell 840 may be configured to supply the gas composition to the hollow core fiber 800 when the radiation source assembly 850 is in use. The gas cell 840 is configured to supply and contain the gas composition. The gas cell may include one or more features known in the art for controlling, adjusting and / or monitoring the composition of the gas composition. During use, the hollow core fiber 800 is positioned inside the gas cell 840 such that a first transparent window is located near the input end 812 of the fiber 800. The first transparent window 816 (also called the input port or input optical port) may be transparent to at least the frequencies of the received input radiation so that the received input radiation 810 (or at least a large portion thereof) can be coupled to the hollow core 802 of the fiber 800 located within the gas cell 840. It should be understood that an optical system (not shown) for coupling the input radiation 810 to the optical fiber 800 may be provided. When in use, the output end 814 of the hollow core fiber 800 may be close to the second transparent window 818 (also called the output port or output optical port). The second transparent window 818 may be transparent to at least the frequencies of the broadband output radiation 820 of the radiation source assembly 850.

[0113] [000112] In order to achieve a wider frequency bandwidth, high-intensity radiation is sometimes desirable. An advantage of having a hollow core fiber is that high-intensity radiation can be achieved through strong spatial confinement of radiation propagating through the fiber 800, and localized high radiation intensity can be achieved. Radiation intensity within an optical fiber can be high, for example, due to strong spatial confinement of the received high-intensity input radiation and / or radiation within the hollow core fiber. A hollow core fiber can confine and guide most of the radiation inside the hollow core 802 of the fiber. A hollow core optical fiber 800 may be able to guide radiation with a wider wavelength range than a solid core fiber, and in particular, a hollow core optical fiber can guide radiation in both the ultraviolet and infrared ranges.

[0114] [000113] Here, an exemplary hollow core fiber 800, as shown in Figures 8(a) and 8(b), will be described in more detail. The fiber 800 may include an elongated body that defines the length of the fiber. The length of the fiber is the longer dimension compared to the other two dimensions of the fiber. This longer dimension may be called the axial direction and may define the axis of the hollow core fiber. As shown in Figure 8(a), the other two dimensions of the fiber define a plane which may be called the transverse plane. Figure 8(a) shows a cross-section of the hollow core fiber 800 in this transverse plane (i.e., perpendicular to the axis). The cross-section of the hollow core fiber 800 may be substantially constant along the fiber axis.

[0115] [000114] The hollow core fiber 800 has a certain degree of flexibility, and therefore it will be understood that the axial direction is not generally uniform along the length of the fiber 800. Terms such as optical axis and cross-section will be understood to mean local optical axis, local cross-section, etc. Furthermore, when the component is described as cylindrical or tubular, these terms will be understood to include shapes that the hollow core fiber 800 may deform when bent.

[0116] [000115] The hollow core fiber may have any length, and it will be understood that the length of the fiber 800 may depend on the application. The length of the fiber may be, for example, 1 cm to 10 m. The length of the hollow core fiber 800 may be, for example, 10 cm to 100 cm.

[0117] [000116] A hollow core fiber may include a hollow core 802 surrounded by a cladding portion 804. A support portion may be provided to surround and support the cladding portion 804. A hollow core fiber 800 can be thought of as including a body (including the cladding portion and the support portion SP) having a hollow core 802. A hollow core fiber 800 may include a plurality of anti-resonant elements 806 for inducing radiation through the hollow core 802. In some implementations, the plurality of anti-resonant elements 806 may be configured to confine radiation propagating through the fiber 800 mainly inside the hollow core 802. The anti-resonant elements may guide radiation along the fiber 800. The hollow core 800 may be substantially located in the central region of the fiber 802, thereby the axis of the fiber 800 may also define the axis of the hollow core 802.

[0118] [000117] In some implementations, the anti-resonance element 806 may include multiple capillaries. The capillaries may be formed by multiple capillaries forming a single ring surrounding the hollow core 802. In a particular example, the cladding portion 804 may include a single ring of six tubular capillaries 806 surrounding the hollow core, each of which may function as an anti-resonance element.

[0119] [000118] In some embodiments, the gas composition may consist of only one or more noble gases, i.e., without hydrogen (or any other molecular gas). For example, the working gas may consist of at least one of argon AR, krypton KR, neon NE, and xenon XE. In these embodiments, a getter placed in the gas cell ensures that a clean gas environment is provided within the closed gas cell.

[0120] [000119] In other embodiments, the gas composition may include a working gas, a cooling gas, and further gas components (plasma quenching gas), such as hydrogen. In these embodiments, a getter placed in the gas cell ensures that the partial pressure of the reactive gas is kept below a threshold at which glassy growth significantly accumulates, while maintaining an optimal amount of plasma quenching gas to prevent plasma buildup.

[0121] [000120] The working gas may include at least one of argon AR, krypton KR, neon NE, and xenon XE. The working gas may be a gas that exhibits significant nonlinear effects when interacting with high-intensity radiation. The working gas may be an atomic gas with sufficiently high optical nonlinearity and ionization potential to (1) produce spectral broadening and (2) reduce the overall ionization level to extend the lifetime.

[0122] [000121] The cooling gas may be a light gas configured to increase the thermal conductivity of the gas composition. The cooling gas may be an atomic gas having sufficiently high thermal conductivity to improve the operation of the radiator assembly at high repeat rates by reducing the thermal effects associated with the white light generation process. The cooling gas may contain at least one of helium (He) or neon (Ne). In certain examples, the cooling gas may be helium gas. The cooling gas may constitute 20% to 70% or 20% to 50% of the gas composition.

[0123] [000122] Further gas components (plasma quenching gases) are added to quench the plasma accumulation at the start of the white light phase and resolve the observed instability described above. The further gas components may be less than 4% of the total gas composition in the hollow core fiber 800, optionally less than 2% of the total gas composition, or optionally less than 1% of the total gas composition in the hollow core fiber 800.

[0124] [000123] Further gaseous components may be provided in an amount ranging from 0.001% to 1% of the gas composition. Further gaseous components may be provided in an amount ranging from 0.01% to 1% of the gas composition. Plasma quenching effects can still be achieved by including further gaseous components in a low proportion of the gas composition. If the amount of further gaseous components present in the gas composition becomes too high, the gas composition may become flammable, which can raise safety concerns. The presence of further gaseous components in the gas composition also increases the risk of contamination by impurities. Therefore, it is desirable to keep the percentage of present further gaseous components below the upper threshold. The threshold mentioned above is 1%, but the upper threshold may be set to 2% or 4% depending on the circumstances.

[0125] [000124] Further gaseous components may include hydrogen gas. Further gaseous components may include at least one isotope of hydrogen gas. The isotope of hydrogen gas may include at least one of deuterium and tritium. Further gaseous components may include nitrogen.

[0126] [000125] The following describes various different implementations that may be used to deploy one or more getters within the gas cell 840 such that one or more getters are at least partially surrounded by the gas composition within the gas cell 840.

[0127] [000126] In all of the different implementations described herein, the getter may be a non-evaporative getter that operates at temperatures in the range of 20 to 200°C and requires high temperatures (e.g., in the range of 400°C to 500°C) for activation. An example is a getter containing a Zr-V-Fe alloy. Other similar getters may be selected from intermetallic zirconium systems. In these examples, the getter may be coupled to an induction heating coil or a wire (for conducting current) to allow heating of the getter.

[0128] [000127] In all of the different implementations described herein, the getter may be a non-evaporative getter that can be used without activation after being placed in the gas cell 840, for example the getter may include Ca3O4 (used to capture moisture) and / or BaLi4 (used for N2 and other active gases). In such cases, exposure of the getter to the surrounding environment must be considered to prevent saturation.

[0129] [000128] In all of the different implementations described herein, the getter may be an irreversible getter. For example, the getter may use manganese oxide, silver oxide and / or cobalt oxide (for example, for hydrogen retention) as a capture medium.

[0130] [000129] In all of the different implementations described herein, the getter may comprise one or more getter elements (e.g., beads or pellets), each of which comprises a porous material and a zeolite crystal.

[0131] [000130] It will be understood that the handling of the getter during installation should be carried out under conditions that maintain its absorption properties. If the getter material is in powder form, the getter will be sealed in a gas-permeable casing.

[0132] [000131] In an implementation where multiple getters are placed within the gas cell 840, it will be understood that the multiple getters may be of the same type or different types.

[0133] [000132] In embodiments of the present invention, the evaporative getter is not used directly in the gas cell 840 because it risks altering the optical properties of the optical surface in the optical path.

[0134] [000133] Figure 9 shows a schematic diagram of a getter 902 located within the radiation source assembly 850. In particular, the getter 902 is enclosed by a gas cell 840 and at least partially surrounded by the gas composition within the gas cell 840. The getter 902 may take any of the examples mentioned herein. Although a single getter 902 is shown enclosed within the gas cell 840, it will be understood that multiple getters may be located within the gas cell 840. A particle filter is not shown in Figure 9, but a particle filter may be provided within the gas cell 840 shown in Figure 9.

[0135] [000134] Figure 10 shows a schematic diagram of several getters arranged within the radiation source assembly 850. In embodiments of the present invention, each getter is located within the radiation source assembly 850, outside the path through which radiation travels through the gas cell, but in a location where the gas composition flows during use (e.g., due to thermal effects). The getters may be located in a position where the flow of the gas composition during use is greater than at other locations within the gas cell.

[0136] [000135] As shown in the arrangement in Figure 10, the getter 902a may be positioned in the gas cell 840 at a location that matches the maximum flow of the gas composition in the gas cell toward the input end 812 of the hollow core fiber 800. In particular, the getter 902a is positioned in the gas cell 840 at a distance (x1) of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the input port 816. As shown in Figure 10, distance (x1) is the distance between the getter 902a and the input port 816 in the axial direction. Alternatively or in addition, the getter 902a is positioned in the gas cell 840 at a distance (y1) of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the input end of the hollow core fiber 800. As shown in Figure 10, distance (y1) is the distance between the getter 902a and the outer surface of the cladding portion 804 at the input end of the hollow core fiber 800 in a direction perpendicular to the axial direction.

[0137] [000136] Alternatively, the getter 902b may be located in the gas cell 840 at a position that matches the maximum flow of the gas composition in the gas cell at the output end 814 of the hollow core fiber 800. In particular, the getter 902b is located in the gas cell at a distance (x2) of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the output port 818. As shown in Figure 10, the distance (x2) is the distance between the getter 902b and the output port 818 in the axial direction. Alternatively, the getter 902b is located in the gas cell 840 at a distance (y2) of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the output end 814 of the hollow core fiber. As shown in Figure 10, the distance (y2) is the distance between the getter 902b and the outer surface of the cladding portion 804 at the input end of the hollow core fiber 800 in a direction perpendicular to the axial direction.

[0138] [000137] Although a particle filter is not shown in Figure 10, a particle filter may be provided within the gas cell 840 shown in Figure 10.

[0139] [000138] As shown in the configuration of Figure 11, the getter 902 may be located within the radiation source assembly 850 near section 1102 of the hollow core fiber 800 where broadband radiation is generated during use. That is, the getter 902 is located within the gas cell 840 at a distance (d) of less than 5 mm, preferably less than 2 mm, more preferably less than 1.5 mm from section 1102 of the hollow core fiber 800 where broadband radiation is generated during use. As shown in Figure 11, distance (d) is the distance between the getter 902 and the outer surface of the cladding portion 804 of section 1102 of the hollow core fiber 800 where broadband radiation is generated during use, in a direction perpendicular to the axial direction. Although a particle filter is not shown in Figure 11, a particle filter may be located within the gas cell 840 shown in Figure 11. In Figure 11, a single getter 902 is shown as being enclosed within the gas cell 840, but it will be understood that multiple getters may be placed within the gas cell 840.

[0140] [000139] Figure 12 shows a schematic diagram of a getter 902 located within a radiation source assembly 850, which includes a gas cell 840 having first and second channels. In particular, the gas cell 840 includes a first channel 1210 containing a hollow core fiber 800 and a second channel 1220. The second channel 1220 is coupled to the first channel 1210. In particular, the second channel 1220 is in fluid communication with the first channel 1210. The arrows shown in Figure 12 indicate the gas flow within the gas cell 840. A gas flow exists inside the gas cell 840 because the dissipation process is higher towards the ends of the fiber. As shown in Figure 12, the gas composition flows through the first channel 1210, and the second channel 1220 provides a feedback path for the gas composition to circulate within the gas cell 840. The getter 902 is located within the second channel. The gas cell 840 may also include a particle filter 1202. As shown in Figure 12, the particle filter 1202 may be located within a second channel. The particle filter 1202 may be positioned away from the getter 902 (as shown in Figure 12) to allow for maximum flow rate and highest efficiency. Two shut-off valves 1204a and 1204b, located on either side of the getter 902, can be opened and closed, respectively, to allow and restrict the gas flow. The two shut-off valves 1204a and 1204b can be used to load and operate the getter 902 into the gas cell 840 without interfering with the rest of the gas cell 840. The geometric shape and orientation of the gas cell 840 are such that they result in an optimized gas flow for cleaning the working gas in the gas composition. Although Figure 12 shows a single getter 902 sealed within the gas cell 840, it will be understood that multiple getters may be arranged within the gas cell 840. For example, multiple getters may be provided within the second channel 1220.

[0141] [000140] Optionally, an external heat source may be used to heat a section of the gas cell 840 in order to heat the gas composition sealed within the gas cell 840 and obtain a convective gas flow within the gas cell 840. The external heat source may be controlled to heat one or more sections of the gas cell 840 during periods when white light is not being generated (e.g., during service hours) and / or during periods when white light is being generated. For example, a periodic heating process may partially overlap with a specific duty cycle in which the white light is switched on and off. The flow rate of the gas composition within the gas cell 840 can be controlled by selecting a specific geometric shape of the gas cell 840.

[0142] [000141] In the configurations shown in Figures 9 to 12, if the getter includes one or more getter elements (e.g., beads or pellets), and each of these getter elements includes a porous material and a zeolite crystal, then it may not be necessary to provide a separate particle filter, considering that the getter itself functions to capture particles such as silica nanoparticles.

[0143] [000142] In the configurations shown in Figures 9 to 12, an external heat source may be used to heat a section of the gas cell 840 in order to heat the gas composition enclosed within the gas cell 840. This heat may be generated asymmetrically along the gas cell 840, which may be influenced by the orientation of the gas cell 840 with respect to the direction of gravity.

[0144] [000143] Figure 13 shows a flowchart of an exemplary method 1300 for generating broadband radiation. Method 1300 includes step 1302 of providing a radiation source assembly 850 according to any embodiment described herein. Method 1300 further includes step S1304 of providing pump radiation to the input end 812 of a hollow core fiber 800 to generate broadband radiation, as described herein.

[0145] [000144] In embodiments in which the gas composition in the gas cell 840 includes a further gas component (e.g., hydrogen), the getter provided in the gas cell 840 is not selective for the further gas component (e.g., it absorbs the further gas component together with other trace gases) and can operate at room temperature without thermal activation. Step 1302 of providing the radiation source assembly 850 may include the step of incorporating the further gas component into the getter. These steps are described below with reference to an example in which the further gas component is hydrogen.

[0146] [000145] After the getter is placed inside the gas cell 840, the method 1300 may include evacuating the gas cell 840 to a pressure below a predetermined pressure value (e.g., 1 millibar) (S1352). The predetermined pressure value may be in the range of 0.5 to 10 millibars, optionally 0.5 to 5 millibars.

[0147] [000146] After the gas cell has been evacuated to below a predetermined pressure, method 1300 may include saturating the getter with hydrogen (i.e., a gas corresponding to further gas components in the gas composition) (S1354). For example, to saturate the getter and thus reduce the getter's ability to absorb the plasma quenching gas of the gas composition when the gas composition is supplied into the gas cell 840, the gas cell 840 may be flushed with a gas mixture containing hydrogen (e.g., an Ar / H2 gas mixture) or pure hydrogen. Once the getter is saturated with hydrogen, this flushing can be stopped.

[0148] [000147] After the getter is saturated with hydrogen, method 1300 may include evacuating the gas cell 840 to a pressure below a predetermined pressure value (S1356).

[0149] [000148] The method 1300 may then include filling the gas cell 840 with a gas composition (containing hydrogen as a further gas component) which will be used to generate broadband radiation (S1358).

[0150] [000149] Figure 14a is a waveform showing the hydrogen pressure in the gas cell while the getter in the gas cell is saturated with hydrogen and the gas cell is filled with a hydrogen-containing gas composition, and Figure 14b is a waveform showing the hydrogen absorption capacity of the getter while the getter in the gas cell is saturated with hydrogen and the gas cell is filled with a hydrogen-containing gas composition. As shown in Figures 14a and 14b, when the gas cell 840 is filled with the gas composition (containing hydrogen as a further gas component) in step S1358 due to the saturation of the getter with hydrogen, the hydrogen in the gas composition is not absorbed, thereby maintaining the optimal level of hydrogen in the gas composition.

[0151] [000150] Figures 13, 14(a), and 14(b) illustrate the use of hydrogen as a plasma quenching gas in a gas composition and thus used to saturate the getter, but this is merely an example, and it will be understood that other molecular gases may be used as additional gas components in the gas composition and thus used to saturate the getter.

[0152] [000151] Further embodiments are disclosed in the following list of numbered clauses. 1. A radiation source assembly for generating broadband radiation, A gas cell containing a hollow core fiber, comprising an input port arranged to receive pump radiation and an output port arranged to output broadband radiation, wherein the hollow core of the gas cell and the hollow core fiber is filled with a gas composition, A gas cell provided with at least one getter, and at least partially surrounded by the gas composition. A radiation source assembly comprising a hollow core fiber, arranged to receive pump radiation at the input end of the hollow core fiber and emit broadband radiation at the output end of the hollow core fiber. 2. At least one of the getters is It is located within the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and further optionally less than 1.5 mm from the input port, and / or The radiation source assembly described in Clause 1 is located within a gas cell at a distance of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the input end of a hollow core fiber. 3. At least one of the getters is It is located within the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the output port, and / or A radiation source assembly according to Clause 1 or 2, positioned within a gas cell at a distance of less than 5 mm, optionally less than 2 mm, and further optionally less than 1.5 mm from the output end of a hollow core fiber. 4. The radiation source assembly according to any one of the clauses 1 to 3, wherein at least one of the getters is located in the gas cell at a distance of less than 5 mm, preferably less than 2 mm, more preferably less than 1.5 mm from the section of the hollow core fiber in which broadband radiation is generated during use. 5. A radiation source assembly according to any one of Clauses 1 to 4, wherein the multiple getters are provided within a gas cell and are at least partially surrounded by a gas composition. 6. A radiation source assembly as described in any one of Clauses 1 to 5, wherein multiple getters are dispersed at different locations along the hollow core fiber within the gas cell. 7. A radiation source assembly according to any one of Clauses 1 to 6, comprising a particle filter provided within a gas cell and at least partially surrounded by a gas composition. 8. The gas cell is, A first channel containing a hollow core fiber, A second channel coupled to a first channel, providing a feedback path for the gas composition to circulate within the gas cell, and at least one of the getters is provided within the second channel. A radiation source assembly as described in any one of clauses 1 to 7, including the one specified in any one of clauses 1 to 7. 9. The particle filter is provided within the second channel of the radiation source assembly as described in Clause 8, as it is subject to Clause 7. 10. A radiation source assembly as described in any one of Clauses 1 to 9, wherein at least one of the getters comprises a zirconium-vanadium-iron alloy. 11. A radiation source assembly according to any one of clauses 1 to 10, wherein at least one of the getters comprises Ca3O4 and / or BaLi4. 12. A radiation source assembly according to any one of the clauses 1 to 11, wherein at least one of the getters comprises at least one of manganese oxide, silver oxide, and cobalt oxide. 13. A radiation source assembly according to any one of Clauses 1 to 12, wherein at least one of the getters comprises one or more getter elements, each of which comprises a porous material and a zeolite crystal. 14. A radiation source assembly according to any one of clauses 1 to 13, wherein the pressure of the gas composition is at least 5 bar, optionally at least 30 bar, or optionally at least 60 bar. 15. A radiation source assembly as described in any one of Clauses 1 to 13, wherein the gas composition comprises at least one noble gas. 16. The gas composition is a radiation source assembly as described in any one of clauses 1 to 15, including the working gas. 17. The working gas of the radiation source assembly as described in Clause 14, comprising at least one of argon, krypton, neon, and xenon. 18. A radiation source assembly according to any one of Clauses 1 to 17, wherein the gas composition comprises a cooling gas, the cooling gas optionally comprising at least one of helium and neon. 19. A radiation source assembly as described in any one of Clauses 1 to 18, wherein the gas composition contains less than 4% of the total gas components in the gas composition within the hollow core fiber. 20. A radiation source assembly as described in Clause 19, wherein the gaseous component comprises hydrogen, at least one isotope of hydrogen, or nitrogen. 21. The hollow core fiber is a hollow core photonic crystal fiber, as described in any one of Clauses 1 to 20 of the radiation source assembly. 22. The hollow core photonic crystal fiber is a radiation source assembly as described in Clause 21, comprising a single ring of multiple capillaries around a hollow core. 23. Broadband radiation, including supercontinuum radiation, is a radiation source assembly as described in any one of clauses 1 to 22. 24. Broadband radiation includes radiation having wavelengths in the range of 200 nm to 2000 nm, as described in any one of clauses 1 to 23. 25. A radiation source assembly according to any one of Clauses 1 to 24, further comprising a pump input assembly configured to provide pump radiation to a hollow core fiber. 26. The pump input assembly is a radiation source assembly as described in Clause 25, including a pulsed pump laser. 27. A measuring device for determining the properties of an object of interest of a structure on a substrate, comprising a radiation source assembly as described in any one of clauses 1 to 26. 28. An inspection apparatus for inspecting structures on a substrate, comprising a radiation source assembly as described in any one of clauses 1 to 26. 29. A lithography apparatus including a radiation source assembly as described in any one of clauses 1 to 26. 30. A lysocell comprising the apparatus described in any one of paragraphs 27, 28, or 29. 31. A method for generating broadband radiation, To provide a radiation source assembly as described in any one of clauses 1 to 26, Pump radiation is provided to the input end of a hollow core fiber to generate broadband radiation. A method that includes this. 32. The gas composition contains gas components that make up less than 4% of the total gas composition in the hollow core fiber, and is provided as such. Evaporating the gas cell to a pressure below a predetermined pressure value, After exhaust, the getter is saturated with the gas corresponding to the gas component in the gas composition, After saturation, the gas cell is evacuated to a pressure below a predetermined pressure value. Filling the gas cell with the gas composition and The method described in Article 31, including the method described in Article 31.

[0153] [000152] While this specification may specifically refer to the use of lithography equipment in the manufacture of ICs, it should be understood that the lithography equipment described herein may also have other applications. Other possible applications include the manufacture of integrated optical systems, induction and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and the like.

[0154] [000153] While embodiments of the present invention may be specifically referred to in relation to lithography apparatus, embodiments of the present invention may be used in other apparatuses. Embodiments of the present invention may form part of any apparatus for measuring or processing objects such as mask inspection apparatuses, measuring apparatuses, or wafers (or other substrates) or masks (or other patterning devices). These apparatuses may generally be called lithography tools. Such lithography tools may operate under vacuum or ambient (non-vacuum) conditions.

[0155] [000154] While specific references to the use of embodiments of the present invention in relation to photolithography have been made above, it will be understood that the present invention is not limited to photolithography and may be used in other applications, such as imprint lithography, as the context permits.

[0156] [000155] Although the terms “measuring device / tool / system” or “inspection device / tool / system” are used specifically, these terms may refer to the same or similar types of tools, devices, or systems. For example, an inspection device or measuring device including embodiments of the present invention can be used to determine the characteristics of a structure on a substrate or wafer. For example, an inspection device or measuring device including embodiments of the present invention can be used to detect defects in a substrate or defects in a structure on a substrate or wafer. In such embodiments, the characteristics of interest of a structure on a substrate may relate to defects in the structure, the absence of a particular part of the structure, or the presence of unwanted structures on the substrate or wafer.

[0157] [000156] Although specific embodiments of the present invention have been described above, it will be understood that the present invention may be carried out in ways other than those described above. The above description is illustrative and not intended to be limiting. Accordingly, it will be apparent to those skilled in the art that modifications to the present invention described above can be made without departing from the claims set forth below.

Claims

1. A radiation source assembly for generating broadband radiation, A gas cell containing a hollow core fiber, comprising an input port for receiving pump radiation and an output port for outputting the broadband radiation, wherein the gas cell and the hollow core of the hollow core fiber are filled with a gas composition, A getter provided within the gas cell and at least partially surrounded by the gas composition, A radiation source assembly comprising a hollow core fiber that receives the pump radiation at the input end of the hollow core fiber and outputs the broadband radiation at the output end of the hollow core fiber.

2. The getter among the at least one getter is Displaced within the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and further optionally less than 1.5 mm from the input port, and / or The radiation source assembly according to claim 1, wherein the radiation source assembly is positioned within the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and further optionally less than 1.5 mm from the input end of the hollow core fiber.

3. The getter among the at least one getter is Displaced within the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and optionally less than 1.5 mm from the output port, and / or The radiation source assembly according to claim 1 or 2, wherein the radiation source assembly is positioned within the gas cell at a distance of less than 5 mm, optionally less than 2 mm, and further optionally less than 1.5 mm from the output end of the hollow core fiber.

4. The radiation source assembly according to any one of claims 1 to 3, wherein the getter of at least one of the getters is located in the gas cell at a distance of less than 5 mm, preferably less than 2 mm, more preferably less than 1.5 mm from the section of the hollow core fiber in which broadband radiation is generated during use.

5. The radiation source assembly according to any one of claims 1 to 4, wherein the plurality of getters are provided within the gas cell and are at least partially surrounded by the gas composition.

6. The radiation source assembly according to any one of claims 1 to 5, wherein the plurality of getters are dispersed at different locations along the hollow core fiber within the gas cell.

7. A radiation source assembly according to any one of claims 1 to 6, comprising a particle filter provided within the gas cell and at least partially surrounded by the gas composition.

8. The getter among the at least one getter is a zirconium vanadium iron alloy, Ca ３ O ４ , BaLi ４ A radiation source assembly according to any one of claims 1 to 7, comprising at least one of manganese oxide, silver oxide, and cobalt oxide.

9. The radiation source assembly according to any one of claims 1 to 8, wherein the getter among the at least one getter comprises one or more getter elements, and each of the one or more getter elements comprises a porous material and a zeolite crystal.

10. The radiation source assembly according to any one of claims 1 to 9, wherein the pressure of the gas composition is at least 5 bar, optionally at least 30 bar, and optionally at least 60 bar.

11. The radiation source assembly according to any one of claims 1 to 10, wherein the gas composition comprises at least one noble gas.

12. The radiation source assembly according to any one of claims 1 to 11, wherein the gas composition comprises less than 4% of the total gas components in the hollow core fiber.

13. The radiation source assembly according to claim 12, wherein the gas component comprises hydrogen, at least one isotope of hydrogen, or nitrogen.

14. A measuring device for determining the characteristics of an object of interest of a structure on a substrate, comprising a radiation source assembly according to any one of claims 1 to 13.

15. A method for generating broadband radiation, To provide a radiation source assembly according to any one of claims 1 to 13, The pump radiation is provided to the input end of the hollow core fiber to generate the broadband radiation. A method that includes this.

Images