Radiation source assembly for generating broadband radiation

Abstract

Radiation source assemblies and methods for generating broadband radiation. A radiation source assembly comprises: a solid-core photonic crystal fiber (SC-PCF) having an input end and an output end, wherein the input end is configured to receive a radiation pulse from a pump source; a hollow-core photonic crystal fiber (HC-PCF) filled with a gaseous working medium and arranged to receive the radiation pulse output from the output end of the SC-PCF at an input end of the HC-PCF; and wherein the SC-PCF is configured to broaden a spectrum of the radiation pulse by providing nonlinearity at normal group velocity dispersion, and the HC-PCF is configured to generate broadband radiation by nonlinear interaction of the radiation pulse with the gaseous working medium, and output the broadband radiation at an output end of the HC-PCF.

Description

Cross-references to related applications

[0001] This application claims priority to EP application 23214793.4, filed on December 7, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to a radiation source assembly and method for generating broadband radiation. Background Technology

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

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

[0005] Low-k1 lithography can be used to handle features smaller than the classical resolution limits of lithography apparatuses. In this process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics in the lithography apparatus, CD is the “critical size” (typically the minimum feature size to be printed, but in this case, half a pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to reproduce patterns on the substrate that are similar in shape and size to those planned by the circuit designer for specific electrical functions and performance. To overcome these difficulties, sophisticated fine-tuning steps can be applied to the lithography projection apparatus and / or design layout. These include, for example, (but are not limited to) optimization of NA, custom illumination schemes, the use of phase-shifting patterning devices, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also called “optical and process correction”) in the design layout), or other methods generally defined as “resolution enhancement techniques” (RET). Alternatively, tight control loops for controlling the stability of the lithography apparatus can be used to improve pattern reproduction at low k1.

[0006] Known radiation source components include a pump source arranged to feed femtosecond radiation pulses into the core of an air-filled hollow photonic crystal fiber (HC-PCF). This component can be generated from white light via modulation instability (MI), which occurs when a high-intensity femtosecond pulse (e.g., with energies of several µJ and a duration of approximately 300 fs) undergoes a spectral explosion as it propagates within the air-filled HC-PCF. While MI produces a high-power spectrum with good flatness, the supercontinuum spectral explosion can lead to significant inter-pulse variations in the spectrum and undesirable high-intensity noise. One effective way to mitigate these variations is to address soliton self-squeezing (SSC) instead of MI: this nonlinear scheme provides a two-order-of-magnitude reduction in intensity noise and can be achieved using the same HC-PCF with a pulse energy 10 times lower within a shorter input pulse. This low energy results in a slight spectral broadening, which is gradually amplified by the time compression of the pulse due to anomalous group velocity dispersion (GVD), ultimately forming a single, long, femtosecond-long spike with a broad spectrum. Summary of the Invention

[0007] The inventors have identified numerous defects in known radiation source components in the prior art.

[0008] Specifically, the required volume of radiation source components known in the prior art poses significant challenges to integrating radiation source components into machines such as measurement tools (MTs) (e.g., scatterometers, level sensors, or alignment sensors).

[0009] The required volume of a femtosecond pump source (such as a femtosecond laser) occupies a large portion of the total volume of known radiation source components, and due to the size of the femtosecond pump source, the output beam must propagate a considerable distance in free space to reach the HC-PCF input. This means that for shorter beam paths, changes in angular pointing can lead to greater misalignment between the focal point and the fiber core.

[0010] Furthermore, upon entering the HC-PCF, the laser beam is focused into a high-pressure gas environment, achieving extremely high peak intensities. This high power can be detrimental, leading to heating and ionization of materials within the system due to spectral broadening. This can cause damage and shorten the radiation source's lifetime. Thermal drift and gas dynamics can severely impair light source performance, requiring continuous compensation through optomechanical alignment or gas flow interruptors, respectively. These thermal drifts can also cause fiber optic damage due to glass ablation.

[0011] The inventors also recognized that an additional pulse compression stage was necessary to make this known radiation source assembly common to both MI and SSC. Furthermore, the white light spectrum generated via SSC is approximately an order of magnitude more sensitive to changes in parameters such as the emitted pump energy and pulse duration, making the aforementioned drift have a greater impact on the spectrum than when white light is generated via MI. Therefore, advanced feedback is required.

[0012] According to one aspect of this disclosure, a radiation source assembly for generating broadband radiation is provided, the radiation source assembly comprising: a solid-core photonic crystal fiber (SC-PCF) having an input end and an output end, wherein the input end is configured to receive radiation pulses from a pump source; a hollow-core photonic crystal fiber (HC-PCF) filled with a gaseous working medium and arranged to receive radiation pulses output from the output end of the SC-PCF at the input end of the HC-PCF; and wherein the SC-PCF is configured to broaden the spectrum of the radiation pulses by providing nonlinearity under normal group velocity dispersion, and the HC-PCF is configured to generate broadband radiation through nonlinear interaction between the radiation pulses and the gaseous working medium, and to output broadband radiation at the output end of the HC-PCF.

[0013] Compared to scenarios without SC-PCF, for the same input parameters (e.g., energy, duration, etc.) of the radiation pulse from the pump source, the spectrally broadened pump radiation after SC-PCF can improve the white light conversion efficiency by up to 100% in subsequent HC-PCF.

[0014] The output of the SC-PCF can be coupled to the input of the HC-PCF.

[0015] The radiation source assembly may also include a gas chamber surrounding at least a portion of the HC-PCF, wherein the gas chamber is filled with a gaseous working medium.

[0016] The input and output terminals of the SC-PCF can be enclosed in a gas chamber, which in turn can completely enclose the HC-PCF. This prevents gas from flowing through the hollow channel within the SC-PCF.

[0017] The output of the SC-PCF can be enclosed within a chamber, and the SC-PCF can be extended so that its input is located outside the chamber, and the chamber can completely enclose the HC-PCF. Because the input of the SC-PCF is located outside the chamber, this advantageously improves the stability of the pump-radiative input coupling at the SC-PCF input. In this way, gas turbulence at the HC-PCF input can be avoided, and the thermally driven airflow through the HC-PCF can be reduced, as the airflow through the narrow channel of the SC-PCF is much weaker compared to that through the hollow channel of the HC-PCF.

[0018] The output of the HC-PCF can be enclosed within a gas chamber; while the input of the HC-PCF and the SC-PCF are located outside the gas chamber. Furthermore, since the input of the SC-PCF is located outside the gas chamber, this advantageously improves the stability of the pump radiation input coupling at the input of the SC-PCF. By enclosing only the output of the HC-PCF, the size of the gas chamber is advantageously reduced. This advantageously reduces the size of the radiation source assembly and makes it easier to manufacture.

[0019] The radiation source may also include another hollow-core photonic crystal fiber, FHC-PCF, wherein the output of SC-PCF can be coupled to the input of FHC-PCF, and the input of HC-PCF can be coupled to the output of FHC-PCF. Inserting FHC-PCF between SC-PCF and HC-PCF can advantageously utilize picosecond pump sources to generate broadband radiation through soliton self-compression.

[0020] The radiation source may also include: a gas chamber surrounding at least a portion of the HC-PCF, wherein the gas chamber is filled with a gaseous working medium; and another gas chamber surrounding at least one end of the FHC-PCF.

[0021] The other chamber can be filled with another gaseous working medium.

[0022] Alternatively, the other chamber may include a vacuum.

[0023] The output of the SC-PCF can be enclosed in another chamber.

[0024] The SC-PCF can be extended so that the input of the SC-PCF is located outside the gas chamber.

[0025] The radiation source assembly may also include a docking fiber for coupling the input of the HC-PCF to the output of the FHC-PCF.

[0026] The input terminal of the HC-PCF can be coupled to the output terminal of the FHC-PCF through the collapsed portion of the HC-PCF and / or the collapsed portion of the FHC-PCF.

[0027] The radiation source assembly may also include a pump source.

[0028] The duration of the radiation pulse can range from 100 fs to 250 fs.

[0029] The duration of the radiation pulse can be at least 250 fs.

[0030] The duration of the radiation pulse can be at least 1 ps, optionally at least 1.5 ps, optionally at least 2 ps, optionally at least 5 ps, or optionally at least 10 ps. The use of picosecond pump sources (e.g., picosecond lasers) advantageously allows for a reduction in the size of the radiation source assembly (e.g., compared to using femtosecond pump sources) because picosecond pump sources have a smaller footprint, while still providing pulses with pulse parameters (e.g., energy, duration, etc.) that are still achieved through broadband radiation generation using gas-filled HC-PCF technology. The advantage of using picosecond pulses for broadband radiation generation is that, compared to femtosecond pulses, picosecond pulses experience significantly less peak power attenuation due to dispersion.

[0031] Gaseous working media may include inert gases.

[0032] Broadband radiation can include supercontinuum radiation.

[0033] According to another aspect of this disclosure, a lithography apparatus is provided, including a radiation source assembly according to any of the embodiments described herein.

[0034] According to another aspect of this disclosure, a measurement apparatus is provided, including a radiation source assembly according to any of the embodiments described herein.

[0035] According to another aspect of this disclosure, a method for generating broadband radiation is provided, the method comprising: providing a radiation pulse from a pump source to an input end of a solid-core photonic crystal fiber (SC-PCF) having an input end and an output end, wherein the SC-PCF is configured to broaden the spectrum of the radiation pulse by providing nonlinearity under normal group velocity dispersion; generating broadband radiation by nonlinear interaction of the radiation pulse with a gaseous working medium in a hollow-core photonic crystal fiber (HC-PCF), the HC-PCF being arranged to receive the radiation pulse output from the output end of the SC-PCF at the input end of the HC-PCF; and outputting broadband radiation at the output end of the HC-PCF. Attached Figure Description

[0036] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 An overview diagram of the photolithography apparatus is depicted; Figure 2 An overview diagram of the photolithography unit is depicted; Figure 3 A schematic diagram depicting the overall photolithography technology illustrates the collaboration between three key technologies for optimizing semiconductor manufacturing; Figure 4 A schematic diagram of the scatterer is depicted; Figure 5 A schematic diagram of a horizontal sensor is depicted; Figure 6 A schematic representation of the alignment sensor is depicted; Figure 7a A schematic representation of a radiation source assembly for generating output broadband radiation according to an embodiment of the present disclosure is depicted; Figure 7b A schematic representation of a radiation source assembly for generating output broadband radiation according to an embodiment of the present disclosure is depicted; Figure 7c A schematic representation of a radiation source assembly for generating output broadband radiation according to an embodiment of the present disclosure is depicted; Figure 8 The illustration shows the spectrum of broadband radiation output from the radiation source assembly without any solid photonic crystal fiber and with solid photonic crystal fiber. Figure 9 A schematic representation of a radiation source assembly for generating output broadband radiation according to an embodiment of the present disclosure is depicted; Figure 10 Depicting Figure 9 The splicing fiber at the interface between the two hollow-core photonic crystal fibers in the radiation source assembly. Figure 11a The illustration shows a solid-core photonic crystal fiber and Figure 9 The evolution of the power spectrum and the time evolution of the pulse power in each of the two hollow-core photonic crystal fibers included in the radiation source assembly. Figure 11b The diagram shows from Figure 9 The spectrum of broadband radiation output by the radiation source component; Figure 12 The diagram illustrates the normalized peak power evolution along a solid-core photonic crystal fiber. Figure 13 This is a schematic cross-sectional view of a hollow optical fiber in its transverse surface (i.e., perpendicular to the fiber's axis), which may form part of a radiation source assembly according to embodiments of this disclosure; and Figure 14a and Figure 14b A cross-section of an example of a hollow photonic crystal fiber used for supercontinuum spectrum generation is schematically depicted. Detailed Implementation

[0037] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., wavelengths ranging from approximately 5 to 100 nm).

[0038] As used herein, the terms “mask,” “mask,” or “patterning device” can be broadly interpreted as any general patterning device that can be used to impart a patterned cross-section to an incident radiation beam, corresponding to a pattern produced in a target portion of a substrate. The term “optical valve” can also be used in this context. Examples of other such patterning devices, besides classic masks (transmission or reflection, binary, phase-shifting, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

[0039] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also called an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) T configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to accommodate a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0040] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example via the beam delivery system BD. The irradiation system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components or any combination thereof, for guiding, shaping, and / or controlling the radiation. The irradiator IL can be used to adjust the radiation beam B to have the desired spatial and angular intensity distribution in a cross-section at the plane of the patterning device MA.

[0041] The term “projection system” PS as used herein should be broadly interpreted to encompass all types of projection systems, including refractive, reflective, antirefractive, distorting, magnetic, electromagnetic, and / or electrostatic optical systems or any combination thereof, suitable for the exposure radiation and / or other factors used, such as the use of immersion or vacuum. Any use of the term “projection lens” herein may be considered synonymous with the broader term “projection system” PS.

[0042] A lithography apparatus LA can be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system PS and the substrate W—this is also known as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0043] The lithography apparatus LA can also be of the type with two or more substrate supports WT (also known as "dual stage"). In such a "multi-stage" machine, the substrate supports WT can be used in parallel and / or steps in preparing for subsequent exposure of the substrate W can be performed on the substrate W located on one of the substrate supports WT, while another substrate W on another substrate support WT is used to expose patterns on the other substrate W.

[0044] In addition to the substrate support WT, the lithography apparatus LA may include a measurement stage. The measurement stage is arranged to house sensors and / or cleaning equipment. The sensors may be arranged to measure properties of the projection system PS or the radiation beam B. The measurement stage may house multiple sensors. The cleaning equipment may be arranged to clean portions of the lithography apparatus, such as portions of the projection system PS or portions of the system providing the immersion solution. The measurement stage may be movable below the projection system PS as the substrate support WT moves away from the projection system PS.

[0045] In operation, a radiation beam B is incident on a patterning device (e.g., a mask MA), which is housed on a mask support T, and the radiation beam B is patterned by a pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be moved precisely, for example, to position different target portions C within the path of the focused and aligned radiation beam B. Similarly, a first positioner PM and possibly another position sensor (in...) Figure 1 (Not explicitly depicted) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 shown occupy dedicated target portions, they can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribing channel alignment marks.

[0046] like Figure 2As shown, the lithography apparatus LA can form part of the lithography unit LC, sometimes referred to as a lithography unit or (lithography) cluster, and typically includes devices for performing pre- and post-exposure processes on the substrate W. Traditionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the resist during exposure, a cooling plate CH, and a baking plate BK, for example, to regulate the temperature of the substrate W, or to regulate the solvent in the resist layer. A substrate processor or robot RO picks up the substrate W from input / output ports I / O1, I / O2, moving it between different process units and transferring the substrate W to the loading / unloading area LB of the lithography apparatus LA. The equipment in the lithography unit (which is often collectively referred to as tracks) is 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 the lithography control unit LACU.

[0047] To ensure correct and consistent exposure of the substrate W by the lithography unit LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, an inspection tool (not shown) can be included in the lithography unit LC. If an error is detected, adjustments can be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, especially if the inspection is performed before other substrates W in the same batch or leg are still exposed or processed.

[0048] An inspection apparatus (also called a measurement apparatus) is used to determine the properties of a substrate W, and specifically, to determine how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary from layer to layer. The inspection apparatus may alternatively be configured to identify defects on the substrate W and may be, for example, part of a photolithography unit LC, or integrated into a photolithography apparatus LA, or even a stand-alone device. The inspection apparatus may measure properties on a latent image (an image in a resist layer after exposure), a semi-latent image (an image in a resist layer after the post-exposure baking step PEB), a developed resist image (where exposed or unexposed portions have been removed), or even an etched image (after a pattern transfer step such as etching).

[0049] Typically, the patterning process in a photolithography (LA) apparatus is one of the most critical steps in the process, requiring highly accurate dimensional marking and placement of structures on the substrate W. To ensure this high accuracy, three systems can be combined in a so-called "holistic" control environment, such as... Figure 3As illustrated schematically, one of these systems is the lithography apparatus LA, which is (virtually) connected to the metrology tool MT (second system) and the computer system CL (third system). The key to this “holistic” environment is optimizing the cooperation between these three systems to enhance the overall process window and provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines a range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device)—typically within this range, process parameters in the lithography or patterning process can vary.

[0050] The computer system CL can use a portion of the design layout to be patterned to predict which resolution enhancement techniques will be used and perform computational lithography simulations and calculations to determine which mask layouts and lithography setups achieve the maximum overall process window for the patterning process (e.g., ...). Figure 3 (As indicated by the double arrows in the first scale SC1). Typically, resolution enhancement techniques are arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect the current operating position of the lithography apparatus LA within the process window (e.g., using input from the metrology tool MT) to predict potential issues due to suboptimal processing (such as...). Figure 3 Is there a possible defect (as indicated by the arrow pointing to "0" in the second scale SC2)?

[0051] The measurement tool MT can provide input to the computer system CL, enabling accurate simulation and prediction, and can also provide feedback to the lithography apparatus LA to identify potential drift, for example, during the calibration state of the lithography apparatus LA (e.g., ...). Figure 3 (As shown by the multiple arrows in the third scale SC3).

[0052] In photolithography, it is desirable to frequently measure the constructed structure, for example, for process control and verification. The tools used to perform these measurements are generally referred to as metrology tools (MTs). Different types of metrology tools (MTs) for such measurements are known, including scanning electron microscopes (SEMs) or various forms of scatterometer metrology tools (MTs). A scatterometer is a multifunctional instrument that allows the measurement of parameters of the photolithography process by placing a sensor in the pupil of the scatterometer's objective lens or its conjugate plane; such measurements are generally referred to as pupil-based measurements. Alternatively, it allows the measurement of parameters of the photolithography process by placing a sensor in the image plane or a plane conjugate to the image plane; in this case, the measurement is generally referred to as image- or field-based measurements. Such scatterometers and related measurement techniques are also described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, all of which are incorporated herein by reference in their entirety. The aforementioned scatterer can use light from soft X-rays, which is visible in the near-IR wavelength range, to measure the grating.

[0053] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, a reconstruction method can be applied to the measured signal to reconstruct or calculate the characteristics of the grating. For example, this reconstruction can be achieved by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0054] In the second embodiment, the scatterer MT is a spectroradiometer MT. In this spectroradiometer MT, radiation emitted by a radiation source is directed onto a target, and reflected or scattered radiation from the target is directed to a spectroradiometer detector, which measures the spectrum of the specular reflected radiation (i.e., a measurement of the intensity as a function of wavelength). Based on this data, the structure or profile of the target that generated the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression or by comparison with a simulated spectral library.

[0055] In the third embodiment, the scatterer MT is an elliptically polarized scatterer. An elliptically polarized scatterer is capable of determining the parameters of a photolithography process by measuring the scattered radiation for each polarization state. This measurement device emits polarized light (such as linear, circular, or elliptical) by using, for example, a suitable polarizing filter in the illumination portion of the measurement device. A light source suitable for the measurement device can also provide polarized radiation. Various embodiments of existing elliptically polarized scatterers are described in U.S. Patent Applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, all of which are incorporated herein by reference.

[0056] Examples of known scatterers typically rely on providing a dedicated measurement target, such as an underfilled target (a target presented as a simple grating or overlapping gratings in different layers, large enough that the measurement beam generates a spot smaller than the grating) or an overfilled target (whereby the irradiated spot partially or completely contains the target). Furthermore, irradiating the underfilled target (such as a grating) with a measurement instrument (e.g., an angle-resolved scatterer) allows for the use of so-called reconstruction methods, where the properties of the grating can be calculated by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with measurements. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0057] In one embodiment of a scattering instrument (MT), the scattering instrument MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring asymmetry in the reflection spectrum (which is related to the degree of overlay) and / or detection configuration. The two (typically overlapping) grating structures can be applied to two different layers (not necessarily contiguous layers) and can be formed approximately at the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, such as that described, for example, in commonly owned patent application EP1,628,164A, so that any asymmetry can be clearly discerned. This provides a simple and straightforward way to measure grating misalignment. Further examples of measuring overlay error between two layers (containing a periodic structure as the target) are obtained by measuring the asymmetry of the periodic structure, which can be found in PCT patent application publication WO 2011 / 012624 or U.S. patent application US 2016016186, both of which are incorporated herein by reference in their entirety.

[0058] Other parameters of interest may be focus and dose. Focus and dose can be determined simultaneously by scattering measurements (or alternatively by scanning electron microscopy), as described in U.S. Patent Application US2011-0249244, which is incorporated herein by reference in its entirety. A single structure can be used that has a unique combination of critical dimension and sidewall angle measurements for each point in the focus energy matrix (FEM—also known as the focus exposure matrix). If these unique combinations of critical dimensions and sidewall angles are available, focus and dose can be uniquely determined based on these measurements.

[0059] For example, the measurement target can be a set of composite gratings formed by photolithography, primarily using resist, but also formed after etching. Typically, the pitch and linewidth of the structures within the grating are strongly dependent on the measurement optics (especially the NA of the optics) to capture the diffraction levels from the measurement target. As previously mentioned, the diffraction signal can be used to determine the displacement between two layers (also known as "overlay"), or to reconstruct at least a portion of the original grating produced by the photolithography process. This reconstruction can provide guidance on the quality of the photolithography process and can be used to control at least a portion of the process. The target can have small sub-segments configured to simulate the dimensions of functional portions of the design layout within the target. Due to this sub-segmentation, the target behaves more similarly to the functional portions of the design layout, so that the overall process parameter measurements better match the functional portions of the design layout. The target can be measured in underfill or overfill modes. In underfill mode, the measurement beam generates a spot smaller than the entire target. In overfill mode, the measurement beam generates a spot larger than the entire target. In this overfill mode, different targets can also be measured simultaneously, thereby determining different processing parameters simultaneously.

[0060] The overall measurement quality of lithography parameters for a specific target is determined at least in part by the measurement formulation used to measure those parameters. The term "substrate measurement formulation" can 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 the substrate measurement formulation is a diffraction-based optical measurement, the one or more parameters measured can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the direction of the radiation relative to the pattern on the substrate, etc. For example, one criterion for selecting a measurement formulation could be the sensitivity of one of the measurement parameters to processing variations. Further examples are described in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US2016 / 0370717A1, both of which are incorporated herein by reference in their entirety.

[0061] Figure 4A measurement device, such as a scatterer SM1, is described. This device includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate 6. The reflected or scattered radiation is transmitted to a spectrometer detector 4, which measures the spectrum 10 of the specular reflected radiation (i.e., the measured value of the intensity INT as a function of wavelength λ). Based on this data, the structure or profile of the detected spectrum can be reconstructed by a processing unit PU, for example, through rigorous coupled-wave analysis and nonlinear regression, or by comparison with a simulated spectral library, such as… Figure 4 As shown at the bottom. Generally, for reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the manufacturing process of the structure. This leaves only a few structural parameters that need to be determined using scattering measurement data. This scatterer can be configured as a vertically incident scatterer or an obliquely incident scatterer.

[0062] A topographic measurement system, a level sensor, or a height sensor (which may be integrated into a photolithography apparatus) is arranged 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, thus indicating the height of the substrate based on its position on the substrate. This height map can then be used to correct the position of the substrate during pattern transfer on the substrate, so as to provide an aerial image of the patterning apparatus at the correct focus position on the substrate. It will be understood that "height" in this context refers to a generalized dimension from the plane to the substrate (also known as the Z-axis). Typically, the level sensor or height sensor performs measurements in a fixed position (relative to its own optical system), while the relative motion between the substrate and the optical system of the level sensor or height sensor produces a height measurement value based on the position on the substrate.

[0063] Examples of level or height sensors (LS) known in the art are as follows: Figure 5 The diagram is shown schematically and only illustrates the operating principle. In this example, the horizontal sensor includes an optical system comprising a projection unit LSP and a detection unit LSD. The projection unit LSP includes a radiation source LSO that provides a radiation beam LSB, which is transmitted by a projection grating PGR of the projection unit LSP. The radiation source LSO can be, for example, a narrowband or broadband radiation source, such as a supercontinuum light source, a polarized or unpolarized light source, a pulsed or continuous light source, such as a polarized or unpolarized beam. The radiation source LSO can include multiple radiation sources with different colors or wavelength ranges, such as multiple LEDs. The radiation source LSO of the horizontal sensor LS is not limited to visible radiation, but can additionally or alternatively cover UV and / or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

[0064] The projection grating PGR is a periodic grating comprising a periodic structure that generates a radiation beam BE1 with periodically varying intensity. The periodically varying intensity radiation beam BE1 is guided at an incident angle ANG to a measurement position MLO on the substrate W, this angle being between 0 and 90 degrees relative to an axis (Z-axis) perpendicular to the incident substrate surface, typically between 80 and 90 degrees. At the measurement position MLO, the patterned radiation beam BE1 is reflected by the substrate W (as indicated by arrow BE2) and guided to the detection unit LSD.

[0065] To determine the height level at the measurement location MLO, the level sensor also includes a detection system comprising a detection grating DGR, a detector DET, and a processing unit (not shown) for processing the output signal of the detector DET. The detection grating DGR can be the same as the projection grating PGR. The detector DET generates a detector output signal indicating the received light, such as indicating the intensity of the received light, like a photodetector, or representing the spatial distribution of the received intensity, like a camera. The detector DET can include any combination of one or more detector types.

[0066] The height level at the measurement location MLO can be determined using triangulation techniques. The detected height level is typically related to the signal strength measured by the detector DET, which exhibits periodicity. This periodicity, among other things, depends on the design of the projection grating PGR and the (oblique) incident angle ANG.

[0067] The projection unit LSP and / or the detection unit LSD may include additional optical elements, such as lenses and / or mirrors, along the path of the patterned radiation beam between the projection grating PGR and the detection grating DGR (not shown).

[0068] In this embodiment, the detection grating DGR can be omitted, while the detector DET can be placed at the location of the detection grating DGR. This configuration provides more direct detection of the image of the projection grating PGR.

[0069] In order to effectively cover the surface of the substrate W, the horizontal sensor LS can be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of measurement regions MLO or light spots that cover a larger measurement range.

[0070] For example, various general-purpose height sensors are disclosed in US7265364 and US7646471, both of which are incorporated herein by reference. A height sensor using UV radiation instead of visible or infrared radiation is disclosed in US2010233600A1, which is also incorporated herein by reference. WO2016102127A1 (incorporated by reference) describes a compact height sensor that uses a multi-element detector to detect and identify the position of a grating image without needing to detect the grating itself.

[0071] In manufacturing complex devices, numerous photolithographic patterning steps are typically performed to form functional features on successive layers on a substrate. Therefore, a key aspect of the performance of a photolithography apparatus is its ability to correctly and accurately place the applied pattern according to the features laid in previous layers (using the same apparatus or different photolithography apparatuses). For this purpose, the substrate is provided with one or more sets of markers. Each marker is a structure whose position can be measured later using a position sensor (typically an optical position sensor). The position sensor can be called an "alignment sensor," and the marker can be called an "alignment mark."

[0072] Photolithography apparatuses may include one or more alignment sensors that can precisely measure the position of alignment marks formed on a substrate. Alignment (or position) sensors can obtain position information from alignment marks formed on the substrate using optical phenomena such as diffraction and interference. An example of an alignment sensor used in current photolithography apparatuses is based on a self-referencing interferometer described in US6961116. Various improvements and modifications to position sensors have been developed, for example, as disclosed in US2015261097A1. The contents of all these disclosures are incorporated herein by reference.

[0073] Markings or alignment marks may comprise a series of strips formed in a layer disposed on a substrate or (directly) formed in the substrate. The strips may be equidistantly distributed and act as grating lines so that the marks can be viewed as diffraction gratings with a well-known spatial period (pitch). Depending on the orientation of these grating lines, the marks may be designed to allow measurement of position along the X-axis or along the Y-axis (whose orientation is substantially perpendicular to the X-axis). Markings comprising strips (set at +45 degrees and / or -45 degrees relative to the X-axis and Y-axis) enable combined X or Y measurements using the techniques described in US2009 / 195768A, which is incorporated herein by reference.

[0074] The alignment sensor optically scans each mark using a radiating spot to obtain a periodically varying signal, such as a sine wave. The phase of this signal is analyzed to determine the position of the mark, and thus the position of the substrate relative to the alignment sensor, which is fixed relative to the reference frame of the lithography apparatus. So-called coarse and fine marks can be provided, associated with different (coarse and fine) mark sizes, so that the alignment sensor can distinguish different periods of the periodic signal and the precise position (phase) within each period. Marks with different pitches can also be used for this purpose.

[0075] The location of the measurement marks can also provide information about the deformation of the substrate on which these marks are set, for example, in the form of a wafer grid. Substrate deformation can be caused by, for example, electrostatically clamping the substrate to a substrate stage and / or heating the substrate when it is exposed to radiation.

[0076] Figure 6 This is a schematic block diagram of a known embodiment of an alignment sensor AS, such as that described, for example, in US6961116, which is incorporated herein by reference. A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is deflected by deflecting optics onto a mark (such as a mark located on a substrate W) as an illumination spot SP. In this example, the deflecting optics include a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP used to illuminate the mark AM may be slightly smaller than the width of the mark itself.

[0077] The radiation diffracted by the marker AM is collimated (in this example, through the objective lens OL) into an information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the marker (which may be referred to as reflection). A self-referenced interferometer SRI (e.g., of the type disclosed in US6961116 above) interferes with the beam IB against itself, after which the beam is received by a photodetector PD. Additional optical elements (not shown) may be included to provide a separate beam if the radiation source RSO produces more than one wavelength. The photodetector may be a single element or may include multiple pixels if desired. The photodetector may include a sensor array.

[0078] Deflecting optics (in this example, including the spot mirror SM) can also be used to block zero-order radiation reflected from the markers so that the information-carrying beam IB only includes higher-order diffraction radiation from the marker AM (this is not necessary for the measurement, but it improves the signal-to-noise ratio).

[0079] The intensity signal SI is provided to the processing unit PU. By combining the optical processing in the block SRI with the computational processing in the unit PU, the values ​​of the X and Y positions on the substrate relative to the reference frame are output.

[0080] A single measurement of the type shown will only fix the position of the mark within a certain range corresponding to one pitch of the mark. Combining this with coarser measurement techniques can identify which time period of the sine wave contains the marked position. The same process at coarser and / or finer levels can be repeated at different wavelengths to improve accuracy and / or for stable detection of the mark, unaffected by the materials used to manufacture the mark or the materials above and / or below it. Wavelengths can be optically multiplexed and demultiplexed for simultaneous processing, and / or these wavelengths can be multiplexed through time division or frequency division.

[0081] In this example, the alignment sensor and the light spot SP remain stationary, while the substrate W moves. Therefore, the alignment sensor can be securely and accurately mounted to the reference frame while effectively scanning the marker AM in the direction opposite to the movement of the substrate W. In this moving process, the substrate W is controlled by its mounting on the substrate support and by the substrate positioning system controlling 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 this embodiment, one or more (alignment) markers are disposed on the substrate support. Measuring the position of the markers disposed on the substrate support allows for calibration of the substrate support position determined by the position sensor (e.g., relative to the frame connected to the alignment system). Measuring the position of the alignment markers disposed on the substrate allows for determination of the substrate position relative to the substrate support.

[0082] Measurement tools (MTs) such as the aforementioned scatterometers, topographic surveying systems, or position measurement systems can perform measurements using radiation from a radiation source component. The characteristics of the radiation used by the measurement tool can affect the type and quality of measurements that can be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure the substrate, for example, broadband radiation can be used. Multiple different frequencies can propagate, illuminate, and diverge on the measurement target without interfering with or minimizing interference with other frequencies. Therefore, different frequencies can be used, for example, to obtain more measurement data simultaneously. Different radiation frequencies can also detect and discover different characteristics of the measurement target. Broadband radiation can be useful in measurement systems (MTs such as level sensors, alignment mark measurement systems, scattering measurement tools, or inspection tools).

[0083] Embodiments of this disclosure relate to a radiation source assembly for generating broadband radiation, the radiation source assembly comprising: a solid-core photonic crystal fiber (SC-PCF) having an input end and an output end, wherein the input end is configured to receive radiation pulses from a pump source; and a hollow-core photonic crystal fiber (HC-PCF) filled with a gaseous working medium and arranged to receive radiation pulses output from the output end of the SC-PCF at the input end of the HC-PCF; wherein the SC-PCF is configured to broaden the spectrum of the radiation pulses by providing nonlinearity under normal group velocity dispersion, and the HC-PCF is configured to generate broadband radiation through nonlinear interaction between the radiation pulses and the gaseous working medium, and to output broadband radiation at the output end of the HC-PCF.

[0084] Figure 7a A radiation source assembly 700 according to one embodiment is depicted for generating output broadband radiation 118 by spectral broadening. The radiation source assembly 700 includes an SC-PCF 106 having an input and an output, wherein the input of the SC-PCF 106 is arranged to receive pulses of input radiation 104 from a pump source 102. The fiber material of the SC-PCF 106 may be a plastic material (such as PMA), glass (such as silica), or soft glass. The pump source 102 may form part of the radiation source assembly described herein, or may be connected to these radiation source assemblies.

[0085] The pulses of input radiation 104 may include electromagnetic radiation of one or more wavelengths between 200 nm and 2 µm. Input radiation 104 may, for example, include electromagnetic radiation with wavelengths of 1.03 µm, 515 nm, or 343 nm. The pulses of input radiation 104 may be set in the infrared and / or visible portions of the spectrum. The pulses of input radiation 104 may have a narrow wavelength range and may be a single wavelength. The wavelength of the pulses of input radiation 104 can be set so that it can be provided by commercially available sources. Examples of wavelengths provided by commercially available sources include wavelengths of 1550 nm, 1030 nm, and wavelengths in the range of 700 nm to 800 nm.

[0086] The repetition rate of the input radiation 104 can be on the order of 1 kHz to 100 MHz, for example, in the range of 1 MHz to 20 MHz, such as 2.5 MHz, 5 MHz, 8 MHz, 10 MHz, or 15 MHz. The average power of the input radiation 104 can be between 100 mW and several hundred watts. The average power of the input radiation can be, for example, between 20 W and 50 W.

[0087] The input radiation 104 can be coherent radiation. The input radiation 104 can also be collimated radiation, which has the advantage of promoting and improving the efficiency of coupling the input radiation 104 to the SC-PCF 106. The input radiation 104 can include a single frequency or a narrow range of frequencies. The input radiation 104 can be generated by a laser.

[0088] SC-PCF 106 is coupled to HC-PCF 108 at interface 110. Figure 7a In one embodiment, HC-PCF 108 is arranged to receive radiation pulses directly from the output of SC-PCF 106 at the input of HC-PCF 108.

[0089] HC-PCF 108 is filled with gaseous working medium 114. Figure 7a In this embodiment, this is achieved by surrounding the output of the HC-PCF 108 within a gas chamber 112. The gas chamber 112 may also be referred to as a housing, container, or reservoir. The gas chamber 112 is configured to contain a gaseous working medium 114. The gas chamber 112 may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the gaseous working medium 114 within the gas chamber 112. The gaseous working medium 114 may include any monatomic (inert) gas, such as helium, neon, argon, krypton, or xenon.

[0090] like Figure 7a As shown, the input terminal of SC-PCF 106 can be located outside the gas chamber 112. That is, in Figure 7a In this embodiment, the input terminal of the SC-PCF 106 was not placed in a high-pressure gas environment. For example... Figure 7a As shown, the interface 110 between SC-PCF 106 and HC-PCF 108 can be located outside the gas chamber 112.

[0091] In embodiments of this disclosure, the SC-PCF 106 is configured to broaden the spectrum of the pulses of the input radiation 104 by providing nonlinearity under normal group velocity dispersion. Specifically, the SC-PCF 106 is configured to broaden the spectrum of the pulses of the input radiation 104 by self-phase modulation (SPM) before the output radiation pulse (e.g., providing the radiation pulse to the HC-PCF 108).

[0092] exist Figures 7a to 7cIn this embodiment, the HC-PCF 108 is configured to generate broadband radiation 118 through the nonlinear interaction of a radiation pulse with a gaseous working medium 114, and to output broadband radiation 118 at the output of the HC-PCF. Broadband radiation can be radiation spanning a wavelength range significantly larger than narrowband or single-wavelength radiation. Broadband radiation includes a continuous or substantially continuous wavelength range. The wavelength range may also be referred to as a spectrum / spectral range. A continuous wavelength range can be in the range of at least 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, 400 nm, or longer. Broadband radiation may have gaps within the wavelength range. These gaps can separate one or more continuous sub-ranges within the wavelength range. A substantially continuous range may have discrete wavelengths(s) and / or narrow wavelength bands(s) that are not within the range, and is still considered continuous. The power spectral density may be discontinuous, and the power may vary within the broadband wavelength range.

[0093] exist Figure 7a In this embodiment, the gas chamber 112 includes a transparent window 116 forming a portion of the wall of the gas chamber 112. In use, the transparent window 116 is located near the output of the HC-PCF 108. The transparent window 116 may be transparent for at least the frequency of the broadband output radiation 118. The transparent window 116 may form an hermetically sealed seal within the wall of the gas chamber 112 so that the gaseous working medium 114 can be contained in the reservoir RSV. It will be understood that the gas WM may be contained within the gas chamber at a pressure different from the ambient pressure of the gas chamber. In this context, the window is transparent for that frequency if at least 50%, 75%, 85%, 90%, 95%, or 99% of the incident radiation at a certain frequency is emitted through the window.

[0094] The broadband radiation 118 provided by the radiation source assembly described herein has an average output power of at least 1 W. The average output power may be at least 5 W. The average output power may be at least 10 W. The broadband radiation 118 may be pulsed broadband output radiation.

[0095] The broadband radiation 118 provided by the described radiation source assembly can be collimated and / or coherent. The broadband range of the output radiation 118 can be a continuous range, including a continuous range of radiation frequencies. The broadband radiation 118 can include supercontinuum spectral radiation. Continuous radiation may be advantageous for use in many applications, such as in measurement applications. For example, a continuous frequency range can be used to probe a large number of characteristics. A continuous frequency range can, for example, be used to determine and / or eliminate the frequency dependence of the measured characteristics. The supercontinuum spectral output radiation ORD can include, for example, electromagnetic radiation with a wavelength range between 500 nm and 900 nm. The lower limit of such supercontinuum spectral radiation wavelength range can be at least 100 nm, at least 200 nm, at least 300 nm, or at least 400 nm. The upper limit of such supercontinuum spectral radiation wavelength range can be 2000 nm or less, 1800 nm or less, 1500 nm or less, or 1200 nm or less. In one example, the broadband light source assembly 100 is configured to generate supercontinuum spectral radiation in a wavelength range of 485 nm to 1800 nm. Supercontinuum radiation can include white light.

[0096] Those skilled in the art will understand that, according to this disclosure, "supercontinuum spectrum" generally refers to a continuous spectral power distribution exhibiting significant flatness. In some examples, a supercontinuum spectrum includes a continuous spectral power distribution with a wavelength range of at least 100 nm. In some examples, the flatness of a supercontinuum spectrum corresponds to a peak-to-valley spectral power ratio of less than 100:1, or 20 dB. In some examples, the flatness of a supercontinuum spectrum corresponds to a peak-to-valley spectral power ratio of less than 10:1, or 10 dB.

[0097] Figure 7b A radiation source assembly 702 according to another embodiment is depicted for generating output broadband radiation 118 by spectral broadening.

[0098] like Figure 7b As shown, the input and output terminals of SC-PCF 106 are both surrounded within air chamber 112, and the air chamber completely surrounds HC-PCF 108. That is, the input and output terminals of HC-PCF 108 are both surrounded within air chamber 112.

[0099] exist Figure 7bIn one embodiment, the gas chamber 112 includes a first transparent window 116 located near the input of the SC-PCF 106. The first transparent window 116 (also referred to as an input port or input optical port) may be transparent to at least the received radiation frequencies so that the received input radiation 104 (or at least a large portion thereof) can be coupled into the SC-PCF 106 located within the gas chamber 112. In use, the output of the HC-PCF 108 may be located near a second transparent window 120 (also referred to as an output port or output optical port). The second transparent window 120 may be transparent to at least the frequencies of the broadband output radiation 120 of the radiation source assembly 702.

[0100] like Figure 7b As shown, the interface 110 between SC-PCF 106 and HC-PCF 108 can be located inside the gas chamber 112.

[0101] Figure 7c A radiation source assembly 704 according to another embodiment is depicted for generating output broadband radiation 118 by spectral broadening.

[0102] like Figure 7c As shown, the output of SC-PCF 106 is enclosed within gas chamber 112, and SC-PCF 106 extends such that the input of SC-PCF 106 is located outside gas chamber 106, and gas chamber 112 completely encloses HC-PCF 108. That is, both the input and output of HC-PCF 108 are enclosed within gas chamber 112.

[0103] like Figure 7c As shown, the input terminal of SC-PCF 106 can be located outside the gas chamber 112. That is, in Figure 7c In this embodiment, the input terminal of the SC-PCF 106 was not placed in a high-pressure gas environment. For example... Figure 7c As shown, the interface 110 between SC-PCF 106 and HC-PCF 108 can be located inside the gas chamber 112.

[0104] exist Figure 7c In one embodiment, the air chamber 112 includes a transparent window 116 forming a portion of the wall of the air chamber 112. In use, the transparent window 116 is located near the output of the HC-PCF 108.

[0105] exist Figures 7a to 7cIn the embodiments described, broadband radiation can be generated in HC-PCF 108 using either a MI spectral broadening process or a SSC spectral broadening process. The inventors have discovered that the duration and energy of the pulse of input radiation 104 are the most important factors determining which broadening process occurs. The lengths of SC-PCF 106 and HC-PCF 108, as well as the pressure of the gaseous working medium 114, can also play a role in determining which broadening process occurs.

[0106] exist Figures 7a to 7c In some embodiments, broadband radiation can be generated in the HC-PCF 108 via a MI spectral broadening process when the pulse duration for input radiation 104 is at least 500 fs (e.g., between 500 fs and 1 ps). The pulse duration for input radiation 104 can be at least 1 ps, optionally at least 1.5 ps, optionally at least 2 ps, optionally at least 5 ps. The maximum pulse duration for the input radiation can be 10 ps. In these embodiments, higher gas pressures and / or heavier gases may be required to achieve sufficient nonlinear broadening with lower peak power over picosecond pulse durations. For example, the working medium WM can include inert gases such as krypton or xenon. The energy of the pulse for input radiation can range from 0.1 µJ to 500 µJ. The energy of the pulse for input radiation can range from 0.1 µJ to 100 µJ, for example, from 1 µJ to 20 µJ. The length of SC-PCF 106 can range from 0.1 cm to 100 cm, while the length of HC-PCF 108 can range from 1 cm to 10 m.

[0107] The inventors have discovered that if the spectrum after SC-PCF 106 extends to the first-order MI gain band (e.g., ω0±ω), MI Beyond the frequencies of [specific frequencies], coupling SC-PCF 106 to HC-PCF 108 can significantly improve the white light conversion efficiency in gas-filled HC-PCF 108. This is because the MI pulse burst is triggered by the gradual amplification of noise time-modulated around these frequencies on the pulse. In the case of narrowband pump radiation (e.g., a 1.5 ps pulse with energy of 4.6 µJ), extremely weak “quantum” noise is amplified, while the overlap of pump radiation with these gain bands provides a significantly larger “noise seed” for amplification.

[0108] Figure 8Output spectrum 802, obtained without any SC-PCF 106, and output spectrum 804, obtained with a 16 cm long SC-PCF 106 coupled to an HC-PCF 108, were compared. Both output spectra 802 and 804 were obtained by pulsed input radiation 104 with a pulse duration of 1.5 ps and a pulse energy of 4.6 µJ. Figure 8 As can be seen, the wider input spectrum provided by SC-PCF 106 produces 100% higher PSD in the valley region (at about 640 nm). Figure 8 The results shown are consistent with those used for radiation source components. Figures 7a to 7c Regardless of the specific arrangement. In embodiments of this disclosure, the broadband radiation is generated in the HC-PCF 108 via a MI spectral broadening process, and the power spectral density of the broadband output radiation 118 over the entire wavelength band can be at least 2 mW / nm.

[0109] The nonlinear dynamics of an ultrashort laser pulse undergoing a MI along an inflatable HC-PCF are primarily determined by the temporal envelope of the instantaneous pulse power, i.e., by its full width at half maximum (FWHM) duration and its peak power. More specifically, transform-constrained pulses (whose duration matches the lower limit supported by a given spectrum) and strongly chirped pulses with a wider spectrum (but except for the same effective duration and peak power) produce (almost exactly) the same propagation dynamics and output spectra. This has been confirmed by the inventors' numerical pulse propagation simulations, which plot the nonlinear evolution of pulses with effective 5 ps lengths and transform-constrained durations τTL of 250 fs (chirped), 2.0 ps (chirped), and 5.0 ps (unchirped). On the plots, the length of the nonlinearity is kept constant only by changing the input pulse energy, and therefore the MI length remains constant. This means that picosecond pump pulses can be directly directed to an inflatable HC-PCF 108 via the SC-PCF 106, so even if the pulse has already undergone spectral broadening via SPM in the SC-PCF 106, dynamic spectral broadening via MI can still occur. This is because SPM keeps the time-domain envelope of the instantaneous pulse power completely unchanged. As is known to those skilled in the art, in a chirped pulse, the instantaneous frequency of the electric field oscillation varies smoothly along its time-domain envelope. A pulse with a constant instantaneous frequency along its envelope is called "transform-limited".

[0110] exist Figures 7a to 7cIn the embodiments, when the pulse duration of the input radiation 104 is in the range of 100 fs to 250 fs and the maximum energy of the pulse of the input radiation 104 is 5 µJ, optionally 4 µJ, optionally 3 µJ, optionally 2 µJ, broadband radiation can alternatively be generated in the HC-PCF 108 by an SSC spectral broadening process. The energy of the pulse of the input radiation 104 can be between 0.2 µJ and 2 µJ, for example, 0.5 µJ. Compared with the case where the SC-PCF 106 is not used, the length of the HC-PCF 108 can be significantly shortened, for example, by 10%, or optionally by 20%, or optionally by 50%. At the same time, with the same radiation parameters at the input of the SC-PCF 106, the conversion efficiency from pump radiation to broadband spectrum is improved, for example, by 10%, or optionally by 20%, or optionally by 50%. The length of the SC-PCF 106 can be in the range of 0.5 cm to 5 cm, for example, 1 to 3 cm. In other words, the length of HC-PCF 108 can range from 5cm to 2m.

[0111] In the above Figures 7a to 7c In one embodiment, the output of SC-PCF 106 is directly coupled to the input of HC-PCF 108 at interface 110. Interface 110 can be implemented using any known method. In one example, the output of SC-PCF 106 is coupled to the input of HC-PCF 108 at interface 110 via a "butt" coupling, where SC-PCF 106 and HC-PCF 108 are "butt-coupled" via an air gap. In another example, the output of SC-PCF 106 is coupled to the input of HC-PCF 108 at interface 110 via a direct splice. Specifically, SC-PCF 106 and HC-PCF 108 can be spliced ​​without effective mold field diameter (MFD) matching. In another example, SC-PCF 106 and HC-PCF 108 can be spliced ​​with effective mold field diameter (MFD) matching. This can be achieved by splicing the intermediate portions to match the mold field diameter. For example, SC-PCF 106 may have a portion with a constant MFD adjacent to an adiabatic downward tapering portion or an upward tapering portion coupled to HC-PCF 108.

[0112] In other embodiments of this disclosure, the output of SC-PCF 106 is not directly coupled to the input of HC-PCF 108, but SC-PCF 106 is still in fluid communication with HC-PCF 108.

[0113] Figure 9A radiation source assembly 900 according to this embodiment is depicted for generating output broadband radiation 118 by spectral broadening, wherein the output of SC-PCF 106 is not coupled to the input of HC-PCF 108.

[0114] like Figure 9 As shown, in addition to SC-PCF 106 and HC-PCF 108, the radiation source assembly 900 also includes another hollow-core photonic crystal fiber FHC-PCF 130, which is also referred to herein as dispersion-compensated hollow-core photonic crystal fiber DC-HCPCF.

[0115] The output of SC-PCF 106 is coupled to the input of FHC-PCF 130 at interface 110, and the input of HC-PCF 108 is coupled to the output of FHC-PCF 130 at interface 140. The method of coupling SC-PCF 106 to an HC-PCF (such as FHC-PCF 130) at interface 110 has been described above. The input of HC-PCF 108 can be coupled to the output of FHC-PCF 130 at interface 140 using a section of spliced ​​fiber 145 without any hollow channel. This section can come from another type of fiber (e.g., "coreless" fiber) or can be created by collapsing one or both of the HC-PCFs involved.

[0116] FHC-PCF 130 can be filled with gaseous working medium 115. Figure 9 In this embodiment, this is achieved by surrounding the input end of the FHC-PCF 130 within a gas chamber 113. The gas chamber 113 surrounds at least one end of the FHC-PCF 130. The gas chamber 113 may also be referred to as a housing, container, or reservoir. The gas chamber 113 is configured to contain a gaseous working medium 115. The gas chamber 113 may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the gaseous working medium 115 within the gas chamber 113. The gaseous working medium 115 may include a light monatomic (inert) gas, such as helium or neon. The gaseous working medium 115 and the FHC-PCF 130 are selected such that the pump wavelength of the input radiation 104 is within a range corresponding to the anomalous group velocity dispersion state of the gaseous working medium 115.

[0117] Alternatively, the gaseous working medium 115 may not be present in the gas chamber 113 so that the gas chamber 113 includes a vacuum.

[0118] HC-PCF 108 is filled with gaseous working medium 117. Figure 9In this embodiment, this is achieved by surrounding the output of the HC-PCF 108 within a gas chamber 123. The gas chamber 123 surrounds the output of the HC-PCF 108. The gas chamber 123 may also be referred to as a housing, container, or reservoir. The gas chamber 123 is configured to contain a gaseous working medium 117. The gas chamber 123 may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the gaseous working medium 117 within the gas chamber 123. The gaseous working medium 117 may include a monatomic (inert) gas, such as argon, krypton, or xenon.

[0119] At least one end of the FHC-PCF 130 is in a different environment than the HC-PCF 108.

[0120] HC-PCF 108 exhibits lower dispersion than FHC-PCF 130, and while HC-PCF 108 utilizes the nonlinear properties of hollow fiber to broaden the radiation spectrum, for FHC-PCF 130, negligible nonlinearity is desirable. The nonlinearity in FHC-PCF 130 can be at least ten times lower than that in HC-PCF 108, for example, one hundred or one thousand times lower. In embodiments where FHC-PCF 130 is filled with a gaseous working medium 115, the gaseous working medium 115 can be a gas lighter than the gas used for the gaseous working medium 117. Alternatively or additionally, the pressure of the gaseous working medium 115 can be lower than the pressure used for the gaseous working medium 117.

[0121] exist Figure 9 In some embodiments, the pulse duration for the input radiation 104 can be at least 250 s. The pulse duration for the input radiation 104 can be at least 500 fs, for example, between 500 fs and 1 ps. The pulse duration for the input radiation 104 can be at least 1 ps, optionally at least 1.5 ps, optionally at least 2 ps, optionally at least 5 ps, optionally at least 10 ps.

[0122] White light generation via direct soliton self-compression of picosecond laser pulses is impossible (in the case of non-zero MI gain) due to the required HC-PCF length. LSSC It will always be about length LMI Longer. Therefore, the MI pulse burst always occurs before the pulse is able to self-compress. This can be easily estimated using analytical empirical relations for the SSC length: And for the MI length: Where τFWHM It is the full width at half maximum (FWHM) pulse duration, A eff β2(ω0) is the effective area of ​​the fiber mode, and β2(ω0) is the group velocity at the pump laser frequency ω0. n 2 It is the nonlinear refractive index of the gas, and P 0 It is the peak power of the pump pulse.

[0123] As a solution, SC-PCF 106 broadens the picosecond pulse of input radiation 104 by self-phase modulation (SPM) before providing the radiation pulse to FHC-PCF 130. As an alternative to free-space pulse compression using a chirped mirror, FHC-PCF 130, providing anomalous GVD, is attached to SC-PCF 106. With gas parameters selected to produce negligible nonlinearity, the pulse, with a broader spectrum and more positively chirped characteristics upon entering SC-PCF 106, is temporally compressed as it propagates through FHC-PCF 130. The radiation pulse propagates through FHC-PCF 130 before entering HC-PCF 108. HC-PCF 108 is configured to generate broadband radiation 118 through the nonlinear interaction of the radiation pulse with the gaseous working medium 114, and outputs broadband radiation 118 at the output of HC-PCF. Figure 9 In one embodiment, broadband radiation 118 is generated in HC-PCF 108 by an SSC spectral broadening process.

[0124] The inventors have discovered that when using a 5-meter-long FHC-PCF 130, the pulse duration at the output of the SC-PCF 106, which is approximately 2 ps, can be reduced to approximately 30 fs. This is as follows: Figure 11a As shown.

[0125] Figure 11a The spectral broadening of a 1.5 ps long input pulse with an energy of approximately 5.1 µJ in a 7.5 cm long SC-PCF 106 is illustrated on the left-hand side. Figure 11a The central illustration shows dispersion compensation in a 5-m long FHC-PCF 130 filled with 1 bar of helium. Figure 11a The right-hand side illustration shows the soliton self-compression of a compression pulse of approximately 30 fs in a 5 cm long HC-PCF 108 filled with 20 bar argon gas. Figure 11a In the diagram, the evolution of the power spectrum is shown in the top row, while the temporal evolution of the pulse power is depicted in the bottom row. Figure 11bThe diagram illustrates the output spectrum of broadband radiation 118 obtained using SSC. In embodiments of this disclosure, the broadband radiation is generated in an HC-PCF 108 via an SSC spectral broadening process, and the power spectral density of the broadband output radiation 118 across the entire wavelength band can be at least 1 mW / nm.

[0126] The length of FHC-PCF 130 can be between 10 cm and 10 m. The length of FHC-PCF 130 can be between 1 m and 10 m, for example, between 1 m and 5 m. In the radiation source assembly 900, the length of HC-PCF 108 can be in the range of 1 cm to 100 cm, for example, 5 cm, 10 cm or 20 cm.

[0127] In embodiments of this disclosure, the length of the SC-PCF 106 is primarily limited by its moderate normal group velocity dispersion, which causes the pump pulse to be time-stretched, resulting in loose peak power (crucial for white light generation in the HC-PCF 108). Its dependence on the functional fiber length (LFF) is given by the following equation: Where β2(ω0) is the group velocity dispersion at (angular) frequency ω0, τ IN It is the duration of the full-width half-peak input pulse at the beginning of the transmission fiber, and E P This is the pulse energy (the coefficient "0.88" applies to Gaussian pulses).

[0128] For three different input pulse durations: 500 fs (line 1202), 1 ps (line 1204), and 2 ps (line 1206). Figure 12 The normalized peak power evolution along a 5 m length of SC-PCF 106 is shown, where at a wavelength of 1030 nm, the (forward) GVD β2 = 170 fs 2 / cm. Figure 12 The chart illustrates another advantage of using picosecond pulses for white light generation: these pulses experience less peak power attenuation than femtosecond pulses. The peak power of a 2 ps pulse remains almost constant over a 5 m length of the SC-PCF106, while 1 ps and 0.5 ps pulses experience attenuation of 3% and 27%, respectively. Therefore, chirp compensation after propagating picosecond pulses (e.g., pulses with a duration of at least 1 ps or at least 2 ps) through the SC-PCF106 is essentially unnecessary.

[0129] To avoid damage to the fiber material of SC-PCF 106 (e.g., its glass core), parameters can be selected such that (1) the peak power of the pulse remains below the critical power for self-focusing; and (2) the integrated flux (energy per effective area of ​​the fiber mode) remains below the material damage limit. To keep the integrated flux as low as possible, a solid-core PCF designed for a large effective mode area (“LMA”) is required. Since the upper limit of the integrated flux is related to τ... p -0.5 (τ) p The picosecond pulse's maximum permissible energy is directly proportional to its pulse duration, and the inventors have discovered that this energy is significantly higher than that of a femtosecond pulse. Specifically, the inventors have found that a picosecond pulse with 590 µm... 2 300 µm 2 and 200 µm 2 Commercially available LMA-PCFs with different effective mode areas are unlikely to be damaged by pulses of 10 ps length, with energies below approximately 20 µJ, approximately 16 µJ, and approximately 8 µJ, respectively.

[0130] Figure 13 This is a schematic cross-sectional view of an optical fiber OF in the transverse plane, which can be used in the radiation source assembly described herein. The optical fiber OF may correspond to HC-PCF 108 or FHC-PCF 130. A similar fiber is disclosed in WO2017 / 032454A1. Figure 13 The actual example of the optical fiber is similar to other embodiments.

[0131] An optical fiber (OF) consists of a slender body, longer in one dimension than in the other two. This longer dimension is called the axial direction and defines the axis of the optical fiber. The other two dimensions define a plane, which can be called the transverse plane. Figure 13 The cross-section of the optical fiber OF in this transverse plane (i.e., perpendicular to the axis) is shown, which is labeled as the xy plane. The transverse cross-section of the optical fiber OF can remain substantially unchanged along the fiber axis.

[0132] It will be understood that optical fibers (OFs) possess a degree of flexibility, therefore the direction of the axis is typically not uniform along the length of the fiber. Terms such as optical axis and transverse cross-section are understood to refer to local optical axis, local transverse cross-section, etc. Furthermore, when components are described as cylindrical or tubular, these terms will be understood to encompass such shapes that may have deformed when the optical fiber (OF) is bent.

[0133] Optical fiber OF can be of any length, and it will be understood that the length of optical fiber OF can depend on the application. The length of optical fiber OF can be between 1 cm and 10 m, for example, the length of optical fiber OF can be between 10 cm and 100 cm.

[0134] An optical fiber (OF) comprises: a hollow core (COR); a cladding portion surrounding the hollow core (COR); and a support portion (SP) surrounding and supporting the cladding portion. An optical fiber (OF) can be considered as a body comprising a hollow core (COR) including the cladding portion and the support portion (SP). The cladding portion includes multiple anti-resonance elements for guiding radiation through the hollow core (COR). Specifically, the multiple anti-resonance elements are arranged to primarily confine radiation propagating through the optical fiber (OF) within the hollow core (HC) and guide radiation along the optical fiber (OF). The hollow core (HC) of the optical fiber (OF) can be generally located in the central region of the optical fiber (OF) such that the axis of the optical fiber (OF) also defines the axis of the hollow core (HC).

[0135] The cladding portion includes multiple anti-resonance elements for guiding radiation propagation through the optical fiber (OF). Specifically, in this embodiment, the cladding portion includes a single ring composed of six tubular capillary CAPs. Each of the tubular capillary CAPs acts as an anti-resonance element.

[0136] A capillary CAP can also be referred to as a tube. The cross-section of a capillary CAP can be circular or can have other shapes. Each capillary CAP includes a generally cylindrical wall portion WP that at least partially defines the hollow core HC of the optical fiber OF and separates the hollow core HC from the capillary cavity CC. It will be understood that the wall portion WP can act as an anti-reflection Fabry-Perot resonator against radiation propagating through the hollow core HC (and this radiation can be incident on the wall portion WP at a grazing incidence angle). The thickness of the wall portion WP can be suitable to ensure that reflections returning to the hollow core HC are generally enhanced, while transmission to the capillary cavity CC is generally suppressed. In some embodiments, the thickness of the capillary wall portion WP can be between 0.01 µm and 10.0 µm.

[0137] It will be understood that, as used herein, the term "cladding portion" refers to the portion of the optical fiber OF used to guide radiation propagating through the optical fiber OF (i.e., the capillary CAP confining said radiation within the hollow core COR). Radiation can be confined in a lateral mode to propagate along the fiber axis.

[0138] The support portion is typically tubular, and supports the six capillary CAPs of the covered portion. If it is an internal support portion SP, the six capillary CAPs are evenly distributed around the inner surface. The six capillary CAPs can be described as being arranged in a generally hexagonal formation.

[0139] The capillary CAPs are arranged such that each capillary does not contact any other capillary CAP. Each capillary CAP contacts the internal support portion SP and is separated from adjacent capillary CAPs in the ring structure. This arrangement can be advantageous because it can increase the transmission bandwidth of the optical fiber OF (e.g., relative to an arrangement in which the capillaries contact each other). Alternatively, in some embodiments, each capillary CAP may contact adjacent capillary CAPs in the ring structure.

[0140] The six capillary tubes (CAPs) of the cladding portion are arranged in a ring structure around the hollow core (COR). The inner surface of the ring structure of the capillary tubes at least partially defines the hollow core (HC) of the fiber OF. The diameter d of the hollow core (HC) (which can be defined as the minimum dimension between relative capillaries, indicated by the arrow d) can range from 10 µm to 1000 µm. The diameter d of the hollow core (HC) can affect the mode field diameter, impact loss, dispersion, modal multivariability, and nonlinear characteristics of the hollow fiber OF.

[0141] In this embodiment, the covering portion includes a single ring arrangement of capillary CAPs (which act as anti-resonance elements). Therefore, any line in any radial direction from the center of the hollow core HC to the outside of the optical OF will pass through no more than one capillary CAP.

[0142] It will be understood that other embodiments may include different arrangements of anti-resonance elements. These arrangements may include arrangements with multiple rings consisting of anti-resonance elements and arrangements with nested anti-resonance elements. Furthermore, although... Figure 13 The embodiment shown includes a ring consisting of six capillaries, but in other embodiments, one or more rings including any number of anti-resonance elements (e.g., 4, 5, 6, 7, 8, 9, 10, 11 or 12 capillaries) may be provided in the covering portion.

[0143] Figure 14a The Kagome fiber, including a Kagome lattice structure, is shown. Figure 14(b) shows a modified embodiment of the above-described HC-PCF, having a single ring composed of tubular capillaries. In the example of Figure 14(b), there are two coaxial rings composed of tubular capillaries 21. To hold the inner and outer rings composed of tubular capillaries 21, a support tube ST can be included in the HC-PCF. The support tube can be made of silicon dioxide.

[0144] Figure 13 as well as Figure 14a and Figure 14b The example tubular capillary can have a circular cross-sectional shape. Other shapes are also possible for tubular capillaries, such as elliptical or polygonal cross-sections. Additionally, Figure 13 as well as Figure 14aand Figure 14b The solid material of the tubular capillary in the example may include plastic materials (such as PMA), glass (such as silicon dioxide), or soft glass.

[0145] Further embodiments are disclosed in the list of subsequent numbered clauses: 1. A radiation source assembly for generating broadband radiation, the radiation source assembly comprising: Solid-core photonic crystal fiber SC-PCF has an input end and an output end, wherein the input end is configured to receive radiation pulses from a pump source; Hollow-core photonic crystal fiber HC-PCF, filled with a gaseous working medium and arranged to receive radiation pulses output from the output of SC-PCF at the input of HC-PCF; and The SC-PCF is configured to broaden the spectrum of the radiation pulse by providing nonlinearity under normal group velocity dispersion, and The HC-PCF is configured to generate broadband radiation through the nonlinear interaction between the radiation pulse and the gaseous working medium, and outputs broadband radiation at the output end of the HC-PCF. 2. The radiation source assembly according to Clause 1, wherein the output of the SC-PCF is coupled to the input of the HC-PCF. 3. The radiation source assembly according to Clause 2 further includes a gas chamber surrounding at least a portion of the HC-PCF, wherein the gas chamber is filled with a gaseous working medium. 4. The radiation source assembly according to Clause 3, wherein the input end of the SC-PCF and the output end of the SC-PCF are surrounded in the gas chamber, and the gas chamber completely surrounds the HC-PCF. 5. The radiation source assembly according to Clause 3, wherein the output terminal of the SC-PCF is surrounded within the gas chamber, and the SC-PCF extends such that the input terminal of the SC-PCF is located outside the gas chamber, and the gas chamber completely surrounds the HC-PCF. 6. The radiation source assembly according to Clause 3, wherein the output terminal of the HC-PCF is surrounded within the gas chamber; and the input terminal of the HC-PCF and the SC-PCF are located outside the gas chamber. 7. The radiation source assembly according to Clause 1 further includes another hollow-core photonic crystal fiber FHC-PCF, wherein the output end of the SC-PCF is coupled to the input end of the FHC-PCF, and the input end of the HC-PCF is coupled to the output end of the FHC-PCF. 8. The radiation source assembly as described in Clause 7 further includes: A gas chamber, surrounding at least a portion of the HC-PCF, wherein the gas chamber is filled with the gaseous working medium; and Another air chamber, wherein the other air chamber surrounds at least one end of the FHC-PCF. 9. The radiation source assembly according to Clause 8, wherein the other gas chamber is filled with another gaseous working medium. 10. The radiation source assembly as described in Clause 8, wherein the other gas chamber comprises a vacuum. 11. The radiation source assembly according to any one of clauses 8 to 10, wherein the output end of the SC-PCF is surrounded in the other gas chamber. 12. The radiation source assembly according to any one of clauses 8 to 11, wherein the SC-PCF extends such that the input end of the SC-PCF is located outside the gas chamber. 13. The radiation source assembly according to any one of Clauses 7 to 12 further includes a docking optical fiber for coupling the input end of the HC-PCF to the output end of the FHC-PCF. 14. The radiation source assembly according to any one of Clauses 7 to 12, wherein the input of the HC-PCF is coupled to the output of the FHC-PCF via a collapsed portion of the HC-PCF and / or a collapsed portion of the FHC-PCF. 15. The radiation source assembly according to any one of the preceding clauses further includes the pump source. 16. The radiation source assembly according to Clause 15, wherein the duration of the radiation pulse is in the range of 100 fs to 250 fs. 17. The radiation source assembly according to Clause 15, wherein the duration of the radiation pulse is at least 250 fs. 18. The radiation source assembly according to Clause 15, wherein the duration of the radiation pulse is at least 1 ps, optionally at least 1.5 ps, optionally at least 2 ps, optionally at least 5 ps, or optionally at least 10 ps. 19. The radiation source assembly according to any one of the preceding clauses, wherein the gas working medium comprises an inert gas. 20. The radiation source assembly according to any one of the preceding clauses, wherein the broadband radiation includes supercontinuum radiation. 21. A photolithography apparatus comprising a radiation source assembly according to any one of the preceding clauses. 22. A measuring device comprising a radiation source assembly according to any one of clauses 1 to 20. 23. The measuring apparatus according to Clause 22, wherein the radiation source is used to provide illumination light. 24. A method for generating broadband radiation, the method comprising: The spectrum of the radiation pulse is broadened by supplying the radiation pulse from a pump source to a solid-core photonic crystal fiber SC-PCF, which has an input end and an output end; Broadband radiation is generated through the nonlinear interaction between the radiation pulse and the gaseous working medium in the hollow photonic crystal fiber HC-PCF, wherein the HC-PCF is arranged to receive the radiation pulse output from the output end of the SC-PCF at its input end; and The broadband radiation is output at the output terminal of the HC-PCF.

[0146] While the use of photolithography apparatus in IC manufacturing is specifically mentioned in this article, it should be understood that the photolithography apparatus described herein can have other applications. Possible other applications include the fabrication of integrated optical systems, guidance and detection modes for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0147] Although embodiments of the invention may be specifically referred to herein within the context of a photolithography apparatus, embodiments of the invention can be used in other apparatuses. Embodiments of the invention can form part of a mask inspection apparatus, a measurement apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses are generally referred to as photolithography tools. Such photolithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0148] Although the use of embodiments of the invention in the context of optical lithography may be specifically mentioned above, it will be understood that the invention is not limited to optical lithography and can be used in other applications, such as imprint lithography, where the context permits.

[0149] While specific embodiments of the invention have been described above, it will be understood that the invention may be practiced in ways other than those described. The above description is intended to illustrate, not limit. Therefore, it will be apparent to those skilled in the art that modifications may be made to the described invention without departing from the scope of the following claims.

[0150] Although the terms "measuring apparatus / tool / system" or "inspection apparatus / tool / system" are specifically mentioned, these terms can refer to the same or similar types of tools, apparatus, or systems. For example, an inspection or measuring apparatus 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 or measuring apparatus 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, a characteristic of interest in a structure on a substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of an unwanted structure on the substrate or wafer.

Claims

1. A radiation source assembly for generating broadband radiation, the radiation source assembly comprising: A solid-core photonic crystal fiber SC-PCF has an input end and an output end, wherein the input end is configured to receive radiation pulses from a pump source; Hollow-core photonic crystal fiber HC-PCF, filled with a gaseous working medium and arranged to receive radiation pulses output from the output end of SC-PCF at the input end of the HC-PCF; as well as The SC-PCF is configured to broaden the spectrum of the radiation pulse by providing nonlinearity under normal group velocity dispersion, and The HC-PCF is configured to generate broadband radiation through the nonlinear interaction between the radiation pulse and the gaseous working medium, and to output the broadband radiation at the output terminal of the HC-PCF.

2. The radiation source assembly of claim 1, wherein the output terminal of the SC-PCF is coupled to the input terminal of the HC-PCF.

3. The radiation source assembly of claim 2 further includes a gas chamber surrounding at least a portion of the HC-PCF, wherein the gas chamber is filled with a gaseous working medium.

4. The radiation source assembly of claim 3, wherein the input end of the SC-PCF and the output end of the SC-PCF are surrounded in the gas chamber, and the gas chamber completely surrounds the HC-PCF.

5. The radiation source assembly of claim 3, wherein the output end of the SC-PCF is surrounded within the gas chamber, and the SC-PCF extends such that the input end of the SC-PCF is located outside the gas chamber, and the gas chamber completely surrounds the HC-PCF.

6. The radiation source assembly of claim 3, wherein the output terminal of the HC-PCF is surrounded within the gas chamber; and the input terminal of the HC-PCF and the SC-PCF are located outside the gas chamber.

7. The radiation source assembly according to claim 1 further comprises another hollow-core photonic crystal fiber FHC-PCF, wherein the output end of the SC-PCF is coupled to the input end of the FHC-PCF, and the input end of the HC-PCF is coupled to the output end of the FHC-PCF.

8. The radiation source assembly according to claim 7, further comprising: A gas chamber surrounding at least a portion of the HC-PCF, wherein the gas chamber is filled with the gaseous working medium; as well as Another air chamber, wherein the other air chamber surrounds at least one end of the FHC-PCF.

9. The radiation source assembly according to claim 7 or 8 further includes a docking optical fiber for coupling the input end of the HC-PCF to the output end of the FHC-PCF.

10. The radiation source assembly according to claim 7 or 8, wherein the input terminal of the HC-PCF is coupled to the output terminal of the FHC-PCF via a collapsed portion of the HC-PCF and / or a collapsed portion of the FHC-PCF.

11. The radiation source assembly according to any one of the preceding claims, further comprising the pump source.

12. The radiation source assembly of claim 11, wherein the duration of the radiation pulse is in the range of 100 fs to 250 fs.

13. The radiation source assembly of claim 11, wherein the duration of the radiation pulse is at least 250 fs.

14. A measuring device comprising a radiation source assembly according to any one of claims 1 to 13 for providing illumination light.

15. A method for generating broadband radiation, the method comprising: A radiation pulse from a pump source is provided to the input of a solid-core photonic crystal fiber (SC-PCF) having an input and an output, wherein the SC-PCF is configured to broaden the spectrum of the radiation pulse by providing nonlinearity under normal group velocity dispersion. Broadband radiation is generated through the nonlinear interaction between the radiation pulse and the gaseous working medium in the hollow photonic crystal fiber HC-PCF, wherein the HC-PCF is arranged to receive the radiation pulse output from the output end of the SC-PCF at the input end of the HC-PCF. as well as The broadband radiation is output at the output terminal of the HC-PCF.

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