Assemblies comprising nonlinear elements and methods of using the same

Abstract

An assembly comprising a nonlinear element configured to generate broadband radiation from input radiation coupled into the nonlinear element. The assembly further comprises an optical element downstream of the nonlinear element, the optical element being configured to reflect a portion of the broadband radiation back into the nonlinear element. The nonlinear element is typically a nonlinear optical fiber, such as a hollow-core photonic crystal fiber (HC-PCF).

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to European application 20166940.5, filed on March 31, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to assemblies including nonlinear elements and methods of using the same. More specifically, the nonlinear element is configured to generate broadband radiation from input radiation coupled to the nonlinear element. Background Technology

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

[0005] To project patterns onto a substrate, photolithography equipment 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. Compared to photolithography equipment using radiation with a wavelength of, for example, 193 nm, photolithography equipment using extreme ultraviolet (EUV) radiation with wavelengths in the 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.

[0006] Low-k1 lithography can be used to process features smaller than the classical resolution limit of lithography equipment. In this process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the radiation wavelength used, NA is the numerical aperture of the projection optics in the lithography equipment, CD is the "critical size" (typically the smallest feature size printed, but in this case, half-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 to achieve specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection equipment and / or design layout. These steps include, but are not limited to, optimizing NA, customizing the illumination scheme, using phase-shifting patterning apparatus, various optimizations of the design layout such as optical proximity correction (OPC, sometimes also called "optical and process correction"), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, tight control loops used to control the stability of the lithography equipment can be used to improve pattern reproduction at low k1.

[0007] Regarding lithography applications, many different types of measurements can be performed both inside and outside the lithography apparatus. Typically, such measurements are performed using a device that illuminates the target with a radiation source and a detection system operable to measure at least one characteristic of a portion of the incident radiation scattered from the target. Examples of measurement devices outside the lithography apparatus include metrology devices and inspection devices. Metering devices can return data relating to one or more characteristics of the substrate, where the data can be quantitative. Inspection devices can detect defects or flaws on the substrate. Examples of measurement systems within the lithography apparatus include topographic measurements, position measurements, and alignment measurements for measuring the characteristics of patterns on the substrate.

[0008] The quality of the measurement can affect the quality of the associated photolithography process. One factor that can affect measurement quality is the quality of the radiation used in the measurement.

[0009] Different types of radiation can be used to probe different properties of a substrate.

[0010] The radiation source (e.g., using hollow photonic crystal fiber) may have low efficiency. For example, up to 40% of the pump power (i.e., input radiation) may escape from the fiber along with the generated radiation (i.e., broadband radiation). Ideally, the input radiation should be converted within the fiber, and only a small fraction of the input radiation should escape from the fiber.

[0011] A radiation source may produce radiation in unpredictable ways, governed by, for example, the radiation source itself. The single emission process is inherently chaotic, dominated by quantum noise within the system, and therefore unrestricted by the radiation source. In this sense, it is impossible to control the spectrum of a single emission, nor is it possible to influence the spectrum emanating from the radiation source. The spectral performance of the radiation source may deteriorate without any way to compensate for or modify the spectrum. Summary of the Invention

[0012] According to a first aspect of the invention, an assembly is provided that includes a nonlinear element configured to generate broadband radiation from input radiation coupled to the nonlinear element, wherein the assembly further includes an optical element located downstream of the nonlinear element, the optical element being configured to reflect a portion of the broadband radiation back into the nonlinear element.

[0013] This may have the advantages of increasing broadband radiation generated from the same amount of input radiation and increasing effective energy conversion efficiency. Furthermore, it may have the advantage of reducing the length of nonlinear components. The system's noise performance can also be improved.

[0014] Nonlinear elements can broaden the wavelength spectrum of input radiation to provide broadband output radiation.

[0015] Optical elements can be configured to reflect at least some of the input radiation at or near one or more wavelengths back into the nonlinear element. A portion of the broadband radiation can be radiation at or near one or more wavelengths of the input radiation. That is, unused input (pump) radiation. The input radiation can include a single wavelength, multiple discrete wavelengths, or a narrowband wavelength range.

[0016] Optical elements can be configured to provide pulse compression for at least some of the input radiation at or near one or more wavelengths. This can have the advantage of increasing the intensity of reflected, unused input radiation to initiate a nonlinear process that generates broadband radiation. Input radiation pulse compression can be achieved through phase modulation.

[0017] Optical elements can be configured to transmit at least some broadband radiation. The optical element can be a transmitting element. Broadband radiation can include the input radiation. Broadband radiation can be supercontinuum radiation.

[0018] The optical element can be configured to transmit 90% to 100% of the broadband radiation, excluding the reflected portion of the broadband radiation. Alternatively, the optical element can be configured to transmit essentially 100% of the broadband radiation, excluding the reflected portion of the broadband radiation.

[0019] The component may further include an additional optical element located between the nonlinear optical element and the optical element, the additional optical element being configured to transmit at least some broadband radiation of the input radiation and reflect at least some radiation at or near one or more wavelengths of the input radiation to the optical element, and reflect the at least some radiation from the optical element back to the nonlinear optical element. The optical element may be a reflective element. The additional optical element may be a dichroic mirror. The optical element may include a chirped mirror, a grating pair, or a prism pair.

[0020] The additional optical element can be configured to transmit 90% to 100% of the broadband radiation, excluding the reflected portion of the broadband radiation. Alternatively, the additional optical element can be configured to transmit essentially 100% of the broadband radiation, excluding the reflected portion of the broadband radiation.

[0021] Optical elements can be configured to reflect 90% to 100% of the input radiation at or near one or more wavelengths.

[0022] Optical elements can be configured to reflect most broadband radiation back into the nonlinear element. Most broadband radiation can include the input radiation. Broadband radiation can be the generated broadband radiation. The reflected broadband radiation can generate additional broadband radiation in the nonlinear element. The optical element can be a reflective element.

[0023] The optical element can be a transmission element. The optical element can be configured to transmit at least some broadband radiation. The optical element can be configured to transmit up to 10% broadband radiation.

[0024] Optical elements can be configured to reflect 90% to 100% of broadband radiation.

[0025] The component may include an auxiliary optical element located upstream of the nonlinear element, the auxiliary optical element being configured to reflect at least some broadband radiation off-axis and transmit at least some of the radiation at or near one or more wavelengths of the input radiation. The auxiliary optical element may reflect the broadband radiation away from the nonlinear element.

[0026] The component may include an upstream optical element located upstream of the nonlinear element, the upstream optical element being configured to reflect at least some broadband radiation back into the nonlinear element. The upstream optical element may transmit the input radiation. The upstream optical element may be configured to reflect 90% to 100% of the broadband radiation.

[0027] The component may include an upstream supplementary optical element located between the nonlinear optical element and the upstream optical element. The upstream supplementary optical element is configured to transmit at least some radiation at or near one or more wavelengths of the input radiation, reflect at least some broadband radiation to and from the upstream optical element back into the nonlinear optical element. The upstream optical element may be a reflective element. The upstream supplementary optical element may be a dichroic mirror. The upstream supplementary optical element may reflect 90% to 100% of the broadband radiation.

[0028] Upstream optics can be configured to shape pulses of broadband radiation. This can have the advantage of allowing the average spectrum from nonlinear elements to be affected and compensating for degraded spectral performance. The broadband radiation can be manipulated as needed for the application. Dynamic elements can be modified during operation (e.g., for pulse shaping or pulse compression).

[0029] Upstream optical elements can be configured for spectral filtering purposes; to filter out specific frequencies from broadband radiation.

[0030] The component according to any one of the preceding claims, wherein the component includes a first lens and a second lens located upstream and downstream of the nonlinear element, respectively, the first lens for focusing radiation onto the nonlinear element and the second lens for providing substantially collimated radiation exiting from the nonlinear element. The downstream optical element may include a spectral filter or an acousto-optic tunable filter.

[0031] The component may include at least one actuator configured as at least one of a moving optical element, an additional optical element, an upstream optical element, an upstream additional optical element, an auxiliary optical element, a first lens, and a second lens. The actuator allows radiation to enter the nonlinear element. Each component may have a separate actuator.

[0032] Nonlinear elements can be hollow optical fibers.

[0033] Hollow optical fiber can be a photonic crystal fiber.

[0034] According to a second aspect of the invention, a measurement arrangement is provided, the measurement arrangement comprising the components detailed above.

[0035] According to a third aspect of the present invention, a measuring device is provided, the measuring device comprising the measuring arrangement detailed above.

[0036] According to a fourth aspect of the present invention, an inspection apparatus is provided, the inspection apparatus comprising the measurement arrangement as detailed above.

[0037] According to a fifth aspect of the present invention, a photolithography apparatus is provided, the photolithography apparatus comprising the components detailed above.

[0038] According to a sixth aspect of the present invention, a photolithography apparatus is provided, the photolithography apparatus comprising the measurement arrangement detailed above.

[0039] According to a seventh aspect of the invention, a method is provided for generating broadband radiation from input radiation coupled to a nonlinear element, the method comprising: reflecting a portion of the broadband radiation back into the nonlinear element from an optical element located downstream of the nonlinear element. Attached Figure Description

[0040] Embodiments of the invention will now be described by way of example only, with reference to the accompanying schematic diagrams, wherein:

[0041] - Figure 1 A schematic schematic diagram of a photolithography apparatus is depicted;

[0042] - Figure 2 A schematic schematic diagram of the photolithography unit is depicted;

[0043] - Figure 3 A schematic diagram of overall photolithography is depicted, representing the collaboration between three key technologies for optimizing semiconductor manufacturing;

[0044] - Figure 4 A schematic diagram of the scatterer is depicted;

[0045] - Figure 5Includes: (a) a schematic diagram of a dark-field scatterer for measuring a target using a first pair of irradiation apertures according to an embodiment of the invention; (b) details of the diffraction spectrum of a target grating given an irradiation direction; (c) a second pair of irradiation apertures that provides additional irradiation modes when performing diffraction-based overlap measurements using the scatterer; and (d) a third pair of irradiation apertures combining the first pair of apertures and the second pair of apertures.

[0046] Figure 6 A schematic schematic diagram of the horizontal sensor is depicted;

[0047] Figure 7 A schematic schematic diagram of the alignment sensor is depicted;

[0048] Figure 8 This is a schematic cross-sectional view of a hollow optical fiber that can form part of a radiation source according to an embodiment in a transverse plane (i.e., perpendicular to the axis of the optical fiber).

[0049] Figure 9 A schematic diagram of a radiation source according to an embodiment for providing broadband output radiation is depicted;

[0050] - Figure 10 (a) and (b) schematically depict cross-sections of examples of hollow-core photonic crystal fiber (HC-PCF) designs for generating supercontinuum.

[0051] - Figure 11 A schematic schematic diagram of an assembly including a hollow-core photonic crystal fiber (HC-PCF) according to an embodiment of the present invention is depicted.

[0052] - Figure 12a A graph depicting reflections from downstream optical elements in a component illustrating an embodiment of the invention;

[0053] - Figure 12b A graph depicting reflections from an upstream optical element in a component according to an embodiment of the invention is shown;

[0054] - Figure 13 A schematic schematic diagram of an assembly comprising a hollow-core photonic crystal fiber (HC-PCF) according to another embodiment of the present invention is depicted.

[0055] - Figure 14 A schematic schematic diagram of an assembly comprising a hollow-core photonic crystal fiber (HC-PCF) according to another embodiment of the present invention is depicted. Detailed Implementation

[0056] 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 in the range of about 5 nm to 100 nm).

[0057] As used herein, the terms "mask," "mask," or "patterning apparatus" can be broadly interpreted to refer to a general patterning apparatus used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be created in a target portion of a substrate. The term "optical valve" may also be used herein. Examples of such patterning apparatuses, besides classic masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

[0058] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also referred to as 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) MT, configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM, configured to accurately position the patterning apparatus MA according to certain parameters; a substrate support (e.g., a wafer stage) WT, configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW, configured to accurately position the substrate support 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 apparatus MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0059] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example, through a beam transmission system BD. The irradiation system IL may include various types of optical components for guiding, shaping, and / or controlling the radiation, including, for example, refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the pattern forming apparatus MA.

[0060] As used herein, the term "projection system" PS should be interpreted broadly to encompass all types of projection systems, including refractive, reflective, reflective-refractive, distorting, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, to suit the exposure radiation used and / or other factors, such as the use of immersion liquids or vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0061] 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.

[0062] The lithography equipment LA can also be of the type with two or more substrate supports WT (also known as "dual platform"). In such a "multi-platform" machine, the substrate supports WT can be used in parallel, and / or subsequent exposure preparation steps for the substrate W can be performed on the substrate W, which is located on one of the substrate supports WT, while the substrate W on the other substrate support WT is used to expose the pattern on the other substrate W.

[0063] In addition to the substrate support WT, the lithography apparatus LA may include a measurement stage. The measurement stage is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure characteristics of the projection system PS or the radiation beam B. The measurement stage may hold multiple sensors. The cleaning devices may be arranged to clean part of the lithography apparatus, such as part of the projection system PS or part of a system providing immersion liquid. The measurement stage may move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0064] In operation, a radiation beam B is incident on a pattern forming apparatus (e.g., a mask MA), which is held on a mask support MT and patterned by a pattern (design layout) present on the pattern forming apparatus MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be precisely moved, for example, to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, a first positioner PM and possibly another position sensor ( Figure 1(Another possible position sensor, not explicitly depicted, can be used to accurately position the pattern forming apparatus MA relative to the path of the radiation beam B.) The pattern forming apparatus 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, as shown, occupy dedicated target portions, they can be located in the space between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, they are referred to as scribing alignment marks.

[0065] like Figure 2 As shown, the lithography equipment LA can form part of a lithography unit LC, which is sometimes also called a lithography cell or (lithography) cluster. The lithography cell or (lithography) cluster typically also includes equipment for performing pre-exposure and post-exposure processing on the substrate W. These devices typically include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chiller CH for regulating the temperature of the substrate W, and a baking plate BK for regulating the solvent in the resist layer. A substrate handler or robot RO picks up the substrate W from input / output ports I / O1 and I / O2, moves the substrate W between different processing devices, and transfers the substrate W to the loading stage LB of the lithography equipment LA. The equipment in the lithography cell (often collectively referred to as tracks) is typically controlled by a track control unit TCU, which itself can be controlled by a monitoring system SCS, which can also control the lithography equipment LA (e.g., via the lithography control unit LACU).

[0066] To ensure that the substrate W exposed by the lithography equipment LA is exposed correctly and consistently, it is desirable to inspect the substrate to measure characteristics of the patterned structure, such as overlap error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, an inspection tool (not shown) can be included in the lithography cell LC. If an error is detected, for example, particularly if the inspection is performed before other substrates W in the same batch or leg of the same substrate are to be exposed or processed, adjustments can be made to the exposure of subsequent substrates or other processing steps to be performed on the substrate W.

[0067] Inspection equipment (also known as measurement equipment) is used to determine the properties of a substrate W, particularly how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary between layers. Inspection equipment can alternatively be configured to identify defects on the substrate W and can be, for example, part of a photolithography unit (LC), integrated into a photolithography apparatus (LA), or even a stand-alone device. Inspection equipment can measure the properties of latent images (images in the resist layer after exposure), semi-latent images (images in the resist layer after the post-exposure baking (PEB) step), or images of developed resist (where exposed or unexposed portions of the resist have been removed), and even the properties of etched images (after pattern transfer steps such as etching).

[0068] Typically, the patterning process in photolithography (LA) equipment is one of the most critical steps in the process, requiring high-precision dimensional determination and structure placement on the substrate W. To ensure this high precision, three systems can be combined in a so-called "holistic" control environment, such as... Figure 3 The diagram illustrates these systems. One of these systems is the lithography apparatus (LA), which is (in effect) connected to the metrology tool (MT) (the second system) and the computer system (CL) (the third system). The key to this “holistic” environment is optimizing the collaboration 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 set of process parameters (e.g., dose, focus, overlap) within which a specific manufacturing process produces a defined result (e.g., a functional semiconductor device)—typically allowing for variations in process parameters within the lithography or patterning process.

[0069] The computer system CL can use the design layout (partially) 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 equipment settings enable the maximum process window (within) the patterning process. Figure 3 (Depicted by double arrows in the first scale SC1). Typically, resolution enhancement techniques are arranged to match the patterning possibilities of the lithography equipment LA. The computer system CL can also be used to detect where the lithography equipment LA is currently (e.g., using input from the metrology tool MT) within the process window to predict whether defects might exist due to, for example, suboptimal processing (in...). Figure 3 (Depicted by an arrow pointing to "0" in the second scale SC2).

[0070] The measurement tool MT can provide input to the computer system CL to achieve accurate simulation and prediction, and for example, in the calibration state of the lithography equipment LA (in Figure 3(Depicted by multiple arrows in the third scale SC3) can provide feedback to the lithography equipment LA to identify possible drifts.

[0071] In photolithography, it is often desirable to measure the created structure for purposes such as process control and verification. The tools used to perform these measurements are commonly referred to as metrology tools (MTs). Different types of metrology tools (MTs) are known for performing these measurements, including scanning electron microscopes (SEMs) or various forms of scatterometer metrology tools (MTs).

[0072] Examples of known scatterers typically rely on providing a dedicated measurement target, such as an underfilled target (a target in the form of a simple grating or overlapping gratings in different layers, large enough that the measurement beam produces a spot smaller than the grating) or an overfilled target (so that the illumination spot partially or completely encompasses the target). Furthermore, the use of measurement instruments (e.g., an angle-resolved scatterer illuminating an underfilled target (e.g., a grating) allows for the use of so-called reconstruction methods, in which the characteristics of the grating are calculated 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 model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0073] A scatterometer is a general-purpose instrument that allows for the measurement of parameters of a photolithography process by mounting a sensor in the pupil of the scatterometer's objective lens, or in a plane conjugate to the pupil of the scatterometer's objective lens, or by mounting the sensor in the image plane or a plane conjugate to the image plane. Measurements are typically referred to as pupil-based measurements, and in this case, as image- or field-based measurements. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned scatterometers can measure gratings using light from soft X-rays and the visible to near-infrared wavelength range.

[0074] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, reconstruction methods can be applied to the measured signal to reconstruct or calculate the characteristics of the grating. For example, such 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.

[0075] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In this spectroscopic scatterer MT, radiation emitted by a radiation source is directed onto the target, while reflected or scattered radiation from the target is directed to a spectroscopic detector that measures the spectrum of the specularly reflected radiation (i.e., 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.

[0076] In the third embodiment, the scatterer MT is an elliptic scatterer. An elliptic scatterer allows for the determination of lithography process parameters by measuring the scattered radiation for each polarization state. This metrology device emits polarized light (e.g., linear, circular, or elliptical polarized light) by using, for example, a suitable polarization filter in the illumination portion of the metrology device. A source suitable for the metrology device can also provide polarized radiation. Several embodiments of existing elliptic 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, 31 / 533,110, and 891,410, all of which are incorporated herein by reference in their entirety.

[0077] In one embodiment of a scattering instrument (MT), the scattering instrument MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or detecting an asymmetry in the configuration, the asymmetry being related to the degree of overlap. The two (typically overlapping) grating structures can be applied to two different layers (not necessarily consecutive layers) and can be formed substantially at the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, for example, described in the co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a direct method for measuring misalignment in gratings. Other examples of measuring overlap errors between two layers, including periodic structures as targets, by means of asymmetry in periodic structures can be found in PCT patent application publication WO 2011 / 012624 or U.S. patent application US 20160161863, which are incorporated herein by reference in their entirety.

[0078] Other parameters of interest may be focus and dose. As described in U.S. Patent Application US2011-0249244, which is incorporated herein by reference in its entirety, focus and dose can be determined simultaneously by scattering measurements (or alternatively by scanning electron microscopy). A single structure can be used, having a unique combination of critical dimensions 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, the focus and dose values ​​can be uniquely determined based on these measurements.

[0079] The measurement target can be an assembly of composite gratings, formed primarily in a resist by a photolithography process, but can also be formed after, for example, an etching process. Typically, the spacing and linewidth of the structures within the gratings are highly dependent on the measurement optics (particularly the NA of the optics) to capture the diffraction order from the measurement target. As previously mentioned, the diffraction signal can be used to determine the offset (also known as "overlap") between two layers 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 smaller sub-segments configured to mimic the dimensions of functional portions of a design layout within the target. Due to this subdivision, the target will behave more closely like the functional portions of the design layout, thus making the overall process parameter measurements more similar to those of the functional portions of the design layout. The target can be measured in underfill or overfill modes. In underfill mode, the measurement beam produces a spot smaller than the entire target. In overfill mode, the measurement beam produces a spot larger than the entire target. In this overfill mode, different targets can also be measured simultaneously, thereby determining different processing parameters at the same time.

[0080] The overall measurement quality of lithography parameters for a specific target is determined at least in part by the measurement scheme used to measure those parameters. The term "substrate measurement scheme" can include one or more parameters of the measurement itself, one or more parameters of the measured pattern, or both. For example, if the measurement used in the substrate measurement scheme is a diffraction-based optical measurement, one or more of the measurement parameters can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. For example, one criterion for selecting a measurement scheme 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, which are incorporated herein by reference in their entirety.

[0081] Figure 4A measurement device, such as a scattering instrument, is described. The device includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate 6. The reflected or scattered radiation is passed to a spectrometer detector 4, which measures the spectrum 10 of the specular reflected radiation (i.e., the intensity as a function of wavelength). Based on this data, it can be processed by a processing unit PU, for example, through rigorous coupled-wave analysis and nonlinear regression, or through... Figure 4 The simulated spectral library shown at the bottom is compared to reconstruct the structure or profile that produces the detected spectrum. Generally, for reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the process of manufacturing the structure, leaving only some parameters of the structure determined from scattering measurement data. This scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0082] Figure 5 (a) An embodiment of the measuring equipment is presented, more specifically, a dark-field scattering instrument. Figure 5 (b) illustrates the target T and the diffracted rays of the measurement radiation used to illuminate the target in more detail. The measurement device illustrated is a type known as a dark-field measurement device. The measurement device can be a stand-alone device or, for example, integrated into a lithography unit LA at a measurement station, or integrated into a lithography unit LC. The dashed line O represents the optical axis with multiple branches throughout the device. In this device, light emitted by a light source 11 (e.g., a xenon lamp) is guided onto the substrate W via a beam splitter 15 through an optical system comprising lenses 12, 14 and objective lens 16. These lenses are arranged in a double sequence of 4F. Different lens arrangements can be used if different lens arrangements still provide an image of the substrate to the detector while allowing access to the intermediate pupil plane for spatial frequency filtering. Thus, the range of angles at which radiation is incident on the substrate can be selected by defining the spatial intensity distribution in the plane presenting the spatial spectrum of the substrate plane, which is referred to here as the (conjugate) pupil plane. Specifically, this can be accomplished by inserting an aperture plate 13 of appropriate form between lenses 12 and 14 in the plane of the back-projected image, which serves as the pupil plane of the objective lens. In the example shown, the aperture plate 13 has different forms, labeled 13N and 13S, which allow for the selection of different illumination modes. The illumination system of this embodiment forms an off-axis illumination mode. In the first illumination mode, for illustrative purposes only, aperture plate 13N provides off-axis illumination in the direction designated "north". In the second illumination mode, while aperture plate 13S is used to provide similar illumination, it provides that illumination from the opposite direction, labeled "south". Other illumination modes are possible by using different apertures. Because any unwanted light outside the desired illumination mode would interfere with the desired measurement signal, the remainder of the pupil plane is desired to be dark.

[0083] like Figure 5 As shown in (b), the target T is placed on a substrate W, which is perpendicular to the optical axis O of the objective lens 16. The substrate W may be supported by a support (not shown). The ray of measurement radiation I, which is incident on the target T from an angle off-axis O, produces a zero-order ray (solid line 0) and two first-order rays (dotted line +1 and double-dotted line -1). It should be remembered that for an overfilled small target, these rays are just one type of many parallel rays covering the area of ​​the substrate that includes the measurement target T and other features. Because the aperture in plate 13 has a finite width (which must allow a useful amount of light to enter), the incident ray I will actually occupy a certain angular range, and the diffracted rays 0 and +1 / -1 will spread out slightly. Depending on the point spread function of the small target, each order +1 and -1 will further spread out over an angular range, rather than a single ideal ray as shown. Note that the grating spacing of the target and the illumination angle can be designed or adjusted so that the first-order rays entering the objective lens are closely aligned with the central optical axis. Figure 5 (a) and Figure 3 The light rays shown in (b) are slightly off-axis, only to make the light rays in the image slightly off-axis. Figure 5 (a) and Figure 3 The light rays shown in (b) are more easily distinguished in the figure.

[0084] At least the 0th and +1st orders of the target T diffracted on the substrate W are collected by objective lens 16 and guided back to the target T diffracted on the substrate W by beam splitter 15. Return to Figure 5 (a) indicates the first and second illumination modes by specifying the diameter-opposite apertures marked North (N) and South (S). When the incident ray I for measuring radiation comes from the north side of the optical axis, i.e., when the first illumination mode is applied using aperture plate 13N, the +1 diffraction ray marked +1 (N) enters the objective lens. Conversely, when the second illumination mode is applied using aperture plate 13S, the -1 diffraction ray (marked 1 (S)) is the ray entering lens 16.

[0085] The second beam splitter 17 divides the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 uses the zeroth-order diffracted beam and the first-order diffracted beam to form the diffraction spectrum (pupil plane image) of the target on the first sensor 19 (e.g., a CCD or CMOS sensor). Each diffraction order illuminates a different point on the sensor, so image processing can compare and contrast these orders. The pupil plane image captured by the sensor 19 can be used for focusing measurement devices and / or normalizing the intensity measurement of the first-order beam. The pupil plane image can also be used for many measurement purposes, such as reconstruction.

[0086] In the second measurement branch, optical systems 20 and 22 form an image of the target T on sensor 23 (e.g., a CCD or CMOS sensor). In this second measurement branch, aperture stop 21 is positioned in a plane conjugate to the pupil plane. Aperture stop 21 acts to block the zero-order diffraction beam, ensuring that the image of the target formed on sensor 23 is formed only by the -1 or +1 order beam. The images captured by sensors 19 and 23 are output to a processor PU that processes the image; the functionality of the processor PU will depend on the specific type of measurement being performed. Note that the term "image" used here is broad. If only one of the -1 or +1 orders is present, such an image of grating lines will not be formed.

[0087] Figure 5 The specific forms of the aperture plate 13 and field stop 21 shown are merely examples. In another embodiment of the invention, on-axis illumination of the target is used and an aperture stop with an off-axis aperture is used to deliver essentially only a first-order diffracted beam to the sensor. In another embodiment, instead of or in addition to the first-order beam, second, third, and higher-order beams ( Figure 5 (Not shown in the image) can be used for measurement.

[0088] To make the measured radiation applicable to these different types of measurements, aperture plate 13 may include multiple aperture patterns formed around a disk that rotates to position the desired pattern in place. Note that aperture plates 13N or 13S can only be used to measure gratings oriented in one direction (X or Y, depending on the setup). For measurements of orthogonal gratings, rotation of the target by 90° and 270° can be utilized. Different aperture plates, such as... Figure 5 As shown in (c) and (d). The use of these devices, as well as many other variations and applications of the devices, are described in the previously published applications mentioned above.

[0089] A topography measurement system, a horizontal sensor, or a height sensor, which can be integrated into a photolithography apparatus, is arranged to measure the topography of the surface of a substrate (or wafer). A topography map of the substrate, also known as a height map, is generated from these measurements, which indicate the height of the substrate as a function of its position on the substrate. This height map can then be used to correct the position of the substrate during pattern transfer on the substrate to provide a spatial image of the patterning apparatus at the appropriate focal position on the substrate. It will be understood that "height" as used herein refers to a broad dimension (also known as the Z-axis) from the plane to the substrate. Typically, the horizontal or height sensor performs measurements in a fixed position (relative to its own optical system), and the relative movement between the substrate and the optical system of the horizontal or height sensor results in a height measurement at a position across the entire substrate.

[0090] exist Figure 6The image schematically illustrates an example of a level or height sensor LS known in the art. Figure 6 This example illustrates only 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) given 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 polarized or unpolarized, pulsed or continuous hypercontinuum light source, such as a polarized or unpolarized laser 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 may additionally or alternatively include UV and / or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

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

[0092] 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 a projection grating PGR. The detector DET generates a detector output signal representing the received light, such as representing the intensity of light received by a photodetector, or representing the spatial distribution of intensity received by a camera, for example. The detector DET can include any combination of one or more detector types.

[0093] 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 depending on the design of the projection grating PGR and the (tilted) incident angle ANG.

[0094] 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 beam between the projection grating PGR and the detection grating DGR (not shown).

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

[0096] In order to effectively cover the surface of the substrate W, the horizontal sensor LS can be configured to project the measurement beam array BE1 onto the surface of the substrate W, thereby generating a measurement area array MLO or spot that covers a larger measurement range.

[0097] Various types of height sensors are disclosed, for example, in US7265364 and US7646471, both of which are incorporated herein by reference. US2010233600A1 discloses a height sensor that uses UV radiation instead of visible or infrared radiation, which is also incorporated herein by reference. WO2016102127A1, also incorporated herein by reference, describes a compact height sensor that uses a multi-element detector to detect and identify the position of a grating image without requiring a detection grating.

[0098] In the fabrication of complex devices, numerous photolithographic patterning steps are typically performed to form functional features in 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 relative to features set in previous layers (using the same or different photolithography apparatus). For this purpose, the substrate is provided with one or more sets of markers. Each marker is structured such that its position can be measured at later using a position sensor, typically an optical position sensor. The position sensor may be referred to as an "alignment sensor," and the marker may be called an "alignment mark."

[0099] Photolithography apparatuses may include one or more alignment sensors that can accurately measure the position of alignment marks set on a substrate. Alignment (or position) sensors can use optical phenomena such as diffraction and interference to obtain positional information from alignment marks formed on the substrate. An example of an alignment sensor used in current photolithography apparatuses is based on a self-reference interferometer described in US6961116. Various enhancements and modifications of position sensors have been developed, such as those disclosed in US2015261097A1. The contents of all these publications are incorporated herein by reference.

[0100] Markings or alignment marks may comprise a series of gratings formed on or within a layer provided on a substrate, or (directly) formed in the substrate. These gratings may be regularly spaced and act as grating lines, thus allowing the marks to be viewed as diffraction gratings with a well-known spatial period (spacing). Depending on the orientation of these grating lines, the marks can be designed to allow measurement of position along the X-axis or along the Y-axis (with the Y-axis oriented substantially perpendicular to the X-axis). Markings comprising gratings arranged at +45 degrees and / or -45 degrees relative to the X and Y axes allow for combined X and Y measurements using techniques as described in US2009 / 195768A, which is incorporated herein by reference.

[0101] The alignment sensor uses a radiating point optical scan to obtain a periodically changing 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 associated with different (coarse and fine) mark sizes can be provided 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.

[0102] Measuring the location of the markings can also provide information about the deformation of the substrate on which the markings are provided, for example, in the form of a wafer grid. The deformation of the substrate may occur, for example, by electrostatically clamping the substrate to a substrate stage and / or heating the substrate when it is exposed to radiation.

[0103] Figure 7 This is a schematic block diagram of a known embodiment of an alignment sensor AS, such as that described in US6961116, which is incorporated herein by reference. A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is directed as an illumination spot SP onto a mark, such as a mark AM located on a substrate W, by a directing optics. In this example, the directing optics include a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP illuminating the mark AM may be slightly smaller than the width of the mark itself.

[0104] Radiation diffracted by the marker AM (in this example, through the objective lens OL) is collimated into an information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the marker (zero-order diffraction can also be referred to as reflection). A self-reference interferometer SRI (such as the type disclosed in US6961116 mentioned above) interferes with the beam IB itself, and the beam is then received by a photodetector PD. In cases where the radiation source RSO generates more than one wavelength, additional optics (not shown) may be included to provide separate beams. The photodetector may be a single element, or it may include multiple pixels, if desired. The photodetector may include a sensor array.

[0105] In this example, the steering optics of the spot reflector SM can also be used to block the zero-order radiation reflected from the marker, so that the information-carrying beam IB includes only the higher-order diffraction radiation from the marker AM (which is not necessary for the measurement but improves the signal-to-noise ratio).

[0106] The intensity signal SI is provided to the processing unit PU. Through a combination of optical processing in the device SRI and computational processing in the unit PU, the values ​​of the X and Y positions on the substrate relative to the reference frame are output.

[0107] A single measurement of this type fixes the mark's position within a specific range corresponding to one pitch of the mark. This is combined with a coarser measurement technique to identify which period of the sine wave includes the mark's position. The same process can be repeated at different wavelengths at coarser and / or finer levels to improve accuracy and / or robust detection of the mark, regardless of the material on which the mark is manufactured and the material on which it is placed. Wavelengths can be optically multiplexed and demultiplexed for simultaneous processing, and / or they can be multiplexed via time-division or frequency-division.

[0108] In this example, the alignment sensor and the light spot SP remain stationary, while the substrate W moves. This allows the alignment sensor to be rigidly and accurately mounted to the reference frame while effectively scanning the marker AM in the direction opposite to the movement of the substrate W. The substrate W is controlled during this movement by its mounting on a substrate support and a substrate positioning system that controls the movement of the substrate support. A substrate support position sensor (e.g., an interferometer) measures the position of the substrate support (not shown). In this embodiment, one or more (alignment) markers are provided on the substrate support. Measuring the position of the markers on the substrate support allows calibration of the substrate support position (e.g., relative to the frame to which the alignment system is attached), as determined by the position sensor. Measuring the position of the alignment markers on the substrate allows determination of the substrate position relative to the substrate support.

[0109] Measurement tools (MTs) (such as the scatterometers, topographic surveying systems, or position measurement systems mentioned above) can perform measurements using radiation derived from a radiation source. The characteristics of the radiation used by the measurement tool can affect the type and quality of the measurements that can be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure the substrate, for example, broadband radiation can be used. Multiple different frequencies may be able to propagate through, illuminate, and scatter on the measurement target with little or no interference to other frequencies. Therefore, different frequencies can be used, for example, to obtain more measurement data simultaneously. Different radiation frequencies may also be able to detect and discover different characteristics of the measurement target. Broadband radiation can be used in measurement systems (MTs), such as level sensors, alignment mark measurement systems, scattering measurement tools, or inspection tools. Broadband radiation sources can be hypercontinuum sources.

[0110] Generating high-quality broadband radiation, such as supercontinuum radiation, can be challenging. One approach to generating broadband radiation is, for example, broadening high-power narrowband or single-frequency input radiation using higher-order nonlinear effects. The input radiation (which can be generated using a laser) can be referred to as pump radiation. Alternatively, it can be called seed radiation. To obtain high-power radiation for the broadening effect, the radiation can be confined to a small region, resulting in strongly confined, high-intensity radiation. In those regions, the radiation can interact with broadening structures and / or materials that form a nonlinear medium, thereby producing broadband output radiation. In the high-intensity radiation region, different materials and / or structures can be used to achieve and / or improve radiation broadening by providing a suitable nonlinear medium.

[0111] In some implementations, see the following references. Figure 9 Furthermore, methods and apparatus for broadening input radiation can utilize optical fibers to confine the input radiation and broaden it to output broadband radiation. The optical fiber can be hollow and may include internal structures to achieve efficient guidance and confinement of radiation within the fiber. The optical fiber can be a hollow-core photonic crystal fiber (HC-PCF), which is particularly suitable for strong radiation confinement primarily within the hollow core of the fiber to achieve high radiation intensity. The hollow core of the fiber can be filled with a gas, which acts as a broadening medium for broadening the input radiation. Such an arrangement of fiber and gas can be used to generate a supercontinuum radiation source. The radiation input to the optical fiber can be electromagnetic radiation, such as radiation from one or more of the infrared, visible, ultraviolet, and extreme ultraviolet spectra. The output radiation can consist of or include broadband radiation, which may be referred to herein as white light.

[0112] Some embodiments relate to novel designs of such broadband radiation sources including optical fibers. The optical fiber is a hollow-core photonic crystal fiber (HC-PCF). Specifically, the optical fiber can be a hollow-core photonic crystal fiber of the type including an anti-resonant structure for confining radiation. Such fibers including anti-resonant structures are referred to in the art as anti-resonant fibers, tubular fibers, single-loop fibers, negative curvature fibers, or suppression-coupled fibers. Various designs of such fibers are known in the art. Alternatively, the optical fiber can be a photonic bandgap fiber (HC-PBF, such as Kagome fiber).

[0113] Various types of HC-PCFs can be designed, each based on a different physical guidance mechanism. Two such HC-PCFs include: hollow-core photonic bandgap fiber (HC-PBF) and hollow-core anti-resonant reflective fiber (HC-ARF). Details regarding the design and manufacture of HC-PCFs can be found in US Patent US2004 / 015085A1 (for HC-PBF) and International PCT Patent Application WO2017 / 032454A1 (for hollow-core anti-resonant reflective fiber), which are incorporated herein by reference. Figure 10 (a) shows a Kagome optical fiber that includes a Kagome lattice structure.

[0114] Now for reference Figure 8 Describe an example of an optical fiber used as a radiation source. Figure 8 This is a schematic cross-sectional view of the optical fiber (OF) in the transverse plane. A similar view is disclosed in WO2017 / 032454A1. Figure 8 Other embodiments of actual examples of optical fibers.

[0115] An optical fiber (OF) consists of an elongated body; this elongated body is longer in one dimension compared to the other two dimensions of the optical fiber OF. This longer dimension can be called the axial direction and can define the axis of the optical fiber OF. The other two dimensions define a plane, which can be called the transverse plane. Figure 8 The cross-section of the optical fiber OF is shown in this (i.e., perpendicular to the axis) transverse plane, which is labeled the xy plane. The cross-section of the optical fiber OF can be substantially constant along the fiber axis.

[0116] It will be understood that optical fibers (OFs) possess a degree of flexibility, therefore the direction of their axis is typically not uniform along their length. Terms such as optical axis or cross-section will be understood to refer to local optical axes, local cross-sections, etc. Furthermore, when components are described as cylindrical or tubular, these terms will be understood to include those shapes that may have deformed when the optical fiber (OF) is bent.

[0117] Optical fiber OF can have any length, and it should be understood that the length of optical fiber OF can depend on the application. Optical fiber OF can have lengths between 1 cm and 10 m, for example, optical fiber OF can have lengths between 10 cm and 100 cm.

[0118] 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 to comprise a body having a hollow core COR (including the cladding portion and the support portion SP). The cladding portion includes multiple anti-resonant elements for guiding radiation through the hollow core COR. Specifically, the multiple anti-resonant 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 substantially 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.

[0119] The cladding portion includes multiple anti-resonant elements for guiding radiation propagating through the optical fiber (OF). Specifically, in this embodiment, the cladding portion includes a single ring of six tubular capillary CAPs. Each tubular capillary CAP serves as an anti-resonant element.

[0120] 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 for propagating radiation through the hollow core HC (which may be incident on the wall portion WP at a grazing angle of incidence). 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 into the capillary cavity CC is generally suppressed. In some embodiments, the capillary wall portion WP can have a thickness between 0.01 μm and 10.0 μm.

[0121] It will be understood that, as used herein, the term "cladding portion" is intended to refer to a portion of the optical fiber OF used to guide the propagation of radiation through the optical fiber OF (i.e., the capillary CAP that confines said radiation within the hollow core COR). The radiation can be confined in a lateral mode to propagate along the fiber axis.

[0122] The support portion is typically tubular and supports six capillary capillaries (CAPs) within the cladding portion. These six capillary capillaries are evenly distributed around the inner surface of the inner support portion (SP). The six capillary capillaries can be described as being arranged in a roughly hexagonal form.

[0123] 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 spaced apart from adjacent capillary CAPs in the annular structure. This arrangement can be advantageous because it can increase the transmission bandwidth of the optical fiber OF (e.g., compared to an arrangement in which capillaries contact each other). Alternatively, in some embodiments, each capillary CAP may contact adjacent capillary CAPs in the annular structure.

[0124] The cladding portion has six capillary capillaries (CAPs) arranged in a ring structure around the hollow core (COR). The inner surface of the ring structure of the capillary capillaries 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 opposing capillaries, indicated by arrow d) can be between 10 μm and 1000 μm. The diameter d of the hollow core HC can affect the mode field diameter, impulse loss, dispersion, modal complexity, and nonlinear characteristics of the hollow core fiber OF.

[0125] In this embodiment, the cladding portion includes a single-ring arrangement of capillary CAPs (which act as anti-resonant elements). Therefore, a line in any radial direction from the center of the hollow HC to the outside of the optical fiber OF passes through no more than one capillary CAP.

[0126] It will be understood that other embodiments may employ different arrangements of anti-resonant elements. These arrangements may include arrangements with multiple anti-resonant element rings and arrangements with nested anti-resonant elements. Furthermore, although... Figure 8 The embodiment shown includes a ring of six capillaries, but in other embodiments, one or more rings including any number of anti-resonant elements (e.g., 4, 5, 6, 7, 8, 9, 10, 11 or 12 capillaries) may be disposed in the cladding portion.

[0127] Figure 10 (b) A variant embodiment of the above-described HC-PCF with a single-ring tubular capillary is shown. Figure 10 In example (b), there are two coaxial tubular capillary rings. To maintain the inner and outer rings of the tubular capillary, the HC-PCF may include a support tube ST. The support tube may be made of silica.

[0128] Figure 8 as well as Figure 10 The tubular capillaries in the examples (a) and (b) can have a circular cross-sectional shape. Other shapes of tubular capillaries are also possible, such as elliptical or polygonal cross-sections. Furthermore, Figure 8 as well as Figure 10 The solid material of the tubular capillary in examples (a) and (b) may include plastic materials such as PMA, glass such as silicon dioxide, or soft glass.

[0129] Figure 9 The radiation source RDS for providing broadband output radiation is described. The radiation source RDS includes a pulse-pumped radiation source PRS or any other type of source capable of generating short pulses of the desired length and energy level; an optical fiber OF with a hollow core COR (e.g., Figure 8 (as shown in the diagram); and the working medium WM (e.g., gas) disposed within the hollow COR. Although in Figure 9 In this context, the radiation source RDS includes Figure 8 The optical fiber OF shown is used, but in alternative embodiments, other types of hollow optical fibers may be used.

[0130] A pulse-pumped radiation source (PRS) is configured to provide the input radiation IRD. The hollow core HC of the optical fiber OF is arranged to receive the input radiation IRD from the PRS and broaden it to provide the output radiation ORD. The operating medium WM is capable of broadening the frequency range of the received input radiation IRD, thereby providing a broadband output radiation ORD.

[0131] The radiation source RDS also includes a storage unit RSV. An optical fiber OF is disposed within the storage unit RSV. The storage unit RSV may also be referred to as a housing, container, or gas chamber. The storage unit RSV is configured to contain a working medium WM. The storage unit RSV may include one or more features known in the art regarding the composition of the working medium WM (which may be a gas) inside the storage unit RSV for controlling, regulating, and / or monitoring. The storage unit RSV may include a first transparent window TW1. In use, the optical fiber OF is disposed within the storage unit RSV such that the first transparent window TW1 is located near the input end IE of the optical fiber OF. The first transparent window TW1 may form part of a wall of the storage unit RSV. The first transparent window TW1 may be transparent at least to the received input radiation frequency, such that the received input radiation IRD (or at least a majority thereof) can be coupled into the optical fiber OF located inside the storage unit RSV. It will be understood that optics (not shown) may be provided to couple the input radiation IRD into the optical fiber OF.

[0132] The storage unit RSV includes a second transparent window TW2, which forms part of the wall of the storage unit RSV. In use, when the fiber optic OF is disposed within the storage unit RSV, the second transparent window TW2 is located near the output end OE of the fiber optic OF. The second transparent window TW2 can be transparent at least to the frequency of the broadband output radiated ORD of the device 120.

[0133] Alternatively, in another embodiment, the two opposite ends of the optical fiber OF can be placed in different containers. The optical fiber OF may include a first end configured to receive input radiation IRD and a second end configured to output broadband output radiation ORD. The first end may be placed in a first storage unit, which includes a working medium WM. The second end may be placed in a second container, wherein the second container may also include the working medium WM. The function of the storage unit may be as described above regarding... Figure 9 As described, the first reservoir may include a first transparent window configured to be transparent to the input radiation IRD. The second reservoir may include a second transparent window configured to be transparent to the broadband output radiation ORD. Both the first and second reservoirs may also include sealable openings to allow the optical fiber OF to be partially placed inside and partially outside the reservoir, thereby sealing the gas inside the reservoir. The optical fiber OF may also include an intermediate portion not included within the reservoir. This arrangement of two separate gas reservoirs may be particularly convenient for embodiments of relatively long optical fiber OFs (e.g., when the length is greater than 1 m). It will be understood that, for this arrangement using two separate gas reservoirs, the two reservoirs (which may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the gas within the two reservoirs) can be considered as providing a means for providing the working medium WM within the hollow core HC of the optical fiber OF.

[0134] In this case, if at least 50%, 75%, 85%, 90%, 95%, or 99% of the incident radiation at that frequency is transmitted through the window, then the window may be transparent for that frequency.

[0135] Both the first transparent window TW1 and the second transparent window TW2 can form an airtight seal within the wall of the storage unit RSV, allowing the working medium WM (which can be a gas) to be contained within the storage unit RSV. It will be understood that the gas WM can be contained within the storage unit RSV at a pressure different from the ambient pressure of the storage unit RSV.

[0136] The working medium WM can include inert gases such as argon, krypton, and xenon; Raman-active gases such as hydrogen, deuterium, and nitrogen; or gas mixtures such as argon / hydrogen mixtures, xenon / deuterium mixtures, krypton / nitrogen mixtures, or nitrogen / hydrogen mixtures. Depending on the type of filling gas, nonlinear optical processes can include modulation instability (MI), soliton fission, Kerr effect, Raman effect, and dispersive wave generation. Details of modulation instability (MI), soliton fission, Kerr effect, Raman effect, and dispersive wave generation are described in WO2018 / 127266A1 and US9160137B1 (both patent documents are incorporated herein by reference). Since the dispersion of the filling gas can be tuned by changing the pressure of the working medium WM (i.e., the gas chamber pressure) in the storage RSR, the resulting broadband pulse dynamics and associated spectral broadening characteristics can be tuned, thereby optimizing frequency conversion.

[0137] In one embodiment, the working medium WM can be positioned within the hollow HC at least during the reception of the input radiation IRD to generate the broadband output radiation ORD. It will be understood that although the optical fiber OF does not receive the input radiation IRD used to generate the broadband output radiation, the hollow COR may be completely or partially devoid of the gas WM.

[0138] To achieve frequency broadening, higher intensity radiation may be required. The advantage of hollow-core fiber optical fibers (OFs) is that they can achieve high-intensity radiation through stronger spatial confinement of radiation propagating through the fiber, thus achieving highly confined radiation intensity. For example, the internal radiation intensity of an OF can be very high due to the high received input radiation intensity and / or due to the strong spatial confinement of radiation within the fiber. Hollow-core fibers also have the advantage of guiding radiation with a wider wavelength range than solid-core fibers, particularly in the ultraviolet and infrared ranges.

[0139] The advantage of using hollow-core optical fiber (OF) is that most of the radiation guided inside the OF is confined within the hollow core (COR). Therefore, the radiation inside the OF primarily interacts with the working medium (WM) located within the hollow core (HC) of the OF. As a result, the broadening effect of the working medium (WM) on the radiation can be increased.

[0140] The received input radiation IRD can be electromagnetic radiation. The input radiation IRD can be received as pulsed radiation. For example, the input radiation IRD can include, for example, ultrafast pulses generated by a laser.

[0141] The input radiation IRD can be coherent radiation. The input radiation IRD can also be collimated radiation; collimation can improve the efficiency of coupling the input radiation IRD to the fiber OF. The input radiation IRD can include a single frequency or a narrow range of frequencies. The input radiation IRD can be generated by a laser. Similarly, the output radiation ORD can be collimated and / or coherent.

[0142] The broadband range of an output radiation ORD can be a continuous range, including a continuous range of radiation frequencies. Output radiation ORDs can include supercontinuum radiation. Continuous radiation can be advantageous for use in many applications, such as measurement applications. For example, a continuous range of frequencies can be used to probe a large number of properties. A continuous range of frequencies can, for example, be used to determine and / or eliminate the frequency dependence of measured characteristics. A supercontinuum output radiation ORD can include, for example, electromagnetic radiation in the wavelength range of 100 nm to 4000 nm. The frequency range of a broadband output radiation ORD can be, for example, 400 nm to 900 nm, 500 nm to 900 nm, or 200 nm to 2000 nm. A supercontinuum output radiation ORD can include white light.

[0143] The input radiation IRD provided by the pulsed-pumped radiation source (PRS) can be pulsed. The input radiation IRD can include electromagnetic radiation of one or more frequencies between 200 nm and 2 μm. For example, the input radiation IRD can include electromagnetic radiation with a wavelength of 1.03 μm. The repetition rate of the pulsed radiation IRD can be on the order of 1 kHz to 100 MHz. The pulse energy can be on the order of 0.1 μJ to 100 μJ, for example, 1 μJ to 10 μJ. The pulse duration of the input radiation IRD can be between 10 fs and 10 ps, ​​for example, 300 fs. The average power of the input radiation IRD can be between 100 mW and several hundred watts. For example, the average power of the input radiation IRD can be between 20 W and 50 W.

[0144] The pulsed pump source (PRS) can be a laser. The spatiotemporal transmission characteristics (e.g., spectral amplitude and phase) of this laser pulse transmitted along the fiber OF can be altered and tuned by adjusting the (pump) laser parameters, the working component (WM), and the fiber OF parameters. These spatiotemporal transmission characteristics can include one or more of the following: output power, output mode distribution, output time distribution, width of the output time distribution (or output pulse width), output spectral distribution, and bandwidth of the output spectral distribution (or output spectral bandwidth). The PRS parameters can include one or more of the following: pump wavelength, pump pulse energy, pump pulse width, and pump pulse repetition rate. The OF parameters can include one or more of the following: fiber length, size and shape of the hollow core 101, size and shape of the capillary, and thickness of the wall surrounding the hollow core. The working component (WM), for example, is filled with a gas, and its parameters can include one or more of the following: gas type, gas pressure, and gas temperature.

[0145] The broadband output radiation ORD provided by the radiation source RDS can have an average output power of at least 1W. The average output power can be at least 5W. The average output power can be at least 10W. The broadband output radiation ORD can be a pulsed broadband output radiation ORD. The broadband output radiation ORD can have a power spectral density of at least 0.01mW / nm across the entire wavelength band of the output radiation. The power spectral density across the entire wavelength band of the broadband output radiation can be at least 3mW / nm.

[0146] Figure 11 An assembly 100 is shown, comprising a hollow-core photonic crystal fiber (HC-PCF) 102 configured to generate broadband radiation 104 from input radiation 106 coupled to the HC-PCF 102. Although in Figure 11 In the diagram, input radiation 106 enters the HC-PCF 102 from the left and exits from the right, but it will be understood that this is merely an example. The HC-PCF 102 broadens the wavelength spectrum of the input radiation 106 to provide broadband output radiation 104. This broadening is due to nonlinear effects. The HC-PCF 102 is an example of a nonlinear element. It will be understood that in other embodiments, the component may include different nonlinear elements. For example, the nonlinear element may be fused silica fiber or a glass plate.

[0147] The input radiation 106 can be provided by a pump laser (not shown) with a specific power; that is, the input radiation 106 can be considered as pump radiation. The input radiation 106 can include a single wavelength, multiple discrete wavelengths, or a narrowband wavelength range. The broadband radiation 104 can be referred to as a signal; that is, the signal is any wavelength other than one or more pump wavelengths generated in the HC-PCF.

[0148] Component 100 includes a first lens 110 (lens element) located upstream of HC-PCF 102 (i.e., in the direction of the pump laser providing input radiation 106 to HC-PCF 102). This is Figure 11 The left side of HC-PCF 102. The first lens 110 is configured to focus the input radiation 106 into HC-PCF 102.

[0149] Component 100 includes a second lens 112 (lens element) located downstream of HC-PCF 102 (i.e., in the direction in which broadband radiation 104 is provided from HC-PCF 102). This is Figure 11 The right side of HC-PCF 102. The second lens 112 is configured to substantially collimate the radiation exiting HC-PCF 102.

[0150] The first lens 110 and the second lens 112 may be made of glass and / or may have one or more coatings.

[0151] A first lens actuator 114A is provided associated with the first lens 110 to enable the input radiation 106 to enter the HC-PCF 102. This is because the core diameter of the HC-PCF 102 may be less than 50 μm and the input radiation beam needs to be positioned and manipulated with ~μm precision in order to be properly coupled into the core of the HC-PCF 102. In other words, the first lens actuator 114A can adjust the position of the first lens 110 so that the input radiation properly enters the HC-PCF 102.

[0152] Component 100 includes an optical element located downstream of HC-PCF 102. In this embodiment, the optical element is as follows: Figure 11 The transmission element shown is located on the right side of HC-PCF 102 and will be referred to as the right transmission element (TER) 116.

[0153] TER 116 is configured to reflect at least some or all of the radiation at or near one or more wavelengths of the input radiation 106. This is in Figure 12a It is shown in the middle, Figure 12aThis is a graph showing the reflection from TER 116. The graph shows the relationship between wavelength (λ) (x-axis) and the intensity of the reflected radiation (y-axis). It can be seen that in the input radiation (or λ... pump There is an intensity peak at the wavelength of ), and relatively little reflection occurs at other wavelengths near this peak. In other words, TER 116 reflects 106 units of input radiation.

[0154] Broadband radiation 104 can be considered to include input radiation 106. TER 116 can be considered to reflect a portion of broadband radiation 104, which in this embodiment is a portion of input radiation 106. That is, a portion of broadband radiation 104 is radiation at or near one or more wavelengths of input radiation 106. TER 116 can be configured to reflect 90% to 100% of the radiation at or near one or more wavelengths of input radiation 106.

[0155] In some embodiments, the reflected input radiation 106 may be subjected to pulse compression.

[0156] TER 116 can be configured to transmit at least some or all of the broadband radiation 104. That is, TER 116 can transmit at least some or all of the radiation at all wavelengths except for those at or near one or more wavelengths of the input radiation 106. More specifically, TER 116 can transmit 90% to 100% of the broadband radiation other than the reflected input radiation 106. In some embodiments, TER 116 can transmit substantially 100% of the broadband radiation 104 except for a reflected portion of the broadband radiation 104, which in this embodiment corresponds to the input radiation 106.

[0157] Component 100 includes an upstream optical element located upstream of HC-PCF 102. In this embodiment, the upstream optical element is as follows: Figure 11 The transmission element shown is located on the left side of HC-PCF 102 and will be referred to as the left transmission element (TEL) 118.

[0158] TEL 118 is configured to reflect broadband radiation 104. This is in Figure 12b As shown in the figure, Figure 12b This is a graph showing the reflection from TEL 118. The graph shows the relationship between wavelength (λ) (x-axis) and the intensity of reflected radiation (y-axis). It can be seen that at the input radiation (or λ... pumpThere is an intensity drop at the wavelength of the input radiation 106, and relatively large reflections at other wavelengths in the vicinity of this drop. In other words, TEL 118 reflects radiation at all wavelengths except those at or near one or more wavelengths of the input radiation 106. TEL 118 can be configured to reflect 90% to 100% of the broadband radiation 104.

[0159] TEL 118 is configured to transmit input radiation 106. That is, TEL 118 transmits radiation at or near one or more wavelengths of input radiation 106. More specifically, TEL 118 can transmit 90% to 100% of the input radiation 106.

[0160] TER 116 and TEL 118 may be made of glass or metal, have one or more coatings and / or have mirrors or partial mirrors that perform reflection and transmission. It will be understood that TER 116 and TEL 118 may be made of any suitable material and have any suitable shape, etc., to perform the desired reflection and transmission.

[0161] In use, the input radiation 106 is generated by the pump laser and passes through TEL 118 (in Figure 11 The input radiation 106 (from left to right) is focused by the first lens 110 and enters the left side of the HC-PCF 102. Then, the input radiation 106 is broadened in the HC-PCF 102, and the broadband radiation 104 and unused input radiation 106 exit the right side of the HC-PCF 102. The HC-PCF 102 generally directs the generated broadband radiation 104, or most of the generated broadband radiation 104, to exit from the right side of the HC-PCF 102. The unused input radiation and broadband radiation 104 are collimated by the second lens 112 and incident on the TER 116.

[0162] TER 116 can reflect unused input radiation 106, i.e., radiation at or near one or more wavelengths of input radiation 106, back to HC-PCF 102. The second lens 112 focuses the reflected unused input radiation 106 into HC-PCF 102. The reflected unused input radiation 106 then generates additional broadband radiation in HC-PCF 102. In this case, HC-PCF 102 typically guides the additional broadband radiation 104, or most of the additional broadband radiation 104 exits from the left side of HC-PCF 102.

[0163] TER 116 transmits broadband radiation 104 from HC-PCF 102. That is, TER 116 can transmit radiation at all wavelengths except those at or near one or more wavelengths of the input radiation 106.

[0164] A second lens actuator 114B associated with the second lens 112 is provided to allow the reflected unused input radiation 106 to enter the HC-PCF 102. This is because the diameter of the core of the HC-PCF 102 may be less than 50 μm and the unused input radiation beam needs to be positioned with ~μm accuracy to be properly coupled into the core of the HC-PCF 102. In other words, the second lens actuator 114B can adjust the position of the second lens 112 so that the reflected unused input radiation 106 enters the HC-PCF 102.

[0165] Furthermore, the first actuator 120A and TER 116 are provided together to allow the reflected unused input radiation 106 to enter the HC-PCF 102. That is, the first actuator 120A can adjust the position of TER 116 so that the reflected input radiation 106 can enter the HC-PCF 102.

[0166] Broadband radiation 104 and unused input radiation 106 also leave the left side of HC-PCF, i.e., travel upstream. Broadband radiation 104 and unused input radiation 106 are collimated by the first lens 110 and incident on TEL 118.

[0167] TEL 118 reflects broadband radiation 104 (i.e., radiation of all wavelengths except those at or near one or more wavelengths of the input radiation 106) back to HC-PCF 102. First lens 110 focuses the reflected broadband radiation 104 into HC-PCF 102. At least some of this reflected broadband radiation 104 will pass through HC-PCF 102, exiting to the right side of HC-PCF 102 and being transmitted through TER 116. This reflected broadband radiation 104 may also generate additional broadband radiation within HC-PCF 102.

[0168] The unused input radiation 106 transmitted by TEL 118 (i.e., unused pump radiation) may have a relatively low intensity due to absorption after passing twice through HC-PCF 102.

[0169] A second actuator 120B is provided together with TEL 118 to allow reflected broadband radiation 104 to enter HC-PCF 102. That is, the second actuator 120B can adjust the position of TEL 118 so that reflected broadband radiation 104 can enter HC-PCF 102. The second actuator 120B can also be used to allow input radiation 106 from the pump laser to enter HC-PCF 102.

[0170] Broadband radiation 104, which has passed TER 116, can be supercontinuum radiation and can be used for a variety of purposes, such as in measurement tools MT, such as level sensors, alignment mark measurement systems, scattering measurement tools, or inspection tools.

[0171] Reflecting the input radiation 106 back to the HC-PCF 102 provides the advantage of increasing the broadband radiation 104 produced by the same amount of input radiation 106. Reusing the input radiation twice will improve the effective energy conversion efficiency, meaning the power of the pump laser may be reduced. Furthermore, reflecting the broadband radiation 104 back to the HC-PCF 102 also increases the generated broadband radiation 104. Additionally, passing the input radiation 106 twice through the HC-PCF 102 provides two broadband radiation pulses (i.e., doubling the repetition rate). Since higher frequencies generally result in lower noise levels, this can improve the noise performance of the system. In some embodiments, there may be more than two pulses. Furthermore, in some embodiments, a pulse from a later radiation beam from the pump laser may be combined with, or at least simultaneously with, a pulse from an earlier input radiation beam from the pump laser. This is likely due to the delay caused by reflection. This can depend on the dimensions of the components (e.g., length), the distance between them, and the frequency of the pump laser.

[0172] The amount of pump radiation absorbed in an HC-PCF can be increased by increasing the fiber length, but this would require the HC-PCF to occupy more space, which is likely undesirable. Furthermore, longer fibers may be more difficult to manufacture, and due to the potential for performance variations along length, longer fibers are more likely to exhibit inhomogeneities. Additionally, longer fibers may be more expensive than shorter fibers. Alternatively, reflection can be added to return the pump and reuse it. Reflection can be achieved using Bragg gratings written into the fiber itself. However, this is generally not possible with HC-PCFs because the fiber core is hollow, thus providing no reflective structure. While some HC-PCF structures can be used for reflection, this is likely to be inefficient.

[0173] Another alternative could be to use, for example, three parallel optical fibers, such that light from the first fiber enters the second fiber, and light from the second fiber enters the third fiber. However, the disadvantages of this alternative system might be that it requires three relatively expensive optical fibers, has three times the chance of contamination, three times the chance of alignment issues, and three times the chance of any fiber failure.

[0174] In some embodiments, the optical elements and upstream optical elements may be configured to reflect a portion of the broadband radiation back into the HC-PCF multiple times (e.g., 2, 3, 4, or 5 or more times). Passing the radiation twice through the nonlinear elements may be preferred because, for example, losses due to the interaction of the radiation with the components of the assembly, passing it more than twice may not provide much of the gain (if any) generated by the broadband radiation.

[0175] In some embodiments, component 100 may include a plurality of optical elements downstream of HC-PCF 102 and / or a plurality of upstream optical elements upstream of HC-PCF 102 to reflect a portion of broadband radiation back to the nonlinear element.

[0176] Figure 13 Another embodiment of an assembly 200 is shown, comprising a hollow-core photonic crystal fiber (HC-PCF) 102 configured to generate broadband radiation 104 from input radiation 106 coupled to the HC-PCF 102.

[0177] Component 200 is similar to Figure 11 The same reference numerals have been used for the same parts as in the previous embodiments, and for the sake of brevity, they will not be discussed further here. However, in this embodiment, the downstream optical element of HC-PCF 102 is a reflective element and will be referred to as the right-side reflective element (RER) 216.

[0178] In this embodiment, RER 216 reflects at least some of the broadband radiation 104 back to HC-PCF 102. RER 216 can reflect most of the broadband radiation 104 back to HC-PCF 102. Most of the broadband radiation 104 may include (unused) input radiation 106 in RER 216. RER 216 can be configured to reflect at least some of the radiation at or near the wavelength of the desired output.

[0179] RER216 can be configured to reflect 90% to 100% of broadband radiation. It will be understood that, in embodiments, a portion of broadband radiation 104 can be considered to include the majority of broadband radiation 104 and / or 90% to 100% of broadband radiation 104.

[0180] In other embodiments, the optical element may be a transmission element. For example, the optical element may transmit at least some of the unused input radiation 106 that has already left the right side of the HC-PCF 102. In this case, the RER 216 may reflect radiation of all wavelengths except those at or near one or more wavelengths of the input radiation 106 back to the HC-PCF 102.

[0181] The reflected broadband radiation 104 can advantageously generate additional broadband radiation in the HC-PCF 102. The broadband radiation 104 generated from the initial input radiation 106 in the HC-PCF 102 (i.e., during the first pass) can be in the stage where the (nonlinear) broadening process is still in progress. The reflected broadband radiation 104 entering the HC-PCF 102 (i.e., during the second pass) is then added to this process, thus completing the generation of broadband radiation 104. This may have the advantage of allowing the use of shorter optical fibers.

[0182] Component 200 includes an auxiliary optical element upstream of HC-PCF 102. The auxiliary optical element is a transmission element located to the left of HC-PCF 102, such as... Figure 13 As shown, it will be referred to as the left supplementary transmission element (STEL) 218.

[0183] STEL 218 is configured to reflect at least some of the broadband radiation 104 off-axis and transmit at least some of the radiation at or near one or more wavelengths of the input radiation 106. That is, STEL 218 reflects the broadband radiation 104 away from HC-PCF 102, so that the broadband radiation 104 can be used, for example, in a measurement tool MT, such as a level sensor, alignment mark measurement system, scattering measurement tool, or inspection tool. STEL 218 can be configured to reflect 90% to 100% of the broadband radiation 104.

[0184] In some embodiments, the RER can transmit some broadband radiation, for example, up to 10% of the broadband radiation incident upon it. This means that there may be two broadband radiation beams, one transmitted through the RER and the other reflected from the STEL. This can be considered as separating some light from the broadband radiation beam reflected from the STEL. For example, observing the light from the broadband radiation beam transmitted through the RER can provide information about the main beam reflected from the STEL. The two beams can be synchronized.

[0185] Figure 14 Another embodiment of a component 300 including a hollow-core photonic crystal fiber (HC-PCF) 102 is shown, the component being configured to generate broadband radiation 104 from input radiation 106 coupled to the HC-PCF 102. Component 300 is similar to... Figure 11 Component 100 (the same reference numerals have been used with) Figure 11 The same components are used in the embodiments, and for the sake of brevity, they will not be discussed further here. However, the downstream optical element of HC-PCF 102 is a reflective element and will be referred to as the right-side reflective element (RER) 316. In addition, the upstream optical element of HC-PCF 102 is a reflective element and will be referred to as the right-side reflective element (REL) 318.

[0186] In this embodiment, RER 316 reflects at least some of the unused input radiation 106 back to HC-PCF 102. RER 316 can be configured to reflect 90% to 100% of the unused input radiation 106.

[0187] In this embodiment, REL 318 reflects at least some of the broadband radiation 104 back to HC-PCF 102. REL 318 can reflect most of the broadband radiation 104 back to HC-PCF 102. Most of the broadband radiation 104 may include some (unused) input radiation 106. REL 318 can be configured to reflect 90% to 100% of the broadband radiation 104.

[0188] Component 300 includes an additional optical element located downstream of HC-PCF 102. In this embodiment, the additional optical element is a dichroic mirror and will be referred to as the right dichroic mirror (DMR) 322. DMR 322 is located between HC-PCF 102 and RER 316. DMR 322 may be a bandpass mirror. DMR 322 may be made of glass or metal, have one or more coatings, and / or have reflective or partial reflective mirrors for reflection and transmission.

[0189] DMR 322 is configured to transmit at least some of the broadband radiation 104 and reflect at least some of the radiation at or near one or more wavelengths of the input radiation 106 to RER 316 and back from RER 316 to HC-PCF 102. DMR 322 can transmit 90% to 100% of the broadband radiation 104, excluding the reflected portion. DMR 322 can transmit essentially 100% of the broadband radiation 104, excluding the reflected portion. It will be understood that in other embodiments, the additional optical element may be a component different from the dichroic mirror.

[0190] Component 300 includes an upstream additional optical element located upstream of HC-PCF 102. In this embodiment, the upstream additional optical element is a dichroic mirror and will be referred to as the left dichroic mirror (DML) 324. DML 324 is located between HC-PCF 102 and REL 318. DML 324 may be a bandpass mirror. DML 324 may be made of glass or metal, have one or more coatings, and / or have mirrors or partial mirrors that perform reflection and transmission.

[0191] DML 324 is configured to transmit at least some of the radiation at or near one or more wavelengths of the input radiation 106 and to reflect at least some of the broadband radiation to REL 318 and from REL 318 back to HC-PCF 102. DML 324 may reflect 90% to 100% of the broadband radiation 104. It will be understood that in other embodiments, the upstream additional optical element may be a component different from the dichroic mirror.

[0192] The third actuator 326A, together with the DMR 322, is provided to allow the reflected unused input radiation 106 to enter the HC-PCF 102. That is, the third actuator 326A can adjust the position of the DMR 322 so that the reflected unused input radiation 106 can enter the HC-PCF 102.

[0193] The fourth actuator 326B is provided together with the DML 324 to allow the reflected broadband radiation 104 to enter the HC-PCF 102. That is, the fourth actuator 326B can adjust the position of the DML 324 so that the reflected broadband radiation 104 can enter the HC-PCF 102.

[0194] In an embodiment, RER 316 is configured to compress pulses of radiation at or near one or more wavelengths of the input radiation 106. That is, RER 316 may be combined with a pulse compression component. This is necessary if the intensity of the reflected unused input radiation 106 is insufficient to initiate the nonlinear process that generates broadband radiation 104. Compression of the input radiation 106 can be achieved through phase modulation. In an embodiment, RER 316 may include a chirped mirror, a grating pair, or a prism pair. This allows unused input radiation 106 to be compressed before being sent back to HC-PCF 102 to generate broadband. It will be understood that in some embodiments, the pulse compression component may be integrally formed with the RER.

[0195] In an embodiment, REL 318 is configured to shape pulses of broadband radiation 104 incident thereon. REL 318 can be configured to spectrally filter the broadband radiation 104. That is, REL 318 can be combined with a spectral filtering component. In an embodiment, this can be, for example, a spectral filter or an acousto-optic tunable filter (AOTF). This allows manipulation of the spectral shape of the reflected broadband radiation 104, and consequently, manipulation of the spectral shape of the final white light (broadband radiation 104) at the output (to the right of HC-PCF 102). It will be understood that in some embodiments, the spectral filtering component can be integrally formed with the REL. It will be understood that in other embodiments, other components (e.g., components downstream of the HC-PCF) can shape the broadband radiation 104.

[0196] Broadband radiation 104 can be manipulated based on application requirements (e.g., if a flatter pulse shape or higher intensity in a wavelength is needed).

[0197] Spectral filtering components and / or pulse compression components (more generally, dynamic elements) can be changed during operation. For example, one application might require broadband radiation with a flat shape, and therefore the components can be changed accordingly. However, in another example, another application might require higher intensity blue light, and therefore the components can be changed to provide this desired spectrum. The ability to change dynamic elements in this way provides flexibility for different applications, for example, without requiring significant modifications to the components.

[0198] Typically, nonlinear elements generate light in an unpredictable manner, dominated by the nonlinear element itself and quantum noise in the system. However, the average spectrum of multiple emissions (e.g., tens, hundreds, thousands, etc.) still characterizes the system's configuration (laser, fiber, and gas). Using the spectral filtering component on the REL 318 allows for the manipulation of the average spectrum from the HC-PCF 102. Thus, for example, if the HC-PCF 102 is experiencing a decline in its spectral performance, the spectral performance can be compensated for or the spectrum modified. Compensating for or modifying the spectrum does not reduce the degradation primarily caused by fiber degradation under high-power laser irradiation. However, modifying the spectrum (e.g., by using the spectral filtering component on the REL 318) provides a method for compensating for spectral changes due to fiber degradation.

[0199] Further embodiments are disclosed in the list of numbered aspects provided below:

[0200] 1. A component comprising a nonlinear element configured to generate broadband radiation from input radiation coupled to the nonlinear element.

[0201] The component further includes an optical element located downstream of the nonlinear element, the optical element being configured to reflect a portion of the broadband radiation back into the nonlinear element.

[0202] 2. The component according to aspect 1, wherein the optical element is configured to reflect at least some of the radiation at or near one or more wavelengths of the input radiation back into the nonlinear element.

[0203] 3. The component according to aspect 2, wherein the optical element is configured to compress pulses of at least some of the radiation at or near one or more wavelengths of the input radiation.

[0204] 4. The component according to aspect 2 or 3, wherein the optical element is configured to transmit at least some of the broadband radiation.

[0205] 5. The component according to aspect 4, wherein the optical element is configured to transmit 90% to 100% of the broadband radiation except for the reflected portion of the broadband radiation.

[0206] 6. The component according to aspect 2 or 3, wherein the component further comprises an additional optical element located between the nonlinear optical element and the optical element, the additional optical element being configured to transmit at least some broadband radiation and reflect at least some radiation at or near the input radiation at one or more wavelengths to the optical element, and return from the optical element to the nonlinear optical element.

[0207] 7. The component according to aspect 6, wherein the additional optical element is configured to transmit 90% to 100% of the broadband radiation except for the reflected portion of the broadband radiation.

[0208] 8. The assembly according to aspects 2 to 7, wherein the optical element is configured to reflect 90% to 100% of the radiation at or near one or more wavelengths of the input radiation.

[0209] 9. The component according to aspect 1, wherein the optical element is configured to reflect most of the broadband radiation back into the nonlinear element.

[0210] 10. The component according to aspect 9, wherein the optical element is configured to reflect 90% to 100% of broadband radiation.

[0211] 11. The component according to aspect 9 or 10, wherein the component includes an auxiliary optical element located upstream of the nonlinear element, the auxiliary optical element being configured to reflect at least some broadband radiation off-axis and transmit at least some of the radiation at or near one or more wavelengths of the input radiation.

[0212] 12. The component according to aspects 1 to 8, wherein the component includes an upstream optical element located upstream of the nonlinear element, the upstream optical element being configured to reflect at least some of the broadband radiation back into the nonlinear element.

[0213] 13. The component according to aspect 12, wherein the component includes an upstream additional optical element located between the nonlinear optical element and the upstream optical element, the upstream additional optical element being configured to transmit at least some radiation at or near one or more wavelengths of the input radiation, reflect at least some broadband radiation to and from the upstream optical element back into the nonlinear optical element.

[0214] 14. The component according to aspect 13, wherein the upstream optical element is configured to shape the broadband radiation.

[0215] 15. The component according to aspect 13 or 14, wherein the upstream optical element is configured to spectrally filter the broadband radiation.

[0216] 16. The component according to any of the foregoing aspects, wherein the component includes a first lens and a second lens located upstream and downstream of the nonlinear element, respectively, the first lens for focusing radiation onto the nonlinear element and the second lens for providing substantially collimated radiation emanating from the nonlinear element.

[0217] 17. The component according to any of the preceding aspects, wherein the component includes at least one actuator configured to be at least one of a moving optical element, an additional optical element, an upstream optical element, an upstream additional optical element, an auxiliary optical element, a first lens, and a second lens.

[0218] 18. The component according to any of the foregoing aspects, wherein the nonlinear element is a hollow optical fiber.

[0219] 19. The component according to aspect 18, wherein the hollow-core optical fiber is a photonic crystal fiber.

[0220] 20. A measuring device comprising the components described in any of the foregoing aspects.

[0221] 21. A measuring device, comprising the measuring device according to aspect 19.

[0222] 22. An inspection device comprising the measuring device according to aspect 19.

[0223] 23. A photolithography apparatus comprising the components described in aspects 1 to 19.

[0224] 24. A photolithography apparatus, comprising the measurement apparatus according to aspect 20.

[0225] 25. A method for generating broadband radiation from input radiation coupled to a nonlinear element, the method comprising:

[0226] A portion of the broadband radiation is reflected back into the nonlinear element from an optical element located downstream of the nonlinear element.

[0227] Although references are specifically made to "measuring equipment / tools / systems" or "inspection equipment / tools / systems," these terms can refer to tools, equipment, or systems of the same or similar type. For example, inspection or measuring equipment including embodiments of the present invention can be used to determine the characteristics of a structure on a substrate or wafer. For example, inspection or measuring equipment including embodiments of the present invention can be used to detect defects in a substrate or defects in a structure on a substrate or wafer. In such embodiments, the characteristics of interest 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 undesirable structure on the substrate or wafer.

[0228] While the use of lithography equipment in IC manufacturing may be specifically mentioned in this article, it should be understood that the lithography equipment described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0229] Although specific reference to embodiments of the invention may be made herein within the context of lithography equipment, embodiments of the invention may be used in other equipment. Embodiments of the invention may form part of mask inspection equipment, metrology equipment, or any equipment for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning apparatus). These devices may generally be referred to as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0230] Although the embodiments of the invention have been specifically referenced above in the context of optical lithography, it will be understood that, where the context permits, the invention is not limited to optical lithography and can be used in other applications (e.g., imprint lithography).

[0231] 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 illustrative and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. An assembly including a nonlinear element configured to generate broadband radiation from input radiation coupled to the nonlinear element. in, The assembly including the nonlinear element further includes an optical element located downstream of the nonlinear element, the optical element being configured to reflect a portion of the broadband radiation back to the output of the nonlinear element and to an additional optical element located between the nonlinear element and the optical element, the additional optical element being configured to transmit at least some of the broadband radiation such that the transmitted at least some of the broadband radiation is transmitted only along the longitudinal direction in which the nonlinear element extends.

2. The assembly including a nonlinear element according to claim 1, wherein, The optical element is configured to reflect at least some of the radiation at or near one or more wavelengths of the input radiation back into the nonlinear element.

3. The assembly including a nonlinear element according to claim 2, wherein, The optical element is configured to compress pulses of at least some of the radiation at or near one or more wavelengths of the input radiation.

4. The assembly including a nonlinear element according to claim 2 or 3, wherein, The optical element is configured to transmit at least some of the broadband radiation.

5. The assembly including a nonlinear element according to claim 4, wherein, The optical element is configured to transmit 90% to 100% of the broadband radiation, excluding the reflected portion thereof.

6. The assembly including a nonlinear element according to claim 2 or 3, wherein, The additional optical element is also configured to reflect at least some of the radiation at or near the input radiation of one or more wavelengths to the optical element and back into the nonlinear optical element.

7. The assembly including a nonlinear element according to claim 6, wherein, The additional optical element is configured to transmit 90% to 100% of the broadband radiation, excluding the reflected portion of the broadband radiation.

8. The assembly including a nonlinear element according to claim 2 or 3, wherein, The optical element is configured to reflect 90% to 100% of the radiation at or near one or more wavelengths of the input radiation.

9. The assembly including a nonlinear element according to claim 1, wherein, The optical element is configured to reflect 90% to 100% of the broadband radiation.

10. The assembly including a nonlinear element according to claim 1 or 9, wherein, The assembly including the nonlinear element includes an auxiliary optical element located upstream of the nonlinear element, the auxiliary optical element being configured to reflect at least some broadband radiation off-axis and transmit at least some of the radiation at or near one or more wavelengths of the input radiation.

11. The assembly including a nonlinear element according to claim 1, wherein, The assembly including the nonlinear element includes an upstream optical element located upstream of the nonlinear element, the upstream optical element being configured to reflect at least some of the broadband radiation back into the nonlinear element.

12. The assembly including a nonlinear element according to claim 11, wherein, The assembly including the nonlinear element includes an upstream additional optical element located between the nonlinear optical element and the upstream optical element, the upstream additional optical element being configured to transmit at least some radiation at or near one or more wavelengths of the input radiation, reflect at least some broadband radiation to the upstream optical element, and reflect it back from the upstream optical element to the nonlinear optical element.

13. The assembly including a nonlinear element according to claim 12, wherein, The upstream optical element is configured to shape the pulses of the broadband radiation.

14. The assembly including a nonlinear element according to claim 12 or 13, wherein, The upstream optical element is configured to perform spectral filtering on the broadband radiation.

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