End facet protection for light sources and methods for metrology applications

Abstract

A system and method for providing a light source are disclosed. In one arrangement, the light source includes a gas cell having a window, an optical fiber that is hollow and has an axial direction, an end of the optical fiber being enclosed within the gas cell and optically coupled to the window via an optical path, and a surface disposed around the end of the optical fiber and extending through the end of the optical fiber in the axial direction toward the window so as to limit one or more of: exchange of gas between the optical path and a remainder of the gas cell, ingress of plasma toward or into the optical fiber, and radical flux toward an etch-sensitive surface.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European application No. 19194369.5, filed on 29 August 2019, European application No. 19204339.6, filed on 21 October 2019, and European application No. 20175193.0, filed on 18 May 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a light source and a method for operating the light source, particularly a broadband light source for use in photolithography equipment or measuring tools. Background Technology

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

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

[0006] Low-k1 lithography can be used to process features with dimensions 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 wavelength of the radiation 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 becomes to reproduce patterns on the substrate that resemble the shape and size 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, for example, but not limited to: NA optimization, custom illumination schemes, use of phase-shifting patterning apparatus, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also called "optical and process correction") in the design layout), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, a tight control loop for controlling the stability of the lithography apparatus can be used to improve the reproduction of the pattern under low k1 conditions.

[0007] The metrology equipment can be used to measure parameters of interest related to the structure on the substrate. For example, the metrology equipment can be used to measure parameters such as critical dimensions, overlap between layers on the substrate, and asymmetry of the pattern on the substrate. A beam of radiation is used to irradiate the substrate. The radiation is diffracted by the structure on the substrate. The diffracted radiation is collected by an objective lens and captured by a sensor.

[0008] The radiation is measured by rays emitted from a light source. This light is directed onto the substrate via a beam splitter and the objective lens, which collects the diffracted radiation from the substrate.

[0009] The light source providing the radiation measurement can be a broadband light source. The broadband light source can be generated using an air-filled optical fiber. A laser source can be connected to the input of the optical fiber of the light source, and the laser is broadened, i.e., its spectrum is widened, within the optical fiber. Summary of the Invention

[0010] The extremely high spectral power density of such light sources and the plasma generated as a byproduct of light production both pose a risk of damaging the hollow core photonic crystal fiber (HC-PCF) material. Therefore, it is desirable, for example, to provide a broadband light source with increased operational lifetime. Specifically, it is desirable to provide a broadband light source comprising an air-filled hollow core photonic crystal fiber that generates less contaminating material during operation. It is also desirable to retain the original and desired spectral and power output, as well as mode content.

[0011] According to a first aspect, a light source is provided, the light source comprising: a gas chamber having a window; an optical fiber that is hollow, an end of the optical fiber being enclosed within the gas chamber and optically coupled to the window via an optical path; and a surface disposed around the end of the optical fiber and extending toward the window beyond the end of the optical fiber to limit one or more of the following: gas exchange between the optical path and the remainder of the gas chamber; plasma entry toward or into the optical fiber; and free radical flux toward an etch-sensitive surface.

[0012] According to a second aspect, a measuring device is provided, the measuring device including a light source of the first aspect, wherein the light source is configured to generate light for projection onto a substrate. Attached Figure Description

[0013] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0014] - Figure 1A A schematic schematic diagram of a photolithography apparatus is depicted;

[0015] - Figure 1B A schematic schematic diagram of the photolithography unit is depicted;

[0016] - Figure 2 A schematic representation of overall photolithography is depicted, illustrating the collaboration between three key technologies to optimize semiconductor manufacturing;

[0017] - Figure 3A A schematic block diagram of the alignment sensor is depicted;

[0018] - Figure 3B A schematic block diagram of the horizontal sensor is depicted;

[0019] - Figure 4A This is a schematic cross-sectional view of a hollow core optical fiber, which, according to an embodiment, may form part of a radiation source in a transverse plane (i.e., perpendicular to the axis of the fiber).

[0020] - Figure 4B A schematic diagram depicts a radiation source for providing broadband output radiation according to an embodiment; and

[0021] - Figure 4C Figures (a) and (b) schematically depict cross-sections of example hollow-core photonic crystal fiber (HC-PCF) designs for supercontinuum generation, each of which, according to embodiments, can constitute part of a radiation source.

[0022] - Figure 5A schematic diagram of an HC-PCF-based light source with an air chamber is depicted.

[0023] - Figure 6A Experimental results describing the variation of the average output power of the HC-PCF-based light source with total operating time are presented.

[0024] - Figure 6B A schematic example of the end of an HC-PCF with pollution growth is depicted;

[0025] - Figure 6C Describes the formation Figure 6B The possible mechanisms of pollution growth described;

[0026] - Figure 7 An embodiment of the light source is described;

[0027] - Figure 8 A second embodiment of the light source is described;

[0028] - Figure 9 A third embodiment of the light source is described;

[0029] - Figure 10 A fourth embodiment of the light source is described; and

[0030] - Figure 11 A fifth embodiment of the light source is described. Detailed Implementation

[0031] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., with wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet radiation (EUV, e.g., with wavelengths in the range of about 5 nm to 100 nm).

[0032] As used herein, the terms “mask,” “mask,” or “patterning apparatus” can be broadly interpreted to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be generated in a target portion of the substrate; the term “light valve” can also be used in this context. Examples of such patterning apparatuses, in addition to classic masks (transmissive or reflective masks; binary masks, phase-shifting masks, hybrid masks, etc.), include programmable mirror arrays and programmable LCD arrays.

[0033] Figure 1AA lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also called an irradiator) IL configured to modulate a radiation beam B (e.g., ultraviolet, DUV, 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 positioning device PM configured to accurately position the patterning apparatus MA according to specific parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioning device PW configured to accurately position the substrate support according to specific parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the patterning apparatus MA to the radiation beam B onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0034] As used herein, the term "projection system" PS should be interpreted broadly to encompass all types of projection systems, including refractive, reflective, refractive-reflective, variable, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, as appropriate, to 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 broader term "projection system" PS.

[0035] In addition to the substrate support WT, the lithography apparatus LA may include a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure properties of the projection system PS or the radiation beam B. The measurement platform may hold multiple sensors. The cleaning devices may be arranged to clean a portion of the lithography apparatus, such as a portion of the projection system PS or a portion of the system providing the immersion liquid. The measurement platform may move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0036] In operation, the radiation beam B is incident on the pattern forming apparatus (e.g., mask MA) held on the mask support MT and patterned by the pattern (design layout) present on the pattern forming apparatus MA. After passing through the mask MA, the radiation beam B is passed through the projection system PS, which focuses the beam onto the target portion C of the substrate W. With the aid of the second positioning device PW and the position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C in a focused and aligned position within the path of the radiation beam B. Similarly, the first positioning device PM and possibly another position sensor ( Figure 1A (Not explicitly depicted) can be used to accurately position the patterning apparatus MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning apparatus MA and the substrate W. 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 scribe alignment marks.

[0037] like Figure 1B As shown, the lithography apparatus LA can form part of a lithography unit LC (sometimes also called a lithography cell or (lithography) cluster), which typically also includes equipment for performing pre-exposure and post-exposure processes on a substrate W. Conventionally, this equipment includes a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chiller CH, and a baking plate BK, for example, to regulate the temperature of the substrate W, and for example, to regulate the solvent in the resist layer. A substrate transport device or robot RO picks up the substrate W from input port I / O1 and output port I / O2, moves them between different process devices, and transfers the substrate W to the loading stage LB of the lithography apparatus LA. The apparatus in the lithography cell, also commonly referred to as a coating and developing system or track, is typically under the control of a coating and developing system control unit or track control unit TCU, which itself can be controlled by a management and control system SCS, which can also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0038] To ensure that the substrate W exposed by the photolithography apparatus LA is correctly and consistently exposed, it is necessary to inspect the substrate to measure properties 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) may be included in the photolithography unit LC. If an error is detected, adjustments can be made, for example, to the exposure of subsequent substrates or to other processing steps to be performed on the substrate W, particularly if the inspection is performed before other substrates W in the same batch or group are still to be exposed or processed.

[0039] The inspection device, also known as a measurement device, is used to determine the properties of the substrate W, particularly how the properties of different substrates W vary, or how the properties associated with different layers of the same substrate W change between layers. The inspection device may alternatively be configured to identify defects on the substrate W, and may be, for example, part of the photolithography unit LC, or integrated into the photolithography apparatus LA, or even a separate device. The inspection device can measure characteristics on latent images (images in the resist layer after exposure), semi-latent images (images in the resist layer after the post-exposure baking step PEB), or developed resist images (where the exposed or unexposed portions of the resist have been removed), or even characteristics on etched images (after a pattern transfer step such as etching).

[0040] Typically, the patterning process in a photolithography apparatus (LA) is one of the most critical steps in the process, requiring high accuracy in the precise dimensionalization and placement of the structures on the substrate W. To ensure this high accuracy, such as... Figure 2 The diagram schematically depicts three systems that can be combined within a so-called "holistic" control environment. One of these systems is the lithography apparatus LA, which is (in effect) connected to the metrology tool MT (the second system) and to the computer system CL (the third system). The key to this "holistic" environment is optimizing the coordination between these three systems to enhance the overall process window and provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines a range of process parameters (e.g., dose, focus, overlap) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device), typically allowing the process parameters during the lithography or patterning process to vary within the defined result.

[0041] The computer system CL can use the design layout (partial) 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 implement the maximum overall process window (in) of the patterning process. Figure 2(Depicted by a double arrow in the first scale SC1). Typically, the resolution enhancement technique is arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect where the lithography apparatus LA is currently operating within the process window (e.g., using input from the metrology tool MT) to predict whether defects exist due to, for example, suboptimal processing (in... Figure 2 (This is depicted by the arrow pointing to "0" in the second scale SC2).

[0042] The measurement tool MT can provide input to the computer system CL to enable accurate simulation and prediction, and can provide feedback to the lithography equipment LA to identify possible drift, for example, when the lithography equipment LA is in calibration or standardization state (in Figure 2 (This is depicted by multiple arrows in the third scale SC3).

[0043] During photolithography, it is desirable to frequently measure the resulting structure, for example, for process control and verification. Different types of metrology equipment (MTs) are known for performing these measurements, including scanning electron microscopes or various forms of scatterometer metrology equipment.

[0044] A scatterometer is a multifunctional instrument that allows for the measurement of parameters of a photolithography process by placing a sensor in the pupil of the objective lens of the scatterometer or in a conjugate plane conjugate to the pupil (this measurement is generally referred to as a pupil-based measurement), or by placing a sensor in an image plane or in a plane conjugate to the image plane (in this case, the measurement is generally referred to as an image- or field-based measurement). These scatterometers and associated measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, the entire contents of which are incorporated herein by reference. The aforementioned scatterometers can measure gratings using light from embodiments of the light sources discussed in this document.

[0045] The overall measurement quality of a lithography parameter for a specific target is determined at least in part by the measurement configuration used to measure that lithography parameter. The term "substrate measurement configuration" 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 a substrate measurement configuration is a diffraction-based optical measurement, the one or more parameters of the measurement 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. One criterion for selecting a measurement configuration can be, for example, the sensitivity of one of the measurement parameters to processing variations. Further examples are described in U.S. Patent Application US2016-0161863 and U.S. Patent Application US2016 / 0370717A1, which are incorporated herein by reference in their entirety. The light source described in this document can be configured to be controllable relative to the light source requirements of these substrate measurement configurations.

[0046] Photolithography apparatuses may include one or more alignment sensors that can accurately measure the position of alignment marks formed on a substrate. The alignment (or position) sensors can use optical phenomena such as diffraction and interference to obtain positional information from the alignment marks formed on the substrate. Examples of alignment sensors used in current photolithography apparatuses are based on self-reference interferometers as described in US6961116. Various enhancements and modifications of position sensors have been developed, for example, as disclosed in US2015261097A1. All of these disclosures are incorporated herein by reference.

[0047] Markings, or alignment marks, may comprise a series of gratings formed on or within a layer disposed on the substrate, or (directly) formed in the substrate. The gratings may be regularly spaced and act as grating lines, thereby allowing the marks to be considered as diffraction gratings with a known spatial period (spacing). Depending on the orientation of these grating lines, the marks may be designed to allow measurement of position along the X-axis or along the Y-axis (which is substantially perpendicular to the X-axis). Markings comprising gratings arranged at +45 degrees and / or -45 degrees relative to both 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.

[0048] The alignment sensor uses a radiation spot to optically scan each mark to obtain a periodically varying signal, such as a sine wave. The phase of this signal is analyzed to determine the position of the mark, and thus the position of the substrate relative to the alignment sensor, which is then fixed relative to the reference frame of the photolithography apparatus. So-called coarse and fine marks associated with different (coarse and fine) mark sizes can be provided, allowing the alignment sensor to distinguish different periods of the periodic signal and the exact position (phase) within each period. Marks with different spacing can also be used for this purpose.

[0049] Measuring the position of the markings can also provide information about the deformation of the substrate on which the markings (e.g., in the form of a wafer grid) are placed. The deformation of the substrate can occur, for example, by electrostatic clamping of the substrate to the substrate stage and / or by heating the substrate when it is exposed to radiation.

[0050] Figure 3A This is a schematic block diagram of an embodiment of a known alignment sensor AS (such as that described, for example, in US6961116, which is incorporated herein by reference). A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is directed by a steering optics onto a marker (such as a marker AM located on a substrate W) as an illumination spot SP. In this example, the steering optics include a spot mirror SM and an objective lens OL. The radiation source RSO may be provided by embodiments of the light source disclosed in this document. The diameter of the illumination spot SP used to illuminate the marker AM may be slightly smaller than the width of the marker itself.

[0051] The radiation diffracted by the marker AM is collimated (in this example via the objective lens OL) into an information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the marker (which may be referred to as reflection). A self-referenced interferometer SRI (such as the type disclosed in US6961116 mentioned above) causes the beam IB to interfere with itself, after which the beam is received by a photodetector PD. In cases where more than one wavelength is generated by the radiation source RSO, additional optics (not shown) may be included to provide multiple separate beams. The photodetector may be a single element, or it may include multiple pixels, if desired. The photodetector may include a sensor array.

[0052] A topography measurement system, a level sensor, or a height sensor, which may be integrated into the lithography apparatus, is arranged to measure the topography of the top surface of a substrate (or wafer). A topography map (also called a height map) of the substrate can be generated based on 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 the transfer of the pattern onto the substrate, so as to provide a spatial image of the pattern forming apparatus at an appropriate focal position on the substrate. It will be understood that "height" in this context refers broadly to the dimension (also called the Z-axis) detached from the plane from the substrate. Typically, the level sensor or the height sensor performs measurements at a fixed location (relative to its own optical system), and the relative movement between the substrate and the optical system of the level or height sensor results in height measurements at multiple locations across the entire substrate.

[0053] Figure 3B An example of a level or height sensor LS known in the art is illustrated schematically, for the purpose of illustrating only its working principle. In this example, the level 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 imparted by a projection grating PGR of the projection unit LSP. The radiation source LSO may include embodiments of the disclosures in this document.

[0054] This invention aims to improve the operational lifetime of light sources, particularly broadband light sources comprising hollow-core photonic crystal fiber (HC-PCF). The broadband light source of this invention can be used in measurement tools, such as scatterometer calibration sensors, height or level sensors, as described above.

[0055] The measurement tools (MTs) mentioned above (such as scatterometers, topography measurement systems, or position measurement systems) can perform measurements using radiation originating from a radiation source. The properties 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 can be advantageous to use multiple radiation frequencies to measure the substrate, for example, broadband radiation can be used. Multiple different frequencies can propagate, irradiate, and scatter away from the measurement target without interfering with other frequencies or with minimal interference. Therefore, different frequencies can be used, for example, to obtain more measurement data simultaneously. Different irradiation frequencies may also be able to interrogate and discover different properties of the measurement target. Broadband radiation can be used in measurement systems (MTs) such as, for example, level sensors, alignment mark measurement systems, scattering measurement tools, or inspection tools. The broadband radiation source can be a supercontinuum source.

[0056] High-quality broadband radiation (e.g., supercontinuum radiation) can be difficult to generate. One approach to generating broadband radiation is, for example, to broaden high-power narrowband or single-frequency input radiation using nonlinear higher-order effects. This input radiation (which can be generated using a laser) can be referred to as pump radiation. Alternatively, it can be referred to as seed radiation. To obtain high-power radiation for the broadening effect, the radiation can be confined to a smaller region, resulting in strongly localized high-intensity radiation. In those regions, the radiation can interact with the broadening structure and / or the material forming the nonlinear medium to generate broadband output radiation. Different materials and / or structures can be used in these high-intensity radiation regions to achieve and / or improve radiation broadening by providing a suitable nonlinear medium.

[0057] In some implementations, the broadband output radiation is generated in a photonic crystal fiber (PCF). In several embodiments, such a PCF has microstructures around its fiber core that help confine the radiation traveling through the fiber core. The fiber core can be made of a solid material with nonlinear properties that can generate broadband radiation when high-intensity pump radiation is transmitted through the fiber core. While generating broadband radiation in a solid-core PCF is feasible, using a solid material can have some disadvantages. For example, if ultraviolet radiation is generated in the solid core, this radiation may not be present in the output spectrum of the fiber because it is absorbed by most solid materials.

[0058] In some implementations, see the following reference: Figure 4BFurthermore, methods and apparatus for broadening input radiation can utilize optical fibers to confine and broaden the input radiation to output broadband radiation. The optical fiber may be a hollow-core fiber and may include internal structures to achieve effective guidance and confinement of radiation within the fiber. The optical fiber may be a hollow-core photonic crystal fiber (HC-PCF), which is particularly suitable for strong radiation confinement primarily within the hollow core of the fiber, thereby achieving high radiation intensity. The hollow core of the optical fiber may be filled with a gas or gas mixture, which serves as a broadening medium for broadening the input radiation. This fiber and gas mixture arrangement can be used to generate a supercontinuum radiation source. The radiation input to the optical fiber may be electromagnetic radiation, such as radiation in one or more of the infrared, visible, ultraviolet, and extreme ultraviolet spectra. The output radiation may consist of or include broadband radiation, which may be referred to herein as white light. The output radiation may cover the ultraviolet, visible, and near-infrared ranges. The exact spectrum and power density of the output radiation will be determined by several parameters, such as the fiber structure, gas mixture composition, gas pressure, energy of the input radiation, pulse duration and pulse shape of the input radiation.

[0059] 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-resonance structure for confining radiation. Such fibers including anti-resonance structures are known in the art as anti-resonance fibers, tubular fibers, single-loop fibers, negative curvature fibers, or suppression-coupling fibers. Various different designs of these fibers are known in the art. Alternatively, the optical fiber can be a photonic bandgap fiber (HC-PBF, such as Kagome fiber).

[0060] A number of 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 of the design and manufacture of HC-PCFs can be found in U.S. Patent US2004 / 015085A1 (for HC-PBF) and International PCT Patent Application WO2017 / 032454A1 (for Hollow Core Anti-Resonant Reflective Fiber), which are incorporated herein by reference. Figure 4C (a) shows a Kagome optical fiber including a Kagome lattice structure.

[0061] Reference Figure 4AAn example of an optical fiber used in the radiation source is described, and Figure 4a is a schematic cross-sectional view of the optical fiber OF in a transverse plane. Similar to... Figure 4A Further embodiments of actual examples of the optical fiber are disclosed in WO2017 / 032454A1.

[0062] The optical fiber (OF) includes an elongated body that is longer in one dimension than in the other two dimensions of the optical fiber. This longer dimension may be referred to as the axial direction and may define the axis of the optical fiber. The two other dimensions define a plane that may be referred to as the transverse plane. Figure 4A The cross-section of the optical fiber OF in a transverse plane (i.e., perpendicular to the axis) is shown. The transverse cross-section of the optical fiber OF can be substantially constant along the fiber axis.

[0063] It will be understood that the optical fiber (OF) has a degree of flexibility or flexibility, and therefore the direction of the axis will not typically be uniform along the length of the optical fiber (OF). Terms such as the optical axis, the transverse section, etc., will be understood to mean local optical axis, local transverse section, etc. Furthermore, when the component is described as cylindrical or tubular, these terms will be understood to cover shapes that may have been deformed when the optical fiber (OF) is flexed.

[0064] The optical fiber OF can have any length, and it will be understood that the length of the optical fiber OF can depend on the application. The optical fiber OF can have a length between 1 cm and 10 m or 0.1 cm and 10 m, for example, the optical fiber OF can have a length between 10 cm and 100 cm.

[0065] The optical fiber OF includes: a hollow core COR; a cladding portion surrounding the hollow core COR; and a support portion SP surrounding and supporting the cladding portion. The optical fiber OF can be considered as a body comprising the hollow core COR (including the cladding portion and the support portion SP). The cladding portion includes a plurality of anti-resonance elements for guiding radiation through the hollow core COR. Specifically, the plurality of anti-resonance elements are arranged to constrain radiation propagating primarily within the hollow core COR through the optical fiber OF, and are arranged to guide the radiation along the optical fiber OF. The hollow core COR of the optical fiber OF can be generally located in the central region of the optical fiber OF, such that the axis of the optical fiber OF can also define the axis of the hollow core COR.

[0066] The cladding portion includes multiple anti-resonance elements for guiding the radiation propagation through the optical fiber (OF). Specifically, in this embodiment, the cladding portion includes a single loop of six tubular capillary CAPs. Each tubular capillary in the tubular capillary CAP acts as an anti-resonance element.

[0067] The capillary CAP can also be referred to as a tube. In cross-section, the capillary CAP can be circular or can have another shape. 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 radiation propagating through the hollow core HC (and the radiation can be incident on the aforementioned wall portion WP at a grazing incidence angle). The thickness of the wall portion WP can be suitable to ensure that reflections returning to the hollow core HC are substantially enhanced, while transmission into the capillary cavity CC is substantially suppressed. In some embodiments, the capillary wall portion WP can have a thickness between 0.01 μm and 10.0 μm.

[0068] It will be understood that, as used herein, the term "covered portion" is intended to mean the portion of the optical fiber OF used to guide propagating radiation through the optical fiber OF (i.e., the capillary CAP that confines the radiation within the hollow core COR). The radiation can be confined in a lateral pattern to propagate along the fiber axis.

[0069] The support portion is typically tubular and supports six capillary CAPs of the covering portion. The six capillary CAPs are evenly distributed around the inner surface of the inner support portion SP. The six capillary CAPs can be described as being arranged in a generally hexagonal shape.

[0070] The capillary CAPs are arranged such that each capillary does not contact any other capillary CAP. Each capillary in the capillary CAP contacts the inner support portion SP and is spaced apart from adjacent capillary CAPs in the ring structure. This arrangement can be advantageous because it can increase the transmission bandwidth of the optical fiber OF (compared to, for example, an arrangement where the capillaries are in contact with each other). Alternatively, in some embodiments, each capillary in the capillary CAP may contact adjacent capillary CAPs in the ring structure.

[0071] The six capillary capillaries (CAPs) of the cladding portion are disposed within a ring structure surrounding 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 optical 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) may affect the mode field diameter, impulse loss, dispersion or scattering, modal complexity, and nonlinear properties of the hollow core optical fiber (OF).

[0072] In this embodiment, the cladding portion comprises a single-ring arrangement of capillary CAPs (which act as anti-resonance elements). Therefore, a line passing through at most one capillary CAP is allowed in any radial direction from the center of the hollow core HC to the outside of the optical fiber OF.

[0073] It will be understood that other embodiments may include different arrangements of anti-resonance elements. These arrangements may include arrangements of multiple rings with anti-resonance elements and arrangements of nested anti-resonance elements. Furthermore, although Figure 4A The illustrated embodiment includes a ring of six capillaries, but in other embodiments, one or more rings including any number of anti-resonance elements (e.g., 4, 5, 6, 7, 8, 9, 10, 11 or 12 capillaries) may be provided in the encapsulation portion.

[0074] Figure 4C (b) shows a modified embodiment of the single-ring HC-PCF with tubular capillaries discussed above. Figure 4C In example (b), there are two coaxial rings of the tubular capillary 21. To maintain the inner and outer rings of the tubular capillary 21, a support tube ST can be included in the HC-PCF. The support tube can be made of silica.

[0075] Figure 4A and Figure 4C The tubular capillary in examples (a) and (b) can have a circular cross-sectional shape. Other shapes are also possible for the tubular capillary, such as elliptical or polygonal cross-sections. Furthermore, Figure 4A and Figure 4C The solid material of the tubular capillary in the examples of (a) and (b) may include a plastic material (such as PMA) or a glass (such as silica or soft glass).

[0076] Figure 4B A radiation source RDS for providing broadband output radiation is described. The radiation source RDS includes: a pulsed pumped radiation source PRS or any other type of source capable of generating short pulses of desired length and energy levels; an optical fiber OF having a hollow core COR (e.g., Figure 4A (as shown in the diagram); and the working medium WM (e.g., gas) disposed within the hollow core COR of the embodiment. Although in Figure 4B In China, the implementation of radiation source RDS includes Figure 4A The illustrated implementation fiber OF can be used, but in alternative embodiments, other types of hollow core fibers may be used.

[0077] The pulsed-pump radiation source (PRS) is configured to provide input radiation IRD. The hollow core HC of the fiber OF is arranged to successfully receive the input radiation IRD from the PRS and broaden the input radiation IRD to provide output radiation ORD. The operating medium WM is capable of broadening the frequency range of the received input radiation IRD to provide broadband output radiation ORD.

[0078] The radiation source RDS also includes a storage unit RSV. The optical fiber OF is disposed inside 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 the working medium WM. The storage unit RSV may include one or more characteristics known in the art for controlling, regulating, and / or monitoring the composition of the working medium WM (which may be a gas) inside the storage unit RSV. The storage unit RSV may include a first transparent window TW1. In use, the optical fiber OF is disposed inside the storage unit RSV such that the first transparent window TW1 is positioned close to the input end IE of the optical fiber OF. The first transparent window TW1 may form a portion of the wall of the storage unit RSV. The first transparent window TW1 may be transparent to at least the received input radiation frequency, such that the received input radiation IRD (or at least a majority thereof) can be coupled to the optical fiber OF located inside the storage unit RSV. It will be understood that optics (not shown) may be provided for coupling the input radiation IRD to the optical fiber OF.

[0079] The storage unit RSV includes a second transparent window TW2 forming a portion of the wall of the storage unit RSV. In use, when the optical fiber OF is disposed inside the storage unit RSV, the second transparent window TW2 is positioned close to the output end OE of the optical fiber OF. The second transparent window TW2 can be transparent to at least the frequency of the broadband output radiation ORD of the device.

[0080] Alternatively, in another embodiment, the two opposite ends of the optical fiber OF can be housed within different storage devices. The optical fiber OF may include a first end segment configured to receive an input radiation IRD and a second end segment configured to output a broadband output radiation ORD. The first end segment may be housed within a first storage device including a working medium WM. The second end segment may be housed within a second storage device, which may also include the working medium WM. The operation of the storage devices can be as described above regarding... Figure 4B The first storage unit may include a first transparent window configured to be transparent to the input radiation IRD. The second storage unit may include a second transparent window configured to be transparent to the broadband output radiation ORD. Both the first and second storage units may also include sealable openings to allow the optical fiber OF to be partially placed inside and partially outside the storage unit, such that gas can be sealed inside the storage unit. The optical fiber OF may also include intermediate segments not contained within the storage unit. This arrangement using two separate gas storage units can be particularly convenient for embodiments where the optical fiber OF is relatively long (e.g., when the length exceeds 1 meter). It will be appreciated that, with this arrangement using two separate gas storage units, the two storage units (which may include one or more characteristics known in the art for controlling, regulating, and / or monitoring the composition of the gas inside the two storage units) can be considered as a device for providing the working medium WM within the hollow core HC of the optical fiber OF.

[0081] In this context, if at least 50%, 75%, 85%, 90%, 95%, or 99% of incident radiation of a certain frequency on the window is transmitted through the window, then the window can be transparent to the frequency.

[0082] Both the first transparent window TW1 and the second transparent window TW2 can form an airtight seal within the wall of the reservoir RSV, allowing the working medium WM (which may be a gas) to be contained within the reservoir RSV. It will be understood that the gas WM can be contained within the reservoir RSV at a pressure different from the ambient pressure of the reservoir RSV.

[0083] The working medium WM can include: rare 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, krypton / helium mixtures, or nitrogen / hydrogen mixtures. Depending on the type of fill gas, nonlinear optical processes can include modulation instability (MI), optical soliton or soliton self-compression, optical soliton splitting, Kerr effect, Raman effect, and diffuse wave generation, detailed in WO2018 / 127266A1 and US9160137B1 (both are hereby incorporated by reference). Because the dispersion of the fill 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 adjusted to optimize frequency conversion.

[0084] In one embodiment, the working medium WM may be disposed within the hollow core HC at least during the reception of the input radiation IRD for generating the broadband output radiation ORD. It will be understood that when the optical fiber OF does not receive the input radiation IRD for generating the broadband output radiation, the gas WM may be wholly or partially absent from the hollow core HC.

[0085] To achieve frequency broadening, high-intensity radiation may be desired. The advantage of hollow-core optical fibers (OFs) is that they can achieve high-intensity radiation through strong spatial confinement of radiation propagating through the OF, thus achieving high localized radiation intensity. The radiation intensity within the OF can be high, for example, due to high received input radiation intensity and / or due to the strong spatial confinement of radiation within the OF. Hollow-core fibers also have the advantage of guiding radiation with a wider wavelength range than solid-core fibers, and in particular, they can guide radiation in both the ultraviolet and infrared ranges.

[0086] The advantage of using a hollow core optical fiber (OF) is that most of the guided radiation within the OF is confined to the hollow core (COR). Therefore, most of the radiation interaction within the OF is with the working medium (WM), which is disposed within the hollow core (HC) of the OF. This enhances the broadening effect of the working medium (WM) on the radiation.

[0087] 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.

[0088] The input radiation IRD can be coherent radiation. The input radiation IRD can be collimated radiation, which has the advantage of facilitating and improving the efficiency of coupling the input radiation IRD to the optical fiber OF. The input radiation IRD can include a single frequency or a narrow frequency range. The input radiation IRD can be generated by a laser. Similarly, the output radiation ORD can be collimated and / or coherent.

[0089] The broadband range of the output radiation ORD can be a continuous range, including a continuous range of radiation frequencies. The output radiation ORD can include supercontinuum radiation. Continuous radiation can be beneficial in a number of applications (e.g., in measurement applications). For example, a continuous range of frequencies can be used to query a large number of properties. A continuous range of frequencies can, for example, be used to determine and / or eliminate the frequency dependence of the measured properties. A supercontinuum output radiation ORD can include, for example, electromagnetic radiation in the wavelength range of 100 nm to 4000 nm, or even up to 10 μm. The frequency range of the broadband output radiation ORD can be, for example, 400 nm to 900 nm, 500 nm to 900 nm, or 200 nm to 2000 nm. The supercontinuum output radiation ORD can include white light.

[0090] The input radiation IRD provided by the pulsed pumped radiation source (PRS) can be pulsed. The input radiation IRD can include electromagnetic radiation at one or more frequencies between 200 nm and 2 μm. The input radiation IRD can, for example, 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 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 100 W values. The average power of the input radiation IRD can, for example, be between 20 W and 50 W.

[0091] The pulsed pump source (PRS) can be a laser. The spatiotemporal transmission characteristics (e.g., its spectral amplitude and phase) of such a laser pulse transmitted along the fiber OF can be altered and tuned by adjusting the (pump) laser parameters, the operating component (WM), and the fiber OF parameters. These spatiotemporal transmission characteristics can include one or more of the following: output power, output mode profile or distribution, output time profile or distribution, the width of the output time profile or distribution (or output pulse width), the output spectral profile or distribution, and the bandwidth of the output spectral profile or 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: the fiber length, size, and shape of the hollow core 101; the size and shape of the capillary; and the thickness of the wall surrounding the hollow core of the capillary. The WM (e.g., filling gas) parameters can include one or more of the following: gas type, gas pressure, and gas temperature.

[0092] The broadband output radiation ORD provided by the radiation source RDS can have an average output power of at least 1 W. The average output power can be at least 5 W. The average output power can be at least 10 W. 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 0.01 mW / nm across the entire wavelength band of the output radiation. The power spectral density of the broadband output radiation across the entire wavelength band can be at least 3 mW / nm.

[0093] Figure 5 An example of a broadband light source device including an HC-PCF is shown. The light source 500 may include a gas chamber 502 in which an HC-PCF 501 is embedded. Each of the two ends of the HC-PCF 501 may be optically coupled to windows 503 / 504 through which the input beam and the output beam travel.

[0094] In use, the gas chamber 502 can be filled with a gas (which may be a gas mixture), and the HC-PCF 501 can be filled with the same or substantially similar gas. Airflow can be established by providing a pressure difference between the inlet and outlet of the HC-PCF 501. This pressure in the gas chamber and / or the HC-PCF 501 can range from 0.1 Bar to 100 Bar. The gas chambers can be composite.

[0095] An input source, such as a pump laser, enters the light source through an input window 503. The input beam 506 is focused and enters the HC-PCF 501. The spectrum of the beam is broadened as it travels through the HC-PCF 501, thereby producing a broadband output beam 505.

[0096] A gap 509 is provided between the end facet of the HC-PCF and the window to prevent dielectric breakdown of the window (especially the output window). Figure 5 As shown, the broadband beam segment 505 diverges as it leaves the HC-PCF output facet, resulting in a lower intensity of the beam once it reaches the output window 503. Therefore, the intensity of the beam incident on the output window 503 is below the dielectric breakdown strength threshold of the window.

[0097] When an HC-PCF-based light source (such as light source 500) is operated, contaminants grow on the end facets of the HC-PCF over time. In particular, the inventors have observed that contaminant growth is significant on the output facets of the HC-PCF. Contaminant growth appears to occur at locations of highest light intensity; specifically, contaminant growth at the output facets of the HC-PCF is greater than at the output windows. Contaminant growth also appears to occur at locations where spectral broadening has occurred; specifically, contaminant growth is less pronounced on the input facets. Furthermore, contamination is primarily observed on the output facets of the HC-PCF, rather than within the HC-PCF itself.

[0098] Contaminants can be generated due to silica particles detached from the windows of the gas chamber or from the HC-PCF. These contaminants can undergo a photoinitiation process using broadened output light from the PCF, altering their chemical structure and / or crystallizing on the output surface. After a certain number of hours during operation (e.g., after a certain dose (J) of laser energy has been transmitted), this contamination leads to a degradation of the fiber's performance; this degradation can be termed glassy growth (GGP): for example, SiO₂ grown at the output end of the fiber. x structure.

[0099] Alternatively, GGP may involve the activity or migration of silicon (as atoms, or volatile substances, such as SiH4) via physical or chemical sputtering, and / or involve plasma-induced deposition or temperature-induced deposition (e.g., via dissociating SiH4 into Si(solid) + 2 H2 or via plasma-induced polymerization) at the output end of the optical fiber.

[0100] The accumulation of these contaminants leads to a decrease in the lifetime of the light source. GGP and the resulting contaminant growth (occurring at the output facet) can protrude into the optical path of the diverging beam. This causes scattering of the output light and thus a decrease in the output power of the light source. GGP shortens the lifetime of the source: GGP causes light scattering, and therefore the optical fiber loses its performance. This may result in the inability to meet the required photon budget for, for example, the sensor after approximately 200 hours. Moreover, GGP causes variations in the light source power / spectral density and mode profile or distribution, which will require frequent recalibration if they are not addressed. Thus, the shorter lifetime of the optical fiber means frequent fiber replacement in the field and may result in very significant downtime (approximately several days) per year for the machine. This is unacceptable for industrial products.

[0101] To reduce the growth of these contaminants and extend the operational life of HC-PCF light sources, it is desirable to prevent contaminant formation, reduce their concentration in the light source equipment, or inhibit GGP growth induced by contaminants. Possible techniques for reducing contaminant concentration and preventing their formation include rigorous cleaning of the gas environment and the light-emitting chamber / bulb section before they are used in the light source. However, achieving thorough cleaning using known cleaning methods is challenging and cannot eliminate all contaminants.

[0102] Figure 6A The inventors' own experimental results show the average output power of the HC-PCF over the overall operational time. After approximately 180 hours, the average output power of the HC-PCF begins to decrease from above 7.50 watts to below 7.00 watts.

[0103] Figure 6B A schematic example of contaminant growth at the output end facet of the HC-PCF after an extended operating cycle is shown.

[0104] The exact source of the contaminants is unknown; however, it is not believed that the contaminants may arise from organic materials in the gas chamber environment, such as residual residues from fiber optic polymer coatings, lubricants from pneumatic components, from the gas chamber manufacturing process, or from the working gas within the gas chamber. Specifically, the following GGP mechanism is assumed:

[0105] 1) Laser- and / or light-induced decomposition occurs at the end of the optical fiber:

[0106] • The ultraviolet and visible components of white light are (at least) strongly absorbed (single or multiphoton absorption) and cause ionization of the gas within each pulse, which explains why there is no GGP at the input of the optical fiber, where only IR laser is incident, and the GGP is present at the output of the optical fiber.

[0107] • The unconstrained plasma (fed by high-frequency optical pulses) reaches a steady state at a certain distance from the end of the optical fiber (here, due to the lack of recombination near or at the wall, the concentration of ions and electrons is significantly higher than that inside the optical fiber).

[0108] • Ions / electrons from unconstrained plasma (at a relatively high concentration) promote light absorption and propagate ballistically toward the optical fiber via bipolar diffusion, potentially carrying the plasma into the fiber. As the plasma enters the narrow channel of the fiber, it decays exponentially with a coefficient of approximately exp(-x / d), where x is the measured distance from the fiber end and d is the inner diameter. This allows the plasma to propagate into the fiber up to several times its (core) diameter.

[0109] 2) The optical fiber material (mostly SiO2) undergoes this plasma; and is sputtered and redeposited:

[0110] • Surface atoms can be sputtered physically (it has been observed that GGP tends to occur only in optical fibers filled with rare gases) due to the presence of high atomic mass ions in the rare gases;

[0111] • Surface atoms can be chemically sputtered due to the presence of activated hydrogen (radicals and ions) in the reaction, such as:

[0112] Silicon atoms are redeposited (and may be immediately re-oxidized) in high electric field regions (such as the ends of optical fibers, where the dielectric constant is discontinuous for propagating light);

[0113] • The peaks of the growth structure act as field / temperature concentrators and can further promote the deposition.

[0114] Alternatively, SiH4 is decomposed under high temperature (or high radical / ion concentration) conditions in an unconstrained plasma, so that silicon is redeposited at the end of the optical fiber.

[0115] Alternatively, SiH4 can readily undergo plasma-initiated polymerization (at the fiber end) and possess branched chains, heavy molecules, or radical Si. x H y or Si x H y O z Deposition of x>>1, y>>1.

[0116] • Prior to inspection, some oxidation of the fluffy silicon structure may occur when the optical fiber is exposed to air.

[0117] Figure 6C This illustration depicts a laser- and / or light-induced decomposition scheme. An optical fiber or HC-PCF 100 includes an input 101 and an output 102. A laser pulse 110 is coupled into the HC-PCF 100 and converted into a co-propagating broadband pulse 121 and a reduced-energy laser pulse 120. The plasma 200 is excited by absorbing the ultraviolet / visible cost of light in the steady-state region 201 of the plasma. Within the numerical aperture (NA) 130 of the light source, a portion of the plasma 202 propagates upstream of the beam and partially enters the output 102 of the optical fiber. The plasma is maintained by regular light pulses.

[0118] Thus, the output end 102 of the optical fiber is subjected to plasma 202 that initiates etching and deposition. This results in the generation of volatile molecules (SiH4) or sputtered atoms (Si) from the end facet of the optical fiber and / or from the channels of the optical fiber (e.g., up to several times the diameter depth). Therefore, GGP structures are grown by the (temperature and / or plasma-induced) decomposition / oxidation of SiH4 or by the direct deposition of (previously sputtered) silicon atoms. It has been observed that the formation of these GGP structures decays exponentially with depth within the optical fiber, such that they almost completely decrease at depth L. s ~(0.2……2)*D f The location disappeared, including D. f This refers to the internal diameter of the fiber optic channel.

[0119] To reduce contaminant growth on the end facets of the HC-PCF, the capillary of the HC-PCF can be collapsed. The tapered end of the capillary can prevent contaminant growth. However, this solution does not address the fundamental problem of contaminants in the device, especially if the tapering in the capillary is imperfect, contaminant growth cannot be adequately prevented.

[0120] Another problem identified by the inventors in the HC-PCF / cell light source is the turbulent airflow within the cell. The HC-PCF / cell light source design can generate Re > 10. 7 The system operates under multiple dimensions and pressures with varying Reynolds numbers, meaning it is extremely prone to turbulence. Turbulence can introduce density inhomogeneities in the gas, leading to dynamic changes in the optical path lengths of the input or output beams. This can cause the output light to flicker. This variability in the light source makes it unreliable, especially for measurement applications where consistent light output from the source is crucial.

[0121] In particular, turbulent airflow in the gap between the end facets of the HC-PCF and the windows to which they are coupled can also cause additional problems. Increased turbulence increases the gas velocity along the path of the input beam 506 / output beam 505, and also increases the rate at which the gas in the input beam 506 / output beam 505 exchanges with the rest of the gas in the gas chamber. Therefore, in the event of contaminant growth caused by a photoinitiated process, increased turbulence will increase the rate at which contaminant particles cross the beam's path, and thus increase the rate at which contaminants can crystallize or otherwise accumulate in the device.

[0122] The inventors have developed a device for preventing or delaying the growth rate of contaminants on HC-PCF in a broadband light source. This disclosure provides a surface for minimizing the volume of gas in beam phase contact with the light source during operation.

[0123] In view of the aforementioned problems in the HC-PCF light source, the surface can perform any combination of the following structural functions: minimizing the first gas volume between the faceted end of the HC-PCF and the window to which it is optically coupled; limiting the rate of gas exchange between this first volume and the rest of the gas chamber; and substantially reducing turbulence in this first volume or in the gas chamber.

[0124] The light source of the embodiment may include: an air chamber having a window; an optical fiber that is hollow and has an axial direction, the end of the optical fiber being enclosed in the air chamber and optically coupled to the window via an optical path; and a surface disposed around the end of the optical fiber and extending toward the window in the axial direction beyond the end of the optical fiber to restrict exchange between the optical path and the remainder of the air chamber.

[0125] The air chamber may have a window on one of its axial ends. The air chamber may include two windows, each disposed on the axial end. The walls of the air chamber may include metal.

[0126] The optical fiber may be HC-PCF. Only the output end of the optical fiber may be contained within the gas chamber. Alternatively, the entire optical fiber may be contained within the gas chamber. The optical fiber may include a second end, which is also optically coupled to a second window of the gas chamber.

[0127] In one embodiment, the surface is provided by the inner surface of the air chamber. The surface may be provided by at least one wall of the air chamber. The thickness of the at least one air chamber wall may vary in the axial direction.

[0128] In an embodiment, the surface is provided by a protective element or shield. In other words, the shield is an embodiment of the surface that minimizes the volume of gas in contact with the beam of the light source when it is operating. The shield may be materially separate from the gas chamber and / or manufactured separately from the gas chamber. The shield may be fixed to the interior of the gas chamber.

[0129] The surface may extend a given length along the optical fiber, wherein the surface is offset from the circumference of the optical fiber to form a gap.

[0130] This gap between the optical fiber and the surface can be considered a "radial gap". The radial gap can be rotationally symmetric relative to the axial direction. The radial gap can be shaped as a cylindrical shell. The radial gap can have a non-uniform shape. The radial gap can be a main path through which gas can flow from the rest of the gas chamber to the optical path. The radial gap can be one of a plurality of gaps allowing gas flow to the optical path. The size of the radial gap can be configured to achieve a certain rate of gas exchange through the radial gap. The size of the radial gap can limit the gas exchange through the radial gap to a maximum of 10. -1 moles per hour, preferably up to 10 -4 moles per hour, preferably up to 10 -7 moles per hour, preferably up to 10 -10 Moles per hour.

[0131] The light source may have a gap between the optical fiber and the surface, and the gap may have a minimum cross-sectional area orthogonal to the axial direction, the minimum cross-sectional area being 100 μm. 2 With 3mm 2 In other words, the surface may not be perfectly conformable to the outer surface of the optical fiber.

[0132] The portion of the surface surrounding the optical fiber may not contact the optical fiber at any point. Alternatively, the portion of the surface surrounding the optical fiber may contact the optical fiber at one or more points. A support member may be formed from the surface and configured to support the optical fiber or mount the optical fiber in a specific location. The support member for the optical fiber may be provided by a structure other than the surface.

[0133] The surface may be adjacent to the optical fiber or sealed to the optical fiber.

[0134] The surface can be sealed to the optical fiber using brazing, welding, or low-degassing adhesive.

[0135] The end of the surface provided by the shield can be adjacent to or sealed to the window, or the surface of the air chamber containing the window.

[0136] The surface may include silicon dioxide. The surface may include a silicon dioxide coating on the inner surface of the air chamber. The shield may include silicon dioxide. The ends of the surface provided by the shield can be sealed to the window using glass-to-glass brazing or laser welding. The ends of the surface provided by the shield can be sealed to the air chamber using laser welding. The shield and the window or air chamber to which it is sealed may be manufactured as a single piece or integral part, or otherwise integrally formed. The single-piece shield and window or air chamber may be manufactured using subtractive manufacturing, optionally selectively laser etching. The single-piece shield and window or air chamber may include silicon dioxide.

[0137] The ends of the surface and the inner surface of the window or gas chamber can be separated by a small gap. This gap between the ends of the surface and, optionally, the shielding element and the inner surface of the window or gas chamber can be considered an "axial gap." The axial gap can be a main path through which gas can flow from the remainder of the gas chamber to the optical path. The axial gap can be one of a plurality of gaps that allow gas flow to the optical path. The size of the gap can be configured to achieve a certain rate of gas exchange through the gap. The size of the axial gap can limit the gas exchange through the axial gap to a maximum of 10. -1 moles per hour, preferably up to 10 -4 moles per hour, preferably up to 10 -7 moles per hour, preferably up to 10 -10 Moles per hour.

[0138] The light source may include a surface disposed on the output end of the optical fiber. The light source may include a shield disposed on the output end of the optical fiber.

[0139] The light source may include a surface disposed on the input end of the optical fiber. The light source may include surfaces disposed on each of the input and output ends of the optical fiber. These surfaces may form a continuous surface. These surfaces may be separated due to surface discontinuities or otherwise separated in material. Each of these surfaces may be provided by a shielding element.

[0140] The components providing the surface (e.g., shielding) may include silicon dioxide, metal, silicon, or other semiconductors. The coating on the inner surface of the gas chamber forming the surface may include silicon dioxide, metal, silicon, or other semiconductors. The shielding may include silicon dioxide, metal, silicon, or other semiconductors. Such a surface may include non-etchable materials that may have low or zero carbon and silicon content (e.g., robust to H* or H+, i.e., unaffected by H* or H+), such as metals, metal oxides, noble metals (as a coating or substrate), and ceramics.

[0141] The surface, chamber wall, and / or shielding that may originate from the light source may include a mixture of materials.

[0142] The gas chamber of the light source may have a non-constant wall thickness. The shield of the light source may have a non-constant wall thickness.

[0143] The wall of the air chamber or shield may be thicker at the axial end surrounding the optical fiber. The wall of the air chamber or shield may be thicker at points where airflow in the remainder of the air chamber is altered. The wall of the air chamber or shield may be thicker where a support member is provided by the surface to hold the optical fiber. The wall of the shield may be thicker where an external support member is provided by the outer surface of the shield to structurally support the shield within the air chamber. One or more external support members may be provided by portions separate from the shield to hold or position the shield within the air chamber.

[0144] The light source may include a surface that is rotationally symmetric with respect to the axial direction.

[0145] The surface may be defined as one of the following shapes: cylindrical, truncated conical, or horn-shaped.

[0146] The outer surface of the shield can be defined as one of the following shapes: cylindrical, truncated conical, or horn-shaped.

[0147] The inner surface of the shield can be defined in one of the following shapes: cylindrical, truncated conical, or horn-shaped.

[0148] Alternatively, the surface may not be rotationally symmetric. The surface, and optionally the outer and / or inner surfaces of the shield, may describe a non-rotationally symmetric shape. The surface may include one or more support members for mounting or otherwise supporting the optical fiber in a specific location within the air chamber. Optionally, the shield may include one or more support members on its inner or outer surface for mounting or otherwise supporting the optical fiber or the shield in a specific location within the air chamber. The surface, optionally the inner and / or outer surfaces of the shield, may include structural features to redirect airflow, reduce turbulence, and / or redirect turbulence away from the optical path. These structures may include structured / textured surfaces, fins, or flow straighteners.

[0149] In addition to the aforementioned surface and shielding, structures can be added to reduce or redirect turbulence within the air chamber. These structures may include structured / textured surfaces, fins, or flow straighteners.

[0150] The surface (e.g., the shield of the light source) may have a non-constant diameter orthogonal to the axial direction. In other words, the surface may define a diameter orthogonal to the axial direction, and the diameter may vary in the axial direction.

[0151] The diameter of the surface (e.g., the shielding element) may be larger at its end near the window. In other words, the cross-section of the surface orthogonal to the axial direction may be larger at its end near the window than at the end of the surface surrounding the optical fiber.

[0152] The inner diameter of the surface (e.g., the shield) can gradually increase from a first smaller diameter surrounding the end of the optical fiber to a larger diameter adjacent to the window.

[0153] The inner diameter of the surface (e.g., the shield) can be greater than the minimum diameter D provided by the following equation. min :

[0154]

[0155] Where w0 is the mode field diameter at the end of the optical fiber, z is the distance from the end of the optical fiber, and z R It is the Rayleigh length.

[0156] The inner diameter of the surface (e.g., the shield) can be the diameter provided by equation (1). In other words, the inner diameter of the shield can be approximately equal to the minimum diameter provided by equation (1).

[0157] Equation (1) is derived from the expected local bundle diameter at a given distance from the output end of the optical fiber. Other equations for evaluating this bundle diameter can be used to determine the dimensions of the surface. It is generally expected that the surface closely follows but does not obstruct the output bundle of the optical fiber. These principles for the dimensions of the surface can also be applied to the input end of the optical fiber. The portion of the surface surrounding the input end of the optical fiber can closely follow but not obstruct the input bundle received by the input end of the optical fiber.

[0158] The shielding element of the light source may have a constant cross-section orthogonal to the axial direction. In other words, the shielding element may have a prism shape. The shielding element may have a cylindrical outer shell, or other prism shape defining a hollow internal space.

[0159] The gas chamber of the light source may include at least one gas selected from the group consisting of: helium, neon, argon, krypton, xenon, hydrogen, oxygen, nitrogen, other molecular gases and mixtures thereof.

[0160] The light source can be coupled to an optical source, which includes a pump laser. The optical source can be coupled to the input of the HC-PCF through a window.

[0161] The measurement device of the embodiment includes a light source according to an embodiment of the present disclosure, wherein the light source is configured to generate light for projection onto a substrate.

[0162] The measuring device can be a scattering instrument.

[0163] The measuring device can be used in measuring applications such as overlap, alignment, and / or leveling.

[0164] Figure 7 The configuration of an embodiment of the light source is shown. The light source includes an air chamber 502 having a window 503, an optical fiber 501 optically coupled to the window 503 across a gap 509, and a protective element or shield 700 providing a surface 710. An output beam 505 is shown exiting the end of the optical fiber 501, and the output beam diverges as it travels to the window 503. The shield 700 is disposed around the end of the optical fiber 501 and extends in two axial directions parallel to the axis of the optical fiber.

[0165] Figure 7 The shielding element has a cylindrical shell shape. A cross-section of the shielding element has been obtained along the axial direction, showing the wall material 701 and internal voids 702. The end of the optical fiber is enclosed within the shielding element.

[0166] Figure 7 The shielding element 700 is rotationally symmetrical with respect to the axial direction of the optical fiber 501. The inner surface 710 of the shielding element 700 always has a constant inner diameter. At the end of the optical fiber in the shielding element, there is a radial gap 703 between the end of the optical fiber and the inner surface 710 of the shielding element 700. At the end of the window in the shielding element, the inner diameter of the shielding element surface 710 is larger than the maximum diameter of the output bundle 505. A small axial gap 704 exists between the end of the shielding element 700 and the window 503.

[0167] The shield 700 restricts the local gas volume surrounding the optical path of the output beam 505. The shield 700 also axially restricts the airflow through the device and substantially limits radial flow from the remainder of the gas chamber to the optical path. In the illustrated embodiment, airflow can only enter the optical path through radial gap 703 and axial gap 704. Therefore, the rate at which contaminants cross the optical path should be reduced compared to the case where the shield is not present at all.

[0168] The gaps 703 and 704 of the shield 700 allow gas in the optical path of the output beam 505 to communicate fluidly with the remainder of the gas chamber, while simultaneously restricting airflow across the entire optical path. Gas is still expected to reach the optical path because the broadband output from the light source depends on gas pressure.

[0169] like Figure 7 As shown, a radial gap 703 can be formed between the outer surface of the optical fiber and the inner surface 710 of the shield 700. The length of this gap in the axial direction can be configured to limit gas exchange to a selected maximum rate. The cross-sectional size of the gap in the radial direction can also be configured to limit gas exchange to a selected maximum rate.

[0170] The size of the axial gap 704 between the end of the shield and the window can also be configured to limit gas exchange at this location to a selected maximum rate.

[0171] The dimensions of the radial clearance 703 and / or the axial clearance 704 can be configured to reduce turbulence entering the optical path region. While achieving laminar flow may not be feasible given specific device size / pressure conditions, reducing the turbulent characteristics of the airflow remains preferred.

[0172] The dimensions of the radial clearance 703 and the axial clearance 704 can be configured, through their combined use, to achieve specific airflow effects. The clearances can be configured to have similar inflow / outflow rates, or to direct flow toward each other to prevent airflow from traversing the entire optical path.

[0173] Alternatively, in this embodiment, the axial clearance 704 may be absent, and the end of the shield may be adjacent to or sealed to the output window.

[0174] In other embodiments, the shape or size of the radial and axial clearances can be configured, either in isolation or in combination, to produce other desired airflow properties. Desired airflow properties may include specific flow topologies that prevent excessive turbulence from being generated in or around the optical path.

[0175] Figure 8 The configuration of another embodiment of the light source is shown. Figure 8 In addition to the shielding member 800 having surface 810, the embodiments also include those with... Figure 7 The same components. The light source includes an air chamber 502 with a window 503, an optical fiber 501 optically coupled to the window 503 across a gap 509, and a protective element or shield 800. An output beam 505 is shown exiting the end of the optical fiber 501, and the output beam diverges as it travels to the window 503. The surface 810 of the shield 800 is disposed around the end of the optical fiber 501 and extends in two axial directions parallel to the axis of the optical fiber.

[0176] Shielding element 800 differs from shielding element 700 because surface 810 abuts the end of optical fiber 501, thereby forming a sealed portion around the entire outer circumference of optical fiber 501. Therefore, in Figure 8 In the embodiment shown, there is no interaction between the surface 810 and the optical fiber 501. Figure 7 The radial clearance 703 corresponds to the clearance. However, in this embodiment, an axial clearance 804 exists, allowing the gas in the optical path to communicate fluidly with the gas in the remainder of the gas chamber 502. Any optional features disclosed for the axial clearance 704 can also be applied to the axial clearance 804.

[0177] The shield 800 is rotationally symmetric with respect to the axial direction of the optical fiber 501, and a cross-section of the shield 800 has been obtained along the axial direction, thereby showing the wall material 801 and the internal void 802.

[0178] The shield 800 also differs from the shield 700 because the surface 810 has a diameter that varies relative to the axial direction. The surface 810 is generally truncated conical in shape, and the larger end of the truncated cone is located at the end of the shield adjacent to the window 503.

[0179] Figure 8 The cross-section of the surface 810 of the shield, as shown by the boundary between the wall material 801 and the internal void 802, follows the shape of the output beam 505. Therefore, in this embodiment, the gas volume ratio around the optical path is... Figure 7 The gas volume within is more limited. Reducing the gas volume surrounding the optical path in this way can decrease the rate at which contaminants in the gas can cross the optical path and thus accumulate.

[0180] However, it is important that the shield 800 and surface 810 do not intersect with or otherwise obstruct the output beam 505, as this would affect the characteristics of the light output from the light source. It may be appropriate to implement a minimum spatial tolerance between the beam diameter and the inner diameter of the inner surface of the shield, wherein the minimum spatial tolerance is within... Figure 8 The gap between the output beam 505 and the surface 810 is indicated in the middle.

[0181] The shield 800 also limits the extent to which turbulent airflow from the rest of the air chamber can enter the optical path. When the optical fiber 501 and the shield 800 form a closed portion, the only path through which the gas in the air chamber can fluidly communicate with the optical path is through the gap 804. When this flow path is radial relative to the optical path, the size of the gap 804 can be configured to limit the flow rate or the turbulent nature of the flow, thereby allowing it to enter the optical path.

[0182] When the shields 700 and 800 of the two embodiments described above have been disclosed separately, it may be desirable to combine features from the two embodiments. For example, it may be desirable to combine a shield having an axial clearance 703, as in shield 700, with a truncated conical inner surface, as in shield 800. The separate disclosure of the two embodiments is not intended to limit the possible combinations of features of the light source used in this disclosure.

[0183] Figure 9 The configuration of another embodiment of the light source is shown. Figure 9The embodiment includes a surface 910 provided by the inner surface of the air chamber (instead of by the shield). The light source also includes an air chamber 502 having a window 503, an optical fiber 501 optically coupled to the window 503 across a gap 509, and surface 910.

[0184] The surface 910 is formed by the contraction or taper of the inner surface of the gas chamber 502 near the end of the optical fiber. The gas chamber 502 therefore has a variable wall thickness in the axial direction. The narrowest point of this contraction or taper forms a radial gap 903 between the surface and the optical fiber. The surface 910 tapers outward from the radial gap 903 to the window 503 to provide space for the optical path 505. The surface 910 thus restricts the local gas volume surrounding the optical path of the output beam 505 and restricts flow from the remainder of the gas chamber to the optical path through the radial gap 903. In the illustrated embodiment, the airflow can only enter the optical path through the radial gap 903. The rate at which contaminants cross the entire optical path should therefore be reduced relative to if the contraction or taper of the surface 910 were not configured in this way.

[0185] The cross-sectional size of the radial gap 903 can also be configured to limit gas exchange to a selected maximum rate.

[0186] The size of the radial clearance 903 can be configured to reduce turbulence entering the optical path region. Achieving laminar flow may not be feasible under certain device size / pressure conditions, but reducing the turbulent nature of the airflow is still preferred.

[0187] Alternatively, in this embodiment, the radial gap 903 may be absent, and the surface 910 may be adjacent to or sealed to the optical fiber 501, optionally surrounding the end of the optical fiber 501. In other words, the inner surface of the air chamber 502 may be adjacent to or sealed to a portion of the optical fiber 501.

[0188] Figure 10 This illustrates the configuration of yet another embodiment of the light source. As... Figure 9 , Figure 10 The embodiment includes a surface 920 provided by the inner surface of the air chamber (instead of by the shield). The light source also includes an air chamber 502 having a window 503, an optical fiber 501 optically coupled to the window 503 across a gap 509, and the surface 920.

[0189] In this embodiment of the light source, the air chamber 502 is shown enclosing only the end of the optical fiber. In other words, the middle portion of the optical fiber 501 is not embedded in the air chamber 502.

[0190] The surface 920 is adjacent to / sealed to the end of the optical fiber 510, thereby forming a seal around the entire outer circumference of the optical fiber 501. The surface 920 tapers outward from the seal to the window 503 to provide space for the optical path 505. The gas chamber 502 therefore has a variable wall thickness in the axial direction to provide the surface 920. The surface 920 limits the local gas volume surrounding the optical path of the output beam 505. As... Figures 7 to 9 In the aforementioned embodiments, reducing the gas volume surrounding the optical path in this way can reduce the rate at which contaminants in the gas can accumulate across the entire optical path.

[0191] Figure 11 The illustration illustrates a configuration according to another embodiment, designed to reduce the flux of corrosive / contaminating substances at the ends of the optical fiber and / or suppress plasma / radical-induced deposition and polymerization (e.g., to suppress GGP growth). The arrangement includes surfaces 405a, 405b defined by the inner walls of a self-aligned, self-centering output element 400. These surfaces 405a, 405b are defined to avoid obstructing and / or absorbing light output from the optical fiber (e.g., defined for NA, optionally with additional margin, such as 30 μm to 300 μm, or 50 μm to 250 μm). Alternatively, or in addition to, this margin, mirror polishing may be provided to one or both of surfaces 405a and 405b.

[0192] The output element 400 can extend sufficiently beyond the end facet of the optical fiber to ensure that the distance between the photoinduced plasma 200 (the center for generating active material) and the output of the optical fiber 102 is maintained sufficiently to prevent significant etching from the optical fiber, thereby suppressing the source of GGP. This distance can be, for example, the inner diameter D of the output element 400 at its output end. protect At least 3 times (e.g., between 3 and 30 times here). In this way, the output element 400 provides sufficient distance between the unrestricted plasma and the output facet of the optical fiber 102, such that no (or very little) plasma-induced reactions and contaminant deposition occur.

[0193] In an embodiment, the output element 400 may include multiple segments (optionally composite); these segments may include:

[0194] • Self-alignment segment 401. The diameter D of the self-alignment segment 401 is... align It can be defined as, for example: (where D) fiber (where the fiber diameter is used); the length of this segment can be, for example...

[0195] • Self-centering segment 402. The diameter D of the self-centering segment 402 is... center It can be defined as, for example: Its length can be, for example:

[0196] • Protection element segment 403, which includes a protection element or shield. The length L of this shield is... protect For example:

[0197]

[0198] One or more of segments 401, 402, and 403 may taper on one or both sides. Although output element 400 is shown as having axial symmetry, asymmetrical or planar symmetric elements (or one or more of its segments 401, 402, and 403) are also possible.

[0199] One or both of segments 401 and 402 are optional, and their functionality can be provided by the fiber optic support element.

[0200] The protective element segment 403 and the end facet of the optical fiber can be arranged such that the end facet and the input cross section of the segment 403 are within 1 mm, or within 0.1 mm to 0.01 mm of each other, and such that the light output from the optical fiber is not blocked by the protective element segment 403.

[0201] In embodiments, the protective device may be composite; for example, having segments 401, 402, 403 aligned by a common rod or screw. To facilitate such alignment, it is proposed to form / drill precision channels with sufficiently small diameters (e.g., less than 10 μm or less than 5 μm) by using laser drilling with, for example, a picosecond laser, by reactive ion design, or by using a focused ion beam.

[0202] The output element 400 can be aligned with and centered on the optical fiber using a support structure referencing the air chamber or another auxiliary support, for example, such that the end facet of the optical fiber is within 1 mm or 0.1 mm of the cross-section of the protective element, and the inner surface angle of the protective element segment 403 is within 0.1 Rad of the NA of the light output from the optical fiber, preferably within 0.01 Rad.

[0203] In alternative embodiments, it is proposed to suppress sputtering of the surface, shielding, or output element material, and / or remove redeposition-induced structures from the material of the device (assuming they should appear at the output of the device rather than at the GGP). This approach may include selecting material surfaces, shielding, or output elements that have not undergone (or have minimal) chemical sputtering in the presence of activated hydrogen. Such materials may include metals, such as Mo, W, stainless steel, or mixtures of other metals, metals, or alloys. Alternatively, or additionally, materials may be selected to have a lower sputtering yield due to rare gas ions (e.g., C, Ti, V). The fact that the surface, shielding, or output element material may be made of or include materials different from those of the optical fiber can also increase fiber lifetime because plasma erodes and / or deposits silicon faster than some other materials.

[0204] Another approach may include selecting a stable (non-oxidizing after sputtering and possible redeposition) material with a melt temperature lower than that of the optical fiber (e.g., glass). This material may include a precious metal, such as gold or silver. This approach may include (e.g., periodically) melting of the material (e.g., a fluffy structure generated during redeposition) by absorbing light (output from the optical fiber itself) or by using an external heater.

[0205] Alternatively, the surface material may include volatile oxides and hydrides, such as C (this part may be made of or coated with amorphous carbon, diamond-like carbon, diamond, or C3N4). In this embodiment, the fluffy structure initialized by the plasma can be oxidized (e.g., periodically), for example by injecting O2 / H2O / H2O2 or other suitable oxidants into the fiber optic environment.

[0206] This method allows for self-cleaning or periodic removal of the formed structure without downtime loss / penalty.

[0207] The materials proposed in these embodiments can be deposited as coatings onto the surface; for example, with a thickness of 1 μm to 100 μm, at least where the surface is in contact with the plasma. Such coatings can be applied to... Figures 7 to 11 Any one of the surfaces described.

[0208] Although disclosed separately Figures 7 to 11 Each embodiment of the light source described herein may be used, but a combination of their features may be desired. For example, it may be desirable to provide a surface using a combination of a shield and the inner surface of the air chamber. The disclosed configuration of the surface to be provided by the shield may alternatively be provided by the inner surface of the air chamber, and vice versa. Moreover, for example, Figure 11 The self-alignment segment and / or self-centering segment can be with Figure 7 or Figure 8 Used together with the embodiments.

[0209] When using separate shielding or protective elements, the fiber end may be adjacent to or inserted into the shielding or protective element.

[0210] In all embodiments, the gas chamber may include an inlet and an outlet, arranged such that an airflow is established when a pressure difference is created between the inlet and outlet of the optical fiber. This airflow removes volatiles, prevents redeposition of concentrated / polymerized substances, reduces pressure at the optical output, and / or suppresses plasma generated by light absorption. Furthermore, this arrangement provides options for introducing pressure (and density) gradients, allowing for additional tuning of the dispersion. Additionally, there is the possibility of tuning the flow versus pressure profile or distribution such that the steady-state pressure in the low-pressure container is significantly reduced, for example, <1 Bar, preferably <0.1 Bar. This means that absorption of the laser pulse and the supercontinuum pulse generated by the gas will be minimized, and plasma excitation at the output end of the optical fiber will be suppressed. For example, two pressurized containers may be present at either end of the optical fiber, and a pressure difference may be established between the two containers (e.g., maintained using external equipment).

[0211] Other embodiments are disclosed in the subsequent list of numbers:

[0212] 1. A light source, the light source comprising:

[0213] An air chamber having optical output;

[0214] An optical fiber, which is hollow and has an axial direction, has its end enclosed in the air chamber and is optically coupled to the optical output via an optical path;

[0215] A surface, said surface being disposed around said end of said optical fiber and extending beyond said end of said optical fiber in said axial direction toward said optical output, in order to limit one or more of the following:

[0216] Gas exchange between the optical path and the rest of the gas chamber;

[0217] Plasma enters or is directed toward the optical fiber; and

[0218] Free radical flux toward etch-sensitive surfaces.

[0219] 2. The light source according to aspect 1, wherein the surface is provided by the inner surface of the gas chamber.

[0220] 3. The light source according to aspect 1, wherein the surface is not provided by the inner surface of the gas chamber, and the surface is provided by a protective element.

[0221] 4. The light source according to aspect 3, wherein the length between the end of the optical fiber and the output end of the protective element is sufficient to prevent or limit plasma from entering the optical fiber.

[0222] 5. The light source according to aspect 4, wherein the length between the end of the optical fiber and the output end of the protective element is at least three times the outer diameter of the optical fiber.

[0223] 6. The light source according to aspect 5, wherein the minimum cross-section of the protective element is in the range of 0.1 to 10 times the outer diameter of the optical fiber.

[0224] 7. The light source according to aspect 5 or 6, wherein the inner surface of the protective element is arranged to not obstruct light output from the optical fiber.

[0225] 8. According to the light source of aspect 7, wherein the inner surface of the protective element has an opening angle in the range of 0.5NA to 5NA of the optical fiber.

[0226] 9. The light source according to any one of aspects 3 to 8, wherein the protective element includes a portion of the output element, and the protective element further includes one or both of a self-alignment section and a self-centering section.

[0227] 10. The light source according to aspect 9, wherein the diameter of the self-aligned segment is larger than the diameter of the optical fiber by a value between 0.1 mm and 0.8 mm, and / or the length of the self-aligned segment is at least 1 mm.

[0228] 11. The light source according to aspect 9 or 10, wherein the diameter of the self-centering segment is larger than the diameter of the optical fiber by a value between 50 μm and 250 μm.

[0229] 12. The light source according to any one of aspects 9 to 11, wherein the output element is a composite output element, wherein one or both of the self-aligning section and the self-centering section are formed separately from the protective element.

[0230] 13. The light source according to any one of aspects 12, wherein one or both of the self-aligning section and the self-centering section, as well as the protective element, are aligned with a common rod and / or screw.

[0231] 14. The light source according to any one of claims 3 to 13, wherein the inner surface of the protective element is arranged at a distance of 10 μm to 1000 μm from the light cone output by the optical fiber, such that at least a portion of the protective element is adjacent to the optical output.

[0232] 15. The light source according to any one of the preceding aspects, wherein the surface extends along the optical fiber for a given length and the surface is offset from the circumference of the optical fiber to form a gap.

[0233] 16. The light source according to any one of the preceding aspects, wherein the gap between the optical fiber and the surface has a minimum cross-sectional area orthogonal to the axial direction, the minimum cross-sectional area being 100 μm. 2 With 3mm 2 between.

[0234] 17. The light source according to any one of aspects 1 to 3, wherein the surface is adjacent to or sealed to the optical fiber.

[0235] 18. The light source according to any one of aspects 3 to 14, wherein the protective element is adjacent to or sealed to the optical output, or the protective element is adjacent to or sealed to the surface of the gas chamber containing the optical output.

[0236] 19. The light source according to any one of the preceding aspects, wherein the optical output includes a window.

[0237] 20. The light source according to any one of the preceding aspects, wherein the surface comprises silicon dioxide, metal, metal alloy, noble metal, metal oxide, nitride, carbide, boride or silicide, silicon, or other semiconductor.

[0238] 21. The light source according to any one of the preceding aspects, wherein the surface comprises a material that limits chemical sputtering in the presence of active hydrogen substances or is not subjected to chemical sputtering.

[0239] 22. The light source according to aspect 21, wherein the material comprises molybdenum, tungsten, or stainless steel.

[0240] 23. The light source according to any of the foregoing aspects, wherein the surface comprises a material having a lower sputtering yield compared to the optical fiber, achieved by rare gas ions.

[0241] 24. The light source according to any one of the preceding aspects, wherein the surface comprises a material that is stable and non-oxidized after any sputtering.

[0242] 25. The light source according to any one of the preceding aspects, wherein the surface comprises a material having a melting temperature lower than that of the optical fiber.

[0243] 26. The light source according to aspect 25, wherein the material includes precious metals.

[0244] 27. The light source according to any one of the foregoing aspects, wherein the surface comprises a material forming both a volatile oxide and a volatile hydride.

[0245] 28. The light source according to aspect 27, wherein the material comprises amorphous carbon, diamond-like carbon, diamond, or C3N4.

[0246] 29. The light source according to any one of aspects 21 to 29, wherein the material is applied to the surface as a coating.

[0247] 30. The light source according to any one of the preceding aspects, wherein the surface comprises a mirror coating.

[0248] 31. The light source according to any one of the foregoing aspects, wherein the gas chamber includes an inlet and an outlet, the inlet and outlet being arranged such that when a pressure difference is established between the inlet and outlet of the optical fiber, an airflow is established to remove volatile substances, prevent redeposition of concentrated / polymerized substances, reduce the pressure at the optical output, and / or suppress plasma flow caused by light absorption.

[0249] 32. The light source according to any one of the preceding aspects, wherein the surface defines a rotationally symmetric shape in the axial direction.

[0250] 33. The light source according to any one of the foregoing aspects, wherein the surface defines a non-constant diameter orthogonal to the axial direction, optionally, the diameter defined by the surface is greater than D. min :

[0251]

[0252] Where w0 is the mode field diameter at the end of the optical fiber, z is the distance from the end of the optical fiber, and z R It is the Rayleigh length.

[0253] 34. The light source according to any one of the preceding aspects, wherein the surface defines a truncated conical shape at least a portion of its length.

[0254] 35. The light source according to any one of the preceding aspects, wherein the gas in the gas chamber comprises at least one gas selected from the group consisting of: helium, neon, argon, krypton, xenon, hydrogen, oxygen, nitrogen, or mixtures thereof.

[0255] 36. The light source according to any one of the preceding aspects, wherein the optical fiber is coupled to an optical source, the optical source comprising a pump laser.

[0256] 37. A measuring device comprising a light source according to any one of the preceding aspects, wherein the light source is configured to generate light for projection onto a substrate.

[0257] 38. The measuring device according to aspect 37, wherein the measuring device is a scattering instrument.

[0258] While specific references may be made herein to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein may have other applications, such as manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc. Those skilled in the art will understand that in the context of these alternative applications, any use of the terms “wafer” or “chip” herein may be considered synonymous with the more general terms “substrate” or “target portion,” respectively. Substrates mentioned herein may be processed before or after exposure in, for example, a track or coating development system (a tool that typically coats a layer of resist onto a substrate and develops the exposed resist), metrology tools, and / or inspection tools. Where applicable, this disclosure may be applied to these and other substrate processing tools. Furthermore, for example, to create multilayer ICs, the substrate may be processed more than once; therefore, the term “substrate” as used herein may also refer to a substrate that already contains one or more processed layers.

[0259] While specific embodiments of the invention have been described above, it should be understood that the invention may be practiced in other ways than those described. For example, the light source disclosed herein may have applications beyond measurement or lithography devices, such as medical and cosmetic diagnostics and imaging, catheter-based interventions (heart, kidney, etc.), skin treatments (e.g., targeted vascular and tattoo removal, among other things), and applications in materials imaging and materials processing.

[0260] The above description is intended to be illustrative and not restrictive. Therefore, those skilled in the art will understand that modifications can be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A light source, the light source comprising: An air chamber having optical output; An optical fiber, which is hollow and has an axial direction, has its end enclosed in the air chamber and is optically coupled to the optical output via an optical path; A shielding element, the shielding element being disposed around the end of the optical fiber, providing a surface; Wherein, the surface of the shield extends in the axial direction toward the optical output beyond the end of the optical fiber, for limiting one or more of the following: Gas exchange between the optical path and the rest of the gas chamber; Plasma enters the optical fiber or into the optical fiber; To reduce the flux of corrosive or contaminating substances at the ends of the optical fiber; and Suppress plasma / free radical-induced deposition and polymerization.

2. The light source according to claim 1, wherein the length between the end of the optical fiber and the output end of the protective element is sufficient to prevent or limit plasma from entering the optical fiber, and the protective element is the shield.

3. The light source according to claim 2, wherein the length between the end of the optical fiber and the output end of the protective element is at least three times the outer diameter of the optical fiber.

4. The light source according to claim 3, wherein the minimum cross-section of the protective element is in the range of 0.1 to 10 times the outer diameter of the optical fiber.

5. The light source according to claim 3 or 4, wherein the inner surface of the protective element is arranged to not obstruct light output from the optical fiber.

6. The light source according to claim 5, wherein the inner surface of the protective element has an opening angle in the range of 0.5NA to 5NA of the optical fiber.

7. The light source according to claim 2, wherein the protective element includes a portion of the output element, and the protective element further includes one or both of a self-alignment section and a self-centering section.

8. The light source according to claim 7, wherein the diameter of the self-aligned segment is larger than the diameter of the optical fiber by a value between 0.1 mm and 0.8 mm, and / or the length of the self-aligned segment is at least 1 mm.

9. The light source according to claim 7 or 8, wherein the diameter of the self-centering segment is larger than the diameter of the optical fiber by a value between 50 μm and 250 μm.

10. The light source according to any one of claims 8 to 9, wherein the output element is a composite output element, wherein one or both of the self-alignment section and the self-centering section are formed separately from the protective element.

11. The light source of claim 10, wherein one or both of the self-aligning section and the self-centering section, as well as the protective element, are aligned with a common rod and / or screw.

12. The light source of claim 2, wherein the inner surface of the protective element is arranged at a distance of 10 μm to 1000 μm from the light cone output from the optical fiber, such that at least a portion of the protective element is adjacent to the optical output.

13. The light source according to any one of the preceding claims, wherein the surface extends along the optical fiber for a given length and the surface is offset from the circumference of the optical fiber to form a gap.

14. The light source according to any one of the preceding claims, wherein the gap between the optical fiber and the surface has a minimum cross-sectional area orthogonal to the axial direction, the minimum cross-sectional area being 100 μm. 2 With 3 mm 2 between.

15. The light source of claim 1, wherein the surface is adjacent to or sealed to the optical fiber.

16. The light source of claim 2, wherein the protective element is adjacent to or sealed to the optical output, or the protective element is adjacent to or sealed to the surface of the gas chamber containing the optical output.

17. The light source according to any one of the preceding claims, wherein the optical output includes a window.

18. The light source according to any one of the preceding claims, wherein the surface comprises silicon dioxide, metal, metal alloy, metal oxide, nitride, carbide, boride or silicide, silicon, or other semiconductor.

19. The light source according to any one of the preceding claims, wherein the surface comprises a material that limits chemical sputtering in the presence of active hydrogen substances or is not subjected to chemical sputtering.

20. The light source of claim 19, wherein the material comprises molybdenum, tungsten, or stainless steel.

21. The light source according to any of the preceding claims, wherein the surface comprises a material having a lower sputtering yield compared to the optical fiber, achieved by rare gas ions.

22. The light source according to any one of the preceding claims, wherein the surface comprises a material that is stable and non-oxidized after any sputtering.

23. The light source according to any one of the preceding claims, wherein the surface comprises a material having a melting temperature lower than that of the optical fiber.

24. The light source according to claim 23, wherein the material comprises a noble metal.

25. The light source according to any one of the preceding claims, wherein the surface comprises a material forming both a volatile oxide and a volatile hydride.

26. The light source according to claim 25, wherein the material comprises amorphous carbon, diamond-like carbon, diamond, or C3N4.

27. The light source according to any one of claims 19 to 26, wherein the material is applied to the surface as a coating.

28. The light source according to any one of the preceding claims, wherein the surface comprises a mirror coating.

29. The light source according to any one of the preceding claims, wherein the gas chamber includes an inlet and an outlet, the inlet and outlet being arranged such that when a pressure difference is established between the inlet and outlet of the optical fiber, an airflow is established to remove volatile substances, prevent redeposition of concentrated / polymerized substances, reduce the pressure at the optical output, and / or suppress plasma flow caused by light absorption.

30. The light source according to any one of the preceding claims, wherein the surface defines a rotationally symmetric shape in the axial direction.

31. The light source according to any one of the preceding claims, wherein the surface defines a non-constant diameter orthogonal to the axial direction, and the diameter defined by the surface is greater than... : in It is the mode field diameter at the end of the optical fiber, and z is the distance from the end of the optical fiber. It is the Rayleigh length.

32. The light source according to any one of the preceding claims, wherein the surface defines a truncated conical shape at least a portion of its length.

33. The light source according to any one of the preceding claims, wherein the gas in the gas chamber comprises at least one gas selected from the group consisting of: helium, neon, argon, krypton, xenon, hydrogen, oxygen, nitrogen, or mixtures thereof.

34. The light source according to any one of the preceding claims, wherein the optical fiber is coupled to an optical source, the optical source comprising a pump laser.

35. A measuring apparatus comprising a light source according to any one of the preceding claims, wherein the light source is configured to generate light for projection onto a substrate.

36. The measuring device according to claim 35, wherein the measuring device is a scattering instrument.

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