Supercontinuum radiation source and related metrology apparatus

Abstract

There is described a supercontinuum radiation source comprising: a modulator operable to modulate pump laser radiation comprising a string of radiation pulses to provide modulated pump laser radiation, the modulation being such that a selective burst of pulses is provided; and a hollow-core photonic crystal fibre operable to receive the modulated pump laser radiation and to excite a working medium contained within the hollow-core photonic crystal fibre to thereby generate supercontinuum radiation.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to EP application 20175307.6, filed on May 19, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a supercontinuum radiation source based on a hollow core photonic crystal fiber, and more particularly, to such a supercontinuum radiation source in relation to measurement applications in integrated circuit manufacturing. Background Technology

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

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

[0006] Low-k1 lithography can be used to process features smaller than the classical resolution limit of lithography equipment. In such a process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of 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 a pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to reproduce patterns on the substrate that are similar in shape and size to those planned by the circuit designer for specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection equipment and / or design layout. These include, for example, but not limited to, optimization of NA, customized illumination schemes, the use of phase-shifting patterning apparatus, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also called "optical process correction") in the design layout), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, a tight control loop used to control the stability of the lithography equipment can be used to improve pattern reproduction at low k1.

[0007] Metrological tools are used in many aspects of the IC manufacturing process, such as alignment tools for properly positioning substrates before exposure, leveling tools for measuring substrate surface topography, and focus-controlled and scattering-based measurement tools for inspecting / measuring exposed and / or etched products in process control. In each case, a radiation source is required. Broadband or white light radiation sources are increasingly used in these metrological applications for various reasons, including measurement robustness and accuracy. There is a desire to improve existing devices for generating broadband radiation. Summary of the Invention

[0008] In a first aspect of the invention, a supercontinuum radiation source is provided, comprising: a modem operable to modulate pump laser radiation comprising a train of radiating pulses to provide modulated pump laser radiation, the modulation such that bursts of the pulses are selectively provided; and a hollow-core photonic crystal fiber operable to receive the modulated pump laser radiation and excite an operating medium contained within the hollow-core photonic crystal fiber to generate supercontinuum radiation.

[0009] In a second aspect of the invention, a measurement apparatus is provided, comprising: a substrate support for supporting a substrate; a supercontinuum radiation source according to the first aspect; an optical system operable to direct supercontinuum radiation from the supercontinuum radiation source onto the substrate; and a processor operable to generate control signals for a modem. Attached Figure Description

[0010] Embodiments of the invention will now be described by way of example only, with reference to the accompanying schematic diagrams, in which:

[0011] Figure 1 A schematic diagram of a photolithography apparatus is depicted;

[0012] Figure 2 A schematic diagram of the photolithography unit is depicted;

[0013] Figure 3 A schematic representation of overall photolithography is depicted, illustrating the collaboration between three key technologies used to optimize semiconductor manufacturing;

[0014] Figure 4 A schematic diagram of a scattering measurement apparatus, which may include a radiation source according to embodiments of the present invention, is depicted.

[0015] Figure 5 A schematic schematic diagram of a horizontal sensor device that may include a radiation source according to embodiments of the present invention is depicted.

[0016] Figure 6A schematic schematic diagram of an alignment sensor device that may include a radiation source according to embodiments of the present invention is depicted.

[0017] Figure 7A It is a schematic cross-sectional view of the hollow core optical fiber that can form part of the radiation source according to the embodiment in the transverse plane (i.e., perpendicular to the axis of the optical fiber).

[0018] Figure 7B A schematic representation of a radiation source for providing broadband output radiation according to an embodiment is depicted; and

[0019] Figure 7C (a) and (b) schematically depict cross-sections of hollow core photonic crystal fiber (HC-PCF) design examples for supercontinuum generation, each HC-PCF being a portion of a radiation source according to an embodiment;

[0020] Figure 8 (a) a prior art measurement device and irradiation source arrangement, and (b) a graph showing the correspondence between pump radiation pulses and time;

[0021] Figure 9 The diagram shows (a) the arrangement of the measurement device and the irradiation source according to an embodiment of the present invention, (b) a correspondence diagram of the pump radiation pulse relative to time, and (c) a correspondence diagram of the trigger signal for controlling the modem; and

[0022] Figure 10 This is a block diagram of a computer system that can assist in implementing the methods and processes according to embodiments of the present invention. Detailed Implementation

[0023] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 365, 248, 193, 157, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., wavelengths in the range of about 5–100 nm).

[0024] As used herein, the terms “mask,” “mask,” or “patterning apparatus” can be broadly interpreted to refer to a general-purpose patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam corresponding to a pattern to be produced in a target portion of a substrate. The term “optical valve” may also be used in this context. Examples of such patterning apparatuses, in addition to classic masks (transmission or reflection masks, binary masks, phase-shifting masks, hybrid masks, etc.), include programmable mirror arrays and programmable LCD arrays.

[0025] Figure 1A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also called an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus MA according to 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 positioner 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 radiation beam B by the patterning apparatus MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0026] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example via the beam transmission system BD. The irradiation system IL may include various types of optical components for guiding, shaping, and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the pattern forming apparatus MA.

[0027] As used herein, the term "projection system" PS should be interpreted broadly to encompass a wide range of projection systems, including refractive, reflective, catadioptric, distorting, magnetic, electromagnetic, and / or electrostatic systems, or any combination thereof, applicable to the exposure radiation and / or other factors (such as the use of immersion liquids or vacuum). Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0028] A lithography apparatus LA can be of the type in which at least a portion of the substrate can be covered by a liquid (e.g., water) having a relatively high refractive index to fill the space between the projection system PS and the substrate W; this is also known as immersion lithography. More information on immersion technology is given in US6952253 (which, by reference and incorporation herein),

[0029] The lithography equipment LA can also be of the type having two (also known as "dual-stage") or more substrate supports WT. In such a "multi-stage" machine, the substrate supports WT can be used in parallel, and / or while subsequent exposure preparation steps for substrate W are performed on substrate W located on one of the substrate supports WT, another substrate W on another substrate support WT is used to expose a pattern on the other substrate W.

[0030] In addition to the substrate support WT, the lithography apparatus LA may include a measurement stage. The measurement stage is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure the properties of the projection system PS or the properties of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning devices may be arranged to clean part of the lithography apparatus, such as part of the projection system PS or part of a system providing immersion liquid. The measurement stage may move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0031] In operation, a radiation beam B is incident on a pattern forming apparatus MA (e.g., a mask) held on a mask support MT and patterned by a pattern (design layout) on the pattern forming apparatus MA. After traversing the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be moved precisely, for example, to position different target portions C at focused and aligned positions along the path of the radiation beam B. Similarly, a first positioner PM and possibly another position sensor (which is not in...) Figure 1 (As explicitly shown) can be used to accurately position the pattern forming apparatus MA relative to the path of the radiation beam B. The pattern forming apparatus MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 occupy dedicated target portions, they can be located in the space between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, they are referred to as scribing alignment marks.

[0032] like Figure 2 As shown, a lithography apparatus LA can form part of a lithography unit LC, sometimes also called a lithography unit or (lithography) cluster. The lithography unit LC typically also includes equipment for performing pre-exposure and post-exposure processes on a substrate W. These devices typically include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chiller CH, and a baking plate BK, for example, to adjust the temperature of the substrate W, or to adjust the solvent in the resist layer. A substrate transport device (or robot) RO picks up the substrate W from input / output ports I / O1, I / O2, moves the substrate W between different processing devices, and transports the substrate W to the loading stage LB of the lithography apparatus LA. The devices in the lithography unit (often collectively referred to as tracks) are typically controlled by a track control unit TCU, which itself can be controlled by a management control system SCS, which can also control the lithography apparatus LA, for example, via the lithography control unit LACU.

[0033] To ensure accurate and consistent exposure of the substrate W exposed by the lithography apparatus LA, it is desirable 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, the lithography unit LC may include inspection tools (not shown). If errors or omissions are detected, especially if the inspection is performed before exposing or processing other substrates W in the same batch or batch, adjustments can be made, for example, to the exposure of subsequent substrates and / or other processing steps to be performed on the substrate W.

[0034] Inspection equipment (also called measurement equipment) is used to determine the properties of a substrate W, particularly how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary between layers. Alternatively, the inspection equipment may be configured to identify defects on the substrate W and may be, for example, part of a photolithography unit LC, or integrated into a photolithography apparatus LA, or even a stand-alone device. The inspection equipment may measure the properties of latent images (images in a resist layer after exposure), or semi-latent images (images in a resist layer after a post-exposure baking (PEB) step), or developed resist images (where the exposed or unexposed portions of the resist have been removed), or even etched images (after a pattern transfer step such as etching).

[0035] Typically, the patterning process in photolithography (LA) equipment is one of the most critical steps in the process of achieving high-precision sizing and placement of structures on a substrate (W). To ensure this high precision, three systems can be combined into a so-called "integrated" control environment, such as... Figure 3 The diagram illustrates this schematically. One of these systems is the lithography apparatus LA, which is connected to the metrology tool MT (second system) and the computer system CL (third system). The key to this “holistic” environment is optimizing the collaboration between these three systems to enhance the overall process window and providing 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 accuracy) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device), typically allowing process parameters in the lithography or patterning process to vary within these ranges.

[0036] The computer system CL can use a portion of the design layout to be patterned to predict which resolution enhancement technique to use and perform computational lithography simulations and calculations to determine which mask layouts and lithography equipment settings enable the largest overall process window (within) the patterning process. Figure 3(Represented by the double arrows in the first scale SC1). Typically, resolution enhancement techniques are arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect where the lithography apparatus LA is currently operating within the process window (e.g., by using input from the metrology tool MT) to predict whether defects might exist due to, for example, suboptimal processes (in...). Figure 3 (This is indicated by the arrow pointing to "0" in the second scale SC2).

[0037] The measurement tool MT can provide input to the computer system CL for accurate simulation and prediction, and can provide feedback to the lithography equipment LA to identify possible drifts in, for example, the calibration state of the lithography equipment LA. Figure 3 (This is represented by multiple arrows in the third scale SC3).

[0038] During photolithography, it is often desirable to measure the resulting structure, for example, for process control and verification. The tools used to perform these measurements are generally called metrology tools (MTs). Different types of metrology tools (MTs) for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools (MTs). A scatterometer is a versatile instrument that allows the measurement of parameters of the photolithography process by placing a sensor in the pupil of the objective lens of the scatterometer or in a plane conjugate to that pupil; such measurements are generally referred to as pupil-based measurements. Alternatively, when measurements are performed by placing the sensor in an image plane or a plane conjugate to the image plane, such measurements are generally referred to as image- or field-based measurements. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A, the entire contents of which are incorporated herein by reference. The aforementioned scatterer can use light from soft X-rays and visible to near-IR wavelengths to measure gratings.

[0039] In the first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, scatterer reconstruction methods can be applied to the measured signal to reconstruct or calculate the properties of the grating. For example, this reconstruction can be obtained by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0040] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In this spectroscopic scatterer MT, radiation emitted by a radiation source is directed to the target, and radiation reflected or scattered from the target is directed to a spectroscopic detector that measures the spectrum of the specularly reflected radiation (i.e., a measurement of intensity as a function of wavelength). Based on this data, the structure or profile of the target that generated the detected spectrum can be reconstructed, for example, through rigorous coupled-wave analysis and nonlinear regression or by comparison with a simulated spectral library.

[0041] In the third embodiment, the scatterer MT is an elliptically polarized scatterer. An elliptically polarized scatterer allows the determination of parameters of the photolithography process by measuring the scattered radiation for each polarization state. Such a measurement device emits polarized light (such as linear, circular, or elliptical) by, for example, using a suitable polarization filter in the illumination portion of the measurement device. A source suitable for the measurement device can also provide polarized radiation. Various embodiments of existing elliptically polarized scatterers are described in U.S. Patent Applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110, and 13 / 891,410, the entire contents of which are incorporated herein by reference.

[0042] Figure 4 A measurement device, such as a scatterer, is described. This device includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate W. The reflected or scattered radiation is transmitted to a spectrometer 4, which measures the spectrum 6 of the specularly reflected radiation (i.e., a measurement of intensity as a function of wavelength). Based on this data, for example, by means of... Figure 3 As shown at the bottom, through rigorous coupled-wave analysis and nonlinear regression, or by comparison with a simulated spectral library, the processing unit (PU) can reconstruct the structure or profile of the detected spectrum. Typically, for reconstruction, the general form of the structure is known, and some parameters are set based on knowledge of the process forming the structure, thus requiring only a few parameters to be determined from the scattering measurement data. This scatterometer can be configured as a normal-incident or oblique-incident scatterometer.

[0043] The overall measurement quality of a lithographic parameter of a target is determined at least in part by the measurement scheme used to measure that lithographic parameter. The term "substrate measurement scheme" can include one or more parameters of the measurement itself, one or more parameters of one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement scheme is a diffraction-based optical measurement, the one or more parameters measured can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, and so on. For example, one of the criteria for selecting a measurement scheme could be the sensitivity of a measurement parameter to processing variations. Further examples are described in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US2016 / 0370717A1, which are incorporated herein by reference in their entirety.

[0044] Another measurement tool used in IC manufacturing is a topography measurement system, a level sensor, or a height sensor. This tool can be integrated into a photolithography apparatus 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 from these measurements, which indicate the substrate's height as a function of its position on the substrate. This height map can then be used to correct the substrate's position during pattern transfer onto the substrate, so that a spatial image of the patterning apparatus is provided at a suitable focused position on the substrate. It will be understood that "height" as used herein refers to the dimension that protrudes significantly from the plane of the substrate (also called the Z-axis). Typically, the level sensor or height sensor performs measurements at a fixed position (relative to its own optical system), and the relative movement between the substrate and the optical system of the level sensor or height sensor allows for height measurements to be taken at a location across the substrate.

[0045] Figure 5 An example of a level sensor or height sensor LS known in the art is illustrated schematically, showing only the principle of operation. 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 applied by a projection grating PGR of the projection unit LSP. The radiation source LSO can be, for example, a narrowband or broadband light source (such as a supercontinuum light source), polarized or unpolarized, pulsed or continuous (such as a polarized or unpolarized laser beam). The radiation source LSO can include multiple radiation sources with different colors or multiple wavelength ranges, such as multiple LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation, but can additionally or alternatively cover UV and / or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

[0046] A projection grating (PGR) is a periodic grating comprising a periodic structure that generates a radiation beam BE1 with periodically varying intensity. The radiation beam BE1 with periodically varying intensity is guided toward a measurement site MLO on a substrate W at an angle ANG between 0 and 90 degrees (typically between 70 and 80 degrees) relative to an axis perpendicular to the surface of the incident substrate (Z-axis). At the measurement site MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and guided toward the detection unit LSD.

[0047] To determine the height level at the measurement location MLO, the level sensor also includes a detection system comprising a detection grating DGR, a detector DET, and a processing unit (not shown) for processing the output signal of the detector DET. The detection grating DGR can be the same as a projection grating PGR. The detector DET generates a detector output signal indicating the received light; for example, a photodetector generates a detector output signal indicating the intensity of the received light, or a camera generates a detector output signal indicating the spatial distribution of the received intensity. The detector DET can include any combination of one or more detector types.

[0048] Using triangulation techniques, the height level at the measurement location MLO can be determined. The detected height level is typically related to the signal strength, as measured by the detector DET, which has a periodicity that is particularly dependent on the design of the projection grating PGR and the (tilted) incident angle ANG.

[0049] The projection unit LSP and / or the detection unit LSD may include other optical elements, such as lenses and / or mirrors, along the path of the patterned radiation beam between the projection grating PGR and the detection grating DGR (not shown).

[0050] In this embodiment, the detection grating DGR can be omitted, and the detector DET can be placed at the location where the detection grating DGR is located. This configuration provides more direct detection of the image of the projection grating PGR.

[0051] To effectively cover the surface of substrate W, the horizontal sensor LS can be configured to project an array of measurement beams BE1 onto the surface of substrate W, thereby generating an array of spots or measurement regions MLO that cover a large measurement area.

[0052] For example, various height sensors of general types are disclosed in US7265364 and US7646471, both of which are incorporated herein by reference. A height sensor using UV radiation instead of visible or infrared radiation is disclosed in US2010233600A1, also incorporated herein by reference. A compact height sensor is described in WO2016102127A1, which uses a multi-element detector to detect and identify the position of a grating image without requiring the detection of the grating itself.

[0053] Another type of measurement tool used in IC manufacturing is the alignment sensor. Therefore, a key aspect of the performance of a lithography apparatus is its ability to correctly and accurately align the applied pattern relative to features laid in previous layers (by the same or different lithography apparatuses). For this purpose, the substrate is provided with one or more sets of marks or targets. Each mark is a structure whose position can be measured later using a position sensor (usually an optical position sensor). The position sensor can be called an "alignment sensor," and the mark can be called an "alignment mark."

[0054] 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.

[0055] Figure 6 This is a schematic block diagram of a known alignment sensor AS (such as that described, for example, in US6961116, which is incorporated 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 diameter of the illumination spot SP used to illuminate the marker AM may be slightly smaller than the width of the marker itself.

[0056] The radiation diffracted by the alignment mark AM is collimated (in this example via the objective lens OL) into an information-carrying beam IB. The term "diffraction" is intended to include zero-order diffraction from the mark (which may be referred to as reflection). A self-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. If desired, the photodetector may be a single element or may include multiple pixels. The photodetector may include a sensor array.

[0057] The steering optics in this example include a speckled mirror SM, which can also be used to block the zero-order radiation reflected from the marker, so that the information-carrying bundle IB includes only the higher-order diffracted radiation from the marker AM (this is not necessary for the measurement, but can improve the signal-to-noise ratio).

[0058] The intensity signal SI is supplied to the processing unit PU. By combining the optical processing performed in the block SRI with the computational processing performed in the unit PU, the values ​​of the X and Y positions on the substrate relative to the reference frame are output.

[0059] The single measurement of the type shown fixes the position of the mark within a specific range corresponding to a spacing of the mark. Coarse measurement techniques are combined with the single measurement to identify which period of the sine wave contains the marked position. The same process can be repeated at coarser and / or finer levels at different wavelengths to increase the accuracy and / or robustness of mark detection regardless of the material the mark is made of or whether the material is placed above and / or below the mark. Wavelengths can be optically multiplexed and demultiplexed to process wavelengths simultaneously, and / or multiplexed via time-division or frequency-division multiplexing.

[0060] In this example, the alignment sensor and the spot SP remain stationary while the substrate W moves simultaneously. Thus, the alignment sensor can be mounted stably and accurately relative to a reference frame, while simultaneously scanning the mark AM effectively in the direction opposite to the direction of movement of the substrate W. This movement of the substrate W is controlled by mounting the substrate W to a substrate support and a substrate positioning system that controls the movement of the substrate support. A substrate support position sensor (e.g., an interferometer) measures the position of the substrate support (not shown). In an embodiment, one or more (alignment) marks are provided on the substrate support. Measuring the position of the marks provided on the substrate support allows for calibration of the substrate support position, as determined by the position sensor (e.g., relative to a frame to which the alignment system is attached). Measuring the position of the alignment marks provided on the substrate allows for determination of the substrate position relative to the substrate support.

[0061] For optical semiconductor measurement and inspection applications using any of the aforementioned measurement tools, a bright light source that outputs coherent radiation while simultaneously covering a wide wavelength range (e.g., from UV to IR) is typically desired. Such a broadband light source can improve the flexibility and robustness of the application by allowing wafers with different material properties to be optically inspected in the same setup / system without any hardware modifications (e.g., changing the light source to have a specific wavelength). Allowing wavelength optimization for specific applications also means that measurement accuracy can be improved.

[0062] Gas lasers that emit multiple wavelengths simultaneously based on gas discharge effects can be used for these applications. However, inherent problems associated with gas lasers, such as high intensity instability and low spatial incoherence, may render them unsuitable. Alternatively, the outputs from multiple lasers with different wavelengths (e.g., solid-state lasers) can be spatially combined into the optical path of a measurement or inspection system to provide a multi-wavelength source. The increasing complexity and high implementation cost with the number of wavelengths required hinder the widespread adoption of this solution. In contrast, fiber-based broadband or white-light lasers (also known as supercontinuum lasers) are capable of emitting radiation with high spatial coherence and wide spectral coverage (e.g., from UV to IR), making them a very attractive and practical option.

[0063] Hollow-core photonic crystal fiber (HC-PCF) is a special type of optical fiber consisting of a central hollow core region and an inner cladding structure surrounding the hollow core, both extending along the entire fiber axis. The inner cladding waveguide structure enables the light guiding mechanism, which can include, for example, thin-walled glass elements. Therefore, radiation is primarily confined within the hollow core and propagates along the fiber in a transverse core mode.

[0064] Measurement tools (MTs) such as scatterometers, topography measurement systems, or position measurement systems described above can perform measurements using radiation originating from a radiation source. The nature of the radiation used by the measurement tool can affect the type and quality of the measurements that may be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure the substrate, for example, broadband radiation can be used. Multiple different frequencies can propagate, illuminate, and scatter the measurement target with minimal or no interference from other frequencies. Therefore, for example, more measurement data can be obtained simultaneously using different frequencies. Different radiation frequencies can also enable the querying and discovery of 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. Broadband radiation sources can be supercontinuum sources.

[0065] Generating high-quality broadband radiation (e.g., supercontinuum radiation) can be challenging. One approach to generating broadband radiation is, for example, to broaden high-power narrowband or single-frequency input radiation using nonlinear, higher-order effects. Alternatively, the input radiation (which can be generated using a laser) can be referred to as pump laser radiation. Alternatively, the input radiation can be called seed radiation. To obtain high-power radiation for the broadening effect, the radiation can be confined to a small region, thus achieving locally enhanced high-intensity radiation. In these regions, the radiation can interact with broadening structures and / or materials forming a nonlinear medium, thereby generating broadband output radiation. In high-intensity radiation regions, different materials and / or structures can be used to achieve and / or improve radiation broadening by setting a suitable nonlinear medium.

[0066] In some implementations, broadband output radiation is generated in a photonic crystal fiber (PCF). In several embodiments, such a PCF has microstructures around its fiber core, which helps to confine radiation traversing the fiber within the fiber core. The fiber core can be made of a solid material with nonlinear properties, and broadband radiation can be generated when high-intensity pump laser radiation propagates through the fiber core. While generating broadband radiation in a solid-core PCF is feasible, using a solid material can have some drawbacks. For example, if UV radiation is generated in a solid core, this radiation may not appear in the fiber's output spectrum because it would be absorbed by most solid materials.

[0067] In some implementations, see the following references. Figure 7BFurther discussion reveals that 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 can be a hollow-core fiber and may include internal structures for effectively guiding and confining radiation within the fiber. The 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 fiber may be filled with a working medium serving as a broadening medium for broadening the input radiation. This arrangement of fiber and working medium can be used to generate a supercontinuum radiation source. The radiation input to the fiber can be electromagnetic radiation, such as radiation from one or more of the infrared, visible, UV, and extreme UV spectra. The output radiation may consist of or include broadband radiation, which may be referred to herein as white light. The output radiation can...

[0068] Some embodiments relate to novel designs of such broadband radiation sources comprising optical fibers. The optical fiber is a hollow-core photonic crystal fiber (HC-PCF). Specifically, the optical fiber can be a type of hollow-core photonic crystal fiber including an anti-resonant structure for confining radiation. Such fibers including anti-resonant structures are known in the art as anti-resonant fibers, tubular fibers, single-loop fibers, negative curvature fibers, or suppression-coupled fibers. Various different designs of such fibers are known in the art. Alternatively, the optical fiber can be a photonic bandgap fiber (HC PBF, such as Kagome fiber).

[0069] Various types of HC PCFs can be designed based on different physical guidance mechanisms. Two such HC-PCFs include: Hollow Core Photonic Bandgap Fiber (HC-PBF) and Hollow Core Anti-Resonant Reflective Fiber (HC-ARF). Details regarding the design and manufacture of HC PCFs can be found in US Patent US2004 / 015085A1 (for HC PBF) and International PCT Patent Application WO2017 / 032454A1 (for Hollow Core Anti-Resonant Reflective Fiber), which are incorporated herein by reference. Figure 7C (a) shows a Kagome optical fiber including a Kagome lattice structure.

[0070] Now for reference Figure 7A Describe an example of the optical fiber used in a radiation source. Figure 7A This is a schematic cross-sectional view of the optical fiber (OF) in the transverse plane. WO2017 / 032454A1 discloses a similar design. Figure 7A Other embodiments similar to the actual examples of optical fibers.

[0071] An optical fiber (OF) includes an elongated body that is longer in one dimension than the other two. This longer dimension may be referred to as the axial direction and defines the axis of the optical fiber. The other two dimensions define planes that may be referred to as transverse planes. Figure 7A A cross-sectional view of the optical fiber OF in a transverse plane (i.e., perpendicular to the axis) is shown, which is labeled the xy plane. The transverse section of the optical fiber OF can be substantially consistent along the fiber axis.

[0072] It will be understood that optical fibers (OFs) possess a degree of flexibility, therefore the direction of the axis will typically vary along the length of the fiber. Terms such as optical axis and cross-section will be understood to refer to local optical axis, local cross-section, etc. Furthermore, when components are described as cylindrical or tubular, these terms will be interpreted to encompass this shape, which may deform when the optical fiber (OF) is bent.

[0073] Optical fiber OF can be of any length, and it will be understood that the length of optical fiber OF can depend on the application. The length of optical fiber OF can be between 1 cm and 10 m, for example, the length of optical fiber OF can be between 10 cm and 100 cm.

[0074] An 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. An optical fiber (OF) can be considered to include a body (including the cladding portion and the support portion SP) having a hollow core (COR). The cladding portion includes multiple anti-resonant elements for guiding radiation through the hollow core (COR). Specifically, the multiple anti-resonant elements are arranged to primarily confine radiation propagating through the optical fiber (OF) within the hollow core (HC) and to guide radiation along the optical fiber (OF). The hollow core (HC) of the optical fiber (OF) can be substantially disposed in the central region of the optical fiber (OF) such that the axis of the optical fiber (OF) can define the axis of the hollow core (HC).

[0075] The cladding portion includes multiple anti-resonant elements for guiding radiation propagation through the optical fiber (OF). Specifically, in this embodiment, the cladding portion includes a single ring having six tubular capillary CAPs. Each tubular capillary CAP serves as an anti-resonant element.

[0076] A capillary CAP can also be referred to as a tube. The cross-section of a capillary CAP can be circular or may have other shapes. Each capillary CAP includes a generally cylindrical wall portion WP that at least partially defines the hollow core HC of the optical fiber OF and separates the hollow core HC from the capillary cavity CC. It will be understood that the wall portion WP can serve as an anti-reflection Fabry-Perot resonator for radiation propagating through the hollow core HC (and which may be incident on the wall portion WP at a grazing angle of incidence). The thickness of the wall portion WP can be adapted to ensure that reflections generally returning to the hollow core HC are enhanced, while generally suppressing transmission into the capillary cavity CC. In some embodiments, the thickness of the capillary wall portion WP can be between 0.01 μm and 10.0 μm.

[0077] It will be understood that, as used herein, the term cladding portion refers to the portion of an optical fiber OF used to guide radiation propagation through the optical fiber OF (i.e., the capillary CAP that confines the radiation within the hollow core COR). The radiation can be confined to propagate along the fiber axis in a lateral mode.

[0078] The support portion is typically tubular, and the support cladding portion has six capillary CAPs. If it is an inner support portion SP, the six capillary CAPs are evenly distributed around the inner surface. The six capillary CAPs can be described as being arranged in a roughly hexagonal shape.

[0079] The capillary CAPs are arranged such that each capillary does not contact any other capillary CAP. Each capillary CAP contacts the inner support portion SP and is spaced apart from adjacent capillary CAPs in the annular structure. This arrangement can be advantageous because it can increase the transmission bandwidth of the optical fiber OF (e.g., relative to an arrangement where capillaries are in contact with each other). Alternatively, in some embodiments, each capillary CAP may contact adjacent capillary CAPs in the annular structure.

[0080] The cladding portion has six capillary capillaries (CAPs) arranged in a ring structure around the hollow core (COR). The inner surface of the ring structure of the capillary capillaries at least partially defines the hollow core (HC) of the optical fiber (OF). The diameter d of the hollow core (HC) (which can be defined as the minimum dimension between relative capillaries, indicated by arrow d) can be between 10 μm and 1000 μm. The diameter d of the hollow core (HC) can affect the mode field diameter, impulse loss, dispersion, mode number, and nonlinear properties of the hollow core optical fiber (OF).

[0081] In this embodiment, the cladding portion comprises a single-ring arrangement of capillary CAPs (which serve as anti-resonant elements). Therefore, no line in any radial direction from the center of the hollow core HC to the outside of the optical fiber OF will pass through more than one capillary CAP.

[0082] It will be understood that other embodiments may have different arrangements of anti-resonant elements. These may include multi-ring arrangements of anti-resonant elements and arrangements with nested anti-resonant elements. Furthermore, although... Figure 7A The illustrated embodiment includes a ring of six capillaries, but in other embodiments, one or more rings may be provided in the cladding portion, the one or more rings including any number of anti-resonant elements (e.g., 4, 5, 6, 7, 8, 9, 10, 11 or 12 capillaries).

[0083] Figure 7C (b) illustrates a modified embodiment of the HC-PCF described above, which has a single-ring tubular capillary. Figure 7C In example (b), there is a tubular capillary 21 with two coaxial rings. To maintain the inner and outer rings of the tubular capillary 21, a support tube ST may be included in the HC-PCF. The support tube may be made of silica.

[0084] Figure 7A as well as Figure 7C The tubular capillaries in examples (a) and (b) can have a circular cross-sectional shape. Tubular capillaries can also be other shapes, such as elliptical or polygonal cross-sections. Additionally, Figure 7A as well as Figure 7C The solid material of the tubular capillary in the examples of (a) and (b) may include plastic materials such as PMA, glass, silica, or soft glass.

[0085] Figure 7B A radiation source RDS for providing broadband output radiation is described. The radiation source RDS includes a pulse-pumped radiation source PRS, or any other type of source capable of generating short pulses with desired length and energy levels; an optical fiber OF with a hollow core COR (e.g., Figure 7A (as shown in the image); and the working medium WM (e.g., gas) disposed within the hollow core COR. Although in Figure 7B In this context, the radiation source RDS includes Figure 7A The optical fiber OF shown is used, but in alternative embodiments, other types of hollow core optical fibers can be used.

[0086] A pulse-pumped radiation source (PRS) is configured to provide an input radiation IRD. The hollow core (HC) of the optical fiber (OF) is arranged to receive the input radiation IRD from the PRS and widen the input radiation IRD to provide an output radiation ORD. The operating medium (WM) is capable of widening the frequency range of the received input radiation IRD to provide a broadband output radiation ORD.

[0087] The radiation source RDS also includes a storage unit RSV. An optical fiber OF is disposed within the storage unit RSV. The storage unit RSV may also be referred to as a housing, container, or gas chamber. The storage unit RSV is configured to contain a working medium WM. The storage unit RSV may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the working medium WM (which may be a gas) within the storage unit RSV. The storage unit RSV may include a first transparent window TW1. In use, the optical fiber OF is disposed within the storage unit RSV such that the first transparent window TW1 is located near the input end IE of the optical fiber OF. The first transparent window TW1 may form a portion of the wall of the storage unit RSV. The first transparent window TW1 may be transparent at least to the received input radiation frequency, such that the received input radiation IRD (or at least a majority thereof) can be coupled into the optical fiber OF located within the storage unit RSV. It will be understood that optics (not shown) may be provided to couple the input radiation IRD into the optical fiber OF.

[0088] The storage unit RSV includes a second transparent window TW2, which forms part of the wall of the storage unit RSV. In use, when the optical fiber OF is placed inside the storage unit RSV, the second transparent window TW2 is located near the output end OE of the optical fiber OF. The second transparent window TW2 can be transparent at least to the frequency of the broadband output radiation ORD of the device 120.

[0089] Alternatively, in another embodiment, the two opposite ends of the optical fiber OF can be housed within different repositories. The optical fiber OF may include a first end portion configured to receive an input radiation IRD and a second end portion configured to output a broadband output radiation ORD. The first end portion may be housed within a first repositories comprising a working medium WM. The second end portion may be housed within a second repositories, wherein the second repositories may also comprise the working medium WM. The repositories may function as described above regarding... Figure 7BThe first reservoir may include a first transparent window configured to be transparent to the input radiation IRD. The second reservoir may include a second transparent window configured to be transparent to the broadband output radiation ORD. Both the first and second reservoirs may also include sealable openings to allow the optical fiber OF to be partially placed inside and partially outside the reservoir, so that the gas can be sealed inside the reservoir. The optical fiber OF may also include an intermediate portion not included inside the reservoir. This arrangement of using two separate gas reservoirs may be particularly convenient for embodiments of relatively long optical fiber OFs (e.g., when the length is greater than 1 m). It will be understood that, for this arrangement using two separate gas reservoirs, the two reservoirs (which may include one or more features known in the art for controlling, regulating, and / or monitoring the composition of the gas inside the two reservoirs) can be considered to be provided with means for supplying the working medium WM into the hollow core HC of the optical fiber OF.

[0090] In this context, the window may be transparent to the frequency if at least 50%, 75%, 85%, 90%, 95%, or 99% of a frequency radiation incident on the window is transmitted through the window.

[0091] Both the first TW1 transparent window and the second TW2 transparent window can form an airtight seal within the wall of the reservoir RSV, allowing the working medium WM (which can 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.

[0092] The working medium WM can include inert gases (such as argon, krypton, and xenon), Raman-active gases (such as hydrogen, deuterium, and nitrogen), or gas mixtures (such as argon / hydrogen mixtures, xenon / deuterium mixtures, krypton / nitrogen mixtures, or nitrogen / hydrogen mixtures). Depending on the type of filling gas, nonlinear optical processes can include modulation instability (MI), soliton self-compression, soliton fission, Kerr effect, Raman effect, and dispersive wave generation, details of which are described in WO2018 / 127266A1 and US9160137B1 (both incorporated herein by reference). Since the pressure of the working medium WM (i.e., the gas cell pressure) in the reservoir RSR can be varied, the resulting broadband pulse dynamics and associated spectral broadening characteristics can be tuned, thereby optimizing frequency conversion.

[0093] In one implementation, the working medium WM may be disposed within the hollow core COR, at least during the process of receiving input radiation IRD to generate broadband output radiation ORD. It will be understood that when the optical fiber OF does not receive input radiation IRD to generate broadband output radiation, the gas WM may be completely or partially absent from the hollow core COR.

[0094] To achieve frequency broadening, high-intensity radiation may be required. The advantage of optical fibers (OFs) with hollow cores is that high-intensity radiation can be achieved by spatially confining the radiation propagating through the fiber, thus enabling locally high radiation intensity. For example, the radiation intensity inside the fiber OF can be high due to the high intensity of received input radiation and / or the strong spatial confinement of radiation within the fiber OF. The advantage of hollow-core fibers is that they can guide radiation with a wider wavelength range than solid-core fibers, and in particular, hollow-core fibers can guide radiation in the ultraviolet and infrared ranges.

[0095] The advantage of using hollow-core optical fiber (OF) is that most of the radiation guided inside the OF is confined to the hollow core (COR). Therefore, most of the radiation interaction inside the OF is with the working medium (WM), which is disposed inside the hollow core (HC) of the OF. This increases the broadening effect of the working medium (WM) on the radiation.

[0096] The received input radiation IRD can be electromagnetic radiation. The input radiation IRD can also be received as pulsed radiation. For example, the input radiation IRD can include, for example, ultrafast pulses generated by a laser.

[0097] The input radiation IRD can be coherent radiation. The input radiation IRD can also be collimated radiation, which has the advantage of promoting and improving the efficiency of coupling the input radiation IRD to the 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 radiation and / or coherent radiation.

[0098] The broadband range of an output radiation ORD can be a continuous range, including a continuous range of radiation frequencies. An output radiation ORD can include supercontinuum radiation. Continuous radiation is beneficial in many applications, such as measurement applications. For example, a continuous range of frequencies can be used to query a large number of properties. For example, a continuous range of frequencies can be used to determine and / or eliminate the frequency dependence of the measured property. For example, a supercontinuum output radiation ORD can include electromagnetic radiation with wavelengths ranging from 100 nm to 4000 nm. For example, the frequency range of a broadband output radiation ORD can be 400 nm to 900 nm, 500 nm to 900 nm, or 200 nm to 2000 nm. A supercontinuum output radiation ORD can include white light.

[0099] The input radiation IRD provided by the pulsed-pumped radiation source (PRS) can be pulsed. The input radiation IRD can include electromagnetic radiation of one or more frequencies (between 200 nm and 2 μm). For example, the input radiation IRD can include electromagnetic radiation with a wavelength of 1.03 μm. The repetition rate of the pulsed radiation IRD can be on the order of 1 kHz to 100 MHz. The pulse energy can be on the order of 0.1 μJ to 100 μJ, for example, 1 μJ–10 μJ. The pulse duration of the input radiation IRD can be between 10 fs and 10 ps, ​​for example, 300 fs. The average power of the input radiation IRD can be between 100 mW and several hundred W. For example, the average power of the input radiation IRD can be 20 W–50 W.

[0100] The pulsed pump source (PRS) can be a laser. By adjusting the (pump) laser parameters, the working component (WM) variation, and the fiber (OF) parameters, the spatiotemporal propagation characteristics (e.g., its spectral amplitude and phase) of this laser pulse propagating along the fiber (OF) can be altered and tuned. These spatiotemporal propagation characteristics can include one or more of the following: output power, output mode distribution, output time distribution, width of the output time distribution (or output pulse width), output spectral distribution, and bandwidth of the output spectral distribution (or output spectral bandwidth). The PRS parameters can include one or more of the following: pump wavelength, pump pulse energy, pump pulse width, and pump pulse repetition rate. The OF parameters can include one or more of the following: fiber length, size and shape of the hollow core 101, size and shape of the capillary, and thickness of the capillary wall surrounding the hollow core. The WM (e.g., filled gas) parameters can include one or more of the following: gas type, gas pressure, and gas temperature.

[0101] The broadband output radiation ORD provided by the radiation source RDS can have an average output power of at least 1W. The average output power can be at least 5W. The average output power can be at least 10W. The broadband output radiation ORD can be a pulsed broadband output radiation ORD. The power spectral density of the output radiation across the entire wavelength band of the broadband output radiation ORD can be at least 0.01mW / nm. The power spectral density of the broadband output radiation across the entire wavelength band can be at least 3mW / nm.

[0102] Figure 8 A known arrangement of white light sources is shown. Figure 8 (a) is a schematic diagram of the main components of this source. The laser unit LU generates the input beam B that enters the gas chamber GC and the optical fiber HC-PCF. in Output beam B from fiber HC-PCF out (Including spectrally broadened pulses) are generated by device unit AU (e.g., regarding...). Figures 4 to 6 (Any device described) is used to generate irradiation beam B ill To irradiate the wafer W. For example, irradiation beam B. ill A target (e.g., a grating) on ​​the wafer can be illuminated. The target can be stationary or can move under the illumination beam. Once data has been acquired from the measurement, the wafer can be positioned to illuminate a new target or can be removed for other processing steps. The control and processing unit (CPU) sends a control signal (CS) and receives a data signal (DS) (e.g., including measurement data) from the device unit (AU). The spectrally broadened pulse can be specifically processed in the device unit (AU) for downstream use.

[0103] In the current white light source, the pump laser radiation pulse LP has a specific repetition rate (f rep ), and is transmitted in the form of a conventional pulse train (e.g., a radiated pulse train), wherein there is an equal time delay (1 / f) between each individual pulse. rep ). Figure 8 (b) This is illustrated; Figure 8 (b) Includes input bundle B in The graph of intensity I versus time t.

[0104] The lifetime of a current white light source can be quantified by monitoring the average output power over time. It can be observed that for pulse train repetition rates of several MHz, the typical operating hours before significant power decay are on the order of several hundred hours. This limited lifetime has a strong impact on the mass production of semiconductor devices because it requires frequent replacement of critical components. It is known that the most critical component is the HC-PCF assembly in the gas chamber (GC). Therefore, there is a strong desire to improve the lifetime of the HC-PCF.

[0105] Another issue is the upper limit of the usable repetition rate. This can be caused by thermal effects (from the average power of the pulse train) and ionization effects (from the high peak power of each individual pulse): increasing the repetition rate beyond this limit leads to significant instability in optical performance. Since both the power spectral density (PSD) and the reduction in pulse-to-pulse noise scale with the repetition rate, operation at a more efficient repetition rate is desirable. The PSD typically scales linearly with the repetition rate, and the pulse-to-pulse noise decreases with the square root of the repetition rate scaling.

[0106] To address this issue, a method was proposed to extract the pump pulse sequence of the pump laser radiation from a pulse train (such as...). Figure 8 (b) is changed to burst mode (as shown) Figure 9 (b) shows the burst pattern. In burst mode, each burst (with burst duration T) burst It consists of multiple pump pulses. Each burst has a time delay T. delay The time delay T delay It can be much longer than the time delay between each individual pump pulse (e.g., 2x, 5x, 10x, or 100x longer). The number of pump pulses per burst and the time delay between bursts can be adjusted as needed.

[0107] The main advantage of this arrangement is that the burst train can be synchronized with the timing of wafer-level measurements. This enables immediate optical response operation and significantly reduces the exposure of the HC-PCF under high-intensity pump pulses. The inventors have determined that the total lifetime of the HC-PCF in the light source is related to the total exposure level; therefore, reducing the exposure rate will directly lead to an increase in the absolute fiber lifetime.

[0108] For example, in an alignment sensor, each measurement target on the wafer can be illuminated for 4 ms. With 50 targets on a wafer, the wafer is scanned over 30 seconds. Assuming perfect instantaneous light response (i.e., 100% synchronization effectiveness), a 150x reduction in exposure for the HC-PCF can be achieved compared to conventional pulse trains. If the lifetime of the HC-PCF does indeed scale with exposure, then tens of thousands (several 10,000) hours of lifetime could be feasible. It can be noted that in instantaneous light response operation, the effective PSD of the target remains unchanged compared to conventional pulse train operation. It is also noteworthy that the total average output power is reduced by the same factor as the exposure (i.e., 150× in this example). In this case, the 15W output power would be reduced to 100mW.

[0109] By reducing the average power, the repetition rate of the pump laser can be increased beyond the upper limit of the pulse train, which has a positive impact on PSD scaling and inter-pulse noise reduction.

[0110] Furthermore, the lower average power results in a lower average thermal load along the optical path following the modem (see below), which includes the HC-PCF within the gas chamber, the application unit, and all optical components. This thermal load may be caused, for example, by the absorption of pump pulses or spectrally broadened pulses by the optical components or by portions of the gas-filled HC-PCF. Therefore, a smaller cooling system can be used to maintain the system within the desired temperature range.

[0111] Furthermore, the reduced heat load lowers the potential misalignment of optical devices due to thermal expansion, thus improving the overall system stability.

[0112] In one embodiment, the system can be arranged so that there are no bursts when no wafer is being measured (i.e., the white light source is off). However, this can adversely affect the stability of the source. Therefore, other arrangements will be described.

[0113] Figure 9 (a) illustrates a measurement arrangement according to an embodiment. This arrangement is similar to... Figure 8 The arrangement of (a) is different. The main difference is the provision of a modem MOD that modulates the input beam to generate modulated pump laser radiation; that is, the modulated input beam B. mod The modem can be controlled by a trigger signal TS or a modem control signal, which can be generated by a processor or a control and processing unit (CPU).

[0114] A modem can be an optomechanical and / or electro-optic component capable of (partially or completely) reflecting / blocking / attenuating / scattering or transmitting pulses from a burst of pulses. Specific examples include acousto-optic filters, flip-up / galvanometer mirrors, motorized baffles, or rotating blades. Appropriate selection can be made based on the desired modulation frequency.

[0115] To enable burst mode operation, such as Figure 9 As shown in (c), the measurement device can provide a trigger signal TG. For example, the control and processing unit (CPU) of the measurement device can generate a trigger signal SG as a feedback signal to control the modem MOD. For example, the control and processing unit (CPU) can be operated to synchronize the generation of bursts with the measurement performed by the measurement device (i.e., so that bursts are generated when a measurement is being performed).

[0116] Burst burst mode operation can also be performed when there is no scan activity (e.g., during wafer swapping) (e.g., with an average delay period T). delay and burst sequence period T burst This avoids changes in thermal load on all relevant components along the optical path from the modem to the application unit.

[0117] Typically, the time T between irradiation of two consecutive targets is... delay The time between the two trigger signals will not be uniform, thus small variations in average output power can be expected. This can negatively impact, for example, the temperature stability of the entire system, leading to potential drift in optical components. To compensate for this, intermediate pulses and / or variable burst lengths with variable durations and timings can be introduced. The desired parameters for these additional pulses will depend on the actual scan pattern on the wafer and the wafer exchange time. These parameters, controlling the intermediate pulse and / or burst length, can then be optimized to achieve high uniformity in output power. High uniformity of average output power is desired within periods of <60s, <30s, <10s, <1s, <300ms, or <100ms; for example, variations not exceeding 10%, 1%, or 0.1%.

[0118] Figure 10 This is a block diagram illustrating a computer system 1600 that can assist in implementing the methods and processes disclosed herein. The computer system 1600 includes a bus 1602 or other communication mechanism for communicating information, and a processor 1604 (or multiple processors 1604 and 1605) coupled to the bus 1602 for processing information. The computer system 1600 also includes a main memory 1606, such as random access memory (RAM) or other dynamic storage device, coupled to the bus 1602 for storing instructions and information to be executed by the processor 1604. The main memory 1606 may also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor 1604. The computer system 1600 also includes a read-only memory (ROM) 1608 or other static storage device coupled to the bus 1602 for storing static information and instructions for the processor 1604. A storage device 1610, such as a magnetic disk or optical disk, is provided and coupled to the bus 1602 for storing information and instructions.

[0119] Computer system 1600 can be coupled via bus 1602 to a display 1612 for displaying information to a computer user, such as a cathode ray tube (CRT), flat panel display, or touch panel display. Input device 1614, including alphanumeric keys and other keys, is coupled to bus 1602 for communicating information and command selections to processor 1604. Another type of user input device is a cursor controller 1616, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to processor 1604 and for controlling cursor movement on display 1612. Such input devices typically have two degrees of freedom on two axes (i.e., a first axis (e.g., x) and a second axis (e.g., y)), allowing the device to specify its position in a plane. Touch panel (screen) displays can also be used as input devices.

[0120] One or more methods as described herein can be performed by computer system 1600 in response to processor 1604 executing one or more sequences of one or more instructions contained in main memory 1606. These instructions can be read into main memory 1606 from another computer-readable medium, such as storage device 1610. Execution of the sequence of instructions contained in main memory 1606 causes processor 1604 to perform the process steps described herein. One or more processors arranged in a multiprocessor configuration may also be employed to execute the sequence of instructions contained in main memory 1606. In alternative embodiments, a hard-wired circuit system may be used instead of or in combination with software instructions. Therefore, the description herein is not limited to any particular combination of hardware circuitry and software.

[0121] As used herein, the term "computer-readable medium" refers to any medium that participates in providing instructions to processor 1604 for execution. Such media can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical discs or magnetic disks, such as storage device 1610. Volatile media include dynamic memory, such as main memory 1606. Transmission media include coaxial cables, copper wires, and optical fibers, including wires containing bus 1602. Transmission media can also take the form of sound waves or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, floppy disks, hard disks, magnetic tape, any other magnetic media, CD-ROMs, DVDs, any other optical media, punched cards, paper tape, any other physical media with a perforated pattern, RAM, PROMs and EPROMs, FLASH-EPROMs, any other memory chips or cartridges, carrier waves as described below, or any other media readable by a computer.

[0122] Various forms of computer-readable media can be used to carry one or more sequences of instructions to processor 1604 for execution. For example, the instructions may initially be carried on the disk of a remote computer. The remote computer may load the instructions into its dynamic memory and transmit the instructions over a telephone line using a modem. A modem local to computer system 1600 may receive data over the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to bus 1602 may receive the data carried in the infrared signal and place the data on bus 1602. Bus 1602 carries the data to main memory 1606, from which processor 1604 fetches and executes instructions. Instructions received by main memory 1606 may optionally be stored on storage device 1610 before or after execution by processor 1604.

[0123] Computer system 1600 also preferably includes a communication interface 1618 coupled to bus 1602. Communication interface 1618 provides bidirectional data communication coupling with network link 1620 connected to local area network 1622. For example, communication interface 1618 may be an Integrated Services Digital Network (ISDN) card or modem to provide data communication connectivity to a corresponding type of telephone line. As another example, communication interface 1618 may be a local area network (LAN) card to provide data communication connectivity to a compatible LAN. A wireless link may also be implemented. In any such implementation, communication interface 1618 transmits and receives electrical, electromagnetic, or optical signals carrying digital data streams representing various types of information.

[0124] Network link 1620 typically provides data communication to other data devices via one or more networks. For example, network link 1620 may provide a connection to host computer 1624 or to data equipment operated by Internet Service Provider (ISP) 1626 via local area network 1622. ISP 1626 then provides data communication services via a global packet data communication network (now commonly referred to as the "Internet" 1628). Both local area network 1622 and Internet 1628 use electrical, electromagnetic, or optical signals to carry digital data streams. Signals passing through various networks and signals on network link 1620 and through communication interface 1618 (which carries digital data to and from computer system 1600) are example forms of carrier waves for transmitting information.

[0125] Computer system 1600 can send messages and receive data including process code via a network, network link 1620, and communication interface 1618. In an Internet example, server 1630 can transmit requested code for an application via the Internet 1628, ISP 1626, local area network 1622, and communication interface 1618. For example, such a downloadable application can provide for one or more techniques described herein. The received code can be executed by processor 1604 upon receipt and / or stored in storage device 1610 or other non-volatile storage device for later execution. In this way, computer system 1600 can obtain application code in carrier form.

[0126] Other embodiments are disclosed in the following list of numbered entries:

[0127] 1. A supercontinuum radiation source, comprising:

[0128] A modem operable to modulate pump laser radiation comprising a radiating pulse train to provide modulated pump laser radiation, the modulation causing selective provision of bursts of the pulses; and

[0129] Hollow-core photonic crystal fiber is operable to receive modulated pump laser radiation and excite the working medium contained within the hollow-core photonic crystal fiber to generate supercontinuum radiation.

[0130] 2. The supercontinuum radiation source according to item 1, wherein the period between consecutive individual pulses of the radiation pulse train before modulation is the same as the period between consecutive individual pulses of the burst train of the modulated pump laser radiation pulses.

[0131] 3. The supercontinuum radiation source according to item 1 or 2, wherein the modulation causes the time delay between consecutive individuals of the burst to be more than twice the time delay between consecutive individual pump pulses.

[0132] 4. The supercontinuum radiation source according to clause 3, wherein the supercontinuum radiation is operable such that the number of pump pulses per burst and the time delay between bursts are controllable.

[0133] 5. The supercontinuum radiation source according to any of the preceding clauses, wherein the modem comprises an optomechanical and / or electro-optical modem.

[0134] 6. The supercontinuum radiation source according to any of the preceding clauses, wherein the modem comprises one or more of the following: one or more acousto-optic filters, one or more flip-flop / galvanometer mirrors, one or more motorized baffles, or one or more rotating blades.

[0135] 7. A supercontinuum radiation source according to any of the preceding clauses, wherein the modem is operable to provide one or more intermediate pulses between successive bursts, and / or to provide a variable burst length for each burst.

[0136] 8. A supercontinuum radiation source according to any one of clauses 7, wherein one or more parameters of the one or more intermediate pulses and / or the variable burst length are optimized to make the average output power of the supercontinuum radiation source with a time period of less than 60 seconds highly uniform.

[0137] 9. A supercontinuum radiation source according to any one of clauses 7, wherein one or more parameters of the one or more intermediate pulses and / or the variable burst length are optimized to make the average output power of the supercontinuum radiation source with a time period of less than 1 second highly uniform.

[0138] 10. The supercontinuum radiation source according to any of the preceding clauses further includes a pump laser for outputting pump pulses from the string.

[0139] 11. A supercontinuum radiation source according to any of the preceding clauses, wherein the supercontinuum radiation includes a wavelength range of 200 nm to 2000 nm or a subrange within the range.

[0140] 12. A supercontinuum radiation source according to any of the preceding clauses, wherein the modem is operable to receive a control signal and modulate the pump laser radiation according to the control signal.

[0141] 13. A measuring device, comprising:

[0142] Substrate support, used to support the substrate;

[0143] The supercontinuum radiation source as described in item 12;

[0144] An optical system operable to guide supercontinuum radiation from the supercontinuum radiation source onto the substrate; and

[0145] The processor is operable to generate the control signals.

[0146] 14. The measuring apparatus according to clause 13, wherein the processor is operable to synchronize the generation of a burst of pulses with the measurement execution of the measuring apparatus.

[0147] 15. The measuring device according to clause 13 or 14, wherein the measuring device is operable as a scattering measuring device.

[0148] 16. The measuring device according to clause 13 or 14, wherein the measuring device is operable as a horizontal sensor or an alignment sensor.

[0149] 17. A measuring device comprising at least one measuring element according to any one of claims 13, 14 and 16 for performing alignment and / or leveling measurements.

[0150] 18. A photolithography unit comprising the photolithography apparatus according to claim 17 and the measurement device according to claim 15.

[0151] While specific references are made to the use of lithography equipment in IC manufacturing herein, it should be understood that the lithography equipment described herein may have other applications. Possible other applications include the integration of optical systems, the patterning and detection of magnetic domain memories, the fabrication of flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and the like.

[0152] Although embodiments of the invention may be specifically referred to herein in the context of lithography equipment, embodiments of the invention can be used in other equipment. Embodiments of the invention can be formed by mask inspection equipment, metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other patterning apparatuses). These devices are generally referred to as lithography tools. Such lithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0153] Although the use of embodiments of the invention may have been specifically referenced above in the context of optical lithography, it should be understood that the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0154] Although specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in ways other than those described. The above description is intended to be illustrative and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A supercontinuum radiation source, comprising: A modem is operable to modulate pump laser radiation comprising a series of radiated pulses to provide modulated pump laser radiation, the modulation such that one or more bursts of the pulses are selectively provided, the time delay between the one or more bursts being longer than the time delay between consecutive individual pump pulses. as well as Hollow-core photonic crystal fiber is operable to receive modulated pump laser radiation having one or more burst strings and to excite the working medium contained within the hollow-core photonic crystal fiber to generate supercontinuum radiation.

2. The supercontinuum radiation source according to claim 1, wherein, The period between consecutive single pulses in the pre-modulated radiation pulse train is the same as the period between consecutive single pulses in the burst train of the modulated pump laser radiation pulse.

3. The supercontinuum radiation source according to claim 1 or 2, wherein, The modulation causes the time delay between consecutive individuals in the burst sequence to be more than twice the time delay between consecutive single pump pulses.

4. The supercontinuum radiation source according to claim 3, wherein the supercontinuum radiation is operable such that the number of pump pulses per burst and the time delay between bursts are controllable.

5. The supercontinuum radiation source according to claim 1 or 2, wherein, The modem includes an optical engine and / or an electro-optical modem.

6. The supercontinuum radiation source according to claim 1 or 2, wherein, The modem includes one or more of the following: one or more acousto-optic filters, one or more flip / galvanometer reflectors, one or more motorized baffles, or one or more rotating blades.

7. The supercontinuum radiation source according to claim 1 or 2, wherein, The modem is operable to provide one or more intermediate pulses between consecutive bursts, and / or to provide a variable burst length for each burst.

8. The supercontinuum radiation source according to claim 7, wherein, One or more parameters of the one or more intermediate pulses and / or variable burst lengths are optimized to ensure high uniformity of the average output power of the supercontinuum radiation source over a time period of less than 60 seconds.

9. The supercontinuum radiation source according to claim 7, wherein, One or more parameters of the one or more intermediate pulses and / or variable burst lengths are optimized to ensure high uniformity of the average output power of the supercontinuum radiation source over a time period of less than 1 second.

10. The supercontinuum radiation source according to claim 1 or 2, further comprising a pump laser for outputting pump pulses from the string.

11. The supercontinuum radiation source according to claim 1 or 2, wherein, The supercontinuum radiation includes a wavelength range of 200 nm to 2000 nm or a subrange within that range.

12. The supercontinuum radiation source according to claim 1 or 2, wherein, The modem is operable to receive control signals and modulate the pump laser radiation according to the control signals.

13. A measuring device, comprising: Substrate support, used to support the substrate; The supercontinuum radiation source according to claim 12; An optical system operable to direct supercontinuum radiation from the supercontinuum radiation source onto the substrate; as well as The processor is operable to generate the control signals.

14. The measuring device according to claim 13, wherein, The processor is operable to synchronize the generation of pulse bursts with the execution of measurements by the measuring device.

15. The measuring device according to claim 13 or 14, wherein, The measuring device can be operated as a scattering instrument.

16. The measuring device according to claim 13 or 14, wherein, The measuring device can operate as a horizontal sensor or an alignment sensor.

17. A lithography apparatus comprising at least one measurement device according to any one of claims 13, 14 and 16 for performing alignment and / or leveling measurements.

18. A photolithography unit, comprising the photolithography apparatus according to claim 17 and the measurement device according to claim 15.

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