Irradiation source and related measurement equipment

Abstract

An irradiation source is disclosed, which includes a gas delivery system having a gas nozzle. The gas nozzle includes an opening in an exit plane of the gas nozzle. The gas delivery system is configured to provide an air flow from the opening for generating emitted radiation at an interaction region. The irradiation source is configured to receive pump radiation having a propagation direction and to provide the pump radiation in the air flow. The geometry of the gas nozzle is adapted to shape the profile of the air flow such that the gas density of the air flow first increases to a maximum value and then sharply decreases in a cut-off region along the propagation direction.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to EP application 19203732.3 filed on October 17, 2019 and EP application 19216363.2 filed on December 16, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to an irradiation source, a metrology device, and a method for delivering a gas in an irradiation source. Background Art

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

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

[0006] Low k1 lithography can be used to process features smaller than the classical resolution limit of a lithographic apparatus. In such a process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation employed, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the "critical dimension" (usually the smallest feature size printed, but in this case the half-pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it is to replicate a pattern on a substrate that resembles the shape and size planned by a circuit designer in order to achieve specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. These include, for example, but are not limited to: optimization of NA, customized illumination schemes, use of phase-shifting patterning devices, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also referred to as "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 lithographic apparatus can be used to improve the reproduction of patterns at low k1.

[0007] In lithography processes, it is often desirable to measure the structures that are created, for example for process control and verification. A variety of tools for making such measurements are known, including scanning electron microscopes, which are commonly used to measure critical dimensions (CD), and dedicated tools for measuring overlay - the alignment accuracy of two layers in a device. More recently, various forms of scatterometers have been developed for the lithography field.

[0008] Examples of known scatterometers typically rely on the provision of dedicated metrology targets. For example, one approach may require a target in the form of a simple grating that is large enough to cause the measurement beam to produce a spot smaller than the grating (i.e., the grating is underfilled). In so - called reconstruction methods, the characteristics of the grating can be calculated by simulating the interaction of scattered radiation with a mathematical model of the target structure. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the real target.

[0009] In addition to measuring feature shape by reconstruction, such devices can be used to measure diffraction - based overlay, as described in the published patent application US2006066855A1. Diffraction - based overlay metrology using dark - field imaging of diffraction orders enables overlay measurements of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by product structures on the wafer. Examples of dark - field imaging metrology can be found in many published patent applications, such as US2011102753A1 and US20120044470A. Multiple gratings can be measured in one image using a composite grating target. Known scatterometers tend to use light in the visible or near - IR wavelength range, which requires the pitch of the gratings to be much coarser than the actual product structures, whose characteristics are actually of interest. Such product features can be defined using X - ray radiation, extreme ultraviolet (EUV), or deep ultraviolet (DUV) with much shorter wavelengths. Unfortunately, such wavelengths are often not available or not suitable for metrology.

[0010] On the other hand, the dimensions of modern product structures are so small that they cannot be imaged by optical metrology techniques. Small features include, for example, those formed by multiple patterning processes and / or pitch multiplication. Thus, targets for high - volume metrology typically use features that are much larger than the overlay error or the critical dimensions of the product for the property of interest. The measurement results are only indirectly related to the dimensions of the actual product structure and may be inaccurate because the metrology target does not suffer the same distortions under the optical projection in the lithography tool and / or different handling in other steps of the manufacturing process. Although a scanning electron microscope (SEM) can directly resolve these modern product structures, the SEM is much more time - consuming than optical measurements. In addition, electrons cannot penetrate thick processing layers, which makes them less suitable for metrology applications. Other techniques - such as measuring electrical properties using contact pads - are also known, but they only provide indirect evidence of the real product structure.

[0011] By reducing the wavelength of the radiation used during measurement (i.e., moving towards the "soft X-ray" wavelength spectrum), smaller structures can be resolved to increase the sensitivity to structural changes in the structure and / or to penetrate further into the product structure. One such method of generating suitable high-frequency radiation (e.g., soft X-rays and / or EUV radiation) can be to use pump radiation (e.g., infrared radiation) to excite a generation medium, thereby generating emitted radiation, optionally generating high-order harmonics including high-frequency radiation. SUMMARY OF THE INVENTION

[0012] According to a first aspect of the present invention, there is provided an irradiation source including a gas delivery system, the gas delivery system including a gas nozzle. The gas nozzle includes an opening in an exit plane of the gas nozzle. The gas delivery system is configured to provide an air flow from the opening for generating emitted radiation at an interaction region. The irradiation source is configured to receive pump radiation having a propagation direction and to provide the pump radiation in the air flow. The geometry of the gas nozzle is adapted to shape the profile of the air flow such that the gas density of the air flow first increases to a maximum value and then rapidly decreases in a cut-off region along the propagation direction.

[0013] Optionally, the profile of the air flow is for suppressing the energy divergence of the pump radiation within the air flow, wherein the energy divergence is caused by the fact that a part of the air flow is ionized by the pump radiation.

[0014] Optionally, the maximum value is higher than the phase matching pressure.

[0015] Optionally, the length of the cut-off region of the profile of the air flow in the propagation direction of the pump radiation is less than 100 μm.

[0016] Optionally, the shape of the opening in the exit plane is asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation.

[0017] Optionally, the width of the opening gradually increases along the propagation direction of the pump radiation.

[0018] Optionally, the shape of the opening is trapezoidal.

[0019] Optionally, the shape of the opening is an isosceles trapezoid.

[0020] Optionally, for at least a part of the gas nozzle, the internal cross-sectional area of the gas nozzle in a plane parallel to the exit plane increases along the air flow direction.

[0021] Optionally, the irradiation source includes an adjustable element for changing the profile of the air flow.

[0022] Optionally, the adjustable element is for changing the profile of the air flow during the generation of the emitted radiation.

[0023] Optionally, the adjustable element is configured to be at least partially positioned within the gas flow.

[0024] Optionally, the irradiation source includes a pump radiation source operable to emit pump radiation.

[0025] Optionally, the irradiation source is for high harmonic generation.

[0026] Optionally, the gas flow is provided by a gas delivery system into an evacuated or near-evacuated space.

[0027] Optionally, the emitted radiation has a wavelength in the X-ray or EUV range, where the wavelength is in the range of 0.01 nm to 100 nm, optionally 0.1 nm to 100 nm, optionally 1 nm to 100 nm, optionally 1 nm to 50 nm or optionally 10 nm to 20 nm.

[0028] Optionally, in operation, the emitted radiation is directed to a target on a wafer.

[0029] Optionally, the emitted radiation is for metrology measurements.

[0030] Optionally, the irradiation source includes a temperature control component.

[0031] According to another aspect of the present invention, a method of delivering gas in an irradiation source is provided, including providing a gas flow from an opening in an exit plane of a gas nozzle for receiving pump radiation having a propagation direction and for generating emitted radiation at an interaction region. The geometry of the gas nozzle is adapted to shape the profile of the gas flow such that the gas density of the gas flow first increases to a maximum value and then rapidly decreases in a cut-off region along the propagation direction.

[0032] According to another aspect of the present invention, a metrology device including the irradiation source as described above is provided.

[0033] According to another aspect of the present invention, an inspection device including the irradiation source as described above is provided.

[0034] According to another aspect of the present invention, a lithography apparatus including the irradiation source as described above is provided.

[0035] According to another aspect of the present invention, a lithography cell including the irradiation source as described above is provided. Description of the Drawings

[0036] Embodiments will now be described by way of example only with reference to the accompanying schematic drawings, in which:

[0037] - Figure 1 A schematic diagram of a lithography apparatus is shown;

[0038] -Figure 2 Shows a schematic diagram of a lithography unit;

[0039] - Figure 3 Depicts a schematic representation of overall lithography, showing the collaboration between three key technologies for optimizing semiconductor manufacturing;

[0040] - Figure 4 Schematically represents a scatterometry device;

[0041] - Figure 5 Shows a schematic representation of metrology equipment in which EUV and / or SXR radiation is used;

[0042] - Figure 6 Shows a simplified schematic diagram of an irradiation source;

[0043] - Figure 7 Depicts (a) a schematic diagram of an asymmetric opening, (b) a plot of gas density distribution, and (c) a contour plot of an air flow;

[0044] - Figure 8 Describes (a) a gas density distribution plot, (b) a schematic diagram of a gas nozzle, and (c) a contour plot of an air flow;

[0045] - Figure 9 Depicts the radiation intensity distribution and contour plot of a gas flow in (a) and (b);

[0046] - Figure 10 Depicts (a) a schematic diagram of a gas contour and (b) a plot of the output power of the emitted radiation;

[0047] - Figure 11 Schematically shows a gas delivery system having a temperature control component;

[0048] Figure 12 A flowchart including steps in a method of generating the emitted radiation. Detailed Description

[0049] As used herein, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation and particle radiation, including ultraviolet radiation (e.g., having wavelengths of 365, 248, 193, 157, or 126 nm), EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 - 100 nm), X-ray radiation, electron beam radiation, and other particle radiation.

[0050] As used herein, the terms "reticle", "mask", or "patterning device" can be broadly interpreted as referring to a general patterning device that can be used to endow an incident radiation beam with a patterned cross-section that corresponds to a pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays in addition to classical masks (transmission or reflection, binary, phase-shifting, hybrid, etc.).

[0051] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA includes an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, EUV radiation, or X-ray radiation); a reticle support (e.g., a reticle stage) T configured to support a patterning device (e.g., a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0052] In operation, the illumination system IL receives the radiation beam from a radiation source SO via, for example, a beam delivery system BD. The illumination system IL can include various types of optical components, such as refractive, reflective, diffractive, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for guiding, shaping, and / or controlling the radiation. The illuminator IL can be used to condition the radiation beam B such that it has a desired spatial and angular intensity distribution in the cross-section at the plane of the patterning device MA.

[0053] The term "projection system" PS as used herein should be broadly interpreted to include various types of projection systems, including refractive, reflective, diffractive, catadioptric, anamorphic, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof, appropriately determined depending on the exposure radiation used, and / or appropriately determined depending on other factors such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein can be considered synonymous with the more general term "projection system" PS.

[0054] The lithographic apparatus LA can be of a type in which at least a portion of the substrate can be covered by a liquid having a relatively high refractive index (e.g., water) in order to fill the space between the projection system PS and the substrate W, which is also known as immersion lithography. More information on immersion techniques is given in US 6952253, the entire content of which is incorporated herein by reference.

[0055] The lithographic apparatus LA can also be of a type having two or more substrate holders WT (also referred to as “dual stage”). In such a “multi-stage” machine, the substrate holders WT can be used in parallel, and / or the steps of preparing a subsequent exposure of the substrate W located on one of the substrate holders WT can be performed while exposing a pattern on another substrate W on another substrate holder WT.

[0056] In addition to the substrate support WT, the lithographic apparatus LA can include a metrology stage. The metrology stage is arranged to hold a sensor and / or a cleaning device. The sensor can be arranged to measure a characteristic of the projection system PS or of the radiation beam B. The metrology stage can accommodate a plurality of sensors. The cleaning device can be arranged to clean a part of the lithographic apparatus, such as a part of the projection system PS or a part of the system providing the immersion liquid. The metrology stage can move under the projection system PS when the substrate holder WT is moved away from the projection system PS.

[0057] In operation, the radiation beam B is incident on a patterning device (e.g., a mask) MA held on a mask support T and is patterned by the pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. By means of a second positioner PW and a position measurement system IF, the substrate holder WT can be moved precisely, for example in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, a first positioner PM and possibly another position sensor ( Figure 1 not explicitly shown in the figure) can be used to position the patterning device MA precisely 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 device MA and the substrate W. Although the shown 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 scribe-lane alignment marks.

[0058] As Figure 2As shown, the lithographic apparatus LA can form part of a lithographic cell LC, which is sometimes also referred to as a lithocell or (lithographic) cluster and which typically also includes equipment for performing pre-exposure and post-exposure processing on a substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH and a bake plate BK, for example for regulating the temperature of the substrate W, for example for regulating the solvent in the resist layer. A substrate handler or robot RO picks up the substrate W from the input / output ports I / O1, I / O2, moves the substrate W between different processing equipment, and transfers the substrate W to the load port LB of the lithographic apparatus LA. Equipment, which is generally also collectively referred to as a track in the lithographic cell, can be controlled by a track control unit TCU, which itself can be controlled by a monitoring system SCS, which in turn can control the lithographic apparatus LA, for example via a lithography control unit LACU.

[0059] In a lithographic process, it is desirable to frequently measure the structures produced, for example for process control and verification. Tools for performing such measurements can be referred to as metrology tools MT. Different types of metrology tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools MT. A scatterometer is a general-purpose instrument that allows the measurement of parameters of a lithographic process by having a sensor in the pupil or in a plane conjugate to the pupil of the objective of the scatterometer (the measurement is generally referred to as pupil-based measurement), or by having a sensor in the image plane or in a plane conjugate to the image plane (in this case, the measurement is generally referred to as image- or field-based measurement). Such scatterometers and related measurement techniques are further described in patent applications US 20100328655, US 2011102753A1, US 20120044470A, US 20110249244, US20110026032 or EP1,628,164A, which are hereby incorporated by reference in their entirety. The above-mentioned scatterometers can measure gratings using light from the soft X-ray, far ultraviolet and visible light to the near-IR wavelength ranges.

[0060] In order for the substrate W exposed by the lithographic apparatus LA to be correctly and consistently exposed, it is desirable to inspect the substrate to measure characteristics of the patterned structures, such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, inspection tools and / or metrology tools (not shown) can be included in the lithographic cell LC. If an error is detected, for example, the exposure of subsequent substrates or other processing steps to be performed on the substrate W can be adjusted, especially if the inspection is completed before the other substrates W in the same batch or stack are still to be exposed or processed.

[0061] An inspection device, which may also be referred to as a metrology device, is used to determine the characteristics of a substrate W, in particular how the characteristics of different substrates W vary or how the characteristics associated with different layers of the same substrate W vary layer by layer. Alternatively, the inspection device may be configured to identify defects on the substrate W and may, for example, be part of a lithography cell LC, or may be integrated into a lithography apparatus LA, or may even be a stand-alone device. The inspection device may measure properties on a latent image (the image in the resist layer after exposure), or a semi-latent image (the image in the resist layer after the post-exposure bake step PEB), or a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even an etched image (after a pattern transfer step such as etching).

[0062] In a first embodiment, the scatterometer MT is an angularly resolved scatterometer. In such a scatterometer, a reconstruction method may be applied to the measurement signal to reconstruct or calculate the characteristics of the grating. For example, such a reconstruction may be obtained by simulating the interaction of the scattered radiation with 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 the real target.

[0063] In a second embodiment, the scatterometer MT is a spectral scatterometer MT. In such a spectral scatterometer MT, the radiation emitted by a radiation source is directed onto a target, and the reflected or scattered radiation from the target is directed onto a spectrometer detector that measures the spectrum of the specularly reflected radiation (i.e., a measure of the intensity as a function of wavelength). Based on this data, the structure or profile of the target that produced the detected spectrum may be reconstructed, for example, by rigorous coupled-wave analysis and non-linear regression or by comparison with a library of simulated spectra.

[0064] In a third embodiment, the scatterometer MT is an ellipsometric scatterometer. An ellipsometric scatterometer allows the determination of parameters of a lithography process by measuring the scattered radiation for each polarization state. Such a metrology device emits polarized light (e.g., linear, circular or elliptical) by using, for example, a suitable polarization filter in the illumination section of the metrology device. Sources suitable for the metrology device may also provide polarized radiation. Various embodiments of existing ellipsometric scatterometers 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.

[0065] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring the reflection spectrum and / or detecting an asymmetry in the detection configuration, the asymmetry being related to the degree of overlay. The two (possibly overlayed) grating structures can be applied in two different layers (not necessarily consecutive layers) and can be formed substantially at the same location on the wafer. The scatterometer can have a symmetric detection configuration, such as described in co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a direct method for measuring misalignment in the grating. Other examples of measuring overlay error between two layers containing periodic structures when measuring a target by the asymmetry of the periodic structure can be found in PCT patent application publication number WO2011 / 012624 or U.S. patent application US20160161863, the entire contents of which are incorporated herein by reference.

[0066] Other parameters of interest can be focus and dose. Focus and dose can be determined simultaneously by scatterometry (or by scanning electron microscopy), as described in U.S. patent application US2011-0249244, the entire contents of which are incorporated herein by reference. A single structure can be used that has a unique combination of critical dimension and sidewall angle measurements for each point in a focus energy matrix (FEM - also known as a focus exposure matrix). If these unique combinations of critical dimension and sidewall angle are available, the focus and dose values can be uniquely determined from these measurements.

[0067] The metrology target can be a collection of composite gratings formed by a lithography process, mainly in the resist, but also, for example, after an etching process. The pitch and linewidth of the structures in the grating can strongly depend on the measurement optics (especially the NA of the optics) in order to be able to capture the diffraction orders from the metrology target. As previously mentioned, the diffraction signal can be used to determine the offset (also called "overlay") between two layers, or can be used to reconstruct at least a portion of the original grating produced by the lithography process. This reconstruction can be used to provide guidance on the quality of the lithography process and can be used to control at least a portion of the lithography process. The target can have smaller sub-segments that are configured to mimic the dimensions of functional portions of the design layout in the target. Due to this sub-segmentation, the target will behave more like the functional portions of the design layout, such that the overall process parameter measurements better resemble the functional portions of the design layout. The target can be measured in an underfill mode or an overfill mode. In the underfill mode, the measurement beam produces a spot smaller than the entire target. In the overfill mode, the measurement beam produces a spot larger than the entire target. In this overfill mode, different targets can also be measured simultaneously, thereby simultaneously determining different process parameters.

[0068] The overall measurement quality using lithography parameters for a specific target is at least partially determined by the measurement recipe used to measure the lithography parameter. The term "substrate measurement recipe" 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 recipe is a diffraction-based optical measurement, 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 patterns on the substrate, etc. One criterion for selecting the measurement recipe can be, for example, the sensitivity of one of the measurement parameters to process variations. More 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.

[0069] The patterning process in the lithography apparatus LA can be one of the most critical steps in the process, which requires high precision in the design and layout of the dimensions of the structures on the substrate W. To ensure this high precision, three systems can be combined in a so-called "integrated" control environment as schematically shown in Figure 3 . One of these systems is the lithography apparatus LA (virtually) connected to the metrology tool MET (the second system) and the computer system CL (the third system). The key to such an "integrated" environment is to optimize the collaboration between these three systems to enhance the overall process window and provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines the range of process parameters (such as dose, focus, overlay) within which a particular manufacturing process produces a defined result (such as a functional semiconductor device) - within this range, process parameter variations in the lithography process or patterning process are allowed.

[0070] The computer system CL can use (part of) the design layout to be patterned to predict which resolution enhancement techniques to use and perform computational lithography simulations and calculations to determine which mask layout and lithography apparatus settings achieve the maximum overall process window for the patterning process (depicted by the double arrow in the first balance pan SC1 in Figure 3 ). The resolution enhancement techniques can be arranged to match the patterning capabilities 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 MET) to predict whether there are defects due to, for example, suboptimal processing (depicted by the arrow pointing to "0" in the second balance pan SC2 in Figure 3 ).

[0071] The metrology tool MET can provide input to the computer system CL to enable accurate simulations and predictions, and can provide feedback to the lithography apparatus LA to identify possible drifts, for example, in the calibration state of the lithography apparatus LA (inFigure 3 Depicted by a plurality of arrows in the third balance pan SC3.

[0072] In a lithography process, it is desirable to frequently measure the structures produced, for example for process control and verification. Various tools for performing such measurements are known, including scanning electron microscopes or various forms of metrology equipment, such as scatterometers. Examples of known scatterometers typically rely on providing dedicated metrology targets, such as underfilled targets (targets in the form of simple gratings or overlay gratings in different layers, which are large enough to cause the measurement beam to produce a speckle smaller than the grating) or overfilled targets (whereby the illumination speckle partially or completely encompasses the target). Additionally, the use of metrology tools, such as angular-resolved scatterometers that illuminate underfilled targets such as gratings, allows the use of so-called reconstruction methods, where the characteristics of the grating can be calculated by simulating the interaction of scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the real target.

[0073] A scatterometer is a general-purpose instrument that allows the measurement of lithography process parameters by having a sensor in the pupil or in a plane conjugate to the pupil of the scatterometer objective (the measurement is typically referred to as pupil-based measurement), or by having a sensor in the image plane or in a plane conjugate to the image plane (in this case, the measurement is typically referred to as image- or field-based measurement). Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US2011024924, US 20110026032 or EP1,628,164A, which are hereby incorporated in their entirety by reference. The aforementioned scatterometers can measure multiple targets from multiple gratings in one image using light from the soft X-ray, far ultraviolet, and visible to near-IR wavelength ranges.

[0074] Figure 4 A metrology device such as a scatterometer is shown. It includes a broadband (e.g., white light) radiation projector 2 that projects radiation 5 onto a substrate W. The reflected or scattered radiation 10 is transmitted to a spectrometer detector 4, which measures the spectrum 6 of the specularly reflected radiation (i.e., a measure of the intensity as a function of wavelength). From this data, it can be processed by a processing unit PU, for example, by rigorous coupled-wave analysis and non-linear regression or by comparison with Figure 4The detected spectrum is reconstructed by comparing it with a simulated spectrum library shown at the bottom to generate the structure or profile of the detected spectrum. Generally, for reconstruction, the general form of the structure is known, and some parameters are assumed based on the knowledge of the process of manufacturing the structure, leaving only a few parameters of the structure to be determined from the scatterometry measurement data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0075] As an alternative to optical metrology methods, the use of soft X-rays or EUV radiation is also considered, for example, radiation in the wavelength range between 0.1 nm and 100 nm, or optionally between 1 nm and 50 nm, or optionally between 10 nm and 20 nm. An example of a metrology tool operating in one of the above wavelength ranges is transmission small angle X-ray scattering (T-SAXS as in US2007224518A, the content of which is incorporated herein by reference in its entirety). Lemaillet et al. discussed the profile (CD) measurement using T-SAXS in "Intercomparison between optical and X-ray scatterometry measurements of finfet structures", Proc. of SPIE, 2013, 8681. Reflection measurement techniques using grazing incidence X-rays (GI-XRS) and extreme ultraviolet (EUV) radiation are known for measuring the properties of layer stacks and films on a substrate. Within the general field of reflection measurement, goniometric and / or spectroscopic techniques can be applied. In goniometry, the variation of the reflected beam with different angles of incidence is measured. On the other hand, a spectral reflectometer measures the spectrum of wavelengths reflected at a given angle (using broadband radiation). For example, EUV reflectometers have been used to inspect mask blanks before manufacturing mask plates (pattern forming devices) for EUV lithography.

[0076] It is possible that the application range makes the use of wavelengths in the soft X-ray or EUV domain insufficient. Therefore, the published patent applications US 20130304424A1 and US 2014019097A1 (Bakeman et al. / KLA) describe hybrid metrology techniques in which measurements using X-rays and optical measurements with wavelengths in the range of 120 nm and 2000 nm are combined to obtain measurements of parameters such as CD. CD measurements are obtained by coupling one or more common components and X-ray mathematical models and optical mathematical models. The content of the cited US patent applications is incorporated herein by reference in its entirety.

[0077] Figure 5 A schematic diagram of a metrology device 302 is shown, where radiation in the wavelength range from 0.1 nm to 100 nm can be used to measure the parameters of a structure on a substrate. Figure 5 The shown metrology device 302 is applicable to the soft X-ray or EUV domain.

[0078] Figure 5 Figure 5 Only a schematic physical arrangement of a metrology apparatus 302 including a spectral scatterometer using grazing-incidence EUV and / or SXR radiation is shown by way of example. Another form of inspection apparatus may be provided in the form of an angular-resolved scatterometer that uses radiation incident at normal or near-normal incidence, which is analogous to conventional scatterometers operating at longer wavelengths.

[0079] The inspection apparatus 302 includes a radiation source or so-called illumination source 310, an illumination system 312, a substrate holder 316, a detection system 318, 398, and a metrology processing unit (MPU) 320.

[0080]

[0079] In this example, the illumination source 310 is used to generate EUV or soft x-ray radiation, which may be based on high harmonic generation (HHG) technology. The main components of the radiation source are a pump radiation source 330 operable to emit pump radiation and a gas delivery system 332. Optionally, the pump radiation source 330 is a laser, and optionally, the pump radiation source 330 is a pulsed high-power infrared or optical laser. The pump radiation source 330 may be, for example, a fiber-based laser with an optical amplifier that generates infrared radiation pulses that may last, for example, less than 1 ns (1 nanosecond) per pulse, and whose pulse repetition rate may be up to several megahertz as required. The wavelength of the infrared radiation may be, for example, in the range of 1 μm (1 micrometer). Optionally, the laser pulse is transmitted as a first pump radiation 340 to the gas delivery system 332, where, in the gas, a portion of the radiation is converted to a higher frequency than the first radiation to become the emitted radiation 342. A gas supply source 334 supplies a suitable gas to the gas delivery system 332, where the gas is optionally ionized by a power supply 336. The gas delivery system 332 may be a cut-off tube as will be discussed hereinafter.

[0081] The emitted radiation can comprise multiple wavelengths. If the emitted radiation is monochromatic, the measurement calculations (e.g., reconstruction) can be simplified, but it is easier to generate radiation having several wavelengths. The emission divergence angle of the emitted radiation can be wavelength-dependent. The gas provided by the gas delivery system 332 defines a gas target, which can be an air flow or a static volume. The gas can be, for example, an inert gas such as neon (Ne), helium (He), or argon (Ar). Gases such as N2, O2, Ar, Kr, Xe can be considered. These can be alternative options within the same device. For example, when imaging structures of different materials, different wavelengths will provide different levels of contrast. For example, to inspect metal or silicon structures, different wavelengths can be selected for imaging features of (carbon-based) resists or for detecting contamination of such different materials. One or more filtering devices 344 can be provided. For example, filters such as aluminum (Al) or zirconium (Zr) thin films can be used to cut off the fundamental IR radiation so that it cannot enter the inspection device further. A grating (not shown) can be provided to select one or more specific harmonic wavelengths from the generated harmonic wavelengths. Some or all of the beam path can be included in a vacuum or near-vacuum environment, bearing in mind that SXR radiation is absorbed when traveling in air. Various components of the radiation source 310 and the illumination optics 312 can be adjustable to achieve different metrology 'formulas' in the same device. For example, different wavelengths and / or polarizations can be selected.

[0082] Depending on the material of the structure being inspected, different wavelengths can provide the desired level of penetration into the underlying layer. To resolve the smallest device features and defects in the smallest device features, short wavelengths may be preferred. For example, one or more wavelengths in the range of 1 - 20 nm or alternatively in the range of 1 - 10 nm or alternatively in the range of 10 - 20 nm can be selected. When reflected from materials of interest in semiconductor manufacturing, wavelengths shorter than 5 nm may suffer from a very low critical angle. Therefore, selecting wavelengths greater than 5 nm will provide a stronger signal at higher incident angles. On the other hand, if the inspection task is for detecting the presence of a certain material, e.g., detecting contamination, wavelengths up to 50 nm may be useful.

[0083] The filtered beam 342 enters the inspection chamber 350 from the radiation source 310. In the inspection chamber 350, the substrate W including the structure of interest is held at the measurement position by the substrate holder 316 for inspection. The structure of interest is labeled T. The atmosphere inside the inspection chamber 350 is maintained at a vacuum or near-vacuum by the vacuum pump 352, so that EUV radiation can pass through this atmosphere without excessive attenuation. The illumination system 312 has the function of focusing the radiation into a focused beam 356, and can include, for example, a two-dimensional curved mirror, or a series of one-dimensional curved mirrors, as described in the above-mentioned U.S. Patent Application US2017 / 0184981A1 (the content of which is incorporated herein by reference in its entirety). When projected onto the structure of interest, focusing is performed to obtain a circular or elliptical spot S with a diameter less than 10 μm. The substrate holder 316 includes, for example, an X-Y translation stage and a rotation stage, through which any part of the substrate W can be brought to the focus of the beam to be in the desired orientation. Thus, a radiation spot S is formed on the structure of interest. Alternatively or additionally, the substrate holder 316 includes, for example, a tilting stage, which can tilt the substrate W at an angle to control the incident angle of the focused beam on the structure of interest T.

[0084] Optionally, the illumination system 312 provides a reference radiation beam to the reference detector 314, which can be configured to measure the spectrum and / or intensity of different wavelengths in the filtered beam 342. The reference detector 314 can be configured to generate a signal 315 provided to the processor 310, and the filter can include information about the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0085] The reflected radiation 360 is captured by the detector 318, and the spectrum is provided to the processor 320 for calculating the characteristics of the target structure T. The illumination system 312 and the detection system 318 thus form an inspection device. This inspection device can include a soft X-ray and / or EUV spectral reflectometer of the type described in US2016282282A1, the content of which is incorporated herein by reference in its entirety.

[0086] If the target T has a certain periodicity, the radiation of the focused beam 356 can also be partially diffracted. The diffracted radiation 397 follows another path at a clearly defined angle relative to the incident angle, and then is the reflected radiation 360. In Figure 5 it, the drawn diffracted radiation 397 is drawn in a schematic manner, and the diffracted radiation 397 can follow many other paths in addition to the drawn path. The inspection device 302 can also include an additional detection system 398 for detecting and / or imaging at least a part of the diffracted radiation 397. In Figure 5A single additional detection system 398 is shown, but embodiments of inspection device 302 may also include more than one additional detection system 398, which are arranged at different positions to detect and / or image diffracted radiation 397 in a plurality of diffraction directions. In other words, the (higher) diffraction orders of the focused radiation beam impinging on target T are detected and / or imaged by one or more additional detection systems 398. One or more detection systems 398 generate signals 399 that are provided to metrology processor 320. Signals 399 may include information on diffracted light 397 and / or may include an image obtained from diffracted light 397.

[0087] To assist in aligning and focusing the speckle S with the desired product structure, inspection device 302 may also use auxiliary radiation to provide auxiliary optics under the control of metrology processor 320. Metrology processor 320 may also communicate with position controller 372 that operates translation stages, rotation stages, and / or tilt stages. Processor 320 receives high-precision feedback on the position and orientation of the substrate through sensors. For example, sensor 374 may include an interferometer, which may provide precision in the picometer range. In the operation of inspection device 302, spectral data 382 captured by detection system 318 is transferred to metrology processing unit 320.

[0088] As described above, alternative forms of inspection device use soft X-ray and / or EUV radiation with normal or near-normal incidence, for example to perform diffraction-based asymmetry measurements. Two types of inspection device may be provided in a hybrid metrology system. Performance parameters to be measured may include overlay (OVL), critical dimension (CD), focus of the lithography apparatus when printing target structures, coherent diffraction imaging (CDI), and alignment resolution overlay (ARO) metrology. Soft X-ray and / or EUV radiation may have a wavelength of less than 100 nm, for example using radiation in the range of 5 - 30 nm, or alternatively in the range of 10 nm to 20 nm. The radiation may be narrow-band or wide-band in character. The radiation may have discrete peaks in a particular wavelength band, or may have a more continuous character.

[0089] Similar to the light scatterometers used in today's production equipment, inspection device 302 can be used to measure structures within the resist material processed within a lithography cell (after development inspection or ADI), and / or to measure structures after they have been formed in a harder material (after etch inspection or AEI). For example, after processing the substrate through a development device, an etch device, an annealing device, and / or other devices, inspection device 302 can be used to inspect the substrate.

[0090] A metrology tool MT, including but not limited to the above-mentioned scatterometer, can perform measurements using radiation from a radiation source. The radiation used by the metrology tool MT can be electromagnetic radiation. The radiation can be optical radiation, such as radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum. The metrology tool MT can use the radiation to measure or inspect the characteristics and aspects of a substrate, such as a lithographic exposure pattern on a semiconductor substrate. The type and quality of the measurement can depend on several characteristics of the radiation used by the metrology tool MT. For example, the resolution of an electromagnetic measurement can depend on the wavelength of the radiation, where a smaller wavelength can measure smaller features, which is due to, for example, the diffraction limit. To measure features with small dimensions, it is preferable to use radiation with a short wavelength, such as EUV and / or soft X-ray (SXR) radiation, to perform the measurement. To perform metrology at a specific wavelength or wavelength range, the metrology tool MT needs access to a source that provides radiation at that / those wavelengths. There are different types of sources for providing radiation at different wavelengths. Depending on the wavelength provided by the source, different types of radiation generation methods can be used. For extreme ultraviolet (EUV) radiation (e.g., 1 nm to 100 nm) and / or soft X-ray (SXR) radiation (e.g., 0.1 nm to 10 nm), the source can use high harmonic generation (HHG) to obtain radiation at the desired wavelength. One of the challenges faced in the development of these sources is how to effectively couple out the emitted radiation from the generation device and separate the emitted radiation from the radiation used to drive the process.

[0091] Figure 6 A simplified schematic diagram of an embodiment 600 of an illumination source 310 is shown, which can be an illumination source for high harmonic generation. Regarding Figure 5 one or more features of the illumination source in the metrology tool described above may also be appropriately present in the illumination source 600. The illumination source 600 includes a chamber 601. The illumination source 600 is configured to receive pump radiation 611 having a propagation direction indicated by an arrow. The pump radiation 611 shown here is an example of pump radiation 340 from a pump radiation source 330, as Figure 5 shown. The pump radiation 611 can be guided into the chamber 601 through a radiation input 605, which can be a viewport made of fused silica or comparable material. The pump radiation 611 can have a Gaussian or hollow (e.g., annular) cross-sectional profile and can be incident on (optionally focused on) an air flow 615 within the chamber 601, the air flow 615 having a flow direction indicated by a second arrow. The air flow 615 includes a small volume (e.g., a few cubic millimeters) of a specific gas (e.g., an inert gas, optionally helium, argon, or neon, nitrogen, oxygen, or carbon dioxide), where the gas pressure is higher than a certain value. The air flow 615 can be a steady flow. Other media, such as metal plasmas (e.g., aluminum plasma), can also be used.

[0092] The gas delivery system of the irradiation source 600 is configured to provide an air flow 615. The irradiation source 600 is configured to provide pump radiation 611 in the air flow 615 to drive the generation of the emitted radiation 613. The region where at least most of the emitted radiation 613 is generated is called the interaction region. The interaction region can vary from several tens of micrometers (for tightly focused pump radiation) to several millimeters or centimeters (for moderately focused pump radiation), or even up to several meters (for extremely loosely focused pump radiation). Optionally, the air flow 615 is provided by the gas delivery system into an evacuated or nearly evacuated space. The gas delivery system includes a gas nozzle 609, as Figure 6 shown, which includes an opening 617 in the exit plane of the gas nozzle 609. The air flow 615 is provided from the opening 617. In almost all prior arts, the gas nozzle has a cut tube geometry, which is a uniform cylindrical internal geometry, and the shape of the opening in the exit plane is circular. As described in the patent application CN101515105B, an elongated opening is also used. The entire content of CN 101515105B is incorporated herein by reference.

[0093] Compared with the use of other gas delivery systems (such as an inflated capillary), an example of this gas delivery system is described in, for example, "Single-shot fluctuations in waveguided high-harmonic generation" by S.J. Goh et al., Optics express, 23(19), 24888. The advantage of using a gas nozzle (optionally with a cut tube or adapted geometry) is that the alignment of the pump radiation and the gas target / flow is easier. When using an inflated capillary, if the alignment is not precise enough, the gas delivery may burn due to the high power of the pump radiation.

[0094] The size of the gas nozzle 609 can also be used in a scaled-up or scaled-down form, ranging from a micrometer-sized nozzle to a meter-sized nozzle. This wide size range comes from the fact that the setup should be scaled such that the intensity of the pump radiation at the air flow ends within a specific range that may be beneficial for the emitted radiation, which requires different size designs for different pump radiation energies. The different pump radiation energies can be pulsed lasers, and the pulse energy can vary from several tens of microjoules to several joules.

[0095] Due to the interaction between the pump radiation 611 and the gas atoms of the air flow 615, the air flow 615 converts part of the pump radiation 611 into the emitted radiation 613, which can be Figure 5An example of the emitted radiation 342 is shown. The central axis of the emitted radiation 613 can be collinear with the central axis of the incident pump radiation 611. The emitted radiation 613 can have a wavelength in the X-ray or EUV range, where the wavelength is in the range from 0.01 nm to 100 nm, optionally from 0.1 nm to 100 nm, optionally from 1 nm to 100 nm, optionally from 1 nm to 50 nm, or optionally from 10 nm to 20 nm.

[0096] In operation, the emitted radiation 613 beam can pass through the radiation output 607 and can subsequently be manipulated and directed by the illumination system 603 (which can be an example of the illumination system 312 in Figure 5 to the wafer to be inspected for metrology measurements. The emitted radiation 613 can be directed, optionally focused, onto a target on the wafer.

[0097] Since air (and indeed any gas) strongly absorbs SXR or EUV radiation, the volume between the gas flow 615 and the wafer to be inspected can be evacuated or nearly evacuated. Since the central axis of the emitted radiation 613 can be collinear with the central axis of the incident pump radiation 611, it may be necessary to block the pump radiation 611 to prevent it from passing through the radiation output 607 and entering the illumination system 603. This can be achieved by incorporating the Figure 5 filter device 344 shown into the radiation output 607, which is placed in the path of the emitted beam and is opaque or nearly opaque to the drive radiation (e.g., opaque or nearly opaque to infrared or visible light), but at least partially transparent to the emitted radiation beam. The filter can be made of zirconium. When the pump radiation 611 has a hollow (optionally annular) cross-sectional profile, the filter can be a hollow (optionally annular) block.

[0098] Methods, devices, and components are described herein for optionally obtaining emitted radiation at a high harmonic frequency of pump radiation. The radiation generated by this process - optional HHG, which uses a non-linear effect to generate radiation at a harmonic frequency of the provided pump radiation - can be provided as radiation in a metrology tool MT for inspecting and / or measuring a substrate. The substrate can be a lithographically patterned substrate. The radiation obtained by this process can also be provided in a lithographic apparatus LA and / or a lithographic cell LC. The pump radiation can be pulsed radiation, which can provide a high peak intensity with a short pulse duration.

[0099] The pump radiation 611 may include radiation having one or more wavelengths higher than one or more wavelengths of the emitted radiation. The pump radiation may include infrared radiation. The pump radiation may include radiation having a wavelength in the range of 800 nm to 1500 nm. The pump radiation may include radiation having a wavelength in the range of 900 nm to 1300 nm. The pump radiation may include radiation having a wavelength in the range of 100 nm to 1300 nm. The pump radiation may be pulsed radiation. The pulsed pump radiation may include pulses having a duration in the femtosecond range.

[0100] For some embodiments, the emitted radiation (optionally, high harmonic radiation) may include one or more harmonics of the pump radiation wavelength. The emitted radiation may include wavelengths in the extreme ultraviolet (EUV), soft X-ray (SXR), and / or hard X-ray portions of the electromagnetic spectrum. The emitted radiation 613 may include wavelengths in the range of 0.01 nm to 100 nm. The emitted radiation 613 may include wavelengths in the range of 0.1 nm to 100 nm. The emitted radiation 613 may include wavelengths in the range of 0.1 nm to 50 nm. The emitted radiation 613 may include wavelengths in the range of 1 nm to 50 nm. The emitted radiation 613 may include wavelengths in the range of 10 nm to 20 nm.

[0101] The irradiation source may be provided, for example, in a metrology device MT, an inspection device, a lithography apparatus LA, and / or a lithography cell LC.

[0102] The properties of the emitted radiation used to perform the measurement may affect the quality of the measurement obtained. For example, the shape and size of the lateral beam profile (cross-section) of the radiation beam, the intensity of the radiation, the power spectral density of the radiation, etc. may affect the measurement performed by the radiation. Therefore, it is beneficial to have a source of radiation with properties that result in high-quality measurements.

[0103] When the emitted radiation is generated by irradiating a radiation generation target (such as a gas, plasma, or solid sample) with pump radiation, the conversion efficiency is typically small. The conversion efficiency may be the ratio of the number of photons of the emitted radiation to the number of photons of the pump radiation. Therefore, it is challenging to develop an irradiation source that generates high output power to achieve metrology measurements with an acceptably high output power. Therefore, to achieve high output power, it is necessary to ensure that at least some of the atoms in the radiation generation target emit their radiation at least partially coherently, which means that the electromagnetic waves constituting the emitted radiation are in phase, which is called coherent emission. The benefit may be that, in the case of coherent emission, the total intensity of the emitted radiation caused by N radiation atoms is proportional to N 2 and this can result in a much higher total power than in the case of incoherent emission of atoms, for which the total intensity is proportional to N.

[0104] The condition for coherent emission can be that the electromagnetic waves constituting the pump radiation and the emitted radiation propagate through the radiation generation target at the same phase velocity (i.e., the wave crest velocity), which is called phase matching. A focused beam naturally obtains a higher phase velocity than an unfocused beam. Therefore, the pump radiation of the focused radiation can naturally have a higher phase velocity than the emitted radiation, thus preventing coherent emission. To compensate for this difference in natural wave velocity, the pump radiation can be slowed down by generating a sufficiently high refractive index in the target. This can be achieved by ensuring a sufficiently high gas pressure (called the phase matching pressure). The maximum value of the gas density of the gas flow may need to be higher than the phase matching pressure to achieve high output power.

[0105] During the generation of the emitted radiation (optional HHG), the gas flow can be partially ionized by the pump radiation, and a plasma can be generated. The role of the plasma is to deteriorate the intensity distribution of the pump radiation through an effect called plasma defocusing, thereby reducing the peak intensity that may be required for high output power and preventing the intensity distribution of the pump radiation required for the best quality of the emitted radiation. The intensity of the plasma defocusing effect can increase with the gas pressure in the gas flow. However, as mentioned above, the gas pressure may be determined by the requirements of phase matching and cannot be freely selected. Therefore, it is usually a challenge to provide a sufficiently high gas pressure to ensure phase matching and a sufficiently low gas pressure to prevent the plasma defocusing effect. The typical result is usually a compromise where both are more or less acceptable, but neither is optimal, which means that the gas pressure can be reduced from the optimal phase matching pressure to limit plasma defocusing, resulting in a reduced output power.

[0106] When a typical gas nozzle is used for gas delivery, this means that the gas nozzle has a cut tube geometry with a uniform cylindrical internal geometry, and the shape of the opening in the exit plane is circular, and the gas flow has a profile with a typical symmetric or approximately symmetric shape along the propagation direction of the pump radiation, as Figure 9 (a) can be seen. Figure 9(a) shows the simulated intensity distribution 901 of the pump radiation, which is a laser beam in this example, propagating from left to right (in the direction of arrow 921) through neon gas with a typical symmetric-shaped gas flow distribution. This means that the gas profile 911 is such that the gas density of the gas flow represented by the P-axis is symmetric along the propagation direction represented by the X-axis. For the gas profile 911, the P-axis represents the gas density, while for the grayscale intensity distribution, the P-axis represents the radial direction of the pump radiation perpendicular to the propagation direction. The dark color in plot 901 represents low pump radiation intensity, while the light color represents high pump radiation intensity. Arrow 921 represents the central axis and propagation direction of the pump radiation. The two vertical dashed lines 931 represent the region of the gas flow 615 along the propagation direction of the pump radiation, which contributes most of the emitted radiation. The gas flow 615 between the two dashed lines 931 can be called the interaction region.

[0107] Using the symmetric gas distribution 911, plasma defocusing moves most of the pump radiation (optionally pump laser radiation) away from the axis 921, thus restricting the highest pump radiation intensity only to the first part (white region) of the gas flow. In addition, plasma defocusing results in a reduction in intensity in the gas region between the dashed lines, which contributes most significantly to the output power. This simulation example shows that plasma formation in the gas flow significantly reduces the peak laser intensity and restricts the high-intensity region of the pump radiation only to the upstream side of the gas flow. In Figure 9 the example shown, this upstream side is the left part of the gas flow. Thus, plasma defocusing affects the output power.

[0108] The characteristics of the emitted radiation can be customized by changing the profile of the gas flow or the so-called gas profile or the so-called gas flow profile - optionally by changing the gas density of the gas flow along the propagation direction. The profile of the gas flow can suppress the energy divergence of the pump radiation within the gas flow, where the energy divergence is caused by the fact that a part of the gas flow is ionized by the pump radiation (optionally by the plasma defocusing effect). The profile of the gas flow can be shaped by adjusting the geometry of the gas nozzle. For example, the shape of the opening in the exit plane is typically symmetric with respect to a plane perpendicular to the propagation direction of the pump radiation, which produces a gas flow with a symmetric or approximately symmetric distribution along the propagation direction, such as Figure 9 the gas profile 911 in (a). The shape of the opening in the exit plane can also be made asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation, which is called an asymmetric opening, such as Figure 7 the opening 701 in (a), which will be discussed in the following text. The asymmetric opening can produce a gas flow with an asymmetric shape along the propagation direction, such as Figure 7The gas profiles 719, 729, and 739 in (c), which will also be discussed in the following text. The asymmetric profile of the gas density of the gas flow that may result from the asymmetric opening can eliminate or suppress the plasma defocusing effect at a sufficiently high gas pressure (optionally above the phase matching pressure), and result in a higher output power, optionally with a better radiation quality.

[0109] In addition to changing the shape of the opening in the exit plane, other parameters of the geometry of the gas nozzle can also be adapted to shape the profile of the gas flow. Optionally, the internal cross-sectional area of the gas nozzle in a plane parallel to the exit plane can be adjusted. Optionally, for at least a portion of the gas nozzle, the internal cross-sectional area can increase along the gas flow direction, optionally linearly. Optionally, the irradiation source can include an adjustable element for changing the profile of the gas flow. Optionally, the adjustable element can be used to change the profile of the gas flow during the generation of the emitted radiation. Optionally, the above parameters of the geometry of the gas nozzle can be adaptively combined.

[0110] In Figure 10 an example of the influence of the gas flow profile on the output power of the emitted radiation was simulated. The gas flow length and the pump radiation were fixed. Figure 10 (a) shows a schematic diagram of the gas pressure profile along the propagation direction X. The vertical axis P represents the pressure or gas density of the gas flow. The two vertical lines represent the gas density at two specific positions on the gas profile, which are respectively referred to as the first pressure and the second pressure. Along the propagation direction X, the gas density gradually increases before the first pressure 1011 and gradually decreases after the second pressure 1013. The gas density varies linearly between the first pressure 1011 and the second pressure 1013. Note that the linear variation between the first pressure 1011 and the second pressure 1013 is only for simplifying the simulation, and in practice, the variation of the gas density between these two vertical lines does not need to be linear. Note that the shape of the simulated gas profile is only an example, and in practice, the profile of the gas flow can have other shapes.

[0111] During the simulation, the first pressure and the second pressure independently vary over a set of different values, and the resulting output power of the emitted radiation as a function of the first pressure and the second pressure, represented by the axes P1013 and P1011, is shown in a grayscale plot of the output power 1003, as Figure 10 (b) shows. The dark color in the plot 1003 represents low output power, while the light color represents high output power. The solid line 1025 represents pairs of the first pressure and the second pressure, where the first pressure and the second pressure are equal, for example, having a profile 911 of the gas flow with a typical symmetric shape along the Figure 9 (a) propagation direction. The dashed line 1027 represents the case where the first pressure is half of the second pressure. Figure 9The two examples 901 and 903 in (a) and (b) are respectively represented by the crosses 1023 and 1021. As Figure 9 As can be seen from the simulation results in (b), in the region near the y-axis, that is, in the region where the first pressure is relatively low, the highest output power is obtained.

[0112] Figure 9 (b) shows Figure 9 A comparative simulation of the simulation in (a), showing the pump radiation intensity distribution 903 with an asymmetric-shaped gas flow profile 913, where the gas density of the gas flow first increases to a maximum and then drops sharply in the cut-off region along the propagation direction. Along the propagation direction, the interaction region can be followed by a sharp cut-off region to reduce the reabsorption of the emitted radiation by the gas flow. Optionally, the length of the cut-off region of the gas flow profile in the propagation direction of the pump radiation is less than 500 μm. Optionally, the length of the cut-off region of the gas flow profile in the propagation direction of the pump radiation is less than 200 μm. Optionally, the length of the cut-off region of the gas flow profile in the propagation direction of the pump radiation is less than 100 μm. Optionally, the length of the cut-off region of the gas flow profile in the propagation direction of the pump radiation is less than 50 μm. The arrow 923 represents the central axis and the propagation direction of the pump radiation. The two vertical dashed lines 933 represent the region of the gas flow 615 along the propagation direction of the pump radiation, which contributes the most to the emitted radiation. The gas flow 615 between the two dashed lines 933 can be called the interaction region. The maximum gas pressure here is the same as Figure 9 that in (a).

[0113] It should be understood that the gas flow distribution 913 is only exemplary to illustrate the principle of the present disclosure. In practice, any similar gas flow profile, such as having a bulge or twist, can have a similar effect, and many specific embodiments can be envisioned according to the principle of the present disclosure.

[0114] In Figure 9 (b), compared with Figure 9 (a), the plasma defocusing effect is smaller because the upstream gas pressure is lower. As a result, the high-intensity region (bright region) extends to the downstream part of the gas flow profile, which, in the Figure 9 example shown, is the right part of the gas flow, resulting in a higher output power of the emitted radiation. In this simulation, compared with the case of a symmetric gas profile in Figure 9 (a), Figure 9 the asymmetric gas profile in (b) results in an increase in the total output power of about 50%.

[0115] The effects of plasma defocusing may be most significant when it occurs in the upstream portion, since the pump radiation may subsequently be affected over the entire length of the gas flow. In contrast, good phase matching may be most important in the downstream portion of the gas, since there the emitted radiation contributes a large portion of the total output power, and the emitted radiation from the downstream portion of the gas profile is least reabsorbed. In one embodiment, the profile of the gas flow is shaped such that the pressure on the downstream side is optimized to achieve optimal phase matching and therefore optimal output power, while the pressure on the upstream side is reduced to reduce the effects of plasma defocusing. In this way, the conflicting requirements of high pressure for phase matching on the one hand and low pressure for reducing plasma defocusing on the other hand can be separated at least to some extent by applying them to different parts of the gas flow profile.

[0116] As described above, by using a gas nozzle with an adjusted geometry, the above-mentioned gas flow profile can be obtained, wherein the gas density of the gas flow first increases to a maximum value and then drops sharply in the cut-off region along the propagation direction. In one embodiment, the width of the opening increases gradually along the propagation direction of the pump radiation. Optionally, the shape of the opening is a trapezoid.

[0117] Figure 7 (a) shows a schematic diagram of an example 701 in which the shape of the opening 711 is a trapezoid, more specifically an isosceles trapezoid. Axis X represents the propagation direction of the pump radiation. Axis Y represents one of the other directions in the outlet plane perpendicular to X. Axis Z represents the direction perpendicular to the outlet plane and makes an acute angle with the gas flow direction. In one embodiment, the length of the first side 725 is 50 μm and the length of the second side 723 is one of 400 μm, 200 μm and 100 μm, in which case the shape of the opening in the outlet plane is asymmetric with respect to the plane perpendicular to the propagation direction of the pump radiation. A second side 723 of 50 μm was also simulated as a reference. The length of the opening 721 along the propagation direction of the pump radiation is 500 μm.

[0118] exist Figure 7 (b) and Figure 7 (c) shows the Figure 7 The corresponding simulated gas density distribution plot 715 and contour plot 703 of the opening 711 in (a) along the airflow propagation direction. Figure 7 In (b), the schematic box 713 represents a part of the gas nozzle 609, wherein the opening 701 is in its outlet plane, which is the bottom side of the box. The length of the second side 723 is 400 μm in this example.

[0119] The drawing 703 includes gas profiles 719, 729, 739, and 749 with lengths of 400 μm, 200 μm, 100 μm, and 50 μm respectively on the second side. The vertical axis P represents gas density. It can be seen that when the second side 723 is greater than the first side 725, the gas profile has an asymmetric shape along the propagation direction, and the gas density of the air flow first increases to a maximum value and then sharply decreases in the cut-off region along the propagation direction represented by X.

[0120] It should be understood that the trapezoidal shape is merely exemplary to illustrate the principles of the present disclosure. In practice, any shape with an opening width that gradually increases along the propagation direction of the pump radiation can produce a similar profile, and many specific implementations can be envisioned in accordance with the principles of the present disclosure.

[0121] As described above, the internal cross-sectional area of the gas nozzle in a plane parallel to the exit plane is optionally adapted together with the adjustable element to change the profile of the air flow, as Figure 8 shown in the embodiment. As Figure 8 visible in the schematic diagram of the gas nozzle 803 in (b), the inner surface 815 of the gas nozzle varies in such a way that for at least a part of the gas nozzle, the internal cross-sectional area increases along the air flow direction, optionally linearly. The part of the gas nozzle with an increasing internal cross-sectional area (which can be referred to as divergent) can cause gas expansion, a decrease in gas density, and / or an increase in gas flow velocity. For the adapted geometry of the gas nozzle as shown in Figure 8 (b), the volume of the air flow has a sharper boundary compared to the air flow without divergence, which can contribute to, for example, generating a relatively small cut-off region length. In the schematic diagram of the gas nozzle 803 in Figure 8 (b), the internal cross-sectional area of the gas nozzle is symmetric along the gas flow direction before leaving the opening, but in practice, the internal cross-section of the gas nozzle can also be asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation, which can produce an asymmetric-shaped gas flow profile, such as Figure 9 the gas flow profile 913 in (b). In one embodiment, the internal cross-section of the gas nozzle has the same shape as the embodiment of the opening 711 in Figure 7 (a), which is asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation, such as the plane including axes Y and Z.

[0122] An example of the gas nozzle 803 can include an adjustable element 813. Figure 8 (a) and Figure 8 (b) show cross-sections of the adjustable element 813. The adjustable element 813 is, for example, wedge-shaped. It should be noted that the adjustable element 813 can also have other shapes. As Figure 8As shown in (b), an adjustable element 813 that can be positioned between the exit plane and the pump radiation can further change the profile of the gas flow. The adjustable element 813 can be configured to be at least partially positioned within the gas flow. After leaving the exit plane, the gas flow can impinge on the adjustable element, and one of the surfaces of the adjustable element is inclined in the direction of the gas flow. The gas flow exits through a gas nozzle, optionally having an increased internal cross-sectional area, and can be compressed by the adjustable element 813 disposed after the exit plane of the gas nozzle. The adjustable element can shape the gas flow profile and can generate a shock wave, which is indicated by the white arrows and dashed lines in Figure 8 (b). The shock wave can compress the gas flow into a high-density region near the adjustable element 813, and this region is represented by the region within the dashed ellipse in Figure 8 (b). The region between the adjustable element 813 and the shock wave can have a higher density, and there can be a sharp change in density across the shock wave. Since the length of the shock wave along the propagation direction of the pump radiation is several tens of micrometers, a relatively small cut-off region length along the propagation direction of the pump radiation can be achieved, optionally a cut-off region length less than 100 μm. After impinging on the adjustable element, the gas flow with a changed profile will further expand into the surrounding, which can be a vacuum or near-vacuum.

[0123] Optionally, the position of the adjustable element relative to the gas flow is adjustable. The adjustable element can be tuned in rotational and translational directions to optimize the emitted radiation during the generation of the emitted radiation. Tuning the adjustable element can shape the profile of the gas flow, which can further change the characteristics of the emitted radiation, optionally further optimizing the characteristics of the emitted radiation.

[0124] In Figure 8 (a) and Fig. (b), the adjustable element is placed along the gas flow direction after the exit plane, while in practice it can also be placed before leaving the exit plane and be part of the inner surface of the gas nozzle, which can shape the profile of the gas flow such that the gas density of the gas flow first increases to a maximum value and then sharply decreases in the cut-off region along the propagation direction, similar to that shown in Figure 8 (c).

[0125] Figure 8(a) A simulated gas density distribution plot 801 with a gas nozzle 811 and an adjustable element 813 is shown in grayscale. Axis X represents the propagation direction of the pump radiation. Axis Y represents one of the other directions perpendicular to X in the exit plane. Axis Z represents the direction perpendicular to the exit plane and makes an acute angle with the gas flow direction. The gas density distribution is represented in grayscale, with dark colors in the plot indicating low gas density and light colors indicating high gas density. The position of the shock wave is shown as a sharp change in gas density. In this embodiment, the divergence is in the Y direction. Note that the divergence does not need to have a symmetric cross-sectional area in a plane parallel to the exit plane.

[0126] An example of the pump radiation 817 propagates through the altered gas flow in the propagation direction shown by the black arrow in Figure 8 (b). The gas density measured along the propagation direction can have a profile for which the gas density of the gas flow first increases to a maximum value and then drops sharply in a cut-off region along the propagation direction. Figure 8 (c) shows the simulated gas distribution along the propagation direction at varying distances from the adjustable element. For the gas profile examples 821, 823, and 825, the distances from the adjustable element are 300 μm, 400 μm, and 500 μm respectively. It can be seen that the gas density of the gas flow first increases to a maximum value and then drops sharply in a cut-off region along the propagation direction. In one embodiment, there may be bulges or so-called kinks in the gas profile on the upstream side and / or downstream side of the gas flow, which form the gas profile into a zigzag shape. The bulges may be caused by boundary effects due to the adjustable element.

[0127] It should be understood that the shapes of the above gas profiles are only exemplary to illustrate the principles of the present disclosure, and many specific embodiments can be envisioned in accordance with the principles of the present disclosure.

[0128] Figure 8 Another benefit of this embodiment in is that it is able to produce an optimal gas profile at a significant distance (optionally 400 μm) from the nozzle, rather than being forced to make a sub-optimal compromise between being as close to the nozzle as possible for, for example, good distribution on the one hand and being far enough away from the nozzle to avoid, for example, damage and laser clipping on the other hand.

[0129] Compared with using a gas shaping element including a hole for transmitting the generated measurement radiation, one embodiment of which is in the patent application WO2018 / 166741A1 Figure 11Compared with (as shown in), the advantage of using the adjustable element 813 is that when the adjustable element 813 is positioned between the exit plane and the pump radiation, the alignment of the pump radiation is easier. When using the embodiments in WO2018166741A1, if the challenging precise alignment here is not achieved, the gas forming element may be prone to burning due to the high power of the pump radiation. WO2018 / 166741A1 is incorporated herein by reference in its entirety.

[0130] In addition to the above embodiments, a system with two gas jets having two different gases can also produce a similar gas profile, an example of which is shown in FIG. 16 of patent application WO2018 / 166741A1. Compared with the system of two gas nozzles, the advantage of using an adapted gas nozzle is that due to the uniform gas composition of the gas flow, the optimization of the emitted radiation is easier, and the vacuum or near-vacuum atmosphere in the inspection chamber 350 is easier to maintain.

[0131] During the generation of the emitted radiation, the gas nozzle may be subjected to both a cooling effect and a heating effect. Due to acceleration and rapid expansion, the gas flow leaving the opening can have a low temperature, optionally about 200K, which can cool the gas nozzle. For a 3mm gas nozzle made of nickel, the shrinkage along the gas nozzle direction can be about 20μm, which is not negligible compared to the distance between the pump radiation and the gas nozzle (e.g., 50 - 100μm) and the focal spot diameter of the pump radiation (e.g., 20 - 30μm). On the other hand, the pump radiation can have a high intensity at or near the interaction region and can heat or even burn the gas nozzle, depending on the distance between the pump radiation and the gas nozzle. During the generation of the emitted radiation, the relative position between the pump radiation and the gas nozzle can be adjusted to optimize the emitted radiation. The combination of the heating effect and the cooling effect can introduce additional thermal expansion / contraction of the gas nozzle along the gas flow direction, and since the gas profile can vary along the gas flow direction, it can cause drift of the emitted radiation. In addition, opening and / or closing the gas flow during the process may also introduce drift.

[0132] Figure 11 A gas delivery system with a temperature control assembly, optionally a gas delivery system for an irradiation source, is schematically shown. The temperature control assembly can include a temperature control element 1109, which can be used to change the temperature of at least a part of the gas nozzle 609 or maintain the temperature near a desired set point. Optionally, the temperature control element 1109 can be a source that emits electromagnetic radiation, optionally a laser, or a heating element, optionally a heating wire. Optionally, the temperature control element 1109 can be a cooling element, such as a thermoelectric cooler or a liquid cooling system. Optionally, the temperature control element 1109 can be a thermostat that maintains at least a part of the gas nozzle near the desired set point.

[0133] The temperature control assembly may include a temperature control detector 1107, which may detect changes in the temperature or geometry of the gas nozzle. Optionally, the temperature control detector 1107 may be a camera. The camera may use the inferred measurements for temperature detection and / or detection of shape differences. Optionally, the temperature control detector 1107 may be a temperature sensor such as a thermometer. The signal obtained by the temperature control detector 1107 may be transmitted to the temperature control processor 1111. Based on the received signal, the temperature control processor 1111 may communicate with the temperature control element 1109 to control the temperature of at least a portion of the gas nozzle, which may be referred to as a feedback control loop.

[0134] All of the above embodiments may be used in a method of generating radiation using an irradiation source, as Figure 12 shown. The first step 200 is to deliver an air flow 615 in the irradiation source, which includes providing the air flow from an opening 617 in the exit plane of the gas nozzle 609 for receiving pump radiation having a propagation direction and for generating the emitted radiation at the interaction region. In this method, the geometry of the gas nozzle may be adapted to shape the profile of the air flow such that the gas density of the air flow first increases to a maximum value and then rapidly decreases in a cut-off region along the propagation direction. Optionally, there may be a second step 202, which provides pump radiation 611 having a propagation direction in the air flow 615. Optionally, there may be a third step 204, which generates the emitted radiation in the interaction region. More details of the method of generating radiation using an irradiation source are provided in the description of the embodiments described above in conjunction with the drawings and text.

[0135] Additional embodiments are disclosed in the subsequent numbered clauses:

[0136] 1. An irradiation source, comprising:

[0137] - A gas delivery system including a gas nozzle, wherein the gas nozzle includes an opening in an exit plane of the gas nozzle,

[0138] wherein the gas delivery system is configured to provide an air flow from the opening for generating the emitted radiation at an interaction region,

[0139] - wherein the irradiation source is configured to receive pump radiation having a propagation direction and to provide the pump radiation in the air flow,

[0140] wherein the geometry of the gas nozzle is adapted to shape the profile of the air flow such that the gas density of the air flow first increases to a maximum value and then rapidly decreases in a cut-off region along the propagation direction.

[0141] 2. The irradiation source according to clause 1, wherein the profile of the gas flow is used to suppress the energy divergence of the pump radiation within the gas flow, and the energy divergence is caused by the fact that a part of the gas flow is ionized by the pump radiation.

[0142] 3. The irradiation source according to clause 1 or 2, wherein the maximum value is higher than the phase matching pressure.

[0143] 4. The irradiation source according to any one of the preceding clauses, wherein the length of the cut-off region of the profile of the gas flow in the propagation direction of the pump radiation is less than 100 μm.

[0144] 5. The irradiation source according to any one of the preceding clauses, wherein the shape of the opening in the exit plane is asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation.

[0145] 6. The irradiation source according to any one of the preceding clauses, wherein the width of the opening gradually increases in the propagation direction of the pump radiation.

[0146] 7. The irradiation source according to clause 5 or 6, wherein the shape of the opening is trapezoidal.

[0147] 8. The irradiation source according to clause 7, wherein the shape of the opening is isosceles trapezoidal.

[0148] 9. The irradiation source according to any one of the preceding clauses, wherein the internal cross-sectional area of the gas nozzle in a plane parallel to the exit plane increases for at least a part of the gas nozzle in the direction of the gas flow.

[0149] 10. The irradiation source according to any one of the preceding clauses, wherein the irradiation source includes an adjustable element for changing the profile of the gas flow.

[0150] 11. The irradiation source according to clause 10, wherein the adjustable element is used to change the profile of the gas flow during the generation of the emitted radiation.

[0151] 12. The irradiation source according to clause 10 or 11, wherein the adjustable element is configured to be at least partially positioned within the gas flow.

[0152] 13. The irradiation source according to any one of the preceding clauses, wherein the irradiation source includes a pump radiation source operable to emit the pump radiation.

[0153] 14. The irradiation source according to any one of the preceding clauses, wherein the irradiation source is used for high harmonic generation.

[0154] 15. An irradiation source according to any of the preceding clauses, wherein the gas flow is provided by the gas delivery system into an evacuated or near-evacuated space.

[0155] 16. An irradiation source according to any of the preceding clauses, wherein the emitted radiation has a wavelength in the X-ray or EUV range, wherein the wavelength is in the range of 0.01 nm to 100 nm, optionally 0.1 nm to 100 nm, optionally 1 nm to 100 nm, optionally 1 nm to 50 nm, or optionally 10 nm to 20 nm.

[0156] 17. An irradiation source according to any of the preceding clauses, wherein in operation, the emitted radiation is directed to a target on a wafer.

[0157] 18. An irradiation source according to any of the preceding clauses, wherein the emitted radiation is used for metrology measurements.

[0158] 19. An irradiation source according to any of the preceding clauses, wherein the irradiation source includes a temperature control component.

[0159] 20. A metrology device comprising an irradiation source according to any one of clauses 1 to 19.

[0160] 21. A lithography unit comprising an irradiation source according to any one of clauses 1 to 19.

[0161] 22. A method for delivering a gas in an irradiation source, comprising:

[0162] - providing a gas flow from an opening in the exit plane of a gas nozzle for receiving pump radiation having a propagation direction and for generating emitted radiation at an interaction region;

[0163] wherein the geometry of the gas nozzle is adapted to shape the profile of the gas flow such that the gas density of the gas flow first increases to a maximum and then rapidly decreases in a cut-off region along the propagation direction.

[0164] 23. An irradiation source, comprising:

[0165] a gas delivery system including a gas nozzle, wherein the gas nozzle includes an opening in the exit plane of the gas nozzle, wherein the gas delivery system is configured to provide a gas flow from the opening for generating emitted radiation at an interaction region, and

[0166] an adjustable element for changing the profile of the gas flow,

[0167] wherein the irradiation source is configured to receive pump radiation having a propagation direction and to provide the pump radiation in the gas flow,

[0168] wherein the adjustable element is positioned between the exit plane and the pump radiation.

[0169] 24. The illumination source according to clause 23, wherein the profile of the gas flow is such that the gas density of the gas flow first increases to a maximum value and then decreases sharply in the cut-off region along the propagation direction.

[0170] 25. The illumination source according to clause 24, wherein the maximum value is higher than the phase matching pressure.

[0171] 26. The illumination source according to any one of the preceding clauses, wherein the profile of the gas flow is used to suppress the energy divergence of the pump radiation within the gas flow.

[0172] 27. The illumination source according to clause 26, wherein the energy divergence is caused by the fact that a part of the gas flow is ionized by the pump radiation.

[0173] 28. The illumination source according to any one of the preceding clauses, wherein the adjustable element is used to change the profile of the gas flow during the generation of the emitted radiation.

[0174] 29. The illumination source according to any one of the preceding clauses, wherein the adjustable element is configured to be at least partially positioned within the gas flow.

[0175] 30. The illumination source according to any one of the preceding clauses, wherein the length of the cut-off region of the profile of the gas flow in the propagation direction of the pump radiation is less than 100 μm.

[0176] 31. The illumination source according to any one of the preceding clauses, wherein the shape of the opening in the exit plane is asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation.

[0177] 32. The illumination source according to any one of the preceding clauses, wherein the width of the opening gradually increases along the propagation direction of the pump radiation.

[0178] 33. The illumination source according to clause 31 or 32, wherein the shape of the opening is trapezoidal.

[0179] 34. The illumination source according to clause 33, wherein the shape of the opening is an isosceles trapezoid.

[0180] 35. The illumination source according to any one of the preceding clauses, wherein the internal cross-sectional area of the gas nozzle in a plane parallel to the exit plane increases for at least a part of the gas nozzle along the direction of the gas flow.

[0181] 36. An illumination source according to any of the preceding clauses, wherein the illumination source comprises a pump radiation source operable to emit the pump radiation.

[0182] 37. An illumination source according to any of the preceding clauses, wherein the illumination source is for high harmonic generation.

[0183] 38. An illumination source according to any of the preceding clauses, wherein the gas flow is provided by the gas delivery system into an evacuated or near-evacuated space.

[0184] 39. An illumination source according to any of the preceding clauses, wherein the emitted radiation has a wavelength in the X-ray or EUV range, wherein the wavelength is in the range of 0.01 nm to 100 nm, optionally 0.1 nm to 100 nm, optionally 1 nm to 100 nm, optionally 1 nm to 50 nm, or optionally 10 nm to 20 nm.

[0185] 40. An illumination source according to any of the preceding clauses, wherein in operation, the emitted radiation is directed to a target on a wafer.

[0186] 41. An illumination source according to any of the preceding clauses, wherein the emitted radiation is for metrology measurements.

[0187] 42. An illumination source according to any of the preceding clauses, wherein the illumination source comprises a temperature control component.

[0188] 43. An illumination source according to any of the preceding clauses, wherein the pump radiation comprises pulses.

[0189] 44. A metrology device comprising an illumination source according to any one of clauses 23 to 43.

[0190] 45. A lithography unit comprising an illumination source according to any one of clauses 23 to 43.

[0191] 46. A method of delivering gas in an illumination source, comprising:

[0192] providing a gas flow from an opening in an exit plane of a gas nozzle for receiving pump radiation having a propagation direction and for generating emitted radiation at an interaction region, and

[0193] changing a profile of the gas flow with an adjustable element,

[0194] wherein the adjustable element is positioned between the exit plane and the pump radiation.

[0195] 47. An illumination source, comprising:

[0196] - A gas delivery system including a gas nozzle, wherein the gas nozzle includes an opening in an exit plane of the gas nozzle,

[0197] - wherein the gas delivery system is configured to provide an air flow from the opening for generating emitted radiation at an interaction region,

[0198] - wherein the irradiation source is configured to receive pump radiation having a propagation direction and provide the pump radiation in the air flow,

[0199] - wherein the shape of the opening in the exit plane is asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation.

[0200] 48. The irradiation source according to clause 47, wherein the geometry of the gas nozzle is adapted to shape the profile of the air flow such that the gas density of the air flow first increases to a maximum value and then sharply decreases in a cut-off region along the propagation direction.

[0201] 49. The irradiation source according to clause 48, wherein the profile of the air flow is used to suppress the energy divergence of the pump radiation within the air flow.

[0202] 50. The irradiation source according to clause 49, wherein the energy divergence is caused by the fact that a part of the air flow is ionized by the pump radiation.

[0203] 51. The irradiation source according to any one of clauses 48 to 50, wherein the maximum value is higher than the phase matching pressure.

[0204] 52. The irradiation source according to any one of clauses 48 to 51, wherein the length of the cut-off region of the profile of the air flow in the propagation direction of the pump radiation is less than 100 μm.

[0205] 53. The irradiation source according to any of the preceding clauses, wherein the width of the opening gradually increases along the propagation direction of the pump radiation, optionally, the shape of the opening is trapezoidal, optionally, the shape of the opening is isosceles trapezoidal.

[0206] 54. The irradiation source according to any of the preceding clauses, wherein the internal cross-sectional area of the gas nozzle in a plane parallel to the exit plane increases for at least a part of the gas nozzle along the direction of the air flow.

[0207] 55. The irradiation source according to any of the preceding clauses, wherein the irradiation source includes an adjustable element for changing the profile of the air flow.

[0208] 56. The irradiation source according to clause 55, wherein the adjustable element is used to change the profile of the gas flow during the generation of the emitted radiation.

[0209] 57. The irradiation source according to clause 54 or 55, wherein the adjustable element is configured to be at least partially positioned in the gas flow.

[0210] 58. The irradiation source according to any of the preceding clauses, wherein the gas flow is provided by the gas delivery system into an evacuated or near-evacuated space.

[0211] 59. The irradiation source according to any of the preceding clauses, wherein the emitted radiation has a wavelength in the X-ray or EUV range, wherein the wavelength is in the range of 0.01 nm to 100 nm, optionally 0.1 nm to 100 nm, optionally 1 nm to 100 nm, optionally 1 nm to 50 nm, or optionally 10 nm to 20 nm.

[0212] 60. The irradiation source according to any of the preceding clauses, wherein the irradiation source includes a temperature control component.

[0213] 61. A metrology device or a lithography unit, comprising the irradiation source according to any one of clauses 47 to 60.

[0214] 62. A method for delivering gas in an irradiation source, comprising:

[0215] Providing a gas flow from an opening in the exit plane of a gas nozzle for receiving pump radiation having a propagation direction and for generating emitted radiation at an interaction region;

[0216] Wherein the shape of the opening in the exit plane is asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation.

[0217] Although specific reference may be made herein to the use of a lithography apparatus in the manufacture of ICs, it should be understood that the lithography apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, the guiding and detecting patterns of magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0218] Although embodiments may be specifically referred to herein in the context of a lithography apparatus, the embodiments may be used in other devices. The embodiments may form part of a mask inspection device, a metrology device or any device for measuring or processing an object such as a wafer (or other substrate) or a mask (or other patterning device). These devices are commonly referred to as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0219] Although embodiments may be specifically referred to herein in the context of inspection or metrology apparatus, the embodiments may be used in other apparatus. Embodiments may form part of a mask inspection apparatus, a lithographic apparatus, or any apparatus for measuring or processing an object such as a wafer (or other substrate) or a mask (or other patterning device). The term "metrology apparatus" (or "inspection apparatus") may also refer to an inspection apparatus or inspection system (or metrology apparatus or metrology system). That is, for example, an inspection apparatus including an embodiment may be used to detect defects on a substrate or defects in a structure on a substrate. In such an embodiment, the property of interest of the structure on the substrate may relate to defects in the structure, the absence of a particular part of the structure, or the presence of an unwanted structure on the substrate.

[0220] Although the use of embodiments has been specifically referred to 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 allows.

[0221] Although the above-described target or target structure (more generally, a structure on a substrate) is a metrology target structure specifically designed and formed for measurement purposes, in other embodiments, the property of interest may be measured on one or more structures that are functional components of a device formed on a substrate. Many devices have a regular grating-like structure. The terms "structure", "target grating" and "target structure" as used herein do not require that the structure be provided specifically for the measurement being performed. Furthermore, the pitch of the metrology target may be close to the resolution limit of the optical system of a scatterometer, or may be smaller, but may be much larger than the size of a typical non-target structure (optionally a product structure) that is fabricated by a lithographic process in the target portion C. In practice, the lines and / or spaces of the nested grating within the target structure may include smaller structures having dimensions similar to those of the non-target structure.

[0222] Although specific embodiments have been described above, it should be understood that the invention may be implemented in a different manner than that described. The above description is intended to be illustrative and not restrictive. Thus, it will be apparent to those skilled in the art that the described invention may be modified without departing from the scope of the claims set forth below.

[0223] Although specific reference is made to "measurement device / instrument / system" or "inspection device / instrument / system", these terms may refer to the same or similar types of tools, devices or systems. That is, for example: an inspection or measurement device including an embodiment of the present invention can be used to determine the characteristics of a structure on a substrate or a wafer. That is, for example: an inspection device or measurement device including an embodiment of the present invention can be used to detect defects of a substrate or defects of a structure on a substrate or a wafer. In such an embodiment, the characteristics of interest of the structure on the substrate may relate to defects in the structure, the absence of a specific part of the structure, or the presence of an unwanted structure on the substrate or the wafer.

[0224] Although specific reference is made to SXR and EUV electromagnetic radiation, it should be understood that, where the context permits, the present invention can be implemented with all electromagnetic radiation, including radio waves, microwaves, infrared rays, (visible) light, ultraviolet rays, X-rays and gamma rays. As an alternative to optical measurement methods, the use of X-rays, optionally hard X-rays, for example radiation having a wavelength range between 0.01 nm and 10 nm, or optionally between 0.01 nm and 0.2 nm, or optionally between 0.1 nm and 0.2 nm, is also contemplated for measurement.

Claims

1. An irradiation source, comprising: - A gas delivery system including a gas nozzle, wherein the gas nozzle includes an opening in an exit plane of the gas nozzle, and - An adjustable element, the adjustable element being fully positioned between the exit plane and pump radiation having a propagation direction, wherein the gas delivery system is configured to provide an air flow from the opening for generating the emitted radiation at an interaction region, wherein the irradiation source is configured to receive the pump radiation and provide the pump radiation in the air flow, wherein the adjustable element is configured to change the profile of the air flow.

2. The irradiation source according to claim 1, wherein the adjustable element is adapted to shape the profile of the air flow such that the gas density of the air flow first increases to a maximum value and then rapidly decreases in a cut-off region along the propagation direction.

3. The irradiation source according to claim 1, wherein the profile of the air flow is used to suppress the energy divergence of the pump radiation within the air flow, wherein the energy divergence is caused by the fact that a portion of the air flow is ionized by the pump radiation.

4. The irradiation source according to claim 2, wherein the maximum value is higher than the phase matching pressure.

5. The irradiation source according to any one of claims 1 to 4, wherein the length of the cut-off region of the profile of the air flow in the propagation direction of the pump radiation is less than 100 μm.

6. The irradiation source according to any one of claims 1 to 4, wherein the shape of the opening in the exit plane is asymmetric with respect to a plane perpendicular to the propagation direction of the pump radiation.

7. The irradiation source according to any one of claims 1 to 4, wherein the width of the opening gradually increases along the propagation direction of the pump radiation.

8. The irradiation source according to claim 6, wherein the shape of the opening is trapezoidal.

9. The irradiation source according to claim 8, wherein the shape of the opening is an isosceles trapezoid.

10. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the internal cross-sectional area of the gas nozzle in a plane parallel to the exit plane increases for at least a portion of the gas nozzle along the direction of the air flow.

11. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the adjustable element is used to change the profile of the air flow during the generation of the emitted radiation.

12. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the adjustable element is configured to be at least partially positioned within the air flow.

13. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the irradiation source includes a pump radiation source capable of operating to emit the pump radiation.

14. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the irradiation source is for high harmonic generation.

15. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the gas flow is provided by the gas delivery system into an evacuated or near - evacuated space.

16. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the emitted radiation has a wavelength in the X - ray or EUV range, wherein the wavelength is in the range of 0.01 nm to 100 nm, optionally 0.1 nm to 100 nm, optionally 1 nm to 100 nm, optionally 1 nm to 50 nm, or optionally 10 nm to 20 nm.

17. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein in operation, the emitted radiation is directed to a target on a wafer.

18. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the emitted radiation is used for metrology measurements.

19. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the irradiation source includes a temperature control component.

20. The irradiation source according to any one of claims 1 - 4, 8, and 9, wherein the pump radiation includes pulses.

21. A metrology device comprising the irradiation source according to any one of claims 1 to 20.

22. A lithography unit comprising the irradiation source according to any one of claims 1 to 20.

23. A method of delivering gas in an irradiation source, comprising: - providing a gas flow from an opening in the exit plane of a gas nozzle for receiving pump radiation having a propagation direction and for generating emitted radiation at an interaction region; - providing an adjustable element positioned entirely between the exit plane and the pump radiation, wherein the adjustable element is configured to change the profile of the gas flow.

24. The method according to claim 23, wherein the profile of the gas flow is changed such that the gas density of the gas flow first increases to a maximum value and then rapidly decreases in a cut - off region along the propagation direction.

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