Illumination source and associated metrology apparatus

Abstract

An illumination source is disclosed, comprising: a gas delivery system configured to provide a gas target for generating emission radiation at an interaction region of the gas target; and an interferometer to illuminate at least a portion of the gas target with interferometer radiation to measure a property of the gas target.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to European Application 20187019.3, filed on 21 July 2020; European Application 20192841.3, filed on 26 August 2020; and European Application 21169180.3, filed on 19 April 2021, the entire contents of which are incorporated herein by reference.

[0003] This invention relates to an irradiation source, a measuring device, and a method for inspecting a gas target, i.e., a gas target, of the irradiation source. Background Technology

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

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

[0006] Low-k1 lithography can be used to process features smaller than the classical resolution limit of the lithography apparatus. In this process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of radiation used, NA is the numerical aperture of the projection optics in the lithography apparatus, CD is the critical size (typically the smallest feature size printed, but in this case, half-pitch), and k1 is an empirical resolution factor. Generally, the smaller k1 is, the more difficult it becomes to reproduce patterns on the substrate that resemble the shape and size planned by the circuit designer to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection apparatus and / or design layout. These steps include, for example, but not limited to: optimization of NA, custom illumination schemes, use of phase-shifted 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 lithography apparatus can be used to improve the reproduction of the pattern at low k1.

[0007] During photolithography, it is often desirable to measure the resulting structure, for example, for process control and verification. Various tools are known for performing such measurements, including scanning electron microscopes, frequently used to measure critical dimensions (CD), and specialized tools for measuring overlap (the accuracy of alignment between two layers in a device). Recently, various forms of scattering instruments have been developed for use in the field of photolithography.

[0008] Examples of known scatterers typically rely on the availability of a dedicated measurement target. For instance, the method might require a target in the form of a simple grating, large enough that the measurement beam produces a spot smaller than the grating (i.e., the grating is not fully filled). In so-called reconstruction methods, the properties of the grating are calculated by simulating the interaction between the scattered radiation and a mathematical model of the target structure. The model parameters are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0009] Besides measuring feature shapes via reconstruction, such devices can also be used to measure diffraction-based overlap, as described in published patent application US2006066855A1. Diffraction-based overlap measurement using dark-field imaging with diffraction orders enables overlap measurements of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by the product structure on a wafer. Examples of dark-field imaging measurements can be found in numerous published patent applications, such as, for example, US2011102753A1 and US20120044470A. Multiple gratings can be measured in a single image using composite grating targets. Known scatterometers tend to use light in the visible or near-infrared (IR) wavelength range, which requires the grating pitch to be much coarser than the actual product structure (whose properties are those of actual interest). Such product features can be defined using deep ultraviolet (DUV) or extreme ultraviolet (EUV) radiation with much shorter wavelengths. Unfortunately, such wavelengths are generally unavailable or unusable for measurement.

[0010] On the other hand, modern product structures are so small that they cannot be imaged using optical metrology techniques. Small features include, for example, those formed by multiple patterning processes and / or pitch multiplication. Therefore, targets used for high-volume metrology typically use features much larger than the product itself (where overlap error or critical dimensions are the properties of concern). Measurement results are only indirectly related to the dimensions of the actual product structure, and may be inaccurate because the measured target is not subjected to the same distortions under optical projection in a lithography apparatus, and / or to different treatments in other steps of the manufacturing process. While scanning electron microscopy (SEM) can directly resolve these modern product structures, SEM is significantly more time-consuming than optical measurements. Furthermore, electrons cannot penetrate thick process layers, making them less suitable for metrology applications. Other techniques, such as using contact pads to measure electrical properties, are also known, but only provide indirect evidence of the actual product structure.

[0011] By reducing the wavelength of the radiation used during measurement, smaller structures can be resolved, increasing sensitivity to structural changes in said structure and / or additional penetration into the product structure. One method for generating suitable high-frequency radiation (e.g., hard X-rays, soft X-rays, and / or EUV radiation) can be to excite the generating medium using pump radiation (e.g., infrared radiation), thereby generating emitted radiation, optionally including the generation of higher harmonics of the high-frequency radiation. Summary of the Invention

[0012] According to a first aspect of this disclosure, an irradiation source is provided, comprising: a gas delivery system configured to provide a gas target for generating emitted radiation at an interaction region of the gas target; and an interferometer configured to irradiate at least a portion of the gas target using interferometer radiation to measure the properties of the gas target.

[0013] Optionally, the irradiation source is configured to receive pump radiation and provide the pump radiation at the interaction region.

[0014] Optionally, the interferometer radiation has an interferometer wavelength, and the pump radiation has a pump wavelength, wherein the interferometer wavelength and the pump wavelength are different.

[0015] Optionally, the interferometer radiation and the pump radiation include pulses.

[0016] Optionally, the pulses emitted by the interferometer and the pulses emitted by the pump are at least partially synchronized.

[0017] Optionally, the interferometer radiation is a second-order or higher-order harmonic of the interferometer pump radiation generated by the harmonic generation process.

[0018] Optionally, the interferometer radiation is a second or third harmonic of the interferometer pump radiation generated by the harmonic generation process.

[0019] Optionally, the interferometer pump radiation and the pump radiation are separated from the radiation source.

[0020] Optionally, the irradiation source includes a reflective surface having a pinhole for separating the interferometer pump radiation and the pump radiation.

[0021] Optionally, during operation, the interferometer pump radiation passes through the pinhole, and the pump radiation is reflected by the reflective surface.

[0022] Optionally, the power of the interferometer pump radiation is at least an order of magnitude lower than the power of the pump radiation.

[0023] Optionally, the irradiation source includes a time delay unit for adjusting the time delay between the pulses radiated by the interferometer and the pulses radiated by the pump.

[0024] Optionally, the irradiation source includes a feedback loop or a feedforward loop based on the properties of the gas target.

[0025] Optionally, the irradiation source includes a feedback loop to control the pump radiation or the properties of the gas delivery system based on the properties of the gas target.

[0026] Optionally, the interferometer includes two branches, wherein the first branch radiation passes at least partially through the gas target, and the second branch radiation does not pass through the gas target, wherein the first branch radiation and the second branch radiation interfere with each other.

[0027] Optionally, the gas delivery system includes a gas nozzle, and the interferometer radiation at least partially illuminates at least a portion of the gas nozzle.

[0028] Optionally, the interferometer includes an adjustable element for changing the propagation direction of the interferometer radiation.

[0029] Optionally, the irradiation source includes a space configured to be emptied, and the gas delivery system is configured to provide the gas target in the space.

[0030] Optionally, the emitted radiation has a wavelength in the X-ray or EUV range, wherein the wavelength is optionally in the range of 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.

[0031] According to another aspect of this disclosure, a measuring device is provided that includes an irradiation source as described above.

[0032] Optionally, the emitted radiation is directed onto a structure on a substrate during operation.

[0033] According to another aspect of this disclosure, a photolithography unit is provided, including an irradiation source or a measurement device as described above.

[0034] According to another aspect of this disclosure, a method for examining a gaseous target of an irradiation source is provided, comprising: using a gas delivery system to provide the gaseous target for generating emitted radiation at an interaction region of the gaseous target; and using interferometer radiation of an interferometer to irradiate at least a portion of the gaseous target to measure the properties of the gaseous target.

[0035] According to another aspect of this disclosure, a method for aligning pump radiation relative to a gas target is provided, comprising the steps of: providing the gas target using a gas delivery system; irradiating at least a portion of the gas target using interferometer radiation from an interferometer to measure the properties of the gas target; irradiating at least a portion of the gas target using pump radiation; and controlling the properties of at least one of the gas delivery system and the pump radiation based on the properties of the gas target measured by the scattering instrument.

[0036] According to another aspect of this disclosure, a method for optimizing emitted radiation output is provided, comprising the steps of: providing a gas target using a gas delivery system; irradiating at least a portion of the gas target using interferometer radiation from an interferometer to measure the properties of the gas target; irradiating at least a portion of the gas target using pump radiation; and controlling the properties of at least one of the gas delivery system and the pump radiation based on the properties of the gas target measured by the scattering instrument.

[0037] According to another aspect of this disclosure, a method for monitoring the evolution of a plasma over time is provided, comprising the steps of: providing a gas target using a gas delivery system; irradiating at least a portion of the gas target using interferometer radiation from an interferometer to measure the properties of the gas target; irradiating at least a portion of the gas target using pump radiation to initiate the evolution of the plasma in the gas target; and monitoring the evolution of the plasma over time based on the properties of the gas target measured by the interferometer. Attached Figure Description

[0038] Embodiments will now be described by way of example only with reference to the accompanying illustrative drawings, in which:

[0039] - Figure 1 A schematic schematic diagram of a photolithography apparatus is depicted;

[0040] - Figure 2 A schematic schematic diagram of the photolithography unit is depicted;

[0041] - Figure 3 A schematic representation depicting overall photolithography, illustrating the collaboration between three key technologies for optimizing semiconductor manufacturing;

[0042] - Figure 4 The scattering measurement device is shown schematically.

[0043] - Figure 5 The transmission scattering measurement device is shown schematically.

[0044] - Figure 6 A schematic representation of the measurement equipment using EUV and / or SXR radiation is depicted.

[0045] - Figure 7 A simplified schematic diagram of the irradiation source is depicted;

[0046] - Figure 8 A schematic representation of an illumination source with an interferometer is depicted;

[0047] - Figure 9 An embodiment of a schematic representation of an illumination source with an interferometer is depicted;

[0048] - Figure 10 The following are descriptions: (a) the stripes, (b) the extracted phase, and (c) the density distribution.

[0049] - Figure 11 A flowchart including the steps in a method for inspecting a gaseous target from an irradiation source;

[0050] - Figure 12 A flowchart including the steps in a method for aligning pump radiation relative to a gas target;

[0051] - Figure 13 Including flowcharts of the steps in the method for optimizing emitted radiation output;

[0052] - Figure 14 A flowchart of steps in a method for monitoring the evolution of plasma over time; -- Figures 15(a), 15(b) and 15(c) show an irradiation source including a gas delivery system configured to provide a first state and a second state. Detailed Implementation

[0053] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic and particle radiation, including ultraviolet radiation (e.g., with wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), EUV radiation (extreme ultraviolet radiation, e.g., with wavelengths in the range of about 5 nm to 100 nm), X-ray radiation, electron radiation, and other particle radiation.

[0054] As used herein, the terms "mask," "mask," or "patterning apparatus" can be broadly interpreted as referring to a general patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be generated in a target portion of a substrate. In this context, the term "optical valve" may also be used. Examples of other such patterning apparatuses besides classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.) include programmable mirror arrays and programmable LCD arrays.

[0055] Figure 1A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also referred to as an irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, EUV radiation, or X-ray radiation); a mask support (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the patterning apparatus MA to the radiation beam B onto a target portion C (e.g., a portion comprising one or more dies) of the substrate W.

[0056] In operation, the irradiation system IL receives a radiation beam from the radiation source SO, for example, via a beam delivery system BD. The irradiation system IL may include various types of optical components for guiding, shaping, and / or controlling the radiation, such as refractive, reflective, diffractive, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof. The irradiator IL can be used to adjust the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the pattern forming apparatus MA.

[0057] The term "projection system" PS as used herein should be broadly interpreted to encompass various types of projection systems suitable for the exposure radiation used and / or for other factors such as immersion in liquids or vacuum, including refractive, reflective, diffractive, reflective-refractive, distorting, magnetic, electromagnetic, and / or electrostatic optical systems or any combination thereof. Any term "projection lens" as used herein may be considered synonymous with the more general term "projection system" PS.

[0058] Photolithography equipment (LA) can fall into the following category: at least a portion of the substrate can be covered by an immersion liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system (PS) and the substrate (W)—this is also known as immersion lithography. More information on immersion technology is given in US6952253, the entire contents of which are incorporated herein by reference.

[0059] Photolithography equipment (LA) can also be of the type with two or more substrate supports (WT) (also known as "dual platforms"). In such "multi-platform" machines, substrate supports (WT) can be used in parallel, and / or another substrate (W) on another substrate support (WT) can be used to expose a pattern on another substrate (W) while a subsequent exposure step is performed on a substrate (W) located on one of the substrate supports (WT) to prepare the substrate (W).

[0060] In addition to the substrate support WT, the lithography apparatus LA may also include a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure the properties of the projection system PS or the properties of the radiation beam B. The measurement platform may hold multiple sensors. The cleaning devices may be arranged to clean part of the lithography apparatus, such as part of the projection system PS or part of the system's immersion liquid. The measurement platform can move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0061] In operation, the radiation beam B is incident on the pattern forming apparatus (e.g., mask) MA held on the mask support T and patterned by the pattern (design layout) presented on the pattern forming apparatus MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto the target portion C of the substrate W. With the aid of the second locator PW and the position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first locator PM and possibly another position sensor (in...) Figure 1 (Not explicitly depicted) can be used to accurately position the patterning apparatus MA relative to the path of the radiation beam B. The patterning apparatus MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2, as illustrated, occupy dedicated target portions, the marks can be located in the space between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, these substrate alignment marks are referred to as scribing alignment marks.

[0062] like Figure 2As shown, a lithography apparatus LA can form part of a lithography unit LC, sometimes referred to as a lithography cell or lithography cluster. The lithography unit LC often includes equipment for performing pre- and post-exposure processes on a substrate W. Typically, these include a spin coater SC for depositing a resist layer, a developer DE for developing the resist after exposure, and, for example, a chiller CH and a baking plate BK for regulating the temperature of the substrate W (e.g., for regulating the solvent in the resist layer). A substrate transfer device or robot RO picks up the substrate W from input / output ports I / O1, I / O2, moves the substrate between different process units, and transfers the substrate W to the feed stage LB of the lithography apparatus LA. The equipment in the lithography unit, often collectively referred to as the track or coating / developing system, is typically under the control of a track or coating / developing system control unit TCU. The track or coating / developing system control unit TCU itself can be controlled by a management control system SCS, which can also control the lithography apparatus LA, for example, via a lithography control unit LACU.

[0063] During photolithography, it is desirable to frequently measure the resulting structure, for example, for process control and verification. The tool used to perform such measurements can be referred to as a measurement tool (MT). Different types of MTs for such measurements are known, including scanning electron microscopes or various forms of scatterometer MTs. A scatterometer is a general-purpose instrument that allows the measurement of parameters of the photolithography process by means of a sensor located in the pupil or a plane conjugate to the pupil of the scatterometer's objective lens; such measurements are typically referred to as pupil-based measurements. Alternatively, it allows the measurement to be performed by means of a sensor located in the image plane or a plane conjugate to the image plane; in this case, the measurement is typically referred to as image- or field-based measurements. Such scatterometers and associated measurement techniques are further described by reference in the following patent applications, US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A. The aforementioned scattering instrument can use light / radiation from soft X-rays and visible to near-IR wavelengths to measure the grating. When the radiation is optionally hard or soft X-rays with wavelengths ranging from 0.01 nm to 10 nm, the aforementioned scattering instrument can optionally be a small-angle X-ray scattering measurement tool.

[0064] To ensure accurate and consistent exposure of the substrate W exposed by the lithography unit LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlap error between subsequent layers, line thickness, critical dimension (CD), and shape of the structure. For this purpose, inspection tools and / or measurement tools (not shown) can be included in the lithography unit LC. If errors are detected, adjustments can be made, for example, to the exposure of subsequent substrates or to other processing steps to be performed on the substrate W, especially when inspection is performed before other substrates W in the same batch or leg are to be exposed or processed.

[0065] An inspection device, also known as a metrology device, is used to determine the properties of a substrate W, and specifically, to determine how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary between layers. The inspection device is alternatively configured to identify defects on the substrate W, and the inspection device may be, for example, part of the lithography unit LC, or may be integrated into the lithography equipment LA, or even a separate device. The inspection device may measure the properties on a latent image (an image in a resist layer after exposure), or a semi-latent image (an image in a resist layer after a post-exposure baking step PEB), or the properties on a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even the properties on an etched image (after a pattern transfer step such as etching).

[0066] In a first embodiment, the scatterer MT is an angle-resolved scatterer. In such a scatterer, a reconstruction method can be applied to the measured signal to reconstruct or calculate the properties of the grating. This reconstruction can, for example, be caused by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measured results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0067] In the second embodiment, the scatterer MT is a spectroscopic scatterer MT. In this spectroscopic scatterer MT, radiation emitted by a radiation source is directed onto the target, and reflected, transmitted, or scattered radiation from the target is directed to a spectroscopic detector, which measures the spectrum of the specularly reflected radiation (i.e., the intensity measurement as a function of wavelength). Based on this data, the structure or profile of the target that generated the detected spectrum can be reconstructed, for example, by rigorously coupled wave analysis and nonlinear regression or by comparison with a simulated spectral library.

[0068] In a third embodiment, the scatterer MT is an elliptic scatterer. The elliptic scatterer allows for the determination of parameters of the photolithography process by measuring the scattered or transmitted radiation for each polarization state. Such a measurement device emits polarized light (such as linear, circular, or elliptical) by using, for example, a suitable polarization filter in the illumination cross section of the measurement device. A source suitable for the measurement device can also provide polarized radiation. Various embodiments of conventional elliptic scatterers are described by reference 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.

[0069] In one embodiment of the scattering instrument MT, the scattering instrument MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflectance spectrum and / or detecting asymmetry in the configuration, the asymmetry relating to the degree of overlap. Two (potentially stacked) grating structures can be applied to two different layers (not necessarily consecutive layers), and the two grating structures can be formed at substantially the same location on the wafer. The scattering instrument can have a symmetrical detection configuration, such as that described, for example, in the commonly owned patent application EP1,628,164A, such that any asymmetry is readily identifiable. This provides a simple and direct method for measuring misalignment in gratings. Further examples of measuring overlap error between two layers of a periodic structure, including the target periodic structure, by means of asymmetry in the periodic structure can be found in PCT patent application WO2011 / 012624 or U.S. patent application US20160161863, which are incorporated herein by reference in their entirety.

[0070] Other parameters of interest may be focal length and dose. Focal length and dose can be determined simultaneously using a scatterometer (or alternatively, 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 with a unique combination of critical dimensions and sidewall angle measurements for each point in the focus energy matrix (FEM—also known as the focal length exposure matrix) can be used. If these unique combinations of critical dimensions and sidewall angles are available, the focal length and dose values ​​can be uniquely determined based on these measurements.

[0071] The measurement target can be the entirety of a composite grating formed primarily in a resist by a photolithography process and also, for example, after an etching process. The pitch and linewidth of the structure in the grating can be largely dependent on the measurement optics (particularly the NA of the optics) to be able to capture the diffraction order from the measurement target. As previously noted, the diffraction signal can be used to determine the offset (also referred to as "overlap") between two layers or can be used to reconstruct at least a portion of the original grating, as produced by the photolithography process. This reconstruction can be used to provide quality guidance for the photolithography process and can be used to control at least a portion of the photolithography process. The target can have smaller subsegments configured to mimic the dimensions of functional portions of the design layout in the target. Due to these subsegments, the target will behave more similarly to the functional portions of the design layout, making the overall process parameter measurements more similar to the functional portions of the design layout. The target can be measured in underfill or overfill modes. In underfill mode, the spot produced by the measurement beam is smaller than the entire target. In overfill mode, the spot produced by the measurement beam is larger than the entire target. In this overfill mode, different targets can be measured simultaneously, thereby determining different processing parameters at the same time.

[0072] The overall measurement quality of lithography parameters performed for a specific target is determined at least in part by the measurement configuration used to measure such lithography parameters. The term "substrate measurement configuration" can include one or more parameters of the measurement itself, one or more parameters of the measured pattern, or both. For example, if the measurement used in the substrate measurement formulation is a diffraction-based optical measurement, the measured parameters can include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One criterion for selecting the measurement configuration can be, for example, the sensitivity of one of the measurement parameters to handling variations. Further examples are described in full in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US20160370717A1, which are incorporated herein by reference.

[0073] The patterning process in the lithography apparatus LA is one of the most critical steps in the process, requiring high accuracy in the dimensional setting and placement of the structures on the substrate W. To ensure this high accuracy, three systems can be combined into a so-called "holistic" control environment, such as... Figure 3The diagram illustrates this schematically. One of these systems is a lithography apparatus (LA), which is (in effect) connected to a metrology tool (MT) (the second system) and a computer system (CL) (the third system). The key to this “holistic” environment is optimizing the collaboration between these three systems to enhance the overall process window and provide a tight control loop, thereby ensuring that the patterning performed by the lithography apparatus (LA) remains within the process window. The process window defines a set of process parameters (e.g., dose, focal length, overlap), within which specific manufacturing processes produce defined results (e.g., functional semiconductor devices)—possibly, the process parameters in the lithography or patterning process are allowed to vary within the defined results.

[0074] The computer system CL can use a portion of the design layout to be patterned to predict which resolution enhancement technique to use and perform computational lithography simulations and calculations to determine which mask layout and lithography equipment setup will achieve the maximum overall process window (within) the patterning process. Figure 3 (Depicted by double arrows in the first scale SC1). The resolution enhancement technique can be arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL can also be used to detect where the lithography apparatus LA is currently operating within the process window (e.g., using input from the metrology tool MET) to predict whether defects may exist due to, for example, suboptimal processing (in... Figure 3 (This is depicted by the arrow pointing to "0" in the second scale SC2).

[0075] The measurement tool (MT) can provide input to the computer system (CL) for accurate simulation and prediction, and can provide feedback to the lithography equipment (LA) to identify possible drifts in, for example, the calibration status of the lithography equipment (LA). Figure 3 (The middle part is depicted by multiple arrows in the third ruler SC3).

[0076] During photolithography, it is desirable to frequently measure the resulting structure, for example, for process control and verification. Various tools are known for performing these measurements, including scanning electron microscopes or various forms of metrology equipment, such as scatterometers. Examples of known scatterometers often rely on providing a dedicated measurement target, such as an underfilled target (a target in the form of a simple grating or a stacked grating in different layers, large enough that the measurement beam produces a spot smaller than the grating) or an overfilled target (whereby the illumination spot partially or completely includes the target). Furthermore, the use of metrology tools (e.g., an angle-resolved scatterometer illuminating an underfilled target (such as a grating)) allows for the use of so-called reconstruction methods, where the properties of the grating can be calculated by simulating the interaction between the scattered radiation and a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0077] A scatterometer is a general-purpose instrument that allows for the measurement of parameters of a photolithography process by means of a sensor located in or near the pupil plane, or in a plane conjugate to the pupil of the scatterometer's objective lens; such measurements are typically referred to as pupil-based measurements. Alternatively, it allows for the measurement by means of a sensor located in or near 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 measurements. Such scatterometers and associated measurement techniques are further described by reference in the following patent applications: US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032, or EP1,628,164A. The aforementioned scatterometers can measure multiple targets from multiple gratings within a single image using light from hard X-rays, soft X-rays, extreme ultraviolet, and visible to near-IR and IR bands.

[0078] Figure 4 An example of a measurement device, such as a scatterer, is described. It may include a broadband (e.g., white light) radiation projector 2 that projects radiation 5 onto a substrate W. The reflected or scattered radiation 10 is passed to a spectrometer detector 4, which measures the spectrum 6 of the specular reflected radiation (i.e., a measurement of intensity I as a function of wavelength λ). Based on this data, the structure or profile 8 of the detected spectrum can be reconstructed by a processing unit PU, for example, through rigorous coupled-wave analysis and nonlinear regression, or through methods such as... Figure 4The reconstruction is performed by comparing the simulated spectral library shown at the bottom. Typically, for reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the process of manufacturing the structure, leaving only a few parameters of the structure to be determined from the scattering measurements. This scatterometer can be configured as a normal-incident scatterometer or an oblique-incident scatterometer.

[0079] As an alternative to optical measurement methods, the use of hard X-rays, soft X-rays, or EUV radiation, for example, radiation in the wavelength range between 0.01 nm and 100 nm, or optionally between 1 nm and 50 nm, or optionally between 10 nm and 20 nm, is also considered. Reflectance measurement techniques using X-rays (GI-XRS) and extreme ultraviolet (EUV) radiation under grazing incidence can be used to measure the properties of films and stacks on a substrate. In the realm of typical reflectance measurement, goniometric and / or spectroscopic techniques can be applied. In goniometrics, the variation of the reflected beam at different incident angles can be measured. On the other hand, spectroscopic reflectance measurement measures the spectrum of wavelengths reflected at a given angle (using broadband radiation). For example, EUV reflectance measurement has been used for inspecting mask substrates prior to the fabrication of masks (patterning apparatuses) used in EUV lithography.

[0080] Figure 5 It shows things like Figure 4 The example shown is a transmission-type version of a measurement device such as a scatterer. The transmitted radiation 11 is passed to a spectrometer detector 4, which measures the spectrum 6, as... Figure 4 As discussed above, this scatterer can be configured as a normal incidence scatterer or an oblique incidence scatterer.

[0081] The scope of applications may render the use of wavelengths in, for example, the soft X-ray or EUV domains insufficient. An example of a metrological instrument operating within one wavelength range presented above is transmitted small-angle X-ray scattering (such as the T-SAXS in US 2007224518A, which is incorporated herein by reference in its entirety). Lemaillet et al. discuss profile (CD) measurements using T-SAXS in “Intercomparison between optical and X-ray scatterometry measurements of FinFET structures” (Proc. of SPIE, 2013, 8681). Published patent applications US 20130304424A1 and US 2014019097A1 (Bakeman et al. / KLA) describe hybrid metrological techniques that combine measurements using X-rays with optical measurements utilizing wavelengths in the 120 nm to 2000 nm range to obtain measurements of parameters such as CD. CD measurements are obtained by coupling an X-ray mathematical model with an optical mathematical model through one or more common elements. The entire contents of the cited U.S. patent application are incorporated herein by reference.

[0082] Figure 6 A schematic representation of a measuring device 302 is shown, wherein radiation with wavelengths ranging from 0.1 nm to 100 nm can be used to measure parameters of a structure on a substrate. Figure 6 The measurement device 302 presented here can be used in the hard X-ray, soft X-ray or EUV domains.

[0083] Figure 6 The illustration, purely as an example, shows a schematic physical arrangement of a measurement apparatus 302 that includes a spectroscopic scatterer that optionally uses hard X-ray (HXR) and / or soft X-ray (SXR) and / or EUV radiation at grazing incidence. An alternative form of the inspection apparatus could be an angle-resolved scatterer that can use normally or near-normally incident radiation similar to conventional scatterers operating at longer wavelengths. An alternative form of the inspection apparatus could be a transmission scatterer. Figure 5 The configuration described is suitable for alternative forms of inspection equipment.

[0084] The inspection device 302 includes a radiation source or so-called irradiation source 310, an irradiation system 312, a substrate support 316, detection systems 318, 398, and a measurement processing unit (MPU) 320.

[0085] In this example, the irradiation source 310 is used to generate EUV, hard X-ray, or soft X-ray radiation. The irradiation source 310 can be based on, for example... Figure 6The high-order harmonic generation (HHG) technique shown in the figure can also be other types of irradiation sources, such as liquid metal jet sources, inverse Compton scattering (ICS) sources, plasma channel sources, magnetic oscillation sources, or free electron laser (FEL) sources.

[0086] For example, HHG source, such as Figure 6 As shown, the main components of the radiation source are a gas delivery system 332 and a pump radiation source 330 operable to emit pump radiation. Optionally, the pump radiation source 330 is a laser, and optionally, it is a pulsed high-power infrared or optical laser. The pump radiation source 330 can be a fiber-based laser with an optical amplifier, thereby generating infrared radiation pulses that can last for, for example, less than 1 ns (1 nanosecond), and the pulse repetition rate can be up to several megahertz when needed. The wavelength of the infrared radiation can be, for example, in the range of 1 μm (1 micrometer). Optionally, the laser pulse is transmitted to the gas delivery system 332 as a first pump radiation 340, wherein a portion of the radiation is converted into emitted radiation 342 at a higher frequency than the first radiation in the gas. A gas supply 334 supplies a suitable gas to the gas delivery system 332, wherein optionally, the gas can be ionized by a power source 336. The gas delivery system 332 can be a cutting tube. The gas supplied by the gas delivery system 332 defines a gas target, which can be a gaseous flow or a static volume. The gas can be supplied within a structure such as a capillary or fiber structure to interact with pump radiation and generate higher-frequency radiation to be emitted. The gas can be, for example, an inert gas such as neon (Ne), helium (He), or argon (Ar). Nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), and xenon (Xe) are all considered. These can be optional within the same device.

[0087] The emitted radiation can include multiple wavelengths. While monochromatic emitted radiation simplifies measurement calculations (e.g., reconstruction), it is easy to generate radiation with multiple wavelengths. The emission divergence angle of the emitted radiation can be wavelength-dependent. When imaging structures of different materials, different wavelengths will, for example, provide different levels of contrast. For the inspection of metallic or silicon structures, different wavelengths can be selected, for example, to image the characteristics of (carbon-based) resists or to detect contamination in these different materials. One or more filtering devices 344 can be provided. For example, filters such as aluminum (Al) or zirconium (Zr) films can be used to cut off the basic IR radiation to prevent further propagation into the inspection equipment. A grating (not shown) can be provided to select one or more specific wavelengths from those generated. Optionally, the irradiation source includes a space configured to be evacuated, and a gas delivery system is configured to provide a gas target in said space. Optionally, some or all of the beam paths can be included in a vacuum environment, remembering that SXR and / or EUV radiation is absorbed when traveling in air. Various components of the radiation source 310 and the irradiation optics 312 can be adjustable to implement different measurement “selective schemes” within the same device. For example, different wavelengths and / or polarizations can be selected.

[0088] Depending on the structural material being inspected, different wavelengths can provide the necessary level of penetration into multiple underlying layers. To resolve the smallest device features and defects within them, shorter wavelengths may be preferred. For example, one or more wavelengths in the range of 0.01 nm to 20 nm, or optionally in the range of 1 nm to 10 nm, or optionally in the range of 10 nm to 20 nm, can be selected. Wavelengths shorter than 5 nm may suffer from very low critical angles when reflected away from the material of interest in semiconductor manufacturing. Therefore, selecting wavelengths greater than 5 nm can provide a stronger signal at larger incident angles. On the other hand, if the inspection task is to detect the presence of a certain material, such as for detecting contamination, then wavelengths up to 50 nm may be useful.

[0089] The filtered beam 342 enters the inspection chamber 350 from the radiation source 310, where the substrate W of the structure of interest is held by a substrate support 316 for inspection at the measurement location. The structure of interest is designated T. Optionally, the atmosphere within the inspection chamber 350 is maintained to near vacuum by a vacuum pump 352, so that SXR and / or EUV radiation can pass through the atmosphere without excessive attenuation. The irradiation system 312 has the function of focusing radiation into a focused beam 356 and may include, for example, a two-dimensional curved mirror or a series of one-dimensional curved mirrors, as described in the published U.S. patent application US2017 / 0184981A1 (the entire contents of which are incorporated herein by reference) mentioned above. 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 support 316 includes, for example, an XY translation platform and a rotation platform, through which any portion of the substrate W can be brought to the focal point of the beam in a desired direction. Thus, the radiation spot S is formed on the structure of interest. Alternatively or additionally, the substrate support 316 includes, for example, a tilting platform that tilts the substrate W at an angle to control the incident angle of the focused beam on the structure of interest T.

[0090] Optionally, the irradiation system 312 provides a reference radiation beam to a 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 related to the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0091] The reflected radiation 360 is captured by detector 318, and the spectrum is provided to processor 320 for calculating the properties of the target structure T. The irradiation system 312 and detection system 318 thus form an inspection apparatus. Such an inspection apparatus may include hard X-ray, soft X-ray, and / or EUV spectroreflectometers of the kind described in US2016282282A1, which is incorporated herein by reference in its entirety.

[0092] If the target Ta has a certain periodicity, the radiation from the focused beam 356 can also be partially diffracted. The diffracted radiation 397 follows a different path relative to the angle of incidence at a clearly defined angle (unlike the reflected radiation 360). Figure 6 In the diagram, the drawn diffracted radiation 397 is schematically absorbed, and the diffracted radiation 397 may follow many other paths besides the drawn path. The inspection device 302 may also include an additional detection system 398 for detecting and / or imaging at least a portion of the diffracted radiation 397. Figure 4In this embodiment, a single additional detection system 398 is used, but embodiments of the inspection device 302 may also include more than one additional detection system 398, which are arranged at different locations to detect and / or image diffracted radiation 397 in multiple diffraction directions. In other words, the (higher) diffraction order of the focused radiation beam illuminating the target Ta is 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 the measurement processor 320. Signals 399 may include information about the diffracted light 397 and / or may include an image obtained from the diffracted light 397.

[0093] To aid in aligning and focusing the spot S with the desired product structure, the inspection device 302 may also provide auxiliary optics using auxiliary radiation under the control of the measurement processor 320. The measurement processor 320 may also communicate with a position controller 372, which operates a translation platform, a rotation platform, and / or a tilt platform. The processor 320 receives highly accurate feedback regarding the position and orientation of the substrate via sensors. The sensor 374 may include an interferometer, for example, capable of providing accuracy in the range of several picometers. During the operation of the inspection device 302, spectral data 382 captured by the detection system 318 is transmitted to the measurement processing unit 320.

[0094] As mentioned, alternative forms of inspection equipment utilize hard X-rays, soft X-rays, and / or EUV radiation, optionally at normal or near-normal incidence, for example, to perform diffraction-based asymmetry measurements. Both types of inspection equipment can be provided in hybrid metrology systems. The performance parameters to be measured can include overlap (OVL), critical size (CD), focal length of the lithography apparatus when the target structure is printed, coherent diffraction imaging (CDI), and overlap at resolution (ARO) measurements. Hard X-rays, soft X-rays, and / or EUV radiation can, for example, have wavelengths less than 100 nm, such as radiation in the range of 5 nm to 30 nm, optionally in the range of 10 nm to 20 nm. The radiation can be narrowband or broadband. The radiation can have discrete peaks in a specific wavelength band or can have more continuous characteristics.

[0095] Similar to optical scattering instruments used in modern manufacturing facilities, inspection equipment 302 can be used to measure structures within resist materials processed within a lithography unit (post-development inspection or ADI) and / or to measure structures formed in harder materials (post-etching inspection or AEI). For example, inspection equipment 302 can be used to inspect substrates after they have been processed by developing equipment, etching equipment, annealing equipment, and / or other equipment.

[0096] Measurement instruments (MTs) (including, but not limited to, the scatterometers mentioned above) can perform measurements using radiation from a radiation source. The radiation used by the measurement instrument 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 measurement instrument MT can use radiation to measure or inspect the properties and aspects of a substrate, such as a pattern exposed by photolithography on a semiconductor substrate. The type and quality of the measurement can depend on several properties of the radiation used by the measurement instrument MT. For example, the resolution of an electromagnetic measurement can depend on the wavelength of the radiation, where smaller wavelengths, for example, can measure smaller features due to diffraction limits. To measure features with small dimensions, radiation with short wavelengths, such as EUV, hard X-rays (HXR), and / or soft X-rays (SXR), can preferably be used to perform the measurement. To perform measurements at a specific wavelength or wavelength range, the measurement instrument MT needs to access or enter a source that provides radiation at that wavelength / those wavelengths. Different types of sources exist for providing different wavelengths of radiation. 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 higher harmonic generation (HHG) Compton scattering (ICS) to obtain radiation at the desired wavelength.

[0097] Figure 7 A simplified schematic diagram of embodiment 600 of the irradiation source 310 is shown. The irradiation source can be an irradiation source used for higher harmonic generation (HHG). (Refer to...) Figure 6 One or more features of the irradiation source in the described measurement instrument may also be present in the irradiation source 600 as appropriate, i.e., as needed. The irradiation source 600 includes a chamber 601 and is configured to receive pump radiation 611 having a propagation direction indicated by the arrow. The pump radiation 611 shown herein is an example of pump radiation 340 from pump radiation source 330, such as... Figure 6As shown in the diagram. The pump radiation 611 can be directed into the chamber 601 via the radiation input 605, which can be a viewport, optionally made of molten silica or a similar material. The pump radiation 611 can have a Gaussian or hollow (e.g., annular) lateral cross-sectional profile and can be incident (optionally focused) on an airflow 615 within the chamber 601, the airflow having a flow direction indicated by the second arrow. The airflow 615 comprises a small volume of a specific gas (e.g., a rare gas, optionally helium, argon, xenon or neon, nitrogen, oxygen, or carbon dioxide) referred to as a gas volume or gas target (e.g., several cubic millimeters), wherein the gas pressure is above a certain value. The airflow 615 can be a steady flow. Other media, such as metallic plasma (e.g., aluminum plasma), can also be used.

[0098] The gas delivery system of the irradiation source 600 is configured to provide an airflow 615. The irradiation source 600 is configured to provide pump radiation 611 in the airflow 615 to drive the generation of emitted radiation 613. The region that generates at least a majority of the emitted radiation 613 is referred to as the interaction region. The interaction region can vary from 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). The gas delivery system is configured to provide the gas target for generating the emitted radiation at the interaction region of the gas target, and optionally, the irradiation source is configured to receive the pump radiation and provide the pump radiation at the interaction region. Optionally, the gas flow 615 is provided by the gas delivery system to an emptied or nearly emptied space. The gas delivery system may include a gas nozzle 609, such as... Figure 6 As shown, the gas nozzle includes an opening 617 in the outlet plane of a gas nozzle 609. A gas flow 615 is supplied from the opening 617. In almost all prior art, the gas nozzle has a cutting tube geometry, which is a uniform cylindrical internal geometry, and the opening in the outlet plane is circular in shape. Elongated openings have also been used, as described in patent application CN101515105B.

[0099] It is also conceivable that the size of the gas nozzle 609 could be used in scaled-up or scaled-down versions ranging from micrometer-sized nozzles to meter-sized nozzles. This wide range of sizing stems from the fact that the setup can be scaled so that the intensity of the pump radiation at the gas flow ultimately falls within a specific range that may be beneficial to the emitted radiation. This requires different sizing for different pump radiation energies, which can be pulsed lasers, and the pulse energy can vary from tens of microjoules to several joules. Optionally, the gas nozzle 609 has thicker walls to reduce nozzle deformation caused by thermal expansion effects, which can be detected, for example, by a camera. A gas nozzle with thicker walls can produce a stable gas volume with reduced variation. Optionally, the irradiation source includes a gas trap located near the gas nozzle to maintain the pressure in the chamber 601.

[0100] Due to the interaction between the gas atoms of the gas flow 615 and the pump radiation 611, the gas flow 615 will convert a portion of the pump radiation 611 into the emitted radiation 613, which can serve as... Figure 6 An example of emitted radiation 342 is shown. The central axis of the emitted radiation 613 may be collinear with the central axis of the incident pump radiation 611. The emitted radiation 613 may have a wavelength in the X-ray or EUV range, wherein the wavelength is in the range of 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.

[0101] In operation, the emitted radiation beam 613 can be transmitted through the radiation output 607 and subsequently irradiated by the irradiation system 603 (which can serve as...). Figure 6 (Example of irradiation system 312) is manipulated and directed to a substrate to be inspected for measurement purposes. The emitted radiation 613 can be directed (optionally focused) onto a structure on the substrate.

[0102] Gas target HHG configurations can be divided into two main categories: gas jet and gas capillary. In Figure 6 The configuration described in the other figures throughout this specification depicts a gas jet-based gas delivery system in which airflow is provided via a gas nozzle 609. However, the features described in this disclosure can also be provided in an irradiation source having a gas capillary-based gas delivery system.

[0103] In a gas capillary configuration, the capillary structure can be configured to include gas within the capillary and to receive and guide pump radiation. The size of the capillary structure holding the gas can be small in the lateral direction, such that it significantly affects the propagation of the pump radiation laser beam. The interaction region that generates emitted radiation via HHG can be located within the capillary structure. The gas target can be located within the capillary structure. The capillary structure can be, for example, a hollow optical fiber, such as a hollow photonic crystal fiber.

[0104] Once generated, the emitted radiation can propagate through the gas capillary structure. The propagation directions of the pump radiation and the emitted radiation can be substantially the same as they exit the capillary structure. Therefore, adjacent to the capillary structure, the irradiation source may include additional optical elements for separating the pump radiation and the generated emitted radiation. These structures may include optical elements configured to diffract the pump radiation away from one or more main propagation directions of the emitted radiation.

[0105] Because air (and virtually any gas) absorbs a large amount of SXR or EUV radiation, the volume between the airflow 615 and the wafer to be inspected can be emptied or nearly emptied. Since the central axis of the emitted radiation 613 can be collinear with the central axis of the incident pump radiation 611, the pump radiation 611 may need to be blocked to prevent it from passing through the radiation output 607 and entering the irradiation system 603. This can be achieved by... Figure 6 The filter 344 shown is incorporated into the radiation output 607, placed in the path of the emitted beam, and is opaque or nearly opaque to the pump 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 using zirconium or multiple materials combined in a multilayered manner. When the pump radiation 611 has a hollow (optionally annular) cross-sectional profile, the filter can be a hollow, optionally annular block. Optionally, the filter is neither perpendicular nor parallel to the propagation direction of the emitted radiation beam to achieve effective pump radiation filtering. Optionally, the filter 344 comprises a hollow block and a thin-film filter, such as an aluminum (Al) or zirconium (Zr) thin-film filter. Optionally, the filter 344 may also include a mirror that effectively reflects the emitted radiation but poorly reflects the pump radiation, or a metal mesh that effectively transmits the emitted radiation but poorly transmits the pump radiation.

[0106] This document describes methods, apparatus, and components for obtaining emitted radiation at optional high-order harmonic frequencies of pump radiation. The radiation generated by the process, optionally an HHG (high-order harmonic radiation) using nonlinear effects to generate radiation at optional harmonic frequencies of the provided pump radiation, can be provided in a metrological instrument (MT) for inspecting and / or measuring a substrate. If the pump radiation comprises short pulses (i.e., small periods), the generated radiation is not necessarily precisely at the harmonics of the pump radiation frequency. The substrate may be a photolithographically patterned substrate. The radiation obtained by the process can also be provided in a photolithography apparatus (LA) and / or a photolithography cell (LC). The pump radiation may be pulsed radiation, which can provide a high peak intensity of a short-duration pulse train.

[0107] The pump radiation 611 may include radiation having one or more wavelengths higher than the emitted radiation. The pump radiation may include infrared radiation. The pump radiation may include radiation with wavelengths in the range of 800 nm to 1500 nm. The pump radiation may include radiation with wavelengths in the range of 900 nm to 1300 nm. The pump radiation may include radiation with wavelengths in the range of 100 nm to 1300 nm. The pump radiation may be pulsed radiation. Pulsed pump radiation may include pulses with a duration between 1 fs and 100 fs.

[0108] In some embodiments, the emitted radiation (optionally higher-order harmonic radiation) may include one or more harmonics of the pump radiation wavelength. The emitted radiation may include wavelengths within the extreme ultraviolet (EUV), soft X-ray (SXR), and / or hard X-ray (HXR) 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.

[0109] Radiation, such as the higher-order harmonic radiation described above, can be provided as source radiation in a metrology tool (MT). The metrology tool (MT) can use this source radiation to perform measurements on a substrate exposed by a photolithography apparatus. These measurements can be used to determine one or more parameters of the structure on the substrate. Using shorter wavelengths of radiation, such as EUV, SXR, and / or HXR wavelengths included in the aforementioned wavelength range, compared to using longer wavelengths (e.g., visible light radiation, infrared radiation), allows the metrology tool to resolve smaller features of the structure. Radiation with shorter wavelengths, such as EUV, SXR, and / or HXR radiation, can also penetrate deeper into materials such as patterned substrates, meaning that measurements of deeper layers on the substrate are possible. Radiation with longer wavelengths may not be able to reach these deeper layers.

[0110] In a measurement tool (MT), source radiation can be emitted from a radiation source and directed onto a target structure (or other structure) on a substrate. The source radiation may include EUV, SXR, and / or HXR radiation. The target structure may reflect, transmit, and / or diffract the source radiation incident on it. The measurement tool (MT) may include one or more sensors for detecting diffracted radiation. For example, the measurement tool (MT) may include detectors for detecting the positive (+1) and negative (-1) first diffraction orders. The measurement tool (MT) may also measure specular reflection or transmission radiation (0th-order diffraction radiation). Additional sensors for measurement may be present in the measurement tool (MT), for example, to measure other diffraction orders (e.g., higher diffraction orders).

[0111] Optionally, the gas target in the HHG source may consist of a relatively small volume of gas with a size comparable to / equivalent to the focal region of the pump radiation, wherein the pump radiation is focused to have a power density above a certain value. In one embodiment, the opening in the outlet plane has a slit shape, wherein the long axis of the slit is oriented along the propagation direction of the pump radiation, and the gas target is tens of μm in a direction perpendicular to the propagation direction of the pump radiation, and several hundred μm in the propagation direction of the pump radiation. The size of the gas target can be designed depending on the size of the focal region of the pump radiation.

[0112] Accurate alignment in a direction perpendicular to both the propagation direction of the pump radiation and the flow direction of the gas flow is crucial to ensure that the pump radiation is focused on the gas target at or near the center. Otherwise, multiple portions of the pump radiation will miss the high-density region at the center, resulting in low CE and asymmetric (i.e., low-quality) emitted radiation.

[0113] Precise alignment with the nozzle, close but not impacting it, in the direction of airflow is crucial for obtaining a specific profile and high density of the airflow without damaging the nozzle. In one embodiment, the gas density of the airflow first increases to a maximum and then drops sharply in a cutoff region along the propagation direction. More information regarding the profile of the airflow is described in patent application NL2024462A, the entire contents of which are incorporated herein by reference. Thermally induced nozzle length variations can be a source of instability in HHG sources, and therefore, source stability can be significantly improved if the distance between the nozzle and the focal region of the pump radiation can be kept constant.

[0114] Accurate positioning is important in the propagation direction of the pump radiation because both the emission CE and the emitted beam divergence are highly sensitive to the position of the gas target relative to the focal region of the pump radiation. Furthermore, it is desirable to be able to measure the position of the interaction region, as the irradiation system (optionally, focusing optics) of the emitted radiation is sensitive to this position when the emitted radiation irradiates the substrate.

[0115] In HHG sources, precise alignment of the pump radiation with the gas target is crucial for achieving high conversion efficiency (CE) and high beam quality of the emitted radiation (e.g., EUV and / or SXR). Simultaneously, the gas target needs to have a small size, optionally resembling an interaction region, to limit plasma defocusing, vacuum contamination, and / or gas consumption.

[0116] Due to drift in the radiation source (such as heating, vibration, etc. of optical components), both the focusing area of ​​the pump radiation and the gas target may shift during operation. This may contribute to drift and / or change in the CE or emitted radiation beam profile, source position change and / or SXR beam pointing change, resulting in changes in the position and quality of the projected emitted radiation spot on the wafer target.

[0117] In HHG sources, the amount of emitted radiation produced by individual atoms in the gaseous target is extremely small. Therefore, it is important to optimize HHG sources so that they output sufficient power with acceptable beam quality to enable, for example, SXR-based integrated circuit technology (ICT) metrology tools. Optimization is challenging due to the many parameters involved in the complex physical processes and the lack of direct and quantitative measurements of the HHG interaction processes.

[0118] A significant and complex problem common to HHG sources is the partial ionization of the gaseous target by high-intensity pump radiation, resulting in plasma. The lifetime of the plasma generated by the pump radiation pulse can be in the nanosecond range. A detrimental effect of this plasma is that it degrades the intensity distribution of the pump radiation beam through a process known as plasma defocusing, thereby preventing the peak intensity required for optimal emission radiation (e.g., SXR and / or EUV) and the intensity distribution required for optimal beam quality of the emitted radiation. Further information regarding plasma defocusing is described in patent application NL2024462A, the entire contents of which are incorporated herein by reference.

[0119] There is a strong need for online quantitative measurement of the plasma generated during HHG. Since the plasma is the direct output of the interaction between the pump radiation and the gaseous target, measuring and monitoring the plasma position directly indicates how the pump radiation is aligned relative to the gaseous target. The shape of the plasma distribution can provide feedback on the HHG process, which can be used to maintain optimal conditions for the emitted radiation output.

[0120] Figure 8 A schematic diagram of an illumination source 800 with an interferometer is depicted. (Reference) Figure 6 and Figure 7 One or more features of the irradiation source in the described measurement tool may also suitably be present in the irradiation source 800. The pump radiation 805 irradiates the gas target 615 to produce the emitted radiation 613. Optionally, the pump radiation 805 has a hollow (e.g., annular) lateral cross-sectional profile to separate the pump radiation 805 from the emitted radiation 613. More information regarding the hollow lateral cross-sectional profile is described in patent applications WO2019219336A1 and WO2020038648A1, the entire contents of which are incorporated herein by reference. Optionally, the irradiation source 800 includes a focusing element 810 (e.g., a focusing lens) for focusing the pump radiation 805 onto the focusing region, optionally onto the interaction region of the gas target 615. Optionally, the pump radiation 805 may be manipulated by a beam shaper. Optionally, the beam shaper is located upstream of the focusing element 810. Examples of beam shapers include spatial light modulators (SLMs), flat-top beam shapers, and deformable mirrors.

[0121] The interferometer in the irradiation source 800 is used to irradiate at least a portion of the gaseous target 615 with interferometer radiation 809 to measure the properties of the gaseous target 615. Note that the properties of the resulting plasma are also considered as properties of the gaseous target 615. The interferometer may include one or more of a detection element 812 and optical elements 807, 817, 827, and 837. Figure 8 and Figure 9 In the illustrated embodiment, optical elements 807 and 837 are beam splitters, while optical elements 817 and 827 are mirrors. The interferometer radiation is split into two branches by beam splitter 807, which can travel in different optical paths, and then combined by a second beam splitter 837 to produce interference. A detection element 812 (e.g., a camera) is used to detect the interferometer signal, which will be described later. Optionally, the interferometer may include optical element 811, which may be an imaging lens upstream of the detection element 812. In one embodiment, the interferometer radiation includes two branches, one of which propagates at least partially through the gas target 615, while the other branch does not propagate through the gas target 615. The two branches are combined downstream and interfere to generate the interferometer signal on the detection element 812. Optionally, the branch propagating through the gas target 615 at least partially illuminates at least a portion of the gas nozzle. Optionally, the interferometer includes an adjustable element, such as a movable mirror, for changing the propagation direction of the interferometer radiation. For example, the propagation direction of the branch passing through the gas target 615 can be changed to allow the gas target 615 to be illuminated at various angles. The properties of the gas target 615 can also be calculated via an algorithm. The branch passing through the gas target 615 can be partially cut by the edge of the gas nozzle, and the gas nozzle can optionally be imaged onto a camera for alignment measurements.

[0122] The interferometer radiation 809 has an interferometer wavelength, and the pump radiation 805 has a pump wavelength. In one embodiment, the interferometer wavelength and the pump wavelength are different, which may be the easiest and preferred design to work together, because the pump radiation 805 can be filtered out from the detected interferometer signal in a direct manner.

[0123] In the second embodiment, the interferometer wavelength and the pump wavelength are the same, but the polarizations of the interferometer radiation 809 and the pump radiation are different. This allows the pump radiation 805 to be filtered out from the interferometer signal using, for example, a polarization filter. During operation, a portion of the interferometer radiation 809 can be transmitted through the gas target 615 containing an inert gas, which can be considered an isotropic medium. An isotropic medium does not alter the polarization of the interferometer radiation 809. Therefore, the pump radiation 805 can be distinguished from the interferometer radiation 809 by polarization isolation.

[0124] Pulsed pump radiation can be necessary for HHG processes, while interferometer radiation can be pulsed or continuous. In the continuous case, the time-averaged state of the gas target can be measured. One example is where the pump radiation repetition rate is so high that the effect of the previous pulse has not yet decayed before the next pulse arrives. In this case, continuous interferometer radiation can be used to monitor the slowly evolving gas state.

[0125] Under most conditions, the pump radiation may comprise multiple short pulses separated by large intervals, the time fraction of the pump radiation interacting with the gas target is small, and pulsed interferometer radiation may be preferred. Alternatively, interferometer radiation similar to pump radiation may comprise pulses with durations, for example, in the femtosecond range. As mentioned above, the lifetime of the plasma generated by the pump radiation pulses can be in the nanosecond range. Therefore, if the arrival times of the pump radiation pulses and the interferometer radiation pulses at the gas target 615 are not accurately controlled, measuring the profile of the plasma can be challenging.

[0126] The irradiation source 800 may include a time delay unit 806, such as Figure 9 As shown, the time delay unit 806 includes one or more mirrors 857 for optionally altering the time difference between the arrival of the interferometer radiation and pump radiation pulses at the gas target. Other suitable means for delaying the radiation pulses may also be used in the time delay unit 806 (such as using a transparent wedge that produces a time delay proportional to the path length of the pulse passing through the transparent wedge).

[0127] In the case of a pulse interferometer, the time during which the interferometer pulse passes through the gas target defines the time window in which the state of the gas target can be measured. During the time window before the arrival of the pump pulse, the detector 812 can record the original state of the gas target without interaction. During the passage of the pump pulse, the detector 812 can record a portion of the period when the plasma is generated. After the passage of the pump pulse, the detector 812 can record the total effect of the pump pulse on the state of the gas target. By comparing the interferometric measurement results with other results having different timing, a shorter time resolution than the interferometer pulse length can be obtained.

[0128] Therefore, synchronization may be necessary to ensure that the interferometer radiation pulses and the pump radiation pulses have equal repetition rates or the same frequency. The pulses of the interferometer radiation 809 and the pump radiation 805 are at least partially synchronized. The definition of synchronization can also be extended to the case where the repetition rate of the interferometer radiation pulse is an integer multiple of the repetition rate of the pump radiation pulse, in which case the plasma generated by one pump radiation pulse can be measured by more than one interferometer radiation pulse. On the other hand, it is possible that only one of the multiple plasmas generated by multiple pump radiation pulses can be measured by one interferometer radiation pulse, and the definition of synchronization can also be extended to the case where the repetition rate of the pump radiation pulse is an integer multiple of the repetition rate of the interferometer radiation pulse.

[0129] Time control using a time delay unit is also important for accurate measurements. The time control regulates the arrival time of the interferometer radiation pulses relative to the arrival time of the pump radiation pulses, optionally at the femtosecond level. An example of time control could be that the pulse's time position is challenged, causing pulses from two sources to coincide in time, optionally in the gas target 615. In this application, time control could also include cases where pulses from two sources have a fixed time delay or a controlled variation of time delay. In one embodiment, the interferometer pulses are time-controlled to measure only once for multiple pump radiation pulses, or multiple interferometer pulses are present to time-control a single pump radiation pulse.

[0130] In many cases, it is also possible to choose an arrangement in which two of the pulses partially overlap in the gas target, but this is not a limitation, as it is also possible to be concerned with the timing of the interferometer radiation pulses before or after the pump radiation pulses, without overlap in the gas target.

[0131] The phase shift introduced by gas and / or plasma can be calculated from the interference fringes on the detection element 812 generated by the interference of the two branches. When plasma is generated by high-intensity HHG source pump radiation 815, the phase shift introduced by both gas and plasma can be measured. When the HHG source pump radiation 815 is blocked by a removable beam or has a sufficiently low intensity to prevent plasma generation, the phase shift introduced by the gas alone can be measured. In embodiments where the pump radiation and the interferometer pump radiation are generated by different sources, the pump radiation source can be turned off to measure the phase shift introduced by the gas alone. The phase shift introduced by plasma alone can be extracted by subtracting the contribution introduced by the gas from the contributions introduced by both.

[0132] Plasma-induced phase shift It is related to plasma density through the following equation:

[0133]

[0134] Among them G e and N e These are the electron Gladstone constant and the electron number density, respectively, and l is the path length of the interferometer radiation through the gas target. Therefore, the phase shift can be derived. The phase shift is the line integral of the plasma density along the propagation direction of the branch passing through the gas target.

[0135] By setting an appropriate time delay between the interferometer pump radiation 804 and pump radiation 805, the final state of the plasma can be measured after the HHG source pump radiation pulse has passed. The strongest signal is expected in the final state, which is beneficial for alignment.

[0136] The plasma buildup during the passage of the pump radiation pulse through the gas target can also be measured by scanning the time delay of the interferometer radiation pulse, such that the time of arrival of the interferometer pulse at the gas target varies between the start and end of the passage of the pump radiation pulse. This measurement method can be used to study, understand, and optimize HHG processes. The rate of plasma decay after the pump radiation pulse passes through the gas target can also be measured by scanning the time delay of the interferometer pulse, such that the time of arrival of the interferometer pulse at the gas target varies between the end of the passage of the pump radiation pulse and the end of the plasma decay delay.

[0137] In one embodiment, the irradiation source 800 may include a feedback loop for controlling the pump radiation or the properties of the gas delivery system based on the properties of the gas target, optionally based on the properties of the plasma. In another embodiment, the irradiation source may include a feedforward loop for controlling downstream elements in a feedforward manner, such as adjusting one or more optical elements of the irradiator that compensate for positional changes of the gas target observed by the interferometer.

[0138] For example, visual feedback regarding the position of the pump radiation 805 relative to the gas target 615 can be provided, allowing for precise tuning of the alignment, and also enabling the measurement of the absolute position of the pump radiation 805 within the gas target 615, i.e., the position of the plasma. During operation, optimal alignment can be maintained through the feedback loop despite system drift or fluctuations.

[0139] The optimal emitted radiation 613 is a sensitive balance between sufficient intensity and pressure and excessive ionization. This balance can be improved and stabilized by observing, for example, the level of ionization and the shape of the pump radiation 805. This invention can help find optimal conditions during setup and maintain HHG dynamics constant during operation.

[0140] Furthermore, this invention also allows for online monitoring of target gas density and profile. Given that the nozzle is very close to the high-intensity region and exposed to plasma, monitoring potential nozzle degradation is important.

[0141] Figure 9 Depicting with Figure 8 The diagram illustrates an embodiment 900 of the interferometer's illumination source 800. In this embodiment, the interferometer radiation 809 is a second-order or higher harmonic of the interferometer pump radiation 804 generated by a harmonic generation process. The interferometer target 808 (or harmonic conversion unit, which may be a nonlinear crystal or a gas target) is irradiated by the interferometer pump radiation 804. When the interferometer radiation is a second-order harmonic of the interferometer pump radiation 804 generated by the harmonic generation process, the interferometer target 808 may be a solid, such as a barium borate (BBO) crystal. When the interferometer radiation is a third-order or higher harmonic of the interferometer pump radiation 804 generated by the harmonic generation process, the interferometer target 808 may be a nonlinear crystal, or a gas target 615 similar to those described above. Optionally, a focusing element 847 is present upstream of the interferometer target 808 for focusing the interferometer pump radiation 804 onto the interferometer target 808.

[0142] The irradiation source 900 may include the time delay unit 806, which includes one or more mirrors 857 for optionally altering the time difference between the arrival of the interferometer radiation and pump radiation pulses at the gas target. The time delay unit 806 may be positioned upstream of the focusing element 847, such as... Figure 9 As shown in the diagram. The time delay unit 806 can also be placed between the interferometer target 808 and the optical element 807.

[0143] In Example 900, HHG source pump radiation 815, which has similar characteristics to the pump radiation 805, can be used as... Figure 8 An embodiment of the pump radiation 805 described herein. The interferometer pump radiation 804 and the HHG source pump radiation 815 originate from the same pump radiation source, for example, such as... Figure 9 As shown, they are split from radiation 801. In this way, the pulses have the same repetition rate. One way to split radiation source 801 in two is to use a reflective surface with a pinhole 803. Alternatively, in operation, the interferometer pump radiation 804 is passed through the pinhole, and the HHG source pump radiation 815 is reflected by the reflective surface. Another example is to use a beam splitter or anything else that can split radiation 801.

[0144] In another embodiment, the interferometer pump radiation 804 and the HHG source pump radiation 815 originate from different pump radiation sources, such as two different laser sources optionally having different wavelengths. The source generating the interferometer pump radiation 804 can be at least partially synchronized with the source generating the HHG source pump radiation 815.

[0145] like Figure 9 As shown, the first advantage of using the second-order or higher harmonics of the interferometer pump radiation 804 as the interferometer radiation 809 is that synchronization and time control between the interferometer radiation 809 and the HHG source pump radiation 815 can be easily achieved. The second advantage is that the interferometer radiation 809 and the HHG source pump radiation 815 will have different wavelengths, which makes it easy to filter out the HHG source pump radiation 815 from the detected interferometer signal.

[0146] In operation, the power of the interferometer pump radiation can be at least an order of magnitude lower than the power of the HHG source pump radiation. For example, when the interferometer pump radiation 804 and the HHG source pump radiation 815 are separated from the radiation source 801, the power of the interferometer pump radiation 804 is at the expense of the HHG source pump radiation 815, which may result in a lower emitted radiation power.

[0147] Figure 10Experimental results for neon gas target density, slit nozzle, and Mach-Zehnder interferometer are shown. Figure 10 (a) shows the stripes recorded by the detection element 812, and Figure 10 (b) shows from Figure 10 The phase shift extracted from the fringes recorded in (a). Figure 10 In (b), the horizontal and vertical axes are located along the propagation direction of the pump radiation and the flow direction of the airflow, respectively. The phase shift can be extracted from the fringe pattern using the classical Fast Fourier Transform (FFT) method. First, a 2D FFT is performed on the fringes to obtain a spectrum. Due to the dense initial fringes introduced by the small angle between the mirrors, this may result in two spectral peaks being symmetrical on the frequency axis. Then, one of the peaks is selected and shifted to the origin of the frequency axis, while the other spectral peak is removed. Finally, the phase associated with the fringe can be extracted by inverse FFT. More details of this method are given in the scientific journal “Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry” by Takeda et al. (J. Opt. Soc. Am., Vol. 72, No. 1, p. 156 (1982)), the entire contents of which are incorporated herein by reference.

[0148] Figure 10 (c) shows the comparison with Figure 10 (b) shows the density distribution of the pump radiation along the propagation direction in the interaction region corresponding to the dashed line. The horizontal axis represents the position along the actual propagation direction of the pump radiation, while the vertical axis represents the density value.

[0149] All the embodiments mentioned above can be used in methods for inspecting gaseous targets exposed to irradiation sources, such as... Figure 11 The first step 110 involves providing a gas target 615 using a gas delivery system 332 to generate emitted radiation 342 at the interaction region of the gas target 615. A second step 111 may be present, in which at least a portion of the gas target 615 is irradiated using interferometer radiation 809 of an interferometer to measure the properties of the gas target 615. Further details regarding a method for examining a gas target from an irradiation source are provided in the description of the embodiments described in relation to the accompanying drawings and text above.

[0150] All the embodiments mentioned above can also be used in methods for aligning pump radiation relative to a gas target, such as... Figure 12The method for examining a gas target 615 is described in the accompanying drawings and text. The first step 120 involves providing a gas target 615 using a gas delivery system 332. A second step 121 may be present, in which at least a portion of the gas target 615 is irradiated using interferometer radiation 809 of an interferometer to measure the properties of the gas target 615. A third step 122 may be present, in which at least a portion of the gas target 615 is irradiated using pump radiation 611. A fourth step 123 may be present, in which the properties of at least one of the gas delivery system, the pump radiation, the downstream optics, and the substrate positioning mechanism are controlled based on the properties of the gas target measured by the interferometer. Further details regarding the method for examining a gas target from an irradiation source are provided in the description of the embodiments described in relation to the foregoing drawings and text.

[0151] All the embodiments mentioned above can also be used in methods for optimizing emitted radiation output, such as... Figure 13 The method for examining a gas target 615 is described in the accompanying drawings and text. The first step 130 involves providing a gas target 615 using a gas delivery system 332. A second step 131 may be present, in which at least a portion of the gas target 615 is irradiated using interferometer radiation 809 of an interferometer to measure the properties of the gas target 615. A third step 132 may be present, in which at least a portion of the gas target 615 is irradiated using pump radiation 611. A fourth step 133 may be present, in which the properties of at least one of the gas delivery system, the pump radiation, the downstream optics, and the substrate positioning mechanism are controlled based on the properties of the gas target measured by the interferometer. Further details regarding the method for examining a gas target from an irradiation source are provided in the description of the embodiments described in relation to the foregoing drawings and text.

[0152] All the embodiments mentioned above can also be used in methods for monitoring the evolution of plasma over time, such as... Figure 14 The method for examining a gas target 615 is described in the accompanying drawings and text. The first step 140 involves providing a gas target 615 using a gas delivery system 332. A second step 141 may be present, in which at least a portion of the gas target 615 is irradiated using interferometer radiation 809 of an interferometer to measure the properties of the gas target 615. A third step 142 may be present, in which at least a portion of the gas target 615 is irradiated using pump radiation 611 to initiate plasma evolution in the gas target 615. A fourth step 143 may be present, in which the evolution of the plasma over time is monitored based on the properties of the gas target 615 measured by the interferometer. Further details regarding the method for examining a gas target from an irradiation source are provided in the description of the embodiments described in relation to the foregoing figures and text.

[0153] The irradiation source described above may have high operating costs. This is likely partly due to the use of expensive gases for providing the gaseous target and generating the emitted radiation. Gases such as neon, xenon, or other gases used to generate the HHG radiation mentioned above can be used in irradiation sources with flow rates in the range of 5 nL / min to 20 nL / min to generate the desired local density in a vacuum environment. Because of the relatively high cost of such gases, the gas flow can be shut off when the irradiation source is idle (i.e., not in use). HHG radiation can be emitted in a vacuum environment where the gas is injected (e.g., at a pressure less than about 10). -6 It is generated in mbar. Therefore, the presence of gas in a region may create a local environment with a pressure higher than the surrounding vacuum (e.g., a pressure of about 10 mbar). -2 mbar).

[0154] However, this interruption of airflow during the first "on" state and the second "idle" state can lead to significantly different conditions within the irradiation source. Turning the airflow on and off between the on and idle states can cause localized pressure changes (e.g., pressure changes from less than 10...). -6 mbar to about 10 -2 (Within the mbar range). This pressure variation can also cause differences in convective cooling in the region. These differences can be significant, for example, up to four orders of magnitude. Due to this difference, thermomechanical instabilities caused by temperature differences may occur. This can lead to misalignment of the focused beam and instability in the conversion efficiency (CE).

[0155] To avoid problems caused by pressure changes, it may be desirable to maintain gas pressure by introducing an airflow when the irradiation source is idle. To save costs and resources, it is suggested to provide a second gas when the irradiation source is idle. Figures 15(a), 15(b), and 15(c) depict an irradiation source 150 including a gas delivery system configured to provide a first state 15(a) and a second state 15(b) or 15(c). Pump radiation 151 is received in a chamber where HHG radiation is emitted, as described above. Figure 6 As described. In the first state depicted in Figure 15(a) (also referred to as the "on" state), the gas delivery system 152 is configured to provide a first state comprising a first gas 153 for forming a gaseous target for generating emitted radiation. The emitted radiation can be generated within an interaction zone where the pump radiation interacts with the first gas, within an airflow 155 comprising the first gas. This can be within a gas jet generated by a gas nozzle, and / or within a capillary structure comprising the gas.

[0156] In Figures 15(b) and 15(c), a second state, also referred to as an idle state, is provided by the gas delivery system 152. This second state may include a second gas 154. In Figure 15(b), the second gas for the second state is delivered via the same supply line as the first gas in the first state. In Figure 15(c), the second gas for the second state is delivered via a separate supply line. This separate supply line may inject the second gas directly into a compartment / chamber separate from the gas nozzle or other delivery system, thereby aiming to deliver the gas to the interaction zone. The nature of the second state can be selected such that its heat transfer coefficient matches that of the first state. This heat transfer coefficient matching can be achieved in some or all regions of the irradiation source 150 where the first gas is present during the first phase. This region may include the interaction zone that generates HHG radiation. Although not specifically mentioned, the gas delivery system having a first state, a second state, and a gas may optionally be provided in combination with any of the embodiments described herein.

[0157] The advantages of using the first state (on) and the second state (idle) can be lower operating costs, especially when the irradiation source is idle, while avoiding negative effects (e.g., alignment, CE stability) caused by temperature variations due to changes in the heat transfer coefficient between the irradiation source and its surrounding environment within the interaction zone of the first gas. Using the idle state to match the heat transfer coefficient conditions of the active "on" state can result in more stable temperature and settings in the irradiation source. Another advantage can be increased throughput and / or efficiency due to reduced temperature variations and the resulting negative effects. Yet another advantage can be improved radiation source performance, as less radiation can escape from the target.

[0158] As mentioned above, the first gas can be any gas used to generate emitted radiation, such as, for example, neon or xenon. The second gas can include gases that are cheaper than the first gas, such as nitrogen, argon, and / or other gases. In some embodiments, the first gas and the second gas can be supplied in the same supply line of the gas delivery system. In an exemplary setup where the first gas includes neon and the second gas includes nitrogen (or other suitable gas), nitrogen can be supplied through the same supply line when the neon flow is shut off when the irradiation source is idle. When using the same supply line, high nitrogen flow rates and pressures may be required.

[0159] In some embodiments, the second "idle" gas may comprise a mixture of gases. The gas mixture may include oxygen. The mixture may, for example, be a mixture of oxygen and nitrogen. In some instances, ultra-clean filtered air may be used. The advantage of providing oxygen is that it can clean the optics within the chamber by reacting with and removing carbon accumulated on the optics during operation of the source. To enable oxygen to clean the optics within the chamber, UV radiation may be provided within the chamber to interact with the oxygen during the idle state. The UV radiation may comprise radiation of one or more wavelengths below 240 nm. Preferably, the UV radiation comprises radiation with a wavelength of approximately 185 nm. The UV radiation may be provided by a source, for example, by installing a mercury UV source for irradiating the chamber.

[0160] Ultraviolet radiation can convert some oxygen into ozone, which can then react with carbon pollutants in the chamber to form volatile products. These volatile products can then be removed from the chamber by pumping them out. The cleaning process can be performed in the chamber for several hours, such as two hours or more. If the irradiation source is idle for a longer period than the cleaning process continues, the cleaning process can be paused, for example, by turning off the UV radiation, and / or by removing oxygen from the airflow mixture.

[0161] In some embodiments, the gas delivery system may include two supply lines for a first gas and a second gas, respectively. When the first supply line for a first state (e.g., using neon) is closed, the second supply line for a second state (e.g., using nitrogen) can be opened. Compared to a setup using a single supply line for both the first and second gases, this separate nitrogen supply line may require a lower nitrogen flow rate and pressure.

[0162] When using separate supply lines, they can provide the same gas in some instances, with the gas flow rate and pressure in the first state being significantly higher than those in the second state. This can still result in lower operating costs and resource consumption during the idle second state of the gas delivery system due to the lower gas flow rate and pressure required when using the second supply line. In some embodiments, the second gas may include recirculated first gas, that is, using first gas already used in the source in the first and / or second states. This can further reduce gas resource consumption.

[0163] In some examples, during the second state, the gate valve can be closed within the irradiation source to reduce pump capacity. The gate valve may be located upstream of the turbomolecular pump (TMP) of the source. Closing or partially closing this valve can reduce the pump capacity during the idle state of the irradiation source, which can result in conditions where a lower gas supply may be required to meet pressure and heat transfer coefficient requirements.

[0164] The two-state on / off gas delivery system described herein can be used in conjunction with an interferometer setup for measuring the properties of the gas target. However, the effect of a gas delivery system that provides gas with a heat transfer coefficient matching that of the gas in the on state of the source can operate independently of features such as the interferometer setup described herein. Therefore, the two-state gas delivery system can operate and be provided independently of the interferometer setup or any optional features of the irradiation source described herein.

[0165] The steps of the methods mentioned above can be in different orders, and these steps can be executed in parallel. The methods mentioned above can also be applied to (e.g., Figure 12 In the feedback loop, step 123 can loop back to step 120.

[0166] The irradiation source can be placed in, for example, a measurement device (MT), an inspection device, a lithography device (LA), and / or a lithography unit (LC).

[0167] The properties of the emitted radiation used to perform the measurement can affect the quality of the obtained measurement. For example, the shape and size of the transverse beam profile (cross-section) of the radiation beam, the intensity of the radiation, and the power spectral density of the radiation can all affect the measurement performed by the radiation. Therefore, it is beneficial to have a source that provides radiation with properties that lead to high-quality measurements.

[0168] Further embodiments are disclosed in the following numbered aspects:

[0169] 1. An irradiation source, comprising

[0170] - A gas delivery system configured to provide a gas target for generating emitted radiation at the interaction region of the gas target; and

[0171] - An interferometer used to irradiate at least a portion of the gaseous target with interferometer radiation to measure the properties of the gaseous target.

[0172] 2. The irradiation source according to aspect 1, wherein the irradiation source is configured to receive pump radiation and provide the pump radiation at the interaction region.

[0173] 3. The irradiation source according to aspect 2, wherein the interferometer radiation has an interferometer wavelength and the pump radiation has a pump wavelength, wherein the interferometer wavelength and the pump wavelength are different.

[0174] 4. The irradiation source according to aspect 2 or 3, wherein the interferometer radiation and the pump radiation comprise pulses.

[0175] 5. The irradiation source according to aspect 4, wherein the pulses of the interferometer radiation and the pulses of the pump radiation are at least partially synchronized.

[0176] 6. The irradiation source according to any one of aspects 4 or 5, wherein the irradiation source includes a time delay unit for adjusting the time delay between the pulses radiated by the interferometer and the pulses radiated by the pump.

[0177] 7. The irradiation source according to any of the foregoing aspects, wherein the interferometer radiation is a second-order or higher-order harmonic of the interferometer pump radiation generated by the harmonic generation process.

[0178] 8. The irradiation source according to aspect 7, wherein the interferometer radiation is a second or third harmonic of the interferometer pump radiation generated by the harmonic generation process.

[0179] 9. The irradiation source according to aspect 7 or 8, wherein the interferometer pump radiation and the pump radiation are separated from the radiation source.

[0180] 10. The irradiation source according to aspect 9, wherein the irradiation source includes a reflective surface having a pinhole for separating the interferometer pump radiation and the pump radiation.

[0181] 11. The irradiation source according to aspect 10, wherein, in operation, the interferometer pump radiation passes through the pinhole and the pump radiation is reflected by the reflective surface.

[0182] 12. The irradiation source according to any one of aspects 7 to 11, wherein the power of the interferometer pump radiation is at least one order of magnitude lower than the power of the pump radiation.

[0183] 13. The irradiation source according to any of the foregoing aspects, wherein the irradiation source includes a feedback loop or feedforward loop based on the properties of the gas target.

[0184] 14. An irradiation source according to aspect 13 of referenced aspect 2, wherein the irradiation source includes a feedback loop to control the properties of at least one of the pump radiation, the gas delivery system, subsequent optics, and substrate positioning mechanism based on the properties of the gas target.

[0185] 15. The irradiation source according to any of the preceding aspects, wherein the interferometer comprises two branches, wherein the first branch radiates at least partially through the gaseous target, and the second branch radiates not through the gaseous target, wherein the first branch radiation and the second branch radiation interfere with each other.

[0186] 16. The irradiation source according to any of the foregoing aspects, wherein the gas delivery system includes a gas nozzle, and the interferometer radiation irradiates at least partially onto at least a portion of the gas nozzle.

[0187] 17. The irradiation source according to any one of aspects 1 to 15, wherein the interaction region is included within the capillary structure.

[0188] 18. The irradiation source according to any of the preceding aspects, wherein the interferometer includes an adjustable element for changing the propagation direction of the interferometer radiation.

[0189] 19. An irradiation source comprising: a gas delivery system configured to provide a first state and a second state; wherein the first state is configured to include a first gas forming a gaseous target for generating emitted radiation at an interaction region of the gaseous target; and wherein the second state is configured to include a second gas during an idle state of the radiation source, such that the heat transfer coefficient of the second state matches the heat transfer coefficient of the first state.

[0190] 20. The irradiation source according to aspect 19, wherein the flow rate of the first gas is in the range of 5 nL / min to 20 nL / min.

[0191] 21. The irradiation source according to any one of aspects 19 to 20, wherein the first gas comprises neon or xenon.

[0192] 22. The irradiation source according to any one of aspects 19 to 21, wherein the gas delivery system includes separate supply lines configured to supply the first gas and the second gas.

[0193] 23. The irradiation source according to any one of aspects 19 to 22, wherein the second gas comprises nitrogen or argon.

[0194] 24. The irradiation source according to any one of aspects 19 to 22, wherein the second gas comprises a gas mixture containing oxygen.

[0195] 25. The irradiation source according to any one of aspects 19 to 24, wherein the second gas comprises a recirculated first gas.

[0196] 26. The irradiation source according to any of the foregoing aspects, wherein the irradiation source includes a space configured to be emptied, and the gas delivery system is configured to provide the gas target in the space.

[0197] 27. The irradiation source according to any of the foregoing aspects, wherein the emitted radiation has a wavelength in the X-ray or EUV range, wherein optionally, the wavelength is in the range of 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.

[0198] 28. A measuring device comprising an irradiation source according to any one of aspects 1 to 27.

[0199] 29. The measuring apparatus according to aspect 28, wherein, in operation, the emitted radiation is directed onto a substrate.

[0200] 30. A photolithography unit comprising an irradiation source according to any one of aspects 1 to 27 or comprising a measurement device according to aspect 28 or 29.

[0201] 31. A method for inspecting a gaseous target exposed to an irradiation source, comprising:

[0202] - Utilizing a gas delivery system to provide a gas target for generating emitted radiation at the interaction region of the gas target; and

[0203] - Use interferometer radiation to irradiate at least a portion of the gaseous target to measure the properties of the gaseous target.

[0204] 32. The method according to aspect 31, wherein the method comprises: controlling the properties of at least one of the gas delivery system, the pump radiation, the subsequent optics, and the substrate positioning mechanism based on the properties of the gas target measured by the scatterometer.

[0205] 33. A method for aligning pump radiation relative to a gaseous target, comprising the following steps:

[0206] - The gas target is provided using a gas delivery system;

[0207] - To measure the properties of the gas target by irradiating at least a portion of the gas target with the interferometer radiation of the interferometer;

[0208] - Irradiating at least a portion of the gaseous target using pump radiation; and

[0209] - The properties of at least one of the gas delivery system, the pump radiation, the subsequent optics, and the substrate positioning mechanism are controlled based on the properties of the gas target as measured by the scatterer.

[0210] 34. A method for optimizing emitted radiation output, comprising the following steps:

[0211] - Utilize a gas delivery system to deliver the gas target;

[0212] - To measure the properties of the gas target by irradiating at least a portion of the gas target with the interferometer radiation of the interferometer;

[0213] - Irradiating at least a portion of the gaseous target using pump radiation; and

[0214] - The properties of at least one of the gas delivery system, the pump radiation, the subsequent optics, and the substrate positioning mechanism are controlled based on the properties of the gas target as measured by the scatterer.

[0215] 35. A method for monitoring the evolution of plasma over time, comprising the following steps:

[0216] - Utilize a gas delivery system to deliver the gas target;

[0217] - To measure the properties of the gas target by irradiating at least a portion of the gas target with the interferometer radiation of the interferometer;

[0218] - Irradiating at least a portion of the gaseous target with pump radiation to initiate the evolution of the plasma within the gaseous target; and

[0219] - The evolution of the plasma over time is monitored based on the properties of the gaseous target measured by the interferometer.

[0220] 36. The method according to aspect 35, wherein the method comprises: controlling the properties of at least one of the gas delivery system, the pump radiation, the subsequent optics, and the substrate positioning mechanism based on the properties of the gas target measured by the scatterometer.

[0221] While this article provides specific references to the use of photolithography equipment in IC manufacturing, it should be understood that the photolithography equipment described herein can have other applications. Possible other applications include the fabrication of integrated optical systems, patterning for guiding and detecting magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0222] While specific references are made herein to embodiments within the context of photolithography equipment, these embodiments can be used with other equipment. Embodiments may form part of mask inspection equipment, metrology equipment, or any equipment for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning apparatus). These devices are generally referred to as photolithography tools. Such photolithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0223] While embodiments are specifically referenced herein in the context of inspection or measurement equipment, these embodiments can be used with other equipment. Embodiments may form part of a mask inspection apparatus, a lithography apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning apparatuses). The term "measurement equipment" (or "inspection equipment") may also refer to an inspection apparatus or inspection system (or a measurement apparatus or measurement system). For example, an inspection apparatus including embodiments may be used to detect defects in a substrate or defects in a structure on or on a substrate. In such embodiments, the characteristics of interest concerning the structure on the substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of an unwanted structure on the substrate.

[0224] Although specific references have been made above to the use of the embodiments in the context of optical lithography, it will be understood that the invention is not limited to optical lithography and can be used in other applications, such as imprint lithography, where circumstances permit.

[0225] While the targets or target structures described above (more generally, structures on a substrate) are measurement target structures specifically designed and formed for measurement purposes, in other embodiments, properties of interest may be measured on one or more structures that are functional components of a device formed on a substrate. Many devices have regular grating-like structures. The terms structure, target grating, and target structure used in this invention do not need to be specifically provided for the measurement being performed. Furthermore, the pitch of the measurement target may be close to or smaller than the resolution limit of the optical system of the scatterer, but may be much larger than the size of the typical non-target structure (optionally, product structure) formed by the photolithography process in the target portion C. In practice, the lines and / or spaces of overlapping gratings within the target structure may be made to create a smaller structure with dimensions similar to the non-target structure.

[0226] While specific embodiments have been described above, it will be understood that the invention may be practiced in ways different from those described. The description above is intended to be exemplary and not restrictive. Therefore, those skilled in the art will understand that modifications can be made to the invention as described without departing from the scope of the claims set forth below.

[0227] While specifically referring to "measuring equipment / tools / systems" or "inspection equipment / tools / systems," these terms can refer to the same or similar types of tools, equipment, or systems. For example, inspection or measuring equipment including embodiments of the present invention can be used to determine the characteristics of structures on a substrate or wafer. For example, inspection or measuring equipment including embodiments of the present invention can be used to detect defects in a substrate or defects in structures on a substrate or wafer. In such embodiments, the characteristics of interest concerning the structure on the substrate may relate to defects in the structure, the absence of a specific portion of the structure, or the presence of unwanted structures on the substrate or wafer.

[0228] Although HXR, SXR and EUV electromagnetic radiation are specifically mentioned, it will be understood that the present invention can be practiced using all electromagnetic radiation, including radiation waves, microwaves, infrared, (visible) light, ultraviolet, X-rays and gamma rays, where circumstances permit.

Claims

1. A method for optimizing emitted radiation, comprising the following steps: - Utilizing a gas delivery system to deliver the gas target. - The gaseous target is irradiated with the first radiation of the interferometer to measure the properties of the gaseous target. - To irradiate at least a portion of the gaseous target using pump radiation to generate the emitted radiation, and - The properties of at least one of the gas delivery system, the pump radiation, the subsequent optics, and the substrate positioning mechanism are controlled based on the measurable properties of the gas target as measured by the interferometer. Wherein, the first radiation has a first wavelength, the pump radiation has a pump wavelength, and the first wavelength and the pump wavelength are different.

2. The method according to claim 1, wherein, The first radiation is a second-order, third-order, or higher-order harmonic of the second radiation generated by the harmonic generation process.

3. The method according to claim 2, wherein, The second radiation and the pump radiation are separated from a single radiation source.

4. The method according to claim 1, comprising: Based on the measured properties of the gas target, a feedback loop is used to control the properties of at least one of the gas delivery system, the pump radiation, the subsequent optics, and the substrate positioning mechanism.

5. The method according to any one of claims 1 to 3, comprising: Based on the measured properties of the gas target, a feedforward loop is used to control the properties of at least one of the gas delivery system, the pump radiation, the subsequent optics, and the substrate positioning mechanism.

6. The method according to claim 1, comprising: An interferometer is used to measure the properties of the gaseous target.

7. The method according to claim 1, wherein, The first radiation includes a pulse.

8. The method according to claim 7, wherein, The pump radiation includes pulses, and the pulses of the first radiation and the pump radiation are at least partially synchronized.

9. The method of claim 8, comprising: A time delay unit is used to adjust the time delay between the pulse of the first radiation and the pulse of the pump radiation.

10. The method according to claim 1, wherein, The gas delivery system includes a gas nozzle, and the first radiation irradiates at least a portion of the gas nozzle.

11. The method according to claim 1, wherein, The step of generating the emitted radiation is the generation of higher-order harmonics.

12. The method according to claim 1, wherein, The emitted radiation is generated from the interaction region by irradiating at least a portion of the gas target with pump radiation, the interaction region being included within the capillary structure.

13. The method according to claim 1, wherein, The emitted radiation has a wavelength in the range of 0.01 nm to 100 nm.

14. An irradiation source, comprising: - A gas delivery system configured to provide a gas target having an interaction zone. - An interferometer for irradiating at least a portion of the gaseous target with a first radiation to measure the properties of the gaseous target. - Pump radiation, said pump radiation being used to irradiate the interaction region to generate emitted radiation at the interaction region, and - A processor configured to control the properties of at least one of the gas delivery system, the pump radiation, subsequent optics, and the substrate positioning mechanism based on measured properties of the gas target as measured by the interferometer. The properties being measured are determined through the first radiation, and The first radiation has a first wavelength, the pump radiation has a pump wavelength, and the first wavelength and the pump wavelength are different.

15. A measuring device, the measuring device comprising the irradiation source according to claim 14, wherein, During operation, the emitted radiation is directed onto the structure on the substrate.

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