Membranes and associated methods and apparatus

Abstract

A pellicle membrane is disclosed, the pellicle membrane comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, the at least one inner layer comprises one or more of boron, zirconium, beryllium, niobium, yttrium, molybdenum and / or carbon and / or one or more compounds of each of these materials, and / or consists of one or more of boron, zirconium, beryllium, niobium, yttrium, molybdenum and / or carbon and / or one or more compounds of each of these materials. Also disclosed is a metrology device that uses such a pellicle membrane as a beam splitter and / or filter.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22176381.6 filed on May 31, 2022 and EP application 22182745.4 filed on July 4, 2022, and the above EP applications are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to metrology applications in the manufacture of integrated circuits. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as a "design layout" or "design") at a patterning device (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, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Typical wavelengths currently used are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Compared to lithographic apparatus using radiation having a wavelength of, for example, 193 nm, lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on a substrate.

[0006] Low k1 lithography can be used to process features with dimensions smaller than the classical resolution limit of the lithographic apparatus. In such a process, the resolution formula can be expressed as CD = k1 × λ / NA, where λ is the wavelength of the radiation employed, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the "critical dimension" (usually the smallest feature size printed, but in this case the half pitch), and k1 is an empirical resolution factor. In general, the smaller the k1, the more difficult it becomes to reproduce a pattern on a substrate that resembles the shape and size planned by the circuit designer in order to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. These steps include, for example, but are not limited to, optimization of the 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 strict control loop for controlling the stability of the lithographic apparatus can be used to improve the reproduction of patterns at low k1.

[0007] During lithography, as well as other manufacturing processes, it is desirable to frequently make measurements of the resulting structures, for example for process control and verification. Various tools are known for making such measurements, including scanning electron microscopes, which are often used to measure critical dimensions (CDs), and specialized tools for measuring overlay (the accuracy of alignment of two layers in a device). In recent years, various forms of scatterometers have been developed for use in the field of lithography. The manufacturing process may be, for example, lithography, etching, deposition, chemical mechanical planarization, oxidation, ion implantation, diffusion, or a combination of two or more of lithography, etching, deposition, chemical mechanical planarization, oxidation, ion implantation, diffusion.

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

[0009] In addition to measuring feature shapes by reconstruction, this device can also be used to measure diffraction-based overlap, as described in published patent application US2006066855A1. Overlap measurements based on diffraction-based imaging using diffraction orders enable overlay measurements of smaller targets. These targets may be smaller than the illumination spot and may be surrounded by product structures on the wafer. Examples of dark field imaging measurements can be found in numerous published patent applications such as US2011102753A1 and US20120044470A. Multiple gratings can be measured in one image using a composite grating target. Known scatterometers tend to use light in the visible or near infrared (IR) wave range, which requires that the pitch of the grating is much coarser than the actual product structure whose properties are actually of interest. Deep ultraviolet (DUV), extreme ultraviolet (EUV), or X-ray radiation with much shorter wavelengths can be used to define such product features. Unfortunately, such wavelengths are generally not suitable for or cannot be used for measurement.

[0010] On the other hand, the size of modern product structures is so small that modern product structures cannot be imaged by optical measurement techniques. Smaller features include, for example, features formed by multiple patterning processes and / or pitch multiplication. Therefore, targets for high-volume measurement often use features that are much larger than products whose overlay error or critical dimensions are properties of concern. The measurement results are only indirectly related to the size of the real product structure and may not be accurate because the measurement target does not suffer the same distortion under optical projection in the lithography equipment, and / or different treatments in other steps of the manufacturing process. Although scanning electron microscopy (SEM) can directly resolve these modern product structures, SEM is much more time-consuming than optical measurement. In addition, electrons cannot penetrate thicker process layers, which makes electrons less suitable for measurement applications. Other techniques such as using contact pads to measure electrical properties are also known, but the other techniques only provide indirect evidence of the real product structure.

[0011] By reducing the wavelength of the radiation used during metrology (e.g., moving toward the "soft X-ray (SXR)" wavelength spectrum), smaller structures can be resolved to increase sensitivity to structural changes in structures and / or to penetrate further into product structures. One such method of generating suitable high-frequency radiation (e.g., hard X-rays, soft X-rays, and / or EUV radiation) may be to use pump radiation (e.g., infrared IR radiation) to excite a generation medium, thereby generating emitted radiation, optionally including higher order harmonic generation of the high-frequency radiation.

[0012] In a metrology tool, it is necessary to split the source radiation into a main illumination branch and a reference sub-branch. The reference sub-branch can be used to monitor the source spectrum or to obtain information about the source spectrum, which can be used to infer the value of the parameter of interest when measuring the structure using the metrology tool. Such beam splitting can be difficult when SXR or EUV radiation is used as the measurement radiation. Although gratings can be used, it is then difficult to maintain high transmission and low scattering of the measurement radiation. Furthermore, including a grating in the illumination path imposes additional constraints on the optical design, making it more difficult to optimize the design for other system requirements.

[0013] It would be desirable to obtain an improved beam splitting of the source illumination into a main illumination branch and a reference sub-branch. Summary of the invention

[0014] In a first aspect of the present invention, a measurement device is provided, the measurement device comprising: an illumination branch, the illumination branch comprising an illumination optical device for guiding a measurement radiation beam onto the structure; a pellicle beam splitter, the pellicle beam splitter is located in the illumination branch, the pellicle beam splitter comprises a pellicle diaphragm, the pellicle diaphragm is operable to separate a source radiation beam from an illumination source into a reference radiation beam and the measurement radiation beam; a measurement detector, the measurement detector is used to detect the measurement radiation beam after the measurement radiation beam is scattered by the structure; and a reference detector, the reference detector is used to detect the reference radiation beam.

[0015] In a second aspect of the present invention, a pellicle diaphragm is provided, comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer comprises and / or consists of boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials.

[0016] In a third aspect of the present invention, a pellicle diaphragm is provided, comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer comprises and / or consists of one or more of silicon, boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials; and the thickness of the at least one outer layer on each side of the at least one inner layer is between 1 nm and 3 nm.

[0017] In a fourth aspect of the present invention, a filter diaphragm is provided, the filter diaphragm comprising at least two materials, wherein at least a first material of the at least two materials comprises or consists of germanium or selenium.

[0018] In a fifth aspect of the invention, a method for detecting radiation-induced damage and / or contamination on an irradiated area is provided.

[0019] The above and other aspects of the invention will be understood from a consideration of the examples described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0021] - Figure 1 A schematic overview diagram depicting a lithographic apparatus;

[0022] - Figure 2 A schematic overview diagram depicting a lithography unit;

[0023] - Figure 3 Depicting a schematic representation of overall lithography showing the cooperation between three key technologies to optimize semiconductor manufacturing;

[0024] - Figure 4 schematically illustrates a scatterometry device;

[0025] - Figure 5 depicts a schematic representation of a metrology apparatus in which EUV and / or SXR radiation is used;

[0026] - Figure 6 A simplified schematic diagram depicting an illumination source that may be used for applications such as Figure 5 An irradiation source generated by high-order harmonics of the measurement device shown in FIG.

[0027] - Figure 7 comprising (a) a schematic diagram of a dark field scatterometer for measuring a target using a first pair of illumination apertures according to an embodiment of the present invention, (b) details of a diffraction spectrum of a target grating for a given illumination direction, (c) a second pair of illumination apertures providing an additional illumination mode when using the scatterometer for diffraction-based overlay measurements, and (d) a third pair of illumination apertures combining the first pair of apertures with the second pair of apertures;

[0028] - Figure 8 is a schematic illustration of a measurement device of a known configuration;

[0029] - Fig. 9 is a schematic illustration of a measurement device according to an embodiment;

[0030] - Fig.10 (a) is a graph of the transmittance Trn of the zirconium filter versus the wavelength λ;

[0031] - Fig.10 (b) is a graph of the transmittance Trn of the germanium filter relative to the wavelength λ;

[0032] - Fig.10 (c) is a graph of transmittance Trn of a selenium filter versus wavelength λ; and

[0033] - Fig.11 is a graph of transmittance Trn versus wavelength λ for each of a germanium and zirconium filter, a selenium and copper filter, and a boron, germanium and zirconium filter. DETAILED DESCRIPTION

[0034] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation and particle radiation, including ultraviolet radiation (e.g., having a wavelength of 365nm, 248nm, 193nm, 157nm or 126nm), EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5nm to 100nm), X-ray radiation, electron beam radiation and other particle radiation.

[0035] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to the pattern to be produced in a target portion of the substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective, binary, phase-shift, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0036] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, EUV radiation, or X-ray radiation), a mask support (e.g., a mask stage) T configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a 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 to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0037] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, diffractive, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for directing, shaping, and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in a cross-section of the radiation beam B at the plane of the patterning device MA.

[0038] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems suitable for the exposure radiation used and / or for other factors such as the use of an immersion liquid or the use of a vacuum, including refractive, reflective, diffractive, catadioptric, synthetic, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0039] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g. water) so as to fill the space between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference in its entirety.

[0040] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or a step of preparing a substrate W for subsequent exposure may be performed on a substrate W on one of the substrate supports WT while another substrate W on another substrate support WT is being used to expose a pattern on another substrate W.

[0041] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning means may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of a system for providing immersion liquid. The measurement platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0042] In operation, a radiation beam B is incident on a patterning device (e.g. a mask) MA held on a mask support T and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example to position different target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM and possibly another position sensor (not shown) are arranged to move the substrate support WT to a position where the radiation beam is focused and aligned. Figure 1Another position sensor (explicitly depicted in FIG. 1 ) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The mask alignment marks M1, M2 and the substrate alignment marks P1, P2 can be used to align the patterning device MA and the substrate W. Although the substrate alignment marks P1, P2 occupy dedicated target portions as illustrated, the substrate alignment marks P1, P2 can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe line alignment marks.

[0043] like Figure 2 As shown in , the lithography apparatus LA may form part of a lithocell LC (sometimes also referred to as a lithocell or (lithography) cluster), which typically also includes equipment for performing pre-exposure processes and post-exposure processes on a substrate W. Conventionally, these equipment include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH and a bake plate BK, for example, for regulating the temperature of the substrate W (for example, for regulating the solvent in the resist layer). A substrate handler or robot RO picks up the substrate W from the input / output ports I / O1, I / O2, moves the substrate W between the different process equipment and transfers the substrate W to a feed table LB of the lithography apparatus LA. The devices in the lithography cell, which are often also collectively referred to as tracks or coating and developing systems, may be under the control of a track control unit TCU, which itself may be controlled by a management control system SCS, which may also control the lithography apparatus LA, for example, via a litho control unit LACU.

[0044] During the lithographic process, it is desirable to frequently measure the generated structures, for example for process control and verification. The tool used to perform such measurements may be referred to as a measurement tool MT. Different types of measurement tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer measurement tools MT. A scatterometer is a multifunctional instrument that allows the measurement of parameters of the lithographic process by arranging a sensor in or near the pupil of an objective lens of the scatterometer, or in a plane conjugated to the pupil, in which case the measurement is generally referred to as pupil-based measurement, or by arranging a sensor in or near the image plane, or in a plane conjugated to the image plane, in which case the measurement is generally referred to as image-based or field-based measurement. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, which are incorporated herein by reference in their entirety. The scatterometer can measure gratings using light from the hard X-ray (HXR), soft X-ray (SXR), extreme ultraviolet (EUV), visible to near IR and IR wavelength ranges. In the case where the radiation is hard X-ray or soft X-ray, the scatterometer can optionally be a small angle X-ray scattering measurement tool.

[0045] In order to correctly and consistently expose the substrate W exposed by the lithographic apparatus LA, it is desirable to inspect the substrate to measure properties of the patterned structure, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), shape of the structure, etc. For this purpose, inspection tools and / or metrology tools (not shown) may be included in the lithography cell LC. If errors are detected, especially if the inspection is performed before other substrates W of the same batch or lot are yet to be exposed or processed, adjustments may be made, for example, to the exposure of subsequent substrates or other processing steps to be performed on the substrates W.

[0046] The detection apparatus, which may also be referred to as a metrology apparatus, is used to determine properties of the substrate W, and in particular, to determine how properties of different substrates W vary or how properties associated with different layers of the same substrate W vary between the different layers. The detection apparatus may alternatively be configured to identify defects on the substrate W, and may for example be part of the lithography cell LC, or may be integrated into the lithography apparatus LA, or may even be a stand-alone device. The detection apparatus may measure properties on a latent image (the image in the resist layer after exposure), or on a semi-latent image (the image in the resist layer after a post-exposure bake step PEB), or on a developed resist image (wherein the exposed or unexposed parts of the resist have been removed), or even on an etched image (after a pattern transfer step such as etching).

[0047] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, reconstruction methods can be applied to the measured signals to reconstruct or calculate the properties of the grating. Such reconstruction can be caused, for example, by simulating the interaction of the scattered radiation with 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 the diffraction pattern observed from a real target.

[0048] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer MT, radiation emitted by a radiation source is directed onto a target and reflected, transmitted or scattered radiation from the target is directed to a spectrometer detector which measures the spectrum of the specularly reflected radiation (i.e. a measure of the intensity as a function of wavelength). From this data, the structure or profile of the target producing the detected spectrum can be reconstructed, for example by rigorous coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra.

[0049] In a third embodiment, the scatterometer MT is an ellipsometric scatterometer. An ellipsometric scatterometer allows the parameters of a lithography process to be determined by measuring scattered radiation for each polarization state (the scattered radiation may be diffracted, reflected or transmitted). Such a metrology device emits polarized light (such as linear, circular or elliptical) by using, for example, an appropriate polarization filter in the illumination section of the metrology device. A source suitable for the metrology device may also provide polarized radiation. Various embodiments of existing ellipsometric scatterometers are described in U.S. patent applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110 and 13 / 891,410, which are incorporated herein by reference in their entirety.

[0050] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflection spectrum and / or an asymmetry in the detection configuration (the asymmetry being related to the extent of the overlap). The two (possibly overlapping) grating structures may be applied in two different layers (not necessarily consecutive layers) and the two grating structures may be formed at substantially the same position on the wafer. The scatterometer may have a symmetrical detection configuration as described, for example, in the co-owned patent application EP1,628,164A, so that any asymmetry can be clearly distinguished. This provides a straightforward way to measure misalignment in the gratings. Other examples of measuring the overlay error between two layers containing a periodic structure as a target via the asymmetry of the periodic structure may be found in PCT Patent Application Publication No. WO2011 / 012624 or in U.S. Patent Application No. US20160161863, which are incorporated herein by reference in their entirety.

[0051] Other parameters of interest may be focus and dose. Focus and dose may be determined simultaneously by scatterometry as described in U.S. Patent Application US2011-0249244, which is incorporated herein by reference in its entirety (or alternatively by scanning electron microscopy). A single structure may be used that has a unique combination of critical dimension and sidewall angle measurements for each point in a focus energy matrix (FEM - also referred to as a focus exposure matrix). If these unique combinations of critical dimension and sidewall angle are available, focus and dose values ​​may be uniquely determined from these measurements.

[0052] The measurement target may be a collection of composite gratings formed primarily in resist by a lithography process and also after other manufacturing processes (e.g., etching processes). The pitch and line width of the structures in the grating may depend heavily on the measurement optics (particularly the NA of the optics) to be able to capture the diffraction orders from the measurement target. As indicated earlier, the diffraction signal may be used to determine the shift between two layers (also referred to as "overlap") or may be used to reconstruct at least a portion of the original grating as produced by the lithography process. This reconstruction may be used to provide quality guidance for the lithography process and may be used to control at least a portion of the lithography process. The target may have smaller sub-segments configured to mimic the size of a functional portion of a design layout in the target. Due to the sub-segmentation, the target will behave more like a functional portion of the design layout, so that the overall process parameter measurement is more similar to the functional portion of the design layout. The target may be measured in an underfill mode or in an overfill mode. In the underfill mode, the measurement beam produces a light spot that is smaller than the overall target. In the overfill mode, the measurement beam produces a light spot that is larger than the overall target. In this overfill mode, different targets may also be measured simultaneously, and therefore different process parameters may be determined simultaneously.

[0053] The overall measurement quality of the lithography parameters performed using a specific target is determined at least in part by a measurement matching scheme for measuring the lithography parameters. The term "substrate measurement matching scheme" can include one or more parameters of the measurement itself, one or more parameters of the measured one or more patterns, or one or more parameters of the measurement itself and one or more parameters of the measured one or more patterns. For example, if the measurement used in the substrate measurement matching scheme is an optical measurement based on diffraction, one or more of the measured parameters may include the wavelength of the radiation, the polarization of the radiation, the incident angle of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. One of the criteria for selecting the measurement matching scheme can be, for example, the sensitivity of one of the measurement parameters to process changes. More examples are described in U.S. Patent Application US2016-0161863 and U.S. Patent Publication Application US 2016 / 0370717A1, which are incorporated herein by reference in their entirety.

[0054] The patterning process in the lithographic apparatus LA may be one of the most critical steps in the process requiring a high accuracy in the dimensioning and positioning of structures on the substrate W. To ensure this high accuracy, three systems may be combined in a Figure 3 . One of these systems is a lithographic apparatus LA, which is (in practice) connected to a metrology tool MT (a second system) and to a computer system CL (a third system). The key to this "holistic" environment is to optimize the cooperation between these three systems to enhance the overall process window and to provide a tight control loop to ensure that the patterning performed by the lithographic apparatus LA is within the process window. The process window defines the range of process parameters (e.g. dose, focus, overlay) within which a particular manufacturing process produces a defined result (e.g. a functional semiconductor device) - possibly allowing for variations in process parameters in the lithographic process or the patterning process within the defined result.

[0055] The computer system CL can use (a portion of) the design layout to be patterned to predict which resolution enhancement technology to use and perform algorithmic lithography simulations and calculations to determine which mask layout and lithography equipment settings achieve the maximum overall process window for the patterning process (in Figure 3 The resolution enhancement technique may be arranged to match the patterning possibilities of the lithographic apparatus LA. The computer system CL may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g. using input from a metrology tool MET) to predict whether defects may be present (e.g. due to suboptimal processing) Figure 3) is depicted by an arrow pointing to “0” in the second scale SC2.

[0056] The metrology tool MT may provide input to the computer system CL to enable accurate simulation and prediction, and may provide feedback to the lithographic apparatus LA to identify, for example, possible drift in the calibration state of the lithographic apparatus LA (in Figure 3 ) as depicted by multiple arrows in a third scale SC3.

[0057] Many different forms of metrology tools MT can be provided for measuring structures produced using lithographic patterning equipment. The metrology tool MT can use electromagnetic radiation to interrogate the structure. The properties of the radiation (e.g. wavelength, bandwidth, power) may affect different measurement characteristics of the tool, with shorter wavelengths generally allowing increased resolution. The wavelength of the radiation has an impact on the resolution that the metrology tool can achieve. Therefore, in order to be able to measure structures including features with smaller dimensions, a metrology tool MT with a short wavelength radiation source is preferred.

[0058] Another way that the wavelength of the radiation may affect the measurement characteristics is the penetration depth, and the transparency / opacity of the material being inspected at the wavelength of the radiation. Depending on the opacity and / or penetration depth, the radiation may be used for measurements of transmission or reflection. The type of measurement may affect whether information is obtained about the surface and / or bulk interior of the structure / substrate. Therefore, penetration depth and opacity are another factor to be considered when selecting a radiation wavelength for a metrology tool.

[0059] In order to achieve higher resolution for the measurement of lithographically patterned structures, a measurement tool MT with a short wavelength is preferred. This can include wavelengths shorter than the visible wavelength, for example in the UV, EUV, and X-ray parts of the electromagnetic spectrum. Hard X-ray methods such as transmission small angle X-ray scattering (TSAXS) take advantage of the high resolution and high penetration depth of hard X-rays, and can therefore operate in transmission. On the other hand, soft X-rays and EUV do not penetrate the target very deeply, but can induce a rich optical response in the material to be detected. This can be attributed to the optical properties of many semiconductor materials, and to the size of the structure being comparable to the detection wavelength. Therefore, the EUV and / or soft X-ray measurement tool MT can operate in reflection, for example by imaging or by analyzing diffraction patterns from lithographically patterned structures.

[0060] For hard X-rays, soft X-rays, and EUV radiation, applications in high volume manufacturing (HVM) applications can be limited due to the lack of available high-brilliance radiation sources at the required wavelengths. In the case of hard X-rays, sources commonly used in industrial applications include X-ray tubes. X-ray tubes, including advanced X-ray tubes (e.g., based on liquid metal anodes or rotating anodes), can be relatively cheap and compact, but may lack the brilliance required for HVM applications. There are currently high-brilliance X-ray sources such as synchrotron light sources (SLS) and X-ray free electron lasers (XFELs), but their size (>100m) and high cost (hundreds of millions of euros) make high-brilliance X-ray sources too large and expensive for metrology applications. Similarly, there is a lack of availability of sufficiently bright EUV and soft X-ray radiation sources.

[0061] During lithography, it is desirable to frequently measure the structures produced, for example for process control and verification. Various tools for making such measurements are known, including scanning electron microscopes or various forms of metrology equipment, such as scatterometers. Examples of known scatterometers often rely on the setup of a dedicated measurement target, such as an underfilled target (a target in the form of a simple grating or overlapping gratings in different layers, which is large enough that the measurement beam produces a light spot that is smaller than the grating) or an overfilled target (whereby the irradiated light spot partially or completely encompasses the target). In addition, the use of a metrology tool (e.g., an angle-resolved scatterometer that irradiates an underfilled target such as a grating) allows the use of so-called reconstruction methods, in which the properties of the grating can be calculated by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulated results with the measured results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to the diffraction pattern observed from a real target.

[0062] Scatterometers are multifunctional instruments that allow measuring parameters of a lithographic process by placing a sensor in the pupil of the objective of the scatterometer or in a plane conjugate to the pupil, the measurement being generally referred to as pupil-based measurement, or by placing a sensor in the image plane or in a plane conjugate to the image plane, in which case the measurement is generally referred to as image-based or field-based measurement. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, which are incorporated herein by reference in their entirety. The aforementioned scatterometers can measure multiple targets from multiple gratings in one image using light from soft x-rays, extreme ultraviolet, and visible to near IR wave ranges.

[0063] Figure 4An example of a metrology device, such as a scatterometer, is depicted in FIG. The metrology device 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 specularly reflected radiation (i.e. a measure of the intensity I as a function of wavelength λ). From this data, the spectrum may be processed by a processing unit PU, for example by rigorous coupled wave analysis and nonlinear regression or by comparing the spectrum to the spectrum of the specularly reflected radiation. Figure 4 The structure or profile that produced the detected spectrum is reconstructed by comparing the simulated spectral library shown at the bottom of FIG8. In general, for the reconstruction, the general form of the structure is known, and some parameters are assumed based on knowledge of the process used to make the structure, leaving only some parameters of the structure to be determined from the scatterometry data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0064] Another example is a transmissive form of a metrology device, such as Figure 4 The transmitted radiation is passed to a spectrometer detector which measures the Figure 4 The spectrum discussed. Such a scatterometer may be configured as a normal incidence scatterometer or an oblique incidence scatterometer. Optionally, a transmission form of hard X-ray radiation having a wavelength of less than 1 nm, optionally less than 0.1 nm, optionally less than 0.01 nm is used.

[0065] As an alternative to optical metrology methods, the use of hard X-rays, soft X-rays, or EUV radiation, such as radiation having at least one of the following wavelength ranges: less than 0.01 nm, less than 0.1 nm, less than 1 nm, between 0.01 nm and 100 nm, between 0.01 nm and 50 nm, between 1 nm and 50 nm, between 1 nm and 20 nm, between 5 nm and 20 nm, and between 10 nm and 20 nm, has also been considered. An example of a metrology tool that functions in one of the wavelength ranges presented above is transmission small angle X-ray scattering (such as 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", SPIE Transactions, 2013, p. 8681. It should be noted that the use of a laser produced plasma (LPP) x-ray source is described in U.S. Patent Publication No. 2019 / 003988A1 and U.S. Patent Publication No. 2019 / 215940A1, which are incorporated herein by reference in their entirety. Reflectometry techniques using X-rays at grazing incidence (GI-XRS) and extreme ultraviolet (EUV) radiation can be used to measure the properties of stacks of thin films and layers on substrates. Within the general field of reflectometry, goniometric and / or spectroscopic techniques can be applied. In goniometrics, the variation of a reflected beam with different angles of incidence can be measured. On the other hand, spectroscopic reflectometry (using broadband radiation) measures the spectrum of wavelengths reflected at a given angle. For example, EUV reflectometry has been used for the inspection of mask blanks prior to the manufacture of reticles (patterning devices) used in EUV lithography.

[0066] The range of applications is such that the use of wavelengths in the hard X-ray, soft X-ray, or EUV domains is insufficient, for example. Published patent applications US 20130304424A1 and US2014019097A1 (Bakeman et al. / KLA) describe hybrid measurement techniques in which measurements using x-rays and optical measurements using wavelengths in the range of 120 nm and 2000 nm are combined to obtain measurements of parameters such as CD. The CD measurement is obtained by coupling the x-ray mathematical model and the optical mathematical model via one or more common parts. The cited US patent applications are incorporated herein by reference in their entirety.

[0067] Figure 5Depicted is a schematic representation of a metrology apparatus 302 in which the aforementioned radiation may be used to measure parameters of structures on a substrate. Figure 5 The metrology device 302 presented in FIG. 3 may be suitable for hard X-ray, soft X-ray, and / or EUV domains.

[0068] Figure 5 Purely by way of example, a schematic physical arrangement of a metrology apparatus 302 comprising a spectroscopic scatterometer using hard X-ray, EUV, and / or SXR radiation at grazing incidence is illustrated. An alternative form of detection apparatus may be provided in the form of an angle-resolved scatterometer which, like conventional scatterometers operating at longer wavelengths, may use radiation at normal or near normal incidence and which may also use radiation having a direction that makes an angle greater than 1° or 2° from a direction parallel to the substrate. An alternative form of detection apparatus may be provided in the form of a transmission scatterometer.

[0069] The detection device 302 comprises a radiation source or so-called illumination source 310 , an illumination system 312 , a substrate support 316 , a detection system 318 , 398 , and a measurement processing unit (MPU) 320 .

[0070] The radiation source 310 in this example is used to generate EUV, hard X-ray, or soft X-ray radiation. The radiation source 310 can be based on Figure 6 The high-order harmonic generation (HHG) technology shown in the figure, and the irradiation source 310 can also be other types of irradiation sources, such as a liquid metal jet source, an inverse Compton scattering (ICS) source, a plasma channel source, a magnetic undulator source, a free electron laser (FEL) source, a compact storage ring source, a discharge-generated plasma source, a soft X-ray laser source, a rotating anode source, a solid anode source, a particle accelerator source, a microfocusing source, or a laser-generated plasma source.

[0071] The HHG source can be a gas jet / nozzle source, a capillary / fiber source, or a gas chamber source.

[0072] For example, a HHG source such as Figure 6As shown in , the main components of the radiation source are a pump radiation source 330 operable to emit pump radiation and a gas delivery system 332. Optionally, the pump radiation source 330 is a laser, optionally, the pump radiation source 330 is a pulsed high power infrared or optical laser. The pump radiation source 330 can be, for example, a fiber-based laser with an optical amplifier, thereby generating pulses of infrared radiation that can last, for example, less than 1 ns (1 nanosecond) per pulse, wherein the pulse repetition rate is up to several megahertz as required. The wavelength of the infrared radiation can be in the range of 200nm to 10μm, for example, about 1μm (1 micrometer). Optionally, the laser pulse is delivered to the gas delivery system 332 as the first pump radiation 340, wherein a portion of the radiation is converted to a higher frequency than the first radiation in the gas to become the emitted radiation 342. The gas source 334 supplies a suitable gas to the gas delivery system 332, wherein the gas is optionally ionized by the power supply 336. The gas delivery system 332 can be a cut-off tube.

[0073] The gas provided by the gas delivery system 332 defines a gas target, which can be a gas flow or a static volume. The gas can be, for example, air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations thereof. These gases can be selectable options within the same device. The emitted radiation can contain multiple wavelengths. If the emitted radiation is monochromatic, the measurement calculation (e.g., reconstruction) can be simplified, but it is easier to generate radiation with multiple wavelengths. The emission divergence angle of the emitted radiation can be wavelength-dependent. Different wavelengths will, for example, provide different levels of contrast when imaging structures of different materials. For example, in order to detect metal structures or silicon structures, different wavelengths can be selected as wavelengths for imaging features of (carbon-based) resists or for detecting contamination of such different materials. One or more filtering devices 344 can be provided. For example, filters such as diaphragms of aluminum (Al) or zirconium (Zr) can be used to cut off fundamental IR radiation from further transmission into the detection device. A grating (not shown) can be provided to select one or more specific wavelengths from the generated wavelengths. Optionally, the illumination source includes a space configured to be evacuated, and the gas delivery system is configured to provide a gas target in the space. Optionally, some or all of the beam path may be contained within a vacuum environment, keeping in mind that SXR and / or EUV radiation is absorbed when traveling in air. Various components of the radiation source 310 and illumination optics 312 may be adjustable to implement different measurement "options" within the same device. For example, different wavelengths and / or polarizations may be made selectable.

[0074] Depending on the material of the structure being inspected, different wavelengths may provide the desired level of penetration into the underlying layers. In order to distinguish the smallest device features and defects in the smallest device features, short wavelengths may be preferred. For example, one or more wavelengths in the range of 0.01nm to 20nm, or alternatively in the range of 1nm to 10nm, or alternatively in the range of 10nm to 20nm may be selected. Wavelengths shorter than 5nm may suffer from extremely low critical angles when reflected from materials of interest in semiconductor manufacturing. Therefore, selecting a wavelength greater than 5nm may provide a stronger signal at higher angles of incidence. On the other hand, if the detection task is to detect the presence of a certain material, for example to detect contamination, wavelengths up to 50nm may be useful.

[0075] From the radiation source 310, the filtered beam 342 may enter a detection chamber 350, wherein a substrate W including a structure of interest is held by a substrate support 316 for detection at a measurement position. The structure of interest is labeled T. Optionally, the atmosphere within the detection chamber 350 may be maintained as a near vacuum by a vacuum pump 352, so that EUV radiation may pass through the atmosphere without undue attenuation. The illumination system 312 has the function of focusing the 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 above-mentioned published U.S. patent application US2017 / 0184981A1 (the contents of US2017 / 0184981A1 are incorporated herein by reference in their entirety). Focusing is performed to achieve a circular or elliptical spot S having a diameter below 10 μm when projected onto the structure of interest. The substrate support 316 includes, for example, an XY translation stage and a rotation stage, by which any part of the substrate W can be brought to the focus of the beam in a desired orientation. Thus, a radiation spot S is formed on the structure of interest. Alternatively or additionally, the substrate support 316 includes, for example, a tilting stage, which can tilt the substrate W at a certain angle to control the incident angle of the focused beam on the structure of interest T.

[0076] Optionally, the illumination 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 that is provided to the processor 320, and the filter can include information about the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0077] The reflected radiation 360 is captured by the detector 318, and the spectrum is provided to the processor 320 for calculating the properties of the target structure T. The illumination system 312 and the detection system 318 thus form a detection device. The detection device may include a hard X-ray, soft X-ray, and / or EUV spectroscopic reflectometer of the type described in US2016282282A1, which is incorporated herein by reference in its entirety.

[0078] If the target Ta has some periodicity, the radiation of the focused beam 356 may also be partially diffracted. The diffracted radiation 397 follows another path at a well-defined angle relative to the angle of incidence and then relative to the reflected radiation 360. Figure 5 , the diffracted radiation 397 shown is shown in a schematic manner, and the diffracted radiation 397 may follow many other paths besides the path shown. The detection device 302 may also include a further detection system 398 that detects at least a portion of the diffracted radiation 397 and / or images at least a portion of the diffracted radiation 397. Figure 5 , although a single further detection system 398 is shown, embodiments of the detection device 302 may also include more than one further detection system 398, which are arranged at different positions to detect the diffracted radiation 397 in multiple diffraction directions and / or to image the diffracted radiation 397. In other words, the (higher) diffraction orders of the focused radiation beam impinging on the target Ta are detected and / or imaged by one or more further detection systems 398. The one or more detection systems 398 generate a signal 399 which is provided to the measurement processor 320. The signal 399 may include information of the diffracted light 397 and / or may include an image obtained from the diffracted light 397.

[0079] To assist in the alignment and focusing of the light spot S with the desired product structure, the detection device 302 may also provide auxiliary optics that use auxiliary radiation under the control of the measurement processor 320. The measurement processor 320 may also communicate with a position controller 372 that operates a translation platform, a rotation platform, and / or a tilt platform. The processor 320 receives highly accurate feedback about the position and orientation of the substrate via a sensor. The sensor 374 may include, for example, an interferometer that can give an accuracy of about several picometers. In the operation of the detection device 302, the spectral data 382 captured by the detection system 318 is delivered to the measurement processing unit 320.

[0080] As mentioned, an alternative form of the detection device uses hard X-rays, soft X-rays, and / or EUV radiation, optionally at normal incidence or near normal incidence, for example to perform diffraction-based asymmetry measurements. Another alternative form of the detection device uses hard X-rays, soft X-rays, and / or EUV radiation having a direction that is angled greater than 1° or 2° from a direction parallel to the substrate. Two types of detection devices can be provided in a hybrid measurement system. The performance parameters to be measured may include overlay (OVL), critical dimension (CD), focal length of the lithography device when the lithography device prints a target structure, coherent diffraction imaging (CDI), and resolution-based overlay (ARO) measurements. The hard X-rays, soft X-rays, and / or EUV radiation may, for example, have a wavelength of less than 100 nm, for example using radiation in the range of 5 nm to 30 nm, optionally in the range of 10 nm to 20 nm. The radiation may be narrowband or broadband in nature. The radiation may have discrete peaks in a particular wavelength band or may have a more continuous characteristic.

[0081] Like optical scatterometers used in today's production facilities, the inspection device 302 can be used to measure structures in resist materials processed in a lithography unit (in development inspection or ADI) and / or to measure structures after they have been formed in harder materials (in etching inspection or AEI). For example, the inspection device 302 can be used to inspect a substrate after it has been processed by a development device, an etching device, an annealing device, and / or other devices.

[0082] The measurement tool MT, including but not limited to the scatterometer mentioned above, can use radiation from a radiation source to perform measurements. The radiation used by the measurement tool MT can be electromagnetic radiation. The radiation can be optical radiation, such as radiation in the infrared part, the visible light part, and / or the ultraviolet part of the electromagnetic spectrum. The measurement tool MT can use radiation to measure or detect properties and aspects of the 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 tool MT. For example, the resolution of the electromagnetic measurement can depend on the wavelength of the radiation, where, for example, due to diffraction limitations, smaller wavelengths can measure smaller features. In order to measure features with smaller sizes, radiation with shorter wavelengths, such as EUV, hard X-rays, and / or soft X-ray (SXR) radiation, can be preferably used to perform measurements. In order to perform measurements at a specific wavelength or wavelength range, the measurement tool MT needs to access a source of radiation provided at the wavelength / those wavelengths. There are different types of sources for providing radiation of different wavelengths. Depending on the (multiple) wavelengths 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 may use high order harmonic generation (HHG) or any other type of illumination source mentioned above to obtain radiation at the desired wavelength(s). One of the challenges faced in the development of these sources is how to efficiently couple the emitted radiation out of the generating device and separate the emitted radiation from the radiation used to drive the process.

[0083] Figure 6 A simplified schematic diagram of an embodiment 600 of an illumination source 310 is shown, which may be an illumination source for high-order harmonic generation. Figure 5 One or more of the features of the illumination source in the described metrology tool may also be present in the illumination source 600, where appropriate. The illumination source 600 comprises a chamber 601. The illumination source 600 is configured to receive pump radiation 611 having a propagation direction indicated by an arrow. The pump radiation 611 shown here is an example of pump radiation 340 from the pump radiation source 330, as shown in FIG. Figure 5. Pump radiation 611 may be directed into chamber 601 via radiation input 605, which may be a viewing port that may be made of fused silica or a comparable material. Pump radiation 611 may have a Gaussian or hollow (e.g., annular) transverse cross-sectional profile and may be incident (optionally focused) on a gas flow 615 having a flow direction indicated by a second arrow within chamber 601. Gas flow 615 includes a small volume of a particular gas (e.g., air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide, and combinations of said air, neon (Ne), helium (He), nitrogen (N2), oxygen (O2), argon (Ar), krypton (Kr), xenon (Xe), carbon dioxide) in which the gas pressure is above a certain value, the small volume being referred to as a gas volume or gas target (e.g., a few cubic millimeters). Gas flow 615 may be a steady flow. Other media such as metal plasma (eg, aluminum plasma) may also be used.

[0084] The gas delivery system of the irradiation source 600 is configured to provide a gas flow 615. The irradiation source 600 is configured to provide pump radiation 611 in the gas flow 615 to drive the generation of emission radiation 613. The region where at least most of the emission radiation 613 is generated is called the interaction region. The interaction region can vary from tens of microns (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 a gas target for generating emission 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 into an evacuated or nearly evacuated space by the gas delivery system. The gas delivery system includes a gas nozzle 609, such as Figure 6 As shown in , the gas nozzle 609 may include an opening 617 in the exit plane of the gas nozzle 609. A gas flow 615 is provided from the opening 617. A gas trap is used to confine the gas flow 615 in a certain volume by extracting the residual gas flow and maintaining a vacuum or near-vacuum atmosphere inside the chamber 601. Optionally, the gas nozzle 609 may be made of a thick-walled tube and / or a high thermal conductivity material to avoid thermal deformation due to the high-power pump radiation 611.

[0085] The dimensions of the gas nozzle 609 can conceivably also be used in scaled-up or scaled-down forms ranging from micron-sized nozzles to meter-sized nozzles. This wide range of sizing comes from the fact that the device can be scaled so that the intensity of the pump radiation at the gas flow is ultimately within a specific range that can be beneficial for the emitted radiation, which requires different sizing for different pump radiation energies that can be pulsed lasers, and the pulse energies 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 that can be detected by, for example, 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 close to the gas nozzle to maintain the pressure of the chamber 601.

[0086] Due to the interaction of the pump radiation 611 with the gas atoms of the gas flow 615, the gas flow 615 will convert a portion of the pump radiation 611 into emission radiation 613, which can be Figure 5 342 is shown in FIG. 34. The central axis of the emitted radiation 613 may be co-linear 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 from 0.01 nm to 100 nm, optionally from 0.1 nm to 100 nm, optionally from 1 nm to 100 nm, optionally from 1 nm to 50 nm, or optionally from 10 nm to 20 nm.

[0087] In operation, the emitted radiation 613 beam may pass through a radiation output port 607, such as an aperture or window, and may then be manipulated and directed to a substrate to be inspected for metrology measurement by an illumination system 603, which may be Figure 5 6. Emitted radiation 613 may be directed (optionally focused) to structures on the substrate.

[0088] Since air (and indeed any gas) absorbs SXR or EUV radiation to a large extent, the volume between the gas flow 615 and the wafer to be inspected may be evacuated or nearly evacuated. Since the central axis of the emitted radiation 613 may be collinear with the central axis of the incident pump radiation 611, the pump radiation 611 may need to be blocked to prevent the pump radiation 611 from passing through the radiation output 607 and entering the illumination system 603. This may be accomplished by placing Figure 6The filter device 344 shown in is implemented by incorporating it into a radiation output end 607, which is located in the emission beam path and is opaque or almost opaque to the pump radiation (for example, opaque or almost opaque to infrared or visible light), but is at least partially transparent to the emission radiation beam. The filter can be made using zirconium or multiple materials combined in multiple layers. When the pump radiation 611 has a hollow (optionally annular) transverse cross-sectional profile, the filter can be a hollow (optionally annular) block. Optionally, the filter is not perpendicular and not parallel to the propagation direction of the emission radiation beam to have efficient pump radiation filtering. Optionally, the filter device 344 includes a hollow block and a membrane filter such as an aluminum (Al) or zirconium (Zr) membrane filter. Optionally, the filter device 344 can also include a reflector that effectively reflects the emission radiation but poorly reflects the pump radiation, or includes a wire mesh that effectively transmits the emission radiation but poorly transmits the pump radiation.

[0089] Methods, devices, and assemblies for obtaining emitted radiation, optionally at high-order harmonic frequencies of pump radiation are described herein. The radiation generated by the process (optionally HHG using nonlinear effects to generate radiation, optionally at harmonic frequencies of the provided pump radiation) can be provided as radiation in a measurement tool MT for detection and / or measurement of a substrate. If the pump radiation comprises short pulses (i.e., a few cycles), the generated radiation may not be exactly at harmonics of the pump radiation frequency. The substrate may be a lithographically patterned substrate. The radiation obtained via the process may also be provided in a lithographic apparatus LA and / or a lithographic cell LC. The pump radiation may be pulsed radiation that can provide high peak intensity in a short burst time.

[0090] The pump radiation 611 may include radiation having one or more wavelengths higher than one or more wavelengths of the emitted radiation. The pump radiation may include infrared radiation. The pump radiation may include radiation having wavelength(s) in the range of 500 nm to 1500 nm. The pump radiation may include radiation having wavelength(s) in the range of 800 nm to 1300 nm. The pump radiation may include radiation having wavelength(s) in the range of 900 nm to 1300 nm. The pump radiation may be pulsed radiation. The pulsed pump radiation may include pulses having a duration in the femtosecond range.

[0091] For some embodiments, the emitted radiation (optionally higher order harmonic radiation) may include one or more harmonics of the pump radiation wavelength(s). The emitted radiation may include wavelengths in the extreme ultraviolet, soft x-ray, and / or hard x-ray portions of the electromagnetic spectrum. The emitted radiation 613 may include wavelengths in one or more of the following ranges: less than 1 nm, less than 0.1 nm, less than 0.01 nm, 0.01 nm to 100 nm, 0.1 nm to 100 nm, 0.1 nm to 50 nm, 1 nm to 50 nm, and 10 nm to 20 nm.

[0092] Radiation such as the high-order harmonic radiation described above can be provided as source radiation in the measurement tool MT. The measurement tool MT can use the source radiation to perform measurements on a substrate exposed by a lithographic device. The measurements can be used to determine one or more parameters of a structure on the substrate. Compared to using longer wavelengths (e.g., visible radiation, infrared radiation), using radiation at shorter wavelengths (e.g., at EUV, SXR, and / or HXR wavelengths included in the wavelength range described above) can allow the measurement 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, which means that measurement of deeper layers on the substrate is possible. It may not be possible to reach these deeper layers using radiation with longer wavelengths.

[0093] In the 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 the target structure. 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 positive one (+1) and negative one (-1) diffraction orders. The measurement tool MT may also measure specularly reflected or transmitted radiation (0th order diffracted radiation). Other sensors for measurement may be present in the measurement tool MT, for example to measure other diffraction orders (e.g., higher diffraction orders).

[0094] In an exemplary lithography metrology application, HHG generated radiation can be focused onto a target on a substrate using an optical column, which can be referred to as an illuminator that transfers radiation from a HHG source to the target. The HHG radiation can then be reflected from the target, detected, and processed, for example, to measure and / or infer properties of the target.

[0095] Gas target HHG configurations can be broadly divided into three separate categories: gas jet, gas chamber, and gas capillary. Figure 7An exemplary gas jet configuration is depicted, wherein a gas volume is introduced into the driving radiation laser beam. In the gas jet configuration, the interaction of the driving radiation with the solid component is kept to a minimum. The gas volume may, for example, comprise a gas flow perpendicular to the driving radiation beam, wherein the gas volume is enclosed inside a gas chamber. In a gas capillary device, the size of the capillary structure containing the gas is small in the lateral direction, so that the capillary structure significantly affects the propagation of the driving radiation laser beam. The capillary structure may, for example, be a hollow core optical fiber, wherein the hollow core is configured to contain the gas.

[0096] Because the spatial distribution of the driving radiation beam in the far field is not subject to the defined restrictions imposed by the gas capillary structure, the gas jet HHG configuration can provide a relative degree of freedom to shape the spatial distribution of the driving radiation beam in the far field. The gas jet configuration can also have less stringent alignment tolerances. On the other hand, the gas capillary can provide an increased interaction area of ​​the driving radiation with the gaseous medium, which can optimize the HHG process.

[0097] In order to use HHG radiation, for example, in measurement applications, the HHG radiation is separated from the driving radiation downstream of the gas target. The separation of HHG radiation from the driving radiation may be different for gas jet configurations and gas capillary configurations. In both cases, the driving radiation suppression scheme may include a metal transmission filter for filtering out any remaining driving radiation from the short wavelength radiation. However, before the filter can be used, the intensity of the driving radiation should be significantly reduced from the intensity of the driving radiation at the gas target to avoid damage to the filter. The methods that can be used for this intensity reduction are different for gas jet configurations and capillary configurations. For gas jet HHG, due to the relative freedom of the shape and spatial profile (the spatial profile can also be referred to as spatial distribution and / or spatial frequency) of the driving radiation beam focused on the gas target, this can be engineered so that in the far field, the driving radiation beam has a lower intensity along the direction of propagation of the short wavelength radiation. This spatial separation in the far field means that the aperture can be used to block the driving radiation and reduce the intensity of the driving radiation.

[0098] In contrast, in a gas capillary structure, the spatial profile of the beam as it passes through the gaseous medium may be primarily dictated by the capillary. The spatial profile of the driving radiation may be determined by the shape and material of the capillary structure. For example, where a hollow core fiber is used as the capillary structure, the shape and material of the fiber structure determines which driving radiation modes are supported for propagation through the fiber. For most standard optical fibers, the supported propagation modes produce a spatial profile where high intensities of the driving radiation overlap with high intensities of the HHG radiation. For example, the driving radiation intensity may be centered in a Gaussian or near-Gaussian profile in the far field.

[0099] Figure 7Another metrology device suitable for use in embodiments of the present invention is shown in (a). It should be noted that this is only one example of a suitable metrology device. Alternative suitable metrology devices may use EUV radiation, such as EUV radiation disclosed in WO2017 / 186483A1. Figure 7 (b) illustrates in more detail the target structure T and the diffracted rays of the measuring radiation used to illuminate the target structure. The illustrated metrology apparatus is of a type known as a dark field metrology apparatus. The metrology apparatus may be a stand-alone device or incorporated in a lithography apparatus LA or a lithography cell LC, for example at a measurement station. An optical axis having several branches running through the apparatus is represented by a dotted line O. In the apparatus, light emitted by a source 11 (e.g. a xenon lamp) is directed onto a substrate W via a beam splitter 15 by an optical system comprising lenses 12, 14 and an objective lens 16. These lenses are configured in a double sequence of a 4F arrangement. Different lens arrangements may be used as long as they still provide an image of the substrate onto the detector and at the same time allow access to an intermediate pupil plane for spatial frequency filtering. Thus, the angular range over which the radiation is incident on the substrate may be selected by defining the spatial intensity distribution in a plane presenting the spatial spectrum of the substrate plane, referred to here as the (conjugate) pupil plane. In particular, this selection can be made by inserting an aperture plate 13 of suitable form between the lenses 12 and 14 in the plane which is the back-projected image of the objective pupil plane. In the illustrated example, the aperture plate 13 has different forms (labeled 13N and 13S), thereby allowing different illumination modes to be selected. The illumination system in the current example forms an off-axis illumination mode. In a first illumination mode, the aperture plate 13N provides off-axis from a direction designated as "North" for descriptive purposes only. In a second illumination mode, the aperture plate 13S is used to provide similar but from an opposite direction labeled "South". Other illumination modes are possible by using different apertures. The rest of the pupil plane is ideally darker, because any non-essential light outside the desired illumination mode will interfere with the desired measurement signal.

[0100] like Figure 7As shown in (b), the target structure T is placed with the substrate W orthogonal to the optical axis O of the objective lens 16. The substrate W may be supported by a support (not shown). A measurement radiation ray I (e.g., comprising the SXR wavelength) impinging on the target structure T from an angle offset from the axis O produces a zero-order ray (solid line 0) and two first-order rays (dotted chain line +1 and double-dotted chain line -1). It should be remembered that in the case of an overfilled small target structure, these rays are only one of many parallel rays covering the area of ​​the substrate including the measurement target structure T and other features. Since the aperture in the plate 13 has a finite width (which is necessary to admit a useful amount of light), the incident ray I will in fact occupy an angular range, and the diffracted rays 0 and +1 / -1 will be slightly spread out. According to the point spread function of the small target, each order +1 and -1 will be further spread throughout the angular range, rather than being a single ideal ray as shown. It should be noted that the grating pitch and the illumination angle of the target structure can be designed or adjusted so that the first-order rays entering the objective lens are closely aligned with the central optical axis. Figure 7 (a) and Figure 7 The rays illustrated in (b) are shown slightly off-axis purely to enable them to be more easily distinguished in the drawing.

[0101] At least the 0th and +1st orders diffracted by the target structure T on the substrate W are collected by the objective lens 16 and directed back through the beam splitter 15. Figure 7 (a) illustrates both the first illumination mode and the second illumination mode by specifying diametrically opposed apertures labeled as north (N) and south (S). When the incident ray I of the measurement radiation comes from the north side of the optical axis, that is, when the first illumination mode is applied using the aperture plate 13N, the +1 diffracted ray labeled as +1 (N) enters the objective lens 16. In contrast, when the second illumination mode is applied using the aperture plate 13S, the -1 diffracted ray (labeled as 1 (S)) is the diffracted ray that enters the lens 16.

[0102] The second beam splitter 17 divides the diffraction beam into two measurement branches. In the first measurement branch, the optical system 18 uses the zero-order diffraction beam and the first-order diffraction beam to form a diffraction spectrum (pupil plane image) of the target structure on a first sensor 19 (e.g., a CCD or CMOS sensor). Each diffraction order hits a different point on the sensor so that image processing can compare and contrast several orders. The pupil plane image captured by the sensor 19 can be used to focus the metrology equipment and / or normalize the intensity measurement of the first-order beam. The pupil plane image can also be used for many measurement purposes such as reconstruction.

[0103] In the second measurement branch, the optical system 20, 22 forms an image of the target structure T on a sensor 23 (e.g. a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is provided in a plane conjugate to the pupil plane. The aperture stop 21 serves to block the zeroth order diffraction beam so that the image of the target formed on the sensor 23 is formed only by the -1 or +1 first order beams. The image captured by the sensors 19 and 23 is output to a processor PU that processes the image, the functionality of which will depend on the specific type of measurement being performed. It should be noted that the term "image" is used in a broad sense. If only one of the -1 and +1 orders is present, then no image of the grating lines will be formed.

[0104] Figure 5 The specific forms of aperture plate 13 and field stop 21 shown in are purely exemplary. In another embodiment of the invention, coaxial illumination of the target is used, and an aperture stop with an off-axis aperture is used to pass substantially only one first-order diffracted light to the sensor. In yet other embodiments, instead of or in addition to the first-order beam, second-order beams, third-order beams, and higher-order beams ( Figure 5 not shown).

[0105] In order to adapt the measurement radiation to these different types of measurements, the aperture plate 13 may include several aperture patterns formed around a disk that is rotated to bring the desired pattern into position. It should be noted that aperture plates 13N or 13S can be used to measure gratings oriented in only one direction (X or Y depending on the device). For measuring orthogonal gratings, target rotations of up to 90° and 270° can be implemented. Figure 7 Different aperture plates are shown in (c) and (d). Numerous other variations and applications of the use of these aperture plates and apparatus are described in the previous published applications referenced above.

[0106] Irradiation sources (such as Figure 5 Source 310 or Figure 6 600) may include a high order harmonic generation (HHG) source. Typically, when performing measurements, it is necessary to continuously or regularly measure the characteristics of the radiation generated by the HHG source in the illumination branch while illuminating a structure (or referred to as a target) on a substrate (optionally a semiconductor wafer or a patterning device) with the radiation. In particular, real-time information about the spectral composition of the source radiation should be measured. This can then be input to an interference algorithm for inferring the parameters of interest of the target as well as the diagnosis of the source from the source radiation after being scattered by the target.

[0107] The inventive method for achieving this object is to provide a reference sub-branch within the illumination branch, wherein a portion of the source radiation is directed into the reference sub-branch by a grating in the illumination branch. The grating may partially reflect the source radiation into the main illumination branch and partially diffract the light into the reference sub-branch, wherein the grating produces spatially separated spectra on a reference detector. The grating may be a stand-alone grating, or a grating fabricated on a focusing mirror (one of the illuminator optics) of the illumination branch.

[0108] Figure 8 is a schematic illustration of such an arrangement. Pump radiation 800 (e.g., infrared radiation) is focused to a HHG generation point 805 (e.g., a gas jet outlet) and used to generate HHG radiation (source radiation) 810. An aperture or spatial filter 815 blocks the pump radiation while allowing the source radiation 810. The focusing mirror 820 includes a grating 822 that is used to separate the source radiation 810 into measurement radiation 825 (e.g., a specular reflection of the scattered radiation scattered by the grating 822 or zero-order radiation) and (dispersed) reference radiation 855 (e.g., one or two of the first diffraction orders of the scattered radiation scattered by the grating 822).

[0109] In one embodiment, source radiation 810 comprises radiation having a wavelength in the range of 10 nm to 20 nm. In one embodiment, source radiation 810 comprises radiation having a wavelength in the range of 8 nm to 18 nm.

[0110] The measurement radiation 825 is used to measure a target 830 (e.g., in certain optional measurement methods, the target may be underfilled; i.e., the measurement spot is smaller than the target). First scattered radiation 870 (e.g., higher-order or first-order scattered radiation) may be detected (e.g., via optics not shown) by one or more measurement detectors 875. Additionally, second scattered radiation 835 (e.g., more specifically, zero-order or specularly reflected radiation) from the target may be captured (e.g., via optics not shown). This scattered radiation 835 may then be dispersed by a dispersive element 840 (e.g., a grating) and then detected on another measurement detector 850.

[0111] The scattered reference radiation 855 may be detected by a reference detector 860, for example, via beam steering optics such as a mirror 865. A processor (not shown) may be used to determine a value of a parameter of interest from the first scattered radiation 870 and / or the scattered scattered radiation 845 using the scattered reference radiation 855 (as captured on the reference detector 860) as a reference (e.g., when determining the parameter of interest from the detected pattern on the detector 875 and / or the detector 850, it may be necessary to know the spectral characteristics of the illumination before being scattered by the target). The scattered reference radiation 855 may also be used to monitor the illumination source, for example, to monitor illumination stability and / or to monitor spectral characteristics of the illumination.

[0112] Optionally there are one or more automatic feedback control loops for controlling the operation of the radiation source arrangement based at least in part on signals detected by one or more of the reference detector 860 and the measurement detectors 850, 875. Optionally there are compensatory optics for wavefront correction of the pump radiation 800 located before the HHG generation point 805. The compensatory optics may be a programmable spatial light modulator (SLM) and / or a deformable mirror.

[0113] Figure 8 There are a number of problems with the configuration illustrated in : The use of grating 822 as a beam splitter results in additional scattering within the mirror beam. This makes it more difficult to underfill small targets. In addition, in the wavelength range typically emitted by such an illumination source (e.g., 10 nm to 20 nm), the grating typically produces orders above the first diffraction order, which results in energy losses. The transmission to the wafer is therefore reduced, resulting in lower throughput. When designing the illuminator optics, there are certain boundary conditions that should be met due to the aforementioned short wavelengths used. These boundary conditions can include, for example, having as few reflective surfaces as possible, having a grazing angle of incidence as far away from the normal as possible, providing extremely smooth surfaces, having to place the reflective surface as close to the target as possible, having the shortest possible distance between the source generation point and the target, and not having too small a local radius of curvature of the surface. Including a grating in the design further complicates this, resulting in a compromise in focusing on the target, transmission of the illuminator, size of the optical path, and reduction of the illuminator. In addition, the manufacturability of such a reflector with a grating is extremely difficult. Positioning a high-end grating on a high-end reflector is risky and complex with respect to the source.

[0114] Disclosed herein is a metrology device for measuring a structure on a substrate, which structure has been patterned on the substrate, optionally in a lithography process, the metrology device comprising: an illumination branch, the illumination branch being used to direct measurement radiation onto the structure on the substrate; a measurement detector, the measurement detector being used to detect the measurement radiation after the measurement radiation is scattered by the structure; a pellicle beam splitter, the pellicle beam splitter being located in the illumination branch, the pellicle beam splitter comprising a pellicle diaphragm operable to separate source radiation from an illumination source into measurement radiation for measuring the structure and reference radiation; and a reference detector, the reference detector being used to detect the reference radiation.

[0115] This concept can also be used with EUV pellicles to protect EUV reticles from contaminant particles by keeping them out of focus of the lithography tool so that such contaminant particles are not imaged. These pellicles are designed (among other requirements) to have low reflectivity / high transmittance.

[0116] In an embodiment, the pellicle diaphragm proposed for the concepts disclosed herein is specifically designed for beam splitting applications. Thus, the pellicle diaphragm can be specifically designed to split a small portion of the (e.g., SXR) measurement radiation beam. In an embodiment, transmission can be maximized, wherein the portion split into a reference branch includes less than 3%, less than 2%, less than 1.5%, less than 1.2% of the total energy of the incident beam. In combination with any of these upper percentage limits, the portion split into a reference branch can include greater than 0.1%, greater than 0.5%, greater than 0.6%, greater than 0.7%, greater than 0.8%, or greater than 0.9%. Thus, in a specific embodiment, the portion split into a reference branch can be between 0.5% and 1.5% or between 0.2% and 1.2% (e.g., about 1%).

[0117] Preferably, the spectral characteristics should be as low as possible (e.g., there should be a flat response over the relevant wavelength range). For example, the transmittance and / or reflectance of the pellicle membrane can vary by less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, or less than 10% over a wavelength range of 10 nm to 20 nm, or over a wavelength range of 5 nm to 30 nm.

[0118] The pellicle beam splitter can be used in conjunction with a dispersive element (eg, a reference grating) to spectrally disperse the split beam prior to detection by a reference detector.

[0119] In embodiments, the pellicle membrane may comprise three or more layers; for example comprising at least one outer layer on each side of at least one inner layer, wherein the at least one outer layer may be the same or different, and / or wherein, optionally, the at least one outer layer may have the same or different thickness, and / or wherein, optionally, the at least one outer layer may comprise the same or different materials. In embodiments, the pellicle membrane may comprise two layers, wherein the two layers may be the same or different, and / or wherein, optionally, the two layers may have the same or different thickness, and / or wherein, optionally, the two layers may comprise the same or different materials.

[0120] In an embodiment, one or more outer layers on each side of the (multiple) inner layers may include and / or consist of one or more oxides. Such oxides may include, for example, one or more of silicon oxide (e.g., SiO2), aluminum oxide (e.g., Al2O3), zirconium oxide (e.g., ZrO2), or yttrium oxide (e.g., YO2 or Y2O3). The oxide layer may act as a protective layer for the inner layer to provide, for example, mechanical, thermal, or chemical stability. In addition, the layer may function in the diaphragm to obtain desired reflective properties that vary with wavelength.

[0121] In an embodiment, the outer layer may be as thin as possible while still ensuring a closed layer. Optionally, the thickness of the at least one outer layer on a single side (or each side) of the at least one inner layer may be less than 4nm, or less than 3nm; for example, the thickness is between 1nm and 3nm, between 1.5nm and 2.5nm, between 1.7nm and 2.3nm, between 1.8nm and 2.2nm, or between 1.9nm and 2.1nm (e.g., about 2nm).

[0122] The reason why the outer layer(s) should not be too thick is that, especially for longer wavelengths, the transmittance of the oxide decreases. In addition, the (thickness of) the outer layer affects the reflectivity. A thicker oxide layer results in a larger variation of the reflectivity within the wavelength. The core function of the thicker oxide layer is a capping layer for chemical stability, which should include a completely closed layer for chemical stability. If the layer becomes too thin, islands will form, making the layer no longer closed. Depending on the material, this boundary is at about 1 nm to 1.5 nm.

[0123] At least one inner layer may include a silicon or silicon compound layer (e.g., pure silicon Si, silicon carbide SiC, silicon dicarbide SiC2, silicon nitride SiN, zirconium silicide ZrSi) and / or a boron layer (e.g., pure boron B) or a boron compound layer (e.g., boron carbide B4C, zirconium diboride ZrB2, boron nitride BN) and / or one or more of zirconium, beryllium, niobium, yttrium, molybdenum, carbon, and / or a compound of each of these materials or a mixture of these materials. Both B4C and BN are mechanically strong and have relatively good transmittance in the full spectrum 8nm to 18nm. Because B4C is stronger and the transmittance of B4C is higher, B4C is better than BN.

[0124] When metals are made into thin films, internal stresses can be generated, which is not preferred for use in diaphragms. A solution is to dope metal materials, such as zirconium, beryllium, niobium, yttrium, and molybdenum, to reduce internal stresses. In one embodiment, at least one internal layer may include a metal doped with one or more of the elements Si, B, C, and / or N.

[0125] In addition to the silicon-based and / or boron-based materials as mentioned above, at least one inner layer may comprise one or more zirconium-based materials, optionally zirconium and / or zirconium compounds.Zirconium-based materials may have excellent optical properties.

[0126] In one embodiment, the pellicle beam splitter is based on one or more of silicon-based materials, optionally silicon or silicon compounds. Silicon-based materials are easy to manufacture and have a high transmittance for radiation having a wavelength of 13.5. However, for source radiation 810, which optionally includes radiation having a wavelength in the range of 8nm to 18nm, the transmission of the silicon-based material for radiation having a wavelength below 13nm is sufficient. One solution is to make the pellicle diaphragm thinner, which makes the diaphragm fragile and not preferred. A second solution is to reduce the silicon content in the silicon-based material to improve the transmittance. In one embodiment, at least one internal layer includes silicon nitride instead of silicon. In another embodiment, at least one internal layer includes silicon carbide (note that the elements Si and C can have any chemical ratio, formulated as Si x C y For broadband radiation, such as radiation having a wavelength of 8 nm to 18 nm, which may be optionally generated by HHG, both silicon nitride and silicon carbide have a higher transmittance than silicon.

[0127] In one embodiment, one or more outer layers are optional.

[0128] In one embodiment, one or more outer layers comprise ruthenium, because ruthenium is more resilient to damage. In one embodiment, the front side (the side facing the incident radiation) of the inner layer is capped with ruthenium, and the back side of the inner layer is capped with one or more outer layers as mentioned above.

[0129] In one embodiment, the front side of the inner layer is covered with an outer layer different from the back side of the inner layer. In one embodiment, only the front side of the inner layer is covered with an outer layer, while the back side of the inner layer is not covered. In one embodiment, only the back side of the inner layer is covered with an outer layer, while the front side of the inner layer is not covered.

[0130] In terms of manufacturability and tensile stress, the internal layer can be as thin as possible; in embodiments, the total internal layer thickness can be less than 20 nm, less than 15 nm, less than 10 nm, or less than 6 nm. In combination with any of these lower thickness limits, the total internal layer thickness can be greater than 1 nm, greater than 2 nm, greater than 4 nm, greater than 6 nm, greater than 8 nm, greater than 10 nm, or greater than 11 nm.

[0131] The minimum inner layer thickness depends on the size of the pellicle membrane. For larger pellicles, such as those used in lithography equipment using EUV radiation, the beam size is larger, e.g. a beam with a diameter greater than 100 cm 2 Size or larger than 120cm 2 Due to the large size of the mask used, the surface film and the internal layers must be thicker, for example, greater than 10 nm. However, for the SXR measurement equipment mentioned above, the source radiation 810 can have a much smaller diameter than 100 cm 2 , for example less than 10mm 2 or about 1mm 2 Thus, for example, a beam size of less than 10 mm 2 or about 1mm 2 A smaller pellicle of size can be used with a thinner pellicle membrane and / or a thinner inner layer. In one embodiment, the total inner layer thickness can be less than 6nm. In one embodiment, the total inner layer thickness can be between 1nm and 6nm.

[0132] The inner layer thickness is optimized for transmission, so a priori the thinner the better. Additionally, for mechanical stability the total layer stack must not be too thin, resulting in a lower boundary. More layers can therefore mean thinner single layers, but the minimum layer thickness should still be about 1 nm to 2 nm to prevent island formation.

[0133] In order to make the device compact, there are volume constraints due to the restricted space inside the device. Therefore, the beam splitter can be positioned relative to the oblique angle of incidence of the source radiation. In addition, the reflectivity of the beam splitter is also affected by the angle of incidence, so the angle of incidence of the source radiation on the beam splitter needs to be carefully selected. In one embodiment, the angle of incidence of the source radiation beam on the beam splitter (film diaphragm) can be between 30 degrees and 70 degrees, between 30 degrees and 60 degrees, between 30 degrees and 50 degrees, between 40 degrees and 50 degrees, or more specifically about 45 degrees.

[0134] One disadvantage of using an incident angle of 45 degrees is that if polarization switching of the source radiation is required (e.g., p-polarization is effectively not reflected at 45 degrees), the incident angle of 45 degrees may not work. In one embodiment, the incident angle of the source radiation beam on the beam splitter (film diaphragm) can be between 20 degrees and 44 degrees, between 30 degrees and 44 degrees, between 35 degrees and 44 degrees, or between 40 degrees and 44 degrees. In one embodiment, the incident angle of the source radiation beam on the beam splitter (film diaphragm) can be between 46 degrees and 70 degrees, between 46 degrees and 60 degrees, between 46 degrees and 55 degrees, or between 46 degrees and 50 degrees. In one embodiment, the incident angle of the source radiation beam on the beam splitter (film diaphragm) can be between 50 degrees and 70 degrees, between 55 degrees and 65 degrees, between 57 degrees and 63 degrees, between 59 degrees and 61 degrees, or about 60 degrees. This incident angle can provide optimal reflection / transmission. For essentially all materials, reflection increases dramatically for angles greater than 70 degrees due to total external reflection. At the same time, for angles near normal incidence, reflection is very small (in magnitude). The optimizer balances reflection and transmission. If the angle is too small, e.g., below 30 degrees, then reflected light (e.g., Fig. 9 The reference radiation 910 in may not be of sufficient intensity and a material with a higher reflectivity may be required.

[0135] Fig. 9 is a schematic diagram of a measuring device according to an embodiment. Figure 8Components and elements of the metrology apparatus common to the metrology apparatus illustrated in . Here, a pellicle beam splitter 900 is used instead of a grating, which separates the source radiation 810 into a measurement radiation 825 and a reference radiation 910. A dispersion element 915 can be used to disperse the reference radiation 910 to obtain a spectrally dispersed reference radiation 920. The spectrally dispersed reference radiation 920 can then be detected using a reference detector 860. The dispersion element 915 can be a grating. The dispersion element 915 can be a reflective dispersion element, such as a reflective grating. The dispersion element 915 can be a transmissive dispersion element, such as a transmissive grating. The advantages of a transmissive dispersion element include: a transmissive dispersion element is not subject to contaminant deposition, optionally not subject to carbon deposition; a transmissive dispersion element does not need to be ground extremely smooth, which is difficult to manufacture; a transmissive dispersion element is relatively easy to manufacture; a transmissive dispersion element is generally cheaper than a reflective dispersion element; and a transmissive dispersion element is easy to calibrate.

[0136] In one embodiment, the pellicle beam splitter 900 may be located upstream of the focusing mirror 820, such as Fig. 9 . When the dispersive element 915 is a transmissive dispersive element (e.g., a transmissive grating), the reference radiation 910 will not be focused. Therefore, in one embodiment, the pellicle beam splitter 900 can be located on the downstream side of the focusing mirror 820, which is preferred because this focuses the reference radiation 910. In one embodiment, the pellicle beam splitter 900 can be located directly before the target 830 without optical elements between the pellicle beam splitter 900 and the target 830. Additional advantages of locating the pellicle beam splitter 900 on the downstream side of the focusing mirror 820 include that the reference branch will calibrate the radiation after the focusing mirror 820 and give more information about the measurement radiation 825 at the wafer level, and that the design tolerances are looser, for example, the pellicle beam splitter 900 can be designed to be switchable (i.e., the pellicle beam splitter 900 can be optionally removed and inserted during operation) without having much impact on the measurement radiation 825.

[0137] Also disclosed is a pellicle beam splitter including a pellicle membrane, the pellicle membrane including three or more layers, the three or more layers including at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer includes one or more of a silicon or silicon compound layer and / or a boron layer (e.g., pure boron B) or a boron compound layer (e.g., B4C, ZrB2, BN) and / or a zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon layer and / or one or more compounds of each of these materials. The outer layer may include and / or consist of one or more oxides. Such oxides may include, for example, one or more of silicon oxide (e.g., SiO2), aluminum oxide (e.g., Al2O3), zirconium oxide (e.g., ZrO2), or yttrium oxide (e.g., YO2 or Y2O3). The pellicle membrane may include any of the thicknesses / sizes disclosed above. In particular, the advantages of boron or boron compounds, yttrium or yttrium compounds, and / or carbon or carbon compounds are, for example, good transmittance in the entire wavelength range of 10 nm to 20 nm (Si has silicon edge).

[0138] Also disclosed is a pellicle beam splitter comprising a pellicle diaphragm, the pellicle diaphragm comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer comprises a boron layer (e.g., pure boron B), a boron compound layer (e.g., B4C, ZrB2, BN), a silicon layer, a zirconium, beryllium, niobium, yttrium, molybdenum, and / or a carbon layer and / or one or more compounds of each of these materials, wherein the combined thickness of the at least one outer layer on a single side (or each side) of the at least one inner layer is between 1 nm and 3 nm (e.g., between 1.5 nm and 2.5 nm, between 1.7 nm and 2.3 nm, between 1.8 nm and 2.2 nm, or between 1.9 nm and 2.1 nm), and the combined thickness of the inner layers is less than 20 nm (e.g., less than 15 nm, less than 13 nm, or less than or equal to 12 nm, and optionally greater than 6 nm, greater than 8 nm, greater than 10 nm, or greater than 11 nm).

[0139] The pellicle diaphragm design described above can provide a diaphragm with 70% to 80% transmittance and 1% to 2% reflectance with an extremely flat response over the wavelength range of interest (e.g., between 10nm and 20nm). In contrast, commercially available EUV beam splitters typically have very poor (non-flat) spectral behavior and low transmittance. Figure 8 Compared to the grating beam splitter shown in , the transmission (and therefore the throughput) is expected to be 5 times greater, and the manufacturing cost is substantially lower.

[0140] In all cases and embodiments, the total thickness of the pellicle membrane may be less than 20 nm or less than 15 nm.

[0141] Although the above description has described a pellicle diaphragm for use as a beam splitter, the disclosed concepts and diaphragms can be used in other applications, such as for attenuation (e.g., attenuating a high intensity full beam on a camera during source beam profile monitoring), for filtering (e.g., for filtering out Figure 5 The filter device 344 or Fig. 9 In the case of use as an attenuating filter, for example, the pellicle membrane can be thicker than described in the context of beam splitting; for example, the pellicle membrane can be thicker than 15 nm or thicker than 20 nm (e.g., up to 1.5 µm).

[0142] Now it will mainly be used in attenuation filtering or driven radiation / infrared filtering (e.g. Figure 5 The filter device 344 or Fig. 9 Further embodiments are described in the context of a spatial filter 815 of the embodiment of the present invention. However, the membrane diaphragm of these other embodiments can also be used in beam splitting (e.g., such as Fig. 9 Diaphragms of all embodiments disclosed herein may be used in any situation where a flat spectral transmission and / or reflection profile is desired for a wavelength range of interest (eg, SXR wavelengths).

[0143] The drive laser filters are currently implemented using materials with the highest ratio of SXR transmission to IR suppression. These filters rely on the transmission properties of the material. Currently, these filters can include, for example, zirconium or aluminum thin film filters.

[0144] Typically, the structures being measured have low diffraction efficiency. In addition to measuring the diffraction signals from such structures (on one or more diffraction signal detectors), the source beam profile can be periodically monitored, for example, on a dedicated detector. Optionally, the dedicated detector is configured to receive the SXR illumination beam for source calibration before the beam is used to measure the structures (i.e., upstream of the wafer stage). Since the beam is measured directly before the low diffraction efficiency structures, the intensity can be very high.

[0145] Currently, attenuation filters can be used to attenuate this high intensity and avoid very low integration times on the detector(s). Currently, this attenuation can be done using thick (e.g., 2µm or thicker) zirconium filters. The benefit of zirconium is that it has its best transmission properties at greater thicknesses; if other materials were used, the filters with the best transmission might be too thin to make / handle.

[0146] By way of example, metrology tool calibration may include performing an alignment of the optics. This optical alignment may be performed using one or more detectors (e.g., cameras) located at the focal length of the primary beam (SXR beam). In this case, the measured intensity may be very high. When aligning the SXR optics in this way, attenuation is currently also typically performed using a zirconium filter.

[0147] Neutral density filters are commercially available down to 120 nm; however, at SXR wavelengths, no suitable examples are commercially available. Attenuation of SXR wavelengths using thick zirconium filters changes the SXR spectrum (i.e., thick zirconium filters do not act as neutral filters in the wavelength range of interest). This is a problem because thick zirconium filters are the "true" source profile that measurements seek. Therefore, when using zirconium filters, monitoring of the source beam profile will be based on incorrect spectral composition. The beam profile is known to be wavelength dependent. This is also true for a focused SXR beam.

[0148] Not attenuating the SXR beam results in an integration time on the detector that may be only a few milliseconds long or even less than one millisecond long. This is shorter than the minimum time the shutter can be open and faster than most high-speed detectors. In addition, the source power may increase significantly in the future, resulting in impossible integration times if attenuation is not used.

[0149] Fig.10 (a) is a graph 1000 of the transmittance Trn of the zirconium filter versus wavelength λ (e.g., 1.2µm in this example). At this thickness, the longer wavelength side of the SXR range is strongly attenuated. This will be worse for higher source powers and / or focused beam measurements due to the attendant requirement for thicker filters.

[0150] As the source power increases, a thicker filter will be needed in order to achieve the desired attenuation, resulting in a stronger change in the spectrum. For example, when a thick zirconium filter is used, only the short wavelength side of the SXR spectrum is retained. Another commonly used material (aluminum) attenuates short wavelengths and only passes the long wavelength side.

[0151] To address this problem, specific filter material combinations will be described that have a substantially or approximately spectrally flat response over a wavelength range of interest (e.g., between 10 nm and 20 nm). The embodiments described herein use a filter diaphragm or film diaphragm comprising two or more different materials, wherein at least one of the materials is germanium (Ge) or selenium (Se).

[0152] Most materials have a higher transmittance on the short wavelength side in the region of 10 nm to 20 nm, such as Fig.10Example of zirconium illustrated in (a). Very few materials show qualitatively different behavior. Germanium and selenium are two examples with increasing transmittance with increasing wavelength. Although aluminum has an absorption edge that can approximate this behavior, this results in undesirably strong spectral variations.

[0153] Fig.10 (b) shows the corresponding Fig.10 (a) is an equivalent graph of the spectral response graph, and Fig.10 (c) shows the equivalent spectral response of selenium, Fig.10 (c) Graph the ideal behavior.

[0154] Therefore, it is proposed to construct a filter comprising a layer of one (or both) of germanium and selenium with one or more other materials in one or more other layers to obtain a filter membrane having a substantially flat spectral profile over the spectral range of interest. Using Ge or Se and other materials, many combinations having desired spectral properties can be made.

[0155] The layers can also be partially or completely mixed or composited. Although this requires more specialized manufacturing equipment, it will probably result in the same performance. This approach will produce a filter with only a single layer.

[0156] For example, specific examples may include germanium and zirconium, boron, germanium and zirconium, carbon, germanium and zirconium, or selenium and copper.

[0157] Fig.11 1 is a graph of the spectral response (transmittance Trn versus wavelength λ) of each of these specific examples over the wavelength range of 10 nm to 20 nm. Specifically, the graphs relate to the germanium and zirconium filter 1110, the selenium and copper filter 1120, and the boron, germanium and zirconium filter 1130. For comparison, the zirconium and aluminum filter spectral response 1100 is also shown; the spectral response varies by + / - 50% for most of its bandwidth and drops to zero transmittance at 20 nm. In contrast, the other three filters have a flatter response over the range shown. As can be seen, for example, the three material combination of boron, germanium and zirconium 1130 has a transmittance that is flat to within + / - 5% over the range of 10 nm to 20 nm.

[0158] While using two separate filters (e.g., one Zr filter and one Al filter) would work as an alternative, a single combined filter such as disclosed herein has its advantages. The combined filter is thicker and mechanically stronger; the combined filter can also be cheaper to produce because the manufacturing process is easier. For example, the peeling process to transfer the thin film on the substrate into the independent film only needs to be performed once.

[0159] The material combination can also be implemented as a continuous discrete filter. However, thicker filters are mechanically stronger and can withstand higher thermal loads.

[0160] The proposed filter membrane may include transmission characteristics such that the transmittance variation is less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, or less than 5% over a wavelength range between 10 nm and 20 nm.

[0161] In each filter combination including germanium, the germanium layer can be, for example, between 30nm and 450nm, between 50nm and 450nm, between 50nm and 300nm, between 100nm and 300nm, between 120nm and 270nm, or between 135nm and 150nm, and the total thickness can be, for example, between 100nm and 700nm, between 100nm and 500nm, between 100nm and 400nm, between 150nm and 400nm, between 200nm and 400nm, between 300nm and 400nm, between 230nm and 270nm.

[0162] In each filter combination including selenium, the selenium layer can be, for example, between 30nm and 600nm, between 30nm and 500nm, between 30nm and 400nm, between 30nm and 400nm, between 30nm and 300nm, between 30nm and 200nm, between 30nm and 100nm, between 30nm and 70nm, or between 40nm and 60nm, and the total thickness can be, for example, between 50nm and 1.5µm, between 50nm and 1µm, between 50nm and 800nm, between 50nm and 500nm, between 50nm and 300nm, between 50nm and 200nm, or between 50nm and 150nm.

[0163] Any references to first layer, second layer, etc. or first material, second material, etc. in the following aspects and claims should be understood to be for differentiation purposes only and do not in any way imply a specific order of layers or materials.

[0164] The filter diaphragm embodiments mentioned above can also use a thin layer of the same material instead of a thick layer for beam separation. The thickness of the thin layer can be the same as the thickness of the pellicle diaphragm layer mentioned above.

[0165] The above mentioned pellicle membrane embodiments may also use thick layers instead of thin layers for filtering. The thickness of the thick layer may be the same as the thickness of the filter membrane layers also mentioned above.

[0166] The above-mentioned embodiments can also be used as, for example Figure 5The filter device 344 acts as an IR blocker and a SXR transmitter, and Fig. 9 A spatial filter 815 with a pinhole.

[0167] The above mentioned diaphragms may be damaged during operation. Damage can be mitigated by periodically moving the diaphragm to find new undamaged areas or replacing the diaphragm. Figure 5 The filtering device 344 is taken as an example, but the embodiments can be practiced for all the above-mentioned diaphragms, filters, films, mirrors and lenses.

[0168] Figure 5 The filtering device 344 may include a metal transmissive diaphragm located in the beam path, typically at normal incidence. Optionally, the metal transmissive diaphragm may be a 300nm to 500nm thick Zr filter including a Zr diaphragm. Although there are other filtering components in the upstream optical path, the Zr filter may be required because some IR (referred to as leakage IR) light always escapes due to scattering and imperfect alignment. Optionally due to high temperature and / or material (e.g., carbon) deposition on the irradiated area, the irradiated area of ​​the leakage IR of the Zr filter is likely to be damaged after long-term and continuous use. Damage and / or contamination can be detected by measuring the same and / or different radiation reflected by the irradiated area. Note that leakage IR is mentioned as an example only for illustrative purposes, and the embodiments are applicable to any film, surface, and / or interface irradiated by any type of radiation. A method for detecting damage and / or contamination optionally caused by a first radiation (e.g., leakage IR) on the irradiated area is reported here. The method includes irradiating a second radiation (e.g., a detection beam) onto the irradiated area of ​​the membrane while the irradiated area of ​​the membrane is also irradiated by the first radiation. The second radiation is reflected by the irradiated area to generate reflected radiation, and the reflected radiation is detected to obtain a signal. Based on the signal, damage and / or contamination information about the irradiated area is obtained.

[0169] In one embodiment, a laser as a detection beam, which is an example of a second radiation, is used to monitor the health of the Zr filter. The laser may be a portion of an IR drive laser beam that is transmitted through a reflector as a detection beam. A small portion of the IR light may be transmitted through the reflector due to the imperfect nature of the reflector and / or pinholes on the reflector. The small portion of the IR light as the detection beam may be reflected off the Zr filter from the same irradiated area where the leaking IR hit the Zr filter. The intensity of the detection beam reflected from the Zr filter may be measured by a detection detector (optionally, a photodiode). If the Zr filter is not degraded, the intensity of the light measured by the photodiode is expected to remain constant over time. If the Zr filter is damaged over time, the signal measured by the photodiode will change. It has also been observed that materials accumulated on the surface of the Zr filter (e.g., carbon deposits) affect SXR transmission. The accumulated carbon can also be monitored by this method. If the quality of the Zr filter is detected to be degraded, the Zr filter can be moved so that the SXR beam is transmitted through a new, undamaged area.

[0170] Real-time temporal feedback of the quality of the Zr filter can help maintain the quality of the transmitted SXR beam and ensure adequate suppression of the leaked IR. The method can also prevent unnecessary changes to the Zr filter. The method can reduce the number of Zr filters required over time. The method can also provide information about contamination on the Zr filter. There may be deposits of hydrocarbon contaminants irradiated by the laser pulses at the surface of the Zr filter. Because the contaminants change the reflectivity of the detection beam, the method can detect the presence of contaminants. The position of the Zr filter can be changed, and the SXR can hit a new area without contamination. It can be expected that the intensity of the detection beam is much weaker than the intensity of the leaked IR, and therefore the detection beam does not affect the Zr filter.

[0171] In practice, the photodiode may be saturated by IR light scattered from various optical components in the system. Therefore, accurate measurement of the detection beam signal may be difficult. Alternatively, it is proposed to optionally monitor the polarization of the detection beam using a half-wave plate and use a polarizer in front of the photodiode to filter out scattered IR light.

[0172] Optionally, a pair of balanced detectors rather than a single photodiode is used as a detection detector. The detection beam is separated into two beams by a beam splitter before being reflected from the Zr filter. One of the two beams is a reference detection beam, which is measured by the first detector in the pair of balanced detectors. The second detector in the pair of balanced detectors measures the other of the two beams, which is the detection beam after reflection from the Zr filter. When the Zr filter is not damaged or contaminated, the signals on the two detectors are balanced and the differential signal is measured, which should be tuned to zero. When the Zr filter is damaged or contaminated, the differential signal may change.

[0173] Alternatively, the detection beams mentioned in the above embodiments may originate from separate lasers. The advantage is that the laser wavelength can be selected so that it can be filtered using a color filter at the detector(s). Thus, the laser wavelength removes any scattered IR light. A separate laser may be cheap and the embodiments also reduce complexity.

[0174] Optionally, the intensity of the detection beam can be measured on a pulse-to-pulse basis. The above embodiments may include a fast detector, such as (multiple) fast photodiodes. The intensity of each pulse after reflection from the Zr filter can be measured. Optionally, there is a delay between the leakage IR pulse and the detection beam pulse that hits the Zr filter. If the delay is carefully selected, the time response of the Zr filter from the leakage IR can be measured. Before the metal surface is damaged due to the accumulation of laser pulses, a brief change in the refractive index can be observed, which is a precursor to damage. Various other phenomena caused by different mechanisms, such as long-lived electronic excitation, changes in phonon coupling rates, etc., can also be observed. Time-resolved measurements can provide evidence of these phenomena. Time-resolved measurements will act as an early indicator of Zr filter damage, which can provide information about possible damage to the Zr filter even before the Zr filter is damaged.

[0175] Optionally, the Zr filter is positioned at an angle oblique to the SXR optical path, and the reflected leakage IR is measured for direct monitoring of the quality of the Zr filter. The incident angle of the source radiation beam on the Zr filter can be between 50 and 70 degrees, between 55 and 65 degrees, between 57 and 63 degrees, between 59 and 61 degrees, or more specifically about 60 degrees. This incident angle can provide optimal reflectivity / transmittance. The range of incident angles balances reflectivity and transmittance. One advantage of having the Zr filter at an angle between 50 and 70 degrees is for better IR suppression.

[0176] The above-mentioned embodiments provide a tool for monitoring the quality of the Zr filter and changing the position of the Zr filter when / before the Zr filter is damaged and / or contaminated, helping to maintain constant SXR transmittance and IR suppression by detecting the presence of damage and / or contaminants on the Zr filter, and reducing the amount of Zr filters required by monitoring the quality of the Zr filter in real time.

[0177] The above-mentioned embodiments for detecting radiation-induced damage and / or contamination on an irradiated area are also applicable to membrane elements, surfaces, and interfaces of lithographic apparatus using extreme ultraviolet (EUV) radiation.

[0178] The illumination source may be provided in, for example, a metrology apparatus MT, a detection apparatus, a lithographic apparatus LA, and / or a lithocell LC.

[0179] The properties of the emitted radiation used to perform the measurement may affect the quality of the measurement obtained. For example, the shape and size of the lateral beam profile (cross-section) of the radiation beam, the intensity of the radiation, the power spectral density of the radiation, etc. may affect the measurement performed by the radiation. Therefore, it is beneficial to have a source that provides radiation with properties that produce high quality measurements.

[0180] Further embodiments are disclosed in subsequently numbered aspects (Aspect Set 1):

[0181] 1. A measuring device comprising:

[0182] an illumination branch comprising illumination optics for directing measurement radiation onto the structure;

[0183] a pellicle beam splitter located in the illumination branch, the pellicle beam splitter comprising a pellicle diaphragm operable to split a source radiation beam from an illumination source into a reference radiation beam and the measurement radiation;

[0184] a measurement detector for detecting the measurement radiation after it has been scattered by the structure; and

[0185] A reference detector is provided for detecting the reference radiation beam.

[0186] 2. The metrology apparatus of clause 1, wherein the reference radiation beam comprises less than 3% of the total energy of the source radiation beam.

[0187] 3. The metrology apparatus of clause 1, wherein the reference radiation beam comprises less than 1.5% of the total energy of the source radiation beam.

[0188] 4. The metrology apparatus of clause 1, 2 or 3, wherein the reference radiation beam comprises more than 0.1% of the total energy of the source radiation beam.

[0189] 5. The metrology apparatus of clause 1, 2 or 3, wherein the reference radiation beam comprises more than 0.8% of the total energy of the source radiation beam.

[0190] 6. A measuring device as described in any of the preceding aspects, wherein the transmittance and / or reflectance of the pellicle membrane varies by less than 25% in the wavelength range of 10 nm to 20 nm.

[0191] 7. The measuring device according to any of the preceding aspects, wherein the transmittance and / or reflectance of the pellicle membrane varies by less than 20% within a wavelength range of 10 nm to 20 nm.

[0192] 8. A metrology apparatus as claimed in any preceding aspect, comprising a dispersive element between the pellicle beam splitter and the reference detector, the dispersive element being operable to spectrally disperse the reference radiation beam.

[0193] 9. The metrology apparatus of any preceding aspect, wherein the pellicle membrane comprises three or more layers including at least one outer layer on each side of at least one inner layer.

[0194] 10. The metrology apparatus of clause 9, wherein the at least one outer layer comprises an oxide material.

[0195] 11. The metrology apparatus of clause 10, wherein the oxide material comprises one or more of silicon oxide, aluminum oxide, zirconium oxide, or yttrium oxide.

[0196] 12. The metrology apparatus of any of clauses 9 to 11, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is less than 4 nm.

[0197] 13. The metrology apparatus of any of clauses 9 to 11, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is less than 3 nm.

[0198] 14. The metrology apparatus of any of clauses 9 to 11, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is less than 2.5 nm.

[0199] 15. The metrology apparatus of any one of clauses 9 to 14, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is greater than 1 nm.

[0200] 16. The metrology apparatus of any of clauses 9 to 14, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is greater than 1.5 nm.

[0201] 17. The metrology apparatus of any one of clauses 9 to 16, wherein the at least one internal layer comprises a silicon layer.

[0202] 18. A measurement device as described in any one of aspects 9 to 17, wherein the at least one internal layer includes one or more of silicon, boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials and / or is composed of one or more of silicon, boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials.

[0203] 19. The metrology apparatus of any of clauses 9 to 18, wherein the at least one internal layer has a thickness of less than 20 nm.

[0204] 20. The metrology apparatus of any of clauses 9 to 18, wherein the at least one internal layer has a thickness of less than 15 nm.

[0205] 21. The metrology apparatus of any of clauses 9 to 18, wherein the at least one internal layer has a thickness of less than 6 nm.

[0206] 22. The metrology apparatus of any of clauses 9 to 21, wherein the at least one internal layer has a thickness greater than 1 nm.

[0207] 23. The metrology apparatus of any one of clauses 9 to 21, wherein the at least one internal layer has a thickness greater than 4 nm.

[0208] 24. A metrology apparatus as described in any preceding aspect, wherein the source radiation beam comprises a wavelength in the range of 5 nm to 30 nm.

[0209] 25. The metrology apparatus of any one of clauses 1 to 23, wherein the source radiation beam comprises a wavelength in the range of 10 nm to 20 nm.

[0210] 26. A metrology apparatus as described in any preceding aspect, wherein the angle of incidence of the source radiation beam onto the pellicle diaphragm is between 45 degrees and 70 degrees.

[0211] 27. A metrology apparatus as described in any preceding aspect, wherein the angle of incidence of the source radiation beam onto the pellicle diaphragm is between 55 degrees and 65 degrees.

[0212] 28. The metrology apparatus of any preceding aspect, wherein the metrology apparatus is configured for measuring structures on a wafer, the structures having been exposed on the wafer in a photolithography process.

[0213] 29. A measurement device as described in any preceding aspect, wherein the total thickness of the pellicle membrane is less than 20 nm.

[0214] 30. A measurement device as described in any preceding aspect, wherein the total thickness of the pellicle membrane is less than 15 nm.

[0215] 31. A pellicle diaphragm comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer comprises and / or consists of one or more of boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials.

[0216] 32. The pellicle membrane of aspect 31, wherein the at least one exterior layer comprises an oxide material.

[0217] 33. The diaphragm membrane of aspect 32, wherein the oxide material comprises one or more of silicon oxide, aluminum oxide, zirconium oxide, or yttrium oxide.

[0218] 34. The pellicle membrane of any one of aspects 31 to 33, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is less than 4 nm.

[0219] 35. The pellicle membrane of any one of aspects 31 to 33, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is less than 3.5 nm.

[0220] 36. The pellicle membrane of any one of aspects 31 to 33, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is less than 3 nm.

[0221] 37. The pellicle membrane of any one of aspects 31 to 33, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is less than 2.5 nm.

[0222] 38. The pellicle membrane of any one of aspects 31 to 37, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is greater than 1 nm.

[0223] 39. The pellicle membrane of any one of aspects 31 to 37, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is greater than 1.5 nm.

[0224] 40. The pellicle membrane of any one of aspects 31 to 39, wherein the at least one interior layer comprises a silicon layer.

[0225] 41. The pellicle membrane of any one of aspects 31 to 40, wherein the at least one interior layer comprises one or more of a boron layer or a boron compound layer.

[0226] 42. The pellicle membrane of any one of aspects 31 to 41, wherein the at least one interior layer has a thickness of less than 20 nm.

[0227] 43. The pellicle membrane of any one of aspects 31 to 41, wherein the at least one interior layer has a thickness of less than 15 nm.

[0228] 44. The pellicle membrane of any one of aspects 31 to 41, wherein the at least one interior layer has a thickness of less than 6 nm.

[0229] 45. The pellicle membrane of any one of aspects 31 to 44, wherein the at least one interior layer has a thickness greater than 1 nm.

[0230] 46. ​​The pellicle membrane of any one of aspects 31 to 44, wherein the at least one interior layer has a thickness greater than 4 nm.

[0231] 47. The pellicle membrane of any one of aspects 31 to 46, wherein the transmittance and / or reflectance of the pellicle membrane varies by less than 25% within a wavelength range of 10 nm to 20 nm.

[0232] 48. The pellicle membrane of any one of aspects 31 to 47, wherein the transmittance and / or reflectance of the pellicle membrane varies by less than 20% within a wavelength range of 10 nm to 20 nm.

[0233] 49. The pellicle membrane of any one of aspects 27 to 48, wherein the total thickness of the pellicle membrane is less than 20 nm.

[0234] 50. The pellicle membrane of any one of aspects 27 to 48, wherein the total thickness of the pellicle membrane is less than 15 nm.

[0235] 51. A pellicle diaphragm comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer comprises and / or consists of one or more of silicon, boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials; and

[0236] The thickness of the at least one outer layer on each side of the at least one inner layer is between 1 nm and 3 nm.

[0237] 52. The pellicle membrane of aspect 51, wherein the thickness of the at least one outer layer on each side of the at least one inner layer is between 1.5 nm and 2.5 nm.

[0238] 53. The pellicle membrane of aspect 51, wherein the at least one exterior layer comprises an oxide material.

[0239] 54. The diaphragm membrane of aspect 53, wherein the oxide material comprises one or more of silicon oxide, aluminum oxide, zirconium oxide, or yttrium oxide.

[0240] 55. The pellicle membrane of any one of aspects 51 to 54, wherein the total thickness of the pellicle membrane is less than 20 nm.

[0241] 56. The pellicle membrane of any one of aspects 51 to 54, wherein the total thickness of the pellicle membrane is less than 15 nm.

[0242] 57. The pellicle membrane of any one of aspects 51 to 56, wherein the at least one interior layer has a thickness of less than 20 nm.

[0243] 58. The pellicle membrane of any one of aspects 51 to 56, wherein the at least one interior layer has a thickness of less than 15 nm.

[0244] 59. The pellicle membrane of any one of aspects 51 to 56, wherein the at least one interior layer has a thickness of less than 6 nm.

[0245] 60. The pellicle membrane of any one of aspects 51 to 59, wherein the at least one interior layer has a thickness greater than 1 nm.

[0246] 61. The pellicle membrane of any one of aspects 51 to 59, wherein the at least one interior layer has a thickness greater than 4 nm.

[0247] 62. The pellicle membrane of any one of aspects 51 to 61, wherein the transmittance and / or reflectance of the pellicle membrane varies by less than 25% within a wavelength range of 10 nm to 20 nm.

[0248] 63. The pellicle membrane of any one of aspects 51 to 62, wherein the transmittance and / or reflectance of the pellicle membrane varies by less than 20% within a wavelength range of 10 nm to 20 nm.

[0249] 64. A pellicle beam splitter comprising the pellicle membrane of any one of aspects 31 to 63.

[0250] 65. An attenuator and / or driven radiation filter comprising a pellicle diaphragm as described in any one of clauses 31 to 63.

[0251] 66. A filter diaphragm comprising at least two materials, wherein at least a first material of the at least two materials comprises or consists of germanium or selenium.

[0252] 67. The filter membrane of clause 66, comprising a transmission characteristic such that the transmission varies by less than 50% over a wavelength range between 10 nm and 20 nm.

[0253] 68. The filter membrane of clause 66, comprising a transmission characteristic such that the transmission varies by less than 30% over a wavelength range between 10 nm and 20 nm.

[0254] 69. The filter membrane of clause 66, comprising a transmission characteristic such that the transmission varies by less than 10% over a wavelength range between 10 nm and 20 nm.

[0255] 70. The filter membrane of any one of aspects 66 to 69, wherein the at least two materials are mixed or composited into a single layer.

[0256] 71. The filter membrane of any one of aspects 66 to 69, wherein each of the at least two materials is included in a corresponding separate layer.

[0257] 72. A filter diaphragm as described in any one of aspects 66 to 71, wherein the first material includes and / or consists of germanium, and the at least two materials further include a second material, the second material includes and / or consists of zirconium.

[0258] 73. The filter membrane of aspect 72, wherein the at least two materials further comprise a third material, the third material comprising and / or consisting of boron or carbon.

[0259] 74. The filter membrane of any of clauses 70 to 73, wherein a first layer of the membrane comprising the first material has a thickness between 30 nm and 450 nm.

[0260] 75. The filter membrane of any of clauses 70 to 73, wherein a first layer of the membrane comprising the first material has a thickness between 50 nm and 300 nm.

[0261] 76. The filter membrane of any one of aspects 70 to 75, comprising a total thickness between 100 nm and 700 nm.

[0262] 77. The filter membrane of any one of aspects 70 to 75, comprising a total thickness between 100 nm and 500 nm.

[0263] 78. A filter membrane as described in any one of aspects 66 to 71, wherein the first material includes selenium and / or consists of selenium, and the at least two materials further include a second material, the second material includes copper and / or consists of copper.

[0264] 79. The filter membrane of clause 78, wherein the first layer of the membrane comprising the first material has a thickness between 30 nm and 600 nm.

[0265] 80. The filter membrane of clause 78, wherein a first layer of the membrane comprising the first material has a thickness between 30 nm and 400 nm.

[0266] 81. The filter membrane of aspects 78, 79 or 80, comprising a total thickness between 50 nm and 1.5 µm.

[0267] 82. The filter membrane of aspect 78, 79 or 80, comprising a total thickness between 50 nm and 500 nm.

[0268] 83. A beam splitter, attenuator, and / or driven radiation filter comprising the filter membrane of any of clauses 66 to 82.

[0269] 84. A metrology apparatus comprising a beam splitter, attenuator, and / or driven radiation filter as described in clause 83.

[0270] 85. A method for detecting damage and / or contamination caused by a first radiation on an irradiated area, the method comprising:

[0271] irradiating a second radiation onto the irradiated area, wherein the irradiated area is also irradiated by the first radiation, wherein the second radiation is reflected by the irradiated area to produce reflected radiation,

[0272] detecting the reflected radiation to obtain a signal, and

[0273] Damage and / or contamination information about the irradiated area is obtained based on the signal.

[0274] 86. The method of clause 85, wherein the irradiated region is a region of the septum.

[0275] 87. The method of clause 85 or 86, wherein the first radiation is inferred.

[0276] 88. The method of any one of clauses 85 to 87, wherein the second radiation is from the same source as the first radiation.

[0277] 89. The method of any one of clauses 85 to 87, wherein the second radiation is from a different source than the first radiation.

[0278] 90. The method of any one of clauses 85 to 89, wherein both the first radiation and the second radiation comprise pulses.

[0279] 91. The method of clause 90, wherein there is a delay between the first radiation and the second radiation.

[0280] 92. A method as described in any of clauses 85 to 91, wherein the reflected radiation is detected by a pair of balanced detectors.

[0281] 93. A method as described in any of clauses 85 to 92, wherein the second radiation is polarized.

[0282] Further embodiments are disclosed in subsequently numbered aspects (Aspect Set 2):

[0283] 1. A diaphragm membrane comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer comprises and / or consists of one or more of silicon carbide, silicon dicarbide, boron carbide and boron nitride, and wherein at least one of the at least one outer layer comprises an oxide material.

[0284] 2. The diaphragm membrane according to aspect 1, wherein the oxide material comprises one or more of silicon oxide, aluminum oxide, zirconium oxide, or yttrium oxide.

[0285] 3. The pellicle membrane of aspect 1 or 2, wherein the at least one internal layer has a thickness of less than 6 nm.

[0286] 4. The pellicle membrane according to any one of the preceding aspects, wherein the at least one internal layer has a thickness greater than 1 nm.

[0287] 5. The pellicle membrane of any of the preceding aspects, wherein at least one of the at least one outer layer comprises ruthenium.

[0288] 6. The pellicle membrane of aspect 5, wherein a front side of the at least one internal layer is capped by the external layer comprising ruthenium, and a back side of the at least one internal layer is capped by the external layer comprising the oxide material.

[0289] 7. A measuring device comprising:

[0290] an illumination branch comprising illumination optics for directing measurement radiation onto the structure;

[0291] a pellicle beam splitter located in the illumination branch, the pellicle beam splitter comprising a pellicle diaphragm operable to split a source radiation beam from an illumination source into a reference radiation beam and the measurement radiation;

[0292] a measurement detector for detecting the measurement radiation after it has been scattered by the structure; and

[0293] a reference detector for detecting the reference radiation beam,

[0294] Wherein, the incident angle of the source radiation beam onto the pellicle beam splitter is between 45 degrees and 70 degrees.

[0295] 8. The metrology apparatus of clause 7, wherein the angle of incidence of the source radiation beam onto the pellicle beam splitter is between 46 degrees and 50 degrees.

[0296] 9. The metrology apparatus of clause 7, wherein the angle of incidence of the source radiation beam onto the pellicle beam splitter is between 55 degrees and 65 degrees.

[0297] 10. A measuring device comprising:

[0298] an illumination branch comprising illumination optics for directing measurement radiation onto the structure;

[0299] a pellicle beam splitter located in the illumination branch, the pellicle beam splitter comprising a pellicle diaphragm operable to split a source radiation beam from an illumination source into a reference radiation beam and the measurement radiation;

[0300] a measurement detector for detecting the measurement radiation after it has been scattered by the structure; and

[0301] a reference detector for detecting the reference radiation beam,

[0302] Wherein, the incident angle of the source radiation beam onto the pellicle beam splitter is between 40 degrees and 44 degrees.

[0303] 11. A metrology apparatus as claimed in any one of clauses 7 to 10, comprising a dispersive element between the pellicle beam splitter and the reference detector, the dispersive element being operable to spectrally disperse the reference radiation beam.

[0304] 12. The metrology apparatus of clause 11, wherein the dispersive element is a transmissive dispersive element.

[0305] 13. A metrology apparatus as claimed in any one of clauses 7 to 12, comprising a focusing mirror.

[0306] 14. The measurement apparatus according to claim 13, wherein the pellicle beam splitter is located on the upstream side of the focusing mirror.

[0307] 15. The measurement apparatus of clause 13, wherein the pellicle beam splitter is located downstream of the focusing mirror.

[0308] 16. A pellicle diaphragm comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein the at least one inner layer comprises one or more of boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials, and / or the at least one inner layer consists of one or more of boron, zirconium, beryllium, niobium, yttrium, molybdenum, and / or carbon and / or one or more compounds of each of these materials, wherein the at least one inner layer has a thickness of less than 6 nm.

[0309] 17. A measuring device comprising:

[0310] an illumination branch comprising illumination optics for directing measurement radiation onto the structure;

[0311] a pellicle beam splitter located in the illumination branch, the pellicle beam splitter comprising a pellicle diaphragm operable to split a source radiation beam from an illumination source into a reference radiation beam and the measurement radiation;

[0312] a measurement detector for detecting the measurement radiation after it has been scattered by the structure;

[0313] a reference detector for detecting the reference radiation beam, and

[0314] a dispersive element located between the pellicle beam splitter and the reference detector and operable to spectrally disperse the reference radiation beam,

[0315] Wherein, the dispersive element is a transmission type dispersive element.

[0316] Although embodiments may be specifically referenced herein in the context of a reflective (or transmissive) membrane, the embodiments may be used in a transmissive (or reflective) membrane. One or more layers forming different embodiments may be further combined to provide higher level functionality (e.g., less variation in transmittance / reflectance).

[0317] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0318] Although specific reference may be made herein to embodiments in the context of lithographic apparatus, embodiments may be used in other apparatuses. Embodiments may form part of mask detection apparatus, metrology apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other pattern forming devices). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0319] Although embodiments may be specifically referenced herein in the context of detection or measurement equipment, embodiments may be used in other devices. Embodiments may form part of mask detection equipment, lithography equipment, or any equipment for measuring or processing objects such as wafers (or other substrates) or masks (or other pattern forming devices). The term "measurement equipment" (or "detection equipment") may also refer to a detection equipment or a detection system (or a measurement equipment or a measuring system). For example, a detection equipment including an embodiment may be used to detect defects in a substrate or defects in a structure on a substrate. In such embodiments, the concerned characteristics of a structure on a substrate may be related to defects in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate.

[0320] Although the above may have made specific reference to the use of embodiments in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography, and may be used in other applications (eg imprint lithography) where the context permits.

[0321] While the targets or target structures (more generally, structures on a substrate) described above are metrology target structures specifically designed and formed for measurement purposes, in other embodiments, the properties of interest may be measured on one or more structures that are functional parts of a device formed on a substrate. Many devices have regular grating-like structures. The terms "structure," "target grating," and "target structure" as used herein do not require that the structure has been provided specifically for the measurement being performed. In addition, the pitch of the metrology target may be close to the resolution limit of the optical system of the scatterometer or may be smaller, but may be much larger than the size of a typical non-target structure (optionally a product structure) made by a lithography process in the target portion C. In practice, the lines and / or spaces of the overlapping gratings within the target structure may be made to include smaller structures that are similar in size to the non-target structures.

[0322] Although specific embodiments have been described above, it will be appreciated that the present invention may be practiced in other ways than as described. The above description is intended to be illustrative, not restrictive. Therefore, it will be apparent to those skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims set forth below.

[0323] Although specific reference is made to "measurement equipment / tool / system" or "detection equipment / tool / system", these terms may refer to the same or similar types of tools, equipment, or systems. For example, a detection or measurement equipment including embodiments of the present invention may be used to determine characteristics of a structure on a substrate or on a wafer. For example, a detection equipment or measurement equipment including embodiments of the present invention may be used to detect defects in a substrate or defects in a structure on a substrate or on a wafer. In such embodiments, the characteristic of interest of a structure on a substrate may be related to a defect in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate or on a wafer.

[0324] Although specific reference is made to HXR, SXR, and EUV electromagnetic radiation, it will be appreciated that the invention may be practiced where the context permits with all electromagnetic radiation, including radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

[0325] Although specific embodiments have been described above, it will be appreciated that one or more of the features in one embodiment may also be present in a different embodiment, and that features from two or more different embodiments may also be combined.

Claims

1. A pellicle membrane comprising three or more layers, the three or more layers comprising at least one inner layer and at least one outer layer on either side of the at least one inner layer, wherein: The at least one inner layer comprises and / or consists of one or more of silicon carbide, silicon dicarbide, boron carbide and boron nitride, and wherein at least one of the at least one outer layer comprises an oxide material.

2. The diaphragm membrane according to claim 1, wherein: The oxide material includes one or more of silicon oxide, aluminum oxide, zirconium oxide, or yttrium oxide.

3. The pellicle diaphragm according to claim 1 or 2, wherein: The at least one internal layer has a thickness of less than 6 nm.

4. A pellicle membrane as claimed in any one of the preceding claims, wherein: The at least one internal layer has a thickness greater than 1 nm.

5. A pellicle membrane as claimed in any one of the preceding claims, wherein: At least one of the at least one outer layer includes ruthenium.

6. The diaphragm membrane according to claim 5, wherein: The front side of the at least one internal layer is capped by the outer layer comprising ruthenium, and the back side of the at least one internal layer is capped by the outer layer comprising the oxide material.

7. A measuring device comprising: an illumination branch comprising illumination optics for directing measurement radiation onto the structure; a pellicle beam splitter located in the illumination branch, the pellicle beam splitter comprising a pellicle diaphragm operable to split a source radiation beam from an illumination source into a reference radiation beam and the measurement radiation; a measurement detector for detecting the measurement radiation after it has been scattered by the structure; and a reference detector for detecting the reference radiation beam, Wherein, the incident angle of the source radiation beam onto the pellicle beam splitter is between 45 degrees and 70 degrees.

8. The measuring device according to claim 7, wherein: The angle of incidence of the source radiation beam onto the pellicle beam splitter is between 46 degrees and 50 degrees.

9. The measuring device according to claim 7, wherein: The angle of incidence of the source radiation beam onto the pellicle beam splitter is between 55 degrees and 65 degrees.

10. A measuring device comprising: an illumination branch comprising illumination optics for directing measurement radiation onto the structure; a pellicle beam splitter located in the illumination branch, the pellicle beam splitter comprising a pellicle diaphragm operable to split a source radiation beam from an illumination source into a reference radiation beam and the measurement radiation; a measurement detector for detecting the measurement radiation after it has been scattered by the structure; and a reference detector for detecting the reference radiation beam, Wherein, the incident angle of the source radiation beam onto the pellicle beam splitter is between 40 degrees and 44 degrees.

11. A metrology apparatus as claimed in any one of claims 7 to 10, comprising a dispersive element between the pellicle beam splitter and the reference detector, the dispersive element being operable to spectrally disperse the reference radiation beam.

12. The measuring device according to claim 11, wherein: The dispersive element is a transmissive dispersive element.

13. A metrology apparatus as claimed in any one of claims 7 to 12, comprising a focusing mirror.

14. The measuring device according to claim 13, wherein: The pellicle beam splitter is located on the upstream side of the focusing mirror.

15. The measuring device according to claim 13, wherein: The pellicle beam splitter is located on the downstream side of the focusing reflector.

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