Metrology method for measuring exposed pattern and associated metrology apparatus

Abstract

To provide a method and a metrology device for executing measurement of an exposed pattern in photoresist on a substrate.SOLUTION: A metrology device 302 for executing measurement of an exposed pattern in photoresist on a substrate comprises: an illumination system 312 to impart a focused beam 356 on the exposed pattern over a measurement area (target Ta) of a size which prevents or mitigates photoresist damage from emitted radiation 342, the beam being capable of forming a measurement spot on the substrate W; at least one detection system 398 capable of detecting diffracted radiation 397, which is radiation after being scattered from the exposed pattern; and a measurement processor 320 capable of determining a value for a parameter of interest from the radiation.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to European Application 20192002.2, filed August 20, 2020, which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present invention relates to metrology applications in the manufacture of integrated circuits. [Background technology]

[0003] A lithographic apparatus is a machine that is configured to apply a desired pattern onto a substrate. Lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (often also referred to as a "design layout" or "design") in a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on the substrate (e.g., wafer).

[0004] 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 in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 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, may be used to form smaller features on a substrate than lithographic apparatus using radiation having a wavelength of, for example, 193 nm.

[0005] low k 1 Lithography may be used to process features with dimensions smaller than the classical resolution limit of the lithographic apparatus. In such processes, the equation for resolution is changed to "CD = k 1x λ / NA”, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the “critical dimension” (generally the smallest feature size to be printed, but in this case the half pitch), and k 1 is an empirical resolution factor. In general, k 1 As the size of the lithography tool decreases, it becomes more difficult to reproduce patterns on a substrate that resemble the shapes and dimensions designed by the circuit designer to achieve a particular electrical function and performance. To overcome these difficulties, sophisticated fine-tuning steps may be applied to the lithography projection apparatus and / or the design layout. These include, but are not limited to, optimization of the design layout, such as, for example, optimization of the NA, customized illumination schemes, use of phase-shifting patterning devices, optical proximity correction (OPC, sometimes denoted as "optical and process correction") in the design layout, or other methods commonly defined as "resolution enhancement techniques" (RET). Alternatively, tight control loops to control the stability of the lithography tool may be used to optimize the low k 1 This may be used to improve the reproducibility of patterns in

[0006] In lithography processes, it is frequently desirable to make measurements of the structures being produced, for example for process control and verification. A variety of tools are known to make such measurements, including scanning electron microscopes, which are often used to measure critical dimensions (CD), and dedicated tools for measuring overlay (the accuracy of the alignment of two layers in a device). Recently, various forms of scatterometers have been developed for use in the lithography field.

[0007] Known examples of scatterometers often rely on the provision of a dedicated metrology target. For example, a method may require a target in the form of a simple grating that is large enough that the measurement beam produces a spot smaller than the grating (i.e. the grating is underfilled). In so-called reconstruction methods, the properties of the grating can be calculated by simulating the interaction of the scattered radiation with a mathematical model of the target structure. Parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the real target.

[0008] In addition to measuring feature shapes by reconstruction, diffraction-based overlay can be measured using an apparatus such as that described in published patent application US2006066855A1. Diffraction-based overlay metrology allows overlay measurements on smaller targets using dark field imaging of diffraction orders. These targets may be smaller than the illumination spot and may be surrounded by product structures on the wafer. Examples of dark field imaging metrology 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 be significantly coarser than the actual product structure whose properties are of actual interest. Such product features may be defined using deep ultraviolet (DUV), extreme ultraviolet (EUV) or X-ray radiation, which have significantly shorter wavelengths. Unfortunately, such wavelengths are not typically available or usable for metrology.

[0009] On the other hand, the dimensions of modern product structures are so small that they cannot be imaged by optical metrology techniques. Small features include, for example, those formed by multiple patterning processes and / or pitch multiplication. Thus, targets used for high volume metrology often use features that are significantly larger than the product where the overlay error or critical dimension is the property of interest. Since the metrology targets do not experience the same distortions under different processing in the optical projection in the lithography apparatus and / or other steps of the manufacturing process, the measurement results may be inaccurate as they are only indirectly related to the dimensions of the real product structures. Scanning electron microscopes (SEMs) can directly resolve these modern product structures, but SEMs take significantly longer than optical measurements. Furthermore, electrons cannot penetrate thick processing layers, making them often unsuitable for metrology applications. Other techniques, such as using contact pads to measure electrical properties, are also known, but provide only indirect evidence of the true product structure. Summary of the Invention [Problem to be solved by the invention]

[0010] In this way, it is advantageous to extract a particular parameter of interest, such as overlay, from a target whose grating width is similar to the critical dimension of the stack. In this context, a target may comprise a metrology target formed for metrology purposes or an actual product structure having a morphology (e.g., sufficient interdependence) that may be measured to obtain the parameter of interest. Thus, the terms "target", "metrology target" or "overlay target" should be clearly understood throughout this text to encompass metrology targets specially formed for metrology purposes and / or product structures having a morphology suitable for metrology. Promising ways to do this are to use hard x-ray (HXR) radiation, soft x-ray (SXR) radiation, and / or extreme ultraviolet (EUV) radiation (e.g., with a wavelength in the range of 10-20 nm). However, it is envisaged that reactions with hydrocarbons, such as SXR or (EUV) radiation, may lead to the deposition of material, such as carbon, on the target during exposure.

[0011] It would also be advantageous to measure overlay on an after-development inspection (ADI) target where the top grating is only present in the developed photoresist, however exposure of such an ADI target to, for example, SXR or EUV radiation leads to resist exposure that is expected to result in changes to the resist, in particular resist shrinkage.

[0012] Material deposition (optionally carbon deposition), resist shrinkage and / or other resist damage may be expressed as target drift. Thus, target drift may be defined as a structural change of the target due to illumination. This may affect the intensities of the -1 and +1 (or higher) diffraction orders and thus the asymmetry of the measured intensities. If the asymmetry is affected, then in turn the accuracy of the determined overlay may be affected (e.g. deteriorated). The determined overlay may therefore differ from the actual overlay due to target drift.

[0013] It is also evident that the problem of target drift is particularly serious when measurements are performed on real product structures, as it may result in structural changes or damage to the real product.

[0014] For this reason, methods are needed to reduce or prevent target drift. [Means for solving the problem]

[0015] Thus, in a first aspect of the invention there is provided a method of performing a measurement of an exposure pattern in photoresist on a substrate, the method comprising applying a beam of measurement radiation onto the exposure pattern over a measurement area sized to prevent or reduce damage to the photoresist from the measurement radiation to form a measurement spot on the substrate, capturing scattered radiation, the measurement radiation after it has been scattered from the exposure pattern, detecting the scattered radiation on at least one detector, and determining a value for a parameter of interest from the scattered radiation.

[0016] In a second aspect of the invention there is provided a metrology device for performing measurements of an exposure pattern in photoresist on a substrate, the metrology device comprising an illumination system operable to apply a beam of measurement radiation onto the exposure pattern over a measurement area sized to prevent or reduce damage to the photoresist from the measurement radiation, the beam of measurement radiation being capable of forming a measurement spot on the substrate, at least one detector operable to detect scattered radiation, the measurement radiation after being scattered from the exposure pattern, and a processor operable to determine a value for a parameter of interest from the scattered radiation.

[0017] In another aspect of the invention there is provided a computer program comprising program instructions which, when executed on a suitable device, are capable of carrying out the method of the first aspect. [Brief description of the drawings]

[0018] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which: [Figure 1]1 depicts a schematic overview of a lithographic apparatus; [Diagram 2] FIG. 1 is a schematic diagram of a lithography cell. [Diagram 3] FIG. 1 is a schematic diagram of Holistic Lithography, which illustrates the collaboration between three key technologies to optimize semiconductor manufacturing. [Figure 4] 1 illustrates a schematic diagram of a scatterometry apparatus; [Diagram 5] 1 illustrates a schematic diagram of a transmission type scatterometry apparatus; [Figure 6] FIG. 1 is a schematic diagram of a metrology setup in which EUV and / or SXR radiation is used. [Figure 7] FIG. 1 is a schematic diagram of an illumination source for harmonic generation. [Figure 8] 1A to 1C are schematic diagrams illustrating a measurement method according to a first embodiment. [Figure 9] 11A to 11C are schematic diagrams illustrating a measurement method according to a second embodiment. [Figure 10] 11A-11C are schematic diagrams of three implementations of a measurement device and a measurement method according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic and particulate radiation, including ultraviolet radiation (e.g., having a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5-100 nm), X-ray radiation, electron beam radiation and other particulate radiation.

[0020] The terms "reticle," "mask," or "patterning device" as used in this text may be broadly interpreted to refer to a general patterning device that may be used to impart an incident beam with a patterned cross-section that corresponds to the pattern to be produced in a target portion of a substrate. The term "light valve" may also be used in this context. Besides the classic mask (transmissive or reflective; binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0021] 1 illustrates diagrammatically a lithographic apparatus LA, which comprises an illumination stem (also denoted 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. mask table) T configured to support a patterning device (e.g. 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. wafer table) WT configured to hold a substrate (e.g. a resist-covered wafer) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern formed in 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.

[0022] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the 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 such that it has a cross-section at the plane of the patterning device MA with a desired spatial and angular intensity distribution.

[0023] The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems including refractive, reflective, diffractive, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, appropriate for the exposure radiation being used and / or other factors such as the use of an immersion liquid or vacuum. Use of the term "projection lens" herein may be interpreted as synonymous with the more general term "projection system" PS.

[0024] The lithographic apparatus LA may be of a type (also referred to as immersion lithography) in which at least a part of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system PS and the substrate W. More information on immersion techniques is given in US6952253, which is incorporated herein by reference in its entirety.

[0025] The lithographic apparatus LA may be of a type having two or more substrate supports WT (also called "dual stage") In such a "multiple stage" apparatus, the substrate supports WT may be used in parallel and / or preparation steps for a subsequent exposure of the substrate W may be performed on a substrate W placed on one substrate support WT while another substrate W on the other substrate support WT is being used to expose a pattern thereon.

[0026] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement stage. The measurement stage is provided to hold a sensor and / or a cleaning device. The sensor may be provided to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold a number of sensors. The cleaning device may be provided to clean part of the lithographic apparatus, for example part of the projection system PS or part of the system for providing immersion liquid. The measurement stage may move below the projection system PS when the substrate support WT is spaced apart from the projection system PS.

[0027] In operation, a radiation beam B is incident on a patterning device, such as a mask MA held on a mask support T, and is patterned by a pattern (design layout) present on the patterning device MA. After the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of a substrate W. By means of a second positioner PW and a position measurement system IF, the substrate support WT may be precisely driven, for example so that different target portions C can be positioned at focusing and alignment positions on the path of the radiation beam B. Similarly, a first positioner PM and other position sensors (not explicitly shown in FIG. 1 ) may be used to precisely position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, they may also be located in spaces between the target portions. The substrate alignment marks P1, P2 which are positioned between the target portions C are known as scribe line alignment marks.

[0028] As shown in FIG. 2, the lithographic apparatus LA may form part of a lithographic cell LC, sometimes denoted as lithocell or (litho)cluster, which often also includes apparatus for performing pre-exposure and post-exposure processes on the substrate W. Conventionally, these include a spin coater SC for forming a resist layer, a developer DE for developing the exposed resist, a cooling plate CH and a bake plate BK for adjusting the temperature of the substrate W (such as the solvent in the resist layer). A substrate handler or robot RO picks up substrates W from input / output ports I / O1, I / O2, moves them between the different processing devices and transports the substrates W to a loading bay LB of the lithographic apparatus LA. The devices in the lithocell, often collectively also referred to as a track, may be under the control of a track control unit TCU, which may itself be controlled by a supervisory control system SCS. The supervisory control system SCS may control the lithographic apparatus LA via a lithography control unit LACU.

[0029] In lithographic processes, it is frequently desirable to perform measurements of the structures being produced, e.g. for process control and verification. A tool for performing such measurements may be referred to as a metrology tool MT. Different types of metrology tools MT are known for performing such measurements, including scanning electron microscopes or various forms of scatterometer metrology tools MT. A scatterometer is a versatile device that allows the measurement of parameters of the lithographic process by having a sensor in the pupil or in a plane conjugate with the pupil of the scatterometer objective (wherein the measurements are usually referred to as pupil-based measurements) or in an image plane or in a plane conjugate with the image plane (wherein the measurements are usually referred to as image- or field-based measurements). Such scatterometers and associated 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. Such scatterometers may measure gratings using hard x-ray, soft x-ray, extreme ultraviolet and light from the visible to near infrared wavelength range. When the radiation is hard x-ray or soft x-ray (optionally with a wavelength in the range of 0.01 nm to 10 nm), such scatterometers may optionally be small angle x-ray scattering metrology tools.

[0030] In order for substrates W exposed by the lithographic apparatus LA to be consistently and correctly exposed, it is desirable to inspect the substrate to measure properties of the patterned structures such as overlay error between subsequent layers, line thickness, critical dimension (CD), shape of the structures, etc. For this purpose, inspection and / or metrology tools (not shown) may be included in the lithocell LC. If an error is detected, particularly if inspection is performed before other substrates W of the same batch or lot are exposed or processed, adjustments may be made, for example, to the exposure of subsequent substrates or to other processing steps performed on the substrate W.

[0031] The inspection apparatus, which may also be denoted as metrology apparatus, is used to determine properties of the substrate W, in particular to determine the variation of properties of different substrates W or the layer-to-layer variation of properties for different layers of the same substrate W. Alternatively, the inspection apparatus may be configured to identify defects on the substrate W and may, for example, be part of a lithocell LC, integrated in the lithographic apparatus LA or be a stand-alone device. The inspection apparatus may measure properties of the latent image (image in the resist layer after exposure), the semi-latent image (image in the resist layer after a post-exposure bake step PEB), the developed resist image (where exposed or unexposed parts of the resist have been removed) or the etched image (after a pattern transfer step such as etching).

[0032] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, a reconstruction method may be applied to the measured signal in order to reconstruct or calculate the properties of the grating. Such a reconstruction may for example be based on simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with those measurements. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to the one observed from the real target.

[0033] 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 radiation reflected, transmitted or scattered from the target is directed to a spectrometer detector that measures the spectrum of the specularly reflected radiation (i.e. a measurement of the intensity as a function of wavelength). From this data, the structure or profile of the target from which the detected spectrum originates may be reconstructed, for example by Rigorous Coupled Wave Analysis and non-linear regression, or by comparison with a library of simulated spectra.

[0034] In a third embodiment, the scatterometer MT is an ellipsometric scatterometer. The ellipsometric scatterometer allows for determining parameters of the lithographic process by measuring the scattered or transmitted radiation for each polarization state. Such a metrology tool emits polarized light (e.g. linear, circular or elliptical), for example by using a suitable polarizing filter in the illumination section of the metrology tool. A source suitable for the metrology tool may provide the 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.

[0035] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring the asymmetry (related to the degree of overlay) in the reflected spectrum and / or the detection configuration. The two (possibly overlapping) grating structures may be applied in two different layers (not necessarily consecutive layers) and may be formed at substantially the same location on the wafer. The scatterometer may have a symmetric detection configuration such that any asymmetry is clearly identifiable, as described, for example, in co-owned patent application EP1,628,164A. This provides a straightforward way to measure misalignment in the gratings. Further examples for measuring the overlay error between two layers containing periodic structures, with the target being measured through the asymmetry of the periodic structures, can be found in PCT patent application publication number WO2011 / 012624 or US patent application US20160161863, which are incorporated herein by reference in their entirety.

[0036] Other parameters of interest may be focus and dose. As described in US Patent Application US2011-0249244, which is incorporated herein by reference in its entirety, focus and dose may be determined simultaneously by scatterometry (or alternatively by scanning electron microscopy). For each point in the focus-energy matrix (also referred to as FEM: focus-exposure matrix), a single structure may be used that has a unique combination of measurements of critical dimensions and sidewall angles. When these unique combinations of critical dimensions and sidewall angles are available, values ​​of focus and dose may be uniquely determined from these measurements.

[0037] The metrology target may be an ensemble of composite gratings formed primarily in the resist (possibly after etching processes, etc.) by a lithography process. The pitch and line width of the structures in the gratings for capturing the diffraction orders coming from the metrology target may strongly depend on the measurement optical elements (particularly the NA of the optical elements). As mentioned above, the diffracted signal may be used to determine the shift between the two layers (also referred to as "overlay") or to reconstruct at least a portion of the original grating generated by the lithography process. This reconstruction may be used to provide guidance on the quality of the lithography process and may be used to control at least a portion of the lithography process. The target may have smaller sub-segmentations configured to mimic the dimensions of the features of the design layout at the target. Due to this sub-segmentation, the behavior of the target is closer to the features of the design layout and the overall process parameter measurement is more similar to the features of the design layout. The target may be measured in underfill mode or overfill mode. In underfill mode, the measurement beam creates a spot that is smaller than the entire target. In overfill mode, the measurement beam creates a spot larger than the entire target, and in such overfill mode it is also possible to measure different targets simultaneously, allowing different process parameters to be determined simultaneously.

[0038] The overall measurement quality of a lithography parameter using a particular target is at least partially determined by the measurement recipe used to measure this lithography parameter. The term "substrate measurement recipe" may include one or more parameters of the measurement itself, one or more parameters of one or more measured patterns, or both. For example, if the measurement used in the substrate measurement recipe is a diffraction-based optical measurement, the one or more parameters of the measurement may include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation to the substrate, the direction of the radiation to the pattern on the substrate, etc. One criterion for selecting a measurement recipe may be, for example, the sensitivity of one measurement parameter to process variations. Many more examples are described in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US2016 / 0370717A1, which are incorporated herein by reference in their entirety.

[0039] The patterning process in the lithography tool LA may be one of the most critical steps, requiring high accuracy in the dimensioning and placement of structures on the substrate W. To ensure this high accuracy, three systems may be combined in a so-called "holistic" control environment, as shown diagrammatically in FIG. 3. One of these systems is the lithography tool LA, which is (virtually) connected to a metrology tool MT (second system) and a computer system CL (third system). The key to such a "holistic" environment is to optimize the interaction between these three systems in order to improve the overall process window and provide a tight control loop to ensure that the patterning performed by the lithography tool LA stays within the process window. The process window defines the range of process parameters (e.g. dose, focus, overlay) within which a particular manufacturing process will yield a defined result (e.g. a functional semiconductor device). For example, within the process window, variations in process parameters in the lithography process or patterning process are allowed.

[0040] The computer system CL may use (part of) the design layout to be patterned to predict which resolution enhancement technique should be used and may be used to perform computational lithography simulations and calculations to determine which mask layout and lithography apparatus settings achieve the largest overall process window of the patterning process (indicated in FIG. 3 by a double-headed arrow at a first scale SC1). The resolution enhancement techniques may be arranged to match the patterning possibilities of the lithography apparatus LA. The computer system CL may be used to detect (e.g. using input from the metrology tool MET) where in the process window the lithography apparatus LA is currently operating, for example to predict whether defects due to non-ideal processing may be present (indicated in FIG. 3 by an arrow pointing to "0" at a second scale SC2).

[0041] The metrology tool MT may provide input to the computer system CL to enable accurate simulations and predictions, and may provide feedback to the lithographic apparatus LA, for example to identify potential drift in the calibration status of the lithographic apparatus LA (indicated in Figure 3 by multiple arrows at the third scale SC3).

[0042] In lithographic processes, it is often desirable to make measurements of the structures being produced, for example for process control and verification. To make such measurements, various tools are known, including various forms of metrology devices such as scanning electron microscopes or scatterometers. Known examples of scatterometers often rely on the provision of dedicated metrology targets, such as underfilled targets (targets in the form of simple gratings or overlapping gratings in different layers, where the measurement beam is large enough to produce a spot smaller than the grating) or overfilled targets (illumination spot partially or completely covers the target). Furthermore, the use of metrology tools such as angle-resolved scatterometers to illuminate underfilled targets such as gratings allows the use of so-called reconstruction methods, where the properties of the grating may be calculated by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with those measurements. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from the real target.

[0043] Scatterometers are versatile devices that allow for the measurement of parameters of lithographic processes by having a sensor in or near the pupil plane or a plane conjugate to the pupil of the scatterometer objective (wherein the measurement is typically referred to as a pupil-based measurement) or in or near the image plane or a plane conjugate to the image plane (wherein the measurement is typically referred to as an image or field-based measurement). Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP 1,628,164A, which are incorporated herein by reference in their entireties. Such scatterometers may measure multiple targets from multiple gratings in one image using light from hard x-ray, soft x-ray, extreme ultraviolet, visible to near infrared and infrared wave ranges.

[0044] An example of a metrology apparatus such as a scatterometer is shown in Figure 4. It may comprise a broadband (e.g. white light) radiation projector 2 which 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. measuring the intensity I as a function of wavelength λ). From this data, the processing unit PU may reconstruct the structure or profile 8 underlying the detected spectrum, for example by rigorous coupled wave analysis and non-linear regression, or by comparison with a library of simulated spectra as shown at the bottom of Figure 4. Typically, for reconstruction, the general morphology of the structure is known and some parameters are estimated from knowledge of the process that fabricates the structure, leaving only a few parameters of the structure to be determined from the scatterometry data. Such a scatterometer may be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0045] As an alternative to optical metrology, the use of hard X-rays, soft X-rays or EUV radiation, such as radiation having wavelengths in at least one of the following ranges, e.g., <0.01 nm, <0.1 nm, <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, is also considered. An example of a metrology tool that operates in any of the wavelength ranges presented above is transmission small angle X-ray scattering (such as T-SAXS in US2007224518A, the contents of which are incorporated herein by reference in their entirety). Profile (CD) measurements using T-SAXS are discussed by Lemaillet et al. in "Intercomparison between optical and X-ray scatterometry measurements of FinFET structures" (Proc. of SPIE, 2013, 8681). The use of laser-produced plasma (LPP) X-ray sources is described in U.S. Patent Publication Nos. 2019 / 003988A1 and 2019 / 215940A1, which are incorporated by reference in their entirety. Reflectometry techniques using X-rays at grazing incidence (GI-XRS) and extreme ultraviolet (EUV) radiation may be used to measure properties of films and stacks of layers on a substrate. Within the general field of reflectometry, angular and / or spectroscopic metrology techniques may be applied. In angular metrology, the change in the reflected beam with different angles of incidence may be measured. On the other hand, spectroscopic reflectometry measures the spectrum of wavelengths reflected at a given angle (using broadband radiation). For example, EUV reflectometry has been used for inspection of mask blanks prior to the manufacture of reticles (patterning devices) for use in EUV lithography.

[0046] A transmission version of an example metrology apparatus such as the scatterometer shown in Figure 4 is shown in Figure 5. The transmitted radiation 11 is passed to a spectrometer detector 4 which measures the spectrum 6 as discussed in relation to Figure 4. Such a scatterometer may be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0047] Depending on the scope of the application, the use of wavelengths, for example, in the soft x-ray or EUV domains, may not be sufficient. An example of a metrology tool that works in any of the wavelength ranges presented above is transmission small angle x-ray scattering (such as T-SAXS in US2007224518A, the contents of which are incorporated herein by reference in their entirety). Profile (CD) measurements using T-SAXS are discussed by Lemaillet et al in "Intercomparison between optical and x-ray scatterometry measurements of FinFET structures" (Proc. of SPIE, 2013, 8681). Published patent applications US20130304424A1 and US2014019097A1 (Bakeman et al / KLA) describe a hybrid metrology technique in which measurements made using x-ray and optical measurements with wavelengths in the range of 120 nm and 2000 nm are combined together to obtain measurements of parameters such as CD. The CD measurements are obtained by coupling an X-ray mathematical model and an optical mathematical model through one or more common points. The contents of the cited U.S. patent applications are hereby incorporated by reference in their entirety.

[0048] Figure 6 is a schematic diagram of a metrology setup 302 in which radiation in the wavelength range from 0.01 nm to 100 nm may be used to measure parameters of structures on a substrate. The metrology setup 302 presented in Figure 6 is suitable for, for example, the hard x-ray, soft x-ray or EUV domain.

[0049] 6 illustrates a schematic physical layout of a metrology apparatus 302 comprising a spectroscopic scatterometer, optionally using hard X-ray (HXR) and / or soft X-ray (SXR) and / or EUV radiation at grazing incidence. Alternative forms of inspection apparatus may be provided in the form of an angle-resolved scatterometer, which may use radiation at normal or near-normal incidence similar to conventional scatterometers operating at longer wavelengths, or may use radiation having a direction more than 1 or 2 degrees from parallel to the substrate. Alternative forms of inspection apparatus may be provided in the form of a transmission scatterometer, in which the configuration in FIG. 5 is applied.

[0050] The inspection apparatus 302 includes a radiation or illumination source 310 , an illumination system 312 , a substrate support 316 , detection systems 318 , 398 and a metrology processing unit (MPU) 320 .

[0051] The illumination source 310 in this example is for the generation of EUV, hard X-ray or soft X-ray radiation. The illumination source 310 may be based on high harmonic generation (HHG) technology as shown in Fig. 6 or may be other types of illumination sources (e.g. liquid metal jet source, inverse Compton scattering (ICS) source, plasma channel source, magnetic undulator source, free electron laser (FEL) source, compact storage ring source, discharge produced plasma source, soft X-ray laser source, rotating anode source, solid anode source, particle accelerator source, microfocus source or laser produced plasma source).

[0052] The HHG source may be a gas jet / nozzle source, a capillary / fiber source or a gas cell source.

[0053] As an example of an HHG source, as shown in FIG. 6, the main components of the radiation source are a pump radiation source 330 capable of emitting pump radiation and a gas delivery system 332. Optionally, the pump radiation source 330 is a laser, and optionally the pump radiation source 330 is a pulsed high power infrared or optical laser. The pump radiation source 330 may be, for example, a fiber-based laser with an optical amplifier that generates pulses of infrared radiation, optionally with a pulse repetition rate up to several megahertz, and that may last less than 1 ns (one nanosecond) per pulse. The wavelength of the infrared radiation may be, for example, in the region of 1 μm (one micron). Optionally, the laser pulses are transmitted as first pump radiation 340 to a gas delivery system 332, where a portion of the radiation is converted in the gas to an emitted radiation 342 of a higher frequency than the first radiation. A gas supply 334 supplies the gas delivery system 332 with a suitable gas, which is optionally ionized by a power supply 336. The gas delivery system 332 may be a cut tube. The gas provided by the gas delivery system 332 defines a gas target, which may be a gas flow or a static volume. The gas may be, for example, a noble gas such as neon (Ne), helium (He), or argon (Ar). 2 , O 2 , Ar, Kr, and Xe gases may all be considered and may be selectable options within the same tool.

[0054] The emitted radiation may include multiple wavelengths. If the emitted radiation is monochromatic, the measurement calculations (e.g., reconstruction) may be simplified, but it is easier to generate radiation with several wavelengths. The radiation divergence angle of the emitted radiation may depend on the wavelength. Different wavelengths provide different levels of contrast, for example, when imaging structures of different materials. For inspection of metal or silicon structures, different wavelengths may be selected, for example, for imaging (carbon-based) features in a resist or to detect contamination of such different materials. One or more filtering devices 344 may be provided. For example, a filter, such as a thin film of aluminum (Al) or zirconium (Zr), may serve to block the radiation from substantially penetrating further into the inspection apparatus. A grating (not shown) may be provided to select one or more specific wavelengths from among the generated wavelengths. Considering that SXR and / or EUV radiation is absorbed when traveling through air, optionally, part or all of the beam path may be included in a vacuum environment. Various components of the radiation source 310 and illumination optics 312 may be adjustable to perform different measurement "recipes" within the same apparatus. For example, different wavelengths and / or polarizations may be selectable.

[0055] Depending on the material of the structure being inspected, different wavelengths may provide the desired level of penetration into lower layers. For resolving the smallest device features and defects in the smallest device features, shorter wavelengths are likely to be preferred. For example, one or more wavelengths in the range of 0.01-20 nm or optionally in the range of 1-10 nm or optionally in the range of 10-20 nm may be chosen. At wavelengths shorter than 5 nm, very small critical angles when reflected from materials of interest in semiconductor manufacturing may be problematic. Thus, choosing a wavelength greater than 5 nm may provide a stronger signal at larger angles of incidence. On the other hand, if the inspection task is to detect the presence of a particular material (e.g., contamination), wavelengths up to 50 nm may be useful.

[0056] From the radiation source 310, the filtered beam 342 enters the inspection chamber 350 where the substrate W containing the structure of interest is held in a measurement position by the substrate support 316 for inspection. The structure of interest is labeled T. Optionally, the atmosphere in the inspection chamber 350 may be maintained in a near vacuum state by a vacuum pump 352 so that the SXR and / or EUV radiation can pass through the atmosphere without being excessively attenuated. The illumination system 312 has the function of focusing the radiation into a focused beam 356, which may comprise, for example, a two-dimensional curved mirror or a series of one-dimensional curved mirrors, as described in the aforementioned published US patent application US2017 / 0184981A1, the contents of which are incorporated herein by reference in their entirety. The focusing is performed to achieve a circular or elliptical spot S of 10 μm or less in diameter when projected onto the structure of interest. The substrate support 316 comprises, for example, an XY translation stage and a rotation stage, by which any part of the substrate W may be positioned at the focus of the beam in a desired orientation. A radiation spot S is thus formed on the structure of interest. Alternatively or additionally, the substrate support 316 may comprise a tilting stage, which may tilt the substrate W at a particular angle, for example to control the angle of incidence of the focused beam on the structure of interest T.

[0057] Optionally, the illumination system 312 provides a reference beam of radiation to a reference detector 314, which may be configured to measure the spectrum and / or intensity of different wavelengths in the filtered beam 342. The reference detector 314 may be configured to generate a signal 315 that is provided to the processor 310 and the filter may comprise information regarding the spectrum of the filtered beam 342 and / or the intensity of different wavelengths in the filtered beam.

[0058] The reflected radiation 360 is captured by detector 318 and a spectrum is provided to processor 320 for use in computing properties of the target structure T. Thus, illumination system 312 and detection system 318 constitute an inspection apparatus that may include a hard x-ray, soft x-ray and / or EUV spectroreflectometer of the type described in US2016282282A1, the contents of which are incorporated herein by reference in their entirety.

[0059] If the target Ta has a certain periodicity, the radiation of the focused beam 356 may be partially diffracted. The diffracted radiation 397 follows other paths at a predefined angle relative to the angle of the incident and reflected radiation 360. In FIG. 6 the diffracted radiation 397 is depicted diagrammatically, the diffracted radiation 397 may follow many other paths different from the depicted path. The inspection apparatus 302 may further comprise a detection system 398 for detecting and / or imaging at least a part of the diffracted radiation 397. Although in FIG. 6 a single further detection system 398 is depicted, an embodiment of the inspection apparatus 302 may comprise multiple further detection systems 398 arranged at different positions to detect and / or image the diffracted radiation 397 in multiple diffraction directions. In other words, the (higher) diffraction orders of the focused radiation beam impinging on the target Ta are detected and / or imaged by the one or more further detection systems 398. The one or more detection systems 398 generate signals 399 that are provided to the metrology processor 320. The signal 399 may include information about the diffracted light 397 and / or an image obtained from the diffracted light 397 .

[0060] To assist in the alignment and focusing of the spot S on the desired product structure, the inspection apparatus 302 may provide auxiliary optical elements using auxiliary radiation under the control of a metrology processor 320. The metrology processor 320 may communicate with a position controller 372 that drives the translation stage, rotation and / or tilting stage. The processor 320 receives highly accurate feedback on the position and orientation of the substrate via sensors. The sensors 374 may include, for example, interferometers that may provide accuracy in the picometer range. In operation of the inspection apparatus 302, spectral data 382 captured by the detection system 318 is transmitted to the metrology processing unit 320.

[0061] As mentioned above, alternative forms of inspection apparatus use hard x-ray, soft x-ray and / or EUV radiation, optionally at normal or near normal incidence, for example, to perform diffraction-based asymmetry measurements. Other alternative forms of inspection apparatus use hard x-ray, soft x-ray and / or EUV radiation with a direction greater than 1 or 2 degrees from parallel to the substrate. Both types of inspection apparatus may be provided in a hybrid metrology system. Measured performance parameters may include overlay (OVL), critical dimension (CD), focus of the lithographic apparatus while it prints the target structure, coherent diffraction imaging (CDI) and resolution overlay (ARO) metrology. The hard x-ray, soft x-ray and / or EUV radiation may have a wavelength, for example, less than 100 nm, using radiation in the range of 5-30 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 particular wavelength bands, or may be more continuous in nature.

[0062] Like optical scatterometers used in today's manufacturing facilities, the inspection tool 302 may be used to measure structures in resist materials processed in a lithocell (post-develop inspection or ADI) and / or to measure structures after they have been formed in harder materials (post-etch inspection or AEI). For example, a substrate may be inspected using the inspection tool 302 after it has been processed by a developer, an etcher, an annealer, and / or other tools.

[0063] A metrology tool MT, including but not limited to the scatterometers mentioned above, may use radiation from a radiation source to perform measurements. The radiation used by the metrology tool MT may be electromagnetic radiation. The radiation may be optical radiation, such as radiation in the infrared, visible and / or ultraviolet parts of the electromagnetic spectrum. The metrology tool MT may use the radiation to measure or inspect properties and aspects of a substrate, such as a lithographic exposure pattern on a semiconductor substrate. The type and quality of the measurement may depend on some characteristics of the radiation used by the metrology tool MT. For example, the resolution of an electromagnetic measurement may depend on the wavelength of the radiation (e.g., due to the diffraction limit, the smaller the wavelength, the smaller the features that can be measured). To measure features with small dimensions, it may be preferable to use radiation with short wavelengths, such as EUV, hard x-ray (HXR) and / or soft x-ray (SXR) radiation. To perform a measurement at a particular wavelength or range of wavelengths, the metrology tool MT requires access to a source providing radiation at that wavelength. Different types of sources exist to provide different wavelengths of radiation. Depending on the wavelengths provided by the source, different types of radiation generation methods may 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 harmonic generation (HHG) or inverse Compton scattering (ICS) to obtain radiation at the desired wavelengths.

[0064] FIG. 7 is a simplified schematic diagram of an embodiment 600 of an illumination source 310, which may be an illumination source for high harmonic generation (HHG). One or more features of the illumination source in the metrology tool described with respect to FIG. 6 may be present in the illumination source 600, where appropriate. The illumination source 600 comprises a chamber 601 and is configured to receive pump radiation 611 having a propagation direction indicated by an arrow. The pump radiation 611 shown here is an example of pump radiation 340 from a pump radiation source 330 as shown in FIG. 6. The pump radiation 611 may be directed into the chamber 601 through a radiation input 605, which may optionally be a viewport formed by fused silica or a similar material. The pump radiation 611 may have a Gaussian or hollow (e.g., annular, transverse line) cross-sectional profile and may be incident on (and optionally collected by) a gas flow 615 within the chamber 601, which has a flow direction indicated by a second arrow. The gas flow 615 comprises a small volume (e.g., a few cubic millimeters) of a particular gas (e.g., a noble gas (optionally helium, argon or neon), nitrogen, oxygen or carbon dioxide) where the gas pressure is greater than a particular value. The gas flow 615 may be a steady flow. Other media such as a metal plasma (e.g., aluminum plasma) may be used.

[0065] The gas delivery system of the illumination source 600 is configured to provide a gas flow 615. The illumination source 600 is configured to provide pump radiation 611 into the gas flow 615 to facilitate the generation of the emitted radiation 613. The region where at least a majority of the emitted radiation 613 is generated is called the interaction region. The interaction region may vary from tens of micrometers (for tightly collected pump radiation) to several mm or cm (for moderately collected pump radiation) or may extend to several meters (for very loosely collected pump radiation). Optionally, the gas flow 615 is provided by the gas delivery system in the evacuated or nearly evacuated space. The gas delivery system may comprise a gas nozzle 609 with an opening 617 at the exit face of the gas nozzle 609 as shown in FIG. 6. The gas flow 615 is provided from the opening 617. In almost all prior art, the gas nozzle has a cut tube geometry with a uniform cylindrical interior geometry and the opening shape at the exit face is round. Extended apertures have also been used, as described in patent application CN101515105B.

[0066] The dimensions of the gas nozzle 609 may conceivably be used in scaled up or down versions ranging from a micrometer sized nozzle to a meter sized nozzle. This wide sizing range comes from the fact that the setup should be scaled to fit within a certain range where the intensity of the pump radiation at the gas flow may be beneficial for the emission radiation, which may be a pulsed laser (pulse energy may vary from tens of microjoules to joules), requiring different sizing for different pump radiation energies. Optionally, the gas nozzle 609 has thicker walls to reduce nozzle deformations caused by thermal expansion effects, which may be detected, for example, by a camera. A gas nozzle with thicker walls may generate a stable gas volume with reduced fluctuations. Optionally, the illumination source comprises a gas catcher close to the gas nozzle to maintain the pressure of the chamber 601.

[0067] Due to the interaction of the pump radiation 611 with gas atoms of the gas flow 615, the gas flow 615 converts a portion of the pump radiation 611 into emitted radiation 613, which may be one example of emitted radiation 342 shown in FIG. 6. The central axis of the emitted radiation 613 may be collinear with the central axis of the incident pump radiation 611. The emitted radiation 613 may have a wavelength in the X-ray or EUV range. The wavelength is in the range of 0.01 nm to 100 nm, optionally in the range of 0.1 nm to 100 nm, optionally in the range of 1 nm to 100 nm, optionally in the range of 1 nm to 50 nm, or optionally in the range of 10 nm to 20 nm.

[0068] In operation, the emitted radiation 613 beam may pass through the radiation output 607 and then be steered by an illumination system 603, which may be an example of the illumination system 312 in Figure 6, and directed towards a substrate being inspected for metrology measurements. The emitted radiation 613 may be guided (and optionally collected) towards a target on the substrate.

[0069] Since air (indeed, any gas) absorbs SXR or EUV radiation to a large extent, a volume between the gas flow 615 and the wafer being 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, it must be blocked to prevent the pump radiation 611 from passing through the radiation output 607 and entering the illumination system 603. This may be done by incorporating a filtering device 344, shown in FIG. 6, in the radiation output 607 that is located in the path of the emitted beam and is opaque or nearly opaque to the pump radiation (e.g., opaque or nearly opaque to infrared or visible light) but at least partially transparent to the beam of emitted radiation. The filter may be manufactured using zirconium or multiple materials combined in multiple layers. If the pump radiation 611 has a hollow (optionally annular, transverse line) cross-sectional profile, the filter may be a hollow (optionally annular) block. Optionally, the filter is non-perpendicular and non-parallel to the propagation direction of the beam of emitted radiation to provide efficient pump radiation filtering. Optionally, the filtering device 344 comprises a hollow block and a thin film filter such as aluminum (Al) or zirconium (Zr).

[0070] Described herein are methods, apparatus and assemblies for obtaining emitted radiation (optionally at a harmonic frequency) of pump radiation. The radiation generated during the process (optionally HHG using non-linear effects to generate radiation at a harmonic frequency of the provided pump radiation) may be provided as radiation in a metrology tool MT for inspection and / or measurement of a substrate. The substrate may be a lithographically patterned substrate. The radiation obtained during the process may be provided in a lithographic apparatus LA and / or a lithographic cell LC. The pump radiation may be pulsed radiation which may provide a high peak intensity over a short period of time.

[0071] The pump radiation 611 may comprise radiation having one or more wavelengths longer than the wavelength or wavelengths of the emitted radiation. The pump radiation may comprise infrared radiation. The pump radiation may comprise radiation having a wavelength in the range between 800 nm and 1500 nm. The pump radiation may comprise radiation having a wavelength in the range between 900 nm and 1300 nm. The pump radiation may comprise radiation having a wavelength in the range between 100 nm and 1300 nm. The pump radiation may be pulsed radiation. The pulsed pump radiation may comprise pulses having a duration in the femtosecond range.

[0072] For some embodiments, the emitted radiation (optionally, harmonic radiation) may comprise one or more harmonics of the pump radiation wavelength. The emitted radiation may comprise a wavelength in the extreme ultraviolet (EUV), soft x-ray (SXR), and / or hard x-ray (HXR) portions of the electromagnetic spectrum. The emitted radiation 613 may comprise a wavelength in the range between 0.01 nm and 100 nm. The emitted radiation 613 may comprise a wavelength in the range between 0.1 nm and 100 nm. The emitted radiation 613 may comprise a wavelength in the range between 0.1 nm and 50 nm. The emitted radiation 613 may comprise a wavelength in the range between 1 nm and 50 nm. The emitted radiation 613 may comprise a wavelength in the range between 10 nm and 20 nm.

[0073] Radiation, such as the harmonic radiation mentioned above, may be provided as source radiation in the metrology tool MT. The metrology tool MT may use the source radiation to perform measurements on a substrate exposed by the lithographic apparatus. The measurements may be for determining one or more parameters of a structure on the substrate. Using radiation at a shorter wavelength (e.g., EUV, SXR and / or HXR wavelengths, such as those configured in the wavelength ranges mentioned above) allows smaller features of the structure to be resolved by the metrology tool compared to using a longer wavelength (e.g., visible radiation, infrared radiation). Radiation with a shorter wavelength (e.g., EUV, SXR and / or HXR radiation) may penetrate deeper into a material, such as a patterned substrate. This means that measurements of deeper layers on the substrate become possible. These deeper layers may not be accessible by radiation with a longer wavelength.

[0074] In the metrology tool MT, source radiation may be emitted from a radiation source and directed onto a target structure (or other structure) on the substrate. The source radiation may comprise EUV, SXR and / or HXR radiation. The target structure may reflect, transmit and / or diffract the source radiation incident on the target structure. The metrology tool MT may comprise one or more sensors for detecting the diffracted radiation. For example, the metrology tool MT may comprise detectors for detecting the positive (+1 order) and negative (-1 order) first diffraction orders. The metrology tool MT may measure the specularly reflected or transmitted radiation (zeroth diffracted radiation). For example, further sensors for metrology may be present in the metrology tool MT to measure further diffraction orders (e.g. higher diffraction orders).

[0075] In general, the methods and apparatus disclosed herein mitigate target drift when measuring parameters of structures fabricated in or on a substrate. As previously mentioned, the term "target drift" describes damage or any change to a target due to material deposition and / or changes in resist (particularly resist shrinkage). Target in this context includes dedicated targets and any product structures (or, more generally, any exposed pattern in resist) that can be measured to determine a value of interest.

[0076] Post-develop inspection (ADI) comprises measurements performed after development and before subsequent semiconductor manufacturing steps (optionally before etching; i.e., on the exposed pattern in the resist). After illumination of a target (or other structure, such as a product structure) with electromagnetic radiation (e.g., SXR / EUV radiation), it has been observed that the intensity of the first-order diffracted radiation from the target is time-dependent (specifically, dependent on the illumination time). That is, the intensity of the diffracted radiation is a function of the amount of time the target is under illumination and dose accumulates. This may be due to contributions to the aforementioned target drift, e.g., from material deposition, such as carbon deposition, and / or resist shrinkage. This time-dependent intensity causes errors in the measured parameters, such as target overlay. If the measurements are performed on the product structure, in addition to causing measurement errors, they may also damage the actual product by directly introducing deformations and / or defects.

[0077] For DUV lithography processes, chemically amplified resist (CAR) may be used, and for EUV lithography processes, chemically amplified resist (CAR), metal oxide resist (MOR) or molecular chain scission may be used. For damage by soft x-rays (e.g., 10-20 nm) etc., if inspection is performed after development, the radiation may lead to shrinkage of features due to loss of small organic molecules. To prevent resist damage, in one embodiment, the dose is less than 10% of the EUV dose-to-clear / dose-to-gel of the resist and less than 1 mJ / cm2.2 The order will be:

[0078] HXR, SXR or EUV metrology tools perform scatterometry measurements using shorter wavelengths that can image and decorrelate features that are difficult to resolve at visible wavelengths. Such measurements may have ADI at-resolution overlay, where "at-resolution" means that the resolution of the measurement has a similar resolution to the product structures (i.e., the target and product structures have similar dimensions). A typical approach is to use the smallest possible measurement spot size (on the wafer), allowing the measurement of small targets. This is because using too large a spot leads to two problems. First, off-target energy can contaminate the measurement signal. Second, off-target energy can damage the resist or the device.

[0079] In addition to the spot size on the wafer, the spot size on the detector (e.g., a high order radiation detector) may be controlled, for example, so that spots of different wavelengths do not overlap so much that spectral resolution is significantly lost. These two spot size constraints are difficult to meet simultaneously because having a small spot on the detector requires having a small beam divergence, which in turn makes imaging of a small spot on the wafer difficult.

[0080] The advantage of using soft x-ray wavelengths is the ability to measure the ADI of devices where somewhat periodic structures such as DRAM or SRAM are available (although irregular logic areas with some underlying pitch may also be suitable). However, this leads to more severe issues of target drift or resist / device damage. It is not just the off-target light that is the problem, but all the light used for the measurement.

[0081] Instead of imaging with a small Gaussian spot (on the wafer) of a few μm to avoid damaging the resist, we used a 100 μm 2 , 200μm 2 , 500μm 2 , 1000μm 2 , 2500μm 2 , 5000μm 2 , 0.01mm 2 , 0.025mm 2 , 0.05mm 2 , 0.1mm 2 , 0.15mm 2 , 0.2mm 2 or 0.25 mm 2 It is proposed to uniformly illuminate the measurement area or larger. For example, the measurement spot may measure an area of ​​about 500x500 μm. For example, the measurement spot may have a diameter (also called spot size) of 10 μm or larger on the wafer.

[0082] The measurement area is determined so that the maximum dose received by the measurement area is less than 0.01 J / cm 2 , 5mJ / cm 2 , 1mJ / cm 2 , 0.5mJ / cm 2 , 0.1mJ / cm 2 , 0.05mJ / cm 2 or 0.01 mJ / cm 2 It may be provided so that:

[0083] However, although this seems simple to implement, it is not necessarily achieved by simply reducing the spot instead of enlarging it, by using poor quality mirrors or by placing the wafer out of focus. This is because the spot size on the detector must still be small enough to allow separation of the wavelengths on the detector. It is also desirable to illuminate the measurement area uniformly in order to keep it as small as possible for a given allowable dose.

[0084] Thus, embodiments may comprise measuring with radiation collected on a detector rather than on the wafer, or measuring on a rectangular area using a measurement spot that is elongated in one direction. Other embodiments use smaller or standard size measurement spots, but may be smaller than 100 μm, so that no measurement area receives enough photons to cause (severe) resist damage. 2 , 200μm 2 , 500μm 2 , 1000μm 2 , 2500μm 2 , 5000μm 2 , 0.01mm 2 , 0.025mm 2 , 0.05mm 2 , 0.1mm 2 , 0.15mm 2 , 0.2mm 2 or 0.25 mm 2 This spot is scanned over the above measurement area.

[0085] Thus, a method is described for performing a measurement of an exposure pattern in photoresist on a substrate, the method comprising applying a beam of measurement radiation onto the exposure pattern over a measurement area of ​​a size (e.g. according to any of the examples above) that prevents or reduces damage to the photoresist from the measurement radiation, capturing scattered radiation, which is the measurement radiation after it has been scattered from the exposure pattern, and determining a value for a parameter of interest from the scattered radiation.

[0086] In a first embodiment, it is proposed to perform measurements with radiation that is not focused on the wafer but on the detector. Thus, instead of placing the wafer on the focal point of the system, the system is adjusted so that the beam is not focused until it hits the detector. The measurement spot, thus defocused, is consequently larger on the wafer. With this approach, it becomes more difficult to focus all colors simultaneously. Typically, this may be done by using special gratings with variable line spacing (used in the SXR reference branch, etc.). This is not done on the measurement area (which may in particular comprise device structures rather than targets). It is also difficult to make such an arrangement adjustable. To measure small targets, the wafer may be switched into focus, but large stage movements are required. Finally, the measurement area is not illuminated uniformly. Rather, the illumination profile there is more like the SXR pupil (typically Gaussian).

[0087] To address at least some of these challenges, a second embodiment may comprise using a large measurement spot on the wafer that extends substantially only in a first direction (or is larger in at least a first direction), the first direction being orthogonal to a second direction that corresponds to the direction on the detector along which different wavelengths of scattered radiation are spatially separated.

[0088] Figure 8 illustrates one such embodiment. An extended measurement spot EMS is shown measuring the product structure PS. This takes advantage of the fact that it is important that the spot size is small on the detector only in the direction that overlaps with other wavelengths. Therefore, a larger spot is tolerated in other directions, both on the wafer and on the detector.

[0089] The downside of this embodiment is that it does not make the most of the available measurement area. A square area may be more attractive to measure than a rectangular area of ​​the same area. In addition, it does not easily switch between small and large spots and may still not be uniformly illuminated (in the second direction).

[0090] 9 illustrates a more flexible option using a small measurement spot MS (e.g. comparable to those currently used) but with a moving spot during exposure (e.g. scanning measurement along a structural spot path SP such that the spot path covers a measurement area having dimensions according to the examples described above). The spot path may follow a serpentine pattern, a straight path or a random movement (e.g. intentionally introducing a moving standard deviation error MSD by vibrating the stage). For example, the spot path may comprise one or more linear scans. The one or more scans may comprise multiple linear scans that together form a serpentine path over the measurement area.

[0091] A value for the parameter of interest may be obtained by averaging (e.g., taking the average) the detector signal over all measurements along the scan path SP. It is also possible to capture time resolved data to obtain even higher resolution, for example allowing high resolution imaging of the entire die. It should be understood that individual values ​​from a single measurement for the parameter of interest (i.e., at a single location on the scan path) will likely be highly inaccurate due to the paucity of photons per individual measurement, but the total amount of information collected will be sufficient.

[0092] FIG. 10 is a simplified schematic diagram of a metrology setup illustrating several proposals for obtaining a moving measurement spot. A drive laser DL, which may be an example of the pump radiation source 330 in FIG. 6, drives infrared drive radiation IR, which may be optionally directed by (at least one) beam steering element or source mirror SM to an HHG generation site HHG where an HHG medium (optionally a gas flow 615) is excited, as shown in FIG. 6, providing pump radiation 340 from the pump radiation source 330. The resulting broadband measurement beam MB, which may be emission radiation 342, is filtered to remove infrared radiation by an infrared filter IRF. The filtered beam is then steered and focused on a target TG on a wafer W by an illumination system or illuminator with (at least one) beam steering element represented by a focusing mirror FM. Scattered radiation in the form of higher diffraction orders (e.g., +1 / -1 diffraction orders (with multiple wavelengths, different shadings in the figure indicate different colors)) is captured on one or more high order detectors HOD. The specularly reflected radiation may be dispersed through a dispersive element such as a spectrometer grating SG, and the resulting spectrally resolved zero-order radiation may be captured on a zero-order detector ZOD. Note that this is a purely exemplary representation, and not all features are required (e.g., depending on the metrology method, the device may be configured to capture only higher diffraction orders). Also, the concept is equally applicable to transmissive arrangements where the beam steering and / or focusing elements are transmissive (e.g., for wavelengths longer than SXR).

[0093] Options for driving the movement of the measurement spot relative to the wafer include a movable focusing mirror FM in the measurement beam path (as illustrated by the arrow labeled A), a movable substrate table (as illustrated by the arrow labeled B) or a movable source mirror SM in the drive laser beam path (as illustrated by the arrow labeled C). Any combination of two or more of these options is also possible. In each of these embodiments, the target may be illuminated using a substantially random or controlled meandering movement to preserve high spatial resolution, as described above.

[0094] These first options may more specifically comprise using two focusing mirrors (or any suitable beam steering element in the illuminator) to move the measurement spot on the wafer without moving the detection spot on the corresponding detector. Note that this is different (although similar) to standard beam steering, where the pointing and positioning of the beam is controlled at a single location. In this embodiment, two degrees of freedom may be used to control the positioning of the beam at two locations. Such a moving beam means that the beam will not be incident on an ideal location on each mirror, which in turn may affect illuminator performance, but this is not a problem as the spot does not need to be ideally small for such a method.

[0095] The option of moving the substrate table relative to the measurement beam has the advantage that it can be easily implemented without changing the control of the beam and allows for a fixed illuminator.

[0096] By moving one or more mirrors in the drive beam path, it is possible to effectively move the source. The advantage here is that in at least some SXR designs there are typically at least two driveable mirrors, allowing beam steering relative to the source. Note that a combination of mirrors may also be used to move the spot on the wafer rather than on the detector (this is an extension of standard beam steering). The disadvantage of this option is that the source is highly optimized for a specific location in the HHG medium (e.g., HHG gas), so intentionally moving it outside that location may affect source performance (e.g., power).

[0097] In each of these configurations, the apparatus may allow for in-line spot size tuning (eg, allowing measurement of both small calibration targets in the scribe line and large areas on the device target using the same tool).

[0098] One embodiment is a method of measuring a property of a structure produced by a lithographic process, comprising illuminating a periodic structure (formed on the substrate by a lithographic process and having periodicity in at least a first direction) with a beam of radiation (having a spot size of 10 μm or more on the substrate) (having a plurality of wavelengths in the range of 1-100 nm) along an illumination direction (greater than 2 degrees from parallel to the substrate), detecting a spectrum of the radiation reflected by the periodic structure, and processing a signal representative of the detected spectrum to determine a property of the periodic structure.

[0099] Many of the embodiments described above may be combined. For example, an elongated spot may be used in a moving or scanning embodiment (e.g., via an illuminator optical element). In this way, scanning is limited to movement along only one axis, and the rectangular spot is smeared to effectively measure a square (or at least long in a second direction) target without smearing in the wavelength direction on the detector. This makes it easier to drive (e.g., no meandering is required), but makes it difficult to switch between large and small spot modes.

[0100] The above-described method may provide some or all of the following advantages (although embodiments using illuminator optics to scan the beam may provide all of these advantages): -Dose is reduced while still acquiring the total number of photons required for the measurement, enabling in-device measurements in HXR / SXR / EUV without resist / device damage. The measuring area can be illuminated almost uniformly, which allows its ideal use. No loss of spectral resolution (no increase in spot size on the detector). Easy to switch to small target mode for measuring on calibration targets etc. (e.g. by not moving the mirror during illumination). The wafer stage can be kept stationary during illumination. Applicable to all illumination wavelengths including soft X-ray tools, hard X-ray tools and EUV (e.g., 0.01-100nm) tools.

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

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

[0103] Further embodiments are disclosed in the following numbered paragraphs: 1. A method for performing measurements of an exposure pattern in photoresist on a substrate, comprising: applying a beam of measurement radiation onto the exposure pattern over a measurement area sized to prevent or reduce damage to the photoresist from the measurement radiation, the beam of measurement radiation forming a measurement spot on the substrate; capturing scattered radiation, the measured radiation after being scattered from the exposure pattern; detecting the scattered radiation on at least one detector; determining a value for a parameter of interest from the scattered radiation; A method for providing the above. 2. The method according to item 1. The total size of the measurement area in which a single value of the parameter of interest is determined is 1000 μm 2 That's all. 3. The total size of the measurement area, in which a single value of the parameter of interest is determined, is 2500 μm 2 The method according to item 1, wherein 4. The total size of the measurement area, in which a single value of the parameter of interest is determined, is 0.025 mm 2 The method according to item 1, wherein 5. The total size of the measurement area, in which a single value of the parameter of interest is determined, is 0.1 mm 2 The method according to item 1, wherein 6. The total size of the measurement area, in which a single value of the parameter of interest is determined, is 0.25 mm 2 The method according to item 1, wherein 7. The measurement area is determined so that the maximum dose received by the measurement area is less than 0.01 J / cm 2 7. The method according to any one of items 1 to 6, wherein 8. The measurement area is determined so that the maximum dose received by the measurement area is less than 1 mJ / cm 2 8. The method according to any one of items 1 to 7, wherein the method is so arranged that 9. The measurement area is determined so that the maximum dose received by the measurement area is less than 0.1 mJ / cm 2 9. The method according to any one of items 1 to 8, wherein 10. The method of any of items 1 to 9, wherein the measurement spot comprises an elongated measurement spot having a first dimension that is greater than a second dimension perpendicular thereto. 11. The method of claim 10, wherein the second dimension corresponds to a direction on the at least one detector along which different wavelengths of scattered radiation are spatially separated. 12. The method according to any of items 1 to 11, wherein the measurement beam is focused on at least one detector instead of the substrate. 13. A method according to any of the preceding claims, wherein the measurement spot formed on the substrate by the beam of measurement radiation comprises an area equal to and defining the measurement area. 14. The measurement spot formed on the substrate by the beam of measurement radiation is smaller than the measurement area and is driven over the measurement area during the applying and capturing steps. 13. The method according to any one of items 1 to 12. 15. The method according to item 14, wherein the movement of the beam over the measurement area is driven by driving one or both of the measurement beam and the substrate. 16. The method of claim 14 or 15, wherein moving over the measurement area comprises one or more scans over the measurement area. 17. The method of claim 16, wherein the one or more scans comprise one or more linear scans. 18. The method of claim 17, wherein the one or more scans comprise a plurality of linear scans that collectively form a serpentine path across the measurement area. 19. The method of claim 14 or 15, wherein moving the beam over the measurement area comprises moving the beam randomly or substantially randomly over the measurement area. 20. The method of any of items 14 to 19, wherein determining a value for the parameter of interest comprises determining an average of all measurements taken over the measurement area. 21. Capturing time resolved measurement data while driving the measurement beam over a measurement area; forming an image from the time-resolved measurement data; 21. The method according to any of items 14 to 20, comprising: 22. The measurement beam is a broadband beam generated via harmonic generation using the drive laser beam; Movement of the beam across the measurement area is driven by actuation of beam steering elements in the paths of one or both of the measurement beam and the drive laser beam. 22. The method according to any one of items 14 to 21. 23. A method according to any of items 14 to 22, wherein the movement of the beam is driven solely by driving a beam steering element in the path of the measurement beam. 24. The method according to any of items 14 to 22, wherein the movement of the beam is driven by driving a substrate table which holds the substrate relative to the measurement beam. 25. The method of any of items 1 to 24, wherein the measurement beam is a broadband beam generated via harmonic generation using the drive laser beam. 26. The method according to any of items 1 to 25, wherein the size of the measurement spot on the substrate is adjustable. 27. A method according to any of items 1 to 26, wherein the position of the scattered radiation on the at least one detector does not move during movement of the measurement spot across the measurement area. 28. The method according to any of items 1 to 27, wherein the exposure pattern comprises a pattern of a product structure. 29. The method according to any of items 1 to 28, wherein the parameter of interest is at least one of overlay, focus, edge placement error, critical dimension or any other dimension of the exposed pattern. 30. The method of any of items 1 to 29, wherein the measurement beam has a wavelength of 100 nm or less. 31. The method according to any of items 1 to 30, wherein the measurement beam has a wavelength of 10 nm or less. 32. A method according to any of items 1 to 31, wherein the different wavelengths of scattered radiation are at least partially spectrally resolved on at least one detector. 33. A metrology device for performing measurements of an exposure pattern in a photoresist on a substrate, comprising: an illumination system capable of applying a beam of measurement radiation onto the exposure pattern over a measurement area sized to prevent or reduce damage to the photoresist from the measurement radiation, the beam of measurement radiation being capable of forming a measurement spot on the substrate; at least one detector capable of detecting scattered radiation, the measurement radiation after being scattered from the exposure pattern; a processor capable of determining a value for a parameter of interest from the scattered radiation; A measuring device comprising: 34. The total size of the measurement area, in which a single value of the parameter of interest is determined, is 1000 μm 2 Item 34. The measuring device according to Item 33. 35. The total size of the measurement area, in which a single value of the parameter of interest is determined, is 2500 μm 2 Item 34. The measuring device according to Item 33. 36. The total size of the measurement area in which a single value of the parameter of interest is determined is 0.025 mm 2 Item 34. The measuring device according to Item 33. 37. The total size of the measurement area, in which a single value of the parameter of interest is determined, is 0.1 mm 2 Item 34. The measuring device according to Item 33. 38. The total size of the measurement area in which a single value of the parameter of interest is determined is 0.25 mm2 Item 34. The measuring device according to Item 33. 39. The measurement area is determined so that the maximum dose received by the measurement area is less than 0.01 J / cm 2 39. The measuring device according to any of items 33 to 38, wherein 40. The measurement area is determined so that the maximum dose received by the measurement area is less than 1 mJ / cm 2 39. The measuring device according to any of items 33 to 38, wherein 41. The measurement area is determined so that the maximum dose received by the measurement area is less than 0.1 mJ / cm 2 39. The measuring device according to any of items 33 to 38, wherein 42. A measurement device according to any of items 33 to 41, wherein the illumination system is capable of forming an elongated measurement spot of measurement radiation on the substrate, the first dimension of the measurement spot being greater than a second dimension perpendicular thereto. 43. The measurement device of item 42, wherein the second dimension corresponds to a direction on the at least one detector along which different wavelengths of scattered radiation are spatially separated. 44. A measurement device according to any of items 33 to 43, wherein the illumination system is adapted to focus the measurement beam onto at least one detector instead of the substrate. 45. A measurement device according to any of items 33 to 44, wherein the illumination system is capable of forming a measurement spot on the substrate with an area equal to and defining the measurement area. 46. ​​The illumination system is capable of forming a measurement spot on the substrate with an area smaller than the measurement area; Furthermore, the measurement device is capable of driving the measurement spot over the measurement area during measurement. 45. The measuring device according to any of items 33 to 44. 47. A measurement device according to item 46, configured such that movement of the beam over the measurement area can be driven by driving one or both of the measurement beam and a substrate table capable of holding the substrate. 48. A metrology device according to item 47, wherein movement of the beam is driven by driving the substrate table relative to the measurement beam. 49. A measuring device according to any of items 46 to 48, wherein the movement across the measurement area is configured to comprise one or more scans across the measurement area. 50. The measurement device of item 49, wherein the one or more scans are configured to comprise one or more linear scans. 51. The measurement device of item 50, wherein the one or more scans are configured to comprise a plurality of linear scans that collectively form a serpentine path across the measurement area. 52. A measurement device according to any of items 46 to 48, wherein moving the beam over the measurement area is configured to comprise performing a random or substantially random movement of the beam over the measurement area. 53. A measuring device according to any of items 46 to 52, wherein the processor is capable of determining a value for the parameter of interest from an average of all measurements taken over the measurement area. 54. Capturing time resolved measurement data while driving the measurement beam over a measurement area; forming an image from the time-resolved measurement data; 54. A measuring device according to any one of items 46 to 53, capable of carrying out the above-mentioned steps. 55. A harmonic generating medium; a drive laser beam delivery system for delivering the drive laser beam to the harmonic generating medium; Equipped with the measurement beam is a broadband beam generated via harmonic generation using the drive laser beam; the drive laser beam delivery system includes at least one beam steering element in a path of one or both of the measurement beam and the drive laser beam; Movement of the beam across the measurement area is driven by actuation of at least one beam steering element. 55. A measuring device according to any of items 46 to 54. 56. The illumination system includes at least one beam steering element in the path of the measurement beam; the movement of the beam is driven solely by driving the at least one beam steering element; 55. A measuring device according to any of items 46 to 54. 57. Harmonic generating medium; a drive laser beam delivery system for delivering the drive laser beam to the harmonic generating medium; Equipped with The measurement beam is a broadband beam generated via harmonic generation using the drive laser beam; 57. The measuring device according to any of items 33 to 54 or 56. 58. A measurement device according to any of items 33 to 57, configured to adjust the size of the measurement spot on the substrate. 59. A measuring device according to any of items 33 to 58, configured such that the position of the scattered radiation on the at least one detector does not move during movement of the measurement spot across the measurement area. 60. A measurement device according to any of items 33 to 59, wherein the parameter of interest is at least one of overlay, focus, edge placement error, critical dimension or any other dimension of the exposed pattern. 61. A measurement device according to any of items 33 to 60, wherein the measurement beam is configured to have a wavelength of 100 nm or less. 62. A measurement device according to any of items 33 to 61, wherein the measurement beam is configured to have a wavelength of 10 nm or less. 63. A measurement device according to any of items 33 to 62, configured such that different wavelengths of scattered radiation are at least partially spectrally resolved on at least one detector. 64. A computer program comprising program instructions which, when executed on a suitable device, are capable of carrying out the method according to any of items 1 to 32. 65. A non-transitory computer program carrier comprising a computer program according to item 64.

[0104] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, 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.

[0105] Although specific reference may be made in this text to embodiments in the context of a lithographic apparatus, the embodiments may be used in other apparatus. The embodiments may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be generally referred to as lithography tools. Such lithography tools may use vacuum or atmospheric (non-vacuum) conditions.

[0106] Although specific reference may have been made in the text to embodiments in the context of an inspection or metrology apparatus, the embodiments may be used in other apparatuses. The embodiments may form part of a mask inspection apparatus, a lithography apparatus or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). The term "metrology apparatus" (or "inspection apparatus") may refer to an inspection apparatus or inspection system (or metrology apparatus or metrology system). For example, an inspection apparatus comprising an embodiment may be used to detect defects in a substrate or in a structure on a substrate. In such an embodiment, the property of interest of the structure on the substrate may relate to defects in the structure, the absence of a particular portion of the structure or the presence of an undesired structure on the substrate.

[0107] Although specific reference may have been made above to the use of embodiments in the context of optical lithography, it will be understood that the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0108] Although the targets or target structures (or more generally structures on a substrate) described above have been metrology target structures specifically designed and formed for measurement purposes, in other embodiments the property of interest may be measured on one or more structures that are features of a device formed on a substrate. Many devices have a regular lattice-like structure. The terms "structure", "target grating" and "target structure" as used herein do not require that a structure is provided for the measurement to be performed. Furthermore, the pitch of the metrology target may be close to or smaller than the resolution limit of the optical system of the scatterometer, but is significantly larger than the dimensions of typical non-target structures (optionally product structures created by lithographic processes in target portion C). In practice, the lines and / or spaces of the overlay grating in the target structure may be made to include smaller structures of similar dimensions to the non-target structures.

[0109] Although specific embodiments have been described above, it will be understood that the invention may be practiced otherwise than as described. The above description is for illustrative purposes and is not intended to be limiting. Thus, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

[0110] Although specific reference may be made to a "metrology apparatus / tool / system" or an "inspection apparatus / tool / system," these terms may represent the same or similar types of tools, apparatus, or systems. For example, an inspection or metrology apparatus comprising an embodiment of the invention may be used to determine characteristics of structures on a substrate or on a wafer. For example, an inspection or metrology apparatus comprising an embodiment of the invention may be used to detect defects in the substrate or in the structures on the substrate or on the wafer. In such an embodiment, the characteristic of interest of the structures on the substrate may relate to defects in the structure, the absence of a particular portion of the structure, or the presence of an undesirable structure on the substrate or on the wafer.

[0111] Although specific reference has been made to HXR, SXR and EUV electromagnetic radiation, it will be understood that the invention may be practiced with all electromagnetic radiation, including radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays and gamma rays, where the context permits.

Claims

1. 1. A method of performing measurements of a pattern on a substrate, comprising the steps of: applying a beam of measurement radiation onto the pattern over a measurement area of ​​a size, the beam of measurement radiation forming a measurement spot on the substrate; capturing scattered radiation, the measurement radiation after being scattered from the pattern; detecting the scattered radiation on at least one detector; determining a value for a parameter of interest from the scattered radiation; and Equipped with the measurement spot formed on the substrate by the beam of measurement radiation is smaller than the measurement area and is driven over the measurement area during the applying and capturing steps. method.

2. The method of claim 1 , wherein movement of the beam is driven by driving a substrate table that holds the substrate relative to a measurement beam.

3. The method of claim 1 or 2, wherein moving over the measurement area comprises one or more scans over the measurement area.

4. The method of claim 1 , wherein determining a value for the parameter of interest comprises determining an average of all measurements taken over the measurement area.

5. acquiring time resolved measurement data while steering a measurement beam across the measurement area; forming an image from the time resolved measurement data; and The method according to any one of claims 1 to 4, comprising:

6. The method of claim 1 , wherein the measurement beam is a broadband beam generated via harmonic generation using the drive laser beam.

7. The method according to any of claims 1 to 6, wherein the position of the scattered radiation on the at least one detector does not move during a movement of the measurement spot across the measurement area.

8. The method of claim 1 , wherein the pattern comprises a pattern of a product structure.

9. The method of any of claims 1 to 8, wherein the parameter of interest is a critical dimension or any other dimension of the pattern.

10. The method according to any of the preceding claims, wherein the measurement beam has a wavelength of 100 nm or less.

11. A method according to any preceding claim, wherein the different wavelengths of the scattered radiation are at least partially spectrally resolved on the at least one detector.

12. The method according to any of the preceding claims, wherein the measurement area is arranged such that the maximum dose received by the measurement area is 0.01 J / cm2.

13. A computer program comprising program instructions which, when executed on a suitable device, are capable of carrying out the method according to any of the preceding claims.

14. A non-transitory computer program carrier comprising a computer program according to claim 13.

15. 1. A metrology device for performing measurements of a pattern on a substrate, comprising: an illumination system capable of applying a beam of measurement radiation onto the pattern over a measurement area of ​​a certain size, the beam of measurement radiation being capable of forming a measurement spot on the substrate; at least one detector capable of detecting scattered radiation, the measurement radiation after being scattered from the pattern; a processor operable to determine a value for a parameter of interest from the scattered radiation; Equipped with the illumination system is capable of forming the measurement spot on the substrate with an area smaller than the measurement area; Further, the measurement device is capable of driving the measurement spot across the measurement area during the measurement. Measuring devices.

16. movement of the beam over the measurement area is configured to be drivable by driving one or both of a measurement beam and a substrate table capable of holding the substrate; the movement of the beam is driven by driving the substrate table relative to the measurement beam.

16. The measuring device of claim 15.

17. 17. A measuring device according to claim 15 or 16, wherein the movement over the measurement area is configured to comprise one or more scans over the measurement area.

18. 18. A measuring device according to any of claims 15 to 17, wherein the processor is capable of determining the value for the parameter of interest from an average of all measurements taken over the measurement area.

19. A harmonic generating medium; a drive laser beam delivery system for delivering a drive laser beam to the harmonic generating medium; Equipped with The measurement beam is a broadband beam generated via harmonic generation using the drive laser beam; A measuring device according to any one of claims 15 to 18.

20. 20. A measurement device according to any of claims 15 to 19, configured such that during movement of the measurement spot across the measurement area the position of the scattered radiation on the at least one detector does not move.

21. A metrology device according to any of claims 15 to 20, wherein the parameter of interest is a critical dimension or any other dimension of the pattern.

22. 22. A measuring device according to any of claims 15 to 21, wherein the measuring beam is configured to have a wavelength of 100 nm or less.

23. 23. A measurement device according to any of claims 15 to 22, configured such that different wavelengths of the scattered radiation are at least partially spectrally resolved on the at least one detector.

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