Irradiation and testing equipment for measuring equipment

Abstract

An illumination and detection apparatus for a metrology tool and related methods are disclosed. The apparatus comprises an illumination device operable to produce a measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band. The detection device comprises a detection beam splitter to split the scattered radiation into a plurality of channels, each channel corresponding to a different one of the wavelength bands; and at least one detector for separately detecting each channel.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 19192284.8 filed on August 19, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The invention relates to an illumination device and an illumination and detection device and a composite prism thereof for a metrology tool for determining characteristics of a structure on a substrate. The invention also relates to a method for determining characteristics of a structure on a substrate. Background Art

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

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

[0006] Low k1 lithography can be used to process features with sizes smaller than the traditional resolution limit of the lithographic equipment. In this process, the resolution formula can be expressed as CD=k1×λ / NA, where λ is the radiation wavelength employed, NA is the numerical aperture of the projection optics in the lithographic equipment, CD is the "critical dimension" (usually the smallest feature size to be printed, but in this case it is half pitch), and k1 is an empirical resolution factor. In general, the smaller the k1, the more difficult it is to replicate a pattern on a substrate that is similar to the shape and size designed by the circuit designer in order to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithographic projection equipment and / or the design layout. These include, for example, but are not limited to, optimization of NA, customized illumination schemes, use of phase-shifted patterning devices, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also called "optical and process correction") in the design layout), or other methods generally defined as "resolution enhancement technology" (RET). Alternatively, a tight control loop for controlling the stability of the lithographic equipment can be used to improve the reproduction of the pattern at low k1.

[0007] In photolithography processes, it is frequently desirable to make measurements of the resulting structures, for example for process control and verification. Various tools for making such measurements are known, including scanning electron microscopes or various forms of metrology equipment, such as scatterometers. A general term referring to such tools may be metrology equipment or inspection equipment.

[0008] In order to improve the measurement robustness, the measurement equipment can use multiple wavelengths for measurement. Currently, these multiple wavelengths are usually measured sequentially. Summary of the invention

[0009] One objective is to reduce acquisition time and increase throughput when performing measurements using multiple wavelengths.

[0010] Embodiments of the invention are disclosed in the claims and the detailed description.

[0011] In a first aspect of the present invention, there is provided an illumination and detection apparatus for a measurement tool, comprising: an illumination device operable to produce a measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; and a detection device comprising: a detection beam splitter for splitting scattered radiation into a plurality of channels, each channel corresponding to a different wavelength band of the plurality of wavelength bands; and at least one detector for separately detecting each channel.

[0012] In a second aspect of the present invention, there is provided an illumination device for a measurement tool, the illumination device being operable to produce a measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; the illumination device comprising: an illumination beam splitter for splitting an input beam into a plurality of sub-beams, each sub-beam comprising a corresponding wavelength band in the discrete wavelength bands; a tuning device for individually tuning the spectrum of each sub-beam within its corresponding wavelength band; and a beam combiner for combining the sub-beams into a beam of the measurement illumination.

[0013] In a third aspect of the present invention, a composite prism device for outputting radiation in a plurality of different wavelength bands is provided, the composite prism device comprising two or more prism elements defining: an input surface for receiving broadband illumination; a plurality of output surfaces for outputting radiation in corresponding wavelength bands of each of the wavelength bands; and a separation surface in an optical path between the input surface and at least one of the output surfaces for separating an incident beam on the separation surface according to wavelength; wherein the separation surface comprises an edge pass filter coating.

[0014] In a fourth aspect of the present invention, a method is provided for performing measurement of a structure using measurement illumination, the measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; the method comprising: dividing a broadband radiation beam into a plurality of sub-beams, each sub-beam having a corresponding wavelength band; individually tuning each of the wavelength bands to form and position the peak within the corresponding wavelength band of the peak; combining the sub-beams into a beam of measurement radiation; measuring the structure using the measurement radiation; and capturing scattered radiation that has been scattered by the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0016] Figure 1 A schematic overview of a lithographic apparatus is depicted;

[0017] Figure 2 A schematic overview of a lithography unit is depicted;

[0018] Figure 3 Depicted is a schematic representation of overall lithography, showing the collaboration between three key technologies used to optimize semiconductor manufacturing;

[0019] Figure 4 is a schematic diagram of the scatterometry equipment;

[0020] Figure 5 is a schematic diagram of a measurement device including an irradiation and detection device according to a first embodiment of the present invention;

[0021] Figure 6 is a schematic diagram of a measurement device including an irradiation and detection device according to a second embodiment of the present invention;

[0022] Figure 7 It is available for Figure 5 or Figure 6 A schematic diagram of a first composite prism in a measurement device; and

[0023] Figure 8 It is available for Figure 5 or Figure 6 Schematic diagram of a second composite prism in a measurement device. DETAILED DESCRIPTION

[0024] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic 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).

[0025] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart to an incident radiation beam a patterned cross-section corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0026] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask stage) T configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to precisely position the patterning device MA according to certain parameters, a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to precisely position the substrate support according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0027] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, 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 so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0028] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, depending on the exposure radiation used, and / or on other factors such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0029] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system PS and the substrate W, which is also known as immersion lithography. More information on immersion technology is given in US6952253, which is incorporated herein by reference.

[0030] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps for preparing for subsequent exposure of the substrate W may be performed on a substrate W on one of the substrate supports WT while another substrate W on another substrate support WT is being used to expose a pattern on another substrate W.

[0031] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measuring table. The measuring table is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measuring table may hold a plurality of sensors. The cleaning means may be arranged to clean parts of the lithographic apparatus, e.g. a part of the projection system PS or a part of a system for providing immersion liquid. The measuring table may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0032] In operation, a radiation beam B is incident on a patterning device (e.g. a mask) MA held on a mask support T and is patterned by a pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through a projection system PS which focuses the radiation beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be precisely moved, for example in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, a first positioner PM and possibly a further position sensor ( Figure 1 The patterning device MA may be positioned relative to the path of the radiation beam B 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 be located in spaces between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe-lane alignment marks.

[0033] like Figure 2 As shown, the lithography apparatus LA may form part of a lithography cell LC, sometimes also referred to as a lithography cell or (lithography) cluster, which typically also comprises equipment for performing pre-exposure and post-exposure processing on a substrate W. Conventionally, these comprise a spin coater SC to deposit a resist layer, a developer DE to develop the exposed resist, a cooling plate CH and a baking plate BK, e.g. for regulating the temperature of the substrate W, e.g. for regulating the dissolution of the resist layer. A substrate handler or robot RO picks up substrates W from input / output ports I / O1, I / O2, moves substrates W between different processing equipment, and transfers substrates W to a loading bay LB of the lithography apparatus LA. The devices in the lithography cell, which are often also collectively referred to as tracks, are typically under the control of a track control unit TCU, which itself may be controlled by a monitoring system SCS, which may also control the lithography apparatus LA, e.g. via a lithography control unit LACU.

[0034] In order for substrates W exposed by lithographic apparatus LA to be correctly and consistently exposed, it is desirable to inspect the substrates to measure properties of the patterned structures, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), etc. For this purpose, inspection tools (not shown) may be included in lithography cell LC. If errors are detected, then, for example, adjustments may be made to the exposure of subsequent substrates or to other processing steps to be performed on substrate W, particularly if the inspection is performed before other substrates W of the same batch or lot are yet to be exposed or processed.

[0035] The inspection apparatus, which may also be referred to as a metrology apparatus, is used to determine properties of a substrate W, and in particular, how properties of different substrates W vary or how properties associated with different layers of the same substrate W vary from layer to layer. Alternatively, the inspection apparatus may be configured to identify defects on the substrate W, and may for example be part of a lithography cell LC, or may be integrated into a lithography apparatus LA, or may even be a stand-alone device. The inspection apparatus may measure properties on a latent image (the image in the resist layer after exposure), or a semi-latent image (the image in the resist layer after a post-exposure bake step PEB), or a developed resist image (wherein exposed or unexposed parts of the resist have been removed), or even an etched image (after a pattern transfer step such as etching).

[0036] Typically, the patterning process in the lithography apparatus LA is one of the most critical steps in the process, which requires high precision in the size and placement of structures on the substrate W. To ensure this high precision, three systems can be combined in a Figure 3 . One of these systems is a lithography apparatus LA which is (virtually) connected to a metrology tool MT (a second system) and a computer system CL (a third system). The key to this "holistic" environment is to optimize the cooperation between these three systems to enhance the overall process window and to provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines the range of process parameters (e.g. dose, focus, overlay accuracy) within which a particular manufacturing process produces a defined result (e.g. a functional semiconductor device) - typically within which variations in process parameters in the lithography process or patterning process are allowed.

[0037] The computer system CL can use (part of) the design layout to be patterned to predict which resolution enhancement techniques to use and perform computational lithography simulations and calculations to determine which mask layout and lithography equipment settings achieve the maximum overall process window for the patterning process (in Figure 3 Typically, the resolution enhancement technique is set to match the patterning possibilities of the lithographic apparatus LA. The computer system CL may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g. using input from the metrology tool MT) to predict whether a resolution enhancement technique is being employed due to, for example, suboptimal processing (e.g., Figure 3 There is a defect (depicted by the arrow pointing to "0" in the second scale SC2).

[0038] The metrology tool MT may provide input to the computer system CL to enable accurate simulation and prediction, and may provide feedback to the lithographic apparatus LA to identify possible drift (e.g., in the calibration state of the lithographic apparatus LA). Figure 3SC3 is depicted by multiple arrows in the third scale SC3).

[0039] In photolithography processes, it is frequently desirable to make measurements of the structures created, for example for process control and verification. Various tools for making such measurements are known, including scanning electron microscopes or various forms of metrology equipment, such as scatterometers. Examples of known scatterometers typically rely on providing a dedicated metrology target, such as an underfilled target (a target in the form of a simple grating or overlapping gratings in different layers that is large enough that the measurement beam generates a spot smaller than the grating) or an overfilled target (whereby the illumination spot partially or completely encompasses the target). Furthermore, the use of a metrology tool, such as an angle-resolved scatterometer illuminating an underfilled target such as a grating, allows the use of so-called reconstruction methods, in which the properties of the grating can be calculated by simulating the interaction of the scattered radiation with a mathematical model of the target structure, and comparing the simulation results with the measurement results. The parameters of the model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from a real target.

[0040] A scatterometer is a versatile instrument that allows measuring parameters of a lithography process by having a sensor in the pupil or a plane conjugate to the pupil of the scatterometer's objective, the measurement being generally referred to as pupil-based measurement, or by having a sensor in the image plane or a plane conjugate to the image plane, in which case the measurement is generally referred to as image-based or field-based measurement. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, which are incorporated herein by reference in their entirety. The above scatterometer can measure multiple targets from multiple gratings in one image using light from soft X-rays and visible to near infrared wavelength ranges.

[0041] Figure 4 A metrology device such as a scatterometer is depicted. It comprises a broadband (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 10 (i.e. a measure of the intensity I as a function of wavelength λ). From this data, the structure or profile 8 giving rise to the detected spectrum can be reconstructed by a processing unit PU (e.g. by rigorous coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra). Typically, for the reconstruction, the general form of the structure is known and some parameters are assumed from knowledge of the process by which the structure was manufactured, leaving only a few parameters of the structure to be determined from scatterometry data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0042] In many existing scatterometer devices, multiple wavelengths are used to improve the robustness of the measurement because some targets or structures may have wavelength-dependent errors when measured. Measurement of such targets using multiple wavelengths facilitates, for example, identification and selection of a preferred (e.g., most accurate) wavelength and / or quantification and error correction.

[0043] In many existing scatterometer arrangements, multiple wavelengths are measured sequentially on a detector. However, this has a negative impact on throughput (particularly when the switching time between wavelengths can be long). Therefore, a method is needed to measure a target at multiple wavelengths in parallel. Thus, a method and related apparatus are proposed, which include illuminating a target with measurement illumination including multiple different wavelengths, such that each of these wavelengths is used simultaneously in a single measurement capture.

[0044] Figure 5 is a schematic diagram of an apparatus suitable for this purpose. The source device SO provides a measurement of the irradiation I M . Measurement of irradiation I M A spectrum having a narrow peak (narrow wavelength band) at each of a plurality of different wavelengths (here three wavelengths λ1, λ2, λ3) within respective individual wavelength bands BD1, BD2, BD3, such that each band does not have more than one wavelength peak. The measurement illumination I M For measuring a target in a measurement device MET (which may include any suitable measurement device for measuring a target or structure using electromagnetic radiation). The scattered radiation from the target is split by a detection beam splitter or detection prism DP into a plurality of detection channels CH1, CH2, CH3, each channel corresponding to a respective wavelength peak λ1, λ2, λ3 and / or wavelength band BD1, BD2, BD3. Each detection channel comprises a respective detector DET CH1, DET CH2, DET CH3, such as a camera or a pixel array, each of the detectors detecting an image for its corresponding wavelength band BD1, BD2, BD3.

[0045] In this way, the illumination and detection device may separately detect radiation in each channel in parallel (eg, simultaneously), thereby detecting scattered illumination corresponding to each of the wavelength bands in parallel during measurement.

[0046] about Figure 5 The described concepts can be implemented in many ways. Figure 6 To generate the irradiation I M An exemplary specific device shows Figure 5Device. A broadband or white light laser WLL generates illumination I. The illumination I is fed to an illumination unit IU, which includes a first illumination beam splitter or a first illumination prism P1, which divides the spectrum of the illumination I between a plurality of sub-beams, each having a corresponding wavelength band (e.g., divided into a first wavelength band BD1, a second wavelength band BD2, and a third wavelength band BD3). Each wavelength band may have the same bandwidth, or one or more wavelength bands may have a bandwidth different from the other wavelength bands. For example, the bandwidths may each be in the range of 50-200 nm wide. A tunable filter TF is provided for each band. Each tunable filter TF may include, for example, an acousto-optic tunable filter (AOTF) dedicated to a specific bandwidth (e.g., and optimized for operation in a specific bandwidth). The tunable filter TF facilitates the tuning of the selection of a separate narrow wavelength band (e.g., with a width of 1-10 nm) within each band (e.g., with corresponding wavelength peaks λ1, λ2, λ3). Since there is a dedicated tunable filter TF to generate each narrowband, the sideband suppression is very high and a smoother well-controlled spectrum can be obtained. The filtered radiation (e.g., filtered sub-beams) is then recombined using a beam combiner or a second illumination prism P2 to form the measurement illumination I M The result is a measured irradiation I consisting of a spectrum with sharp peaks (with high sideband suppression) M The measurement irradiation I M is directed to a measurement device for target illumination.

[0047] Although AOTFs are preferred for tunable filters TF, due to their fast switching speed, any other wavelength selection device may be used to select individual wavelengths; for example, a filter wheel. Each tunable filter / AOTF may (optionally) be optimized in terms of its response to its corresponding wavelength band (e.g., crystal type, orientation, coating, etc.). Additionally, although Figure 5 and Figure 6 It is shown in each case how to generate a spectrum for three wavelengths, but this is only an example and it is obvious that the same method can be extended to any number of wavelengths and bands.

[0048] If the laser source WLL comprises a supercontinuum laser or the like (e.g., generating a supercontinuum), a single tunable filter TF or AOTF can be used to generate a spectrum comprising multiple peaks. A disadvantage of this approach is that the use of a single AOTF results in an increase in the energy of the sidebands around the main peak, which may cause process-dependent errors. Therefore, while this single filter approach is within the scope of the present disclosure, it may be preferred to provide filters dedicated to each wavelength band.

[0049] On the detection side, a detection beam splitter or detection prism DP is used to separate the scattered radiation from the target according to the wavelength bands BD1, BD2, BD3. At each output of the detection prism DP, a separate image detector DET CH1, DET CH2, DET CH3 is provided. Each image detector can (optionally) be optimized for its corresponding wavelength band. For example, wavelengths in a lower wavelength band (e.g., a range of 400-500 nm) can be detected using an image detector with a quantum efficiency QE optimized for lower wavelengths, and similarly, wavelengths in a higher wavelength band (e.g., a range of 700-900 nm) can be detected using an image detector with a quantum efficiency QE optimized for higher wavelengths. Alternatively or additionally, the detectors can be such that the pixel size differs between these detectors; for example, the detector pixel size can be optimized for each channel / band.

[0050] Each of the prisms P1, P2, DP may include a composite prism similar to a Phillips prism. Phillips prisms are used in broadcast cameras, where R, G, B (red-green-blue) channels are detected on separate cameras. However, for the applications proposed herein, such composite prisms may be modified. More specifically, instead of the bandpass coatings typically used on Phillips prisms, edge-pass coatings may be used on the separation surfaces of the composite prisms. Using edge-pass coatings, specific wavelengths may be reflected forward or transmitted into another channel. Edge-pass filters are available with edge transition regions less than 5 nm wide; for example, on the order of 1 nm wide. In addition, the optical path length of the channel may be optimized to compensate for the axial color response of the objective lens of the measurement device. Typically, such an objective lens cannot focus all wavelengths on the same focal length. Therefore, when multiple wavelengths are used to illuminate an object simultaneously, the resulting images are not focused simultaneously. To compensate, the channel length of each band may vary (e.g., a few millimeters) so that each wavelength band is in optimal focus.

[0051] Figure 7A schematic example of a composite prism is illustrated. This specific example shows a schematic diagram of a three-color beam splitter prism that splits an input beam I into a first beam B1 using a first wavelength band (e.g., band BD1), a second beam B2 using a second wavelength band (e.g., band BD2), and a third beam B3 using a third wavelength band (e.g., band BD3). Two triangular prism elements 710, 720 and one quadrangular prism element 730 are integrated into the assembly. There is an air gap 740 between the two triangular prism elements 710, 720. The quadrangular prism element 730 is optically integrated onto a surface of one of the triangular prisms 720 that is opposite to the air gap joint surface. A dichroic filter coating (more specifically, an edge pass coating) is provided on the surfaces of the two triangular prisms. The first beam B1 and the third beam B3 undergo total internal reflection once at the air gap 740 and the air / glass boundary, respectively, while the other reflections are dichroic. This composite prism can be used as Figure 6 Prisms P1, P2 and DP in a 3-wavelength embodiment of the device.

[0052] Figure 8 A schematic illustration of an example composite prism for providing five beams is shown: a first beam B1 in a first wavelength band, a second beam B2 in a second wavelength band, a third beam B3 in a third wavelength band, a fourth beam B4 in a fourth wavelength band, and a fifth beam B5 in a fifth wavelength band. As previously described, edge pass coatings are provided on appropriate faces of the prism elements of the prism. Such a composite prism can be used as Figure 6 Prisms P1, P2 and DP in the 5 wavelength embodiment of the arrangement. Other prism arrangements may be used to provide any number of different wavelength bands.

[0053] In use, the tunable filter TF can select a specific wavelength within each measurement band for each detection channel. For example, this approach provides great flexibility in the wavelength selection for dual wavelength measurements, so that even if only three bands / channels are provided, most combinations of two wavelengths can be accommodated (e.g., assuming they are in different channels). Providing more bands / channels enables more combinations. Moreover, in each measurement in such a "dual wavelength" measurement (where there are more than two channels / bands), simultaneous capture in other channels (e.g., at one or more additional wavelengths) will be obtained, which can also be used to make the measurement more robust.

[0054] If a particular (e.g., desired) wavelength happens to fall on the transition region between the two bands, it will be partially transmitted and reflected toward different image detectors. In this case, the images detected by the two sensors can be digitally aligned and added to reconstruct the original image corresponding to the desired wavelength. In another embodiment, a beam tilt mechanism can be included before the prism so that the beam enters the detection prism slightly tilted. This will cause the transition band to shift slightly. As an alternative to tilting the beam, the prism can be mounted on a tilting stage to produce the desired effect of shifting the transition band. Another approach may be to equip the prism with an adjustable bandpass filter (e.g., on a filter wheel) to change the edge position of the edge filter.

[0055] It should be understood that Figure 5 The source SO may be completely and in principle different from Figure 6 The examples provided in , and any means of providing radiation in parallel in multiple discrete wavelength bands may be used. For example, this may include combining the outputs of several single wavelength lasers; or using different beam splitting and / or filter means than described on a broadband source.

[0056] The above-mentioned irradiation and detection devices can be used in combination with any suitable measurement equipment that uses electromagnetic radiation to perform measurements, including inspection equipment and alignment equipment. In addition to the above-mentioned scatterometer type measurement device (and similar devices), this method can be used in a measurement method using a computational imaging / phase recovery method, which has been described in US Patent Publication US2019010778 (which is incorporated herein by reference). Such a measurement device can use a relatively simple sensor optics, which has non-exceptional or even relatively ordinary aberration performance. In this way, the sensor optics can be allowed to have aberrations, and thus produce relatively abnormal images. Of course, only allowing large aberrations in the sensor optics will have an unacceptable impact on image quality unless something is done to compensate for the effects of these optical aberrations. Therefore, computational imaging techniques are used to compensate for the negative impact of relaxation on aberration performance in the sensor optics. This computational imaging technique may include a phase recovery technique, in which the intensity and phase of the target are recovered from one or more intensity measurements of the target. Phase recovery can use a priori information of the measurement target (for example, included in the loss function that forms the starting point for obtaining / designing the phase recovery algorithm). Alternatively, or in combination with a priori information methods, different measurements may be made. In particular, one example of diversity includes measurements of a target at different wavelengths, for which the concepts herein may help to increase speed and throughput.

[0057] Another specific type of metrology sensor is recently described in European applications EP 18195488.4 and EP 19150245.9, which are incorporated herein by reference, and for which the concepts disclosed herein may be used. The metrology sensor has alignment and product / process monitoring metrology applications. The metrology device is configured to produce illumination with optimized coherence in that the illumination comprises a plurality of spatially incoherent beams of measurement illumination, each of the beams (or two beams of a measurement pair of the beams, each measurement pair corresponding to a measurement direction) having a corresponding region in its cross section for which the phase relationship between the beams at these regions is known; i.e. there is a mutual spatial coherence of the corresponding regions. In this way, the beams of each direction pair are spatially incoherent except for a corresponding small coherent region (e.g. corresponding to about the size of a pixel). This provides the advantages of spatially coherent illumination (no speckle) and spatially incoherent radiation (facilitating dark field off-axis imaging on small gratings).

[0058] Other metrology techniques to which the concepts disclosed herein are also applicable include one or more of: in-device metrology (IDM), reconstruction metrology (eg, based on angle-resolved measurements or otherwise), diffraction-based overlay (DBO) techniques, and alignment sensors.

[0059] Further embodiments are disclosed in the following numbered clauses:

[0060] 1. An irradiation and detection device for a measurement tool, comprising:

[0061] an illumination device operable to produce measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; and

[0062] The detection device comprises:

[0063] a detection beam splitter for splitting the scattered radiation into a plurality of channels, each channel corresponding to a different one of the plurality of wavelength bands; and

[0064] At least one detector is used to detect each channel separately.

[0065] 2. An illumination and detection device according to clause 1, comprising a separate detector for each channel.

[0066] 3. An illumination and detection apparatus according to clause 2, wherein each detector comprises an image sensor.

[0067] 4. An illumination and detection apparatus according to clause 2 or 3, wherein each detector is optimized for its respective wavelength band.

[0068] 5. An irradiation and detection apparatus according to any of the preceding clauses, wherein the irradiation means comprises:

[0069] an illumination beam splitter for splitting an input beam into a plurality of sub-beams, each sub-beam having a peak wavelength within a respective one of the discrete wavelength bands;

[0070] tuning means for individually tuning the spectrum of each beamlet within its respective wavelength band; and

[0071] A beam combiner is used to combine the sub-beams into the beam of measurement illumination.

[0072] 6. An illumination and detection apparatus according to clause 5, wherein the tuning means comprises a respective tunable filter for each beamlet, the respective tunable filter being operable to tune the spectral position of the peak wavelength within each respective wavelength band.

[0073] 7. An illumination and detection apparatus according to clause 6, wherein each tunable filter comprises an acousto-optic tunable filter.

[0074] 8. An illumination and detection apparatus according to clause 6, wherein each tunable filter comprises a filter wheel or a movable filter arrangement.

[0075] 9. An illumination and detection apparatus according to clause 6, 7 or 8, wherein each tunable filter is optimized for its respective wavelength band.

[0076] 10. An illumination and detection apparatus according to any of clauses 5 to 9, wherein the detection beam splitter, illumination beam splitter and beam combiner each comprise a compound prism device comprising two or more prismatic elements defining:

[0077] An input surface for receiving broadband illumination;

[0078] a plurality of output faces for outputting radiation in a respective wavelength band of each of said wavelength bands; and

[0079] a separation surface, in an optical path between the input surface and at least one of the output surfaces, for separating an incident beam on the separation surface according to wavelength;

[0080] Wherein the separation surface comprises an edge pass filter coating.

[0081] 11. An illumination and detection apparatus according to clause 10, wherein the composite prisms each comprise an adjustable filter arrangement to vary the position of a transition region between at least two of the wavelength bands.

[0082] 12. An illumination and detection apparatus according to any preceding clause, wherein each peak defines a narrow wavelength band within each wavelength band.

[0083] 13. An illumination and detection apparatus according to clause 12, wherein the width of the narrow wavelength band is less than 10 nm.

[0084] 14. An illumination and detection apparatus according to any of the preceding clauses, wherein the width of each wavelength band is between 50 nm and 200 nm.

[0085] 15. An illumination and detection apparatus according to any of the preceding clauses, wherein the number of discrete wavelength bands and the number of corresponding channels are each greater than two.

[0086] 16. An illumination and detection apparatus according to any of the preceding clauses, wherein the number of discrete wavelength bands and the number of corresponding channels are each greater than three.

[0087] 17. An illumination and detection apparatus according to any of the preceding clauses, wherein the detection means is such that the path length of each of the channels is individually optimised for best focus for each wavelength band.

[0088] 18. An illumination and detection device according to any of the preceding clauses, comprising a beam tilt mechanism for tilting the scattered radiation before it enters the detection beam splitter so as to change the position of the transition region between at least two of the wavelength bands.

[0089] 19. An illumination and detection apparatus according to any preceding clause, comprising a broadband radiation source for providing broadband radiation to the illumination means.

[0090] 20. An illumination and detection device according to any of the preceding clauses, wherein the transition band between the two channels is less than 5 nm.

[0091] 21. An illumination and detection device according to any preceding clause operable to separately detect radiation in each channel in parallel, thereby detecting said scattered radiation corresponding to each of said wavelength bands in parallel.

[0092] 22. A metrology tool comprising the illumination and detection apparatus of any of the preceding clauses.

[0093] 23. A measuring tool according to clause 22, comprising:

[0094] a substrate holder for holding a substrate, the substrate comprising a structure,

[0095] projection optics for projecting said measurement illumination onto the structure;

[0096] Detection optics for capturing scattered radiation resulting from said measurement illumination having been scattered by the structure.

[0097] 24. The metrology tool of clause 23, wherein the projection optics and the detection optics comprise at least some common optical elements.

[0098] 25. A metrology tool as described in 23 or 24 according to any of clauses 20 to 24, operable to perform measurements of the structure simultaneously in each of the wavelength bands.

[0099] 26. A metrology tool according to any of clauses 23 to 25, further comprising a processor operable to calculate a value of a parameter of interest related to the structure or its location based on one or more characteristics of the scattered radiation.

[0100] 27. A measurement tool according to any one of clauses 23 to 26, wherein, when the peak wavelength of at least one of the wavelength bands falls on a transition region between two wavelength bands, the measurement tool is operable to separately detect scattered radiation corresponding to the peak wavelength in two channels corresponding to each of the two wavelength bands; and the processor is operable to process the scattered radiation corresponding to the peak wavelength to create a single image for the peak wavelength.

[0101] 28. An illumination apparatus for a metrology tool, the illumination apparatus being operable to produce measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; the illumination apparatus comprising:

[0102] an illumination beam splitter for splitting an input beam into a plurality of sub-beams, each sub-beam having a peak wavelength within a respective one of the discrete wavelength bands;

[0103] tuning means for individually tuning the spectrum of each beamlet within its respective wavelength band; and

[0104] A beam combiner is used to combine the sub-beams into the beam of measurement illumination.

[0105] 29. An illumination apparatus according to clause 28, wherein the tuning means comprises a respective tunable filter for each beamlet, the respective tunable filter being operable to tune the spectral position of the peak wavelength within each respective wavelength band.

[0106] 30. The illumination apparatus of clause 29, wherein each tunable filter comprises an acousto-optic tunable filter.

[0107] 31. The illumination apparatus of clause 29, wherein each tunable filter comprises a filter wheel or a movable filter arrangement.

[0108] 32. An illumination apparatus according to clause 29, 30 or 31, wherein each tunable filter is optimized for its respective wavelength band.

[0109] 33. An illumination apparatus according to any of clauses 28 to 32, wherein the detection beam splitter, illumination beam splitter and beam combiner each comprise a compound prism device comprising two or more prismatic elements defining:

[0110] An input surface for receiving broadband illumination;

[0111] a plurality of output faces for outputting radiation in a respective wavelength band of each of said wavelength bands; and

[0112] a separation surface, in an optical path between the input surface and at least one of the output surfaces, for separating an incident beam on the separation surface according to wavelength;

[0113] Wherein the separation surface comprises an edge pass filter coating.

[0114] 34. An illumination device according to clause 33, wherein the composite prism comprises adjustable filter means to modify the position of a transition region between at least two of the wavelength bands.

[0115] 35. An illumination apparatus according to any of clauses 28 to 34, wherein each peak defines a narrow wavelength band within each wavelength band.

[0116] 36. An illumination device according to clause 35, wherein the width of the narrow wavelength band is less than 10 nm.

[0117] 37. An illumination apparatus according to any of clauses 28 to 36, wherein the width of each wavelength band is between 50 nm and 200 nm.

[0118] 38. An illumination apparatus according to any of clauses 28 to 37, wherein the number of discrete wavelength bands and the number of corresponding channels are each greater than two.

[0119] 39. An illumination apparatus according to any of clauses 28 to 37, wherein the number of discrete wavelength bands and the number of corresponding channels are each greater than three.

[0120] 40. A composite prismatic device for outputting radiation in a plurality of different wavelength bands, the composite prismatic device comprising two or more prismatic elements, the two or more prismatic elements defining:

[0121] An input surface for receiving broadband illumination;

[0122] a plurality of output faces for outputting radiation in a respective wavelength band of each of said wavelength bands; and

[0123] a separation surface, in an optical path between the input surface and at least one of the output surfaces, for separating an incident beam on the separation surface according to wavelength;

[0124] Wherein the separation surface comprises an edge pass filter coating.

[0125] 41. A method for performing measurements on a structure using measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; the method comprising:

[0126] splitting a broadband radiation beam into a plurality of sub-beams, each sub-beam having a corresponding wavelength band;

[0127] individually tuning each of the wavelength bands to form and position the peak within its corresponding wavelength band;

[0128] combining the sub-beams into a beam of measuring radiation;

[0129] Measuring structures using measurement radiation; and

[0130] Captures scattered radiation that has been scattered by the structure.

[0131] 42. The method according to clause 41, further comprising:

[0132] separating the captured scattered radiation into a plurality of channels, each channel corresponding to a different one of the wavelength bands; and

[0133] Each channel is detected individually on the corresponding detector.

[0134] 43. A method as described in clause 41 or 42, wherein each peak defines a narrow wavelength band within each wavelength band.

[0135] 44. A method according to clause 43, wherein the width of the narrow wavelength band is less than 10 nm.

[0136] 45. A method according to any of clauses 41 to 44, wherein the width of each wavelength band is between 50 nm and 200 nm.

[0137] 46. ​​A method according to any of clauses 41 to 45, wherein the number of discrete wavelength bands is each greater than two.

[0138] 47. A method according to any of clauses 41 to 45, wherein the number of discrete wavelength bands is each greater than three.

[0139] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0140] Although specific reference may be made herein to embodiments of the invention in the context of inspection or measurement equipment, embodiments of the invention may be used in other equipment. Embodiments of the invention may form part of a mask inspection equipment, a lithography equipment, or any equipment for measuring or processing an object such as a wafer (or other substrate) or a mask (or other pattern forming device). The term "measurement equipment" may also refer to an inspection equipment or an inspection system. That is, for example: an inspection equipment including an embodiment of the invention may be used to detect defects in a substrate or defects in a structure on a substrate. In such embodiments, the characteristic of interest of a structure on a substrate may relate to a defect in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate.

[0141] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0142] While the targets or target structures described above (more generally, structures on a substrate) are metrology target structures that are specifically designed and formed for measurement purposes, in other embodiments, the properties of interest may be measured on one or more structures that are functional components of a device formed on a substrate. Many devices have regular grating-like structures. The terms "structure," "target grating," and "target structure" as used herein do not require that the structure be provided specifically for the measurement being made. In addition, the pitch P of the metrology target may be close to the resolution limit of the optical system of the scatterometer, or may be smaller, but may be much larger than the size of a typical product feature made by a photolithographic process in the target portion C. In practice, the lines and / or spaces of the overlapping gratings within the target structure may be made to include smaller structures that are similar in size to the product features.

[0143] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be implemented in a manner other than that described. The above description is intended to be illustrative rather than limiting. Therefore, it will be apparent to those skilled in the art that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. An irradiation and detection device for a measurement tool, comprising: an illumination device comprising an illumination beam splitter for splitting an input beam into a plurality of sub-beams and operable to produce a measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; as well as The detection device comprises: a detection beam splitter for splitting the scattered radiation into a plurality of channels, each channel corresponding to a different one of the wavelength bands; as well as At least one detector is used to detect each channel separately.

2. An illumination and detection device according to claim 1, comprising a separate detector for each channel.

3. The illumination and detection apparatus of claim 2, wherein each detector comprises an image sensor.

4. An illumination and detection device according to claim 2 or 3, wherein each detector is optimized for its respective wavelength band.

5. The irradiation and detection device according to claim 1, wherein the irradiation device further comprises: Tuning means for individually tuning the spectrum of each beamlet within its respective wavelength band; as well as A beam combiner is used to combine the sub-beams into the beam of measurement illumination.

6. An illumination and detection apparatus according to claim 5, wherein the tuning means comprises a respective tunable filter for each beamlet, the tunable filter being operable to tune the spectral position of the peak wavelength within each respective wavelength band.

7. The illumination and detection apparatus of claim 6, wherein each tunable filter comprises an acousto-optic tunable filter or a movable filter arrangement.

8. The illumination and detection apparatus of claim 5, wherein the detection beam splitter, the illumination beam splitter, and the beam combiner each comprise a compound prism arrangement comprising two or more prismatic elements, the two or more prismatic elements defining: An input surface for receiving broadband illumination; a plurality of output faces for outputting radiation in a respective wavelength band of each of said wavelength bands; and a separation surface, in an optical path between the input surface and at least one of the output surfaces, the separation surface being used to separate an incident beam on the separation surface according to wavelength; Wherein the separation surface comprises an edge pass filter coating.

9. An illumination and detection device according to claim 8, wherein each prism of the composite prism arrangement comprises an adjustable filter arrangement to modify the position of a transition region between at least two of the wavelength bands.

10. The illumination and detection apparatus of claim 1, comprising a broadband radiation source for providing broadband radiation to the illumination means.

11. An illumination and detection device according to claim 1, operable to separately detect radiation in each channel in parallel, thereby detecting the scattered radiation corresponding to each of the wavelength bands in parallel.

12. The illumination and detection apparatus of claim 6, wherein each tunable filter comprises a filter wheel.

13. A metrology tool comprising the illumination and detection apparatus of any preceding claim.

14. An illumination device for a metrology tool and operable to produce measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; the illumination device comprising: an illumination beam splitter for splitting an input beam into a plurality of sub-beams, each sub-beam having a peak wavelength within a respective one of the discrete wavelength bands; Tuning means for individually tuning the spectrum of each beamlet within its respective wavelength band; as well as A beam combiner is used to combine the sub-beams into the beam of measurement illumination.

15. A method for performing measurements on a structure using measurement illumination, the measurement illumination comprising a plurality of discrete wavelength bands and comprising a spectrum having at most a single peak within each wavelength band; the method comprising: splitting a broadband radiation beam into a plurality of sub-beams, each sub-beam having a corresponding wavelength band; individually tuning each of the wavelength bands to form and position the peak within its corresponding wavelength band; combining the sub-beams into a beam of measuring radiation; measuring the structure using the measurement radiation; as well as Scattered radiation that has been scattered by the structure is captured.

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