Illumination module and associated method and measurement device

Abstract

An illumination module for a metrology device is disclosed. The illumination module comprises: a configurable illumination module operable to provide measurement illumination over a configurable range of illumination angles; the grating light valve module is used for controllably configuring spectral configuration of measurement illumination; and a controller operable to control the configurable illumination module and the raster light valve module such that a spectral configuration of the measurement illumination varies according to illumination angles within the illumination angle range in order to obtain desired detection conditions for detecting diffracted radiation from the diffraction structure resulting from measuring the diffraction structure using the measurement illumination.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22174619.1 filed on May 20, 2022 and EP application 22217043.3 filed on December 28, 2022, which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to methods and apparatus which can be used, for example, to manufacture a device by lithographic techniques and to methods of manufacturing a device using lithographic techniques. The present invention more particularly relates to a metrology sensor and a lithographic apparatus having such a metrology sensor and more particularly also to an illumination arrangement for such a metrology sensor. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (usually applied to a target portion of a substrate). A lithographic apparatus can be used, for example, in the manufacture of an integrated circuit (IC). In this example, a pattern forming device (alternatively referred to as a mask or reticle) can be used to generate a circuit pattern to be formed on each layer of the IC. The pattern can be transferred to a target portion (e.g., including a portion of a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually via imaging onto a radiation-sensitive material (resist) layer provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are continuously patterned. These target portions are generally referred to as "fields."

[0005] In the manufacture of complex devices, typically many lithographic patterning steps are performed to form functional features in successive layers on a substrate. Therefore, a key aspect of the performance of a lithographic apparatus is the ability to correctly and accurately place the applied pattern with respect to features laid down in a previous layer (either by the same apparatus or by a different lithographic apparatus). For this purpose, the substrate is provided with one or more sets of alignment marks. Each mark is a structure whose position can be measured at a later time using a position sensor, typically an optical position sensor. The lithographic apparatus comprises one or more alignment sensors by which the position of the marks on the substrate can be accurately measured. Different types of marks and different types of alignment sensors are known from different manufacturers and from different products of the same manufacturer.

[0006] In other applications, metrology sensors are used to measure exposed structures on the substrate (in the resist and / or after etching). A fast and non-invasive form of specialized inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the substrate surface and the properties of the scattered or reflected beam are measured. Examples of known scatterometers include angle-resolved scatterometers of the type described in US2006033921A1 and US2010201963A1. In addition to measuring feature shapes by reconstruction, diffraction-based overlay can also be measured using such a device, as described in published patent application US2006066855A1. Diffraction-based overlay metrology using dark field imaging of diffraction orders can enable overlay measurements on smaller targets. Examples of dark field imaging metrology can be found in international patent applications WO 2009 / 078708 and WO 2009 / 106279, which are incorporated herein by reference in their entirety. Further developments of this technology have been described in published patent publications US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A and WO2013178422A1. These targets can be smaller than the irradiation spot and can be surrounded by product structures on the wafer. Multiple gratings can be measured in one image using a composite grating target. The contents of all these applications are also incorporated herein by reference.

[0007] In some metrology applications, such as in some scatterometers or alignment sensors, imperfections in the measurement target may result in wavelength / polarization-dependent variations in the measurements from the target. Thus, correction and / or mitigation of such variations is sometimes achieved by performing the same measurement using multiple different wavelengths and / or polarizations (or more generally, multiple different illumination conditions). However, different wavelengths may diffract to different angles, complicating the detection of the diffracted radiation carrying the desired signal.

[0008] It is desirable to improve the detection of diffracted radiation of different wavelengths. Summary of the invention

[0009] In a first aspect, the present invention provides an illumination module for a measurement device, comprising: a configurable illumination module, operable to provide measurement illumination over a configurable illumination angle range; a grating light valve module, for controllably configuring a spectral configuration of the measurement illumination; and a controller, operable to control the configurable illumination module and the grating light valve module so that the spectral configuration of the measurement illumination changes according to the illumination angle within the illumination angle range, so as to obtain desired detection conditions for detecting diffraction radiation from a diffraction structure generated by measuring the diffraction structure using the measurement illumination.

[0010] In a second aspect, the present invention provides an illumination module for a measurement device, comprising: a beam steering device for scanning the beam of the measurement illumination over the illumination angle range during measurement to provide measurement illumination over a configurable illumination angle range; a color selection module for controllably configuring the spectral configuration of the measurement illumination; and a controller operable to control the beam steering device and the color selection module so that the spectral configuration of the measurement illumination varies according to the illumination angle within the illumination angle range so as to obtain desired detection conditions for detecting diffracted radiation from a diffraction structure generated by measuring the diffraction structure using the measurement illumination.

[0011] The present invention provides in a third aspect a method for measuring a diffraction structure using measurement illumination that selectively includes a plurality of desired wavelengths, the method comprising: scanning the beam of the measurement illumination over an illumination angle range to illuminate the diffraction structure, the illumination angle range corresponding to a fully filled detection numerical aperture for each of a plurality of desired wavelengths to illuminate the diffraction structure; and during the scanning, for each illumination angle within the illumination angle range, selecting all wavelengths of the plurality of desired wavelengths at which desired diffraction order radiation diffracted by the diffraction structure will be captured within the detection numerical aperture.

[0012] In a fourth aspect, the present invention provides a method for measuring a diffraction structure using measurement illumination, the method comprising: scanning the beam of the measurement illumination over an illumination angle range to illuminate the diffraction structure; and during the scanning, for each illumination angle within the illumination angle range, selecting only the combination of the spectral configuration of the measurement beam and the illumination angle of the measurement beam that is associated with the corresponding sensitivity value of the parameter of interest having the same sign.

[0013] Also disclosed is a measuring device comprising a measuring device, wherein the measuring device comprises the irradiation module of the first aspect or the second aspect.

[0014] The above and other aspects of the invention will be understood by considering the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0016] Figure 1 The photolithographic 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 to optimize semiconductor manufacturing;

[0019] Figure 4 depicts a schematic overview of a scatterometry apparatus used as a metrology device, which may include a dark-field digital holographic microscope according to an embodiment of the present invention;

[0020] Figure 5 Included are (a) a schematic diagram of a dark field scatterometer for measuring a target using a first pair of illumination apertures, (b) details of the diffraction spectrum of the target grating in a given illumination direction;

[0021] Figure 6 is a schematic illustration of a grating light valve illustrating its basic operation in (a) a top view, (b) an end view in a first configuration, and (c) an end view in a second configuration;

[0022] Figure 7 is a schematic illustration of the operating principles of a source selection module that may be used for the concepts disclosed herein, showing (a) an input spectrum, (b) a top view of radiation incident on a grating light valve, (c) an end view of radiation incident on a grating light valve, and (d) a resultant output spectrum;

[0023] Figure 8 is a schematic illustration of the operating principle of a programmable illumination module that scans a beam over a programmable angular range and thereby scans the beam within a programmable area of ​​an illumination pupil plane, thereby defining a programmable illumination profile;

[0024] Fig. 9 is a pupil plane representation of the objective of a metrology tool illustrating the problem of diffracted radiation being diffracted at an angle that depends on the wavelength;

[0025] Fig.10 (a) Fig.10 (b) and Fig.10 (c) each shows an illumination module scanning a beam at respective different angles according to an embodiment, wherein a color selection module selects an appropriate wavelength depending on the scanning angle;

[0026] Fig.11 is a pupil plane representation of the objective lens of the measuring tool, illustrating the Fig.10 (a), 10(b) and 10(c) are the result of the operating principles described, wherein diffracted radiation of different wavelengths are all diffracted to the same angle;

[0027] Fig.12 is a pupil plane representation of an objective of a metrology tool, illustrating an additional embodiment wherein the color selection module is a programmable illumination module controlled during scanning so as to prevent detection of diffraction orders higher than a desired (e.g., first) diffraction order;

[0028] Fig.13(a) shows a number of pupil plane sensitivity graphs corresponding to different wavelengths, illustrating the problem of overlay sensitivity variation with very high illumination angles, resulting in very low average sensitivity of the image captured at the field plane focused at said angle;

[0029] Fig.13 (b) shows a plurality of pupil plane sensitivity graphs and color selection module control graphs according to an embodiment, conceptually illustrating the solution Fig.13 (b) the approach to the problem described;

[0030] Fig.14 (a) Schematic illustration of conventional micro-diffraction-based overlay (μDBO) measurement of a target, Fig.14 (b) schematically illustrates micro-diffraction based overlay (μDBO) measurement according to an embodiment, and Fig.14 (c) schematically illustrates micro-diffraction based overlay (μDBO) measurement of a target according to another embodiment; and

[0031] Fig.15 is a block diagram illustrating a computer system that can assist in implementing the methods and processes disclosed herein. DETAILED DESCRIPTION

[0032] Before describing embodiments of the present invention in detail, it is helpful to present an example environment in which embodiments of the present invention may be implemented.

[0033] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 365nm, 248nm, 193nm, 157nm or 126nm) and EUV (extreme ultraviolet radiation, e.g., wavelengths in the range of about 5nm to 100nm).

[0034] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. In this context, the term "light valve" may also be used. 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.

[0035] Figure 1A 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 table) MT constructed to support a pattern forming device (e.g. a mask) MA and connected to a first positioner PM (configured to accurately position the pattern forming device MA according to certain parameters), a substrate support (e.g. a wafer stage) WT constructed to hold a substrate (e.g. a resist coated wafer) W and connected to a second positioner PW (configured to accurately position the substrate support according to certain parameters), and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the pattern forming device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0036] In operation, the illumination system IL receives a radiation beam from a radiation source SO (e.g., 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 as to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0037] 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, as appropriate with respect to the exposure radiation used and / or 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.

[0038] 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, 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.

[0039] 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 a substrate W for subsequent exposure may be performed on a substrate W located on one of the substrate supports WT, while another substrate W on another substrate support WT is used to expose a pattern on another substrate W.

[0040] 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 equipment. 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 equipment may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of a system for providing immersion liquid. The measuring table may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0041] In operation, a radiation beam B is incident on a patterning device (e.g. a mask) MA and is patterned by a pattern (design layout) present on the patterning device MA, which is held on a mask support MT. After passing through 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. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, the first positioner PM and possibly another position sensor (not shown) are also provided. Figure 1 The pattern forming device MA (depicted explicitly in FIG. 1 ) can be used to accurately position the pattern forming device MA relative to the path of the radiation beam B. The pattern forming device MA and the substrate W can be aligned using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, they can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, these are called scribe alignment marks.

[0042] like Figure 2 As shown, the lithography apparatus LA may form part of a lithography cell LC, which is sometimes also referred to as a lithography cell or (lithography) cluster, which typically also includes apparatus for performing pre- and post-exposure processes on a substrate W. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH and a bake plate BK, for example, for regulating the temperature of the substrate W (e.g. for regulating 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 process apparatuses, and delivers the substrates W to a feed station LB of the lithography apparatus LA. The equipment in the lithography cell (often also collectively referred to as a track) is typically controlled by a track control unit TCU, which itself may be controlled by a supervisory control system SCS, which may also control the lithography apparatus LA, for example via a lithography control unit LACU.

[0043] In order for substrates W exposed by the lithography 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, an inspection tool (not shown) may be included in the lithography cell LC. If errors are detected, for example, adjustments may be made to the exposure of subsequent substrates or other processing steps to be performed on the substrate W, particularly if the inspection is done before other substrates W of the same batch or lot are still to be exposed or processed.

[0044] The inspection apparatus (which may also be referred to as a metrology apparatus) is used to determine properties of the substrate W, in particular how properties vary from one substrate to another W, or how properties associated with different layers of the same substrate W vary from layer to layer. The inspection apparatus may alternatively be configured to identify defects on the substrate W, and may for example be part of the lithography cell LC, or may be integrated into the lithography apparatus LA, or may even be a stand-alone device. The 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 (where exposed or unexposed parts of the resist have been removed), or even on an etched image (after a pattern transfer step such as etching).

[0045] Typically, the patterning process in the lithography apparatus LA is one of the most critical steps in the process, which requires high accuracy in dimensioning and placement of structures on the substrate W. To ensure this high accuracy, the three systems can be combined into a so-called "holistic" control environment, such as Figure 3 Schematically depicted in . One of these systems is the lithography apparatus LA, which is (in practice) 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 stays within the process window. The process window defines the range of process parameters (e.g. dose, focus, overlay) within which a specific manufacturing process will produce a defined result (e.g. a functional semiconductor device), and typically within which process parameters in a lithography process or patterning process are allowed to vary.

[0046] The computer system CL can use (a portion 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 layouts and lithography apparatus settings achieve the maximum overall process window (in Figure 3Typically, the resolution enhancement technique is arranged to match the patterning possibilities of the lithographic apparatus LA. The computer system CL may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g. using input from a metrology tool MT) to predict whether defects may be present (e.g. due to suboptimal processing). Figure 3 ), depicted by an arrow pointing to “0” in the second scale SC2.

[0047] 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 to identify possible drift, for example in the calibration condition of the lithographic apparatus LA (in Figure 3 SC3).

[0048] In a lithographic process, it is desirable to frequently measure the structures created, for example for process control and verification. The tool that performs such measurements is typically referred to as a metrology tool MT. Different types of metrology tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools MT. A scatterometer is a versatile instrument that allows measurement of parameters of a lithographic process by placing a sensor in the pupil of a scatterometer objective or in a plane conjugate to the pupil - these measurements are often referred to as pupil-based measurements, or by placing the sensor in an image plane or in a plane conjugate to the image plane - in this case, these measurements are often referred to as image-based 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. The scatterometer described above can measure the grating using light from soft x-rays and visible to the near IR wavelength range.

[0049] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, reconstruction methods may be applied to the measured signals to reconstruct or calculate the properties of the grating. For example, such a reconstruction may be caused by simulating the interaction of the scattered radiation with a mathematical model of the target structure and comparing the simulation results with the measurement results. The parameters of the mathematical model are adjusted until the simulated interaction produces a diffraction pattern similar to that observed from an actual target.

[0050] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectral scatterometer MT, radiation emitted by a radiation source is directed onto a target and reflected or scattered radiation from the target is directed to a spectrometer detector which measures the spectrum (i.e., intensity measurements as a function of wavelength) of the specularly reflected radiation. From this data, the structure or profile of the target that produced the detected spectrum can be reconstructed, for example by rigorous coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra.

[0051] In a third embodiment, the scatterometer MT is an ellipsometer. An ellipsometer allows the parameters of a lithography process to be determined by measuring the scattered radiation for each polarization state. Such a measurement device emits polarized light (such as linear, circular or elliptical) by using, for example, appropriate polarization filters in the illumination section of the measurement device. A source suitable for the measurement device may also provide polarized radiation. Various embodiments of existing ellipsometers 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.

[0052] Figure 4 A metrology device such as a scatterometer is depicted in FIG. It comprises a broadband (white light) radiation projector 2 which projects radiation onto a substrate W (optionally having been spectrally filtered to a narrow band before the substrate W). The reflected or scattered radiation is passed to a spectrometer detector 4 which measures the spectrum 6 (i.e. a measure of intensity as a function of wavelength) of the specularly reflected radiation. From this data, for example by rigorous coupled wave analysis and nonlinear regression or by comparing Figure 4 The structure or profile 8 that produces the detected spectrum can be reconstructed by the processing unit PU by comparing it with the simulated spectrum library shown at the bottom. Typically, for the reconstruction, the general form of the structure is known and some parameters are assumed by knowledge of the process by which the structure was manufactured, with only a few parameters of the structure to be determined by scatterometry data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0053] The overall measurement quality of the lithographic parameters measured via the measurement target is at least partially determined by the measurement scheme used to measure the lithographic parameters. The term "substrate measurement scheme" may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement scheme is an optical measurement based on diffraction, the one or more parameters measured may include (multiple) wavelengths of radiation (e.g., a single wavelength or (optionally weighted) wavelength groups), polarization of radiation, radiation incident angle relative to the substrate, radiation orientation relative to the pattern on the substrate, etc. One of the criteria for selecting the measurement scheme may be, for example, the sensitivity of one of the measurement parameters to process variations. More examples are described in U.S. Patent Application US2016-0161863 and published U.S. Patent Application US2016 / 0370717A1, which are incorporated herein by reference in their entirety. It can be appreciated that measurement schemes (e.g., different schemes for X targets and Y targets) may be configured or determined separately for specific targets or target categories.

[0054] Another type of measuring device is Figure 5 (a). The target T and the diffracted rays of the measurement radiation used to illuminate the target are Figure 5(b) is illustrated in more detail. The illustrated measurement device is a type known as a dark field measurement device. The measurement device depicted herein is exemplary only to provide an explanation of dark field measurement. The measurement device can be a stand-alone device or incorporated into the lithography device LA, for example at a measurement station, or incorporated into the lithography unit LC. The optical axis having several branches throughout the device is represented by a dotted line O. In the device, light emitted by a source 11 (e.g. a xenon lamp) is guided to the substrate W via a beam splitter 15 by an optical system comprising lenses 12, 14 and an objective lens 16. These lenses are arranged in a double sequence of a 4F arrangement. Different lens arrangements can be used, provided that it still provides a substrate image to the detector while allowing access to the intermediate pupil plane for spatial frequency filtering. Therefore, the angular range in which the radiation is incident on the substrate can be selected by defining the spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane (here referred to as the (conjugate) pupil plane). In particular, this can be accomplished by inserting an aperture plate 13 of suitable form between the lenses 12 and 14 in the plane of the back-projected image of the objective pupil plane. In the illustrated example, the aperture plate 13 has different forms, labeled 13N and 13S, allowing different illumination modes to be selected. The illumination system in this example forms off-axis illumination modes. In a first illumination mode, aperture plate 13N provides off-axis to a direction designated as 'North', for illustration only. In a second illumination mode, aperture plate 13S is used to provide similar illumination, but from the opposite direction, labeled 'South'. Other illumination modes are possible by using different apertures. The rest of the pupil plane is preferably dark, as any unwanted light beyond the desired illumination mode will interfere with the desired measurement signal.

[0055] like Figure 5 As shown in (b), the target T is placed with a substrate W having an optical axis O orthogonal to the objective lens 16. The substrate W may be supported by a support (not shown). A ray of measurement radiation I striking the target T from an angle offset from the axis O produces a zero-order ray (solid line 0) and two first-order rays (dash-dotted line +1 and dash-dotted line -1). It should be remembered that with an overfilled small target, these rays are only one of many parallel rays covering the substrate area (including the measurement target T and other features). Since the aperture in the plate 13 has a finite width (necessary to allow an effective amount of light to enter), the incident ray I will in fact occupy a certain angle range, and the diffracted rays 0 and +1 / -1 will be slightly spread out. Depending on the point spread function of the small target, each order +1 and -1 will be further spread out to a certain angle range, rather than the single ideal ray shown. It should be noted that the grating pitch and illumination angle of the target can be designed or adjusted so that the first-order rays entering the objective are closely aligned with the central optical axis. Figure 5The rays illustrated in (a) and 3(b) are shown slightly off-axis purely to make them easier to distinguish in the drawings.

[0056] At least the 0th and +1st orders diffracted by the target T on the substrate W are collected by the objective lens 16 and directed back through the beam splitter 15. Return to Figure 5 (a), the first illumination mode and the second illumination mode are each illustrated by specifying diametrically opposed apertures labeled as north (N) and south (S). When the incident ray I of the measurement radiation comes from the north side of the optical axis, that is, when the first illumination mode is applied using the aperture plate 13N, the +1 diffracted ray labeled as +1 (N) enters the objective lens 16. In contrast, when the second illumination mode is applied using the aperture plate 13S, the -1 diffracted ray (labeled as 1 (S)) is the ray that enters the lens 16.

[0057] A second beam splitter 17 divides the diffracted beam into two measurement branches. In the first measurement branch, an optical system 18 forms a diffraction spectrum (pupil plane image) of the target on a first sensor 19 (e.g., a CCD or CMOS sensor) using the zero-order and first-order diffracted beams. Each diffraction order hits a different point on the sensor so that image processing can compare and contrast the orders. The pupil plane image captured by the sensor 19 can be used to focus the metrology device and / or normalize the intensity measurement of the first-order beam. The pupil plane image can also be used for many measurement purposes, such as reconstruction.

[0058] In the second measurement branch, the optical systems 20, 22 form an image of the target T on a sensor 23 (e.g. a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is provided in a plane conjugate to the pupil plane. The aperture stop 21 is used to block the zero-order diffraction beam so that the target image formed on the sensor 23 is formed only by the -1 or +1 first-order beam. The image captured by the sensors 19 and 23 is output to a processor PU that processes the image, the function of which will depend on the specific type of measurement being performed. Note that the term 'image' is used here in a broad sense. If only one of the -1 and +1 orders is present, such a raster line image will not be formed.

[0059] Figure 5The specific forms of the aperture plate 13 and field stop 21 shown are examples only. In another embodiment of the invention, on-axis illumination of the target is used, and an aperture stop with an off-axis aperture is used to pass essentially only one first-order diffracted light to the sensor. In other examples, a two-quadrant aperture may be used. As described in the above-mentioned US2010201963A1, this may enable simultaneous detection of positive and negative orders. As described in the above-mentioned US2011102753A1, embodiments with a wedge (a segmented prism or other suitable element) in the detection branch may be used to separate the order of spatial imaging in a single image. In other embodiments, 2nd, 3rd and higher order beams ( Figure 5 21 ) can be used for measurement instead of or in addition to the first order beam. In other embodiments, a segmented prism can be used instead of the aperture stop 21, resulting in the ability to capture both the +1st and -1st orders at spatially separated locations on the image sensor 23.

[0060] To make the measurement radiation adaptable to these different types of measurements, the aperture plate 13 may include multiple aperture patterns formed around a disk that rotates to place the desired pattern in place. Note that aperture plates 13N or 13S can only be used to measure gratings oriented in one direction (X or Y, depending on the setup). For measurements of orthogonal gratings, target rotations of 90° and 270° can be achieved.

[0061] Light sources for measurement applications that can be used for the concepts disclosed herein can include any broadband source and color selection arrangement to select one or more colors from a broadband output. By way of example, the radiation source can be based on a hollow core or solid core fiber, such as a hollow core photonic crystal fiber (HC-PCF) or a solid core photonic crystal fiber (SC-PCF). For example, in the case of HC-PCF, the hollow core of the optical fiber can be filled with a gas that acts as a widening medium for widening the input radiation. This optical fiber and gas arrangement can be used to create a supercontinuum radiation source. The radiation input to the optical fiber can be electromagnetic radiation, such as radiation in one or more of the infrared, visible, UV, and extreme UV spectra. The output radiation can consist of or include broadband radiation, which can be referred to as white light in this article. This is just one example of a broadband light source technology that can be used in the methods and devices disclosed herein, and other suitable technologies can be used.

[0062] When using metrology sensors, including those described above and / or other types of metrology sensors (eg, alignment sensors, leveling sensors), it is often desirable to control the illumination spectrum, eg, switch the illumination between different wavelengths (colors) and / or wavefront profiles.

[0063] To perform color selection, a color selection module has been proposed that uses Grating Light Valve (GLV) technology, such as sold by Silicon Light Machines (SLM), for example described in US6947613B, which is incorporated herein by reference. GLV is an electrically programmable diffraction grating based on Micro-Electro-Mechanical Systems (MEMS) technology. Figure 6 The diagram illustrates the principle. Figure 6 is a schematic illustration of a GLV pixel or assembly 500 starting with (a) and (b), (c) above. The GLV assembly includes two types of alternating GLV reflective strips: static or bias strips 510, which are typically grounded together with a common electrode, and driven or active strips 520, which are driven by an electronic driver channel. A GLV module may include any number of these GLV assemblies 500 arranged in an array. The active strips and bias strips may be substantially identical except for the manner in which they are driven. When no voltage is applied to the active strips 520, they are coplanar with the bias strips, as shown in FIG. Figure 6 (b) The configuration shown in FIG. 1A . In this configuration, the GLV essentially acts as a mirror, where incident light is reflected by the mirror. When a voltage is applied to the active strip 520, as shown in FIG. Figure 6 (c) they are deflected relative to the bias strip 510, creating a square well diffraction grating. In this state, incident light is diffracted to a fixed diffraction angle. By controlling the voltage on the active strip 520, the ratio of reflected light relative to diffracted light can be continuously changed, which controls the amplitude of their deflection. Thus, the amount of light diffracted by the GLV can be controlled in an analog fashion from zero (full specular reflection) to all incident light (zero specular reflection).

[0064] The GLV module can be used in zero-order mode, so that the diffracted radiation is blocked / dumped and the specularly reflected (zero-order) radiation is provided to the metrology tool. This has the advantage of maintaining etendue.

[0065] Figure 7 is a schematic diagram conceptually explaining how a GLV-based source selection module may operate. Figure 7 (a) is a graph of intensity I versus wavelength λ, showing an exemplary input spectrum IP describing dispersed broadband radiation from a broadband radiation source SO. In this example, the broadband radiation includes five color bands λ1 to λ5 of equal intensity. Of course, this is just an illustrative example, and there may be more or fewer color bands in the input spectrum, the input spectrum may be continuous across a wavelength range, and / or there may be some intensity variation between colors. Similarly, the GLV module may be operable to selectively attenuate more or fewer bands than the five bands shown here.

[0066] Figure 7(b) shows each of these color bands on a corresponding portion of the GLV module (shown looking down on the GLV bands). The illustrative figures show the color bands for each GLV component, although each color band can be incident on a corresponding plurality of GLV components (i.e., using multiple GLV components to control each color). The plane defined by the GLV surface (e.g., the plane defined by the static bands) includes the spectrally dispersed image plane of the system.

[0067] Figure 7 (c) conceptually illustrates how the GLV is used to modulate the input spectrum IS. In the specific example shown, the GLV module portions of the incident colors λ1 and λ5 are fully reflective (i.e., no voltage is applied to the active strips 520, so the active strips 520 are not displaced so that they are coplanar with the static strips 510). Arrow R λ1 , R λ5 The width of represents the amount of light reflected by the colors λ1 and λ5. λ1 , D λ5 = represents negligible or zero light diffracted by the GLV to higher (non-zero) diffraction orders. For colors λ2, λ3, λ4, the active strip 520 is displaced by different amounts relative to the static strip 510 forming a diffraction grating with correspondingly different diffraction efficiencies. Again, arrow R λ2 , R λ3 , R λ4 The width of represents the amount of light reflected by colors λ2, λ3, and λ4 and is labeled D λ2 , D λ3 , D λ4 The size of the block represents the amount of light diffracted by the GLV to higher (non-zero) diffraction orders of colors λ2, λ3, and λ4. All diffracted light D λ2 , D λ3 , D λ4 (If not exactly zero, then D λ1 , D λ5 ) are blocked by the aperture ST or higher-order blocks, so that only the reflected radiation R λ1 , R λ2 , R λ3 , R λ4 , R λ5 is transmitted to the measuring device.

[0068] The stop ST can be located in the pupil plane of the system. The GLV module induces dispersion of all orders except the zeroth order, leaving the zeroth order unaffected (e.g., no increase in the zeroth order etendue). This higher order dispersion results in a different beam position at the stop ST, allowing it to be blocked. Since the zeroth order is unaffected, the output beam will remain (close to) a Gaussian / single mode beam. This is particularly desirable for alignment applications (i.e., for use in alignment sensors), since such alignment applications typically require a Gaussian or single mode beam.

[0069] Figure 7 (d) is a graph of intensity I versus wavelength λ, showing the Figure 7 (c) The composite output spectrum OP of the illustrated GLV module configuration. It can be seen that the intensity I of each spectral component λ1, λ2, λ3, λ4, λ5 corresponds to the GLV configuration of the corresponding part of the GLV module of that color. In this way, the intensity of each spectral component can be continuously varied between minimum and maximum transmittance. For example, the minimum transmittance can be less than 10%, less than 5%, less than 3%, less than 2%, less than 1%, less than 0.5% or less than 0.1%. For example, the maximum transmittance can be greater than 90%, greater than 95%, greater than 97%, greater than 98%, greater than 99%, greater than 99.5% or greater than 99.9%. In this way, a specific spectral profile can be configured for any measurement, thereby improving measurement accuracy.

[0070] The GLV-based color selection module is an example of a color selection module that can be used in any suitable measurement device. Other fast switching color segment arrangements can also be used instead of GLV, such as other light valve technologies, or more generally other spatial light modulation devices (e.g., acousto-optic modulation devices, such as acousto-optic tunable filters, digital micromirror devices (DMD) technology, and / or LCOS (liquid crystal on silicon) devices). The concepts described below are primarily described in the context of using a GLV-based color selection module, although the present disclosure is not necessarily limited to such color selection technology (at least in some aspects).

[0071] A number of illumination and detection concepts will now be described which may be combined with the above described color selection module in an illumination (or combined illumination and detection) strategy.

[0072] Figure 8is a simplified schematic illustration of the proposed fast programmable illumination. An input beam 800 is incident on a beam steering device 805, such as a fast micro-electromechanical system (MEMS) tiltable mirror. The steered beam 810 can be split into four copies 820 of the original beam using, for example, beam splitting optics or beam replicating optics 815 or kaleidoscope optics. In this way, by controlling the beam steering device 805, the beam 825 is steered or scanned very quickly over a configurable or programmable illumination angle range, thereby being steered or scanned within an illumination area in an illumination pupil plane. The scan can be fast enough relative to the measurement duration so that the scanned illumination within the illumination area is integrated within the measurement time. For example, the scan time over a typical expected illumination angle range of the beam steering device or MEMS mirror 815 can be less than 1 ms or less than 0.5 ms. The illumination area 825 is shown in dashed lines at different positions associated with different illumination colors (gray dashed lines represent different colors). These different positions include illumination pupil regions for each respective wavelength (for a given detection pitch) corresponding to appropriate detection (e.g., desired detection conditions) at the detection aperture 830 (e.g., which may be located at a fixed position). Depending on the wavelength of the illumination beam, the beam steering device 815 may be controlled to scan the beam over the appropriate illumination region for that wavelength.

[0073] While in many arrangements the detection pupil or detection area may be fixed, another suggestion may be to use switchable detection. This may be achieved in different ways, such as by placing a device similar to an illumination mode selector (IMS) in the detection path. IMS is a known illumination selection method in which different fixed apertures are arranged on an aperture wheel so that they can be selectively switched or rotated into the illumination beam path as required. In a similar manner, the selected detection aperture (and / or wedge) may be switched into the detected radiation depending on the application. The detection aperture or sub-aperture (detection area) may also be shifted in the pupil plane to accommodate changes in wavelength / pitch (in conjunction with or separate from the illumination).

[0074] For many measurement applications, such as applications based on incoherent imaging techniques, it may be desirable or necessary to overfill the detection area (detection mask or detection numerical aperture NA), i.e., so that at least the entire detection area is substantially filled with the detected (diffracted) radiation. In the context of the present disclosure, "substantially filled" may describe the entire detection area being filled more than 80%, filled more than 85%, filled more than 90%, filled more than 95%, filled more than 98%, filled more than 99%, filled more than 99.5% or filled 100%. This may enable simpler computational corrections and / or reduce crosstalk. In contrast, partial filling of the detection mask will result in (partially) incoherent imaging, which will increase the sensitivity to crosstalk.

[0075] Because of this, configurable illumination profiles are often provided (e.g. using an IMS or a programmable illuminator such as Figure 8 ), an illumination profile is selected or configured based on the wavelength and target pitch so as to obtain a substantially filled or overfilled detection pupil. The configurable illumination profile can also be configured to prevent second-order diffracted light from leaking into the detection pupil. Existing methods for achieving this are satisfactory when a single illumination wavelength is used. However, when measuring in parallel with multiple wavelengths, the selected mechanical aperture or programmed illumination mask is suboptimal (suboptimal illumination NA) for each wavelength or all wavelengths except one. Therefore, the detection mask may not be completely (or substantially) filled for one or more wavelengths. Because of this, when performing multi-wavelength measurements on a single target, mechanical operations can be performed in the IMS to switch between apertures. However, in this case, the illumination pupil is not always effectively utilized due to the limited available (e.g., four) apertures.

[0076] Fig. 9 The problem of configuring illumination when multiple wavelengths are used in parallel is illustrated. It shows a pupil plane representation (e.g. of an objective of a metrology device), divided into an illumination pupil (upper left and lower right quadrants) and a detection pupil (upper right and lower left quadrants); the order of these quadrants is arbitrary, and the pupil plane may be divided between illumination and detection areas in any suitable way. It is desired to fill a fixed detection area or detection mask 900 (shaded) with the detected illumination overfill. The illumination area or illumination mask 910 is configured so that this is achieved for one of the illumination wavelengths λ2, as indicated by the detected illumination positions 920 for that wavelength. λ2 However, for the two other wavelengths λ1, λ3 present in the illumination used in this example, the detection area 900 is only partially filled, as indicated by the respectively detected illumination positions 920 λ1 ,920 λ3 indicated. When multiple wavelengths are selected simultaneously, for example by GLV, this may result in partially filled detections for some wavelengths. As explained, this is undesirable and should be avoided.

[0077] A proposed method and illumination module are provided, which synchronize wavelength selection (spectral configuration of illumination) with programmable or configurable illumination angle and / or detection angle range, so that at any time only wavelengths are selected that result in the correct detection (i.e., for a specific structural pitch of the measured diffraction structure) or the desired detection conditions. The module may include: a grating light valve module (or other color selection module, such as a fast switching MEMS or other light valve color selection module) for controllably configuring the spectral configuration of the measurement illumination (e.g., wavelength, combination of wavelengths, or weighted combination); a configurable illumination module operable to provide measurement illumination within a configurable illumination angle range; and a controller for controlling the configurable illumination module and the grating light valve module.

[0078] The configurable illumination module may include a beam steering device, for example, which scans the beam across the illumination pupil (e.g., across an illumination angle range) quickly enough to define a desired illumination angle range or illumination shape in the pupil plane. In an embodiment, such a module may include a beam scanning device, a GLV module, and a controller, the controller being configured to scan across the illumination angle range while controlling the GLV module to select a wavelength (a single wavelength or a combination of multiple wavelengths) that will be correctly detected by the detection mask (within the detection NA), the selection of color depending on the illumination angle (beam position in the illumination pupil) during the scan. In this context, correct detection (i.e., desired detection conditions) may include maintaining the detection area (detection NA) overfilled. In this context, overfilling may mean substantially filling the detected radiation or diffraction order radiation (e.g., as defined above) that is generated by the scanned illumination being diffracted by the target or other diffractive structure at each of the multiple desired wavelengths. Alternatively or additionally, correct detection may mean that diffracted radiation of multiple desired wavelengths is detected in a substantially common area in the detection pupil plane.

[0079] The detection mask / detection NA may be fixed, or it may be configurable / movable so that the GLV color selection is synchronized with the illumination beam position and / or the detection mask position.

[0080] The switching speed of the GLV can reach several μs, which is much faster than the scanning speed of the MEMS mirror (e.g., 0.5ms to 1ms), which can be used to scan the illumination over the illumination area. Therefore, if the scanning of the MEMS mirror over the illumination area takes 1ms or more, the GLV module can turn the color on and off about 50 to 100 times during a single scan. This can include switching colors individually and / or switching multiple colors simultaneously, and can also optionally include non-binary control of each wavelength, so that the intensity of each wavelength can be attenuated by less than 100% (e.g., attenuation at multiple values ​​or continuous attenuation between 0% and 100%).

[0081] Fig.10 The principle is illustrated schematically. Fig.10 (a) shows the beam IB being directed by the beam steering element BS during scanning through the range of illumination angles. λ1 The first instant or snapshot at the point passing through the first angle θ1 is directed, thus being the first position in the illumination pupil plane IPP of the objective lens OL. Based on this angle (and the target pitch), the controller CO controls the GLV module receiving the broadband illumination beam IB to provide the illumination beam IB with λ1 Select the appropriate wavelength or wavelengths. Fig.10 (b) shows a second moment during the same scan, where the beam steering element BS directs the beam IB λ2 The steer passes through a second angle θ2 and is therefore a second position in the illumination pupil plane IPP. Based on this angle (and the target pitch), the controller CO controls the GLV module to provide the illumination beam IB with λ2 Select the appropriate wavelength or wavelengths. Fig.10 (c) shows the third moment during the scan, where the beam steering element BS directs the beam IB λ3 The steering passes through a third angle θ3 and is therefore a third position in the illumination pupil plane IPP. Based on this angle (and the target pitch), the controller CO controls the GLV module to provide the illumination beam IB with λ3 Select the appropriate wavelength or wavelengths.

[0082] Fig.11 An example pupil plane representation is shown, where the illumination NA or angular range (for a given target pitch) of the scan by illumination and the spectral configuration of the scanned beam are controlled together with the (fixed) detection NA 1100 to ensure overfill detection of the detection NA for all desired wavelengths measured. Fig.11 In FIG. 1 , an irradiation area 1110 of three wavelengths λ1, λ2, and λ3 is shown. λ1 ,1110 λ2 ,1110 λ3 (marked for only one of the four beams - it should be appreciated that the disclosed concepts are also applicable to dual beam measurements, e.g., only for x or y targets, and / or single beam measurements), which results in an overfilled detection NA for the desired diffracted order radiation 1120 (e.g., the first diffracted order radiation) for each wavelength λ1, λ2, λ3. In this way, for each wavelength, the desired diffracted order radiation 1120 will be at the same pupil plane position. These illumination areas 1110 λ1 ,1110 λ2 ,1110 λ3 The area can be determined for all desired wavelengths (e.g., by calculation using well-known diffraction laws or observation). The scan of the illumination can cover the illumination area 1110 λ1,1110 λ2 ,1110 λ3 The entire range of wavelengths is captured while selecting the appropriately relevant wavelength or wavelengths for each pixel location.

[0083] Thus, for each respective illumination area corresponding to a particular wavelength used or wavelength of interest, the GLV module (or other color selection module) can be controlled to always select the wavelength corresponding to the illumination area being scanned. In the event that these illumination areas overlap, two or more wavelengths corresponding to the overlapping illumination areas should be selected.

[0084] For example, if it is decided to measure a particular target with a combination of three wavelengths λ1, λ2, λ3, the GLV module can be controlled during the illumination scan to select all three of these wavelengths when scanning in the illumination plane area, where all three illumination areas 1110 λ1 ,1110 λ2 ,1110 λ3 Overlap in the illumination pupil plane. For the illumination area 1110 marked λ1 ,1110 λ2 ,1110 λ3 The corresponding beam is shown as a shadow. Similarly, when the three irradiation areas 1110 λ1 ,1110 λ2 ,1110 λ3 When scanning in an illumination plane region where two illumination regions overlap, only these two wavelengths should be turned on via the GLV module, and for regions where the illumination regions do not overlap each other, only the wavelength corresponding to the illumination region should be turned on. In this way, the detection region 1100 should be overfilled for each wavelength.

[0085] As an alternative to using the described scanning beam and beam steering device, discrete switching of the illumination angle (eg via an IMS) where the GLV provides a different spectrum for each selected illumination aperture.

[0086] The detection angle range defined by the detection mask / NA may be fixed.In an optional refinement, for certain detection aperture masks it may also be possible / beneficial to shift the detection aperture mask together with the illumination aperture mask, for example to achieve the Littrow condition.

[0087] Fig.11 An illumination solution is provided for a proposed incoherent detection method, which can use computational imaging techniques to correct for measurement aberrations resulting from simplified optics, for example. However, the method disclosed herein can also be used with currently used illumination modes, for example using quadrant illumination, such as currently used for micro-diffraction based overlay (μDBO) or focus (μDBF) techniques.

[0088] Fig.12 Illustrated is a method for controlling the spectral profile of a scanned beam used to define a quadrant illumination profile, which is currently used in many metrology techniques, for a single quadrant and a single direction to ensure that the first diffraction order of each wavelength is captured, but higher orders are excluded. Solid pupil area 1210 λ1 ,1210 λ2 ,1210 λ3 The positions of the desired diffracted order radiation, i.e. the first diffracted order for each wavelength λ1, λ2, λ3, are shown relative to the detection pupil (upper left quadrant in the figure) produced by a single quadrant illumination comprising three wavelengths λ1, λ2, λ3 captured in the pupil plane. Unfilled pupil area 1230 λ1 , 1230 λ2 , 1230 λ3 The positions of unwanted diffraction order radiation, i.e., unwanted second diffraction orders for each wavelength λ1, λ2, λ3 captured in the pupil plane relative to the detection pupil are shown. During scanning of the illumination angles that map to unwanted second orders captured within the detection pupil, the spectral configuration of the beam can be controlled to turn off wavelengths (e.g., turn them off via a GLV module) that would otherwise result in unwanted captured second orders.

[0089] By way of specific example, when scanning the pupil and the second-order diffraction area 1230 λ1 When the corresponding illumination area is turned off, the corresponding wavelength λ1 can be turned off. This should be performed for both illumination quadrants in both directions where applicable. It can be appreciated that this is a completely different application of the concepts disclosed herein, as ensuring overfill detection is not important for such an embodiment (in which the imaging mechanism may be partially irrelevant). In this case, correct detection of the detected radiation (desired detection conditions) can be understood to mean detecting only the desired orders (e.g. the first diffraction order and not higher orders of radiation).

[0090] Will refer to Fig.13 Another application of the concepts disclosed herein is described. In many metrology applications, particularly overlay metrology applications, measurement performance strongly depends on many illumination parameters, such as: wavelength, polarization, angle, and phase of the illumination beam. In many existing metrology tools, no hardware is provided for controlling angle or phase; wavelength and / or polarization may be selected universally for all angles, but not for every angle. In certain use cases, the lack of angle-based parameter control may result in non-ideal metrology (e.g., overlay) performance.

[0091] For example, especially for relatively thick stacks (e.g., thicker than 1.5 μm or thicker than 2 μm), the wavelength and angle dependence of the overlay sensitivity (K) becomes stronger, so the correct choice of wavelength and angle becomes more important. Fig.13 In the example shown in (a), the calculated overlay sensitivity K of a target (e.g., here an x-direction target) is presented in grayscale as a function of pixel position in the exit pupil plane (of the objective of the metrology tool) for 6 different, closely spaced wavelengths λ1 to λ6. In this specific example, the wavelengths may be spaced 20 nm apart between λ1 = 600 nm and λ6 = 700 nm (e.g., λ2 = 620 nm, λ3 = 640 nm, etc.). As will be described, this spacing actually depends on the stack thickness. Thus, each figure includes a sensitivity map resolved in the pupil plane. More generally, each figure includes sensitivity data for a parameter of interest.

[0092] Due to the large stack thickness and interference effects inherent in the diffraction-based overlay method, the K value varies greatly in the pupil plane, so that for each of these (and all other) wavelengths, it includes alternating positive values ​​(darker areas) and negative values ​​(brighter areas) in the annular region. In particular, the position or "phase" of the variation of the overlay sensitivity K in the annular region varies depending on the stack thickness. The term phase describes the fact that these alternating regions may actually represent oscillations of the sensitivity between positive and negative values ​​in the pupil plane. Because of this, K may vary very significantly for a given pixel position between different measurement locations on the wafer. In μDBO measurement, a single intensity value is measured for each target / sub-target in the field plane image, so all K values ​​in the detection area of ​​the pupil plane are summed to one K value in the field plane. Therefore, the positive and negative K values ​​at different pupil positions (angles) cancel each other, resulting in an average overlay sensitivity K value in the detected μDBO image that is close to zero (i.e., the image is largely insensitive to overlay).

[0093] In this embodiment, it is recommended to change the wavelength (e.g. via a GLV or other color selection module) during scanning illumination through the pupil plane (through the angle of illumination NA) in order to ensure a good average overlay (or other parameter of interest) sensitivity K magnitude (e.g. on an amplitude scale between 0 and 1, the overlay sensitivity K magnitude is above a threshold value such as 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8). "Illumination angle NA" or "illumination angle" may be understood to encompass or describe a coordinate in the pupil plane, which may be expressed using a combination of polar and azimuthal angles).

[0094] This can be achieved by using only the combinations of spectral configurations of the measurement beam and the illumination angles that maximize the average parameter of interest sensitivity value. This can be further achieved by selecting a wavelength (or combination of wavelengths) and scanning that wavelength over a region of the pupil plane that corresponds to only one sign of the parameter of interest sensitivity. Note that, in theory, there is no finite scale for the actual sensitivity value K. The value here refers to a normalized scale (between 0 and 1) based on the absolute maximum value K present in the synthetic pupil response.

[0095] In an embodiment, such a method may include switching between two (or more) wavelengths (or a combination of two or more wavelengths) during portion of the scan such that the sign of the overlay sensitivity K does not change during the scan (e.g., it always remains positive or negative, it does not matter which one).

[0096] Refer again Fig.13 (a) It will be appreciated that certain wavelength pairs (or wavelength combination pairs) will produce complementary corresponding overlay sensitivity diagrams; that is, the positive sensitivity regions in the sensitivity diagram for a first determined wavelength correspond largely in pupil position to the negative sensitivity regions in the sensitivity diagram for a second determined wavelength.

[0097] Fig.13 (b) A proposed method for exploiting this is conceptually illustrated. Two wavelengths (or wavelength combinations) are determined which have complementary overlay sensitivity maps (more generally complementary corresponding parameter of interest sensitivity data), as described; these wavelengths can be determined mathematically. Once the wavelengths have been determined, the corresponding sensitivity maps can be predicted based on known stack parameters, in particular stack thickness (grating spacing). Alternatively, the sensitivity maps can be measured.

[0098] exist Fig.13 In (b), the two wavelengths selected are λ1 and λ2. To understand the method conceptually, first consider the wavelength λ1. The corresponding sensitivity graph SP for this wavelength is shown. λ1 . Color selection control graphics CP λ1 It is shown that the area of ​​this color can be turned on (dark shading) and off (no shading) during the illumination scan in the pupil plane (which can be achieved, for example, via a beam steering device and a color selection module (such as the GLV module already described)). The actual scan will of course be much finer than the very rough path shown for illustration. As can be observed in the figure, the area turned on for wavelength λ1 corresponds to the sensitivity pattern SP λ1 The region corresponding to the common sign of the sensitivity (i.e., all positive or all negative) is selected. In this specific example, the negative region is selected. The result is a customized or configured sensitivity map SP λ1 The same situation is also shown for wavelength λ2, which shows the equivalent sensitivity graph SP for this wavelength.λ2 . From the color selection control graphics CP λ2 It can be observed that the area of ​​the pupil plane that is open for the wavelength λ2 corresponds to the sensitivity graph SP λ2 The sensitivity of the region has the same sign as the region selected for the first wavelength. The result is a customized or configured sensitivity map SP λ2 '.

[0099] Note that the selected regions from the two single wavelength sensitivity graphs may overlap to obtain the configured sensitivity graph. For each wavelength, select regions with expected high sensitivity, which may overlap.

[0100] In a practical embodiment, the graphics CP λ1 and CP λ2 The color selection control signal represented by φ is implemented in a single scan through the pupil plane so that the illumination switches between two wavelengths (or wavelength combinations) during the scan to obtain a sensitivity pattern SP′. λ1+λ2 The synthetic pupil, the sensitivity graph SP' λ1+λ2 Substantially only negative (or substantially only positive) overlay sensitivity K values. In such embodiments, the sensitivity values ​​comprising substantially only one sign may describe a sensitivity value comprising one sign for a scanned pupil area or a scanned illumination angle (e.g., of pixels within a scanned area); that is, greater than 70%, greater than 80%, greater than 90%, greater than 95%, or greater than 99% of the configured illumination NA.

[0101] This concept of the method can be generalized by choosing wavelengths of similar expected phase with overlay sensitivity K for all pupil pixel positions, for example ±π / 4.

[0102] In the measurement method, all K values ​​in the pupil plane are summed to one value in the field plane, which will result in a ratio Fig.13 (a) The higher average sensitivity K value of the conventional method shown, where positive and negative K values ​​cancel each other, resulting in K close to zero in the field plane. Therefore, the overlay performance will be improved.

[0103] For challenging cases, the response may still be close to zero for a chosen phase of K due to (unknown) stack-up variations across the wafer. To address this, three measurements at different phases of K can be used to ensure that the extreme values ​​are always captured.

[0104] Although the described embodiments use two complementary wavelengths (i.e., have complementary pupil sensitivity patterns), improvements over the prior art would be obtained by using a single wavelength that is only turned on when scanning the area corresponding to one symbol of overlay sensitivity. Fig.13 (b), Sensitivity graph of the configuration SPλ1 ' or SP λ2 'Any one of them will be compared with the sensitivity map SP λ1 or SP λ2 Produces better performance (higher average sensitivity).

[0105] Although this embodiment is described with respect to measuring thick stacks, the concepts are also applicable to thinner stacks and in-device metrology (IDM) techniques where pupil K variations are less strong but still exist. For example, pupil variations may also occur due to non-ideal grating shapes (side wall angles, floor tilt, etc.).

[0106] Fig.13 (b) describes a binary wavelength control (ON or OFF). However, wavelength combinations weighted depending on the illumination angle may be used. Moreover, the spectral configuration may additionally include the polarization state of the illumination, which may also vary when scanning across the pupil.

[0107] The above description has been about increasing the average signal intensity, however, selective pupil sampling can also be used to accommodate (known) sensor aberrations, where the effect on the pupil can be attenuated via wavelength intensity.

[0108] exist Fig.13 In the example of (b), the two wavelengths provide K-diagrams that are almost complementary to each other, i.e., such that the position of the positive K-region for wavelength λ1 is spatially complementary to that for wavelength λ2. The following estimate shows how to find such a pair of wavelengths for a given stack.

[0109] It is well known that in diffraction-based overlay metrology, the intensity difference ΔI between the +1 and -1 diffraction orders in the presence of overlay OV is given by:

[0110]

[0111] Where A and B describe the diffraction efficiency at the top and bottom gratings, respectively; p is their pitch, T is the spacing between the top and bottom gratings, θ is the incident angle, and λ is the wavelength. When the overlay OV is small:

[0112]

[0113] In order to maximize the overlay sensitivity K, the sign of K given by λ2 should be different from that given by λ1, and the wavelength difference Δλ (Δλ = λ2-λ1) should be as small as possible, so:

[0114]

[0115] This yields:

[0116]

[0117] Therefore, Equation 4 can be used to determine a suitable pair of wavelengths as a pair of wavelengths separated by Δλ calculated from the stack and measured properties.

[0118] In this embodiment, the parameter of interest is mainly described as overlay. However, this is not the only parameter of interest to which these methods apply. Other such parameters of interest may include: critical dimension, sidewall angle, process variation. Such parameters of interest may also lead to (e.g. weak but noticeable) KPI variations in the pupil that would benefit from the same concepts.

[0119] It can be appreciated that the method just disclosed can also reduce the amount of stray light in the measurement tool. In the disclosed method, only two graphics CP λ1 , CP λ2 The illumination angles represented by the shaded "1" region above are where illumination is "on" and used for overlay inspection, and illumination at other angles is off. In contrast, in current metrology technology, illumination angles outside these regions are also turned on; these do not contribute to overlay, but can cause stray light within the tool.

[0120] The above embodiments disclose beam steering and color selection (e.g., GLV) synchronization for pupil plane scanning. In other embodiments, it is proposed to extend the concept to scan the illumination spot on the image plane; for example, on a measured target. In an embodiment, the target may include the well-known micro-diffraction based overlay (μDBO) target. The beam steering device may include at least one steerable mirror device (e.g., one or more MEMS mirrors). For example, the beam steering device may include a 2D steerable mirror device or a pair of 1D steerable mirror devices.

[0121] Fig.14 (a) A typical μDBO target and measurement technique are schematically illustrated. The μDBO target comprises one or more sub-targets, each sub-target comprising a pair of gratings in a separate layer. Any positional offset between these gratings manifests itself as an asymmetry in the sub-targets. As is well known, each μDBO target may comprise one or more sub-targets in each measurement direction (e.g., a first direction and a second direction perpendicular to each other in the plane of the substrate, conventionally designated as the X-direction and the Y-direction). As is well known, each μDBO target may comprise a pair of offset sub-targets or a pair of offset sub-targets in each direction, wherein each sub-target in each pair of offset sub-targets comprises a different offset. This enables the overlay inferred from the target to be corrected (at least partially) from the effects of other (undesired) target asymmetries.

[0122] Thus, a typical μDBO target 1400 may include a first pair of offset (X direction) sub-targets 1410X and a second pair of offset (Y direction) sub-targets 1410Y, for example arranged in a 2x2 block. The target is typically measured in an overfilled manner, where the illumination spot 1420 is larger than the target 1400 so that the entire target is illuminated during measurement. During processing, a region of interest (ROI) 1430 is identified within each sub-target, typically including a central area away from the edge of the target. A single intensity value (e.g., average intensity) can be determined for each ROI 1430, and the overlay is determined by these intensity values.

[0123] Note that a similar approach and similar target design are known for micro-diffraction based focus (μDBF) targets, except that each sub-target is formed in a single layer with focus (and / or dose) dependent asymmetry. Thus, these targets can be used for focus and / or dose metrology rather than overlay metrology. The following embodiments will be described in the context of μDBF metrology, but will be understood to be equally applicable to μDBF metrology.

[0124] Fig.14 (b) schematically illustrates the proposed embodiment. A measurement illumination beam (now much smaller than each sub-target) forming an illumination spot 1440 (e.g. a laser spot) is scanned only over the (at least one) region of interest 1430 of each sub-target, e.g. only over a range of illumination positions within the region of interest. In this way, the illumination spot 1440 may be scanned over the target (e.g. using a beam steering device or a (e.g. 2D) MEMS mirror), while the illumination is controlled (e.g. via a GLV) to switch on the illumination only when the illumination spot 1440 is within the region of interest; the illumination is switched off outside these regions of interest. This is represented in the figure by arrow 1445, which indicates the path of the illumination spot 1440 when switched on.

[0125] The cross-sectional diameter of the illumination beam may be less than 1 / 4, 1 / 5, 1 / 6, 1 / 8 or 1 / 10 of the length of the target in any planar dimension of the substrate.

[0126] In this embodiment, the illumination condition that is varied is the illumination intensity, i.e., on (full intensity) or off (zero intensity). An illumination configuration module (such as a GLV module) can be used to selectively change the illumination condition of the beam of the measurement illumination during the scan, e.g., turn the beam on and off. However, a simple switch or other switching device can be used for this embodiment.

[0127] By acquiring μDBO images while scanning over the region of interest in this way, a (completely) incoherent μDBO image can be obtained while significantly reducing target crosstalk, since edges and surrounding structures are not illuminated.

[0128] Fig.14 (c) illustrates a refinement of this embodiment. Fig.14 (a) It will be appreciated that with current overfilled μDBO measurements, all sub-targets, and therefore the X and Y targets, always receive illumination with the same illumination conditions or spectral configuration (e.g., color(s) and / or polarization) in an acquisition. However, to improve or optimize μDBO performance, it is sometimes desirable or necessary to use different color / polarization schemes for different sub-targets; in particular, to use a different color / polarization scheme for the X sub-target 1410X than for the Y sub-target 1415Y. Thus, overfilled μDBO measurements require two separate acquisitions to sequentially provide different illumination conditions for the X sub-target and the Y sub-target, resulting in a time or throughput penalty.

[0129] In this embodiment, it is suggested to configure the illumination condition or spectral configuration for each sub-target separately, for example, different colors and / or polarizations are provided for the X sub-target and the Y sub-target. Thus, when scanning within a first subset of target regions of interest, for example, for regions of interest within the X sub-targets (as indicated by arrows 1450 in the figure), the illumination spot 1440 can be turned on and configured to have a first illumination condition, and when scanning within a second subset of target regions of interest, for example, for regions of interest within the Y sub-targets (as indicated by arrows 1455 in the figure), the illumination spot 1440 can be turned on and configured to have a second illumination condition. As before, the illumination spot can be turned off outside these regions of interest 1430.

[0130] As with other embodiments, illumination condition selection or spectral configuration may be accomplished via an illumination configuration module (such as a GLV module) operable to selectively alter the spectral and / or polarization configuration of the illumination.

[0131] In all of the above examples and embodiments, the relative intensity of the various wavelengths may be controlled / attenuated via the GLV module using the methods already described.

[0132] In all of the above examples and embodiments, all captured wavelengths may be captured in a single camera acquisition. Alternatively, if the illumination mask for each wavelength is defined quickly enough (e.g. via a single moving sub-aperture or a smaller spot with a fast enough mirror), the wavelength range may also be captured sequentially using a high frame rate camera synchronized with the illumination sub-aperture shape for each wavelength and the movement of the GLV module.

[0133] Fig.151 is a block diagram illustrating a computer system 1500 that can assist in implementing the methods and processes disclosed herein. The computer system 1500 includes a bus 1502 or other communication mechanism for transferring information and a processor 1504 (or multiple processors 1504 and 1505) coupled to the bus 1502 for processing information. The computer system 1500 also includes a main memory 1506, such as a random access memory (RAM) or other dynamic storage device, which is coupled to the bus 1502 for storing information and instructions to be executed by the processor 1504. The main memory 1506 can also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor 1504. The computer system 1500 also includes a read-only memory (ROM) 1508 or other static storage device, which is coupled to the bus 1502 for storing static information and instructions for the processor 1504. A storage device 1510, such as a magnetic disk or optical disk, is provided and coupled to the bus 1502 for storing information and instructions.

[0134] The computer system 1500 can be coupled to a display 1512, such as a cathode ray tube (CRT) or a flat panel or touch panel display, via the bus 1502 for displaying information to a computer user. An input device 1514 including alphanumeric and other keys is coupled to the bus 1502 for communicating information and command selections to the processor 1504. Another type of user input device is a cursor control 1516, such as a mouse, trackball, or cursor direction keys, for communicating direction information and command selections to the processor 1504 and controlling cursor movement on the display 1512. The input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), which allows the device to specify a position in a plane. A touch panel (screen) display can also be used as an input device.

[0135] In response to processor 1504 executing one or more sequences of one or more instructions contained in main memory 1506, one or more methods described herein may be performed by computer system 1500. Such instructions may be read into main memory 1506 from another computer-readable medium such as storage device 1510. Execution of the sequences of instructions contained in main memory 1506 causes processor 1504 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory 1506. In alternative embodiments, hard-wired circuit devices may be used in place of or in combination with software instructions. Therefore, the description herein is not limited to any specific combination of hardware circuit devices and software.

[0136] The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to processor 1504 for execution. Such media can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device 1510. Volatile media include dynamic memory, such as main memory 1506. Transmission media include coaxial cables, copper wires, and optical fibers, including the wires that make up bus 1502. Transmission media can also take the form of sound waves or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, foldable disks, hard disks, magnetic tape, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tape, any other physical media with a pattern of holes, RAM, PROMs and EPROMs, flash EPROMs, any other memory chips or memory cartridges, carrier waves described below, or any other media from which a computer can read.

[0137] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the processor 1504 for execution. For example, the instructions may initially be carried on a disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system 1500 can receive the data on the telephone line and use an infrared transmitter to convert the data into an infrared signal. An infrared detector coupled to the bus 1502 can receive the data carried in the infrared signal and place the data on the bus 1502. The bus 1502 carries the data to the main memory 1506, from which the processor 1504 retrieves and executes the instructions. The instructions received by the main memory 1506 may optionally be stored on the storage device 1510 before or after execution by the processor 1504.

[0138] Preferably, computer system 1500 also includes a communication interface 1518 coupled to bus 1502. Communication interface 1518 provides a bidirectional data communication coupling to network link 1520, which is connected to local network 1522. For example, communication interface 1518 can be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface 1518 can be a local area network (LAN) card to provide a data communication connection with a compatible LAN. A wireless link can also be implemented. In any such implementation, communication interface 1518 sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0139] The network link 1520 typically provides data communication to other data devices through one or more networks. For example, the network link 1520 can provide a connection to a host computer 1524 or data equipment operated by an Internet service provider (ISP) 1526 through a local network 1522. The ISP 1526, in turn, provides data communication services through a global packet data communication network, now commonly referred to as the "Internet" 1528. Both the local network 1522 and the Internet 1528 use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on the network link 1520 and through the communication interface 1518, which carry the digital data to and from the computer system 1500, are exemplary forms of carrier waves that transport the information.

[0140] The computer system 1500 can send messages and receive data, including program code, through the network(s), network link 1520, and communication interface 1518. In the Internet example, server 1530 can send a request code for an application program through Internet 1528, ISP 1526, local network 1522, and communication interface 1518. For example, one such downloaded application can provide one or more of the techniques described herein. The received code can be executed by processor 1504 as it is received, and / or stored in storage device 1510 or other non-volatile storage for later execution. In this way, computer system 1500 can obtain application code in the form of a carrier wave.

[0141] Other embodiments are disclosed in the following numbered clause lists:

[0142] 1. An illumination module for a measuring device, comprising:

[0143] a configurable illumination module operable to provide measurement illumination over a configurable range of illumination angles;

[0144] a grating light valve module for controllably configuring the spectral configuration of the measurement illumination; and

[0145] A controller is operable to control the configurable illumination module and the grating light valve module so that the spectral configuration of the measuring illumination varies according to the illumination angle over the illumination angle range so as to obtain desired detection conditions for detecting diffracted radiation from the diffraction structure generated by measuring the diffraction structure using the measuring illumination.

[0146] 2. An illumination module as defined in clause 1, wherein for each desired wavelength of a plurality of desired wavelengths of said measurement illumination, the desired detection condition comprises substantially filling a detection numerical aperture with a desired diffraction order radiation resulting from said measurement of said diffraction structure.

[0147] 3. An illumination module as defined in clause 2, wherein the controller is operable to simultaneously:

[0148] controlling the configurable illumination module to provide measurement illumination over a range of illumination angles corresponding to a substantially filled detection numerical aperture for each of the plurality of desired wavelengths; and

[0149] The grating light valve module is controlled to select all of the plurality of desired wavelengths for each illumination angle within the illumination angle range for which the desired diffraction order radiation is to be captured within the detection numerical aperture.

[0150] 4. An illumination module as defined in clause 1, wherein the desired detection conditions include detecting, within a detection numerical aperture, only one or more desired diffraction order radiations produced by the measurement of the diffraction structure for each desired wavelength of the measurement illumination, and not detecting any unwanted diffraction order radiations produced by the measurement of the diffraction structure.

[0151] 5. An illumination module as defined in clause 4, wherein the unwanted diffraction order radiation comprises diffraction order radiation higher than a first diffraction order.

[0152] 6. An illumination module as defined in any one of clauses 2 to 5, wherein the desired diffraction order radiation comprises one or more first diffraction orders.

[0153] 7. An illumination module as defined in any one of the preceding clauses, wherein the configurable illumination module comprises a beam steering device for scanning a beam of the measurement illumination over the illumination angle range during measurement.

[0154] 8. An illumination module as defined in clause 7, wherein the controller is operable to vary the spectral configuration of the measurement illumination as a function of the illumination angle during a single scan of the beam of the measurement illumination over the range of illumination angles.

[0155] 9. An illumination module as defined in clause 8, wherein the desired detection condition comprises obtaining an average parameter-of-interest sensitivity magnitude for the measurements, the average parameter-of-interest sensitivity magnitude being greater than 0.5 on a scale between 0 and 1.

[0156] 10. An illumination module as defined in clause 9, wherein the parameter of interest is overlay.

[0157] 11. An illumination module as defined in clause 9 or 10, wherein the controller is operable to control the configurable illumination module and the grating light valve module so as to select only the combination of the spectral configuration and illumination angle of the measurement beam that maximizes the average sensitivity value of the parameter of interest for substantially each illumination angle in the illumination angle range.

[0158] 12. An illumination module as defined in any one of clauses 9 to 11, wherein the controller is operable to control the configurable illumination module and the grating light valve module so as to select, for substantially each illumination angle in the illumination angle range, only the combination of the spectral configuration and illumination angle of the measurement beam associated with the corresponding sensitivity value of the parameter of interest having the same sign.

[0159] 13. An illumination module as defined in clause 12, wherein the controller is operable to select a corresponding spectral configuration from one or more different spectral configurations at an illumination angle during a single scan of the beam of the measured illumination, the illumination angle corresponding to a parameter of interest sensitivity value, the parameter of interest sensitivity value having substantially the same sign in the corresponding parameter of interest sensitivity data for each of the one or more spectral configurations, the parameter of interest sensitivity data describing, for each of the one or more different spectral configurations, a change in the parameter of interest sensitivity with angle.

[0160] 14. An illumination module as defined in clause 13, wherein the one or more different spectral configurations include a first wavelength and a second wavelength, the first wavelength and the second wavelength having corresponding parameter-of-interest sensitivity data that are substantially complementary, such that a positive parameter-of-interest sensitivity region in the parameter-of-interest sensitivity data associated with the first wavelength substantially corresponds in terms of illumination angle to a negative sensitivity region in the parameter-of-interest sensitivity data associated with the second wavelength, and vice versa.

[0161] 15. An illumination module as defined in clause 14, wherein the first wavelength and the second wavelength are separated by a difference, the difference being determined based on a thickness of the diffractive structure and an angle of incidence of the measured illumination on the diffractive structure.

[0162] 16. An illumination module as defined in any one of the preceding clauses, wherein the detection angle range defined by the detection numerical aperture is fixed.

[0163] 17. An illumination module as defined in any of clauses 1 to 15, wherein the detection angle range defined by the detection numerical aperture is variable depending on the illumination angle and / or spectral configuration.

[0164] 18. An illumination module for a measuring device, comprising:

[0165] a beam steering device for scanning the beam of measurement illumination over the illumination angle range during measurement so as to provide measurement illumination over a configurable illumination angle range;

[0166] A color selection module for controllably configuring the spectral configuration of the measurement illumination; and

[0167] A controller is operable to control the beam steering device and the color selection module so that the spectral configuration of the measuring illumination varies according to the illumination angle within the illumination angle range so as to obtain desired detection conditions for detecting diffracted radiation from the diffraction structure generated by measuring the diffraction structure using the measuring illumination.

[0168] 19. An illumination module as defined in clause 18, wherein for each desired wavelength of a plurality of desired wavelengths of said measurement illumination, the desired detection condition comprises substantially filling a detection numerical aperture with a desired diffraction order radiation resulting from said measurement of the diffractive structure.

[0169] 20. An illumination module as defined in clause 19, wherein the controller is operable to:

[0170] controlling the beam steering device to provide measurement illumination over a range of illumination angles corresponding to a substantially filled detection numerical aperture for each of a plurality of desired wavelengths; and

[0171] The color selection module is simultaneously controlled to select, for each illumination angle within the illumination angle range, all of the plurality of desired wavelengths at which the desired diffraction order radiation is to be captured within the detection numerical aperture.

[0172] 21. An illumination module as defined in clause 18, wherein the desired detection conditions include detecting, within a detection numerical aperture, only one or more desired diffraction order radiations produced by the measurement of the diffraction structure for each desired wavelength of the measurement illumination, and not detecting any unwanted diffraction order radiations produced by the measurement of the diffraction structure.

[0173] 22. An illumination module as defined in clause 21, wherein the unwanted diffraction order radiation comprises diffraction order radiation higher than a first diffraction order.

[0174] 23. An illumination module as defined in any one of clauses 19 to 22, wherein the desired diffraction order radiation comprises one or more first diffraction orders.

[0175] 24. An illumination module as defined in any preceding clause, wherein the controller is operable to vary the spectral configuration of the measurement illumination as a function of the illumination angle during a single scan of the beam of the measurement illumination over the range of illumination angles.

[0176] 25. An illumination module as defined in clause 24, wherein the desired detection condition comprises obtaining an average parameter-of-interest sensitivity magnitude of the measurements, the average parameter-of-interest sensitivity magnitude being greater than 0.5 on a scale between 0 and 1.

[0177] 26. An illumination module as defined in clause 25, wherein the parameter of interest is overlay.

[0178] 27. An illumination module as defined in clause 25 or 26, wherein the controller is operable to control the configurable illumination module and the grating light valve module so as to select only the combination of spectral configuration and illumination angle of the measurement beam that maximizes the average sensitivity value of the parameter of interest for substantially every illumination angle in the illumination angle range.

[0179] 28. An illumination module as defined in any one of clauses 25 to 27, wherein the controller is operable to control the beam steering device and the color selection module so as to select only the combination of the spectral configuration and illumination angle of the measurement beam associated with the corresponding sensitivity value of the parameter of interest having the same sign for substantially each illumination angle in the illumination angle range.

[0180] 29. An illumination module as defined in clause 28, wherein the controller is operable to select a corresponding spectral configuration from one or more different spectral configurations at an illumination angle during a single scan of the beam of the measured illumination, the illumination angle corresponding to a parameter of interest sensitivity value, the parameter of interest sensitivity value having substantially the same sign in the corresponding parameter of interest sensitivity data for each of the one or more spectral configurations, the parameter of interest sensitivity data describing, for each of the one or more different spectral configurations, a change in the parameter of interest sensitivity with angle.

[0181] 30. An illumination module as defined in clause 29, wherein the one or more different spectral configurations include a first wavelength and a second wavelength, the first wavelength and the second wavelength having corresponding parameter of interest sensitivity data that are substantially complementary, so that a positive parameter of interest sensitivity region in the parameter of interest sensitivity data associated with the first wavelength substantially corresponds to a negative sensitivity region in the parameter of interest sensitivity data associated with the second wavelength in terms of illumination angle, and vice versa.

[0182] 31. An illumination module as defined in clause 30, wherein the first wavelength and the second wavelength are separated by a difference determined by the thickness of the diffractive structure and by measuring the angle of incidence of the illumination on the diffractive structure.

[0183] 32. An illumination module as defined in any one of clauses 17 to 31, wherein the detection angle range defined by the detection numerical aperture is fixed.

[0184] 33. An illumination module as defined in any of clauses 17 to 31, wherein the detection angle range defined by the detection numerical aperture is variable depending on the illumination angle and / or spectral configuration.

[0185] 34. A method of measuring a diffractive structure using a measurement illumination selectively comprising a plurality of desired wavelengths, the method comprising:

[0186] scanning the beam of measurement illumination over a range of illumination angles corresponding to a substantially filled detection numerical aperture for each desired wavelength of the plurality of desired wavelengths so as to illuminate the diffractive structure; and

[0187] During the scan, for each illumination angle within the illumination angle range, all wavelengths of the plurality of desired wavelengths are selected at which desired diffraction order radiation diffracted by the diffractive structure is to be captured within the detection numerical aperture.

[0188] 35. A method as defined in clause 34, wherein the desired diffraction order radiation comprises one or more first diffraction orders.

[0189] 36. A method as defined in clause 34 or 35, wherein the detection angular range defined by the detection numerical aperture is fixed.

[0190] 37. A method as defined in clause 34 or 35, comprising varying the detection angle range defined by the detection numerical aperture as a function of the illumination angle and / or wavelength.

[0191] 38. A method for measuring a diffraction structure using a measuring radiation, the method comprising:

[0192] scanning the beam of measurement illumination over a range of illumination angles so as to illuminate the diffractive structure; and

[0193] During the scan, for each illumination angle within the illumination angle range, only combinations of spectral configurations of the measurement beam and illumination angles of the measurement beam that are associated with respective sensitivity values ​​of the parameter of interest having the same sign are selected.

[0194] 39. A method as defined in clause 38, wherein the parameter of interest is overlay.

[0195] 40. A method as defined in clause 38 or 39, comprising:

[0196] For each of the one or more different spectral configurations, obtaining corresponding parameter of interest sensitivity data describing a variation of the parameter of interest sensitivity with angle; and

[0197] During a single scan of the beam of the measurement illumination, a corresponding spectral configuration among the one or more different spectral configurations is selected at an illumination angle corresponding to a parameter of interest sensitivity value having substantially the same sign in the corresponding parameter of interest sensitivity data for each of the one or more spectral configurations.

[0198] 41. A method according to claim 40, wherein the one or more different spectral configurations include a first wavelength and a second wavelength, the first wavelength and the second wavelength having corresponding parameter of interest sensitivity data that are substantially complementary, so that a positive parameter of interest sensitivity region in the parameter of interest sensitivity data associated with the first wavelength substantially corresponds to a negative sensitivity region in the parameter of interest sensitivity data associated with the second wavelength in terms of illumination angle, and vice versa.

[0199] 42. A method as defined in clause 41, comprising determining the first wavelength and the second wavelength by the thickness of the diffractive structure and measuring the angle of incidence of light on the diffractive structure.

[0200] 43. A metrology apparatus comprising an illumination module according to any of clauses 1 to 33 or 46 to 52, the illumination module being configured to provide measurement illumination.

[0201] 44. A metrology device as defined in clause 43, wherein the metrology device comprises a scatterometer.

[0202] 45. Measuring equipment as defined in clause 43 or 44, including:

[0203] a support for a substrate;

[0204] an optical system for directing the measurement radiation to the diffractive structure on the substrate; and

[0205] A detector for detecting the measurement radiation scattered by the structure on the substrate.

[0206] 46. ​​An illumination module for a measuring device, comprising:

[0207] a beam steering device operable to scan the beam of measurement illumination over a range of illumination positions on the substrate during measurement;

[0208] an illumination configuration module operable to selectively vary illumination conditions of said beam of said measurement illumination for different said illumination positions during said scan; and

[0209] A controller is operable to control the beam steering device and the illumination configuration module so that the beam of measurement illumination is turned on only for illumination locations within one or more regions of interest on the substrate.

[0210] 47. An illumination module as defined in clause 46, wherein the controller is further operable to control the illumination configuration module to selectively vary the spectrum and / or polarization configuration of the measurement illumination beam for different said illumination positions during said scanning.

[0211] 48. An illumination module as defined in clause 46 or 47, wherein the controller is further operable to control the illumination configuration module to selectively change the spectral and / or polarization configuration of the measurement illumination beam for different said regions of interest during said scanning.

[0212] 49. An illumination module as defined in any one of clauses 46 to 48, wherein the illumination module is configured to measure a target on the substrate, and wherein the cross-sectional diameter of the measurement illumination beam is less than one quarter of the length of the target in any substrate planar dimension.

[0213] 50. An illumination module as defined in any one of clauses 46 to 49, wherein the illumination configuration module comprises a grating light valve module.

[0214] 51. An illumination module as defined in any one of clauses 46 to 50, wherein the beam steering device comprises at least one steerable mirror device.

[0215] 52. An illumination module as defined in any one of clauses 46 to 51, wherein the beam steering device comprises a 2D steerable mirror device or a pair of 1D steerable mirror devices.

[0216] 53. A method for measuring a target on a substrate, the target comprising one or more sub-targets, the method comprising:

[0217] scanning a beam of the measurement illumination over a range of illumination positions on the target during measurement;

[0218] The illumination conditions of the beam of the measurement illumination are selectively changed for different illumination positions during the scan, such that the illumination beam is turned on only for illumination positions within one or more regions of interest.

[0219] 54. A method as defined in clause 53, wherein the region of interest comprises a corresponding central region of the one or more sub-targets.

[0220] 55. A method as defined in clause 53 or 54, comprising selectively varying the spectral and / or polarisation configuration of said beam of measurement illumination for different said illumination positions during said scanning.

[0221] 56. A method as defined in any of clauses 53 to 55, comprising selectively varying the spectral and / or polarisation configuration of said beam of measurement illumination of different said regions of interest during said scanning.

[0222] 57. A method as defined in any one of clauses 53 to 56, wherein said selectively changing the spectral and / or polarization configuration comprises selecting a corresponding different spectral and / or polarization configuration for:

[0223] at least one of the one or more sub-targets for measurement in a first direction in the plane of the substrate, and

[0224] At least one of the one or more sub-targets is used for measurement in a second direction of the substrate plane.

[0225] 58. A method as defined in any one of clauses 53 to 57, wherein the cross-sectional diameter of the illumination beam is less than one quarter of the length of the target in any substrate planar dimension.

[0226] 59. A method as defined in any one of clauses 53 to 58, comprising detecting diffracted and / or scattered radiation from the target resulting from performing the method; and

[0227] At least one parameter of interest is determined from the diffracted and / or scattered radiation.

[0228] 60. A method as defined in clause 59, wherein the parameter of interest is one or more of overlay, dose or focus.

[0229] It should be appreciated that the term color is used herein synonymously with wavelength or spectral component, and that color may include colors outside the visible band (eg, infrared or ultraviolet wavelengths).

[0230] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0231] Although specific reference may have been made above to the use of embodiments of the present invention in the context of optical lithography, it will be appreciated that the present invention may be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern created on the substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate, whereupon the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein.

[0232] The terms "radiation" and "beam" as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength equal to or approximately 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 1 nm to 100 nm), as well as particle beams, such as ion beams or electron beams.

[0233] The term "lens", where the context permits, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components. Reflective components are likely to be used in devices operating in the UV and / or EUV range.

[0234] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. An illumination module for a measuring device, comprising: a beam steering device for scanning the measurement illumination beam over the illumination angle range during measurement so as to provide measurement illumination over the configurable illumination angle range; a color selection module for controllably configuring the spectral configuration of the measurement illumination; as well as A controller is operable to control the beam steering device and the color selection module so that the spectral configuration of the measuring illumination varies according to the illumination angle within the illumination angle range so as to obtain desired detection conditions for detecting diffracted radiation from the diffraction structure generated by measuring the diffraction structure using the measuring illumination.

2. The illumination module of claim 1 , wherein for each desired wavelength of a plurality of desired wavelengths of the measurement illumination, the desired detection condition comprises substantially filling a detection numerical aperture with a desired diffraction order radiation produced by the measurement of the diffractive structure.

3. The illumination module of claim 2, wherein the controller is operable to: controlling the beam steering device to provide measurement illumination over a range of illumination angles corresponding to a substantially filled detection numerical aperture for each of the plurality of desired wavelengths; and The color selection module is simultaneously controlled to select, for each illumination angle within the illumination angle range, all of the plurality of desired wavelengths at which the desired diffraction order radiation is to be captured within the detection numerical aperture.

4. The illumination module of claim 1 , wherein the desired detection conditions include detecting, for each of a plurality of desired wavelengths of the measurement illumination, only one or more desired diffraction order radiations produced by the measurement of the diffraction structure within a detection numerical aperture, and not detecting any unwanted diffraction order radiations produced by the measurement of the diffraction structure.

5. The illumination module of claim 4, wherein the unwanted diffraction order radiation comprises diffraction order radiation higher than a first diffraction order.

6. An illumination module according to any one of claims 2 to 5, wherein the desired diffraction order radiation comprises one or more first diffraction orders.

7. An illumination module according to any preceding claim, wherein the controller is operable to vary the spectral configuration of the measurement illumination as a function of the illumination angle during a single scan of the beam of the measurement illumination within the illumination angle range.

8. The illumination module of claim 7, wherein the desired detection condition comprises obtaining an average parameter-of-interest sensitivity magnitude for the measurements, the average parameter-of-interest sensitivity magnitude being greater than 0.5 on a scale between 0 and 1.

9. The illumination module of claim 8, wherein the parameter of interest is overlay.

10. An illumination module according to claim 8 or 9, wherein the controller is operable to control the configurable illumination module and the grating light valve module so as to select only the combination of the spectral configuration and illumination angle of the measurement beam that maximizes the average parameter of interest sensitivity value for substantially every illumination angle in the illumination angle range.

11. An illumination module according to any one of claims 8 to 10, wherein the controller is operable to control the beam steering device and the color selection module so as to select only the combination of the spectral configuration and illumination angle of the measurement beam associated with the corresponding sensitivity value of the parameter of interest having the same sign for substantially each illumination angle of the illumination angle range.

12. An illumination module according to claim 11, wherein the controller is capable of operating to select a corresponding spectral configuration from one or more different spectral configurations at an illumination angle during a single scan of the beam of the measured illumination, the illumination angle corresponding to a parameter of interest sensitivity value, the parameter of interest sensitivity value having substantially the same sign in the corresponding parameter of interest sensitivity data of each of the one or more spectral configurations, and for each spectral configuration of the one or more different spectral configurations, the parameter of interest sensitivity data describes the change of the parameter of interest sensitivity with angle.

13. The illumination module of claim 12, wherein the one or more different spectral configurations include a first wavelength and a second wavelength having corresponding parameter-of-interest sensitivity data that are substantially complementary, such that a positive parameter-of-interest sensitivity region in the parameter-of-interest sensitivity data associated with the first wavelength substantially corresponds in terms of illumination angle to a negative sensitivity region in the parameter-of-interest sensitivity data associated with the second wavelength, and vice versa.

14. A method of measuring a diffractive structure using a measurement illumination selectively comprising a plurality of desired wavelengths, the method comprising: scanning the beam of measurement illumination over a range of illumination angles corresponding to a substantially filled detection numerical aperture for each desired wavelength of the plurality of desired wavelengths to illuminate the diffractive structure; as well as During the scan, for each illumination angle within the illumination angle range, all wavelengths of the plurality of desired wavelengths are selected at which desired diffraction order radiation diffracted by the diffractive structure is to be captured within the detection numerical aperture.

15. A metrology device comprising an illumination module according to any one of claims 1 to 13, the illumination module being configured to provide measurement illumination.

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