Aberration correction optical system

Abstract

An optical device for aberration correction comprises: a beam dispersion element for spatially dispersing a broadband radiation beam in a first lateral direction; a focusing lens for focusing the broadband radiation beam after said dispersion, wherein said focusing lens is arranged such that the dispersed broadband radiation beam passes through at least one eccentric position of the focusing lens in at least one pass, wherein the eccentric position is a position displaced from the center of the focusing lens in a second transverse direction, and the first transverse direction and the second transverse direction are perpendicular to each other and parallel to the focal plane of the focusing lens; and at least one aberration compensation lens displaced in a second lateral direction relative to at least a portion of the broadband radiation beam to substantially compensate for lateral chromatic aberration.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22200778.3 filed on October 11, 2022, EP application 22217039.1 filed on December 28, 2022, EP application 23150734.4 filed on January 9, 2023, and EP application 23171386.8 filed on May 3, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a broadband optical system for controlling a broadband optical beam, particularly relevant to metrology applications in the manufacture of integrated circuits. Background Art

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

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

[0006] Low-k 1 Photolithography can be used to process features whose size is smaller than the classical resolution limit of the photolithography equipment. In this process, the resolution formula can be expressed as CD = k 1 × λ / NA, where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection optics in the lithographic apparatus, CD is the “critical dimension” (usually the smallest feature size printed, but in this case it is half the pitch), and k 1 is the empirical resolution factor. Usually, k 1The smaller it is, the more difficult it is to reproduce on a substrate a pattern that is similar in shape and size to what the circuit designer planned to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithography projection equipment and / or the design layout. These include, for example, but not limited to, optimization of the NA, customized illumination schemes, the use of phase-shift patterning devices, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also referred to as "optical and process correction") in the design layout), or other methods generally defined as "resolution enhancement technology" (RET). Alternatively, a tight control loop for controlling the stability of the lithography equipment can be used to improve the reproduction of patterns at low k1.

[0007] Metrology tools are used in many aspects of the IC manufacturing process, such as alignment tools for correct positioning of substrates before exposure, leveling tools for measuring the surface topology of substrates, focus control and scatterometry-based tools for checking / measuring exposure and / or etching products in process control. In each case, a radiation source is required. Broadband or white light radiation sources are increasingly used for such metrology applications for a variety of reasons, including robustness and accuracy of measurement. It is desirable to improve existing devices to better control broadband radiation (e.g., multi-wavelength or band selection, wavelength-based intensity control). Summary of the invention

[0008] According to a first aspect of the present invention, there is provided an optical arrangement for aberration correction, the optical arrangement comprising: a beam dispersing element for spatially dispersing a broadband radiation beam in a first lateral direction; a focusing lens for focusing the broadband radiation beam after the above-mentioned dispersion, wherein the above-mentioned focusing lens is arranged so that the dispersed broadband radiation beam passes through at least one eccentric position of the focusing lens in at least one pass, wherein the above-mentioned eccentric position is a position displaced from the center of the focusing lens in a second lateral direction, wherein the first lateral direction and the second lateral direction are perpendicular to each other and parallel to the focal plane of the focusing lens; and at least one aberration compensation lens displaced in the second lateral direction relative to at least a portion of the broadband radiation beam to substantially compensate for lateral chromatic aberration imposed by the focusing lens on at least a portion of the broadband radiation beam.

[0009] According to a second aspect of the invention, there is provided a method for optimizing an optical device according to the first aspect, the method comprising: determining an amount of aberration imposed by a focusing lens on a broadband radiation beam; and displacing at least one aberration compensation lens relative to the broadband radiation beam to impose an amount of reverse aberration on the broadband radiation beam to substantially compensate for the aberration imposed by the focusing lens.

[0010] Other aspects of the present invention include a metrology device comprising the optical device according to the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0012] Figure 1 A schematic diagram of a photolithography apparatus is depicted;

[0013] Figure 2 A schematic diagram of a lithography unit is depicted;

[0014] Figure 3 A schematic diagram depicting holistic lithography shows the collaboration between three key technologies to optimize semiconductor manufacturing;

[0015] Figure 4 depicts a schematic diagram of a scatterometry apparatus for use as a metrology device, which may include a radiation source according to an embodiment of the present invention;

[0016] Figure 5 depicts a schematic diagram of a level sensor apparatus according to an embodiment of the present invention, the level sensor apparatus may include a radiation source;

[0017] Figure 6 depicts a schematic diagram of an alignment sensor apparatus according to an embodiment of the present invention, the alignment sensor apparatus may include a radiation source;

[0018] Fig. 7A Schematic depiction of the transmission of a broadband beam through a singlet lens causing substantial lateral chromatic aberration;

[0019] Figure 7B Schematic depiction of the transmission of a broadband beam through a single lens resulting in substantial axial chromatic aberration;

[0020] Figure 7C Schematic depiction of the transmission of a broadband beam through an achromatic lens resulting in a significant reduction in the amount of chromatic aberration;

[0021] Fig. 8AA top view of a broadband optical device is shown, the arrangement comprising a beam dispersive element for spatially dispersing a broadband light beam and an optical lens for focusing the dispersed broadband light beam into a plurality of focus spots;

[0022] Figure 8B Shows Fig. 8A A side view of a broadband optical device, wherein the dispersed broadband light beam passes through the center of the optical lens in the Y direction;

[0023] Figure 8C Shows Fig. 8A A side view of a broadband optical device, wherein the dispersed broadband light beam passes through an off-center position of an optical lens in the Y direction;

[0024] Fig. 9A FIG. 4 shows different focal spots of different wavelengths in the focal plane of the optical lens when arranged for coaxial focusing in the Y direction (e.g., Figure 8B shown); Fig. 9B shows the different wavelengths λ in the focal plane of the optical lens when arranged for off-axis focusing in the Y direction 1 , 2 , 3 , 4 , 5 of different focal spots (e.g. Figure 8C shown);

[0025] Fig. 10A A top view of a grating light valve (GLV) based wavelength selector configured for zero-order mode operation is shown, wherein a broadband beam passes through an achromatic lens twice in the Y direction at off-center positions;

[0026] Fig. 10B A GLV-based wavelength selector configured for zero-order mode operation (e.g., as Fig. 10A ) and a spot diagram showing a simulated focal spot of the output beam;

[0027] Fig.11 (a) shows a top view of the grating light valve;

[0028] Fig.11 (b) shows a grating light valve in a first configuration (e.g., Fig.11 (a) an end view of the

[0029] Fig.11 (c) shows an end view of the grating light valve in a second configuration;

[0030] Fig.12A side view of a GLV-based wavelength selector and a pattern showing a simulated focal spot of an output beam according to one embodiment is shown, wherein the broadband beam passes through an achromatic lens twice at an off-center position in the Y direction, and the output lens is displaced in the Y direction to optimize the overlapping of the focal spots of the output beams;

[0031] Fig.13 shows a side view of another GLV-based wavelength selector and a pattern showing simulated focal spots of output beams according to one embodiment, wherein the broadband beam passes through the achromatic lens twice, wherein only the second pass is at an off-center position in the Y direction, and the output lens is displaced in the Y direction to optimize the overlap of the focal spots of the output beams; Fig.14 (a) Schematic depiction of an example of a diffraction-based overlay metrology setup;

[0032] Fig.14 (b) is a schematic diagram of illuminating the pupil;

[0033] Fig.14 (c) is a schematic diagram of the detection pupil;

[0034] Fig.14 (d) shows the arrangement of the imaging lenses relative to the four quarters of the detection pupil;

[0035] Fig.14 (e) shows an example image of overlapping objects;

[0036] Fig.15 (a) schematically depicts an example of a diffraction-based overlay metrology setup equipped with four aberration-compensating lenses;

[0037] Fig.15 (b) is a schematic diagram of illuminating the pupil;

[0038] Fig.15 (c) is a schematic diagram of the detection pupil;

[0039] Fig.15 (d) shows the arrangement of four aberration compensation lenses relative to the four quarters of the detection pupil;

[0040] Fig.15 (e) shows an example image of overlapping objects;

[0041] Fig.16 depicts a block diagram of a computer system for controlling a broadband radiation source;

[0042] Fig.17 (a) shows a top view of a first example case where the incident light beam is aimed at the central area of ​​the GLV belt;

[0043] Fig.17 (b) shows a side view of a first example situation in which the incident light beam is aimed at the central area of ​​the GLV belt;

[0044] Fig.17 (c) shows a top view of a second example case where the incident beam is aimed at an off-center position closer to one edge of the GLV tape;

[0045] Fig.17 (d) shows a side view of a second example case where the incident beam is aimed at an off-center position closer to one edge of the GLV tape;

[0046] Fig.18 shows a graph of the measured optical contrast of a GLV versus the relative position or spot offset of the incident light beam with respect to the center of the GLV strip;

[0047] Fig.19 (a) and Fig.19 (b) schematically depicts another example situation in which an elliptical broadband radiation beam is focused to an off-center position closer to one edge of the GLV belt;

[0048] Fig. 20A shows a top view of a GLV-based wavelength selector with reduced sensitivity to misalignment of a broadband radiation beam according to one embodiment;

[0049] Fig. 20B A wavelength selector based on a GLV is shown (e.g., Fig. 20A a side view of the

[0050] Fig.21 Schematically depicts an embodiment beam shaping assembly including a pair of cylindrical lenses;

[0051] Fig. 22 Schematically depicts an embodiment beam shaping assembly including a pair of anamorphic prisms;

[0052] Fig.23 schematically depicts an embodiment beam shaping assembly including an optical fiber having an elliptical core;

[0053] Fig.24A shows a top view of a grating light valve (GLV) based wavelength selector configured for first order mode operation, wherein a broadband beam passes through an achromatic lens twice in the Y direction at off-center positions;

[0054] Fig. 24B A grating light valve (GLV) based wavelength selector (e.g., as shown) configured for first order mode operation is shown. Fig.24A a side view of the

[0055] Fig.24C A GLV-based wavelength selector configured for first-order mode operation (e.g., as Fig.24A or Fig. 24B An example pupil representation of ;

[0056] Fig.25A shows a top view of another GLV-based wavelength selector configured for first-order mode operation, where a broadband beam passes through an achromatic lens twice, where only the second pass is at an off-center position in the Y direction, and the output lens is displaced in the Y direction to optimize overlap of the focal spots of the output beams; and

[0057] Fig.25B A GLV-based wavelength selector configured for first-order mode operation (e.g., as Fig.25A side view shown). DETAILED DESCRIPTION

[0058] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., wavelengths in the range of about 5-100 nm).

[0059] 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 an incident radiation beam with a patterned cross-section corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0060] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to precisely position the patterning device MA according to certain parameters, a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to precisely position the substrate support according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0061] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0062] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof, depending on the exposure radiation used and / or 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 a synonym for the more general term "projection system" PS.

[0063] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g. water) 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.

[0064] 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 "multiple stage" machine, the substrate supports WT may be used in parallel, and / or preparation steps for subsequent exposure of the substrate W 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.

[0065] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measuring table. The measuring table is arranged to accommodate sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measuring table may accommodate a plurality of sensors. The cleaning means may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the 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.

[0066] In operation, a radiation beam B is incident on a patterning device (e.g. a mask MA) which is held on a mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the help of a second positioner PW and a position measurement system IF, the substrate support WT can be moved precisely, for example to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor ( Figure 1 The patterning device MA (not explicitly shown) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The patterning 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 substrate alignment marks P1, P2 as shown 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, they are called scribing alignment marks.

[0067] like Figure 2 As shown, the lithography apparatus LA may form part of a lithography cell LC, sometimes also referred to as a lithography cell or (lithography) cluster, which typically also includes equipment for performing pre-exposure and post-exposure processing on a substrate W. Conventionally, these equipment include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH and a baking plate BK, for example for regulating the temperature of the substrate W, for example for regulating a solvent layer in the resist. A substrate handler or robot RO picks up substrates W from input / output ports I / O1, I / O2, moves them between different processing equipment, and transports the substrates W to a loading area LB of the lithography apparatus LA. The devices in the lithography cell (also often collectively referred to as tracks) are typically controlled by a track control unit TCU, which itself may be controlled by a monitoring system SCS, which may also control the lithography apparatus LA, for example via a lithography control unit LACU.

[0068] In order for the substrate W exposed by the lithography apparatus LA to be correctly and consistently exposed, the substrate needs to be inspected to measure properties of the patterned structure, such as overlay errors between subsequent layers, line thickness, critical dimensions (CD), etc. To this end, an inspection tool (not shown) may be included in the lithography cell LC. If an error is detected, the exposure of subsequent substrates or other processing steps to be performed on the substrate W may be adjusted, particularly if the inspection is performed before other substrates W of the same batch or lot are yet to be exposed or processed.

[0069] The inspection apparatus (which may also be referred to as a metrology apparatus) is used to determine properties of the substrate W, in particular to determine 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 apparatus. The inspection apparatus may measure properties on a latent image (the image in the resist layer after exposure), on a semi-latent image (the image in the resist layer after a post-exposure bake step PEB), on 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).

[0070] Typically, the patterning process in the lithography apparatus LA is one of the most critical steps in the process, which requires high precision in determining the size and placement of structures on the substrate W. To ensure this high precision, the patterning process can be performed in a manner such as Figure 3 Three systems are combined in a so-called "holistic" control environment as shown. One of these systems is a lithography apparatus LA, which is (virtually) connected to a metrology tool MT (a second system) and to a computer system CL (a third system). The key to this "holistic" environment is to optimize the cooperation between these three systems to enhance the overall process window and to provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines a range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device), and process parameters in a lithography process or a patterning process are typically allowed to vary within these parameter ranges.

[0071] The computer system CL can use (a portion of) the design layout to be patterned to predict which resolution enhancement technology to use, and perform computational lithography simulations and calculations to determine which mask layout and lithography equipment settings achieve the maximum overall process window for the patterning process (e.g., Figure 3 Typically, 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 the current operating position of the lithographic apparatus LA within the process window (e.g. using input from a metrology tool MT) to predict whether defects (e.g. due to suboptimal processing) may exist. Figure 3 (as indicated by the arrow pointing to “0” in the second scale SC2).

[0072] 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 drifts, e.g. in the calibration state of the lithographic apparatus LA (e.g. Figure 3(as shown by the multiple arrows in the third scale SC3).

[0073] In the lithography process, it is necessary to frequently measure the created structures, for example for process control and verification. The tool used to perform such measurements is generally referred to as a measurement tool MT. Different types of measurement tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer measurement tools MT. A scatterometer is a versatile instrument that can measure parameters of a lithography process by having a sensor in the pupil of a scatterometer objective or in a plane conjugated to the pupil, generally referred to as pupil-based measurement, or by having a sensor in an image plane or in a plane conjugated to the image plane, in which case the measurement is generally referred to as image-based or field-based measurement. Such scatterometers and related measurement techniques are further described in patent applications US20100328655, US2011102753A1, US20120044470A, US20110249244, US20110026032 or EP1,628,164A, the entire contents of which are incorporated herein by reference. The scatterometers described above can measure gratings using light from soft x-rays and visible to near IR wavelength ranges.

[0074] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, reconstruction methods can be applied to the measurement signals to reconstruct or calculate the properties of the grating. For example, such a reconstruction can be achieved 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 a real target.

[0075] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer MT, radiation emitted by a radiation source is directed onto a target, and reflected or scattered radiation from the target is directed to a spectrometer detector which measures the spectrum of the specularly reflected radiation (i.e. a measure of the intensity as a function of wavelength). From these data, the structure or profile of the target that gave rise to 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.

[0076] 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 in each polarization state. Such a measurement device emits polarized light (such as linear, circular or elliptical) by using appropriate polarization filters in the illumination portion of the measurement device. A source suitable for the measurement device can 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, the entire contents of which are incorporated herein by reference.

[0077] In one embodiment of the scatterometer MT, the scatterometer MT is suitable for measuring the overlap of two misaligned gratings or periodic structures by measuring the reflection spectrum and / or an asymmetry in the detection configuration, the asymmetry being related to the degree of overlap. The two (usually overlapping) grating structures can be applied to two different layers (not necessarily continuous layers) and can be formed at substantially the same position on the wafer. The scatterometer can have a symmetrical detection configuration, such as described in co-owned patent application EP1,628,164A, so that any asymmetry can be clearly distinguished. This provides a method for directly measuring misalignment in the grating. Other examples of measuring the overlap error between two layers containing a periodic structure as a target by means of the asymmetry of the periodic structure can be found in PCT patent application publication number WO 2011 / 012624 or in US patent application US20160161863, the entire contents of which are incorporated herein by reference.

[0078] Other parameters of interest may be focus and dose. Focus and dose may be determined simultaneously by scatterometry (or alternatively by scanning electron microscopy), as described in U.S. Patent Application US2011-0249244, the entire contents of which are incorporated herein by reference. A single structure may be used that has a unique combination of critical dimension and sidewall angle measurements for each point in the focus energy matrix (FEM, also referred to as the focus exposure matrix). If these unique combinations of critical dimensions and sidewall angles are available, focus and dose values ​​may be uniquely determined from these measurements.

[0079] The metrology target can be a collection of composite gratings formed by a lithography process, mainly in resist, but also after an etching process. Typically, the pitch and line width of the structures in the gratings strongly depend on the measurement optics (particularly the NA of the optics) in order to be able to capture the diffraction orders from the metrology target. As mentioned before, the diffraction signal can be used to determine the offset between two layers (also called "overlay") and can also be used to reconstruct at least a portion of the original grating produced by the lithography process. This reconstruction can be used to provide guidance on the quality of the lithography process and can be used to control at least a portion of the lithography process. The target can have smaller sub-divisions that are configured to mimic the size of a functional portion of the design layout in the target. Due to this sub-division, the behavior of the target will be more similar to the functional portion of the design layout, so that the overall process parameter measurement better resembles the functional portion of the design layout. The target can be measured in an unfilled mode or an overfilled mode. In the unfilled mode, the spot generated by the measurement beam is smaller than the entire target. In the overfilled mode, the spot generated by the measurement beam is larger than the entire target. In this overfilled mode, different targets can also be measured simultaneously, so that different process parameters can be determined simultaneously.

[0080] The overall measurement quality of a lithography parameter using a particular target is at least partially determined by the measurement configuration used to measure the lithography parameter. The term "substrate measurement configuration" may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns measured, or both. For example, if the measurement used in the substrate measurement configuration is a diffraction-based optical measurement, the one or more parameters measured may include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, and the like. For example, one of the criteria for selecting a measurement configuration may be the sensitivity of one of the measurement parameters to process variations. More examples are described in U.S. patent application US2016-0161863 and the disclosed U.S. patent application US 2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0081] Measurement devices such as scatterometers Figure 4 It comprises a broadband (white light) radiation projector 2 which projects radiation onto a substrate 6. The reflected or scattered radiation is passed to a spectrometer detector 4 which measures the spectrum 10 of the specularly reflected radiation (i.e. a measure of the intensity as a function of wavelength). From these data, the processing unit PU can reconstruct the structure or profile that gave rise to the detected spectrum, for example by rigorous coupled wave analysis and nonlinear regression, or by comparing it with Figure 3The simulated spectral library shown at the bottom is used for comparison. Typically, for the reconstruction, the general form of the structure is known and some parameters are assumed based on knowledge of the process used to make the structure, leaving only a few parameters of the structure to be determined from the scatterometry data. Such a scatterometer can be configured as either a normal-incidence scatterometer or an oblique-incidence scatterometer.

[0082] The overall measurement quality of the lithography parameters achieved by measuring the measurement target is at least partially determined by the measurement configuration scheme used to measure the lithography parameters. The term "substrate measurement configuration scheme" may include one or more parameters of the measurement itself, one or more parameters of the one or more patterns measured, or both. For example, if the measurement used in the substrate measurement configuration scheme is a diffraction-based optical measurement, the one or more parameters measured may include the wavelength of the radiation, the polarization of the radiation, the angle of incidence of the radiation relative to the substrate, the orientation of the radiation relative to the pattern on the substrate, etc. For example, one of the criteria for selecting the measurement configuration scheme may be the sensitivity of one of the measurement parameters to process variations. More examples are described in U.S. patent application US2016 / 0161863 and the disclosed U.S. patent application US 2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0083] Another metrology tool used in IC manufacturing is a topography measurement system, level sensor or height sensor. Such a tool can be integrated into a lithography apparatus for measuring the topography of a substrate (or wafer). A topography map (also called a height map) of the substrate can be generated based on these measurements to indicate the height of the substrate based on the position on the substrate. The height map can then be used to correct the position of the substrate during pattern transfer on the substrate so as to provide an aerial image of the patterned device at an appropriate focus position on the substrate. It will be understood that in this case, "height" refers to a dimension that is substantially beyond the plane of the substrate (also called the Z axis). Typically, the level or height sensor measures at a fixed position (relative to its own optical system), and the relative motion between the substrate and the optical system of the level or height sensor results in height measurements at different locations on the substrate.

[0084] Examples of level or height sensors LS known in the art are Figure 5 As schematically shown in Figure 5Only the operating principle is illustrated. In this example, the level sensor comprises an optical system comprising a projection unit LSP and a detection unit LSD. The projection unit LSP comprises a radiation source LSO, which provides a radiation beam LSB applied by a projection grating PGR of the projection unit LSP. The radiation source LSO can be, for example, a narrowband or broadband light source, such as a supercontinuum light source, polarized or non-polarized, pulsed or continuous, such as a polarized or non-polarized laser beam. The radiation source LSO may include a plurality of radiation sources with different colors or wavelength ranges, such as a plurality of LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation, but may additionally or alternatively include UV and / or IR radiation and any wavelength range suitable for reflection from the substrate surface.

[0085] The projection grating PGR is a periodic grating comprising a periodic structure that generates a radiation beam BE1 with a periodically varying intensity. The radiation beam BE1 with a periodically varying intensity is directed to a measurement position MLO on the substrate W at an incident angle ANG between 0 and 90 degrees, typically between 70 and 80 degrees, relative to an axis (Z axis) perpendicular to the incident substrate surface. At the measurement position MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and directed to the detection unit LSD.

[0086] In order to determine the height level at the measuring position MLO, the level sensor further comprises a detection system comprising a detection grating DGR, a detector DET and a processing unit (not shown) for processing an output signal of the detector DET. The detection grating DGR may be identical to the projection grating PGR. The detector DET generates a detector output signal indicative of the received light, for example indicating the intensity of the received light, such as a photodetector, or representing the spatial distribution of the received intensity, such as a camera. The detector DET may comprise any combination of one or more detector types.

[0087] By means of triangulation techniques the height level at the measurement position MLO can be determined. The detected height level is usually related to the signal intensity measured by the detector DET, which has a periodicity that depends inter alia on the design of the projection grating PGR and the (tilted) angle of incidence ANG.

[0088] The projection unit LSP and / or the detection unit LSD may comprise further optical elements such as lenses and / or mirrors (not shown) along the path of the patterned radiation beam between the projection grating PGR and the detection grating DGR.

[0089] In one embodiment, the detection grating DGR may be omitted and the detector DET may be placed where the detection grating DGR is located. This configuration provides a more direct detection of the image of the projection grating PGR.

[0090] In order to effectively cover the surface of the substrate W, the level sensor LS may be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of spots or measurement areas MLO covering a larger measurement range.

[0091] Various general types of height sensors are disclosed, for example, in US7265364 and US7646471, both of which are incorporated herein by reference. A height sensor using UV radiation rather than visible or infrared radiation is disclosed in US2010233600A1, which is incorporated herein by reference. In WO2016102127A1, which is incorporated by reference, a compact height sensor is described that uses a multi-element detector to detect and identify the position of a grating image without the need for a detection grating.

[0092] Another metrology tool used in IC manufacturing is the alignment sensor. Therefore, a key aspect of the performance of a lithographic apparatus is the ability to correctly and accurately place the applied pattern relative to features laid down in previous layers (either by the same apparatus or by a different lithographic apparatus). To this end, one or more sets of marks or targets are provided on the substrate. Each mark is a structure whose position can be measured later using a position sensor, typically an optical position sensor. The position sensor may be referred to as an "alignment sensor" and the mark may be referred to as an "alignment mark".

[0093] The lithographic apparatus may include one or more (e.g., multiple) alignment sensors, by which the positions of alignment marks provided on the substrate can be accurately measured. The alignment (or position) sensor can obtain position information from alignment marks formed on the substrate using optical phenomena such as diffraction and interference. An example of an alignment sensor currently used in lithographic apparatus is based on a self-referencing interferometer described in US6961116. Various enhancements and modifications of position sensors have been developed, for example, as disclosed in US2015261097A1. The contents of all these publications are incorporated herein by reference.

[0094] Figure 6 is a schematic block diagram of an embodiment of a known alignment sensor AS, such as described in US6961116, which is incorporated herein by reference. A radiation source RSO provides a radiation beam RB of one or more wavelengths, which is steered by steering optics onto a mark, such as a mark AM located on a substrate W, as an illumination spot SP. In this example, the steering optics include a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP for illuminating the mark AM may be slightly smaller than the width of the mark itself.

[0095] Radiation diffracted by the alignment mark AM is collimated (in this example via the objective lens OL) into a beam IB carrying the information. The term "diffraction" is intended to include the zeroth order diffraction from the mark (which may be referred to as reflection). A self-referencing interferometer SRI (e.g., of the type disclosed in the aforementioned US6961116) causes the beam IB to interfere with itself, after which the beam is received by a photodetector PD. If the radiation source RSO produces multiple wavelengths, additional optics (not shown) may be included to provide separate beams. The photodetector may be a single element, or, if desired, may comprise a plurality of pixels. The photodetector may comprise an array of sensors.

[0096] The steering optics comprising a spot mirror SM in this example can also be used to block zero-order radiation reflected from the mark so that the information-carrying beam IB comprises only high-order diffracted radiation from the mark AM (which is not necessary for the measurement but can improve the signal-to-noise ratio).

[0097] The intensity signal SI is provided to the processing unit PU. By a combination of optical processing in block SRI and computational processing in unit PU, values ​​of the X and Y position on the substrate relative to the reference system can be output.

[0098] A single measurement of the type shown only fixes the position of the mark within a certain range corresponding to one pitch of the mark. A coarser measurement technique is used in conjunction with this to identify which period of the sine wave contains the mark position. The same process at a coarser level and / or a finer level can be repeated at different wavelengths to increase accuracy and / or robustly detect the mark regardless of the material the mark is made of and the material on and / or below which the mark is placed. The wavelengths can be multiplexed and demultiplexed optically for simultaneous processing, and / or they can be multiplexed by time or frequency division.

[0099] In this example, the alignment sensor and the spot SP remain stationary, while the substrate W moves. Thus, the alignment sensor can be rigidly and accurately mounted to a reference frame, while effectively scanning the mark AM in a direction opposite to the direction of movement of the substrate W. The substrate W is controlled in this movement by mounting it on a substrate support and by a substrate positioning system that controls the movement of the substrate support. A substrate support position sensor (e.g., an interferometer) measures the position of a substrate support (not shown). In one embodiment, one or more (alignment) marks are provided on the substrate support. Measurement of the position of the marks provided on the substrate support allows calibration of the position of the substrate support determined by the position sensor (e.g., relative to a frame connected to the alignment system). By measuring the position of the alignment marks provided on the substrate, the position of the substrate relative to the substrate support can be determined.

[0100] A measurement tool MT (such as a scatterometer, a topography measurement system or a position measurement system as described above) may perform measurements using radiation originating from a radiation source. The characteristics of the radiation used by the measurement tool may affect the type and quality of measurements that can be performed. For some applications, it may be advantageous to use multiple radiation frequencies to measure a substrate, for example broadband radiation may be used. Multiple different frequencies may be able to propagate, illuminate and scatter the measurement target without interfering with or with minimal interference with other frequencies. Thus, for example, different frequencies may be used to acquire more measurement data simultaneously. Different radiation frequencies may also be able to query and discover different characteristics of the measurement target. Broadband radiation may be used for a measurement system MT, such as a level sensor, an alignment mark measurement system, a scattering measurement tool or an inspection tool. The broadband radiation source may be a supercontinuum source.

[0101] In many applications (such as the above-mentioned metrology applications), broadband optical systems are often used to transmit broadband output radiation from a broadband radiation source to an application plane (e.g., a wafer plane). In addition to achieving efficient (or low-loss) transmission of broadband radiation, such optical systems can also be configured to control or adjust one or more characteristics of the broadband output radiation to obtain, for example, a desired lateral beam profile, a desired temporal profile, and / or a desired spectral profile.

[0102] Broadband optical systems can include a variety of different reflective (e.g., optical mirrors) and / or transmissive (e.g., optical lenses) optical elements that are generally optimized for reflecting or transmitting broadband output radiation. For example, each optical element can include one or more optical coatings that have high transmittance (in the case of a transmissive optical element) or high reflectivity (in the case of a reflective optical element) at least within the wavelength range of the broadband output radiation. However, due to the effects of material absorption and / or dispersion, when the spectral coverage of the broadband output radiation becomes sufficiently wide, the optical element (particularly the transmissive optical element) may not maintain its designed performance. As a result, such performance degradation of the optical element may result in optical losses and / or distortions, and thereby in changes in the characteristics of the broadband output radiation, which is undesirable for downstream applications. Here, material dispersion refers to the fact that the refractive index of the transmissive optical element varies with the wavelength of light.

[0103] An example type of optical distortion is chromatic aberration, which occurs when a broadband light beam is focused using an optical lens. There are two types of chromatic aberration: lateral (or transverse) chromatic aberration and axial chromatic aberration, which are Fig. 7A and Figure 7B As shown. Fig. 7A As shown, when different wavelengths λ 1 , 2 , 3Lateral aberration occurs when the wavelengths (e.g. blue, green and red wavelengths) are focused at different lateral positions in the focal plane FP of the optical lens LEN. Lateral shifts in focus due to wavelength variations occur when the beams are parallel and overlapping but incident at an angle not equal to zero. 2 It can correspond to the design (or nominal) wavelength of the lens LEN when it is designed and manufactured. Therefore, the wavelength λ 2 The wavelengths λ are focused at the coaxial position L2 (i.e., on the optical axis OA) in the focal plane FP, while other wavelengths λ are focused at the coaxial position L2 (i.e., on the optical axis OA) in the focal plane FP, and other wavelengths λ are focused at the coaxial position L2 in the focal plane FP, while other wavelengths λ are focused at the coaxial position L2 in the focal plane FP, and other wavelengths λ are focused at the coaxial position L 1 and λ 3 Focusing at different positions L1 and L3 in the focal plane FP. Figure 7B As shown, when different wavelengths λ 1 ',λ 2 ',λ 3 When focusing along the optical axis OA' of the optical lens LEN' at different axial positions L1', L2', and L3', axial aberration occurs. 1 ',λ 2 ',λ 3 ' corresponds to different focal lengths. Here, the focal length is defined as the distance between the lens and the focal position. In this example, the wavelength λ 2 ' can correspond to the design (or nominal) wavelength of the lens LEN' when it is designed and manufactured. Therefore, the wavelength λ 2 The focal position L2' of the lens LEN' is close enough to the designed focal position, and due to the influence of the material dispersion of the lens LEN', other wavelengths λ 1 ',λ 3 ''s focal position deviates further from the designed focal position.

[0104] Although both types of chromatic aberration can occur simultaneously, lateral chromatic aberration is usually observed at short focal lengths, while axial chromatic aberration is usually observed at long focal lengths. Fig. 7A and Figure 7B The optical lenses LEN, LEN' shown are both single lenses made of one optical glass. In order to minimize or correct chromatic aberration and other aberrations (e.g., spherical aberration), achromatic lenses (or achromat) have been developed and are now widely used in optical systems. An achromatic lens is a composite lens in which two or more materials with different refractive indices and different dispersions are assembled together. Figure 7CThe focusing of a broadband light beam by an example achromatic lens ALEN is schematically illustrated. The example achromatic lens ALEN is formed by assembling (e.g., optically bonding) two lens elements LA and LB together. Such a two-element achromatic lens ALEN is also referred to as an achromatic doublet lens. The two lens elements LA and LB can be made of, for example, crown glass and flint glass, respectively. Figure 7C As shown, compared with a single lens (e.g., Fig. 7A and Figure 7B Compared to the above, the combination of the two lens elements LA and LB can reduce or minimize both lateral and axial chromatic aberrations, and thus the corresponding wavelength λ 1 ”、λ 2 ”、λ 3 The focal positions L1", L2", and L3" of "are closer to each other and also closer to the designed (or nominal) positions. Although chromatic aberration is effectively reduced in the case of coaxial focusing (e.g., Figure 7C ), but the off-axis performance of the achromat may not be acceptable. This is probably due to the fact that the achromat ALEN is corrected to have zero lateral and longitudinal primary aberrations at two wavelengths. At other wavelengths, the achromat ALEN still has (much smaller) aberrations, called secondary colors, which may cause focus shifts in the focal plane FP. More details will be given below in reference Figure 8A-8C and Figure 9A-9B Give a description.

[0105] Fig. 8A and Figure 8B The top view and the side view of the broadband optical device are shown respectively, the arrangement includes a beam dispersive element DE (e.g., a prism) configured to spatially disperse the broadband light beam and an optical lens OL (e.g., a lens) configured to focus the dispersed broadband light beam into a plurality of focal spots. Figure 7C The broadband optical device is configured so that the broadband light beam is spatially dispersed in the X direction and all wavelengths of the beam pass through the center position of the optical lens OL in the Y direction (or through a coaxial position in the Y direction). Fig. 9A shows the different wavelengths λ in the focal plane FP of the optical lens OL when arranged for coaxial focusing in the Y direction. 1 , 2 , 3 , 4 , 5 Since the performance (e.g., chromatic aberration) of the optical lens OL is optimized (e.g., minimized) for coaxial focusing, the different wavelengths λ 1 , 2 , 3 , 4 , 5The position difference between different focal spots in the Y direction is minimized or negligible. 1 , 2 , 3 , 4 , 5 The plurality of focal spots of the optical lens OL form a straight focal line substantially in the X direction. However, due to spatial dispersion in the X direction, some wavelengths of the broadband light beam (e.g., at the periphery of the dispersed light beam) pass through the eccentric position of the optical lens OL in the X direction and thus experience greater chromatic aberration than wavelengths passing through the central position of the optical lens OL in the X direction (or along the path of the optical axis OA of the optical lens OL). Therefore, different wavelengths λ 1 , 2 , 3 , 4 , 5 The position difference between the different focal spots in the X direction is suboptimal (or not minimized).

[0106] Figure 8C Broadband optical devices (e.g., Fig. 8A or Figure 8B ) in which the dispersed broadband light beam passes through an off-center position of the optical lens OL, which is offset in the Y direction relative to the optical axis OA of the optical lens OL by a distance D. This means that the dispersed broadband light beam passes through an off-center position of the optical lens OL in the Y direction and is therefore smaller than Figure 8B The on-axis focus scene shown experiences higher chromatic aberration. Fig. 9B shows the different wavelengths λ in the focal plane FP of the optical lens OL when arranged for off-axis focusing in the Y direction. 1 , 2 , 3 , 4 , 5 For example, Figure 8C As shown in the off-axis focusing, the larger the offset distance D is (or the closer the beam is to the periphery of the optical lens OL), the stronger the aberration the beam will experience. 2 and λ 4 ) or the wavelength on the optical axis OA (e.g., λ 3 ) is relatively far from the optical axis OA of the optical lens (e.g., λ 1 and λ 5 ) has a larger displacement or offset in the Y direction. Therefore, different wavelengths λ 1 , 2 , 3 , 4 , 5Multiple focal spots of different wavelengths λ form curved focal lines in the XY plane. 1 , 2 , 3 , 4 , 5 The position difference of different focal spots in the X direction is similar to the position difference of the coaxial focus scene (for example, Fig. 9A Note that different wavelengths λ 1 , 2 , 3 , 4 , 5 The multiple focal spots can be moved to opposite sides of the X axis (or Fig. 9B shown moving downward rather than upward, and they may not be symmetrical about the Y axis).

[0107] In many applications, it may be necessary to intentionally allow a broadband beam to pass through an off-center position of the optical lens OL, such as Figure 8C The off-axis focusing scenario shown allows the broadband beam to pass through the optical lens OL two or more times. This multi-pass arrangement eliminates the need for any additional lenses (e.g., additional collimating lenses for collimating the focused broadband beam), thereby reducing the total number of optical elements in the optical system, leading to lower cost and more compact system design. However, in order to do this, off-axis chromatic aberration should be better managed or compensated.

[0108] Assume that the optical lens is an achromatic doublet consisting of two lens elements LA and LB (e.g. Figure 7C As shown), the Y-axis displacement of the focal spot is dy dC It can be concluded as follows [JM Geary's "Introduction to Lens Design with Practical Examples", published by Willmann-Bell GmbH, 2002, incorporated herein by reference]:

[0109]

[0110] Where y represents the y-axis offset of the beam entry position relative to the lens optical axis (e.g., Figure 8C The offset D) shown, V d represents the Abbe number relative to the Fraunhofer d line; and Respectively represent the refractive power of lens element LA and lens element LB; P dCrepresents the partial dispersion ratio of the lens element. To reduce or minimize off-axis aberrations, an apochromat can be used. The portion between the brackets of equation [1] is considered to be apochromatic, and usually requires an additional lens element, i.e. at least three lens elements, rather than a two-element achromatic lens (e.g., Figure 7C ). Note that while apochromatic doublets do exist (in the visible range), they require specific glass selection. The required glass is more difficult to polish and has a lower refractive index, resulting in greater curvature. This limits focal length and results in greater spherical aberration (i.e., spherical aberration caused by wavelength changes). Therefore, a three-lens element solution is usually preferred.

[0111] Due to the aging issues of conventional cemented optical lenses, in which two or more lens elements are cemented together, it is preferred and advantageous to design and manufacture multi-element lenses in such a way that any two adjacent lens elements are connected with an air spacer. Transmission efficiency is one of the important parameters of a multi-element optical lens, and therefore it is desirable to use as few lens elements as possible. This is because a larger number of lens elements means a larger number of air-glass interfaces, and thus a higher transmission loss through the lens elements. It has also been found to be very difficult to design and manufacture apochromatic lenses that operate over a desired broadband wavelength (e.g., from 400nm to 1600nm). For example, many of the special glasses required to manufacture apochromatic lenses are typically very soft and therefore difficult to manufacture. In addition, when the target wavelength range is too wide (e.g., from 400nm to 1600nm), it is very challenging and sometimes impossible to fully compensate for the dispersion of multiple lens elements of different glasses. Note that for simplicity, in the following paragraphs, the term "achromatic lens" specifically refers to an achromatic lens or an achromatic doublet lens having two lens elements.

[0112] The purpose of the present disclosure is to provide an effective and more practical method to solve the above-mentioned problems. According to a first aspect of the present disclosure, an optical device for aberration correction is provided, the optical device comprising: a beam dispersion element for spatially dispersing a broadband radiation beam in a first lateral direction; a focusing lens for focusing the broadband radiation beam after the above-mentioned dispersion, wherein the above-mentioned focusing lens is arranged so that the dispersed broadband radiation beam passes through at least one eccentric position of the focusing lens in at least one pass, wherein the above-mentioned eccentric position is a position displaced from the center of the focusing lens in a second lateral direction, wherein the first lateral direction and the second lateral direction are perpendicular to each other and parallel to the focal plane of the focusing lens; and at least one aberration compensation lens displaced in the second lateral direction relative to at least a portion of the broadband radiation beam to substantially compensate for the lateral chromatic aberration imposed by the focusing lens on at least a portion of the broadband radiation beam.

[0113] In one embodiment, the optical device may include a spectral configuration element configured to selectively transmit, diffract or reflect at least a portion of a broadband radiation beam, the at least a portion of the broadband radiation beam comprising one or more wavelengths of the broadband radiation beam. In one embodiment, the spectral configuration element may include a grating light valve (GLV) comprising a configurable diffractive structure for selectively reflecting or diffracting a broadband radiation beam incident thereon into at least a portion of the broadband radiation beam. Thus, at least a portion of the broadband radiation beam may be a spectrally shaped beam that has been modulated by the GLV, for example.

[0114] The following embodiments are described with respect to a wavelength selection device based on GLV technology. However, it should be understood that the basic concept on which all embodiments are based can be used in many other different applications.

[0115] As an example and reference Fig. 10A and Fig. 10B , an example wavelength selector (also referred to as a color selection module or source selection module) is configured to focus a broadband beam off-axis and subsequently captured by a single achromatic lens L2. The example wavelength selector uses GLV technology, such as sold by Silicon Light Machines (SLM) and described in US6947613B, which is incorporated herein by reference. GLV is an electrically programmable diffraction grating based on micro-electromechanical systems (MEMS) technology.

[0116] Fig.11 (a)- Fig.11 (c) Diagram showing the working principle. Fig.11 (a)- Fig.11 (c) are schematic diagrams of a GLV pixel or component 500 from above and from the end, respectively. Note that Fig.11 (a)- Fig.11 The GLV assembly shown in (c) is only an example design, and other different GLV designs (e.g., the "real GLV" design used in the G1088 and G8192 modules sold by SLM) may also be used Fig. 10A and Fig. 10B The GLV assembly includes two types of alternating GLV reflective ribbons: static ribbons or bias ribbons 510, which are typically grounded together with a common electrode, and drive ribbons or active ribbons 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 (e.g., a 1D or 2D array). The active ribbons and bias ribbons may be substantially identical except for the way they are driven. When no voltage is applied to the active ribbons 520, they are coplanar with the bias ribbons, such as Fig.11(b) The GLV essentially acts as a mirror, and incident light is specularly reflected (i.e., forms specularly reflected radiation or zero diffraction order radiation). When a voltage is applied to the active strip 520, as shown in FIG. Fig.11 (c) , they are deflected relative to the bias band 510 to form a square well diffraction grating. In this state, the incident light is diffracted into a fixed diffraction angle. By controlling the voltage on the active band 520, the ratio of reflected light to diffracted light can be continuously changed, which controls their deflection magnitude. Therefore, the amount of light diffracted by the GLV can be controlled in an analog manner from zero (full specular reflection) to all incident light (zero specular reflection). In the context of the present disclosure, this control of the amount of reflected radiation relative to the amount of radiation diffracted to non-zero diffraction orders can be referred to as modulated illumination.

[0117] The GLV module can be used in zero-order mode, thereby blocking / discarding diffracted radiation and using specularly reflected (zero-order diffracted) radiation. This has the advantage of maintaining etendue. Therefore, an aperture stop or beam block can be provided in the pupil plane of the GLV or its conjugate, with the aim of maximizing transmission of the zero-order and maximizing blocking (minimizing transmission) of the first (and other diffracted) orders.

[0118] Reference again Fig. 10A and Fig. 10B In the exemplary wavelength selector, the broadband light beam emitted from the broadband light source LS is dispersed in the X direction by a beam dispersive element DE, which may be, for example, a prism or a grating. The dispersion of the broadband light beam is achieved based on the principle that the direction of the light emitted from the beam dispersive element DE is related to the wavelength. Before being dispersed by the beam dispersive element DE, the broadband light beam may be dispersed by a first optical lens L 1 Then, the dispersed broadband beam is collimated by the second optical lens L 2 Focusing on the zone of GLV, GLV is basically located at the second lens L 2 The beam dispersive element DE and the second optical lens L 2 The layout and Figure 8C That is, the dispersed broadband light beam passes through the first eccentric position Y1 in the Y direction (reference Fig. 10B in the coordinate system).

[0119] Due to the off-axis chromatic aberration, the focal spots of different wavelengths of the broadband beam may form a curved focal line on the GLV (e.g. Fig. 9B), where each focal position (or focal spot) corresponds to a certain wavelength. The GLV can be configured in zero-order mode and is operable to apply a certain spatial modulation to the focused broadband beam so as to selectively reflect the desired wavelength and diffract the undesired wavelengths. In some embodiments, the GLV can be operated in a wavelength selection mode to select only one or more selected wavelengths. That is, the GLV bands corresponding to the selected wavelengths can be set to equal heights so that they act as standard reflectors for the selected wavelengths. The other bands are actuated in a manner to form a grating so that the undesired wavelengths incident on these bands are diffracted into higher diffraction orders, such as -1 and +1 diffraction orders. These higher diffraction orders are then blocked or discarded by beam blocks BL1 and BL2, respectively. The GLV can also be operated in an intermediate mode to form a grating that partially reflects and partially diffracts the incident radiation, thereby attenuating but not completely blocking specific wavelengths. The degree of attenuation can be controlled by the zonal configuration. In this way, the spectral composition of the output radiation can be controlled.

[0120] The spatially modulated reflected (zero-order) radiation from the GLV is reflected by the second optical lens L 2 Capture, where the spatially modulated beam passes through lens L at a second eccentric position Y2 in the Y direction 2 The spatially modulated beam is recombined on the return path using the same dispersive element DE as used to disperse the beam on the outward path. The return path within the dispersive element DE may be substantially parallel to the outward path and displaced in the Y direction relative to the outward path. The recombined beam is directed by a steering mirror SM to a third optical lens L 3 , the third optical lens L 3 Acts as an output lens and focuses the light beam into the measurement device MET; for example via a suitable optical fiber, such as a single-mode photonic crystal fiber.

[0121] refer to Fig. 10B , the pattern SPD1 shows a plurality of simulated focal spots of the output beam, each focal spot corresponding to a different wavelength of the output beam. The positions of the plurality of focal spots can be mainly determined by the second optical lens L 2 The applied lateral chromatic aberration is determined by the lateral chromatic aberration. When the light beam has no aberration (e.g., lateral chromatic aberration) and passes through the third optical lens L 3 Ideally, the focal spots should substantially overlap each other in the center of (i.e., coaxial focusing). However, since both passes through the second optical lens L at an eccentric position, 2 , the output beam is not aberration-free, so the focal spots are spatially displaced relative to each other. When this spatial displacement is the same as or larger than the core diameter of the transmission fiber, some wavelengths may not be coupled into the fiber, resulting in significant coupling losses and distortion of the spectrum of the output beam.

[0122] refer to Fig.12, one embodiment of a wavelength selector may include Fig. 10A and Fig. 10B The same optical elements as shown. The second optical lens L 2 It can also be arranged so that the broadband beam passes through the lens twice at corresponding different eccentric positions (e.g., Y1 and Y2 positions) in the Y direction. 2 The aberrations imposed, especially lateral chromatic aberration, the third optical lens L 3 The third optical lens L may be displaced in the Y direction relative to the output beam to apply an appropriate amount of counter-aberration (e.g., lateral chromatic aberration) to the output beam. 3 The output beam may be directed in a transverse plane perpendicular to the path of the output beam (e.g. Fig.12 Therefore, the difference in the positions of multiple focal spots of the output beam is minimized, such as Fig.12 In other words, the focal spots of the output beams substantially overlap each other. Note that due to off-axis focusing, the focal spots of the dispersed broadband beam may form a curve on the GLV (e.g., Figure 8C and Fig. 9B ). In some extreme cases, the focal lines may be too curved to be properly spatially modulated by the GLV.

[0123] refer to Fig.13 Another embodiment of the wavelength selector can be arranged so that the broadband beam passes through the lens twice, where only the second pass (or return pass) is in the Y direction at an off-center position (e.g., Y3 position). In this embodiment, the GLV can be rotated relative to the incident beam to allow the reflected spatially modulated radiation to pass through the second lens L at the off-center position Y3. 2 Due to on-axis focusing (on the first or outward pass), the focal spot of the dispersed broadband beam can be formed into a straight line on the GLV. This can help maintain the efficiency of the GLV and also relax the tolerances on the optical alignment of the GLV. Fig.12 Similar to the embodiment shown, the third optical lens L 3 The output beam may be displaced in the Y direction relative to the output beam to apply an appropriate amount of negative aberration (e.g., lateral chromatic aberration) to the output beam. Thus, the differences in the positions of the multiple focal spots of the output beam are minimized, such as Fig.13 The pattern SPD3 is shown in the figure.

[0124] for Fig.12 and Fig.13 The two embodiments shown are as follows: 3 Instead of or in addition to applying reverse aberration, the first optical lens L 1The optical beam can be displaced in the Y direction relative to the broadband beam to introduce an appropriate amount of aberration (e.g., lateral chromatic aberration) to fully or partially pre-compensate for the optical aberration caused by the second optical lens L. 2 The lateral chromatic aberration is applied. 3 In the case of being arranged for coaxial focusing, the first optical lens L 1 The magnitude of the lateral chromatic aberration applied can be substantially equal to that imposed by the second optical lens L 2 In the case where the third optical lens is configured for off-axis focusing (eg, displaced in the Y direction relative to the output beam), the lateral chromatic aberration imposed by the first optical lens L 1 and the third optical lens L 3 The combined amplitude of the lateral chromatic aberration applied can be substantially equal to that imposed by the second optical lens L 2 The goal of aberration compensation can be to minimize the position difference between the focal spots of the output beams so that the third optical lens L 3 The focal spots of the light beams are then substantially overlapped with each other. 2 The displacement of the first optical lens L 1 and / or a third optical lens L 3 The displacement may be in the opposite manner (eg, in the opposite direction). Referring again to Fig.12 , the first optical lens L 1 can be displaced to substantially minimize the curvature of the focal line on the GLV, and the third optical lens L 3 can be displaced to minimize the positional differences of the multiple focal spots of the output beam. This example implementation may have an allowable ratio Fig.13 The advantage of the smaller (and therefore cheaper) achromatic lens L2 employed in the embodiment of FIG. 1 is that the embodiment can only reduce or minimize the curvature of the focal line on the GLV, which means that the focal line on the GLV may still be slightly curved (or have residual non-linearity). In contrast, the dispersed broadband radiation is allowed to pass through the second optical lens L 2 The center of the GLV (on its first pass) can eliminate the curvature and thereby produce a straight focal line on the GLV.

[0125] The broadband radiation beam may include a spectrum that partially overlaps with a range of 200nm to 2000nm or a range of 400nm to 1600nm. In one embodiment, the broadband radiation beam may include a spectrum from 200nm to 2000nm. In one embodiment, the broadband radiation beam may include a spectrum from 500nm to 900nm. The broadband radiation beam may include a spectrum with a full width at half maximum (FWHM) width of at least 500nm, at least 300nm, at least 200nm.

[0126] According to a second aspect of the present disclosure, there is provided a method for optimizing an output beam of the optical device of the first aspect. The method comprises: determining an amount of aberration imposed by a focusing lens on a broadband radiation beam; and displacing at least one aberration compensation lens relative to the broadband radiation beam to impose an amount of reverse aberration on the broadband radiation beam to substantially compensate for the aberration imposed by the focusing lens.

[0127] In one embodiment, at least one aberration compensation lens may be an output lens located downstream of the focusing lens, and the step of determining the amount of aberration may include: simulating or measuring one or more positions of the output radiation at the focal plane of the output lens; and determining the wavelength-dependent variation of the one or more positions of the output radiation; and calculating the amount of aberration based on the determined wavelength-dependent variation of the one or more positions of the output radiation.

[0128] In one embodiment, at least one aberration compensation lens may include one or both of the following: an output lens located downstream of the focusing lens, and an input lens located upstream of the beam dispersive element, the method comprising: displacing one or both of the input lens and the output lens to the above-mentioned amount of reverse aberration, the output lens located downstream of the focusing lens and the input lens located upstream of the beam dispersive element, the method further comprising: displacing the input lens to apply a second amount of reverse aberration, which second amount of reverse aberration combined with the amount of reverse aberration applied by the output lens is substantially equal to the amount of aberration applied by the focusing lens.

[0129] It should be understood that the above embodiments are provided to illustrate the proposed concepts and are not intended to limit the scope of the present disclosure. Of course, other embodiments can be envisioned.

[0130] For example, the concept of displacing one optical lens relative to the beam to compensate for the aberration imposed by another optical lens can be applied to diffraction-based metrology devices. Diffraction-based overlay metrology using dark-field imaging of diffraction orders can make 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, the entire contents of which are incorporated herein by reference.

[0131] Fig.14 (a) Schematically illustrates an example of a diffraction-based overlay metrology apparatus. As shown, an overlay target OT (e.g., a micro-diffraction-based overlay μDBO target) on a wafer WA is illuminated using a quarter illumination mask that defines an illumination NA consisting of two diagonally opposite quarters (e.g., the upper left quarter and the lower right quarter). The other two diagonally opposite quarters (e.g., the upper right quarter and the lower left quarter) are used for detection and define the detection NA. Fig.14(b) is a schematic diagram of the illumination pupil IP of the device, with the grey quarter used for illumination and the black quarter used for detection. In this example device, radiation scattered from the overlapping target OT, including the +1, -1 and (optionally) zero diffraction orders, is collected by the objective lens OB and then transmitted through the intermediate lens assembly including the first lens L1 and the second lens L2. The 4-part wedge assembly WG is placed at the detection pupil plane of the device and is arranged to redirect each diffraction order (including the captured zeroth order) to a corresponding different optical path and thus to a corresponding different detector plane position. Fig.14 (c) is an exemplary schematic diagram of the detection pupil of the device, where the upper left corner and the lower right corner of the detection pupil only contain the zero diffraction order, and the upper right corner and the lower left corner only contain the -1 and +1 diffraction orders. If the overlapping target OT includes an X-pad (having a grating aligned in the X direction) and a Y-pad (having a grating aligned in the Y direction), each pad can generate a -1 diffraction order and a +1 diffraction order, as shown in FIG. Fig.14 (c) is shown. Then, the imaging lens IL focuses all diffraction orders onto the image sensor IS. This arrangement is able to image +1, -1 and zero orders simultaneously.

[0132] Fig.14 (d) shows the corresponding area of ​​the imaging lens IL for imaging the four quarters of the detection pupil onto the image sensor IS. Fig.14 (e) shows an example image of an overlapping target OT captured by the image sensor IS. In the detection image, the X slice and the Y slice are adjacent to each other. If aberrations are present, there will be XY crosstalk between these slices, which will negatively affect the overlap retrieval results. One set of aberration factors is due to the -1 and +1 diffraction orders passing through the high NA (edge) regions of the lens, where the lens quality or performance is expected to be worse than the low NA parts (see above for details). Figure 8C off-axis aberration). Fig.14 The dashed boxes in mark the locations where the diffraction orders pass through the high NA (edge) regions of the lens.

[0133] In order to compensate for off-axis aberrations, it is suggested to replace the imaging lens IL before the image sensor IS with four separate imaging lenses IL1-IL4 (acting as aberration compensation lenses), each of which is arranged to focus on a quarter of the detection pupil. Fig.15 (a) schematically illustrates an example implementation of the proposed method. Fig.14 Compared to the example shown in (a), the only change is the replacement of the single imaging lens with four separate imaging lenses IL1-IL4. Fig.15 (b) Fig.15 (c) and Fig.15 (e) respectively Fig.14(b) Fig.14 (c) and Fig.14 (e) Similar. Fig.15 (a) and Fig.15 As shown in (d), the four imaging lenses IL1-IL4 can be individually displaced laterally relative to their corresponding quarters so that the corresponding radiation in each quarter of the detection pupil passes through the edge region of the corresponding lens IL1, IL2, IL3, IL4 in a manner opposite to the other lenses of the device. Here, lateral displacement refers to displacement in a lateral plane perpendicular to the optical axis of the device. For example, lens IL1 can be displaced laterally relative to the lower left quarter of the detection pupil so that the radiation in this quarter passes through the upper right region of lens IL1. The direction of the lateral displacement of lens IL1 can be determined based on the fact that the same radiation passes through the lower left region of each other lens in the device (e.g., lenses OB, L2, L1). The lateral displacement amounts and optical properties (e.g., focal lengths) of the four lenses can be selected so that they compensate for aberrations caused by diffraction orders passing through high NA regions of other lenses (e.g., lenses OB, L2, L1).

[0134] In many applications, the performance of a GLV-based wavelength selector depends on the optical contrast of the GLV. The optical contrast of the GLV is the ratio between the power of radiation selected by the GLV when the active strips are applied with a first voltage corresponding to actuation of the strips up to one quarter of the corresponding wavelength (e.g., to provide minimum specular reflection or maximum diffraction for an incident light beam) and the power of radiation selected by the GLV when the active strips of the GLV are applied with a second voltage setting all strips to equal height (e.g., to provide maximum specular reflection or minimum diffraction for an incident light beam). For example, Fig. 10A and Fig. 10B The wavelength selector shown is configured to utilize radiation selectively reflected by the GLV and block radiation diffracted by the GLV. In this configuration, the optical contrast can be defined as the ratio between the maximum reflected power obtained without applied bias and the minimum reflected power with applied bias. The higher the optical contrast of the GLV, the better the performance of the wavelength selector.

[0135] It has been found that wavelength selectors based on GLVs (e.g. Fig. 10A , Fig. 10B The optical contrast of the GLV tape (as shown) is very sensitive to the alignment of the incident light beam on the GLV tape (e.g., relative to the center region of the GLV tape). Typically, when a bias voltage is applied, the GLV tape is not flat near its two edges (defining the length of each tape). Therefore, the center region of the GLV tape can refer to the area where the tape is substantially flat along the length of each tape.

[0136] Fig.17(a) and Fig.17 (b) schematically depicts a first example case where the incident beam OB is aligned on the central region of the GLV strip. Fig.17 As shown in (a), each GLV strip extends along the Y direction (i.e., along the length of each strip), and the periodicity of the GLV strips is along the X direction (i.e., along the direction perpendicular to the length of each strip). Fig.17 (a) and Fig.17 In the example of (b), it can be seen that the beam OB is incident on the flat central region of the GLV strip, and is therefore sufficiently far from the strip edge RE where the strip is no longer flat. Therefore, the beam OB will receive the best phase modulation provided by the GLV strip, and thus the optical contrast of the GLV can reach its maximum value. In contrast, Fig.17 (c) and Fig.17 (d) schematically depicts a second example case where the incident beam OB is aimed at an off-center position closer to one edge RE of the GLV tape. In this example, a portion of the beam OB is incident on the curved edge region of the GLV tape and will therefore be subject to a different or suboptimal phase modulation provided by the GLV tape than another portion of the beam OB that is incident on the flat center region of the GLV tape. Fig.17 (a) and Fig.17 Compared to the example in (b), the optical contrast of the GLV will be lower.

[0137] Fig.18 A graph of the measured optical contrast OC of the GLV is shown as a function of the relative position of the incident light beam OB relative to the center of the GLV strip, or spot offset SO. The GLV is configured to selectively reflect the incident light beam OB. As shown, the measured optical contrast OC reaches a peak at a position where the incident light beam OB coincides with the center of the strip (i.e., the spot offset SO between the light beam and the center of the strip is zero, ΔX=0). This is consistent with Fig.17 (a) corresponds to the example case shown. As the spot offset SO increases, the measured optical contrast OC decreases rapidly. In the case of a non-zero spot offset, for example, corresponding to Fig.17 (c) shows an example case of ΔX = -D, where the measured optical contrast is significantly below the maximum. Therefore, it is desirable to reduce the sensitivity of the GLV to the alignment of the incident beam.

[0138] refer to Fig.19, it is suggested that as the width of the incident light beam OB along the Y direction or along the length of each strip is reduced, the optical contrast of the GLV is less sensitive to the misalignment of the light beam OB. In other words, as the light beam OB moves away from the center of the GLV strip and toward either edge of the GLV strip (i.e., as the spot offset SO increases), the optical contrast of the GLV decreases more slowly. This advantageous effect may be due to the fact that when the light beam is misaligned along the Y direction, the light beam OB having a smaller beam size in the Y direction is less likely to reach the non-flat edge region RE of the strip. Based on this concept, embodiments of the method and apparatus are disclosed below.

[0139] According to a third aspect of the present disclosure, an optical device is provided, the optical device comprising: a beam shaping component for receiving a substantially circular broadband radiation beam and outputting an elliptical broadband radiation beam having a short axis along a first transverse direction and a long axis along a second transverse direction; a dispersive element for spatially dispersing the elliptical broadband radiation beam in the first transverse direction; and a focusing lens for focusing the elliptical broadband radiation beam after the above-mentioned dispersion, wherein the above-mentioned focusing lens is arranged so that the dispersed elliptical broadband radiation beam passes through at least one eccentric position of the focusing lens in at least one pass. wherein the above-mentioned eccentric position is a position displaced from the center of the focusing lens in the second lateral direction, wherein the first lateral direction and the second lateral direction are perpendicular to each other and parallel to the focal plane of the focusing lens; and a grating light valve, which includes a configurable diffraction structure, which is used to selectively reflect or diffract a focused elliptical broadband radiation beam incident thereon into at least a portion of the elliptical broadband radiation beam, wherein the grating light valve is arranged so that the configurable diffraction structure extends along the first lateral direction; and wherein the above-mentioned beam dispersion element is also arranged to recombine at least a portion of the elliptical broadband radiation beam into an output beam.

[0140] Fig. 20A A top view of a GLV-based wavelength selector with reduced sensitivity to misalignment of a broadband radiation beam is shown according to one embodiment. Fig. 20B A wavelength selector based on a GLV is shown (e.g., Fig. 20A side view shown). Fig. 20A The wavelength selector shown may include Fig. 10A All optical elements of the wavelength selector shown. Note that for simplicity, the same reference numerals are used in all figures to represent the same optical elements. In addition, Fig. 20A The wavelength selector shown may further comprise a beam shaping assembly BE configured to receive a substantially circular broadband radiation beam and output an elliptical broadband radiation beam having its minor axis and its major axis. The minor axis and the major axis of the elliptical beam may coincide with the X' direction and the Y' direction, respectively, with reference to Fig. 20AThe beam shaping component BE may be located upstream of the beam dispersive element DE, for example somewhere between the steering mirror SM and the beam dispersive element DE, or at the first optical lens L 1 Somewhere between and the light source LS.

[0141] In one embodiment, the beam shaping assembly BE may be arranged such that the diameter on the minor axis (also referred to as the shortest diameter) of the elliptical broadband radiation beam is substantially the same as the diameter of the circular broadband radiation beam. The diameter on the major axis (also referred to as the longest diameter) of the elliptical broadband radiation beam may be 2, 4, 6, 8 or 10 times the diameter of the circular broadband radiation beam (and hence the diameter on the minor axis of the elliptical beam). When such an elliptical broadband radiation beam is dispersed by the beam dispersive element DE and then focused onto the GLV by the achromatic lens, the resulting focused spots may each have an elliptical beam shape with the longest diameter along the X direction and the shortest diameter along the Y direction (e.g., as Fig.19 For each focused elliptical spot, the diameter along the X direction may be 2, 4, 6, 8, or 10 times greater than the diameter along the Y direction. In one embodiment, the longest diameter of the focused elliptical spot on the GLV may be substantially the same or similar to the diameter of the focused circular spot (e.g., as shown in FIG. Fig.17 (a) or Fig.17 (c)), the focused circular spot corresponds to the case where the GLV-based wavelength selector does not include a beam shaping component BE (e.g., Fig. 10A This arrangement can allow each focused elliptical spot to cover a sufficient number (e.g., 2, 4, 6, 8 or more) of GLV bands to obtain good grating phase modulation performance.

[0142] refer to Fig.21 In one embodiment, the beam shaping assembly BE1 may include a pair of cylindrical lenses, namely a first cylindrical lens CL1 and a second cylindrical lens CL2. The first cylindrical lens CL1 and the second cylindrical lens CL2 may be arranged to increase the diameter d1 of the broadband radiation beam along the Y direction. In one embodiment, the first cylindrical lens CL1 and the second cylindrical lens CL2 may be arranged to substantially maintain the diameter d1 of the broadband radiation beam along the X direction. In one embodiment, the first cylindrical lens CL1 may be a plano-concave lens, and the second cylindrical lens CL2 may be a plano-convex lens, wherein the plano-concave lens is located upstream of the plano-convex lens. The beam shaping assembly BE1 may output an elliptical broadband radiation beam, wherein the longest diameter d2 is along the Y direction, and the shortest diameter d1 is along the X direction.

[0143] refer to Fig. 22In one embodiment, the beam shaping assembly BE2 may include a pair of prisms, namely, a first prism PM1 and a second prism PM2, which are arranged to increase the diameter d1 of the broadband radiation beam along the Y direction. In one embodiment, the first prism PM1 and the second prism PM2 may be arranged to substantially maintain the diameter d1 of the broadband radiation beam along the X direction. In one embodiment, the first prism PM1 may be a first deformed prism, and the second prism PM2 may be a second deformed prism. In one embodiment, the first deformed prism and the second deformed prism may be the same. Fig. 22 As shown, a circular broadband radiation beam can enter the first prism PM1 (in the YZ plane) from the first surface at a Brewster angle and can leave the first prism PM1 from the second surface at a normal angle. The broadband radiation beam can then pass through the second prism PM2 in the same manner. While the first prism PM1 can change the beam radius / diameter on one axis alone, the second prism PM2 helps manipulate the ellipticity of the radiation beam while maintaining the original propagation direction. The beam shaping assembly BE2 can output an elliptical broadband radiation beam with the longest diameter d2 along the Y direction and the shortest diameter d1 along the X direction.

[0144] refer to Fig.23 In one embodiment, the beam shaping assembly BE3 may include a fiber bundle FB including a plurality of optical fibers (e.g., a circular to linear fiber bundle sold by THORLABS). At an input end IE of the fiber bundle, the plurality of optical fibers may be arranged in a circular configuration to receive a circular broadband radiation beam. At an output end OE of the fiber bundle, the plurality of optical fibers may be arranged in a linear configuration to output an elliptical broadband radiation beam. In one embodiment, each of the plurality of optical fibers may be a multimode optical fiber having a substantially circular core. In one embodiment, the beam shaping assembly BE3 may also include one or more optical lenses arranged to further adjust or modulate the beam parameters of the elliptical broadband radiation beam before the elliptical broadband radiation beam is dispersed by the beam dispersing element DE.

[0145] In one embodiment, the beam shaping assembly BE may include an elliptical beam mask (beammask) arranged to shape the circular broadband radiation beam to generate an elliptical broadband radiation beam. Unlike the above-described embodiments of the beam shaping assemblies BE1-BE3, the elliptical beam mask (not shown) may be located upstream of the first optical lens, for example, between the light source LS and the first optical lens. In one embodiment, the elliptical beam mask may be in the form of a plate with an elliptical hole, which is arranged to directly define the output beam shape by blocking a portion of the input circular beam. In one embodiment, the elliptical beam mask may be in the form of an optical fiber with an elliptical core (e.g., an elliptical core optical fiber sold by IVG fiber).

[0146] The GLV module may be used in a first order mode, thereby blocking / discarding specularly reflected (zeroth order diffraction) radiation, and using first order diffraction radiation (e.g., +1 and -1 orders). Thus, an aperture stop or beam block may be provided in the pupil plane of the GLV or its conjugate, with the goal of maximizing the transmission of one or two first orders, and maximizing the blocking of the zeroth order (minimizing its transmission).

[0147] Although a GLV-based wavelength selector configured for zero-order mode operation (e.g., Fig. 10A and Fig. 10B The zero-order configuration can provide good wavelength selection performance, but it may be difficult to achieve the high out-of-band spectral suppression ratio (or blocking ratio) required by many applications, such as Figures 4 to 6 is used as a radiation source in the measurement tool shown. Here, the out-of-band spectral suppression ratio is defined as the ratio of the intensity of the out-of-band leakage light to the intensity of the in-band light. The terms "out-of-band" and "in-band" correspond to unwanted (or blocked) colors and wanted (selected) colors, respectively. With this zero-order mode configuration, there will always be a small but significant amount of unwanted (one or more) colors (or out-of-band light) leaking into the output illumination beam. For example, when configured in zero-order mode, it is difficult (if not impossible) to reduce the leakage to significantly below 0.1% (i.e., typically at least 0.1% of the incident radiation is reflected from the GLV areas, and the GLV areas are configured to diffract / block all incident radiation on these areas). This out-of-band leakage is typically caused by incident light being reflected by the gaps between the GLV bands and / or the protective window in front of the GLV chip, and propagating in essentially the same direction as the selected zero-order diffracted light. For measurement applications, this leakage should be at least one order of magnitude smaller than this, i.e. a suppression of at least four orders of magnitude smaller than the full signal (at most 0.01%).

[0148] Configuring a GLV strip to form a grating with sufficiently high diffraction efficiency to achieve 0.01% or better leakage is difficult or impossible because there is always a gap between the strip and the protective window in front of the GLV chip, which causes unwanted light to be reflected. To address this limited diffraction efficiency, and thus the out-of-band rejection problem, it is recommended to invert the configuration so that diffracted radiation (e.g., first order, although other non-zero orders can also be used) is used, and specular zeroth order radiation is rejected; that is, to configure the GLV device in "first-order mode". In this configuration, diffraction efficiency becomes less critical; while some diffraction inefficiency may represent some (wanted) radiation loss, it will not affect out-of-bound rejection. Little or no radiation incident on a region of the GLV configured to reflect away radiation will be diffracted in the same direction(s) as the desired first order(s), so out-of-bound rejection will be very good.

[0149] Fig.24A and Fig. 24B An example of a GLV-based wavelength selector configured for first-order mode operation is illustrated. Fig.24A is a top view of the device. Fig. 24B is a side view of the device. In this example, the wavelength selector is configured for first-order mode operation; that is, to transmit the source beam SB (e.g., a broadband beam) and the first diffraction order (for clarity, only two colors +1 are shown) selectively diffracted by the GLV module when interacting with the broadband beam λ1 、+1 λ2 , -1 λ1 , -1 λ2 , both colors are chosen by the GLV; of course, there can be more and / or a continuous spectrum), and the zeroth diffraction order 0 is blocked λ1 , 0 λ2 More specifically, in the depicted example, two wavelengths are shown as being transmitted through the device λ 1 , 2 (i.e., both are selected by GLV), the resulting diffraction order is +1 λ1 , -1 λ1 、+1 λ2 , -1 λ2 , which is formed by the lens L 3 The beam block BL is arranged in the pupil plane and is arranged to maximally block the zeroth diffraction order 0 λ1 , 0 λ2 , and maximally transmit one or two first diffraction orders.

[0150] Many components such as Fig. 10A and Fig. 10B has been described, and will not be repeated. Fig.24C is the pupil plane representation P1 , which comprises a zero-order stop BL positioned to block only the zeroth order (specular radiation), thereby defining an aperture AP that transmits the first order (and / or other higher orders) 1 .

[0151] As previously mentioned, the beam block BL should maximize the transmission of the zero-order beam (for all selected wavelengths) and minimize the transmittance of the first-order beam for all wavelengths, and vice versa. Given the constraints of the arrangement and the required trade-offs, maximizing transmission (e.g., transmission of a diffracted, e.g., first-order beam or zero-order beam for all wavelengths) should be understood to mean increasing the transmission as much as possible to re-minimize the transmission of blocked radiation. Similarly, under these same constraints and trade-offs, minimizing transmission (e.g., transmission of the zero-order or first-order for all wavelengths) should be understood to mean blocking these orders as much as possible. In particular, the spots have spatially overlapping tails (if a plot of the intensity or amplitude of each spot versus the pupil position is considered), which makes it necessary to pass some unwanted light (resulting in poor out-of-band contrast) or block the tail of the desired zero-order, resulting in a reduced signal and thus a reduced throughput. The larger these spots are compared to the separation of the orders (i.e., the larger the NA of the beam), the more severe this problem is.

[0152] In one embodiment, maximizing transmission may include transmitting 90% or more, 95% or more, 98% or more, 99% or more, 99.9% or more, or 99.99% or more of the transmitted radiation. In one embodiment, minimizing transmission may include blocking 90% or more, 95% or more, 98% or more, 99% or more, 99.9% or more, or 99.99% or more of the blocked radiation.

[0153] Although providing higher spectral contrast, first-order mode configurations (e.g. Fig.24A and Fig. 24B ) have similar chromatic aberration-inducing problems as the zero-order mode configuration (e.g. Fig. 10A and Fig. 10B That is, different wavelengths will cause different aberrations in the wavelength selector, which will lead to wavelength-dependent misalignment on the GLV module and the output beam at the output lens L. 3 The wavelength-dependent change in the position of the focal plane. Fig. 24B , the broadband beam passes through the second optical lens L twice at eccentric positions (e.g., Y1 and Y2 positions) in the Y direction 2 The broadband beam passes through the lens L for the first time. 2 The chromatic aberration introduced during the process causes the focal spots of different wavelengths of the incident light beam to form curved focal lines on the GLV (e.g., Fig. 9B), where each focal position (or focal spot) corresponds to a specific wavelength. Such curved focal lines may negatively affect the spatial modulation of the GLV module. In addition, the first diffraction order passes through the second lens L for the second time. 2 This introduces further chromatic aberration into the output beam. 3 When focusing the light beam into the measurement device MET, for example via a suitable optical fiber, such as a single-mode photonic crystal fiber, the wavelength-dependent position variation of the output beam will lead to high coupling losses at the fiber.

[0154] Therefore, it is recommended to Fig.12 and Fig.13 The same aberration correction concept of the illustrated embodiment is applied to a wavelength selector configured for first order mode operation; that is, at least one aberration compensation lens of the wavelength selector is displaced relative to the broadband radiation beam to impart an amount of reverse aberration on the broadband radiation beam to substantially compensate for the aberration caused by the focusing lens (e.g., the second optical lens L) of the wavelength selector. 2 ) is imposed by the aberration. Continue to refer to Fig. 24B In one embodiment, in order to compensate for the second optical lens L 2 The aberrations imposed (particularly lateral chromatic aberration), the third optical lens L 3 can be displaced in the Y direction relative to the output beam to apply an appropriate amount of reverse aberration (e.g., lateral chromatic aberration) to the output beam. Thus, the differences in the positions of the multiple focal spots of the output beam are minimized in a manner similar to Fig.12 The pattern SPD2 is shown in the figure.

[0155] Fig.25A and Fig.25B Another GLV-based wavelength selector configured for first-order mode operation is shown, where the broadband beam passes through the achromatic lens L twice. 2 , only the second pass is in the Y direction at an off-center position (e.g., Y3 position). Fig.25A is a top view of the device. Fig.25B In this embodiment, the GLV module can be rotated relative to the incident beam to allow the reflected spatially modulated radiation to pass through the second lens L at an off-center position Y3. 2 Thanks to on-axis focusing (on the first or outward pass), the focal spot of the dispersed broadband beam can be formed into a straight line on the GLV. This can help maintain the efficiency of the GLV module and also relax the tolerance of the optical alignment of the GLV module. Fig.12 and Fig.13 Similar to the embodiment shown, the third optical lens L 3can be displaced in the Y direction relative to the output beam to apply an appropriate amount of reverse aberration (e.g., lateral chromatic aberration) to the output beam. Thus, the differences in the positions of the multiple focal spots of the output beam are minimized in a manner similar to Fig.13 The pattern SPD3 is shown in the figure.

[0156] It should be understood that the use of a beam shaping component BE (e.g., Figure 20A-20B and Figure 21-23 The concept of shaping a broadband radiation beam such that the optical contrast of a GLV module is less sensitive to misalignment of the incident beam is also applicable to wavelength selectors configured for first-order mode operation (e.g., as Figure 24A-24B or Figure 25A-25B The technical effect of using a beam shaping assembly BE in a wavelength selector configured for first-order mode operation will be substantially the same as that in a wavelength selector configured for zero-order mode operation.

[0157] Fig.15 1 is a block diagram illustrating a computer system 1500 that can help implement the methods and processes disclosed herein. The computer system 1500 includes a bus 1502 or other communication mechanism for transmitting 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, coupled to the bus 1502 to store 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 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 to store information and instructions.

[0158] The computer system 1500 may 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 to display information to a computer user. An input device 1514, including alphanumeric and other keys, is coupled to the bus 1502 to communicate 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, which is used to communicate direction information and command selections to the processor 1504 and to control 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 may also be used as an input device.

[0159] One or more methods as described herein may be performed by computer system 1500 in response to processor 1504 executing one or more sequences of one or more instructions contained in main memory 1506. Such instructions may be read into main memory 1506 from another computer-readable medium such as storage device 1510. Execution of the sequence of instructions contained in main memory 1506 causes processor 1504 to perform the processing steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequence of instructions contained in main memory 1506. In alternative embodiments, hard-wired circuitry 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 circuitry and software.

[0160] 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 a variety of 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, flexible disks, hard disks, magnetic tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tapes, any other physical media with hole patterns, RAM, PROMs and EPROMs, FLASH-EPROMs, any other memory chips or cartridges, carrier waves described below, or any other media that a computer can read.

[0161] Various forms of computer readable media may be involved in carrying one or more sequences of instructions to processor 1504 for execution. For example, the instructions may initially be stored on a disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system 1500 may 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 bus 1502 may receive the data carried in the infrared signal and place the data on bus 1502. Bus 1502 transfers the data to main memory 1506, from which processor 1504 retrieves and executes the instructions. The instructions received by main memory 1506 may optionally be stored on storage device 1510 before or after execution by processor 1504.

[0162] The computer system 1500 also preferably includes a communication interface 1518 coupled to the bus 1502. The communication interface 1518 provides a bidirectional data communication coupling with a network link 1520 connected to a local network 1522. For example, the 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, the communication interface 1518 can be a local area network (LAN) card to provide a data communication connection to a compatible LAN. A wireless link can also be implemented. In any such implementation, the communication interface 1518 sends and receives electrical, electromagnetic or optical signals carrying digital data streams representing various types of information.

[0163] The network link 1520 typically provides data communication to other data devices through one or more networks. For example, the network link 1520 may provide a connection to a host computer 1524 or to 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, as well as the signals on the network link 1520 and the signals through the communication interface 1518, are exemplary forms of carrier waves that transport the information, and these signals carry the digital data to and from the computer system 1500.

[0164] 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 the requested code of the application through Internet 1528, ISP 1526, local area network 1522, and communication interface 1518. For example, one such download application can provide one or more of the techniques described herein. The received code can be executed by processor 1504 when received, and / or stored in storage device 1510 or other non-volatile memory for later execution. In this way, computer system 1500 can obtain application code in carrier wave form.

[0165] Additional embodiments are disclosed in the following list of numbered clauses:

[0166] 1. An optical device for aberration correction, comprising:

[0167] a beam dispersing element for spatially dispersing the broadband radiation beam in a first lateral direction;

[0168] a focusing lens for focusing the broadband radiation beam after the dispersion, wherein the focusing lens is arranged such that the dispersed broadband radiation beam passes through at least one off-center position of the focusing lens in at least one pass, wherein the off-center position is a position displaced from a center of the focusing lens in a second transverse direction, wherein the first transverse direction and the second transverse direction are perpendicular to each other and parallel to a focal plane of the focusing lens; and

[0169] At least one aberration compensating lens is displaced in the second lateral direction relative to at least a portion of the broadband radiation beam to substantially compensate for lateral chromatic aberration imposed by the focusing lens on the at least a portion of the broadband radiation beam.

[0170] 2. An optical device according to clause 1, arranged so that the broadband radiation beam passes through an off-center position of the at least one aberration compensation lens.

[0171] 3. An optical device according to clause 2, arranged such that the decentered position of the at least one aberration compensation lens compensates the at least one decentered position of the focusing lens in terms of lateral chromatic aberration.

[0172] 4. The optical device according to any of the preceding clauses further comprises a spectral configuration element, which is configured to selectively transmit, diffract or reflect at least a portion of the broadband radiation beam, wherein the at least a portion of the broadband radiation beam includes one or more wavelengths of the broadband radiation beam.

[0173] 5. An optical device according to clause 4, wherein the spectral configuration element is substantially located at the focal plane of the focusing lens.

[0174] 6. An optical device according to claim 5, wherein the spectral configuration element comprises a grating light valve, the grating light valve comprising a configurable diffraction structure, the configurable diffraction structure being used to selectively reflect or diffract the broadband radiation beam incident thereon into at least a portion of the broadband radiation beam.

[0175] 7. An optical device according to clause 6, wherein the grating light valve is configured to selectively diffract the incident broadband radiation beam so that at least a portion of the broadband radiation beam includes at least one higher diffraction order selectively diffracted by the grating light valve.

[0176] 8. An optical device according to clause 7, wherein the at least one higher diffraction order comprises one or both of the first (+1 and -1) diffraction orders.

[0177] 9. An optical device according to clause 7 or 8, further comprising a beam block disposed in a pupil plane and arranged to maximally block the zeroth diffraction order from the grating light valve while allowing maximum transmission of one or both of the first diffraction orders.

[0178] 10. An optical device according to any of clauses 6 to 9, wherein the beam dispersive element is further arranged to recombinate the at least a portion of the broadband radiation beam into an output beam.

[0179] 11. The optical device according to claim 10 is arranged so that the broadband radiation beam passes through the center of the focusing lens to reach the spectral configuration element, and at least a portion of the broadband radiation beam from the spectral configuration element passes through at least one eccentric position of the focusing lens.

[0180] 12. An optical device according to clause 11, wherein the aberration compensation lens is displaced relative to the broadband radiation beam in a direction opposite to the direction in which the focusing lens is displaced.

[0181] 13. The optical device according to claim 10 is arranged so that the broadband radiation beam passes through a first eccentric position of the focusing lens to reach the spectral configuration element, and at least a portion of the broadband radiation beam from the spectral configuration element passes through a second eccentric position of the focusing lens.

[0182] 14. An optical device according to clause 13, wherein the first off-center position and the second off-center position are symmetrical about the optical axis.

[0183] 15. An optical device according to any one of clauses 10 to 14, further comprising an output lens arranged to focus the output beam; and wherein the at least one aberration compensation lens is arranged to compensate for the lateral chromatic aberration imposed by the focusing lens so that wavelength-dependent variations in the position of the output beam at the focal plane of the output lens are minimized.

[0184] 16. An optical device according to clause 15, wherein the at least one aberration compensation lens comprises one or both of the following:

[0185] the output lens located downstream of the focusing lens; and / or

[0186] An input lens is located upstream of the beam dispersing element.

[0187] 17. An optical device according to any of the preceding clauses, wherein one or more of the focusing lens and each at least one aberration compensation lens comprises an achromatic lens.

[0188] 18. An optical device according to clause 17, wherein the achromatic lens is an achromatic doublet.

[0189] 19. An optical device according to any of the preceding clauses, wherein the beam dispersive element comprises a prism or a grating.

[0190] 20. An optical device according to any of the preceding clauses, wherein the broadband radiation beam comprises a spectrum partially overlapping the range of 200 nm to 2000 nm.

[0191] 21. An optical device according to any of the preceding clauses, wherein the broadband radiation beam comprises a spectrum partially overlapping the range of 400nm to 1600nm.

[0192] 22. An optical device according to any of the preceding clauses, wherein the broadband radiation beam comprises a spectrum having a full width half maximum (FWHM) width of at least 500 nm.

[0193] 23. An optical device according to any of the preceding clauses, wherein the broadband radiation beam comprises a spectrum having a FWHM width of at least 300 nm.

[0194] 24. An optical device according to any of the preceding clauses, wherein the broadband radiation beam comprises a spectrum having a FWHM width of at least 200 nm.

[0195] 25. An optical device according to any of the preceding clauses, wherein the broadband radiation beam comprises a spectrum from 500nm to 900nm.

[0196] 26. An optical device according to any one of clauses 6 to 25, further comprising a beam shaping component operable to impose an elliptical profile on the broadband radiation beam to obtain elliptical broadband radiation having a short axis along the first transverse direction and a long axis along the second transverse direction.

[0197] 27. An optical device according to clause 26, wherein the beam shaping component is located upstream of the beam dispersive element.

[0198] 28. An optical device according to clause 27, wherein the beam shaping component is configured to not substantially change the diameter of the broadband radiation beam, so that the minor axis diameter along the minor axis of the elliptical broadband radiation beam is substantially similar to the diameter of the broadband radiation.

[0199] 29. An optical device according to any of clauses 26 to 28, wherein the beam shaping assembly comprises a pair of cylindrical lenses.

[0200] 30. An optical device according to clause 29, wherein the pair of cylindrical lenses includes a plano-concave lens and a plano-convex lens, the plano-concave lens being located upstream of the plano-convex lens.

[0201] 31. An optical device according to any of clauses 26 to 28, wherein the beam shaping assembly comprises a pair of prisms arranged to increase the diameter of the broadband radiation beam in the second lateral direction.

[0202] 32. An optical device according to clause 31, wherein the pair of prisms includes a first deformable prism and a second deformable prism.

[0203] 33. An optical device according to any one of clauses 26 to 28, wherein the beam shaping component comprises a fiber optic bundle, the fiber optic bundle comprising a plurality of optical fibers; wherein at an input end of the fiber optic bundle, the plurality of optical fibers are arranged in a circular configuration to receive the broadband radiation beam, and at an output end of the fiber optic bundle, the plurality of optical fibers are arranged in a linear configuration to output the elliptical broadband radiation beam.

[0204] 34. An optical device according to clause 33, wherein each optical fiber of the plurality of optical fibers is a multimode optical fiber having a substantially circular core.

[0205] 35. An optical device according to any of clauses 26 to 28, wherein the beam shaping component comprises an elliptical beam mask.

[0206] 36. An optical device according to clause 35, wherein the elliptical beam mask comprises an optical fiber having an elliptical core.

[0207] 37. An optical device comprising:

[0208] a beam shaping assembly for receiving a broadband radiation beam and imparting an elliptical profile on the broadband radiation beam to obtain elliptical broadband radiation having a minor axis along a first transverse direction and a major axis along a second transverse direction;

[0209] a beam dispersing element for spatially dispersing the elliptical broadband radiation beam in the first transverse direction;

[0210] a focusing lens for focusing the elliptical broadband radiation beam after the dispersion, wherein the focusing lens is arranged such that the dispersed elliptical broadband radiation beam passes through at least one off-center position of the focusing lens in at least one pass, wherein the off-center position is a position displaced from the center of the focusing lens in the second transverse direction, wherein the first transverse direction and the second transverse direction are perpendicular to each other and parallel to a focal plane of the focusing lens; and

[0211] a grating light valve comprising a configurable diffractive structure for selectively reflecting or diffracting a focused elliptical broadband radiation beam incident thereon into at least a portion of said elliptical broadband radiation beam, wherein said grating light valve is arranged such that said configurable diffractive structure extends along said first lateral direction;

[0212] Wherein the beam dispersive element is further arranged to recombine said at least a portion of said elliptical broadband radiation beam into an output beam.

[0213] 38. An optical device according to clause 37, wherein the beam shaping component is configured to not substantially change the diameter of the broadband radiation beam, so that the minor axis diameter along the minor axis of the elliptical broadband radiation beam is substantially similar to the diameter of the broadband radiation.

[0214] 39. An optical device according to clause 37 or 38, wherein the beam shaping assembly comprises a pair of cylindrical lenses arranged to increase the diameter of the broadband radiation beam in the second lateral direction.

[0215] 40. An optical device according to clause 39, wherein the pair of cylindrical lenses includes a plano-concave lens and a plano-convex lens, and the plano-concave lens is located upstream of the plano-convex lens.

[0216] 41. An optical device according to clause 37 or 38, wherein the beam shaping assembly comprises a pair of prisms arranged to increase the diameter of the broadband radiation beam in the second lateral direction.

[0217] 42. An optical device according to clause 41, wherein the pair of prisms includes a first deformable prism and a second deformable prism.

[0218] 43. An optical device according to clause 37 or 38, wherein the beam shaping component comprises a fiber optic bundle, the fiber optic bundle comprising a plurality of optical fibers; wherein at an input end of the fiber optic bundle, the plurality of optical fibers are arranged in a circular configuration to receive the circular broadband radiation beam, and at an output end of the fiber optic bundle, the plurality of optical fibers are arranged in a linear configuration to output the elliptical broadband radiation beam.

[0219] 44. An optical device according to clause 43, wherein each optical fiber of the plurality of optical fibers is a multimode optical fiber having a substantially circular core.

[0220] 45. An optical device according to clause 37 or 38, wherein the beam shaping component comprises an elliptical beam mask.

[0221] 46. ​​An optical device according to clause 45, wherein the elliptical beam mask comprises an optical fiber having an elliptical core.

[0222] 47. An optical device according to any one of clauses 37 to 46, further comprising at least one aberration compensation lens, wherein the at least one aberration compensation lens is displaced in the second lateral direction relative to at least a portion of the broadband radiation beam to substantially compensate for the lateral chromatic aberration imposed by the focusing lens on the at least a portion of the broadband radiation beam.

[0223] 48. An optical device according to clause 47, arranged so that the broadband radiation beam passes through an off-centre position of the at least one aberration compensating lens.

[0224] 49. An optical device according to clause 48, arranged so that the decentered position of the at least one aberration compensation lens compensates the at least one decentered position of the focusing lens in terms of lateral chromatic aberration.

[0225] 50. An optical device according to any one of clauses 37 to 49, wherein the grating light valve is configured to selectively diffract the incident focused elliptical broadband radiation beam so that at least a portion of the elliptical broadband radiation beam includes at least one higher diffraction order selectively diffracted by the grating light valve.

[0226] 51. An optical device according to clause 50, wherein the at least one higher diffraction order includes one or both of the first (+1 and -1) diffraction orders.

[0227] 52. An optical device according to clause 50 or 51, further comprising a beam block disposed in a pupil plane and arranged to maximally block the zeroth diffraction order from the grating light valve while allowing maximum transmission of one or both of the first diffraction orders.

[0228] 53. A metrology device comprising an optical device according to any of the preceding clauses.

[0229] 54. The metrology apparatus of clause 47, comprising a scatterometer measurement device, a level sensor or an alignment sensor.

[0230] 55. A method for optimizing an optical device according to any one of clauses 1 to 52, comprising:

[0231] determining an amount of aberration imposed by the focusing lens on the broadband radiation beam; and

[0232] The at least one aberration compensating lens is displaced relative to the at least a portion of the broadband radiation beam to apply an amount of reverse aberration on the at least a portion of the broadband radiation beam to substantially compensate for the aberration imposed by the focusing lens.

[0233] 56. A method according to clause 55, wherein the step of determining the amount of aberration comprises:

[0234] simulating or measuring one or more positions of an output beam at a focal plane of said output lens, said output beam being formed from said at least a portion of said broadband radiation beam;

[0235] determining wavelength-dependent variations in the one or more locations of the output beam; and

[0236] The amount of aberration is calculated based on the determined wavelength-dependent variation of the one or more positions of the output radiation.

[0237] 57. The method of clause 55 or 56, wherein the at least one aberration compensating lens comprises one or both of:

[0238] an output lens located downstream of the focusing lens, and

[0239] An input lens located upstream of the beam dispersive element, the method comprising:

[0240] One or both of the input lens and the output lens are shifted to the amount of reverse aberration.

[0241] Although the use of lithography equipment in IC manufacturing may be specifically mentioned herein, it should be understood that the lithography equipment described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns of magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0242] Although specific reference may be made herein to embodiments of the invention in the context of lithographic equipment, embodiments of the invention may also be used in other equipment. Embodiments of the invention may form part of a mask inspection equipment, a metrology equipment, or any equipment that measures or processes an object, such as a wafer (or other substrate) or a mask (or other patterning device). These equipment may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0243] Although specific reference may be 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 is not limited to optical lithography and may also be used in other applications, such as imprint lithography, where the context permits.

[0244] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in a manner other than that described. The above description is intended to be illustrative rather than limiting. Therefore, it will be appreciated by those skilled in the art that modifications may be made to the present invention described without departing from the scope of the following claims.

Claims

1. An optical device for aberration correction, comprising: a beam dispersing element for spatially dispersing the broadband radiation beam in a first lateral direction; a focusing lens for focusing the broadband radiation beam after the dispersion, wherein the focusing lens is arranged such that the dispersed broadband radiation beam passes through at least one off-center position of the focusing lens in at least one pass, wherein the off-center position is a position displaced from a center of the focusing lens in a second transverse direction, wherein the first transverse direction and the second transverse direction are perpendicular to each other and parallel to a focal plane of the focusing lens; as well as At least one aberration compensating lens is displaced in the second lateral direction relative to at least a portion of the broadband radiation beam to substantially compensate for lateral chromatic aberration imposed by the focusing lens on the at least a portion of the broadband radiation beam.

2. An optical device according to claim 1, arranged so that the broadband radiation beam passes through an off-center position of the at least one aberration compensation lens.

3. An optical device according to claim 2, arranged so that the decentered position of the at least one aberration compensation lens compensates the at least one decentered position of the focusing lens in terms of lateral chromatic aberration.

4. The optical device according to any of the preceding claims, further comprising a spectral configuration element, which is configured to selectively transmit, diffract or reflect at least a portion of the broadband radiation beam, wherein the at least a portion of the broadband radiation beam includes one or more wavelengths of the broadband radiation beam.

5. The optical device of claim 4, wherein the spectrum configuration element is substantially located at the focal plane of the focusing lens.

6. An optical device according to claim 5, wherein the spectral configuration element comprises a grating light valve, the grating light valve comprises a configurable diffraction structure, and the configurable diffraction structure is used to selectively reflect or diffract the broadband radiation beam incident thereon into at least a portion of the broadband radiation beam.

7. An optical device according to claim 6, wherein the beam dispersive element is further arranged to recombine the at least a portion of the broadband radiation beam into an output beam.

8. The optical device according to claim 7 is arranged so that the broadband radiation beam passes through the center of the focusing lens to reach the spectral configuration element, and at least a portion of the broadband radiation beam from the spectral configuration element passes through at least one eccentric position of the focusing lens, and optionally, the aberration compensation lens is displaced relative to the broadband radiation beam in a direction opposite to the direction of displacement of the focusing lens.

9. The optical device according to claim 7 is arranged so that the broadband radiation beam passes through a first eccentric position of the focusing lens to reach the spectral configuration element, and at least a portion of the broadband radiation beam from the spectral configuration element passes through a second eccentric position of the focusing lens, and optionally, the first eccentric position and the second eccentric position are symmetrical about the optical axis.

10. An optical device according to any one of claims 7 to 9, further comprising an output lens arranged to focus the output beam; and wherein the at least one aberration compensation lens is arranged to compensate for the lateral chromatic aberration imposed by the focusing lens so that wavelength-dependent variations in the position of the output beam at the focal plane of the output lens are minimized.

11. The optical device of claim 10, wherein the at least one aberration compensation lens comprises one or both of the following: the output lens located downstream of the focusing lens; and / or An input lens is located upstream of the beam dispersing element.

12. An optical device according to any one of the preceding claims, wherein the broadband radiation beam comprises a spectrum partially overlapping the range of 200nm to 2000nm.

13. An optical device according to any one of the preceding claims, wherein the broadband radiation beam comprises a spectrum having a FWHM width of at least 200 nm.

14. A metrology device comprising an optical device according to any one of the preceding claims.

15. A method for optimizing an optical device according to any one of claims 1 to 13, comprising: determining an amount of aberration imposed by the focusing lens on the broadband radiation beam; as well as The at least one aberration compensating lens is displaced relative to the at least a portion of the broadband radiation beam to apply an amount of reverse aberration on the at least a portion of the broadband radiation beam to substantially compensate for the aberration imposed by the focusing lens.

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