Illumination module for metrology device

Abstract

Disclosed is an illumination configuration module comprising: a polarization and wavelength separation device operable to separate an input broadband illumination into at least a first dispersed illumination comprising a first polarization state and a second dispersed illumination comprising a second polarization state; a single spatial light modulation device operable to individually modulate each of the first dispersive illumination and the second dispersive illumination to obtain a first spectral configuration illumination and a second spectral configuration illumination; and output optics operable to combine the first spectral configuration illumination and the second spectral configuration illumination into an output illumination beam.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to EP application 22204014.9, filed on October 27, 2022, the entire content of which is incorporated herein by reference. Field of the Invention

[0003] The present invention relates to an illumination configuration module for configuring an illumination beam, and in particular to such an illumination configuration module related to metrology applications in integrated circuit manufacturing. Background Art

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

[0006] Low-k 1 Lithography can be used to process features smaller than the classical resolution limit of a lithographic apparatus. In such a 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 the half-pitch), and k 1 is an empirical resolution factor. Typically, k 1The smaller it is, the more difficult it is to reproduce on a substrate a pattern similar in shape and size to that planned by a circuit designer to achieve a specific electrical function and performance. To overcome these difficulties, complex fine-tuning steps can be applied to the lithographic projection apparatus and / or the design layout. These include, for example but not limited to, optimization of the NA, customized illumination schemes, use of phase-shifting patterning devices, various optimizations of the design layout (such as optical proximity correction (OPC, sometimes also referred to as "optical and process correction") in the design layout), or other methods generally defined as "resolution enhancement techniques" (RET). Alternatively, a tight control loop for controlling the stability of the lithographic apparatus 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 an alignment tool for correct positioning of the substrate before exposure, a leveling tool for measuring the surface topology of the substrate, and a focus control and scatterometry-based tool for inspecting / measuring the exposure and / or etching product, for example, in process control. In each case, a radiation source is required. For various reasons, including the robustness and accuracy of the measurement, broadband or white light radiation sources are increasingly used for such metrology applications. In many cases, not all spectral and / or polarization components of the white light are used for a specific measurement. For example, for a specific measurement, it is often desirable to vary the spectral and / or polarization characteristics of the radiation. This can be achieved by filtering and polarization switching. However, this results in a loss of system throughput, because using existing methods to switch the radiation characteristics causes a significant loss of switching time.

[0008] There is a desire to improve the configurability of measuring the radiation characteristics. Summary of the Invention

[0009] According to a first aspect of the present invention, there is provided an illumination configuration module, which includes: a polarization element for separating the incident radiation into a first polarization component having a first polarization state and a second polarization component having a second polarization state; a dispersion element arranged to receive and spectrally disperse an input broadband illumination beam or each of the first polarization component and the second polarization component, the polarization element and the dispersion element together being arranged to separate the input broadband illumination beam into at least a first dispersed illumination including the first polarization state and a second dispersed illumination including the second polarization state; at least one spatial light modulation device operable to individually modulate each of the first dispersed illumination and the second dispersed illumination to obtain a first spectrally configured illumination and a second spectrally configured illumination; and an output optical device operable to combine the first spectrally configured illumination and the second spectrally configured illumination into an output illumination beam.

[0010] According to a second aspect of the present invention, there is provided an illumination configuration module, the illumination configuration module comprising: a polarization and wavelength separation device operable to separate an input broadband illumination into at least a first dispersed illumination including a first polarization state and a second dispersed illumination including a second polarization state; at least one grating light valve device operable to individually modulate each of the first dispersed illumination and the second dispersed illumination to obtain a first spectrally configured illumination and a second spectrally configured illumination; and an output optical device operable to combine the first spectrally configured illumination and the second spectrally configured illumination into an output illumination beam.

[0011] According to a third aspect of the present invention, there is provided an illumination configuration module, the illumination configuration module comprising: a filter device including a plurality of dichroic filters for splitting an input broadband radiation beam into a plurality of beams, each beam having different spectral characteristics; a polarization beam splitting device operable to split each of the beams having different spectral characteristics into corresponding different polarization beams; at least one spatial light modulation device operable to individually modulate each of the different polarization beams to obtain different polarization beams with different spectral configurations; and an output optical device operable to combine the different polarization beams with different spectral configurations into an output illumination beam.

[0012] Other aspects of the present invention include a metrology device, the metrology device comprising an illumination device according to the first aspect, the second aspect or the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0014] - Figure 1 A schematic diagram of a lithographic apparatus is depicted;

[0015] - Figure 2 A schematic diagram of a lithography cell is depicted;

[0016] - Figure 3 A schematic diagram of overall lithography is depicted, showing the cooperation between three key technologies to optimize semiconductor manufacturing;

[0017]

[0018] - Figure 4 A schematic diagram of a scatterometry device used as a metrology device is depicted, which may

[0019] include a radiation source according to an embodiment of the present invention;

[0020] - Figure 5 A schematic diagram of a liquid level sensor device according to an embodiment of the present invention is depicted,

[0021] the liquid level sensor device may include a radiation source;

[0022] - Figure 6 Schematically depicts an alignment sensor device according to an embodiment of the present invention,

[0023] the alignment sensor device may include a radiation source;

[0024] - Figure 7 (a), Figure 7 (b) and Figure 7 (c) schematically depict a grating light valve (GLV), with (a) a top view, (b) an end view of a first configuration, and (c) a bottom

[0025] view illustrating its basic operation;

[0026] - Figure 8 (a) and Figure 8 (b) respectively schematically depict a GLV-based illumination configuration

[0027] module in a top view and a side view;

[0028] - Figure 9 Schematically depicts a GLV-based illumination configuration

[0029] module according to a first embodiment in a top view;

[0030] - Figure 10 Schematically depicts a GLV-based illumination configuration

[0031] module according to a second embodiment in a top view;

[0032] - Figure 11 (a) and Figure 11 (b) schematically depict a GLV arrangement configured

[0033] for phase control between two polarization channels;

[0034] - Figure 12 Schematically depicts a GLV-based illumination configuration

[0035] module according to a third embodiment;

[0036] - Figure 13 Schematically depicts a GLV-based illumination configuration

[0037] module according to a fourth embodiment;

[0038] - Figure 14 (a) schematically depicts a GLV-based illumination configuration module according to a fifth embodiment, Figure 14 (b) shows the light passing through the beam splitter device of this embodiment

[0039] Ray diagram of a line path; and

[0040] - Figure 15 A block diagram depicting a computer system for controlling a broadband radiation source is shown. Detailed implementation

[0041] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including visible light (e.g., 400 nm to 700 nm), (near) infrared radiation (700 nm to 1000 nm), ultraviolet radiation (e.g., wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), and EUV (extreme ultraviolet radiation, e.g., wavelengths in the range of about 5 nm - 100 nm), one, some, or all of which.

[0042] The terms "reticle", "mask", or "patterning device" as used herein can be broadly interpreted to refer to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam corresponding to a pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays in addition to classical masks (transmission or reflection, binary, phase-shifting, hybrid, etc.).

[0043] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA includes: an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask table) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters; a substrate support (e.g., a wafer table) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0044] In operation, the illumination system IL receives a radiation beam from a radiation source SO, e.g., via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, which are used to direct, shape and / or control the radiation. The illuminator IL may be used to condition the radiation beam B such that it has a desired spatial and angular intensity distribution in a plane of the patterning device MA in its cross-section.

[0045] The term “projection system” PS as used herein should be broadly interpreted to cover 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 an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as a synonym for the more general term “projection system” PS.

[0046] The lithographic apparatus LA may be of a type in which at least a portion of the substrate is covered by a liquid having a relatively high refractive index (e.g., water) so as to fill the space between the projection system PS and the substrate W, which is also referred to as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0047] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as “dual stage”). In such a “multi-stage” machine, the substrate supports WT may be used in parallel, and / or preparatory steps for a subsequent exposure of a substrate W may be carried out on the substrate W on one of the substrate supports WT while another substrate W on another substrate support WT is being exposed to a pattern.

[0048] In addition to the substrate support WT, the lithographic apparatus LA may also include a metrology stage. The metrology stage is arranged to accommodate sensors and / or cleaning devices. The sensors may be arranged to measure characteristics of the projection system PS or of the radiation beam B. The metrology stage may accommodate a plurality of sensors. The cleaning devices may be arranged to clean a part of the lithographic apparatus, e.g., a part of the projection system PS or a part of the system providing the immersion liquid. The metrology stage may be movable under the projection system PS when the substrate support WT is moved away from the projection system PS.

[0049] In operation, a radiation beam B is incident on a patterning device, such as a mask MA, which is held on a mask support MT and 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 a substrate W. With the help of a second positioner PW and a position measurement system IF, the substrate support WT can be moved precisely, e.g., to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, a first positioner PM and possibly another position sensor ( Figure 1 not explicitly shown in

[0050] as Figure 2 shown) can be used to position the patterning device MA precisely relative to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 as shown occupy dedicated target portions, they can be located in the spaces between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, they are called scribe alignment marks.

[0051] To ensure that the substrate W exposed by the lithographic apparatus LA is exposed correctly and uniformly, it is necessary to inspect the substrate to measure characteristics of the patterned structures, such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. For this purpose, an inspection tool (not shown) can be included in the lithographic cell LC. If an error is detected, the exposure of subsequent substrates or other processing steps to be performed on the substrate W can be adjusted, especially when the inspection is carried out before other substrates W of the same batch or lot still need to be exposed or processed.

[0052] An inspection device (which may also be referred to as a metrology device) is used to determine the characteristics of a substrate W, in particular how the performance of different substrates W varies, or how the performance associated with different layers of the same substrate W varies layer by layer. The inspection device can alternatively be configured to identify defects on the substrate W and can, for example, be part of a lithography cell LC, or can be integrated into a lithography apparatus LA, or can even be a stand-alone device. The inspection device can measure characteristics on a latent image (the image in the resist layer after exposure), a semi-latent image (imaging in the resist layer after a post-exposure bake step PEB), a developed resist image (where the exposed or unexposed portions of the resist have been removed), or even an etched image (after a pattern transfer step such as etching).

[0053] Generally, the patterning process in a lithography apparatus LA is one of the most critical steps in the process, which requires determining the dimensions and placement of structures on the substrate W with high precision. To ensure such high precision, three systems can be combined in a so-called "holistic" control environment, as Figure 3 shown. One of these systems is the lithography apparatus LA, which is (virtually) connected to a metrology tool MT (the second system) and a computer system CL (the third system). The key to such a "holistic" environment is to optimize the collaboration 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 typically allows the process parameters in a lithography process or patterning process to vary within this range.

[0054] The computer system CL can use (a part of) the design layout to be patterned to predict which resolution enhancement techniques to use and perform computational lithography simulations and calculations to determine which mask layout and lithography apparatus settings achieve the maximum overall process window for the patterning process (as shown by the double arrow in the first scale SC1 in Figure 3 ). Generally, the resolution enhancement techniques are arranged to match the patterning capabilities of the lithography apparatus LA. The computer system CL can also be used to detect the current operating position of the lithography apparatus LA within the process window (e.g., using input from the metrology tool MT) to predict whether there will be defects due to, for example, sub-optimal processes (as shown by the arrow pointing to "0" in the second scale SC2 in Figure 3 ).

[0055] The metrology tool MT can provide input to the computer system CL to enable accurate simulations and predictions and can provide feedback to the lithography apparatus LA to identify possible drifts, for example, in the calibration state of the lithography apparatus LA (as shown in Figure 3as indicated by the multiple arrows in the third scale SC3).

[0056] In a lithography process, it is necessary to frequently measure the created structures, for example for process control and verification. Tools used to perform such measurements are commonly referred to as metrology tools MT. Different types of metrology tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometry metrology tools MT. A scatterometer is a versatile instrument that can measure parameters of the lithography process by having a sensor in the pupil of the scatterometer objective or in a plane conjugate to the pupil, which is typically referred to as pupil-based measurement, or by having a sensor in the image plane or in a plane conjugate to the image plane, in which case the measurement is usually referred to as image- 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 above-mentioned scatterometers can use light from the soft x-ray and visible light to the near-IR wavelength range to measure gratings.

[0057] In a first embodiment, the scatterometer MT is an angular-resolved scatterometer. In such a scatterometer, a reconstruction method can be applied to the measurement signal to reconstruct or calculate the characteristics of the grating. For example, such 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 the real target.

[0058] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer MT, the radiation emitted by a radiation source is directed onto the target, and the reflected or scattered radiation from the target is directed onto a spectrometer detector that measures the spectrum of the specularly reflected radiation (i.e., the measurement of intensity as a function of wavelength). Based on these data, the structure or profile of the target that produced the detected spectrum can be reconstructed, for example, by rigorous coupled-wave analysis and non-linear regression, or by comparison with a simulated spectral library.

[0059] In a third embodiment, the scatterometer MT is an ellipsometer. An ellipsometer allows for the determination of parameters of a lithography process by measuring the scattered radiation for each polarization state. Such metrology devices emit polarized light (such as linear, circular or elliptical) by using appropriate polarization filters in the illumination section of the metrology device. Sources suitable for metrology devices 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.

[0060] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlay of two misaligned gratings or periodic structures by measuring the reflection spectrum and / or detecting an asymmetry in a detection configuration, the asymmetry being related to the degree of overlay. These two (usually overlapping) grating structures can be applied to two different layers (not necessarily consecutive layers) and can be formed substantially at the same location on the wafer. The scatterometer can have a symmetric detection configuration, as described in the co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a method for directly measuring grating misalignment. Other examples of measuring overlay errors between two layers that include a periodic structure as a target by the asymmetry of the periodic structure can be found in PCT Patent Application Publication No. WO 2011 / 012624 or U.S. Patent Application US20160161863, the entire contents of which are incorporated herein by reference.

[0061] Other parameters of interest can be focus and dose. Focus and dose can 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 can be used that has a unique combination of critical dimension and sidewall angle measurements for each point in a Focus Energy Matrix (FEM, also known as a Focus Exposure Matrix). If these unique combinations of critical dimension and sidewall angle are available, the focus and dose values can be uniquely determined from these measurements.

[0062] The measurement target can be a set of composite gratings formed by a lithography process, mainly formed in the resist, but also formed after an etching process. Generally, the pitch and linewidth of the structures in the grating strongly depend on the measurement optics (especially the NA of the optics) in order to be able to capture the diffraction orders from the measurement target. As mentioned before, the diffraction signal can be used to determine the offset (also called "overlay") between two layers and can also be used to reconstruct at least a part of the original grating generated by the lithography process. Such reconstruction can be used to provide guidance on the quality of the lithography process and can be used to control at least a part of the lithography process. The target can have smaller sub-divisions that are configured to mimic the dimensions of the functional parts of the design layout in the target. Due to such sub-division, the behavior of the target will be more similar to the functional parts of the design layout, thus making the overall process parameter measurement better resemble the functional parts of the design layout. The target can be measured in an under-filled mode or an over-filled mode. In the under-filled mode, the spot generated by the measurement beam is smaller than the overall target. In the over-filled mode, the spot generated by the measurement beam is larger than the entire target. In this over-filled mode, different targets can also be measured simultaneously, thereby determining different process parameters simultaneously.

[0063] The overall measurement quality of the lithography parameters using a specific target is at least partially determined by the measurement recipe used to measure the lithography parameter. The term "substrate measurement recipe" can include one or more parameters of the measurement itself, one or more parameters of the one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement recipe is a diffraction-based optical measurement, one or more parameters of the measurement can 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 a measurement recipe can 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 published U.S. Patent Application US 2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0064] A metrology device, such as a scatterometer, is as Figure 4 shown. It includes a broadband (white light) radiation projector 2 that projects radiation onto a substrate 6. The reflected or scattered radiation is transmitted to a spectrometer detector 4 that measures the spectrum 10 of the specularly reflected radiation (i.e., the measurement of intensity as a function of wavelength). Based on this data, a processing unit PU can reconstruct the structure or profile that generated the detected spectrum, for example, by rigorous coupled-wave analysis and non-linear regression, or by comparison with Figure 3Compare with the simulated spectral library shown at the bottom. Generally, for reconstruction, the general form of the structure is known, and some parameters are assumed based on the knowledge of the process of manufacturing the structure, leaving only several parameters of the structure to be determined from the scattering measurement data. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0065] The overall measurement quality of lithography parameters achieved by measuring a metrology target is at least partially determined by the measurement recipe used to measure the lithography parameter. The term "substrate measurement recipe" can include one or more parameters of the measurement itself, one or more parameters of one or more patterns being measured, or both. For example, if the measurement used in the substrate measurement recipe is a diffraction-based optical measurement, one or more parameters of the measurement can 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 a measurement recipe can 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 published U.S. Patent Application US 2016 / 0370717A1, the entire content of which is incorporated herein by reference.

[0066] Another metrology tool used in IC manufacturing is a topography measurement system, a level sensor, or a height sensor. Such a tool can be integrated into a lithography apparatus for measuring the topography of the top surface of a substrate (or wafer). A topographic map of the substrate (also referred to as a height map) can be generated based on these measurements to indicate the height of the substrate as a function of the position on the substrate. This height map can then be used to correct the position of the substrate during pattern transfer onto the substrate to provide a spatial image of the patterning device at an appropriate focus position on the substrate. It can be understood that in this case, "height" refers to the dimension generally extending beyond the plane of the substrate (also referred to as the Z-axis). Generally, a level or height sensor makes measurements at a fixed position (relative to its own optical system), and the relative movement between the substrate and the optical system of the level or height sensor results in height measurements at different positions on the substrate.

[0067] Examples of level or height sensors LS known in the art are schematically shown in Figure 5 and Figure 5Only the operating principle is illustrated. In this example, the liquid level sensor includes an optical system, which includes a projection unit LSP and a detection unit LSD. The projection unit LSP includes a radiation source LSO, which provides a radiation beam LSB that is applied by the 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 unpolarized, pulsed or continuous, such as a polarized or non-polarized laser beam. The radiation source LSO can include a plurality of radiation sources with different colors or wavelength ranges, such as a plurality of LEDs. The radiation source LSO of the liquid level sensor LS is not limited to visible radiation, but can additionally or alternatively include UV and / or IR radiation and any wavelength range suitable for reflection from the substrate surface.

[0068] The projection grating PGR is a periodic grating that includes a periodic structure, which generates a radiation beam BE1 with a periodically varying intensity. The radiation beam BE1 with a periodically varying intensity is guided to a measurement position MLO on the substrate W, and the incident angle ANG with respect to the axis (Z-axis) perpendicular to the incident substrate surface is between 0 degrees and 90 degrees, usually between 70 degrees and 80 degrees. At the measurement position MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by the arrow BE2) and directed towards the detection unit LSD.

[0069] To determine the height level at the measurement position MLO, the liquid level sensor further includes a detection system, which includes a detection grating DGR, a detector DET, and a processing unit (not shown) for processing the output signal of the detector DET. The detection grating DGR can be the same as the projection grating PGR. The detector DET generates a detector output signal indicating 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 can include any combination of one or more detector types.

[0070] Through the triangulation technique, 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, and the signal intensity has a periodicity that depends on the design of the projection grating PGR and the (tilt) incident angle ANG, etc.

[0071] The projection unit LSP and / or the detection unit LSD can include other 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.

[0072] In one embodiment, the detection grating DGR can be omitted, and the detector DET can be placed at the position where the detection grating DGR is located. This configuration provides a more direct detection of the image of the projection grating PGR.

[0073] To effectively cover the surface of the substrate W, the liquid level sensor LS can be configured to project an array of measurement beams BE1 onto the surface area of the substrate W, thereby generating a measurement region MLO or a spot array that covers a larger measurement range.

[0074] 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 that uses UV radiation instead of visible or infrared radiation is disclosed in US2010233600A1, which is incorporated herein by reference. In WO2016102127A1, which is incorporated herein 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 to detect the grating.

[0075] Another metrology tool used in IC manufacturing is an alignment sensor. Thus, a key aspect of the performance of a lithographic apparatus is the ability to place the applied pattern correctly and accurately relative to features placed in a previous layer (by the same apparatus or a different lithographic apparatus). For this purpose, 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 can be referred to as an "alignment sensor", and the mark can be referred to as an "alignment mark".

[0076] The lithographic apparatus may include one or more (e.g., multiple) alignment sensors through which the position 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 used in current lithographic apparatuses is based on the self-referencing interferometer described in US6961116. Various enhancements and modifications of the position sensor have been developed, such as those disclosed in US2015261097A1. The content of all these publications is incorporated herein by reference.

[0077] Figure 6 is a schematic block diagram of an embodiment of a known alignment sensor AS, such as that described in US6961116, which is incorporated herein by reference. The radiation source RSO provides a radiation beam RB of one or more wavelengths, and the radiation beam RB is steered onto the mark by steering optics, such as a mark AM located on the substrate W, as an illumination point SP. In this example, the steering optics include a point mirror SM and an objective lens OL. The diameter of the illumination point SP for illuminating the mark AM can be slightly smaller than the width of the mark itself.

[0078] The radiation diffracted by the alignment mark AM is collimated (in this example via the objective lens OL) into a beam IB carrying information. The term "diffraction" is intended to include the zero-order diffraction of the mark (which may be referred to as reflection). The self-reference interferometer SRI (e.g., of the type disclosed in the above-mentioned US6961116) causes the beam IB to interfere with itself, after which the beam is received by the photodetector PD. If the radiation source RSO produces multiple wavelengths, additional optical devices (not shown) may be included to provide separate beams. The photodetector may be a single element or, if desired, may include multiple pixels. The photodetector may include a sensor array.

[0079] In this example, the steering optics including the point mirror SM can also be used to block the zero-order radiation reflected from the mark, such that the beam IB carrying information only includes the higher-order diffracted radiation from the mark AM (this is not necessary for the measurement but can improve the signal-to-noise ratio).

[0080] The intensity signal SI is provided to the processing unit PU. By combining the optical processing in the block SRI and the computational processing in the unit PU, the values of the X and Y positions on the substrate relative to the reference frame can be output.

[0081] A single measurement of the type shown only fixes the position of the mark within a specific range corresponding to one pitch of the mark. A coarser measurement technique is used in combination with this to determine which period of the sine wave contains the mark position. The same process can be repeated at coarser and / or finer levels at different wavelengths to improve the accuracy and / or robustly detect the mark, regardless of what material the mark is made of and the materials on and / or under which the mark is provided. The wavelengths can be optically multiplexed and demultiplexed for simultaneous processing, and / or they can be multiplexed by time division or frequency division.

[0082] 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 precisely mounted to the 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 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 the substrate support (not shown). In one embodiment, one or more (alignment) marks are provided on the substrate support. Measuring 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.

[0083] A metrology tool MT (such as the above-described scatterometer, profiler, or position measurement system) can perform measurements using radiation from a radiation source. The characteristics of the radiation used by the metrology tool can affect the type and quality of the measurements that can be performed. For some applications, it can be advantageous to use multiple radiation frequencies and / or polarization states to measure a substrate, for example, broadband radiation can be used. Multiple different frequencies can be able to propagate, illuminate, and scatter the metrology target without interfering with or minimally interfering with other frequencies. Thus, for example, different frequencies can be used to simultaneously obtain more metrology data. Different radiation frequencies can also be able to interrogate and discover different characteristics of the metrology target. Broadband radiation can be used in metrology systems MT, such as level sensors, alignment mark measurement systems, scatterometry tools, or inspection tools. The broadband radiation source can be a supercontinuum source.

[0084] In many metrology applications (such as metrology applications based on scatterometry or interferometry), for example, for pre-exposure metrology (such as alignment) or post-exposure metrology (e.g., overlay, CD, focus, or other parameter metrology of interest), different information can be obtained from measurements of the same structure depending on the wavelength and polarization state of the measurement illumination used. For example, some existing metrology systems provide measurement illumination that can be configured with multiple colors and three polarization settings (horizontal, vertical, and both). However, the illumination configuration modules (color switching modules) currently used in such systems tend to be based on slow and bulky mechanical modules. In addition, when selecting the polarization of the incident beam, such modules only provide three options: all wavelengths in the first polarization state (e.g., horizontal H), all wavelengths in the second polarization state (e.g., vertical V), or all wavelengths in both polarization states. At some wavelengths, any one of the polarization selections is likely to be suboptimal. To measure each wavelength at the optimal polarization, the number of measurements required is twice that of single-polarization measurements, with a slow polarization switch in between. In addition, it is currently not possible at all to arbitrarily combine different polarization states.

[0085] A fast illumination configuration module or color switching module based on the grating light valve (GLV) concept has been described. The GLV module disperses light (already dispersed onto the GLV), such that the module can selectively remove or modulate light at one or more specific wavelengths. The resulting spectrum can be configured to include any desired shape and can be varied at very high frequencies, possibly up to the MHz range. Such engineered spectra are a fast (microsecond-switchable) way to extract a large amount of information from a target. However, the known literature on GLV-based illumination configuration only describes color selection and does not have any polarization selection function. Wavelength is only one degree of freedom. The polarization of the measurement illumination is another useful degree of freedom that can be exploited in metrology.

[0086] As an example, refer to Figure 7 and Figure 8, the GLV-based illumination configuration module will now be described, which is configured to selectively transmit or block (diffract or reflect) at least a portion of the incident broadband illumination. GLV is an electroprogrammable diffraction grating based on microelectromechanical systems (MEMS) technology. The GLV device may include a configurable diffraction structure that is used to selectively reflect or diffract the incident broadband illumination into an output radiation beam. Thus, the output radiation illumination from such a module may include a spectrally configured light beam modulated by the GLV device. The GLV device used in the embodiments disclosed herein may be a GLV device sold by Silicon Light Machines (SLM), and / or based on the GLV concept described in US6947613B (which is incorporated herein by reference).

[0087] Figure 7 (a)- Figure 7 (c) illustrates the operating principle behind the GLV. Figure 7 (a)- Figure 7 (c) are schematic views of the GLV pixel or component 500 from above and at the end, respectively. Note that Figure 7 (a)- Figure 7 (c) The GLV components shown are just an example design, and other different GLV designs (e.g., the "true GLV" designs used in the G1088 and G8192 modules sold by SLM) can also be used in any of the illumination configuration modules disclosed herein.

[0088] The GLV component includes two types of alternating GLV reflection bands: static or biased bands 510 that are typically grounded together with a common electrode and driven or active bands 520 that are driven by an electronic driver channel. The GLV device may include any number of these GLV components 500 arranged in an array (e.g., a 1D or 2D array). Except for the driving method, the active bands and the biased bands may be substantially the same. In one embodiment, when no voltage is applied to the active bands 520, they are coplanar with the biased bands, as shown in Figure 7 (b). In this configuration, the GLV essentially acts as a mirror, and the incident light is specularly reflected (i.e., forms specularly reflected radiation or zero-order diffraction radiation). When a voltage is applied to the active bands 520, as shown in Figure 7 (c), they deflect relative to the biased bands 510, forming a square-well diffraction grating. In this state, the incident light is diffracted at a fixed diffraction angle. By controlling the voltage on the active bands 520, the ratio of the reflected light to the diffracted light can be continuously changed, which controls their deflection magnitude. Thus, the amount of light diffracted by the GLV can be controlled in an analog manner from zero (full specular reflection) to all of the 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 a non-zero diffraction order may be referred to as modulating the illumination.

[0089] The GLV device can be used in the zero - order mode such that the diffracted radiation is blocked / collected and the specularly reflected (zero - diffraction - order) radiation is selected (e.g., transmitted into the output illumination beam). This has the advantage of maintaining the light - collection rate. Thus, an aperture stop can be provided in the pupil plane with the aim of maximizing the transmission of the zero - order and maximizing the blocking (minimizing its transmission) of the first - order (and other diffraction orders). However, it can be understood that this can be reversed such that the specular radiation is collected and the diffracted radiation is transmitted to the output.

[0090] Figure 8 (a) and Figure 8 (b) schematically illustrate known illumination configuration modules from two different angles. The broadband beam emitted from the broadband light source LS is dispersed in the X - direction by the beam - dispersion element DE, which can include, for example, a prism or a grating. The dispersion of the broadband beam is achieved based on the principle that the direction of the light emerging from the beam - dispersion element DE is wavelength - dependent. Optionally, the broadband beam can be collimated by the first optical lens L 1 before being dispersed by the beam - dispersion element DE. Then, the dispersed broadband beam can be focused (e.g., by the second optical lens L 2 ) onto the strip of the GLV device, which is substantially located at the focal plane of the second lens L 2 . Different shadings indicate different wavelengths of the dispersed radiation.

[0091] The GLV device can be configured in the zero - order mode and is operable to impose a certain spatial modulation on the focused broadband beam so as to selectively reflect the desired wavelengths and diffract away the undesired wavelengths. In some embodiments, the GLV device can operate in a wavelength - selection mode to fully select one or more selected wavelengths (e.g., with no significant attenuation) and fully block the non - selected wavelengths. That is, the strips of the GLV device corresponding to the selected wavelengths can be set to equal heights such that they act as standard mirrors at the selected wavelengths, while the other strips are actuated in such a way that they form a grating to diffract the undesired wavelengths into higher diffraction orders, such as - 1 and + 1 diffraction orders. Then, these higher diffraction orders are blocked or collected by the beam blocks BL1, BL2 respectively. The GLV device can also operate in an intermediate mode or a spectral - shaping mode, e.g., to form a grating that partially reflects and partially diffracts the incident radiation of one or more wavelengths to attenuate but not fully block these one or more wavelengths. The degree of attenuation can be controlled via the strip configuration (the offset of the active strips relative to the static strips). In this way, the spectral shape / composition of the output radiation can be dynamically controlled.

[0092] The spatially - modulated reflected (zero - order) radiation from the GLV device can be by the second optical lens L 2Capture. The spatially modulated beams are recombined on the return path, e.g., using the same dispersive element DE as used for dispersing the beam on the outward path (alternatively, a separate dispersive element can be used for dispersion and recombination). The return path within the dispersive element DE can be substantially parallel to the outward path and displaced in the Y direction relative to the outward path. Then, the steering mirror SM can direct the recombined output illumination beam, e.g., towards a third optical lens L. 3 . This third optical lens L 3 can be used as an output lens to focus the beam into the metrology device; e.g., via a suitable optical fiber such as a single-mode photonic crystal fiber.

[0093] It is proposed to improve such an illumination configuration module to achieve full wavelength and polarization configuration of the output illumination radiation, e.g., such that the output illumination can be configured to include any combination of available wavelengths and polarizations. For example, it is proposed that the output illumination can be configurable to include different wavelengths of different polarization states; e.g., it can include one or more wavelengths in a first polarization state, one or more wavelengths in a second polarization state, and / or one or more wavelengths in both of these polarization states. In other embodiments, more than two polarization states can be selected. The proposed illumination configuration module can enable switching of the wavelength and / or polarization with a switching time on the order of microseconds.

[0094] The following embodiments are described with respect to using a spatial modulation device based on GLV technology for spectral shaping and / or wavelength selection. However, it should be understood that in at least some embodiments, the spatial modulation device can include another type of spatial light modulation device and / or MEMS device.

[0095] The proposed embodiments can separate the input broadband illumination into at least a first dispersive illumination including a first polarization state and a second dispersive illumination including a second polarization state (more dispersive illuminations including additional polarization states can be provided additionally). This can be achieved by using polarization and wavelength separation means (e.g., polarization elements and dispersive elements). Then, a spatial light modulation device such as a GLV device can be used to individually modulate each of the first dispersive illumination and the second dispersive illumination to obtain a first spectrally configured illumination and a second spectrally configured illumination. Then, the first spectrally configured illumination and the second spectrally configured illumination can be used as measurement illuminations in a measurement; e.g., by using output optical means to combine them into an output illumination beam or a measurement illumination beam.

[0096] In this way, the spectrum included in the output illumination beam can be designed based on the intensity versus wavelength and polarization versus wavelength relationships.

[0097] Figure 9Schematically illustrates a first embodiment of an illumination configuration module in accordance with the concepts disclosed herein. A broadband illumination source LS provides (e.g., unpolarized) broadband input illumination IIL. A polarization element PE or polarization beam splitter splits the input illumination into a first polarized illumination P1 including a first polarization state and a second polarized illumination P2 including a second polarization state. For example, the first and second polarization states may include linearly polarized states orthogonal to each other (e.g., H and V polarization states). For example, the polarization element PE or polarization beam splitter may include a birefringent element (e.g., a birefringent crystal) whose refractive index strongly depends on polarization. Such a birefringent crystal can split an incident beam into two such output beams, respectively including horizontal polarization and vertical polarization.

[0098] The first polarized illumination P1 and the second polarized illumination P2 can be dispersed by a dispersion element DE. Note that the order of the polarization element PE and the dispersion element DE can be reversed such that the input beam is dispersed before being polarized into two (or more) different polarizations. Thus, in the context of the present disclosure, the polarization and wavelength separation device may include at least one dispersion element DE and at least one polarization element PE in any order.

[0099] Since the illumination is now spatially separated into a first dispersed illumination DP1 and a second first dispersed illumination DPA2, each dispersed illumination including a different polarization state, each of these scattered illuminations DP1, DP2 can be projected onto different regions of the GLV device (or on different respective GLV devices) and spectrally shaped separately. The illumination specularly reflected (or diffracted) by the GLV device can be recombined into a single output beam OB by the output optics, which can be steered (e.g., towards a metrology device) using a steering mirror SM as needed. As shown here, the output optics may include the same polarization and wavelength separation device (e.g., a dispersion element DE and a polarization element PE) as used for dispersing and polarizing / splitting the incident radiation.

[0100] The illumination configuration module system is shown as including one lens and one GLV; however, it can be implemented using two (or more) separate lenses and / or GLVs. The diffraction orders of the GLV are not drawn but can be blocked in the same manner as shown in Figure 8 (a). Considering the relatively large range of two points, a slightly longer lens focal length can be used to ensure sufficient separation of the diffraction orders.

[0101] In the above example, the incident beam is unpolarized. Depending on the light source, the beam can instead be circularly polarized or linearly polarized; in the latter case, an input waveplate can be provided to convert the linearly polarized radiation to include (e.g., equal amounts of) H and V radiation (e.g., such that it is circularly polarized). Thus, the radiation incident on the polarization element can be unpolarized, circularly polarized, or 45-degree linearly polarized.

[0102] In the above embodiments, a polarization element PE and a dispersion element DE are used in combination to convert a broadband unpolarized (or linearly or circularly polarized, etc.) light beam into two separate dispersion spectra having orthogonal polarization states. One way to achieve this is to directly mount a birefringent material onto one face of a dispersion prism. Other shapes and arrangements of birefringent crystals (such as Wollaston prisms) can also achieve the same result.

[0103] If a material has an appropriate balance between dispersion and birefringence, this material can be used to form a prism that can perform both polarization and dispersion functions simultaneously, thereby generating two independent dispersion spectra having orthogonal polarization states.

[0104] Figure 10 An illumination configuration module according to such an embodiment is illustrated, where the polarization and wavelength separation means are a single element. Thus, the only difference is that the polarization element PE and the dispersion element DE have been replaced by a single dispersive polarization element DPE (such as a birefringent dispersion prism). One advantage of using such a birefringent dispersion prism is that it includes fewer optical surfaces compared to the separate elements DE, PE, and thus has lower losses due to reflection and aberration.

[0105] The above embodiments allow control of the illumination intensity in two (or more) polarization channels according to wavelength. In another embodiment, it is proposed to provide additional control of the phase between these channels at each wavelength, such that other polarization states can be included in the combined output illumination beam. In this way, a spectrum with a completely arbitrary polarization state can be designed. This method requires a beam with a well-defined polarization. Thus, if the source is unpolarized, an additional polarizer can be provided at a position after the source.

[0106] For example, this can be achieved by adding a spatial light modulator (SLM) in the path of the illuminator. For example, a transmissive SLM can be located between the lenses that focus the dispersed radiation onto the GLV module (e.g., Figures 8 to 10 between the lens L2 and the GLV module in ). Each SLM pixel will correspond to a GLV position and can be set to a desired phase delay. This is just an example, and any other optically equivalent arrangement can be implemented, including using a reflective SLM. In fact, the SLM can completely replace the GLV, using the same position and orientation. The phase ramp at a given SLM position can be used to selectively deflect that part of the spectrum onto the beam collector. A flat phase will set the phase of the color and polarization combination at that position.

[0107] Alternatively, a more compact implementation of such phase control can be achieved by configuring the GLV device to provide intensity and phase control on each pixel. As an explanation, a light beam including equal amounts of H and V light can be diagonally polarized, circularly polarized, or elliptically polarized depending on the relative phase between the H component and the V component. In addition to the conventional GLV operation, the GLV providing phase control enables the control of the relative phase and thus the generation of a specific polarization state.

[0108] Reference will be made to Figure 11 explain this concept. In a conventional GLV, as Figure 11 (a) shows, the individual strips are divided into two groups: the active strips AR and the (static) bias strips BR. The active strips AR are selectively applied with a first voltage level V 1 , and the bias strips BR are held at the ground voltage V G . Thus, only the active strips AR move. In the proposed embodiment, as Figure 11 (b) shows, an additional voltage level V 2 is provided such that the first voltage level V 1 sets the first group of active strips AR1, and the second voltage level sets the second group of active strips AR2. In this way, each group of strips AR1, AR2 can have its position (height) changed, enabling the change of the path length and phase between the radiated portions (e.g., between the first dispersive illumination and the second dispersive illumination). Using such a device, full polarization control spectral weighting can be performed without changing the components. This design provides control of the phase between the two polarization channels for each individual color. Since the two phase-controlled polarization channels are coherently recombined in the output branch, each color will exhibit the desired arbitrary polarization state according to the phase between the channels and the desired intensity.

[0109] Spectrally polarized shaped light can be used in metrology devices, for example, such that a spatial modulation device (illumination device) generates a radiation spectrum that is discretized into a plurality of wavelength intervals. Each interval can provide programmable intensity and programmable polarization state.

[0110] Such a metrology device can be capable of optimizing illumination characteristics, for example, having maximum sensitivity to the parameter of interest. It is well known that spectral shaping (where each wavelength interval has its own programmed intensity) provides other advantages in overlay measurements. A device that can set the polarization state for each wavelength interval can further optimize the illumination characteristics because the optimal polarization state will depend on the wavelength.

[0111] Depending on the implementation, the polarization state can be selected between two polarization states (such as horizontal and vertical), or can be selected from a continuous range of polarization states including circular polarization and elliptical states therebetween.

[0112] A number of embodiments will now be described which do not use dispersive elements or prisms and birefringent crystals, but instead use a filter device comprising a plurality of dichroic filters to split an input illumination into a plurality of beams, each having different spectral characteristics, and a polarization beam splitter to split each wavelength into two (or more) corresponding differently polarized beams, which can then be modulated into two or more spectrally configured differently polarized beams.

[0113] The dichroic filter and the polarization (micro or macro) beam splitter can be combined into a composite optical element. Such a composite optical element can be directly attached to the GLV device, for example at the position of the cover window of the GLV device and / or in place of it. This type of integrated optical element can be found, for example, in digital LCD projectors, where they are typically used for polarization recycling but usually do not have a color separation function.

[0114] Figure 12 is a schematic diagram of this concept. Broadband circularly polarized radiation CPR is incident on a first dichroic long-pass filter LP1. The first component of the spectrum (e.g., the blue component) is split off and transmitted to the first pair of beam splitters in the polarization beam splitter array PBSA. The remainder of the illumination is transmitted and split at a second long-pass filter LP2, where a second portion is directed to the second pair of beam splitters of the polarization beam splitter array PBSA. This can be repeated for a third long-pass filter LP3 and up to any number N of additional filters. The polarized beams can be shaped by (optional) shaping optics SO before being modulated by the GLV device.

[0115] The filter can be, for example, a dichroic LP filter with a steep filter edge. Alternatively, a short-pass filter can be used, in which case the beam separation occurs in the opposite spectral direction (e.g., starting from (near) infrared wavelengths). As another alternative, a filter that reflects a small peak from the incident beam (e.g., a notch filter) can be used. In this way, each "picked up" beam can have a very narrow width.

[0116] Regardless of which filter configuration is chosen, the broadband spectrum will be split into spatially separated wavelength components / peaks. The effect of the PBS array on such beams depends on the initial polarization state of the incident light. In one embodiment, the incident radiation can be circularly polarized (e.g., by the action of a quarter-wave plate on a linearly polarized broadband source). Linearly polarized light at 45 degrees can also be used; however, the exact polarization angle orientation of the incident beam relative to the PBS array will determine the exact splitting ratio between the two polarization states at the output of the PBS array. Using circularly polarized light will ensure a 50%-50% split between the two output branches. Thus, circularly polarized illumination can be preferred. In one embodiment, a quarter-wave plate can be placed after each long-pass filter, optimized for its corresponding color in each case.

[0117] The PBS array will transmit the first polarization of the incident circularly polarized light and reflect its second polarization. By placing two identical PBS cubes adjacent to each other, the two polarizations will be spatially separated. Thus, for each color, two adjacent light beams will be incident on the GLV, including mutually perpendicular polarization states.

[0118] Alternatively, an array including Wollaston prisms can be used instead of the PBS array. However, due to the nature of polarization splitting in such a device, the two output light beams may not be parallel, such that at least one of these light beams may need to be steered or redirected to the GLV device.

[0119] If the GLV device includes a dual-band GLV (or two separate GLVs), the number of addressable bands is not limited by the PBS size, but only depends on the color separation optics. Such an arrangement is as Figure 13 shown, where the GLV includes a first active region GLV for the color of the first polarization state (e.g., P-polarized radiation) P and a second active region GLV for the color of the second polarization state (e.g., S-polarized radiation). S . In this example, the radiation has been separated into different colors, for example, by Figure 12 the color filter stack as implemented. These filtered wavelength components can be projected adjacent to each other onto a stack of two elongated PBSs (or two polarization-dependent dichroic mirrors). In this case, a micro-optical device MO can be used to focus the light, but a large single lens (e.g., Figures 8 to 10 the lens L 2 ) can also be used off-axis to separate the incident light beam and the output light beam.

[0120] Figure 14 (a) illustrates another embodiment, which includes a dual PBS unit DPBS configured as shown and a quarter-wave plate QWP in front of the GLV device. The micro-optical device MO and the dual-band GLV are as shown above. The dual PBS unit can include two pairs of PBSs, the internal splitting surfaces of which are oriented in opposite directions in the direction between the input surface and the quarter-wave plate QWP.

[0121] In this arrangement, due to passing through the quarter-wave plate QWP twice, the polarization state of the light propagating towards the GLV is switched. Then, the two reflected light beams with orthogonal polarization states will be steered downward (as shown) to form an output light beam. In this output light beam, the two polarization states are combined in one light beam, which helps to recombine all the color bands into a single light beam, for example, coupled into a free-space optical fiber to enter the sensor module. The incident light can also be circularly polarized, because the first PBS element will be responsible for splitting the light into two orthogonally polarized beams.

[0122] Figure 14 (b) shows the optical path through the dual PBS unit DPBS and the quarter-wave plate QWP (for one color), and shows the monochromatic more in detail. In this example, the input beam IB is shown as entering from the upper left side, represented as including an S-polarization component (gray) and a P-polarization component (black). This input radiation can be unpolarized, circularly polarized, or otherwise include both S and P polarizations (e.g., a 50:50 split of them). First considering the S-polarization component (gray), the two PBSs in the upper part of the figure will transmit this S-polarized radiation and reflect the P-polarized radiation. The quarter-wave plate QWP converts the polarized radiation into circularly polarized radiation (gray dots), which is transmitted to the GLV module. The reflected radiation generated by the GLV module will pass through the quarter-wave plate QWP again to become P-polarized (black). Therefore, the return beam will be turned downward by the PBS in the upper right corner. The PBS at the bottom transmits the P-polarized light and reflects the S-polarized light, so the light will be further transmitted downward from the top into the output beam OB.

[0123] The P-polarization component will follow a different route. The incident P-polarization component (black) will strike the PBS in the upper left corner and be reflected. The PBS in the lower left corner reflects the P-polarized light (this PBS can be replaced by a mirror). As mentioned before, the PBS in the lower right corner transmits the P-polarized light. The light passes through the quarter-wave plate QWP on the way to the GLV and becomes circularly polarized (black dots). After being reflected at the GLV and passing through the quarter-wave plate QWP again to become S-polarized, the light will be reflected by the PBS in the lower right corner and also be turned downward into the output beam OB.

[0124] The advantage of this geometry is that the incident and outgoing beams are perpendicular, so the outgoing and incident optical paths can be easily separated.

[0125] For correct operation, the illumination can be properly focused onto the GLV. This can be achieved by shaping optics (such as a microlens array) in front of the GLV, or by integrated optical elements combined with the GLV window or PBS array.

[0126] The reflected light beam from the GLV needs to be collected. This can be achieved in a variety of ways, depending on the implementation. For example, the radiation can be configured to be incident on the GLV at an angle such that the incident and return beam paths can be separated. In the return path, a second PBS array (e.g., similar to the array shown in the input path) can be used to overlap pairs of light beams with the same color but different polarization states into a combined light beam that can be modulated both in polarization and amplitude. These combined light beams can be further combined again using a second set of dichroic filters or dispersive elements / prisms. Illumination collection and higher-order separation can be achieved by relay optics such as a fly-eye lens array or a microlens array, for example.

[0127] In addition, by adding a quarter-wave plate, the polarization can be changed. After the light beam subsequently passes through the PBS, the polarization will separate the incident and outgoing light beams by 90 degrees. Since the incident and outgoing light beams are exactly 90 degrees, all other angles can be filtered out because this is the angular space where unwanted higher reflection orders exist. In addition, the input filter array can be extended in one dimension such that the same array is used for both coupling in and coupling out. Depending on the space requirements and the final position requirements, there can be several implementations.

[0128] Using the methods and arrangements described herein, multiple metrology devices (such as those described and shown herein) (e.g., scatterometers, liquid level sensors, alignment sensors, holographic microscopes, etc.) can benefit from polarization-resolved spectral weighting.

[0129] Figure 15 FIG. 1500 is a block diagram of a computer system 1500 that can assist in implementing the methods and processes disclosed herein. The computer system 1500 includes a bus 1502 or other communication mechanism for conveying information, and a processor 1504 (or processors 1504 and 1505) coupled to the bus 1502 for processing information. The computer system 1500 also includes a main memory 1506 coupled to the bus 1502 for storing information and instructions to be executed by the processor 1504, such as random access memory (RAM) or other dynamic storage devices. 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.

[0130] The computer system 1500 can be coupled via a bus 1502 to a display 1512, such as a cathode ray tube (CRT) or a flat panel or touch panel display, to display information to a computer user. An input device 1514 (including alphanumeric and other keys) is coupled to the bus 1502 to pass 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 convey direction information and command selections to the processor 1504 and to control cursor movement on the display 1512. This input device typically has two degrees of freedom in two axes (a first axis (e.g., x) and a second axis (e.g., y)), which allows the device to specify a position in a plane. A touch panel (screen) display can also be used as an input device.

[0131] One or more of the methods described herein can be performed by the computer system 1500 in response to one or more sequences of one or more instructions contained in the main memory 1506 being executed by the processor 1504. Such instructions can be read into the main memory 1506 from another computer-readable medium, such as a storage device 1510. Execution of the instruction sequence contained in the main memory 1506 causes the processor 1504 to perform the processing steps described herein. One or more processors in a multiprocessing arrangement can also be employed to execute the instruction sequence contained in the main memory 1506. In alternative embodiments, hardwired circuitry can be used in place of or in combination with software instructions. Accordingly, the description herein is not limited to any specific combination of hardware circuitry and software.

[0132] The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to the processor 1504 for execution. Such a medium can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as the storage device 1510. Volatile media includes dynamic memory, such as the main memory 1506. Transmission media includes coaxial cables, copper wire, and fiber optics, including the wires that make up the bus 1502. Transmission media can also take the form of acoustic 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 tape, any other magnetic medium, CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with hole patterns, RAM, PROM, and EPROM, FLASH-EPROM, any other memory chip or cartridge, the carrier waves described below, or any other medium from which a computer can read.

[0133] Computer-readable media of various forms may be involved in carrying one or more sequences of instructions to the processor 1504 for execution. For example, the instructions may initially be stored on a magnetic 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 the computer system 1500 may receive the data on the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to the bus 1502 may receive the data carried in the infrared signal and place the data on the bus 1502. The bus 1502 transfers the data to the main memory 1506, and the processor 1504 retrieves and executes the instructions from the main memory. The instructions received by the main memory 1506 may optionally be stored on the storage device 1510 before or after being executed by the processor 1504.

[0134] The computer system 1500 also preferably includes a communication interface 1518 coupled to the bus 1502. The communication interface 1518 provides a two-way data communication coupling to a network link 1520 connected to a local network 1522. For example, the communication interface 1518 may 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 may be a Local Area Network (LAN) card to provide a data communication connection to a compatible LAN. A wireless link may 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.

[0135] 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 a data device operated by an Internet Service Provider (ISP) 1526 through the local network 1522. The ISP 1526 in turn provides data communication services through the 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 carrying digital data streams. Signals through various networks, as well as signals on the network link 1520 and signals through the communication interface 1518, are example forms of carrier waves that transmit information, which carry digital data to and from the computer system 1500.

[0136] The computer system 1500 can send messages and receive data, including program code, via (a) network(s), network link 1520, and communication interface 1518. In an Internet example, server 1530 can send request code for an application via 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 upon receipt, and / or stored in storage device 1510 or other non-volatile memory for later execution. In this manner, the computer system 1500 can obtain application code in the form of a carrier wave.

[0137] Other embodiments are disclosed in the following numbered clause list:

[0138] 1. An illumination configuration module, comprising:

[0139] A polarization element for separating incident radiation thereon into a first polarization component having a first polarization state and a second polarization component having a second polarization state;

[0140] A dispersion element arranged to receive and spectrally disperse an input broadband illumination beam or each of the first polarization component and the second polarization component, the polarization element and the dispersion element together being arranged to separate the input broadband illumination beam into at least a first dispersed illumination including the first polarization state and a second dispersed illumination including the second polarization state;

[0141] At least one spatial light modulation device operable to separately modulate each of the first dispersed illumination and the second dispersed illumination to obtain a first spectrally configured illumination and a second spectrally configured illumination; and

[0142] Output optics operable to combine the first spectrally configured illumination and the second spectrally configured illumination into an output illumination beam.

[0143] 2. The illumination configuration module according to clause 1, wherein the polarization element comprises a polarization beam splitter.

[0144] 3. The illumination configuration module according to clause 2, wherein the polarization element comprises a birefringent element.

[0145] 4. The illumination configuration module according to any of the preceding clauses, wherein the dispersion element comprises a prism or a grating.

[0146] 5. The illumination configuration module according to any of the preceding clauses, wherein the polarization element and the dispersion element are separate elements.

[0147] 6. The illumination configuration module according to clause 5, wherein the dispersive element is located between the polarization element and the at least one spatial light modulation device, such that the polarization element separates the input broadband illumination beam into the first polarization component and the second polarization component, and the dispersive element disperses each of the first polarization component and the second polarization component to obtain the first dispersed illumination and the second dispersed illumination.

[0148] 7. The illumination configuration module according to clause 5, wherein the polarization element is located between the dispersive element and the at least one spatial light modulation device, such that the dispersive element disperses the input broadband illumination beam, and the polarization element separates the dispersed input broadband illumination beam into the first dispersed illumination and the second dispersed illumination.

[0149] 8. The illumination configuration module according to any one of the preceding clauses, wherein the polarization element is directly mounted on the face of the dispersive element.

[0150] 9. The illumination configuration module according to clause 1, wherein the polarization element and the dispersive element are implemented as a single dispersive polarization element.

[0151] 10. The illumination configuration module according to clause 9, wherein the single dispersive polarization element includes a dual polarization dispersive prism.

[0152] 11. The illumination configuration module according to any one of the preceding clauses, includes only a single dispersive element.

[0153] 12. The illumination configuration module according to any one of the preceding clauses, includes only a single polarization element.

[0154] 13. The illumination configuration module according to any one of the preceding clauses, includes an input waveplate, and the input waveplate is operable to convert a linearly polarized input broadband illumination into a circularly polarized broadband illumination.

[0155] 14. The illumination configuration module according to any one of the preceding clauses, wherein the first polarization state and the second polarization state include mutually orthogonal polarization states.

[0156] 15. The illumination configuration module according to any one of the preceding clauses, wherein the at least one spatial light modulation device includes at least one grating light valve device.

[0157] 16. The illumination configuration module according to clause 15, wherein the at least one grating light valve device includes an active region, and the active region is operable to modulate the first dispersed illumination and the second dispersed illumination on different corresponding regions of the active region.

[0158] 17. The illumination configuration module according to clause 15, wherein the at least one grating light valve device comprises a dual-band grating light valve device, the dual-band grating light valve device comprising a first active region operable to modulate the first dispersive illumination and a second active region operable to modulate the second dispersive illumination.

[0159] 18. The illumination configuration module according to clause 15, wherein the at least one grating light valve device comprises a first grating light valve device operable to modulate the first dispersive illumination and a second grating light valve device operable to modulate the second dispersive illumination.

[0160] 19. The illumination configuration module according to any one of clauses 15 to 18, wherein each of the at least one grating light valve devices comprises a first set of active bands and a second set of active bands so as to be operable to control the phase between the first dispersive illumination and the second dispersive illumination and thereby impose an arbitrary polarization state on the output illumination beam.

[0161] 20. The illumination configuration module according to any one of clauses 1 to 18, comprising an additional spatial light modulation device operable to selectively impose a phase delay on the first dispersive illumination and / or the second dispersive illumination.

[0162] 21. The illumination configuration module according to any one of clauses 1 to 18, wherein the at least one spatial light modulation device is also operable to selectively impose a phase delay on the first dispersive illumination and / or the second dispersive illumination.

[0163] 22. The illumination configuration module according to any one of the preceding clauses, wherein the output optics comprises the polarization element and the dispersion element.

[0164] 23. The illumination configuration module according to any one of the preceding clauses, wherein the at least one spatial light modulation device is operable to control the intensity of each spectral component of the first spectrally configured illumination and the second spectrally configured illumination.

[0165] 24. An illumination configuration module, comprising:

[0166] a polarization and wavelength separation device operable to separate an input broadband illumination into at least a first dispersive illumination comprising a first polarization state and a second dispersive illumination comprising a second polarization state;

[0167] at least one grating light valve device operable to individually modulate each of the first dispersive illumination and the second dispersive illumination to obtain a first spectrally configured illumination and a second spectrally configured illumination; and

[0168] An output optical device capable of operating to combine the first spectral configuration illumination and the second spectral configuration illumination into an output illumination beam.

[0169] 25. An illumination configuration module, comprising:

[0170] A filter device including a plurality of dichroic filters for splitting an input broadband radiation beam into a plurality of beams, each beam having different spectral characteristics;

[0171] A polarization beam splitting device capable of operating to split each of the beams having different spectral characteristics into corresponding different polarization beams;

[0172] At least one spatial light modulation device capable of operating to individually modulate each of the different polarization beams to obtain spectrally configured different polarization beams; and

[0173] An output optical device capable of operating to combine the spectrally configured different polarization beams into an output illumination beam.

[0174] 26. The illumination configuration module according to clause 25, wherein the plurality of dichroic filters include all long-pass filters or all short-pass filters, and the filters are arranged in the order of the filter wavelengths.

[0175] 27. The illumination configuration module according to clause 25, wherein the plurality of dichroic filters include a plurality of notch filters.

[0176] 28. The illumination configuration module according to any one of clauses 25 to 27, wherein each of the polarization beam splitting devices includes a corresponding pair of polarization beam splitters for each of the beams having different spectral characteristics.

[0177] 29. The illumination configuration module according to any one of clauses 25 to 27, wherein the polarization beam splitting device includes a pair of elongated polarization beam splitters.

[0178] 30. The illumination configuration module according to any one of clauses 25 to 27, wherein the polarization beam splitting device includes two pairs of elongated polarization beam splitters and a quarter-wave plate.

[0179] 31. A measurement device, comprising the illumination configuration module according to any one of the preceding clauses, the measurement device being capable of operating to use the output illumination beam as a measurement illumination for measurement.

[0180] 32. The measurement device according to clause 31, wherein the measurement device includes a scatterometer, an interferometer or a holographic microscope.

[0181] 33. The measurement device according to clause 31 or 32, wherein the measurement device includes an alignment sensor or a liquid level sensor.

[0182] Although the lithographic apparatus may be specifically referred to herein as being used in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, the guiding and detecting of patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0183] Although embodiments of the invention may be specifically referred to herein in the context of a lithographic apparatus, embodiments of the invention may also be used in other apparatuses. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing an object such as a wafer (or other substrate) or a mask (or other patterning device). Such apparatuses are generally referred to as lithographic tools. Such lithographic tools may operate under vacuum conditions or ambient (non-vacuum) conditions.

[0184] Although the embodiments of the invention may be specifically referred to above as being used in the context of optical lithography, it should be understood that, where the context allows, the invention is not limited to optical lithography and may also be used in other applications, such as imprint lithography.

[0185] Although specific embodiments of the invention have been described above, it should be understood that the invention may be practiced in a manner different from that described. The foregoing description is intended to be illustrative and not restrictive. Thus, those skilled in the art will appreciate that the invention described may be modified without departing from the scope of the following claims.

Claims

1. An illumination configuration module, comprising: a polarization element configured to separate incident radiation thereon into a first polarization component having a first polarization state and a second polarization component having a second polarization state; a dispersion element arranged to receive and spectrally disperse an input broadband illumination beam or each of the first and second polarization components, the polarization element and the dispersion element being arranged together to separate the input broadband illumination beam into at least a first dispersed illumination including the first polarization state and a second dispersed illumination including the second polarization state; at least one spatial light modulation device operable to individually modulate each of the first and second dispersed illuminations to obtain a first spectrally configured illumination and a second spectrally configured illumination; and output optics operable to combine the first and second spectrally configured illuminations into an output illumination beam.

2. The illumination configuration module according to claim 1, wherein the polarization element comprises at least one of the following: a polarization beam splitter, the polarization element comprising a birefringent element.

3. The illumination configuration module according to any one of the preceding claims, wherein the dispersion element comprises a prism or a grating.

4. The illumination configuration module according to any one of the preceding claims, wherein the polarization element and the dispersion element are separate elements.

5. The illumination configuration module according to claim 4, wherein the dispersion element is located between the polarization element and the at least one spatial light modulation device such that the polarization element separates the input broadband illumination beam into the first and second polarization components and the dispersion element disperses each of the first and second polarization components to obtain the first and second dispersed illuminations.

6. The illumination configuration module according to claim 4, wherein the polarization element is located between the dispersion element and the at least one spatial light modulation device such that the dispersion element disperses the input broadband illumination beam and the polarization element separates the dispersed input broadband illumination beam into the first and second dispersed illuminations.

7. The illumination configuration module according to any one of the preceding claims, wherein the polarization element is directly mounted on a face of the dispersion element.

8. The illumination configuration module according to claim 1, wherein the polarization element and the dispersion element are implemented as a single dispersive polarization element, and optionally, wherein the single dispersive polarization element comprises a birefringent dispersive prism.

9. The illumination configuration module according to any one of the preceding claims, comprising only a single dispersion element.

10. The illumination configuration module according to any one of the preceding claims, comprising only a single polarization element.

11. The illumination configuration module according to any one of the preceding claims, comprising an input waveplate operable to convert a linearly polarized input broadband illumination into a circularly polarized broadband illumination.

12. The illumination configuration module according to any one of the preceding claims, wherein the first polarization state and the second polarization state include mutually orthogonal polarization states.

13. The illumination configuration module according to any one of the preceding claims, wherein the at least one spatial light modulation device includes at least one grating light valve device.

14. The illumination configuration module according to claim 13, wherein the at least one grating light valve device includes one of the following options: An active region capable of operating to modulate the first dispersed illumination and the second dispersed illumination on different respective regions of the active region, A dual-band grating light valve device including a first active region capable of operating to modulate the first dispersed illumination and a second active region capable of operating to modulate the second dispersed illumination, and A first grating light valve device and a second grating light valve device, the first grating light valve device being capable of operating to modulate the first dispersed illumination and the second grating light valve device being capable of operating to modulate the second dispersed illumination.

15. A measurement device including the illumination configuration module according to any one of the preceding claims, the measurement device being capable of operating to use the output illumination beam as a measurement illumination for measurement.

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