Device and method for filtering measurement radiation

Abstract

The source selection module includes an adjustable diffractive element including a plurality of pixels. The source selection module also includes a light dispersing element configured to receive the first light and the second light. The light dispersing element distributes the first light over the first pixel to generate zero and non-zero order diffraction. The light dispersing element also spatially distributes the second light over the second pixel to generate zero and non-zero order diffraction. The source selection module includes a continuously variable filter including a first region and a second region. The zeroth order of the first light received by the first region and the zeroth order of the second light received by the second region are transmitted or reflected. A non-zero order of the first light is blocked outside the first region, and a non-zero order of the second light is blocked outside the second region.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to EP application 22201858.2 filed on October 17, 2022, EP application 23160954.6 filed on March 9, 2023, and EP application 23170044.4 filed on April 26, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to methods and apparatus that can be used, for example, in the manufacture of devices by lithographic techniques, and to methods of manufacturing devices using lithographic techniques. The present invention more particularly relates to metrology sensors and lithographic apparatus having such metrology sensors, and more particularly still to an illumination arrangement for such metrology sensors. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, typically a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device (alternatively referred to as a mask or reticle) can be used to generate a circuit pattern to be formed on an individual layer of the IC. The pattern can be transferred onto a target portion (e.g., including a part of a die, a single die, or multiple dice) on the substrate (e.g., a silicon wafer). The transfer of the pattern is typically provided onto the substrate via imaging onto a layer of radiation-sensitive material (photoresist). Generally, a single substrate will contain a network of adjacent target portions that are continuously patterned. These target portions are typically referred to as “fields”.

[0005] In the manufacture of complex devices, typically many lithographic patterning steps are performed to form functional features in successive layers on a substrate. 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 defined in a previous layer (by the same apparatus or a different lithographic apparatus). For this purpose, the substrate is provided with one or more sets of alignment marks. Each mark is a structure whose position can be measured later using a position sensor (typically an optical position sensor). A lithographic apparatus includes one or more alignment sensors through which the position of the marks on the substrate can be accurately measured. Different types of marks and different types of alignment sensors are known from different manufacturers as well as from different products of the same manufacturer.

[0006] In other applications, metrology sensors are used to measure the exposed structures on a substrate (in the photoresist and / or after etching). A fast and non-invasive dedicated inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the substrate surface, and the properties of the scattered or reflected beam are measured. Examples of known scatterometers include angle-resolved scatterometers of the type described in US2006033921A1 and US2010201963A1. In addition to reconstructing the measured feature shape, diffraction-based overlay can also be measured using a device such as that described in the published patent application US2006066855A1. Diffraction-based overlay metrology using diffraction order dark field imaging enables overlay measurements on smaller targets. Examples of dark field imaging metrology can be found in international patent applications WO2009 / 078708 and WO2009 / 106279, the entire contents of which are incorporated herein by reference. Further developments of this technology have been described in the published patent publications US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A and WO2013178422A1. These targets can be smaller than the illumination spot and can be surrounded by product structures on the wafer. Using a composite grating target, multiple gratings can be measured in one image. The contents of all these applications are also incorporated herein by reference.

[0007] In some metrology applications, such as in some scatterometers or alignment sensors, defects in the metrology target may cause the measured values from that target to vary with wavelength / polarization. Thus, sometimes the correction for and / or mitigation of such variations is effected by performing the same measurement using multiple different wavelengths and / or polarizations (or more generally, multiple different illumination conditions). For such metrology applications, it is desirable to improve the switching and selection of the spectral components of the illumination. SUMMARY OF THE INVENTION

[0008] According to one aspect of the present disclosure, a source selection module is provided, including a tunable diffraction element, which includes a plurality of pixels. The source selection module further includes a light dispersion element configured to receive first light of a first wavelength and second light of a second wavelength. The light dispersion element spatially distributes the first light above a first pixel among the plurality of pixels to generate a zero-order diffraction of the first light and a non-zero-order diffraction of the first light. The light dispersion element also spatially distributes the second light above a second pixel among the plurality of pixels to generate a zero-order diffraction of the second light and a non-zero-order diffraction of the second light. The source selection module includes a continuously variable filter, which includes a first region and a second region. The continuously variable filter is arranged such that the zero-order of the first light received by the first region and the zero-order of the second light received by the second region are transmitted or reflected by the continuously variable filter. The non-zero-order of the first light is blocked outside the first region by the continuously variable filter, and the non-zero-order of the second light is blocked outside the second region by the continuously variable filter.

[0009] Optionally, each of the plurality of pixels may include a controllable grating.

[0010] Optionally, the tunable diffraction element may include a grating light valve.

[0011] Optionally, the continuously variable filter may be arranged on the optical path between the light dispersion element and the tunable diffraction element.

[0012] Optionally, the continuously variable filter may be arranged at a certain distance from the tunable diffraction element or at a certain distance from the conjugate image plane of the tunable diffraction element such that the zero-order diffraction and non-zero-order diffraction of the first light are spatially separated from the zero-order diffraction and non-zero-order diffraction of the second light.

[0013] Optionally, the light dispersion element may include a prism.

[0014] Optionally, the light dispersion element may include a light dispersion grating.

[0015] Optionally, the continuously variable filter may include a continuously varying bandpass layer.

[0016] Optionally, the plane of the continuously variable filter may be inclined with respect to the plane of the tunable diffraction element.

[0017] Optionally, the continuously variable filter may be translated parallel to the tunable diffraction element and thereby may modify the local transmission / reflection properties at one or more pixel positions of the diffraction element.

[0018] Optionally, the filtering characteristics for transmitting / reflecting and blocking radiation are linearly distributed over the region of the continuously variable filter.

[0019] Optionally, a module according to any one of claims 1 to 9, wherein the filtering characteristics are non-linearly distributed over a region of a continuously variable filter.

[0020] Optionally, the continuously variable filter may have a first optical filtering characteristic in a first region and a second optical filtering characteristic in a second region.

[0021] Optionally, both the first wavelength and the second wavelength may be in the range of 400 nm to 900 nm. In some embodiments, both the first wavelength and the second wavelength may be in the range of 400 nm to 2000 nm, or in the range of 400 nm to 1600 nm.

[0022] According to another aspect of the present disclosure, a method is provided. First light of a first wavelength and second light of a second wavelength are received. An optical dispersion element spatially distributes the first light on a first pixel of an adjustable diffraction element including a plurality of pixels, and spatially distributes the second light on a second pixel among the plurality of pixels of the adjustable diffraction element. The first pixel generates a zero-order diffraction of the first light and a non-zero-order diffraction of the first light. The second pixel generates a zero-order diffraction of the second light and a non-zero-order diffraction of the second light. The continuously variable filter receives the zero-order diffraction of the first light in a first region of the continuously variable filter and receives the zero-order of the second light in a second region of the continuously variable filter. The continuously variable filter also receives the non-zero-order diffraction of the first light outside the first region and receives the non-zero-order diffraction of the second light outside the second region. The continuously variable filter transmits or reflects the zero-order diffraction of the first light in the first region and the zero-order diffraction of the second light in the second region. The continuously variable filter blocks the non-zero-order of the first light outside the first region and blocks the non-zero-order of the second light outside the second region.

[0023] According to another aspect of the present disclosure, a non-transitory computer program product is provided, which includes machine-readable instructions. The instructions, when executed by a computer system, may be configured to cause the computer system to control a source selection module as described herein to perform the method as described above.

[0024] According to another aspect of the present disclosure, a processor and an associated storage medium are provided. The storage medium may include the above non-transitory computer program, such that the processor is operable to control a source selection module as described herein to perform the method as described above.

[0025] According to another aspect of the present disclosure, a metrology device is provided, including the above-described processor and an associated storage medium, so as to be operable to control a source selection module as described herein to perform the method as described above.

[0026] According to another aspect of the present disclosure, a lithography apparatus is provided, including a source selection module as described herein.

[0027] According to another aspect of the present disclosure, there is provided a lithography device including the processor and the associated storage medium as described above, so as to be operable to control the source selection module as described herein to perform the method as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the present invention will now be described with reference to the drawings by way of example only, in which:

[0029] Figure 1 a lithography apparatus is depicted;

[0030] Figure 2 a schematic diagram of a lithography device is depicted;

[0031] Figure 3 a schematic representation depicting the cooperation between three key technologies to optimize the overall lithography in semiconductor manufacturing is depicted;

[0032] Figure 4 a schematic diagram of a scatterometry device used as a metrology device is depicted, which may include a dark-field digital holographic microscope according to an embodiment of the present invention;

[0033] Figure 5 (a) shows a schematic diagram of a dark-field scatterometer used in measuring a target using a first reference illumination aperture;

[0034] Figure 5 (b) shows details of the diffraction spectrum of a target grating for a given illumination direction;

[0035] Figure 5 (c) shows a second pair of apertures used in the illumination branch;

[0036] Figure 5 (d) shows a third pair of apertures used in the illumination branch;

[0037] Figure 6 (a) shows a top view of a grating light valve;

[0038] Figure 6 (b) shows an end view of the grating light valve in a first configuration (e.g., as shown in Figure 6 (a));

[0039] Figure 6 (c) shows an end view of the grating light valve in a second configuration (e.g., as shown in Figure 6 (a));

[0040] Figure 7(a) is a schematic representation of the interaction of radiation with a grating light valve, where the pixels of the grating light valve are not biased and thus act as mirrors for the input radiation.

[0041] Figure 7 (b) is a schematic representation of the interaction of radiation with a grating light valve, where the pixels of the grating light valve are biased and thus act as a diffraction grating for the input radiation;

[0042] Figure 8 (a) is a schematic representation of input radiation having multiple (e.g., N = 5) wavelengths;

[0043] Figure 8 (b) shows a top view of a grating light valve having multiple pixels, where each of the multiple wavelengths of the input radiation is incident on one of the multiple pixels (e.g., N = 5);

[0044] Figure 8 (c) shows a side view of the grating light valve (e.g., as shown in Figure 8 (b)), where the unbiased pixels act as mirrors and the biased pixels act as diffraction gratings, and the aperture stop is arranged to transmit the zero - order diffracted radiation;

[0045] Figure 8 (d) is a schematic representation of the output radiation that has passed through the aperture stop (e.g., as shown in Figure 8 (c));

[0046] Figure 9 is a schematic representation of an example setup of a wavelength - selection module configured for zero - order mode operation;

[0047] Figure 10 is a schematic representation of an aperture stop for selecting zero - order diffracted radiation;

[0048] Figure 11 is a schematic representation of an example source - selection module including a continuously variable filter;

[0049] Figure 12 (a) is a schematic representation of the interaction (e.g., diffraction and reflection) between input radiation of a certain wavelength and a tunable diffraction element;

[0050] Figure 12 (b) is a schematic representation of single - wavelength selection using a tunable diffraction element and a continuously variable filter;

[0051] Figure 12 (c) is a schematic representation of multi - wavelength selection using a tunable diffraction element and a continuously variable filter;

[0052] Figure 13is a schematic representation of a continuously variable filter that can be moved by a first actuator and / or can be moved by a second actuator;

[0053] Figure 14A shows a top view of an example setup of a wavelength selection module configured for first-order mode operation;

[0054] Figure 14B shows a side view of an example setup of a wavelength selection module configured for first-order mode operation;

[0055] Figure 14C shows an example pupil representation of an example wavelength selection module (e.g., as shown in Figure 14A or Figure 14B );

[0056] Figure 15 is a schematic representation of a continuously variable filter (also known as a wedge filter) according to an embodiment, including a substrate with a multi-layer coating;

[0057] Figure 16 shows an example transmission spectrum of a wedge filter (e.g., as shown in Figure 15 ), where multiple separated transmission bands respectively correspond to multiple regions of the wedge filter (each region having a central position);

[0058] Figure 17A shows an example transmission profile along the wedge direction of a wedge filter (e.g., as shown in Figure 15 ), the wedge filter being configured for use in a wavelength selection module configured for zero-order mode operation (e.g., as shown in Figure 9 ); and

[0059] Figure 17B shows an example transmission profile along the wedge direction of a wedge filter, the wedge filter being configured for use in a wavelength selection module configured for first-order mode operation (e.g., as shown in Figures 14A - 14C ). Detailed Description

[0060] Before describing embodiments of the present invention in detail, it is beneficial to introduce an example environment in which embodiments of the present invention can be implemented.

[0061] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation and particle radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm), EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 nm to 100 nm), X-ray radiation, UV, visible light and IR radiation (e.g., in the range of 100 nm to 2,000 nm), electron beam radiation and other particle radiation.

[0062] The term "reticle", "mask" or "patterning device" as used in this text can be broadly interpreted to refer to a general patterning device that can be used to impart a patterned cross-section to an incoming radiation beam that corresponds 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.).

[0063] 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, EUV radiation or X-ray radiation); a reticle support (e.g., a reticle stage) T constructed to support a patterning device (e.g., a reticle) 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 stage) WT constructed to hold a substrate (e.g., a wafer coated with a photoresist) 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.

[0064] In operation, the illumination system IL receives the radiation beam from a radiation source SO, e.g., via a beam delivery system BD. The illumination system IL can include various types of optical components, such as refractive, reflective, diffractive, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for guiding, shaping and / or controlling the radiation. The illuminator IL can be used to condition the radiation beam B such that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0065] The term "projection system" PS as used herein should be broadly interpreted to cover various types of projection systems, including refractive, reflective, diffractive, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, adapted to the exposure radiation being used, and / or other factors such as the use of an immersion liquid or the use of a vacuum. Any use herein of the term "projection lens" may be considered synonymous with the more general term "projection system" PS.

[0066] 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), thereby filling the space between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion techniques is given in US6952253, the entire content of which is incorporated herein by reference.

[0067] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps preparatory to a subsequent exposure of a substrate W located on one of the substrate supports WT may be carried out while another substrate W on another substrate support WT is being used for exposing a pattern on that other substrate W.

[0068] In addition to the substrate support WT, the lithographic apparatus LA may also include a metrology stage. The metrology stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure properties of the projection system PS or of the radiation beam B. The metrology stage may hold a plurality of sensors. The cleaning device may be arranged to clean a part of the lithographic apparatus, such as a part of the projection system PS or a part of the system providing the immersion liquid. The metrology stage may move under the projection system PS when the substrate support WT is moved away from the projection system PS.

[0069] In operation, the radiation beam B is incident on a patterning device (e.g., a mask) MA held on a mask support T and is patterned by the pattern (design layout) present on the patterning device MA. After passing through the mask MA, the radiation beam B passes through the projection system PS which focuses the beam onto a target portion C of the substrate W. By means of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example, in order to position different target portions C of 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 depicted in the figure) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning device MA and the substrate W. Although the illustrated substrate alignment marks P1, P2 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 referred to as scribe alignment marks.

[0070] As Figure 2 shown, the lithographic apparatus LA can form part of a lithographic cell LC, sometimes also referred to as a lithocell or (lithographic) cluster, which often also includes equipment for performing pre-exposure and post-exposure processes on the substrate W. Conventionally, these include a spin coater SC for depositing a photoresist layer, a developer DE for developing the exposed photoresist, a cooling plate CH and a baking plate BK, for example for regulating the temperature of the substrate W, for example for regulating the solvent in the photoresist layer. A substrate handler or robot RO picks up the substrates W from the input / output ports I / O1, I / O2, moves them between different process devices, and delivers the substrates W to the load platform LB of the lithographic apparatus LA. The equipment in the lithographic cell is typically also collectively referred to as a track, and they can be under the control of a track control unit TCU, while the track control unit TCU itself can be controlled by a monitoring and control system SCS, which can also control the lithographic apparatus LA, for example via a lithography control unit LACU.

[0071] During the lithography process, it is necessary to frequently measure the created structures, for example, for process control and verification. A tool for performing such measurements can be referred to as a metrology tool MT. Different types of metrology tools MT for performing such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools MT. A scatterometer is a versatile instrument that allows the measurement of parameters of the lithography process. By placing a sensor in or near the pupil of the scatterometer objective lens or in or near a plane conjugate to the pupil, such measurement is generally referred to as pupil-based measurement, or by placing a sensor in or near the image plane or in or near a plane conjugate to the image plane, such measurement is generally referred to as image- or field-based measurement. Such scatterometers and associated 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 hard X-ray (HXR), soft X-ray (SXR), extreme ultraviolet (EUV), visible to near-infrared (IR), and IR wavelength ranges to measure gratings. In the case where the radiation is hard X-ray or soft X-ray, the above-mentioned scatterometer can optionally be a small-angle X-ray scattering metrology tool.

[0072] In order for the substrate W to be exposed by the lithography apparatus LA to be correctly and consistently exposed, it is necessary to inspect the substrate to measure the properties of the patterned structures, such as overlay errors between subsequent layers, line thickness, critical dimension (CD), structure shape, etc. For this purpose, an inspection tool and / or a metrology tool (not shown) can be included in the lithography device LC. If an error is detected, then, for example, the exposure of subsequent substrates or other processing steps to be performed on the substrate W can be adjusted, especially if the inspection is carried out before the same batch or other substrates W in the batch are still to be exposed or processed.

[0073] An inspection device (which can also be referred to as a metrology device) is used to determine the properties of the substrate W, in particular how the properties of different substrates W vary or how the properties associated with different layers of the same substrate W vary layer by layer. Alternatively, the inspection device can be configured to identify defects on the substrate W and can be, for example, part of the lithography device LC, or can be integrated into the lithography apparatus LA, or can even be a stand-alone device. The inspection device can measure properties regarding a latent image (the image in the photoresist layer after exposure), or regarding a semi-latent image (the image in the photoresist layer after the post-exposure bake step PEB), or regarding a developed photoresist image (where the exposed or unexposed portions of the photoresist have been removed), or even regarding an etched image (after a pattern transfer step such as etching).

[0074] In a first embodiment, the scatterometer MT is an angle-resolved scatterometer. In such a scatterometer, a reconstruction method can be applied to the measurement signal to reconstruct or calculate properties of the grating. Such reconstruction can be obtained, for example, 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 the diffraction pattern observed from the real target.

[0075] In a second embodiment, the scatterometer MT is a spectroscopic scatterometer MT. In such a spectroscopic scatterometer MT, the radiation emitted by the radiation source is directed onto the target, and the radiation reflected, transmitted or scattered from the target is directed to a spectrometer detector that measures the spectrum of the specularly reflected radiation (i.e., measures the intensity as a function of wavelength). Based on this data, the structure or profile of the target that produced the detected spectrum can be reconstructed, for example, by rigorous coupled-wave analysis and non-linear regression or by comparison with a simulated spectral library. Additionally and / or alternatively, the scatterometer MT can measure the intensity of the measured radiation.

[0076] In a third embodiment, the scatterometer MT is an ellipsometric scatterometer. An ellipsometric scatterometer allows determination of parameters of a lithography process by measuring the scattered or transmitted radiation for each polarization state. Such a metrology device emits polarized light (such as linear, circular or elliptical) by using, for example, an appropriate polarization filter in the illumination section of the metrology device. Sources suitable for this metrology device can also provide polarized radiation. Various embodiments of existing ellipsometric scatterometers are described in U.S. Patent Applications 11 / 451,599, 11 / 708,678, 12 / 256,780, 12 / 486,449, 12 / 920,968, 12 / 922,587, 13 / 000,229, 13 / 033,135, 13 / 533,110 and 13 / 891,410, the entire contents of which are incorporated herein by reference.

[0077] In one embodiment of the scatterometer MT, the scatterometer MT is adapted to measure the overlap of two misaligned gratings or periodic structures by measuring the reflection spectrum and / or detecting the asymmetry in the detection configuration, which asymmetry is related to the degree of overlap. The two (possibly overlapping) grating structures may be applied to two different layers (not necessarily consecutive layers) and may be formed at substantially the same location on the wafer. The scatterometer may have a symmetric detection configuration, as described, for example, in the co-owned patent application EP1,628,164A, such that any asymmetry can be clearly distinguished. This provides a direct method for measuring misalignment in the grating. Additional examples of the overlap error between two layers containing periodic structures resulting from measuring the target by the asymmetry of the periodic structure can be found in PCT patent application publication number WO2011 / 012624 or U.S. patent application US20160161863, the entire contents of which are incorporated herein by reference.

[0078] Other parameters of interest may be focus and dose. The 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 may 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 dimensions and sidewall angles are available, the focus and dose can be uniquely determined from these measurements.

[0079] The metrology target may be a collection of composite gratings primarily in the photoresist, formed by the lithography process, but may also be formed after other manufacturing processes (e.g., an etching process). The pitch and linewidth of the structures in the grating may strongly depend on the measurement optics (especially the NA of the optics) in order to be able to capture the diffraction orders from the metrology target. As indicated earlier, the diffraction signal can be used to determine the offset (also known as "overlay") between two layers, or can be used to reconstruct at least a portion of the original grating produced by the lithography process. This reconstruction can be used to provide guidance on the quality of the lithography process and can be used to control at least a portion of the lithography process. The target may have smaller sub-segments that are configured to mimic the dimensions of the functional portions of the design layout in the target. Due to such sub-segments, the behavior of the target will be more similar to the functional portions of the design layout, such that the overall process parameter measurements are more similar to the functional portions of the design layout. The target can be measured in an underfill mode or an overfill mode. In the underfill mode, the spot generated by the measurement beam is smaller than the total target. In the overfill mode, the spot generated by the measurement beam is larger than the total target. In such an overfill mode, it is also possible to measure different targets simultaneously, thereby determining different process parameters simultaneously.

[0080] The overall measurement quality using lithography parameters for a specific target is at least partly determined by the measurement scheme used to measure the lithography parameter. The term "substrate measurement scheme" 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 scheme 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. One of the criteria for selecting the measurement scheme can be, for example, the sensitivity of one of the measurement parameters to process variations. More examples are described in U.S. Patent Application US2016-0161863 and Published U.S. Patent Application US2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0081] The patterning process in the lithography apparatus LA can be one of the most critical steps in the process, which requires high-accuracy sizing and placement of structures on the substrate W. To ensure such high accuracy, three systems can be combined in a so-called "integrated" control environment, as Figure 3 schematically depicted. 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 an "integrated" environment is to optimize the collaboration between these three systems to enhance the overall process window and provide a tight control loop to ensure that the patterning performed by the lithography apparatus LA remains within the process window. The process window defines the range of process parameters (e.g., dose, focus, overlay) within which a particular manufacturing process produces a defined result (e.g., a functional semiconductor device) - the process parameters in the lithography process or patterning process are allowed to vary within this range.

[0082] The computer system CL can use (a portion of) the design layout to be patterned to predict which resolution enhancement techniques are to be used and perform computational lithography simulations and operations to determine which mask layout and lithography apparatus settings can achieve the maximum overall process window for the patterning process (depicted by the double arrow in the first scale SC1 in Figure 3 ). The resolution enhancement techniques can be arranged to match the patterning capabilities of the lithography apparatus LA. The computer system CL can also be used to detect (e.g., using input from the metrology tool MET) the current operating position of the lithography apparatus LA within the process window to predict whether there may be defects due to, for example, suboptimal processing (depicted by the arrow pointing to "0" in the second scale SC2 in Figure 3 ).

[0083] A metrology tool MT can provide input to a computer system CL to enable accurate simulation and prediction, and can provide feedback to a lithographic apparatus LA to identify possible offsets, e.g., in the calibration state of the lithographic apparatus LA (depicted by multiple arrows in Figure 3 by the third scale SC3).

[0084] Many different forms of metrology tool MT can be provided for measuring structures created using a lithographic patterning device. The metrology tool MT can use electromagnetic radiation to interrogate the structure. The properties of the radiation (e.g., wavelength, bandwidth, power) can affect different measurement characteristics of the tool, and shorter wavelengths generally allow higher resolution. The radiation wavelength has an impact on the resolution that can be achieved by the metrology tool. Thus, to be able to measure structures with small feature sizes, a metrology tool MT with a short wavelength radiation source is preferred.

[0085] Another way in which the radiation wavelength can affect the measurement characteristics is the penetration depth, and the transparency / opacity of the material to be inspected at the radiation wavelength. Depending on the opacity and / or penetration depth, the radiation can be used for measurements in transmission or reflection. The type of measurement can affect whether information about the surface and / or the interior of the structure / substrate is obtained. Thus, the penetration depth and opacity are other elements to be considered when selecting the radiation wavelength for the metrology tool.

[0086] To achieve higher resolution in the measurement of lithographically patterned structures, a metrology tool MT with a short wavelength is preferred. This can include wavelengths shorter than the visible wavelength (e.g., UV, EUV, and the X-ray part of the electromagnetic spectrum). Hard X-ray methods (such as transmission small angle X-ray scattering (TSAXS)) utilize the high resolution and high penetration depth of hard X-rays and can thus operate in transmission mode. On the other hand, soft X-rays and EUV do not penetrate the target very far, but may induce a rich optical response in the material to be probed. This may be due to the optical properties of many semiconductor materials and due to the fact that the size of the structure is comparable to the probing wavelength. Thus, EUV and / or soft X-ray metrology tools MT can operate in reflection mode, e.g., by imaging or by analyzing the diffraction pattern from the lithographic pattern structure.

[0087] For hard X-rays, soft X-rays, and EUV radiation, applications in high-volume manufacturing (HVM) may be limited due to the lack of available high-brightness radiation sources at the required wavelengths. In the case of hard X-rays, sources commonly used in industrial applications include X-ray tubes. X-ray tubes (including, for example, advanced X-ray tubes based on liquid-metal anodes or rotating anodes) may be relatively inexpensive and compact, but may lack the brightness required for HVM applications. High-brightness X-ray sources such as synchrotron light sources (SLS) and X-ray free-electron lasers (XFEL) currently exist, but their size (>100 m) and high cost (hundreds of millions of euros) make them too large and expensive for metrology applications. Similarly, there is a lack of ways to obtain sufficiently bright EUV and soft X-ray radiation sources.

[0088] Figure 4 An example of a metrology device (such as a scatterometer) is depicted. It may include a broadband (e.g., white light) radiation projector 2 that projects radiation 5 onto a substrate W. The reflected or scattered radiation 10 is transmitted to a spectrometer detector 4 that measures the spectrum 6 of the specularly reflected radiation (i.e., measures the intensity I as a function of the wavelength λ). Based on this data, for example, through rigorous coupled-wave analysis and non-linear regression or by comparison with a simulation spectrum library as shown at the bottom, a processing unit PU can reconstruct the structure or profile 8 that generated the detected spectrum. Generally, for the reconstruction, the general form of the structure is known, and some parameters are assumed from knowledge of the structure manufacturing process, leaving only some structural parameters to be determined from the scatterometry measurement data. Such a scatterometer can be configured as a normal-incidence scatterometer or an oblique-incidence scatterometer. Figure 4 The overall measurement quality of lithography parameters obtained via measurement of a metrology target is at least partially determined by the measurement scheme used to measure the lithography parameter. The term "substrate measurement scheme" 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 scheme 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. One of the criteria for selecting a measurement scheme can be, for example, the sensitivity of one of the measurement parameters to process variations. More examples are described in U.S. Patent Application US2016 / 0161863 and Published U.S. Patent Application US2016 / 0370717A1, the entire contents of which are incorporated herein by reference.

[0089]

[0090] Figure 5 Figure 5 (a) shows another type of metrology device. Figure 5(b) shows more details of the target T and the diffracted rays of the measurement radiation used to irradiate the target. The illustrated metrology device is of the type known as a dark-field metrology device. The metrology device depicted here is purely exemplary to provide an explanation of dark-field metrology. The metrology device can be a stand-alone device or can be incorporated into a lithographic apparatus LA (e.g., at a measurement station) or a lithographic cell LC. The optical axis has several branches throughout the device, denoted by the dashed line O. In this device, light emitted by a source 11 (e.g., a xenon lamp) is guided by an optical system via a beam splitter 15 onto a substrate W, the optical system including lenses 12, 14, and an objective lens 16. These lenses are arranged in a double sequence in a 4F arrangement. Different lens arrangements can be used as long as it still provides an image of the substrate onto the detector and at the same time allows access to the intermediate pupil plane for spatial frequency filtering. Thus, the angular range of the radiation incident on the substrate can be selected by defining the spatial intensity distribution in the plane that presents the spatial spectrum of the substrate plane (here called the (conjugate) pupil plane). In particular, this can be done by inserting an aperture plate 13 of an appropriate form between lenses 12 and 14 in the plane that is the back-projected image of the objective lens pupil plane. In the illustrated example, the aperture plate 13 has different forms, labeled 13N and 13S, thus allowing the selection of different illumination modes. The illumination system in this example forms an off-axis illumination mode. In the first illumination mode, the aperture plate 13N provides off-axis illumination from a direction designated as "north" (for descriptive purposes only). In the second illumination mode, the aperture plate 13S is used to provide a similar illumination but from the opposite direction labeled "south". Other illumination modes are possible by using different apertures. The rest of the pupil plane is expected to be dark because any unwanted light outside the desired illumination mode will interfere with the desired measurement signal.

[0091] As Figure 5 As shown in (b), the target T is placed such that the substrate W is perpendicular to the optical axis O of the objective lens 16. The substrate W can be supported by a support (not shown). Rays of the measurement radiation I impinge on the target T at an angle off the axis O, generating a zero-order ray (solid line 0) and two first-order rays (dot-dashed line +1 and double dot-dashed line -1). It should be remembered that for a small overfilled target, these rays are just one of many parallel rays that cover the substrate area (including the metrology target T and other features). Since the apertures in the plate 13 have a finite width (required to admit a useful amount of light), the incident rays I will actually occupy a certain angular range, and the diffracted rays 0 and +1 / -1 will be slightly spread. According to the point spread function of the small target, each order +1 and -1 will be further spread into a certain angular range rather than a single ideal ray as shown. Note that the grating pitch and illumination angle of the target can be designed or adjusted such that the first-order rays entering the objective lens are closely aligned with the central optical axis.Figure 5 (a) and Figure 5 the rays illustrated in (b) are shown as being slightly off-axis, purely for the purpose of making them more distinguishable in the figure.

[0092] The 0 and +1 orders diffracted at least by the target T on the substrate W are collected by the objective lens 16 and guided back through the beam splitter 15. Back to Figure 5 (a), both the first illumination mode and the second illumination mode are illustrated by designating the apertures diametrically opposite the diameters marked North (N) and South (S). When the incident ray I of the measured radiation comes from the north side of the optical axis, that is, when the first illumination mode is applied using the aperture plate 13N, the +1 diffracted ray (marked as +1(N)) enters the objective lens 16. Conversely, when the second illumination mode is applied using the aperture plate 13S, the -1 diffracted ray (marked as 1(S)) is the diffracted ray entering the lens 16.

[0093] The second beam splitter 17 divides the diffracted beam into two measurement branches. In the first measurement branch, the optical system 18 uses the zero-order diffracted beam and the first-order diffracted beam to form a diffracted spectrum (pupil plane image) of the target on the first sensor 19 (e.g., a CCD or CMOS sensor). Each diffracted order hits a different point on the sensor, enabling image processing to compare and contrast the orders. The pupil plane image captured by the sensor 19 can be used for focusing metrology devices and / or normalizing the intensity measurement of the first-order beam. The pupil plane image can also be used for many measurement purposes (such as reconstruction).

[0094] In the second measurement branch, the optical systems 20, 22 form an image of the target T on the sensor 23 (e.g., a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is provided in a plane conjugate to the pupil plane. The aperture stop 21 is used to block the zero-order diffracted beam, such that the image of the target formed on the sensor 23 is formed only by the -1 or +1 first-order beam. The images captured by the sensors 19 and 23 are output to the processor PU, which processes the images, and the functions of the processor PU depend on the specific type of measurement being performed. Note that the term "image" is used here in a broad sense. If only one of the -1 order and +1 order exists, an image of the grating lines will not be formed.

[0095] Figure 5The specific forms of the aperture plate 13 and the field stop 21 shown in [reference] are merely examples. In another embodiment of the present invention, on-axis illumination of the target is used, and an aperture stop with an off-axis aperture is used to transmit substantially only a first-order diffracted light to the sensor. In other examples, a two-quadrant aperture can be used. This can enable the simultaneous detection of positive and negative orders, as described in US2010201963A1 mentioned above. Embodiments having a optical wedge (segmented prism or other suitable element) in the detection branch can be used to separate the orders for spatial imaging in a single image, as described in US2011102753A1 mentioned above. In still other embodiments, second-order beams, third-order beams, and higher-order beams ( Figure 5 not shown in [reference]) can be used in the measurement, instead of or in addition to the first-order beam. In still other embodiments, a segmented prism can be used instead of the aperture stop 21, thereby enabling the simultaneous capture of +1st order and -1st order at spatially separated positions on the image sensor 23.

[0096] To adapt the measurement radiation to these different types of measurements, the aperture plate 13 can include several aperture patterns formed around a disk, and the disk rotates to bring the desired pattern into position. It should be noted that the aperture plate 13N or 13S can only be used for measuring gratings oriented in one direction (X or Y, depending on the setting). For the measurement of orthogonal gratings, rotating the target by 90° and 270° can be achieved.

[0097] The light source (which can also be referred to as a radiation source) that can be used for the metrology applications of the concepts disclosed herein can include a broadband source and a color selection arrangement (which can also be referred to as a wavelength selection arrangement or module) to select one or more colors from the broadband output. By way of example, the radiation source can be based on a hollow-core or solid-core optical fiber (such as a hollow-core photonic crystal fiber (HC-PCF) or a solid-core photonic crystal fiber (SC-PCF)). For example, in the case of an HC-PCF, the hollow core of the fiber can be filled with a gas, which acts as an expanding medium for expanding the input radiation. Such a fiber and gas arrangement can be used to create a supercontinuum radiation source. The radiation input to the fiber can be electromagnetic radiation, such as radiation in one or more of the infrared, visible light, UV, and extreme UV spectra. The output radiation can consist of or include broadband radiation, which can be referred to as white light herein. This is just one example of the broadband light source technology that can be used in the methods and devices disclosed herein, and other suitable technologies can be employed instead. The output radiation can include radiation in the range from 400 nm to 900 nm. The output radiation can include radiation in the range from 400 nm to 3000 nm, from 400 nm to 2000 nm, or from 400 nm to 1600 nm.

[0098] When using metrology sensors, including the above-described and / or other types of metrology sensors (e.g., alignment sensors, leveling sensors), it is often desirable to control the illumination spectrum, e.g., to switch the illumination between different wavelengths (colors) and / or wavefront profiles.

[0099] To perform color selection, a color selection module (also referred to as a wavelength selection module or a source selection module) is proposed, which uses grating light valve (GLV) technology (such as that sold by Silicon Light Machines (SLM)), e.g., as described in US6947613B, the entire content of which is incorporated herein by reference. A GLV is an electroprogrammable diffraction grating based on microelectromechanical systems (MEMS) technology. Figure 6 (a)- Figure 6 (c) schematically illustrates the operating principle. Figure 6 (a)- Figure 6 (c) is a schematic illustration of a GLV pixel, which is also referred to as a GLV component 500 in Figure 6 (a) and below in Figure 6 (b), Figure 6 (c). Note that Figure 6 (a)- Figure 6 (c) The GLV component shown is only an example design, and other different GLV designs (e.g., the "true GLV" design used in the G1088 and G8192 modules sold by SLM) can also be used in the wavelength selection module (e.g., as shown in Figure 9 、 Figures 14A - 14B ). Each pixel / component of the GLV can include a controllable grating. The controllable grating can include two types of alternating GLV reflection bands: static or bias bands 510 that are typically grounded together with a common electrode, and drive or active bands 520 that are driven by an electronic driver channel. The GLV module can include any number of these GLV components 500 arranged in an array. Except for their driving methods, the active bands and the bias bands may be substantially the same as each other. When no voltage is applied to the active bands 520, they are coplanar with the bias bands, which is the configuration illustrated in Figure 6 (b). In this configuration, the GLV basically acts as a mirror, and the incident light is specularly reflected (i.e., forms specularly reflected radiation or zero-order diffracted radiation). When a voltage is applied to the active bands 520, as in Figure 6As illustrated in (c), they are deflected relative to the bias strip 510, thereby establishing a square well diffraction grating. In this state, incident light can be diffracted at a fixed diffraction angle (corresponding to the diffraction order). By controlling the voltage on the active strip 520, the ratio of reflected light to diffracted light can be continuously changed, thereby controlling the amplitude of its deflection. Thus, the amount of light diffracted by the GLV can be controlled in an analog manner from zero (total specular reflection) to all incident light (zero specular reflection). In the context of the present disclosure, this control of the specularly reflected radiation amount relative to the radiation amount diffracted at non-zero orders of diffraction can be referred to as modulated illumination.

[0100] Figure 7 Depicts a schematic representation of the radiation after interaction with the GLV pixel 500. In Figure 7 (a), the GLV pixel 500 is in an unbiased state and specularly reflects the radiation 712 (also referred to as zero-order diffracted radiation 712), like a mirror 710. In Figure 7 (b), a bias voltage is applied to create a diffraction grating 720 in the GLV pixel 500. The diffraction grating 720 can diffract a portion of the radiation into zero-order diffraction 722. Another portion of the radiation can be diffracted into higher (non-zero) order diffractions 724 (such as the positive first +1 diffraction order and the negative first -1 diffraction order). The portion of the radiation directed away from the zero-order diffraction 722 (into the non-zero order diffractions 724) can be controlled by tuning the depth of the grating 720 through the active pixel 520 relative to the static pixel 510.

[0101] The GLV can include multiple strips, and at least a portion of the strips can be configured to be movable. Other light valve technologies (such as digital light processing (DLP), liquid crystal displays (LCD), and liquid crystal on silicon (LCoS)) can be used in implementations in video projector devices (such as rear projection TVs and digital projectors). Microelectromechanical systems (MEMS) used in optical applications are referred to as optical MEMS or micro-optoelectromechanical structures (MOEMS), which enable the combination of mechanical, electrical, and optical components to be possible at very small sizes.

[0102] The GLV module can be used in the zero-order mode to block / dump the non-zero order diffracted radiation and provide the specularly reflected (zero-order diffracted) radiation to the metrology tool. This can have the advantage of preserving the étendue. Thus, an aperture stop can be provided in the pupil plane, the purpose of which is to maximize the transmission of the zero order and maximize the blocking (minimize the transmission of the first diffraction order (and other non-zero order diffractions)).

[0103] Figure 8(a) depicts an example setup using zero-order mode radiation, which shows an input radiation 810, which may include radiation in wavelength ranges 810(1), 810(2), 810(3), 810(4), 810(5). In Figure 8 (b), each radiation wavelength 810(1), 810(2), 810(3), 810(4), 810(5) may be incident on separate GLV pixels 820(1), 820(2), 820(3), 820(4), 820(5). In some embodiments, each element 820(1), 820(2), 820(3), 820(4), 820(5) may represent multiple GLV pixels. In Figure 8 (c), a side view of GLV pixels 830(1), 830(2), 830(3), 830(4), 830(5) with an applied bias is shown. Pixels 830(1) and 830(5) do not have the applied bias and can thus be used as mirrors, specularly reflecting output radiations 850(1) and 850(5), as Figure 8 (d) shows. Pixels 830(2), 830(3) and 830(4) have the applied bias to form a diffraction grating such that a portion of the radiation is diffracted to non-zero orders. The portion of the zero-order radiation may depend on the depth of the grating (i.e., depends on the applied bias). For example, in Figure 8 (c), relative to each other, pixel 830(4) has a smaller grating depth, pixel 830(3) has a larger grating depth, while pixel 830(2) has a medium grating depth. The resulting intensity of the radiation diffracted to zero order is lower in 850(3), medium in 850(2), and higher in 850(4). The remaining portion of the radiation not diffracted to zero order is diffracted to non-zero orders. This non-zero order diffracted radiation may be blocked / prevented by aperture stops 840(1), 840(2), 840(3), 840(4), 840(5). Although depicted as a set of discrete wavelengths in Figure 8 , the radiations 810(1), 810(2), 810(3), 810(4), 810(5) may additionally and / or alternatively include radiation in one or more continuous wavelength ranges.

[0104] There can be challenges in using an aperture stop to filter out diffracted radiation. The diffraction angle of the radiation depends on the wavelength. Additionally, the spot size in the pupil plane can also be wavelength-dependent, such that each color has a different spot size in the pupil plane. For example, sources currently used in some metrology applications may include different optical spreads for different color lights, such that the corresponding beam widths for different colors are different. Thus, it is difficult to configure the aperture stop to maximize the transmission of the zero order and the blocking of the first order for all wavelengths of interest (e.g., the wavelength band covered by the source selection module). Any particular shape or configuration for a hard aperture stop may be sub-optimal for some wavelength ranges (e.g., may result in too much blocking of the zero order and / or too much leakage of the first order in the transmission window). As the wavelength range used increases, the problem becomes greater.

[0105] The problem is exacerbated when using a beam with a high optical spread. A beam with a high optical spread makes it difficult to minimize the spot size (per wavelength) on the GLV and have a low numerical aperture (NA) per order. Small spots on the GLV are highly desirable in order to operate on the flat regions of the active band and thus not lose contrast. A low order NA is beneficial for the separation of the zero order and the first order over several wavelengths.

[0106] Known color selection module arrangements based on controllable diffraction elements such as GLVs can include a beam dispersion element for dispersing a broadband illumination beam; a controllable diffraction element or GLV module for spatially modulating the broadband illumination beam after dispersion; an aperture stop in the far field (the pupil plane of the GLV or its conjugate) for removing all orders except the desired order (e.g., removing all orders except the zero order, see the example arrangement in Figure 9 ; however, this can be reversed such that the zero order is blocked and the first order is transmitted, see the example arrangement shown in Figures 14A - 14C ); and a beam combining element for recombining the spatially modulated broadband illumination beam to obtain an output source beam. The beam dispersion element can disperse the colors of a white light source in the first direction on the GLV (e.g., where the GLV is included in the image plane or field plane of the system). The combining element and the dispersion element can be different elements or a single element.

[0107] A metrology tool MT (such as the scatterometer, topographic measurement system, or position measurement system mentioned above) can perform measurements using radiation from a radiation source. The properties 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 may be advantageous to measure a substrate using different and / or multiple radiation frequencies, such as broadband radiation, or one or more frequency bands within a broadband range. In some instances, narrowband radiation may be advantageous for measurements. Multiple different frequencies can be capable of propagating, irradiating, and scattering a metrology target without interfering or minimally interfering with other frequencies. Thus, for example, different frequencies can be used to obtain more metrology data simultaneously. Different radiation frequencies may also be capable of interrogating and revealing different properties of the metrology target. Broadband radiation can be used in a metrology system MT (such as, for example, a level sensor, an alignment mark measurement system, a scatterometry tool, or an inspection tool). The broadband radiation source can be a supercontinuum source. In some instances, some frequency bands within the broadband radiation range can be selected to perform measurements.

[0108] In some metrology tools, narrowband radiation near a predefined wavelength can be controllably selected from the provided broadband radiation. The radiation can, for example, include broadband light ranging from 400 nm to 900 nm, or broadband light ranging from 400 nm to 2000 nm. The selection of the narrowband radiation can be achieved, for example, using a grating light valve, which can be based on the disclosure in US6947613B, for example. Figure 9 An example schematic representation of an arrangement for selecting narrowband radiation from received broadband input radiation using a grating light valve is shown. The input broadband radiation 902 can be provided by a broadband input source. The prism 904 can spatially distribute the broadband radiation across wavelengths. The spatially divided radiation of different wavelengths can be directed onto different pixels of the GLV 906. The GLV can be electrically driven (e.g., receiving instructions from one or more connected processors as to which biases to apply to the pixels) to set how much radiation is diffracted (and / or specularly reflected) to zero order. The zero-order diffracted radiation can be referred to as the output spectrum. The output spectrum can be directed back through a prism, which can be the same prism 904 used to separate the input radiation or a different prism (not shown). The prism can combine the distributed output spectrum to form the output radiation 908, which includes a combination of different wavelengths of the output spectrum. Optical elements (e.g., L1, L2, L3) can be used to direct the radiation through the arrangement. Non-zero-order radiation can be blocked, for example, by a radiation aperture 910. The mirror 912 can be an active / movable mirror or a static folding mirror, which can be used to direct the output radiation 908.

[0109] In the designs described herein, a trade-off may be required between zero-order transmission and spectral contrast (e.g., out-of-band radiation suppression / blocking ratio). Figure 10A schematic illustration of an aperture stop 1010 for selecting some radiation and blocking other radiation is depicted. In the image, the central zero-order diffracted radiation 1002(3) (e.g., red light of a longer wavelength) diffracted by the tunable diffraction element (GLV) 1030 can pass through the aperture opening 1020, while the non-zero-order diffracted radiations 1002(1), 1002(2) (e.g., green and violet light of shorter wavelengths) can be blocked by the aperture 1020.

[0110] The aperture opening 1020 can have a small enough size to block all non-zero-order wavelengths. However, making the aperture opening smaller to block more non-zero-order radiation may cause some of the zero-order radiation to also be blocked. This can lead to a reduction in transmission and thus a decrease in power efficiency. On the other hand, making the aperture opening larger to increase zero-order radiation transmission may allow more non-zero-order radiation to pass through, making the aperture 1010 less efficient at blocking non-zero-order diffracted radiation. This can result in a worse spectral contrast in the output spectrum (i.e., more noise / unwanted radiation). Additionally, chromatic aberration may make it difficult to position the aperture to effectively select / block different wavelengths across the received radiation spectrum. Due to the challenges presented by the aperture stop in blocking and selecting radiation of different wavelengths, alternative solutions may be desirable.

[0111] What is proposed herein is to provide a source selection module 1100 according to Figure 11 The source selection module may also be referred to as a wavelength selection module. The module can include a color selection arrangement as described above. As with the above Figure 9Similarly, input radiation 1102 can be provided. The input radiation can be referred to as light. A light dispersion element 1104 (such as a prism, a light dispersion grating, a combination of a prism and a light dispersion grating, etc.) can be configured to receive the light 1102, which includes first light of a first wavelength and second light of a second wavelength (different from the first light / first wavelength). The first light and the second light can be spatially distributed by the light dispersion element 1104 such that they hit first and second pixels of an adjustable diffraction element 1106 (e.g., a grating light valve), where the first pixel and the second pixel are different pixels. The grating light valve can also be configured to be capable of generating first light of zero-order diffraction and first light of non-zero-order diffraction. The grating light valve can also be configured to be capable of generating second light of zero-order diffraction and second light of non-zero-order diffraction. A continuously variable filter 1110 is also provided as part of the source module, including a first region and a second region, where the first region is configured to transmit (or reflect) the first light, and where the second region is configured to transmit (or reflect) the second light. The continuously variable filter is arranged at a certain position in the source selection module 1100 such that the zero-order of the first light is received by the first region, and the zero-order of the second light is received by the second region. The continuously variable filter is also configured to block the first light outside the first region and block the second light outside the second region. The mirror 1112 can be either an active / movable mirror or a static folding mirror, which can be used to direct the output radiation 1108.

[0112] An advantage of using the source selection module as described above may be that an aperture stop used to block non-zero-order diffracted radiation may no longer be needed. Instead, the wavelength-specific transmission property of the continuously variable filter (CVF) can be used to block non-zero-order radiation at the same position where the zero-order radiation is transmitted (or reflected) in its corresponding region. Using the CVF can improve the performance of the source selection module. The improved performance can include, for example, higher zero-order transmission and / or higher spectral contrast (better blocking of unwanted radiation). Using the CVF can also reduce the chromatic aberration and the risk of misalignment of the optical elements in the source selection module.

[0113] The adjustable diffraction element can include a grating light valve. Each of the pixels of the adjustable diffraction element can include a controllable diffraction grating. The input radiation can be broadband radiation. In this context, controllable can refer to tunable, for example, as described above with respect to Figure 5 and Figure 6 described.

[0114] Although the first light and the second light are described above with respect to Figure 11 the continuously variable filter can be used for multiple N different wavelengths (N≥2), where each wavelength of the nth light is configured to be transmitted by the corresponding nth region on the continuously variable filter CVF and blocked by the region outside the corresponding nth region.

[0115] A continuously variable filter can be commercially available. The CVF can be a side-pass CVF. The CVF can include a continuously variable band-pass layer (also referred to as a band-pass CVF). A band-pass CVF with high transmittance (for a desired wavelength) and high contrast (i.e., high blocking for other wavelengths) can be achieved. In an exemplary embodiment of the band-pass CVF, the band-pass coating can vary continuously along the direction of the CVF. The coating can, for example, include repeated alternating thin layers of two or more different materials (e.g., SiO 2 and Ta 2 O 5 alternating layers). This layer configuration is provided only as an example, and other layer configurations are known and can be used herein. Changing the thickness of the layer along the dimension of the CVF can result in different positions along this direction providing narrow transmission bands near a specific central wavelength. The central wavelength can vary continuously along one direction, which is along the varying thickness of the band-pass coating. This can result in the transmission bands along the varying direction of the CVF becoming narrower for varying wavelengths. Since the filter is a band-pass filter, radiation at wavelengths outside the narrow band-pass band can be blocked by the filter.

[0116] Figure 12 (a)- Figure 12 (c) depict schematic representations of a continuously variable filter combined with a tunable diffraction element to achieve the function of wavelength selection. In Figure 12 (a), a GLV (a tunable diffraction element) is shown, where a bias has been applied to the pixels receiving radiation at wavelength 1302(3). In the top image, the input radiation 1302(3) is incident on the pixels to which the diffraction grating has been applied. In the bottom image, the radiation is diffracted, with a portion of the radiation diffracted into the zero order and other portions diffracted into higher non-zero diffraction orders (+1 order and -1 order as illustrated in the figure). The zero-order radiation will take the same optical path as the incident radiation 1302(3), which means that both the incident radiation and the outgoing zero-order radiation pass through the same position on the CVF. In Figure 12 (b), a continuously variable filter CVF is added to the setup. The GLV still diffracts the received radiation 1302(3) as in Figure 12 (a). The non-zero order diffracted radiation is incident on a certain position of the CVF, which is configured to block radiation at wavelength 1302(3). Only the zero-order diffracted radiation of 1302(3) passes through the CVF at the position where radiation at the wavelength of 1302(3) is transmitted. As a result, the non-zero order diffracted radiation is blocked. In Figure 12In (c), multiple radiations 1302(1), 1302(2), 1302(3), 1302(4), 1302(5) of different wavelengths can be incident on multiple different pixels of the GLV. Each pixel can have a bias voltage applied thereto to select how much radiation is diffracted / specularly reflected to the zero order. Then, the CVF blocks non-zero order diffracted radiation incident at a certain position on the CVF, at which position its wavelength does not fall within the transmission band of the continuously variable filter. The module can be arranged such that the separated wavelengths incident on the GLV can be aligned with the corresponding bandpass center wavelengths of the CVF.

[0117] The continuously variable filter can be arranged in the optical path between the optical dispersion element and the tunable diffraction element. The position of the continuously variable filter, particularly its distance from the tunable diffraction element, may affect its functionality regarding blocking and / or transmitting (or reflecting) radiation wavelengths.

[0118] The position of the CVF can determine the position at which the non-zero order diffracted radiation hits the CVF. The position of the CVF along a plane perpendicular to the optical path of the zero order diffracted radiation can be selected based on its position relative to the GLV (and the optical dispersion element). For example, this can be selected such that the path of the distributed wavelength is aligned with the transmission band of the CVF for that wavelength. These, in turn, can be aligned with the pixels of the GLV (or other equivalent tunable diffraction element) configured to diffract the radiation of that particular distributed wavelength. The position of the CVF along a direction parallel to the zero order diffracted radiation path can be selected to be close to the GLV. The aim is to provide sufficient separation of the non-zero order diffracted radiation in a plane perpendicular to the zero order optical path such that the non-zero order diffracted radiation does not hit the CVF within the transmission window for that wavelength. Separation of the zero order and non-zero order diffractions is required at the CVF. This can be achieved, for example, by allowing the diffracted radiation to propagate a distance L and placing the CVF at a distance L from the surface of the GLV. For a ±1 order diffraction angle θ, the distance d between the zero order radiation and the first order radiation at the CVF can be d = L tan(θ).

[0119] In the approximate calculations of the example distances and angles used in the source selection module described herein, the GLV can be provided with a pitch of approximately 8.5 μm. Based on this pitch and incident radiation in the range of 400 nm to 900 nm, the resulting diffraction angle can be calculated as: arcsin([400 nm - 900 nm] / 8.5 μm) = 2.7 - 6.1 degrees = θ. The effect of a small deviation of the incoming radiation from normal incidence on the spectral performance of the CVF can be neglected. If a distance L = 5 mm between the CVF and the GLV is used, the first diffraction order will be projected onto the CVF at a position laterally offset d from the zero order: d = 5 mm * tan(θ) = 236 μm - 534 μm (for 400 nm–900 nm incident light). When the GLV is used with a 16 mm array size for a 400 nm - 900 nm radiation range (and thus a 500 nm range width), the (average) variable ratio of the CVF may be approximately 31 nm / mm (500 nm / 16 mm = 31.25 nm / mm ≈ 31 nm / 33). That is, the bandpass wavelength variation of the CVF along a 1 mm distance of the CVF is 31 nm. It should be understood that the calculations listed herein are approximate and are a simplified version of a real-world setup. They are for illustrative purposes only and should not be considered limiting. For a CVF with a variable ratio of 31 nm / mm, the short wavelength hits the CVF with a lateral offset of 0.236 mm, which corresponds to a wavelength offset of ±7.3 nm from the aligned 400 nm wavelength bandpass. For a CVF with a variable ratio of 31 nm / mm, the long wavelength hits the CVF with a lateral offset of 0.534 mm, which corresponds to a wavelength offset of ±16.6 nm from the aligned 900 nm wavelength bandpass. These wavelength offsets may be sufficient to block the first diffraction order hitting the CVF. In some embodiments, a wavelength downshift of 1 - 2 nm may be acceptable for blocking the desired diffraction order.

[0120] For incident wavelengths other than the 400 nm - 900 nm working example described above, the required dimensions and the range of diffraction angles can be adjusted accordingly. As shown in the example above, when the propagation length L decreases, the resulting distance between the zero order and the first order also decreases. In the applications described herein, overlap between different diffraction orders (especially between the zero order and the ±1 orders) is not desired. Thus, when the zero order and the first order diffraction spots are next to each other, the minimum separation distance d can be determined. min . For example, in the working example of the previous paragraph, the spot size may be on the order of 50 μm - 70 μm. A d of 70 μm can be selected. min, for the above example setup, this may result in a propagation length L of approximately 1.5 mm. As L increases, the separation between the orders (e.g., the zero order and the ±1 orders) on the CVF increases. This can make it easier to transmit and block the desired order. However, the placement of the CVF may be limited by other elements in the optical system. For example, the placement of the CVF may be limited by the last lens in front of the LV, and thus, in the example embodiment, the placement of such a lens can limit the length L. The maximum propagation length L (the distance between the GLV and the CVF) may be, for example (approximately), in the range of 50 mm to 100 mm.

[0121] In addition to the position of the CVF near the tunable diffraction element as described above, alternatively, the CVF can also be placed in an equivalent position (i.e., the same distance) in the conjugate plane of the tunable diffraction element in the optical path of the source selection module.

[0122] The continuously variable filter can have a filtering characteristic (e.g., a bandpass filtering characteristic) that is linearly distributed over the area of the continuously variable filter. The CVF can be, for example, a rectangular strip where the filtering characteristic varies linearly along a first direction. This can be the same direction in which the wavelengths of the incoming radiation are distributed, and / or the same direction in which the different pixels of the tunable diffraction element are positioned. The filtering characteristic can be constant along a second direction of the CVF. The second direction can be perpendicular to the first direction.

[0123] In some embodiments, the filtering characteristic can be non-linearly distributed over the area of the continuously variable filter. For example, the non-linear distribution can be designed to match the wavelength of the radiation and / or the non-linear distribution of the GLV pixels. For example, depending on the dispersion property of an optical dispersion element (e.g., a prism), the wavelengths of the incident broadband light can be dispersed in a non-linear manner. The pixel distribution on the GLV and / or the wavelength-dependent bandpass window of the CVF can be designed to match this non-linear distribution.

[0124] The CVF can be placed at a proximity L close to the GLV, as discussed above. In another embodiment, the CVF can be used to replace the protective window of the GLV. In some embodiments, the protective window of the GLV can be coated with a CVF coating. A protective window can be provided to protect the MEMS (microelectromechanical system) components of the tunable diffraction element. As a MEMS device, the GLV may require a protective window. The protective window can be tilted so as to reduce the virtual reflection from the window. The tilt angle of the window can transfer the virtual reflection beam to an area outside the zero order beam, thus preventing interference between the two. In embodiments where the CVF replaces the protective window or is combined with the protective window, the CVF layer can be tilted with respect to the plane of the tunable diffraction element. The advantage of replacing the protective window with the CVF is that the number of surfaces through which the radiation passes is reduced, which can increase the transmission, and / or can reduce the aberration / noise.

[0125] As described above, the source selection module can provide a light dispersion element for spatially distributing multiple wavelengths, and an adjustable diffraction module capable of turning on / off the diffraction radiated to the zero order. Therefore, the source selection module can be capable of individually turning on or off multiple wavelengths. By tuning each of the pixels of the adjustable diffraction element, the ratio of the incident radiation diffracted into the zero-order diffraction and the non-zero-order diffraction can be controlled. This can be used to turn on / off the wavelengths incident on each pixel and perform spectral shaping on the output radiation. This can be used, for example, for wavelength selection.

[0126] The radiation input to the source selection module can be broadband radiation (such as supercontinuum radiation). This can provide a substantially continuous input wavelength spectrum over the broadband radiation range. In such an instance, and due to the limited physical width of the pixels, the radiation incident on an individual pixel can include a range of wavelengths (also referred to as the spectral width of the pixel). A specific range of wavelengths can be incident on a specific pixel. When referring to the wavelength incident on a pixel, this can refer to the central wavelength of a range of wavelengths incident on the pixel. In addition, each pixel can be composed of multiple individual elements (for example, in the case of a controllable grating, each pixel can include multiple (for example, 3) bands). This can result in one or more specific wavelengths being incident between the elements of a pixel or between two pixels. For example, if a particular wavelength is of interest, that wavelength may deviate from the central wavelength modulated by the pixel, or may fall in the space between the grating bands and / or between the pixels. This can affect the quality of the output at that wavelength, resulting in limited performance and / or limited resolution of the source selection module.

[0127] In some embodiments, a movable continuously variable filter can be provided. The continuously variable filter can be provided with an actuator to move it. The actuator can be a piezoelectric actuator (for example, a piezoelectric stack, an extended pixel resolution actuator). The actuator can be configured to move the continuously variable filter in a first direction parallel to the surface of the continuously variable filter. The first direction can be substantially perpendicular to the direction of the zero-order diffracted radiation. The actuator can quickly change the position of the continuously variable filter, for example, with a moving speed of less than 1 ms or significantly less than 1 ms from the initial position to the target position. The moving time from the initial position to the target position can be in the range of 0.0225 μs to 1 ms, for example, in the range of 500 μs to 1 ms, preferably in the range of 1 μs to 500 μs, preferably in the range of 0.0225 μs to 1 μs. Preferably, the actuation moving time between the initial position and the target position can be faster than the moving (adjusting) time of the adjustable diffraction element. In the case where the adjustable diffraction element is a grating light valve, the moving time can be about 1 μs, but embodiments with other moving times are also possible.

[0128] Pixels of the tunable diffraction element can have dimensions on the order of 1 μm. For example, the stripes of a grating light valve can have widths in the range from 1 μm to several μm. The length of the stripe can be greater than the width of the stripe. The precision of the continuously variable filter (at dimensions smaller than the width of the stripe) can be better (i.e., more precise) than at the dimension of the pixel. Preferably, the precision of the continuously variable filter can be at least a factor n better than the dimension of the pixel, where n can be in the range from 2 to n. For example, the precision of the continuously variable filter can be in the range from 10 μm to 5 μm, or preferably in the range from 5 μm to 1 μm, or preferably in the range from 1 μm to 100 nm. The actuator can move the continuously variable filter precisely (e.g., within 1 μm). Moving the continuously variable filter can have advantages over moving another part of the source module, such as one or more lenses or the tunable diffraction element. This may be because moving the lens or the tunable diffraction element may be slow and / or have greater inertia relative to the continuously variable filter.

[0129] In some alternative embodiments, the continuously variable filter can perform the function of spatially separating radiation in place of the optical dispersion element. That is, a source selection module can be provided, where broadband radiation can be directed to the continuously variable filter. The continuously variable filter can filter the incident radiation such that a specific wavelength is present at a specific location at the output of the filter. This can enable radiation of a specific wavelength to be projected onto a specific pixel of the tunable diffraction element. The radiation can then be diffracted as described above. An advantage of this arrangement may be that there is no need to provide a prism, a grating, or other dispersion elements. A disadvantage of using the continuously variable filter in place of the optical dispersion element may be that a large portion of the radiation that would be filtered out by the continuously variable filter is lost.

[0130] Another advantage of using the continuously variable filter in place of a prism or a grating may be that all alignment of the radiation onto the tunable diffraction element is performed by the continuously variable filter. Thus, if the continuously variable filter is made movable, such as by an actuator as described above, the position of the continuously variable filter can be changed, resulting in a change in the spectrum reaching each pixel of the tunable diffraction element. By providing precise control of the position of the continuously variable filter, the central wavelength projected onto each pixel of the tunable diffraction element can be precisely controlled. This can provide improved spectral control of the radiation output by the source selection module.

[0131] Using the continuously variable filter to spatially distribute radiation for different wavelengths can also have the advantage of performing a dual filtering action. This may be because in both the inbound and outbound paths of the radiation (i.e., before and after interacting with the tunable diffraction element), essentially only one wavelength (or a very narrow wavelength range) is transmitted at a certain position along the continuously variable filter. This can increase the optical contrast of the radiation.

[0132] Removing the optical dispersion element by performing spatial separation of different wavelengths using a continuously variable filter can simplify the setup of the source selection module. Removing the optical dispersion element can make it easier to use the entire surface / length of the tunable diffraction element. A dispersion element (such as a prism) may cause radiation from different wavelengths not to propagate along parallel paths (e.g., forming a slightly arched spectral spread). Such an arched radiation path may limit the use of the surface of the tunable diffraction element and the control of the radiation incident thereon. By making broadband radiation incident on the continuously variable filter and filtering out different wavelengths at different positions on the filter, the problems associated with the arched path may no longer exist. This can reduce the aberration at the surface of the tunable diffraction element.

[0133] In some embodiments, the continuously variable filter may be provided in combination with a microlens array. The microlens array may receive the filtered radiation from the CVF and form radiation spots on the surface of the tunable diffraction element. This can cause the reflected radiation from the tunable diffraction element to propagate parallel to each other. This setup can use, for example, a collimated radiation beam received from a supercontinuum radiation source or other broadband radiation source.

[0134] In a particular embodiment, a source selection module is provided with an actuator (configured to move the continuously variable filter for spectral tuning), which can greatly improve the spectral selection accuracy of the module. In this context, spectral accuracy can refer to the accuracy of the central wavelength of the wavelength band incident on the pixel that can be selected. The wavelength range incident on the pixel can depend on the width of the pixel and other parameters. For a 400nm - 900nm broadband radiation range, a variable ratio of about 31nm / mm of the continuously variable filter can be used. A grating light valve can be provided as the tunable diffraction element, where a single band has a width of about 8.5μm. This results in a pixel with a width of 25.5μm. If the radiation spot covers approximately 2 pixels, the minimum spectral width of the pixel may be about 1.6nm. The spot size may vary as a function of wavelength, which means that the minimum spectral width of the wavelength band may be in the range of approximately 1.5nm to 2.5nm. This spectral width value can represent the accuracy of the central wavelength of the wavelength band that can be selected in a setup without a CVF actuator. By adding an actuator (such as a piezoelectric actuator that drives the movement of the continuously variable filter) to move the continuously variable filter, this accuracy can be improved. The amount of improvement can depend on the accuracy and / or speed of the movement and positioning of the piezoelectric actuator. The positioning accuracy of the piezoelectric actuator can be much lower than 1μm (e.g., as low as the order of 10nm). This can result in the spectral accuracy of the central wavelength of the wavelength band being improved by an order of magnitude of ≥10 times. This can result in an accuracy up to sub-nanometer accuracy, for example, an accuracy of the central wavelength in the range as low as 0.1nm.

[0135] In some embodiments, one or more second actuators can be provided, which are configured to move the continuously variable filter in a second direction. The second actuator can be a piezoelectric actuator. The second actuator can have the same characteristics as the first actuator. The second direction can be substantially perpendicular to the first direction of the first actuator mentioned above. The second direction can be perpendicular to the surface of the tunable diffraction element. In some embodiments, the actuator can be configured such that an inclination angle can be variably introduced between the continuously variable filter and the tunable diffraction element. In some embodiments, the surface of the continuously variable filter and the surface of the tunable diffraction element can be substantially parallel. Introducing the inclination angle can enable fine-tuning of the projection of the radiation passing through the continuously variable filter onto the tunable diffraction element, because the range can be compressed or expanded by adding tilt to the system. In addition, the local band edges of the continuously variable filter may depend on the incident angle of the incoming radiation. By tuning the incident angle (e.g., by changing / tuning the inclination angle of the continuously variable filter using an actuator, for example), the local band edge position can be fine-tuned. Tuning the inclination angle / incident angle of the incident radiation can also fine-tune the steepness of the band edge.

[0136] Figure 13 A schematic representation of a continuously variable filter 1404 is depicted, which can be moved in a first direction 1412 by a first actuator 1406. It is also shown that the continuously variable filter can be moved in a second direction 1414 by two second actuators 1408 and 1410. It is possible to provide both the first actuator 1406 and the second actuators 1408, 1410, or to provide the first actuator 1406 without providing the second actuators. It is also possible to provide one or two second actuators 1408, 1410 without providing the first actuator 1406. The second actuators 1408, 1410 can enable changing the distance d between the continuously variable filter and the tunable diffraction element (grating light valve 1402). The distance d can be measured along a second direction 1414 perpendicular to the surface of the grating light valve 1402. The second actuators 1408 and 1410 can also enable changing the inclination angle between the continuously variable filter and the tunable diffraction element. The inclination angle can be measured relative to the entrance plane of the tunable diffraction element. The entrance plane can be the plane of the tunable diffraction element into which the radiation is incident. The entrance plane can be perpendicular to the propagation direction of the radiation. The entrance plane is not parallel to the propagation direction of the radiation.

[0137] The GLV module can be used in a first-order mode such that specularly reflected (zero-order diffracted) radiation is blocked / dumped, and first-order diffracted radiation (e.g., +1 order and -1 order) is used. Thus, an aperture stop or beam blocker can be provided in the pupil plane of the GLV or its conjugate, with the aim of maximizing the transmission of one or both of the first orders and maximizing the blocking of the zero order (minimizing its transmission).

[0138] Although a GLV-based wavelength selection module configured for zero-order mode operation (e.g., as shown in Figure 9 ) can provide good wavelength selection performance, the zero-order configuration may be difficult to achieve the high out-of-band spectral suppression (or blocking ratio) required for many applications, such as including being used as a radiation source in a metrology tool (such as Figure 4 and Figure 5 illustrated). Here, the out-of-band spectral suppression ratio is defined as the ratio of the intensity of out-of-band leakage light to the intensity of in-band light. The terms "out-of-band" and "in-band" correspond to the unwanted (or to be blocked) color and the wanted (to be selected) color, respectively. For such a zero-order mode configuration, there will always be a small but significant amount of unwanted color leaking into the output illumination beam. For example, when configured in the zero-order mode, it is difficult (if not impossible) to reduce the leakage to significantly less than 0.1% (i.e., typically at least 0.1% of the incident radiation is reflected from the GLV regions configured to diffract / block all incident radiation in these regions). This out-of-band leakage is typically caused by the incident light being reflected by the gaps between the GLV bands and / or by the protective window in front of the GLV chip and propagating in substantially the same direction as the selected zero-order diffracted light. For metrology applications, this leakage should be at least one order of magnitude smaller than this, i.e., the suppression ratio is at least four orders of magnitude smaller than the full signal (at least 0.01%).

[0139] It is difficult or impossible to configure the GLV bands to form a grating with a diffraction efficiency high enough to achieve a leakage of 0.01% or better because there is always a gap between the bands and the protective window in front of the GLV chip, which causes unwanted light to be reflected. To address this limited diffraction efficiency and the resulting out-of-band suppression problem, an inverted configuration is proposed such that diffracted radiation (e.g., the first order, although other non-zero orders can be used) is used and specular zero-order radiation is rejected; i.e., the GLV device is configured in the "first-order mode". In such a configuration, the diffraction efficiency becomes less critical; although some low diffraction efficiency may mean some (wanted) radiation loss, it does not affect the out-of-band suppression. Very little or no radiation incident on the GLV regions configured to reflect radiation will diffract in the same direction as the wanted first order, so the out-of-band suppression effect will be very good.

[0140] Figure 14A and Figure 14B illustrate an example GLV-based wavelength selection module configured for first-order mode operation. Figure 14A is a top view of the arrangement, and Figure 14Bis a side view of the arrangement. In this example, the wavelength selection module is configured for first-order mode operation; i.e., configured to transmit the source beam 1502 (e.g., a broadband beam) and the first diffraction order selectively diffracted by the GLV module 1506 when interacting with the broadband beam 1502 (for clarity, only two colors +1 λ1 、+1 λ2 、-1 λ1 、-1 λ2 are shown, both of which are selected by the GLV; of course, there can be more and / or a continuous spectrum), and block the zero-order diffraction 0 λ1 、0 λ2 . More specifically, in the depicted example, two wavelengths are shown, which are transmitted through the arrangement λ 1 、λ 2 (i.e., both of these wavelengths are selected by the GLV module 1506), while the resulting diffraction orders +1 λ1 、-1 λ1 、+1 λ2 、-1 λ2 are captured by the lens L3. The beam stop 1510 is provided in the pupil plane of the GLV module 1506 or its conjugate, and is arranged to block the zero-order diffraction 0 λ1 、0 λ2 to the maximum extent and transmit one or both of the first-order diffractions to the maximum extent.

[0141] Figure 14A or Figure 14B of the wavelength selection module, such as the input radiation 1502, the optical dispersion element 1504, the tunable diffraction element 1506 (e.g., a grating light valve), the mirror 1512, and the optical lenses L1 - L3 as described with respect to Figure 9 and Figure 11 and will not be described further. Figure 14C is the pupil plane representation P 1 , including the zero-order aperture stop 1510 positioned to block only the zero-order (specular radiation), thereby defining the aperture AP 1 that transmits the first order (and / or other higher orders).

[0142] As already explained, the beam blocker 1510 should maximize the transmission of the zero-order beam (for all selected wavelengths) and minimize the transmission of the first-order beam for all wavelengths, or vice versa. Maximizing the transmission (e.g., of the zero-order beam or a diffracted beam such as the first-order beam for all wavelengths) should be understood as increasing the transmission as much as possible, taking into account the trade-offs required to minimize the transmission of the blocked radiation and the limitations of the arrangement. Similarly, minimizing the transmission (e.g., of the first-order or zero-order for all wavelengths) should be understood as meaning blocking these orders as much as possible, taking into account these same limitations and trade-offs. In particular, the fact that the spots have spatially overlapping tails (if considering a plot of the intensity or amplitude of each spot versus pupil position) makes it necessary to either pass some unwanted light (resulting in poor out-of-band contrast) or block the tails of the desired zero-order, resulting in a reduction in signal and thus a decrease in throughput. The larger these spots are (i.e., the larger the NA of the beam) compared to the separation of the orders, the more severe this problem becomes.

[0143] In an embodiment, maximizing the transmission can include transmitting 90% or more, transmitting 95% or more, transmitting 98% or more, transmitting 99% or more, transmitting 99.9% or more, or transmitting 99.99% or more of the transmitted radiation. In an embodiment, minimizing the transmission can include blocking 90% or more, blocking 95% or more, blocking 98% or more, blocking 99% or more, blocking 99.9% or more, or blocking 99.99% or more of the blocked radiation.

[0144] It is noted that the concept of using a CVF to improve the performance of a wavelength selection module configured for zero-order mode operation (e.g., as shown in Figure 11 applies to a wavelength selection module (or source selection module) configured for first-order mode operation (e.g., as shown in Figures 14A - 14C ). The improved performance can include, for example, a higher first-order transmittance and / or a higher spectral contrast (better blocking of unwanted zero-order radiation).

[0145] Figure 15 Schematically depicted is a bandpass CVF or wedge filter according to an embodiment that includes a substrate SUB coated with a multilayer coating CT. This type of CVF is suitable for use with a wavelength selection module (or source selection module) configured for either zero-order or first-order mode operation when operating with a tunable diffractive element (e.g., a GLV module) and provides the same wavelength selection function as described above with respect to Figure 12

[0146] As Figure 15As shown, the substrate SUB of the wedge filter is transparent to input radiation (e.g., broadband radiation) that can be incident from either the coating side or the substrate side. The substrate SUB can be made of a type of glass (such as fused silica). A multilayer coating CT is deposited on one side of the substrate SUB and can include thin layers of two different coating materials MAT1, MAT2 that alternate (i.e., multiple repeating pairs of thin layers). In this specific example, the two alternating materials MAT1, MAT2 are SiO 2 and Ta 2 O 5 , although other materials can also be used. The thickness of each coating increases continuously along the wedge direction (e.g., according to the Z direction of the coordinate reference system shown in Figure 15 ). The total number, materials, and thickness of the thin layers of the multilayer coating CT can be carefully selected to obtain certain transmission characteristics. It should be understood that in other configurations, the multilayer coating CT can include multiple repeating groups of thin layers, each group including thin layers of three or more different coating materials.

[0147] Figure 16 shows an example transmission spectrum of the wedge filter (e.g., as shown in Figure 15 ). The transmission spectrum of the wedge filter can include multiple (e.g., seven in this case) separate narrow transmission bands B1 - B7, corresponding respectively to multiple (e.g., seven in this case) different regions of the filter (each region having a central position P1 - P7). As described above, the characteristics of the transmission spectrum (such as the position of each transmission band, the full width at half maximum (FWHM), and the maximum transmittance TM (between 0 and 100%)) depend on the coating configuration employed. Thus, different coating configurations (e.g., based on three or more coating materials) can be used to achieve different transmission characteristics, such as pushing the rising or falling edge of a transmission band outside a given spectral range, thereby effectively forming a low - pass or high - pass filter within that spectral range.

[0148] Figure 17A shows an example transmission profile along the wedge direction of the wedge filter (e.g., as shown in Figure 15 ), which is configured to be used in a wavelength - selection module configured for zero - order mode operation (e.g., as shown in Figure 9 ). As shown in the lower part of Figure 17A , the wedge filter is configured such that the transmission profile of the wedge filter includes three component transmission profiles, each component transmission profile having a single transmission band TD1 - TD3 with a predefined transmittance TM. The three component transmission profiles correspond respectively to three different (central) wavelengths λ 1 , λ 2 , λ 3correspond, and the three transmission bands TD1 - TD3 each have a predefined width in both the spectral domain and the spatial domain. In the spectral domain, the three transmission bands TD1 - TD3 may have the same or different spectral widths (e.g., in terms of FWHM). In the spatial domain, the three transmission bands TD1 - TD3 overlap with each other at a certain position POS on the wedge filter and have different spatial widths, each spatial width being appropriately sized to maximize the transmission of the zero - order diffracted radiation beam at the corresponding wavelength 0 λ1 、0 λ2 、0 λ3 (e.g., TM close to 100%) and to maximize the blocking of all first - order diffracted radiation beams - 1 λ1 、 - 1 λ2 、 - 1 λ3 、 + 1 λ1 、 + 1 λ2 、 + 1 λ3 (e.g., TM close to 0).

[0149] Figure 17B shows an example transmission profile along the wedge direction of the wedge filter (e.g., as shown in Figure 15 ), which is configured to be used in a wavelength - selection module configured for first - order mode operation (e.g., as shown in Figures 14A - 14C ). Compared with the transmission profile shown in Figure 17A , the transmission profile shown in Figure 17B includes three component transmission profiles, each component transmission profile having two or a pair of complementary transmission bands; namely: TD1_ + 1 and TD1_ - 1, TD2_ + 1 and TD2_ - 1, TD3_ + 1 and TD3_ - 1 with a predefined transmittance TM. Each pair of complementary transmission bands may be associated with a pair of complementary diffraction orders from the GLV (e.g., + 1 and - 1, although higher - order pairs may exist). The three component transmission profiles are respectively at three different (central) wavelengths λ 1 、λ 2 、λ 3Correspondingly, the transmission bands TD1_+1, TD1_-1, TD2_+1, TD2_-1, TD3_+1, TD3_-1 each have a predefined width in both the spectral domain and the spatial domain. In the spectral domain, the transmission bands TD1_+1, TD1_-1, TD2_+1, TD2_-1, TD3_+1, TD3_-1 may have the same or different spectral widths (e.g., in terms of FWHM). In the spatial domain, each complementary transmission band pair TD1_+1 and TD1_-1, TD2_+1 and TD2_-1, or TD3_+1 and TD3_-1 constituting the transmission profile is substantially similar to each other (e.g., in terms of transmittance and spatial width), and may be symmetrical about a blocking band BD located at a certain position POS on the wedge filter. In each of the three component transmission profiles, the corresponding complementary transmission band pairs TD1_+1 and TD1_-1, TD2_+1 and TD2_-1 or TD3_+1 and TD3_-1 are configured to maximize the transmission of the two corresponding first-order diffracted radiation beams at the corresponding wavelength -1 λ1 and +1 λ1 , or -1 λ2 and +1 λ2 , or -1 λ3 and +1 λ3 ) and maximizes the transmission of all zeroth-order diffracted radiation beams 0 λ1 , 0 λ2 , 0 λ3 The wedge filter has a blocking of 0 (e.g., TM is close to 0). The transmission band in one of its transmission profiles is spatially separated from the transmission band in any of the other transmission profiles. Thus, the wedge filter acts as a position-dependent spectral bandpass filter.

[0150] When the GLV-based wavelength selective module is configured in the first order mode, in embodiments where only one of the diffraction orders is used, the three component transmission profiles may each include only a single respective transmission band.

[0151] It should be appreciated that for a wavelength selective module configured for first order mode operation (e.g., Figures 14A - 14C ), in the case where the input radiation includes a spectrum having a bandwidth of one octave or wider, a wedge filter (e.g., having Figure 17B The transmission profile shown in ) is particularly advantageous and in many cases necessary. For example, and refer back to Figure 17B , the third wavelength λ 3 The first wavelength λ may be 1 twice (i.e. λ 3 =2λ 1 ), and thus the first wavelength λ 1 The second diffraction order (-2 λ1, +2 λ1 ) will overlap spatially with the first diffraction order (-1 3 , +1 λ3 ) of the third wavelength λ λ3 . In addition, the diffraction of the gap order of the first wavelength λ 1 (generated by the interaction with the gap of the GLV) may also overlap with the first order (-1 3 , +1 λ3 ) of the third wavelength λ λ3 . In this case, the aperture stop can no longer effectively block and select the radiation of different wavelengths (e.g., those overlapping diffraction orders), while the wedge filter can still achieve good wavelength selection performance.

[0152] Further embodiments are disclosed in the following numbered clauses:

[0153] 1. A source selection module, comprising:

[0154] An adjustable diffraction element, the adjustable diffraction element comprising a plurality of pixels;

[0155] A light dispersion element, the light dispersion element being configured to receive first light of a first wavelength and second light of a second wavelength, spatially distribute the first light on a first pixel among the plurality of pixels to generate a zero order diffraction of the first light and a non - zero order diffraction of the second light, and spatially distribute the second light on a second pixel among the plurality of pixels to generate a zero order diffraction of the second light and a non - zero order diffraction of the second light; and

[0156] A continuously variable filter, the continuously variable filter comprising at least one first region and at least one second region;

[0157] wherein the continuously variable filter is arranged in such a position that the zero order of the first light received by at least one first region and the zero order of the second light received by at least one second region are transmitted or reflected by the continuously variable filter, the non - zero order of the first light is blocked outside at least one first region by the continuously variable filter, and the non - zero order of the second light is blocked outside at least one second region by the continuously variable filter; or

[0158] wherein the continuously variable filter is arranged in such a position that the non - zero order of the first light received by at least one first region and the non - zero order of the second light received by at least one second region are transmitted or reflected by the continuously variable filter, the zero order of the first light is blocked outside at least one first region by the continuously variable filter, and the zero order of the second light is blocked outside at least one second region by the continuously variable filter.

[0159] 2. The source selection module according to clause 1, wherein each of the plurality of pixels comprises a controllable grating.

[0160] 3. The source selection module according to clause 2, wherein the tunable diffraction element includes a grating light valve.

[0161] 4. The source selection module according to any one of the preceding clauses, wherein the continuously variable filter is arranged on the optical path between the optical dispersion element and the tunable diffraction element.

[0162] 5. The source selection module according to any one of the preceding clauses, wherein the continuously variable filter is arranged at a certain distance from the tunable diffraction element or at a certain distance from the conjugate image plane of the tunable diffraction element, such that the zero-order diffraction and non-zero-order diffraction of the first light are spatially separated from the zero-order diffraction and non-zero-order diffraction of the second light.

[0163] 6. The source selection module according to any one of the preceding clauses, wherein the optical dispersion element includes a prism.

[0164] 7. The source selection module according to any one of clauses 1 to 5, wherein the optical dispersion element includes an optical dispersion grating.

[0165] 8. The source selection module according to any one of the preceding clauses, wherein the continuously variable filter includes a substrate coated with a continuously varying bandpass layer.

[0166] 9. The source selection module according to clause 8, wherein the continuously varying bandpass layer includes a repeating group of sub-layers, each group including at least two different coating materials.

[0167] 10. The source selection module according to clause 9, wherein the at least two different coating materials include SiO 2 and Ta 2 O 5 .

[0168] 11. The source selection module according to clause 9 or 10, wherein the thickness of each of the sub-layers continuously increases along a direction in the plane of the interface surface between the substrate and the continuously varying bandpass layer.

[0169] 12. The source selection module according to any one of the preceding clauses, wherein the plane of the continuously variable filter is inclined with respect to the plane of the tunable diffraction element.

[0170] 13. The source selection module according to any one of the preceding clauses, wherein the filtering characteristics are linearly distributed over the region of the continuously variable filter.

[0171] 14. The source selection module according to any one of clauses 1 to 12, wherein the filtering characteristics are non-linearly distributed over the region of the continuously variable filter.

[0172] 15. A source selection module according to any one of the preceding clauses, wherein the continuously variable filter has a first optical filtering characteristic in at least one first region and a second optical filtering characteristic in at least one second region.

[0173] 16. A source selection module according to any one of the preceding clauses, wherein both the first wavelength and the second wavelength are in the range of 400 nm - 900 nm, and optionally, wherein both the first wavelength and the second wavelength are in the range of 400 nm to 1600 nm.

[0174] 17. A source selection module according to any one of the preceding clauses, further comprising a first actuator configured to move the position of the continuously variable filter along a first direction, and wherein the position of the continuously variable filter along the first direction is configured to be adjusted to tune the first wavelength and the second wavelength.

[0175] 18. A source selection module according to any one of the preceding clauses, further comprising one or more second actuators configured to move the continuously variable filter along a second direction, and wherein the position of the continuously variable filter along the second direction is configured to tune the distance between the continuously variable filter and the tunable diffractive element, and / or wherein the second actuator is configured to tune the tilt angle of the continuously variable filter relative to the entrance plane of the tunable diffractive element.

[0176] 19. A source selection module, comprising:

[0177] A tunable diffractive element comprising a plurality of pixels;

[0178] A continuously variable filter comprising at least one first region and at least one second region, the at least one first region being configured to transmit light of a first wavelength, and the at least one second region being configured to transmit light of a second wavelength;

[0179] wherein the continuously variable filter is configured to:

[0180] Receive radiation comprising light of a first wavelength and light of a second wavelength; and

[0181] Filter the incident radiation such that light of the first wavelength is incident on a first pixel among the plurality of pixels to generate a zero-order diffraction of the first light and a non-zero order of the first light, and such that light of the second wavelength is incident on a second pixel among the plurality of pixels to generate a zero-order diffraction of the second light and a non-zero order diffraction of the second light; and

[0182] The continuously variable filter is arranged in such a position that the zero - order of the first light received by at least one first region and the zero - order of the second light received by at least one second region are transmitted by the continuously variable filter, the non - zero orders of the first light are blocked outside at least one first region by the continuously variable filter, and the non - zero orders of the second light are blocked outside at least one second region by the continuously variable filter; or

[0183] The continuously variable filter is arranged in such a position that the non - zero orders of the first light received by at least one first region and the non - zero orders of the second light received by at least one second region are transmitted or reflected by the continuously variable filter, the zero - order of the first light is blocked outside at least one first region by the continuously variable filter, and the zero - order of the second light is blocked outside at least one second region by the continuously variable filter.

[0184] 20. The source selection module according to clause 19, wherein light of a first wavelength and light of a second wavelength are incident on at least one first region of the continuously variable filter, and light of the first wavelength and light of the second wavelength are incident on at least one second region of the continuously variable filter.

[0185] 21. The source selection module according to any one of the preceding clauses, wherein no light of the second wavelength is incident on the first pixel, and no light of the first wavelength is incident on the second pixel.

[0186] 22. The source selection module according to any one of clauses 19 to 21, further comprising a first actuator configured to move the position of the continuously variable filter along a first direction, and wherein the position of the continuously variable filter along the first direction is configured to be adjusted to tune the first wavelength and the second wavelength.

[0187] 23. The source selection module according to any one of clauses 19 to 22, further comprising one or more second actuators configured to move the continuously variable filter along a second direction, and wherein the position of the continuously variable filter along the second direction is configured to tune the distance between the continuously variable filter and the tunable diffraction element, and / or wherein the second actuator is configured to tune the tilt angle of the continuously variable filter relative to the entrance plane of the tunable diffraction element.

[0188] 24. The source selection module according to any one of clauses 19 to 23, wherein each of the plurality of pixels includes a controllable grating.

[0189] 25. The source selection module according to clause 24, wherein the tunable diffraction element includes a grating light valve.

[0190] 26. A source selection module according to any one of clauses 19 to 25, wherein the continuously variable filter is arranged at a certain distance from the tunable diffraction element or at a certain distance from the conjugate image plane of the tunable diffraction element, such that the zero-order diffraction and non-zero-order diffraction of the first light are spatially separated from the zero-order diffraction and non-zero-order diffraction of the second light.

[0191] 27. A source selection module according to any one of clauses 19 to 26, wherein the continuously variable filter comprises a substrate coated with a continuously variable bandpass layer.

[0192] 28. A source selection module according to clause 27, wherein the continuously variable bandpass layer comprises a repeating group of sub-layers, each group comprising at least two different coating materials.

[0193] 29. A source selection module according to clause 28, wherein the at least two different coating materials comprise SiO 2 and Ta 2 O 5 .

[0194] 30. A source selection module according to clause 27 or 28, wherein the thickness of each of the sub-layers increases continuously along a direction in the plane of the interface surface between the substrate and the continuously variable bandpass layer.

[0195] 31. A source selection module according to any one of clauses 19 to 30, wherein the plane of the continuously variable filter is inclined with respect to the plane of the tunable diffraction element.

[0196] 32. A source selection module according to any one of clauses 19 to 31, wherein the filtering characteristics are linearly distributed over the region of the continuously variable filter.

[0197] 33. A source selection module according to any one of clauses 19 to 32, wherein the filtering characteristics are non-linearly distributed over the region of the continuously variable filter.

[0198] 34. A source selection module according to any one of clauses 19 to 33, wherein the continuously variable filter has a first optical filtering characteristic in at least one first region and a second optical filtering characteristic in at least one second region.

[0199] 35. A source selection module according to any one of clauses 19 to 34, wherein both the first wavelength and the second wavelength are in the range of 400 nm - 1600 nm, and optionally, wherein both the first wavelength and the second wavelength are in the range of 400 nm to 1600 nm.

[0200] 36. A method, comprising:

[0201] Receiving first light of a first wavelength and second light of a second wavelength,

[0202] A first light is spatially distributed by an optical dispersion element onto a first pixel of an adjustable diffraction element including a plurality of pixels, and a second light is spatially distributed onto a second pixel among the plurality of pixels of the adjustable diffraction element;

[0203] A zero-order diffraction of the first light and a non-zero-order diffraction of the first light are generated by the first pixel, and a zero-order diffraction of the second light and a non-zero-order diffraction of the second light are generated by the second pixel; and

[0204] The zero-order diffraction of the first light is received by a continuously variable filter in at least one first region of the continuously variable filter, the zero-order of the second light is received in at least one second region of the continuously variable filter, the non-zero-order diffraction of the first light is received outside at least one first region, and the non-zero-order of the second light is received outside at least one second region;

[0205] The zero-order diffraction of the first light in at least one first region and the zero-order diffraction of the second light in at least one second region are transmitted or reflected by the continuously variable filter; and

[0206] The non-zero-order of the first light is blocked outside at least one first region and the non-zero-order of the second light is blocked outside at least one second region by the continuously variable filter; or

[0207] The non-zero-order diffraction of the first light in at least one first region and the non-zero-order diffraction of the second light in at least one second region are transmitted or reflected by the continuously variable filter; and

[0208] The zero-order of the first light is blocked outside at least one first region and the zero-order of the second light is blocked outside at least one second region by the continuously variable filter.

[0209] 37. A non-transitory computer program product including machine-readable instructions that, when executed by a computer system, are configured to cause the computer system to control a source selection module according to any one of clauses 1 - 35 to perform the method according to clause 30.

[0210] 38. A processor and an associated storage medium, the storage medium including the non-transitory computer program of clause 15, such that the processor is operable to control a source selection module according to any one of clauses 1 - 35 to perform the method according to clause 36.

[0211] 39. A metrology device including the processor of clause 16 and an associated storage medium so as to be operable to control a source selection module according to any one of clauses 1 - 35 to perform the method according to clause 36.

[0212] 40. A lithography apparatus including a source selection module according to any one of clauses 1 - 35.

[0213] 35. A lithographic device includes the processor of clause 37 and an associated storage medium, operable to control a source selection module according to any one of clauses 1–35 to perform the method according to clause 36.

[0214] Although this text may specifically refer to the use of a lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0215] Although embodiments may be specifically referred to herein in the context of a lithographic apparatus, the embodiments can be used in other apparatuses. The embodiments can 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). These apparatuses are generally referred to as lithographic tools. Such lithographic tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0216] Although embodiments may be specifically referred to herein in the context of an inspection or metrology apparatus, the embodiments can be used in other apparatuses. The embodiments can form part of a mask inspection apparatus, a lithographic apparatus, or any apparatus for measuring or processing an object such as a wafer (or other substrate) or a mask (or other patterning device). The term "metrology apparatus" (or "inspection apparatus") can also refer to an inspection apparatus or inspection system (or a metrology apparatus or metrology system). For example, an inspection apparatus including an embodiment can be used to detect defects in a substrate or defects in a structure on the substrate. In such an embodiment, the properties of interest of the structure on the substrate may be related to defects in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate.

[0217] Although the above may specifically refer to the use of embodiments in the context of optical lithography, it should be understood that, where the context permits, the invention is not limited to optical lithography and can be used in other applications (e.g., imprint lithography).

[0218] Although the above-described target or target structure (more generally, a structure on a substrate) is a metrology target structure specifically designed and formed for measurement purposes, in other embodiments, an attribute of interest may be measured on one or more structures that are functional parts of a device formed on a substrate. Many devices have regular grating-like structures. As used herein, the terms structure, target grating, and target structure do not require that the structure be provided specifically for the measurement being performed. Additionally, the pitch of the metrology target may be close to or smaller than the resolution limit of the optical system of the scatterometer, but may be much larger than the dimensions of conventional non-target structures, which are optionally product structures fabricated in the target portion C by a lithography process. In practice, the lines and / or spaces of the overlapping gratings within the target structure may include smaller structures similar in dimension to the non-target structures.

[0219] Although specific embodiments have been described above, it should be understood that the present invention may be practiced in ways different from those described. The above description is intended to be illustrative, not restrictive. Thus, those skilled in the art will appreciate that the present invention may be modified without departing from the scope of the claims set forth below.

[0220] Although specifically referred to as a "metrology device / instrument / system" or an "inspection device / instrument / system", these terms may refer to the same or similar types of tools, devices, or systems. For example, an inspection or metrology device including an embodiment of the present invention may be used to determine the characteristics of a structure on a substrate or wafer. For example, an inspection device or metrology device including an embodiment of the present invention may be used to detect defects on a substrate or defects in a structure on a substrate or wafer. In such embodiments, the attribute of interest of the structure on the substrate may be related to a defect in the structure, the absence of a particular portion of the structure, or the presence of an unwanted structure on the substrate or wafer.

[0221] Although specifically referred to certain types of electromagnetic radiation, it should be understood that, where the context permits, the present invention may be practiced using all electromagnetic radiation, including radio waves, microwaves, infrared rays, (visible) light, ultraviolet light, EUV, SXR, HXR, and gamma rays.

[0222] Although specific embodiments have been described above, it should be understood that one or more features in one embodiment may also be present in different embodiments, and features in two or more different embodiments may also be combined.

Claims

1. A source selection module, comprising an adjustable diffraction element, the adjustable diffraction element including a plurality of pixels; a light dispersion element configured to receive first light of a first wavelength and second light of a second wavelength, spatially distribute the first light on a first pixel among the plurality of pixels to generate a zero-order diffraction of the first light and a non-zero-order diffraction of the first light, and spatially distribute the second light on a second pixel among the plurality of pixels to generate a zero-order diffraction of the second light and a non-zero-order diffraction of the second light; and a continuously variable filter including at least one first region and at least one second region; wherein the continuously variable filter is arranged at a position such that the zero-order of the first light received by the at least one first region and the zero-order of the second light received by the at least one second region are transmitted or reflected by the continuously variable filter, the non-zero-order of the first light is blocked outside the at least one first region by the continuously variable filter, and the non-zero-order of the second light is blocked outside the at least one second region by the continuously variable filter; or wherein the continuously variable filter is arranged at a position such that the non-zero-order of the first light received by the at least one first region and the non-zero-order of the second light received by the at least one second region are transmitted or reflected by the continuously variable filter, the zero-order of the first light is blocked outside the at least one first region by the continuously variable filter, and the zero-order of the second light is blocked outside the at least one second region by the continuously variable filter.

2. The source selection module according to claim 1, wherein each pixel among the plurality of pixels includes a controllable grating, and optionally, the adjustable diffraction element includes a grating light valve.

3. The source selection module according to any one of the preceding claims, wherein the continuously variable filter is arranged on the optical path between the light dispersion element and the adjustable diffraction element.

4. The source selection module according to any one of the preceding claims, wherein the continuously variable filter is arranged at a certain distance from the adjustable diffraction element or at a certain distance from the conjugate image plane of the adjustable diffraction element such that the zero-order diffraction and the non-zero-order diffraction of the first light are spatially separated from the zero-order diffraction and the non-zero-order diffraction of the second light.

5. The source selection module according to any one of the preceding claims, wherein the light dispersion element includes a prism and / or a light dispersion grating.

6. The source selection module according to any one of the preceding claims, wherein the continuously variable filter includes a continuously varying bandpass layer.

7. The source selection module according to any one of the preceding claims, wherein the plane of the continuously variable filter is inclined with respect to the plane of the adjustable diffraction element.

8. The source selection module according to any one of the preceding claims, wherein the filtering characteristics are linearly distributed over the region of the continuously variable filter.

9. The source selection module according to any one of claims 1 to 7, wherein the filtering characteristics are non-linearly distributed over the region of the continuously variable filter.

10. The source selection module according to any one of the preceding claims, wherein the continuously variable filter has a first optical filtering characteristic in the first region and a second optical filtering characteristic in the second region.

11. The source selection module according to any one of the preceding claims, wherein both the first wavelength and the second wavelength are in the range from 400 nm to 900 nm.

12. A method comprising: receiving first light of a first wavelength and second light of a second wavelength; spatially distributing the first light by an optical dispersion element on a first pixel of an adjustable diffraction element including a plurality of pixels, and spatially distributing the second light on a second pixel among the plurality of pixels of the adjustable diffraction element; generating a zero-order diffraction of the first light and a non-zero-order diffraction of the first light by the first pixel, and generating a zero-order diffraction of the second light and a non-zero-order diffraction of the second light by the second pixel; and receiving the zero-order diffraction of the first light by the continuously variable filter in at least one first region of the continuously variable filter, receiving the zero-order of the second light in at least one second region of the continuously variable filter, receiving the non-zero-order diffraction of the first light outside the at least one first region, and receiving the non-zero-order of the second light outside the at least one second region; transmitting or reflecting, by the continuously variable filter, the zero-order diffraction of the first light transmitted or reflected by the at least one first region and the zero-order diffraction of the second light transmitted or reflected by the at least one second region; and blocking, by the continuously variable filter, the non-zero-order of the first light outside the at least one first region and blocking the non-zero-order of the second light outside the at least one second region; or transmitting or reflecting, by the continuously variable filter, the non-zero-order diffraction of the first light transmitted or reflected by the at least one first region and the non-zero-order diffraction of the second light transmitted or reflected by the at least one second region; and blocking, by the continuously variable filter, the zero-order of the first light outside the at least one first region and blocking the zero-order of the second light outside the at least one second region.

13. A non-transitory computer program product including machine-readable instructions that, when executed by a computer system, are configured to cause the computer system to control the source selection module according to any one of claims 1-11 to perform the method according to claim 12.

14. A processor and an associated storage medium, the storage medium including the non-transitory computer program according to claim 13, such that the processor is operable to control the source selection module according to any one of claims 1-11 to perform the method according to claim 12.

15. A measurement device includes the processor and associated storage medium according to claim 14, so as to be operable to control the source selection module according to any one of claims 1-11 to perform the method according to claim 12.

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