X-ray focusing with wavelength selection systems for semiconductor metrology

Abstract

An x-ray illumination system for use in x-ray based metrology of a sample, the x- ray illumination system includes x-ray energy adjustable optics that comprises a plurality of subsets of one or more x-ray optical elements, different subsets are associated with different x-ray energies out of multitude of selectable and monochromatic x-ray energies; wherein the x-ray energy adjustable optics is arranged to (a) receive an input x-ray beam that is polychromatic or partially monochromatic, and (b) generate a focused monochromatic x-ray beam having a selected x-ray energy, using a selected subset that is associated with the selected x-ray energy, the selected x-ray energy belongs to the multitude of selectable and monochromatic x-ray energies.

Description

X-RAY FOCUSING WITH WAVELENGTH SELECTION SYSTEMS FOR SEMICONDUCTOR METROLOGYCROSS REFERENCE

[0001] This application claims priority from US provisional patent serial number 63 / 601,743 filing date November 21, 2023 which is incorporated herein by reference. BACKGROUND OF THE INVENTION

[0002] X-ray metrology in the Semiconductor metrology environment generally requires small footprint x-ray delivery and focusing systems. Since Fab space is expensive, many high brightness x-ray sources as employed in national labs utilizing Synchrotron radiation (SR), Free Electron Lasers (FEL), are not only prohibitive in operating cost but also too large to be used for metrology and inspection. Other more scalable high-brightness x-ray sources include electron beam induced gas or solid plasma sources, e-beam generated x- rays from solid targets (fluorescent of bremsstrahlung), e-beam / Liquid metal jet sources. Some select representative metrology applications are X-ray scattering (XRS), X-ray diffraction (XRD, Small-angle X-ray Scattering (SAXS), X-ray Fluorescence (XRF) Total Reflection X-ray Fluorescence (TXRF), as well as X-ray Photoelectron Spectroscopy (XPS). Each of these applications requires different range of exciting x-ray energies (wavelengths) and thus different focusing or collimating systems, as well as differences in x-ray energy bandwidth,BRIEF DESCRIPTION OF THE DRAWINGS

[0003] FIG. 1 illustrates an example of x-ray optics;

[0004] FIG. 2 illustrates an example of a reflectivity of a multilayer substrate;

[0005] FIGs. 3-7 illustrate examples of x-ray optics;

[0006] FIGs. 8-10 illustrate examples of x-ray illumination systems;

[0007] FIGs. 11-12 illustrate examples of Bragg angle vs. x-ray wavelength;

[0008] FIGs. 13-14 illustrate examples of x-ray illumination systems;

[0009] FIG. 15 illustrate an example of a method; and

[0010] FIG. 16 illustrates example of properties of crystal diffractors of different properties used for providing x-ray beams of different energies.DETAILED DESCRIPTION OF THE DRAWINGS

[0011] The most common x-ray energy utilized in XPS is AlKa (1486.7eV) which is typically transported and focused onto a wafer surface via a monochromator in order to narrow the natural line width of the emission line for chemical state identification.Photoelectrons generated by AlKa radiation will have a kinetic maximum energy of ~1486.7eV, thus limiting the analysis depth to ~ lOnm and providing a limited range of secondary x-ray fluorescence lines which can be detected simultaneously and used as independent and complementary input parameters for the total dose of the analyzed material. The most commonly used focusing and monochromator system consists of an ellipsoidal or toroidal substrate that is populated with quartz (100) crystal platelets and provides point-to point focus of the target emission to the sample surface with an energy bandwidth ~0.5 eV.

[0012] Figure 1 illustrates a micro-focused electron beam (e-beam) 11 impinging on anode 12 to form a non-monochromatic x-ray ray beam 15 that impinges on the monochromator 16 (including an ellipsoidal or toroidal substrate) to form a monochromatic x-ray beam 17 that impinges on wafer 14.

[0013] Figure 2 illustrates (see display 20) reflectivity of a multilayer substrate at fixed angle for an energy range from 100-lOOOeV with strong suppression of other incoming x- ray lines.

[0014] The advantage of these systems is that monochromators with large angular acceptance and thus high transport efficiency can be manufactured.

[0015] A monochromator focusing system of this type may also transport when optimized for the 1storder Bragg diffraction for AlKa can also focus discrete higher order diffraction orders (energies) according to nX=2d sin(0) (d is the crystal lattice spacing) to the wafer surface.

[0016] However, the coverage of focusable energies is discrete by nature and intermediate energies other than n . equivalent can by design not be transported to the sampling area. Lower x-ray energies are not accessible or focusable at the sample surface with such a monochromator and would require a larger 2d lattice spacing applied to the substrate.

[0017] Existing systems to monochromate and focus different x-ray wavelengths X as given by hc / E where h is Planck’s constant, c=speed of light, and E the x-ray energy canbe produced by applying crystals of different crystal plane orientation and / or crystal materials to an ellipsoidal substrate.

[0018] The limitation that only x-ray energies according to nX=2d sin(0) or E=n / [(hc)2d sin(0)] can be monochromated and focused onto a wafer site with the lower cut-off determined by the 2d crystal lattice spacing. The higher the 1storder diffraction Energy, the larger the energy difference of higher diffraction orders.

[0019] In general, monochromator crystals for the higher energy range require smaller 2d lattice spacing and are quite readily available using various crystal plane orientations and crystals. These crystals can be applied to a substrate and focus monochromatic x-rays to the sampling region.

[0020] For X-ray energies requiring 2d-lattice spacings larger than 27 A, natural crystals are no longer available with defined lattice structure, and multilayer mirror monochromators are used.

[0021] Multilayers can be deposited on a substrate - for example an ellipsoidal substrate- to focus a monochromatic x-ray beam from the x-ray source to the sampling surface.

[0022] A specific example may be use of a W / Ti multilayer with 1 ,4nm period and relative layer thickness of 0.55 having 300 repeating layers onto the substrate. For example, for an x-ray energy of 452.2eV (Ti La), maximum reflectivity ideally 25% occurs at a Bragg angle of 78.3 degrees.

[0023] This engineered multilayer on a substrate provides a monochromatic x-ray beam that is focusable on to a wafer substrate (see figures 1 and 2).

[0024] Following this method, such a multilayer structure can be deposited on other optical systems, such as a Schwarzschild objective of suitable focusing geometry to provide a largely monochromatic and focused beam spot on a target sampling area. The Schwarzschild optics (denoted 30 in figure 3) is primarily applicable for the low-energy x- ray range in the water window since it requires a near-normal reflection geometry, i.e., Bragg angles in the range of >80 and <90 degrees.

[0025] Zone Plate optics represent another type of energy-selective focusing systems and are typically based on multilayers. These systems (denoted 40 in figure 4) may provide focusing in-lane transmission mode or in a reflective configuration. The principle is based a set of concentric ellipses around the object point with increasing size and common foci(source-object) to satisfy the Bragg diffraction condition over a larger diameter: rn=sqrt[(nX / 2)2+nXf] , where f is the focal length.

[0026] The resolution of zone plates is determined by the outermost zone width.

[0027] Reflection off-axis zone plate structures having appropriate geometry can be deposited on a substrate to provide spatially separated x-ray images according to incoming wavelength for a polychromatic incoming x-ray beam

[0028] Non-energy selective (achromatic) focusing systems operate using total external or internal reflection. For x-ray energies well above 2-3 keV, the most commonly employed focusing optics is poly-capillary optics (denoted 50 in figure 5). The focusing system consist of bundled glass capillaries which can be shaped to provide either point-to-parallel, parallel-point, or point-to-point focus and utilize total internal reflection.

[0029] For the lower energy range, the effectiveness of poly-capillary optics is generally lower than shaped reflective optics mirrors due to the higher critical angle of metal coated surfaces, for example Pt or other metal coating.

[0030] The reflective optics can be shaped to provide similar focusing conditions as polycapillary systems, i.e., provide point-to-parallel, parallel-point, or point-to-point focus. The shape of the reflective optics for point-to parallel x-ray transport is an effective paraboloid, shaped to match a given working distance as illustrated in Figure 4.

[0031] Single-bounce optics must employ a true parabolic shape and can be highly efficient for an x-ray energy range of several keV (depending on the metal coating). Type 1 through 3 Wolters optics utilizes total reflection as well, in double-bounce geometry with nested parabolic and elliptical mirrors to focus a near-parallel beam to a point (and the reverse - a point to parallel beam) (see Wolters optics 60 of figure 6).

[0032] In select applications, Reflective Wolters optics, Kirkpatrick-Baez mirror and Poly-capillary optics have been used in combination to increase the wavelength range of the collimating or focusing optics, i.e., poly-capillary optics inside Wolters optic.

[0033] There is provided a system and method for x-ray micro-focusing used for x-ray photoelectron spectroscopy (XPF) and / or x-ray fluorescence (XRF) metrology applications using different x-ray energies and energy bandwidth as a representative but not exclusive example which may readily be extended to other metrology use cases. In particular methods for focusing monochromatic x-ray beams of multiple but selectableenergies from 0.01 keV to 6keV onto a wafer surface will be described. The selectable energies are not limited to nX=2d sin(0).

[0034] State-of-the-art x-ray focusing systems incorporate dedicated x-ray optics which is optimized for a specific x-ray energy. However, dedicated x-ray monochromatic focusing system tend lack flexibility at the expense to achieve this performance, the cost factor becomes prohibitive where a larger range of x-ray energies is beneficial to the application, i.e., 2 or more monochromator focusing systems for 2 or more x-ray energies.

[0035] According to an embodiment, there are provided solutions to enable a high brightness broadband (0.01-6 KeV) x-ray beam illumination systems (also referred to as x-ray transport systems) and that select a selected diffractor (such as a narrow band diffractor with Bragg crystal or a multilayered diffractor), and collect and to focus (at different points of time) a multitude of selectable and monochromatic x-ray energies (wavelengths) through to the metrology site. The multitude of selectable and monochromatic x-ray energies are not limited to nX=2d sin(0).

[0036] X-ray targets from gas, solid, or liquid metal jet high brightness x-ray sources not only generate characteristic x-ray lines from the target but also varying intensity of continuum radiation knows as Bremsstrahlung. High intensity continuum radiation can be used as excitation source for specific applications, in particular when the x-ray focusing system of a compact scale can provide a continuously or quasi-continuously tunable monochromatic x-ray beam which can be focused to the metrology site.

[0037] According to an embodiment, there are provided solutions for provide x-ray illumination systems which can provide at least one of the following: a. An x-ray transport from a polychromatic or partially monochromatic x-ray source beam of 0.3-100pm in diameter through an optics configuration that results in a monochromatic focus at the sample (especially at an analysis site of the sample). b. Collect x-rays (using point to parallel converter or a point to focus optics), monochromate the x-ray beam, and subsequently collect and focus to the analysis site.c. Provide x-ray focusing of a monochromatic x-ray beam of selected energy selected from a multitude of selectable and monochromatic x-ray energies. The multitude of selectable and monochromatic x-ray energies may be discrete and / or spaced apart from each other. d. Continuously energy -tuned x-ray energy over a defined (for example limited) energy range of x-rays.

[0038] According to an embodiment, there is provided an x-ray illuminating system featuring a discretely selectable x-ray energy (0.01-6keV). According to an embodiment, the x-ray illuminating system includes fixed focusing elements in combination with a monochromator crystal or multilayer.

[0039] As a representative example, use of an achromatic point-to-parallel optics (also referred to as point to parallel converter) from an x-ray source a to flat monochromator crystal or multilayer diffractor that provided a given Bragg angle 0b. A second reversed point-parallel optic (also referred to as parallel to point converter) is placed at the outgoing angle of the monochromator crystal to focus the x-ray beam to the metrology site (also referred to as analyte site). Such a configuration is illustrated in figure 7 for a Bragg angle of 60 degrees - but other Bragg angles may be provided. Other configurations are possible such point to point focusing or tapered, as illustrated below.

[0040] According to an embodiment, there is provided an x-ray illumination system that includes several crystal diffractors with the same Bragg condition arranged either side-by- side (see figure 8) or mounted on a turret wheel to select crystal diffractors (see figure 9) In figure 8, the crystal diffractors are mounted on a stage 85 that is movable along a longitudinal axis as illustrated in Figure 9. The stage may be moved along other exes.

[0041] According to an embodiment, for an assumed Bragg angle of 60 degrees, the x-ray illumination system may use fixed optics location (fixed distance between the sample and the selected diffractor) and angle (fixed angle of illumination) could be applicable for the following x-ray energies using selectable monochromator crystals at fixed height and angle as listed in table 1 of figure 16. Table 1 provides examples of an approximate transmittedand focusable x-ray energies for different monochromator crystals and multilayers at an assumed fixed Bragg angle of 60 degree with achromatic input and output optics.

[0042] According to an embodiment, Multilayers diffractors can be optimized for different x-ray energies by utilizing different material combinations, layer ratio and thickness, as well as number of layers on the substrate. This applies for WSi and CrTi multilayers. The multilayers diffractors can be designed to optimize “reflectivity” and energy selectivity to act as high- efficiency diffractors at a given x-ray energy. Diffractor crystals offer a fixed crystal spacing according to material and crystal plane orientation.

[0043] Figures 8 and 9 illustrate examples of an X-ray transport from x-ray source via point-to-parallel optics 82 to monochromator (selected diffractor 84-k) and focusing (using parallel to point converter 87) the resultant monochromatic x-ray beam (of selected energy) to the metrology site 88.

[0044] As an extension to Figures 8 and 9 the x-ray focusing system may use flat crystals as Bragg diffractors.

[0045] In figures 8 and 9 there are a plurality (K) of diffractors denoted 84-1 till 84-K (diffractor 84-k being a selected diffractor, where k may be of any value between 1 to K). The diffractors are moved so that at a given selected x-ray beam energy - the appropriate diffractor is used. In figure 8 the diffractors form a linear array that is moved along its longitudinal axis. In figure 9 the diffractors are connected to facets of a multi-facet turret 91 and K equals six. K may have other values.

[0046] In figures 8 and 9, source 81 followed by point to parallel converter 81 (which is achromatic) that outputs a collimated x-ray beam 83 onto selected diffractor 84-k, to provide a monochromatic collimated x-ray 86 that is focused by parallel to point converter 87 (which is achromatic) to illuminate the sample 88 with a focused monochromatic x-ray beam of a selected energy.

[0047] The point to parallel converter is an example of a collimating optics following the x-ray source emission. The diffractor is an example of a flat monochromator crystal for x-ray energy selection provides a collimated output beam at the Bragg angle of the diffractor.

[0048] According to an embodiment, the distance between the selected diffractor and at least one of the x-ray source and the sample is matched to the geometry requirements ofthe x-ray delivery system due to x-ray beam collimation. It is noted that with parallel beam transport, the distance between optical elements is extremely flexible and elements can in principle be located at arbitrary distance.

[0049] According to an embodiment, the monochromatic x-ray beam is in turn focused onto the wafer with a half focusing optics with working distance to be matched to the spot size requirements for wafer metrology. According to an embodiment and since the x- ray beam following monochromatizating is parallel, the final focusing optics (parallel-to- point) provides focal spots according to its focal length or in this case working distance. Smaller f results in smaller final spot size.

[0050] According to an embodiment, a more flexible method to enable continuous or at last quasi-continuous x-ray illumination is achieved by changing a combined tilt of the input and output optics in order to change the Bragg condition.

[0051] In figure 10, source 81 is followed by point to parallel converter 81 (which is achromatic) that outputs a collimated x-ray beam 83 onto diffractor 101, to provide a monochromatic collimated x-ray 86 that is focused by parallel to point converter 87 (which is achromatic) to illuminate the sample 88 with a focused monochromatic x-ray beam of a selected energy.

[0052] According to an embodiment, a change in the Bragg angle (and therefore the energy of the x-ray beam) is achieved by changing the distance between the diffractor 101 and the sample and by rotating the source and focusing optics.

[0053] Figure 10 illustrates two examples for obtaining two different Bragg angles - in the first example (A) the distance between the diffractor 101 and the sample is denoted DI 111 and exceeds a distance (denoted D2 112) between the diffractor 101 and the sample at the second example (B). The angles of the source illumination (of the diffractor) denoted a and the angle of impingement of the focused monochromatic x-ray beam (denoted 0) also change to the value of the new Bragg angle.

[0054] While figure 10 illustrates two angles - the Bragg angle can be changed continuously or almost continuously (depending on the angular rotation and / or the distance change resolution) between these angles - or between any minimal and maximal angular values.

[0055] According to an embodiment, since a change in Bragg angle also alters the outgoing monochromatic x-ray beam toward the final focusing optics, the distance between the diffractor and the source and well as the distance between the diffractor and the focusing optics (parallel to point converter) is changed at the same time. For shallower Bragg angles, i.e., higher energy x-ray transport, the diffractor is moved closer to the incoming parallel x-ray beam, as well as the opposite angular compensation of the focusing optics (opposite sign or the source focusing optics) to allow for a stationary fixed x-ray spot at the metrology site.

[0056] Figure 11 illustrates (display 120) Bragg angle vs. x-ray wavelength for some selected monochromator / diffractor crystals between from 0.6 to 20 A.

[0057] Figure 12 illustrates (display 122) Bragg angle vs. x-ray wavelength for some selected monochromator / diffractor crystals between 20 and 120 A.

[0058] According to an embodiment, the collection efficiency as well as the final spot size of an x-ray focusing system for each specific x-ray energy as determined by the monochromator may be controlled or improved by a focusing optics imaging the x-ray source emission spot to a focal point of an ellipsoidal or toroidal monochromator which in turn focuses and transports x-rays at its design energy.

[0059] According to an embodiment, the ellipsoidal or toroidal monochromator is selected out of a set of ellipsoidal or toroidal monochromators - whereas each ellipsoidal or toroidal monochromator of the set is associated with a selected ellipsoidal or toroidal monochromator x-ray energy of a multitude of selectable and monochromatic x-ray energies.

[0060] Figures 13 and 14 illustrates a plurality (J) of ellipsoidal or toroidal monochromators 135-1 - 135- J, in these figures J equals five - but may differ than five.

[0061] According to an embodiment, the monochromatic x-ray focus of the monochromator is imaged onto the wafer surface.

[0062] According to an embodiment, and as illustrated in figures 13 and 14, a second optics (such as point to point achromatic demagnifying optics 137) has a focal point that is placed at the conjugate image location (136) of the monochromator to image / demagnify the monochromatic x-ray beam spot to the sample - for example - wafer 138.

[0063] According to an embodiment, the second optics is used to de-magnify the monochromatic image onto the wafer to a spot size smaller than the spot generated at the monochromator focus.

[0064] In figures 13 and 14 the ellipsoidal or toroidal monochromator has source conjugate 134 placed at the focal point of a point to point achromatic optics 133 that is located between a high brightness x-ray plasma source 132 illuminated by an electron beam or a laser beam source 131.

[0065] Figure 14 differs from figure 13 by not including the point of a point to point achromatic optics 132 and having the high brightness x-ray plasma source 132 positioned at the source conjugate 134.

[0066] According to an embodiment, the focal point is located at a location that corresponds to a specific x-ray energy.

[0067] According to an embodiment, the x-ray illuminating system includes imaging optics that are achromatic reflective or poly-capillary optics

[0068] Figure 15 illustrates an example of method 200 for illuminating a sample during x- ray based metrology of the sample.

[0069] According to an embodiment, figure 15 includes illuminating a sample using any system illustrated in figures 8, 9, 13 and 14.

[0070] According to an embodiment, method 200 includes step 210 of receiving an input x-ray beam that is polychromatic or partially monochromatic.

[0071] According to an embodiment, step 210 is followed by step 220 of generating a focused monochromatic x-ray beam having a selected x-ray energy, using a selected subset of one or more x-ray optical elements, the selected subset is associated with the selected x- ray energy, the selected x-ray energy belongs to a multitude of selectable and monochromatic x-ray energies, the selected subset belongs to a plurality of subsets of x- ray optical elements, different subsets are associated with different x-ray energies out of the multitude of selectable and monochromatic x-ray energies.

[0072] According to an embodiment, the input-x-ray beam is converted by a point to parallel optics to provide a collimated x-ray beam before impinging on the selected subset.

[0073] According to an embodiment, step 220 includes parallel to point conversion.

[0074] According to an embodiment, step 220 includes (or is followed by) demagnification.

[0075] According to an embodiment, method 200 includes positioning the selected subset in a position that impacts the input-x ray beam.

[0076] According to an embodiment, step 220 is followed by step 230 of illuminating the sample by the focused monochromatic x-ray beam. According to an embodiment, step 230 is executed during a metrology process that is selected out of XPS or XRF.

[0077] According to an embodiment, step 230 includes illuminating one or more measurement and completing, at least in part, one or more metrology measurements.

[0078] According to an embodiment, the suggested solution is a compact, stepwise energy selectable x-ray focusing system for semiconductor metrology.

[0079] According to an embodiment, there is provided a compact system capable of collecting, transporting and focusing a monochromatic x-ray beam of quasi-continuous x- ray energy focusing system from a high brightness laser or electron beam plasma source to direct and focus a monochromatic x-ray beam to the metrology site.

[0080] According to an embodiment, there is provided an x-ray illumination system for use in x-ray based metrology of a sample, the x-ray illumination system comprising: x-ray energy adjustable optics that is dynamically adjusted to receive an input x-ray beam that is polychromatic or partially monochromatic, and output a focused monochromatic x- ray beam having a selectable x-ray energy out of multitude of selectable and monochromatic x-ray energies.

[0081] According to an embodiment, the x-ray illumination system includes a controller for dynamically adjusting the x-ray energy adjustable optics according to the selectable x- ray energy.

[0082] According to an embodiment, the x-ray energy adjustable optics includes a plurality of diffractors that are associated with the multitude of selectable and monochromatic x-ray energies, and a selection unit for positioning a selected diffractor associated with the selectable x-ray energy in a path of the input x-ray beam.

[0083] According to an embodiment, the selection unit includes a rotatable turret, wherein different diffractors of the plurality of diffractors are mounted on different facets of the rotatable turret.

[0084] According to an embodiment, the selection unit includes a movable planar array of diffractors.

[0085] According to an embodiment, the diffractors are crystal diffractors.

[0086] According to an embodiment, the diffractors are multilayer diffractors.

[0087] According to an embodiment, the plurality of diffractors exhibit a same Bragg condition.

[0088] According to an embodiment, the x-ray energy adjustable optics is configured to maintain a fixed spatial relationship between a source of the input x-ray beam, the selected diffractor and the sample.

[0089] According to an embodiment, the x-ray energy adjustable optics includes a point to parallel converter that is upstream to the selected diffractor.

[0090] According to an embodiment, the x-ray energy adjustable optics includes a parallel to point converter that is downstream to the selected diffractor.

[0091] According to an embodiment, parallel to point converter is achromatic and the point to parallel converter is achromatic.

[0092] According to an embodiment, the x-ray energy adjustable optics includes a point to parallel converter, a diffractor, a parallel to point converter, and a selection unit that is configured to adjust an angular relationship and a spatial relationship between the point to parallel converter, the diffractor and the parallel to point converter according to selectable x-ray energy.

[0093] According to an embodiment, different selectable x-ray energies of the multitude of selectable and monochromatic x-ray energies are associated with different Bragg angles of the diffractor.

[0094] According to an embodiment, the x-ray energy adjustable optics includes a source point to point achromatic optics, a monochromator and a point to point achromatic demagnification optics.

[0095] According to an embodiment, the x-ray energy adjustable optics includes a monochromator and a point to point achromatic demagnification optics.

[0096] In the foregoing detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced withoutthese specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0097] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings.

[0098] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0099] Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.

[0100] Any reference in the specification to a method should be applied mutatis mutandis to a system capable of executing the method and / or should be applied mutatis mutandis to a non-transitory computer readable medium that stores instructions for executing the method.

[0101] Any reference in the specification to a system should be applied mutatis mutandis to a method that may be executed by the system and / or should be applied mutatis mutandis to a non-transitory computer readable medium that stores instructions executable by the system.

[0102] Any reference in the specification to a non-transitory computer readable medium should be applied mutatis mutandis to a method that may be execute instructions stored in the non-transitory computer readable medium and / or should be applied mutatis mutandis to a system capable of executing the instructions.

[0103] In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.

[0104] Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

[0105] The connections as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connection that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals.

[0106] Although specific conductivity types or polarity of potentials have been described in the examples, it will be appreciated that conductivity types and polarities of potentials may be reversed.

[0107] Each signal described herein may be designed as positive or negative logic. In the case of a negative logic signal, the signal is active low where the logically true state corresponds to a logic level zero. In the case of a positive logic signal, the signal is active high where the logically true state corresponds to a logic level one. Note that any of the signals described herein may be designed as either negative or positive logic signals. Therefore, in alternate embodiments, those signals described as positive logic signals maybe implemented as negative logic signals, and those signals described as negative logic signals may be implemented as positive logic signals.

[0108] Furthermore, the terms "assert" or “set" and "negate" (or "deassert" or “clear”) are used herein when referring to the rendering of a signal, status bit, or similar apparatus into its logically true or logically false state, respectively. If the logically true state is a logic level one, the logically false state is a logic level zero. And if the logically true state is a logic level zero, the logically false state is a logic level one.

[0109] Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality.

[0110] Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

[0111] Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.

[0112] However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

[0113] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence ofother elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first" and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0114] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

WE CLAIM1. An x-ray illumination system for use in x-ray based metrology of a sample, the x- ray illumination system comprising: x-ray energy adjustable optics that comprises a plurality of subsets of one or more x-ray optical elements, different subsets are associated with different x-ray energies out of multitude of selectable and monochromatic x-ray energies; wherein the x-ray energy adjustable optics is arranged to (a) receive an input x-ray beam that is polychromatic or partially monochromatic, and (b) generate a focused monochromatic x-ray beam having a selected x-ray energy, using a selected subset that is associated with the selected x-ray energy, the selected x-ray energy belongs to the multitude of selectable and monochromatic x-ray energies.

2. The x-ray illumination system according to claim 1 , wherein the plurality of subsets are a plurality of diffractors.

3. The x-ray illumination system according to claim 2, further comprising a selection unit that is arranged to position the selected subset in an x-ray processing position.

4. The x-ray illumination system according to claim 3, wherein the selection unit comprises a rotatable turret, wherein different diffractors of the plurality of diffractors are mounted on different facets of the rotatable turret.

5. The x-ray illumination system according to claim 3, wherein the selection unit comprises a movable planar array of diffractors.

6. The x-ray illumination system according to claim 3, wherein the diffractors are crystal diffractors.

7. The x-ray illumination system according to claim 3, wherein the diffractors are multilayer diffractors.

8. The x-ray illumination system according to claim 3, wherein the plurality of diffractors exhibit a same Bragg condition.

9. The x-ray illumination system according to claim 3, wherein the x-ray energy adjustable optics is configured to maintain a fixed spatial relationship between a source of the input x-ray beam, the selected diffractor and the sample.

10. The x-ray illumination system according to claim 3, wherein the x-ray energy adjustable optics comprises a point to parallel converter that is upstream to the selected diffractor.

11. The x-ray illumination system according to claim 10, wherein the x-ray energy adjustable optics comprises a parallel to point converter that is downstream to the selected diffractor.

12. The x-ray illumination system according to claim 11, wherein parallel to point converter is achromatic and the point to parallel converter is achromatic.

13. The x-ray illumination system according to claim 1 , wherein the plurality of subsets are a plurality of monochromators.

14. The x-ray illumination system according to claim 13, whereon the plurality of monochromators are toroidal monochromators.

15. The x-ray illumination system according to claim 13, whereon the plurality of monochromators are ellipsoidal monochromators.

16. The x-ray illumination system according to claim 13, comprising a point to point achromatic demagnifying optics that is upstream to a selected monochromator of the plurality of monochromators.

17. The x-ray illumination system according to claim 13, comprising a source point to point achromatic optics that is upstream to a selected monochromator of the plurality of monochromators.

18. The x-ray illumination system according to claim 17, comprising a point to point achromatic demagnifying optics that is upstream to a selected monochromator of the plurality of monochromators.

19. A method for illuminating a sample during x-ray based metrology of the sample, the method comprising: receiving an input x-ray beam that is polychromatic or partially monochromatic; and generating a focused monochromatic x-ray beam having a selected x-ray energy, using a selected subset of one or more x-ray optical elements, the selected subset is associated with the selected x-ray energy, the selected x-ray energy belongs to a multitude of selectable and monochromatic x-ray energies, theselected subset belongs to a plurality of subsets of x-ray optical elements, different subsets are associated with different x-ray energies out of the multitude of selectable and monochromatic x-ray energies.

20. A non-transitory computer readable medium for illuminating a sample during x-ray based metrology of the sample, the non-transitory computer readable medium stores instructions that once executed by an x-ray illumination system cause the x- ray illumination system to: receive an input x-ray beam that is polychromatic or partially monochromatic; and generate a focused monochromatic x-ray beam having a selected x-ray energy, using a selected subset of one or more x-ray optical elements, the selected subset is associated with the selected x-ray energy, the selected x-ray energy belongs to a multitude of selectable and monochromatic x-ray energies, the selected subset belongs to a plurality of subsets of x-ray optical elements, different subsets are associated with different x-ray energies out of the multitude of selectable and monochromatic x-ray energies.

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