Reflection optics and microscope with reflection optics

Abstract

A reflection optic (1) for focusing electromagnetic radiation (300) into a focal plane (100), comprising at least the following components: - a central stop (12) which is arranged on an optical axis (200) of the reflection optics (1) and is configured to prevent electromagnetic rays (300) incident into the reflection optics (1) along the optical axis (200) from propagating parallel to the optical axis (200), - a reflection-based focusing element (11) with a tube (11-1) extending at least between the center stop (12) and the focal plane (100) along the optical axis (200) of the reflection optics (1) and defining a first volume (V1) radially around the optical axis (200), such that electrons (e) generated by electromagnetic radiation in the first volume (V1) - ) be shielded, - a massive window (13) which limits the first volume (V1) towards the focal plane (100) and is enclosed all around by the tube (11-1), wherein the massive window (13) is designed such that electrons generated by electromagnetic radiation in the first volume (V1) are shielded from the focal plane (100) by the massive window (13).

Description

[0001] The invention relates to a reflection optic for electromagnetic radiation in the extreme UV range and soft X-ray range, and to a microscope with the reflection optic according to the invention.

[0002] Focusing electromagnetic radiation is an essential element of microscopes that operate in the far field.

[0003] In the visible spectral range down to the UV range, refractive optics such as lenses can be used, but these are no longer applicable at increasingly short wavelengths due to the necessary material properties in the deep UV range and especially in the extreme UV (EUV) range around 100 nm.

[0004] Conversely, diffraction optics used in X-ray microscopes have a very short working distance in the EUV and soft X-ray ranges, which complicates their use in these photon energy ranges. Furthermore, due to their strong chromatic aberration, diffraction optics are not suitable for focusing polychromatic electromagnetic radiation onto a focal plane with sufficient quality.

[0005] X-ray microscopes are used to study materials with nanometer-scale resolution. In scanning X-ray microscopes, a sample is scanned with focused X-rays.

[0006] Typically, X-rays in the soft and tender X-ray range, i.e. in the range of 0.124 nm to 124 nm or in the energy range of 10 eV to 10 keV, are used, which are focused onto the sample by means of an X-ray optic comprising a Fresnel zone plate - for simplicity in the context of the specification also referred to as a zone plate.

[0007] The interaction of X-rays with the sample enables various imaging contrast mechanisms. In transmitted X-rays, both absorption and phase shifts within the sample can be determined. Furthermore, the interaction on the X-ray optics or excitation side generates X-ray fluorescence and photoelectrons that can emanate from the sample near the surface. These latter secondary signals, like transmitted X-rays, allow for the imaging of complementary information.

[0008] Fig. Figure 1 shows the typical setup of a scanning X-ray microscope with the corresponding detectors. The X-ray optics define a focal plane in which a sample can be positioned. The focal plane encompasses an X-ray focus generated by the X-ray optics and is orthogonal to an optical axis of the X-ray optics. The focal plane, in turn, defines an excitation space that extends on the X-ray optics side up to the focal plane and a transmission space extending on the other side of the focal plane.

[0009] On the transmission side, i.e., in the transmission chamber, a photon detector is arranged, which is designed to detect transmitted X-ray photons. This detector can, for example, include a suitable photodiode.

[0010] Exposure of the sample to X-rays also induces an electrical sample current, which can be detected using a picoammeter.

[0011] On the transmission side, the X-ray radiation also generates photoelectrons on the back side of the sample, which can be detected using a channel electron multiplier (also known as a channeltron). Furthermore, on the excitation side, the X-ray radiation produces a fluorescence signal, which can also be recorded using a photodetector.

[0012] The photoelectrons emerging from the sample near the surface on the excitation chamber side cannot yet be counted individually because the interaction of the X-ray radiation with the diffractive X-ray optics, in particular with the zone plate used to focus the radiation, leads to a large number of photoelectrons (component-generated electrons) that would interfere with such a measurement.

[0013] Typically, the distance between the zone plate and the focal plane, and thus between the sample and the component, is only a few millimeters, so that applying an electrical potential does not allow for separation between the component-generated electrons and the electrons from the X-ray focus in the sample.

[0014] Current X-ray microscopes therefore measure the so-called sample current without the possibility of counting these electrons generated on the excitation side of the sample, for example by means of a suitably arranged channeltron.

[0015] A disadvantage of these measurements is the associated high radiation exposure, as otherwise the generated currents in the sample would be too low to be reliably measurable, as would the necessary conductivity of the sample.

[0016] On the other hand, measuring the photoelectrons emitted from the sample on the transmission side is only possible for measuring samples that are so thin that the X-ray radiation generates a sufficient number of electrons on the transmission side despite absorption by the sample.

[0017] To measure the surface area of ​​thicker samples, it is therefore essential to measure the electrons on the excitation side. In principle, this can also be done using photoemission electron microscopy (PEEM), however, the samples to be measured with PEEM are ideally limited to conductive materials.

[0018] Especially in the range of photon energies in the EUV to very low soft X-ray range, the use of zone plates or the use of diffractive optics for the visible spectral range is unsuitable, so other solutions must be found.

[0019] JP H08-146 197 A discloses a holding device for a Wolter-type mirror assembly in an X-ray microscope. The holding device is designed as a hollow body in which the Wolter-type mirror assembly is arranged. The holding device, in turn, is mounted in the X-ray microscope.

[0020] A rotationally symmetric mirror system consisting of four mirrors arranged in series for an X-ray optic is disclosed in JP S63 192 000 A. The first mirror in the beam path is, for example, shaped as a hyperboloid of revolution, and the second mirror is cylindrical, followed by a cylindrical mirror and then another shaped as a hyperboloid of revolution. All mirrors are integrally manufactured. In the beam path within the mirrors, the first cylindrical mirror has a circular beam stop followed by a circular aperture, resulting in ring-shaped X-rays that are focused onto a sample. The X-rays diffracted by the sample are then collected by rotationally symmetric mirrors.

[0021] German patent DE 10 2005 056 404 B4 discloses an X-ray microscope with a condenser-monochromator arrangement with high spectral resolution. The X-ray microscope comprises a monochromator in which a capillary optic is used as the condenser. A monochromatic beam of light, tunable in wavelength with a bandwidth of 1 to 0.1 per mille by means of a tunable monochromator, is focused by the capillary optic, which has an annular aperture, onto a focal spot positioned independently of the wavelength at a distance of a few millimeters behind the capillary optic, with a diameter typically less than 0.1 mm. The object to be examined is positioned in the plane of the focal spot.

[0022] The object of the invention is therefore to provide a device which eliminates the aforementioned disadvantages, particularly for microscopy in the EUV and low X-ray range, for example in the range of 10 eV to 100 eV or 50 eV to 500 eV.

[0023] The problem according to the invention is solved by a reflection optic according to claim 1. Advantageous embodiments of the invention are specified in the dependent claims and are described below.

[0024] According to a first aspect of the invention, a reflection optic, in particular a total internal reflection optic, for focusing electromagnetic radiation in the range of 50 eV to 500 eV and in particular in the range of 10 eV to 200 eV into a focal plane, comprises at least the following components: - a center stop located on an optical axis of the reflection optics and designed to prevent electromagnetic rays incident along the optical axis into the reflection optics from propagating parallel to the optical axis, - a reflection-based focusing element comprising a tube extending between the center stop and the focal plane along the optical axis of the reflection optics and with a wall bounding a first volume radially around the optical axis, wherein the wall is configured such that electrons generated by electromagnetic radiation in the first volume are shielded from the focal plane by the wall, in particular wherein the wall forms an annular aperture in an entrance region of the tube with the center stop, wherein the focusing element is configured to focus the electromagnetic radiation onto the focal plane, in particular into a focal region (focal point), - a massive window that limits the first volume towards the focal plane in the area of ​​an exit region and is completely sealed off by the wall of the tube, wherein the massive window is designed such that electrons generated by electromagnetic radiation in the first volume are shielded from the focal plane by the massive window, in particular wherein at least a part of the electromagnetic radiation radiated into the tube can propagate through the massive window to the focal plane.

[0025] According to the invention, the reflection optics are designed to focus electromagnetic radiation with energies in the range of 10 eV to 10 keV, in particular in the range of 50 eV to 500 eV.

[0026] Reflection optics can be found, in particular, in an X-ray microscope. The focal lengths of the reflection optics are dimensioned accordingly.

[0027] According to one embodiment of the invention, the reflection optics has a focal length in the range of 1 mm to 100 mm, the focal length depending on the photon energy.

[0028] The wall can be designed to reflect electromagnetic radiation accordingly by choosing a suitable material, for example glass.

[0029] The wall can be coated with a conductive coating or comprise an electrically conductive material, so that the wall can be set to a predetermined electrical potential.

[0030] In particular, the inner surface of the wall can be provided with one or more, preferably different, layers that improve the reflection of electromagnetic radiation. Specifically, the multiple layers can comprise a sequence in the pattern ABAB, where A and B are different materials. The layers can comprise one or more materials selected from the group consisting of carbon, molybdenum, and silicon.

[0031] The annular aperture is specifically designed to allow electromagnetic radiation to enter the focusing element only via the annular aperture, so that it can propagate further in the direction of the focal plane.

[0032] Using reflection optics, an excitation beam direction can be defined, where the excitation beam direction runs along the optical axis and establishes a propagation direction along the optical axis. Thus, the center stop is positioned further from the focal plane along this direction than the solid window. The first volume is therefore open on the side of the annular aperture, opposite to the propagation direction.

[0033] The center stop can include an absorber material designed to absorb electromagnetic radiation in the wavelength range of 0.124 nm to 124 nm, or in the energy range of 10 eV to 10 keV. For example, the center stop can include or be made of gold.

[0034] The center stop comprises, in particular, a disc-shaped element having a circular surface contour oriented substantially perpendicular to the optical axis. The annular aperture can have an outer diameter in the range of 0.01 mm to 10 mm, in particular a diameter in the range of 0.05 mm to 0.3 mm.

[0035] The focusing element is, in particular, a reflective (as opposed to a refractive or diffracting) focusing element.

[0036] The reflection of electromagnetic radiation in the focusing element is primarily caused by total internal reflection. In particular, the reflection of electromagnetic radiation in the focusing element is essentially caused exclusively by total internal reflection.

[0037] The wall of the tube is shaped in such a way as to completely shield the optical axis, thereby limiting the first volume, which is bounded along the optical axis by the center stop and the solid window, and radially, for example, by the wall of the tube. This achieves shielding of electrons that are generated within the first volume, for example, by the interaction of excitation X-rays with the focusing element or by interaction with a side of the solid window facing into the first volume.

[0038] Such electrons, generated by reflection optics or other device components in interaction with electromagnetic radiation, are also referred to as component-generated electrons in the context of the specification, particularly in contrast to electrons generated by irradiating a sample arranged in a focal plane.

[0039] The solid window is in particular a plate or a sheet and advantageously a foil or membrane, which has two plane-parallel surfaces and is solid in the sense that it is made of a material transparent to the intended X-ray radiation and in the solid state or of a transparent and amorphous material, thus also solid in the sense of a material-containing window.

[0040] In a direction opposite to the direction of the excitation beam, i.e. in the direction of the optical axis away from the focal plane, the first volume is transparent to excitation radiation at least in the area of ​​the ring-shaped aperture, so that electromagnetic radiation can be radiated into the reflection optics.

[0041] The wall extends, in particular, over a length along the optical axis such that component-generated electrons cannot propagate out of the first volume in the direction of the excitation beam. Specifically, the wall extends over a length of between 5 mm and 100 mm, and more specifically over a length of between 10 mm and 30 mm, along the optical axis.

[0042] In particular, the massive window and the center stop are rigidly connected to the wall of the focusing element.

[0043] In this way, a reflection optic is provided that makes it possible to perform quantitative measurements on the excitation side with respect to the number of electrons originating from a sample. Thus, the reflection optic according to the invention allows the realization of an epigeometry with respect to an electron detector, such as a channeltron or an X-ray microscope, and therefore the surface measurement of samples that are so thick that no or only a marginal fraction of electromagnetic radiation is measurable in transmission.

[0044] In particular, the reflection optics according to the invention allow these measurements to be carried out in the EUV and low X-ray range.

[0045] According to a further embodiment of the invention, the tube is a hollow, in particular straight, tube.

[0046] At least the wall can contain an electron-absorbing material.

[0047] The tube has a particularly cylindrical wall, with the exit area limited by the solid window.

[0048] However, the cross-section of the tube does not necessarily have to be circular, but can be at least partially or completely angular, oval or elliptical.

[0049] According to a further embodiment of the invention, the tube has an inner diameter of the wall that tapers towards the focal plane, in particular so that electromagnetic radiation reflected on an inner side of the tube is focused onto the focal plane.

[0050] The narrowing can be linear along the optical axis, or, for example, hyperbolic, parabolic, or elliptical.

[0051] According to a further embodiment of the invention, the reflection optics has an electron detector which is arranged on the same side as the focusing element with respect to the focal plane (epi-geometry).

[0052] This arrangement allows a sample to be measured in epi-geometry using the reflection optics according to the invention, i.e. excitation and detection take place on the same side of the focal plane, which makes it possible to measure thick samples that cannot be penetrated by the excitation radiation.

[0053] According to a further embodiment of the invention, the center stop is arranged on a first end face of the tube, i.e. the tube does not extend beyond the center stop, but rather terminates with it.

[0054] According to a further embodiment of the invention, the solid window is arranged on a second end face of the tube, which is located in the exit area of ​​the focusing element.

[0055] According to a further embodiment of the invention, the center stop is designed as a circular disk which is held centrally on the optical axis by means of struts, and wherein the annular aperture is formed between the center stop and the wall in a radial direction, through which electromagnetic rays can propel into the tube.

[0056] In particular, the struts are rigidly connected to the wall.

[0057] According to a further embodiment of the invention, the tube, in particular its wall, is shaped as a paraboloid of revolution or as an ellipsoid of revolution, which points to the focal plane at its vertex.

[0058] This shape of the tube wall allows for particularly good focusing on the focal plane. In this embodiment, focusing is achieved primarily through total internal reflection at the tube wall.

[0059] According to a further embodiment of the invention, the focusing element has a Wolter optic type I.

[0060] The focusing element can be designed such that the wall of the tube on an inner side of the tube is such that it reflects electromagnetic rays and is therefore part of Wolter optics type I.

[0061] Advantageously, in this embodiment, the wall of the tube is shaped as a paraboloid of revolution in the inlet area and as a hyperboloid of revolution in the outlet area, which is closer to the focal plane.

[0062] Reflection on the inside of the tube wall occurs particularly for electromagnetic radiation that intersects the inside of the wall at an acute angle, i.e., particularly through total internal reflection.

[0063] A Wolter type I lens is a versatile X-ray lens that is relatively easy to manufacture. Wolter lenses are well-known in the field of X-ray telescopy and are designed as mirror systems. Type I Wolter lenses consist of a combination of a paraboloid and a hyperboloid mirror system. In type I Wolter lenses, reflection always occurs on the inner surfaces of the mirror systems.

[0064] According to a further embodiment of the invention, the focusing element comprises a Wolter optic of type II. In a Wolter optic of type II, the first reflection occurs on the inside of the paraboloid mirror and the second reflection on the outside of the hyperboloid mirror.

[0065] The tube can serve as an enclosure for the Wolter optic type II, radially enclosing it so that electrons generated by the interaction of electromagnetic radiation with the Wolter optic type II are shielded from the focal plane by the enclosure, particularly in conjunction with the solid window. In this embodiment, the Wolter optic type II is located within the first volume. Therefore, the tube does not form a reflective component for focusing the electromagnetic radiation. Reflection and focusing are achieved solely by the components of the Wolter optic type II.

[0066] Alternatively, the tube can be part of the Wolter optics type II, wherein the wall of the tube is shaped on an inner surface to reflect electromagnetic rays to another tubular optical element. This element extends along the optical axis, in particular concentrically to the wall of the tube, and is configured to reflect incident electromagnetic radiation towards the focal plane. Thus, the tube and the tubular optical element form the reflecting components of the Wolter optics type II, with the tube simultaneously serving as an enclosure.

[0067] In particular, the tubular optical element is shaped as a hyperboloid of revolution, with its vertex pointing towards the focal plane. Advantageously, in this embodiment, the wall of the tube is shaped as a paraboloid of revolution, with its vertex pointing towards the focal plane.

[0068] Reflection on the inside of the tube wall occurs particularly for electromagnetic radiation that intersects the inside of the wall at an acute angle, i.e., particularly via total internal reflection.

[0069] According to a further embodiment of the invention, the wall on an inner side is designed such that electromagnetic rays incident below a predefined angle are at least partially reflected, in particular wherein the angle is in the range of 0° and 40°.

[0070] The Wolter Type II optics allow for improved focusing of electromagnetic radiation onto the focal plane.

[0071] In this optical system, the electromagnetic radiation introduced through the annular aperture is initially reflected towards the tubular optical element, where it is reflected at an acute angle (particularly by total internal reflection) and passes through the solid window to the focal plane. In cases where the tube is part of the Wolter Type II optic, the introduced electromagnetic radiation is reflected by an inner surface of the tube wall towards the tubular optical element. The cross-sections of the tube and the tubular optical element are then configured accordingly and taper towards the focal plane.

[0072] According to a further embodiment of the invention, the focusing element comprises a Wolter optic of type III. In this case, the X-ray radiation is first reflected off the outside of a paraboloid and then focused on the inside of an ellipsoidal mirror.

[0073] The tube can serve as an enclosure for the Wolter optic type III, radially enclosing it so that electrons generated by the interaction of the Wolter optic type III with the electromagnetic radiation are shielded from the focal plane by the enclosure, particularly in conjunction with the solid window. In this embodiment, the Wolter optic type III is located within the first volume. According to this embodiment, the tube does not form a reflective component for focusing the electromagnetic radiation. Reflection and focusing are achieved solely by the components of the Wolter optic type III.

[0074] Alternatively, the tube can be part of the Wolter optics type III.

[0075] According to this embodiment, the Wolter optic type III has a tubular optical element extending along the optical axis from the center stop towards the focal plane, in particular concentrically to the wall of the tube, and configured to reflect incident electromagnetic radiation towards the inside of the tube (in particular by total internal reflection), in particular wherein the annular aperture is formed between the center stop and an annular wall section which extends radially from the inside of the tube towards the center stop in the entrance region, such that an outer diameter of the annular aperture is smaller than an inner diameter of the tube at the level of the center stop, wherein the wall of the tube is shaped on an inner side of the tube such that it reflects electromagnetic rays towards the tubular optical element.which extends along the optical axis, in particular concentrically to the wall of the tube, and is designed to reflect incident electromagnetic radiation towards the focal plane. Thus, the tube and the tubular optical element form the reflecting components of the Wolter optics type III, with the tube simultaneously functioning as an enclosure.

[0076] In particular, the tubular optical element is shaped as a paraboloid of revolution, with its vertex pointing away from the focal plane. Advantageously, in this embodiment, the wall of the tube is shaped as an ellipsoid of revolution.

[0077] Reflection on the inside of the tube wall occurs particularly for electromagnetic radiation that intersects the inside of the wall at an acute angle, i.e., particularly via total internal reflection.

[0078] The Wolter Type III optics allow for improved focusing of the electromagnetic radiation onto the focal plane, especially for smaller beam diameters of the incident electromagnetic radiation.

[0079] Unlike Wolter optics type II, in Wolter optics type III, electromagnetic radiation introduced into the focusing element is first reflected by the tubular optical element towards the wall of the tube (if it is part of the Wolter optics type III) or towards another reflecting element of the Wolter optics type III (if the tube merely serves as an enclosure) and from there focused towards the focal plane. In this type of optics, the center stop is typically smaller than, for example, in a Wolter optics type II.

[0080] Advantageous cross-sectional profiles, i.e., curvatures and tapering of the wall of the tube and / or the further tubular optical element of Wolter optics type I, II and III, are known to the skilled person and can be found in relevant textbooks.

[0081] According to a further embodiment of the invention, the focusing element comprises a Schwarzschild optic, with a convex central mirror and a concave focusing mirror with a central aperture, wherein the center stop is formed by the convex central mirror, wherein the central mirror is arranged in the tube, in particular wherein the tube is completely sealed around its wall by the concave focusing mirror.

[0082] In a Schwarzschild optic, the electromagnetic radiation is not necessarily reflected by the wall of the focusing element's tube, which can be advantageous with regard to component-generated electrons. Specifically, component-generated electrons are only produced at the central mirror and the focusing mirror.

[0083] According to a further embodiment of the invention, the electron detector has a detector wall which has a detection opening on an end face that points towards the focal plane, wherein the detector wall has a recess in which the tube is arranged.

[0084] Depending on the type of detector, the detector wall can be shaped like a tube or a dome.

[0085] The recess can be an opening.

[0086] This arrangement of the reflection optics allows for recordings in epi-geometry, in which no component-generated electrons reach the detector from the focusing element.

[0087] The recess allows the reflection optics to be positioned sufficiently close to a sample located in the focal plane, minimizing interference with the detector geometry.

[0088] The recess in the detection wall allows for an ultra-compact design, in which the focusing element and the detection optics, comprising the detection wall and electron detector, can be arranged within the excitation chamber. In particular, the recess is large enough to provide the tube with lateral adjustment.

[0089] The recess takes the form of a fully enclosed opening in the detection wall. The opening can be up to 10% to 50% larger in circumference than the tube.

[0090] According to a further embodiment of the invention, the detector wall is designed as a detection tube and is funnel-shaped, wherein a funnel axis of the funnel-shaped detection tube is curved, and the detection tube widens towards the detection opening of the detection tube.

[0091] In particular, the funnel axis and the optical axis can coincide in the focal plane.

[0092] This design of the detection wall allows the electron detector to be positioned laterally offset from the optical axis of the excitation beam. This is particularly important because the focusing element is already located along the optical axis, and an electron detector cannot also be positioned on the optical axis due to space constraints.

[0093] According to a further embodiment of the invention, the electron detector consists of one or more detectors of the group comprising - a Channeltron, - an electron energy-resolving electron detector, - an electron angle-resolving electron detector, selected.

[0094] According to this embodiment, suitable electron detectors include, for example, the channeltron mentioned in the introduction or an electron energy and / or angle-resolving detector, wherein the kinetic energy of the detected electrons can be determined using the energy-resolving detector and / or wherein the propagation direction of the detected electrons can be determined using the angle-resolving detector. The energy- and angle-resolving detector can be implemented in a single detector system, so that the energy and angle can be determined using the detector system.

[0095] The detector can therefore be an angle-sensitive and energy-dispersive detector configured to detect electrons over part or all of the hemisphere on the side of the focal plane where the focusing element is located. Such an arrangement allows the determination of an electron distribution from the focal plane in epigeometry and, optionally or alternatively, the determination of the electron energy distribution.

[0096] The electron detector can be designed as a LEED detector.

[0097] Such detectors are known, for example, in connection with measurement methods and apparatuses called LEED (from the English: LEED: Low-Energy Electron-Diffraction).

[0098] This embodiment allows for the determination of additional information about the sample structure and sample properties.

[0099] According to a further embodiment of the invention, the reflection optics comprise a protective aperture which can be moved from a first position to a second position, wherein the protective aperture in the first position covers a detection aperture of the electron detector, wherein the protective aperture in the second position exposes the detection aperture, in particular completely exposes it, and in particular wherein the protective aperture is designed such that ions emitted from a focal plane and / or an ion source, such as a fine-beam ion source, are absorbed and / or reflected by the protective aperture when it is in the first position.

[0100] This protective aperture allows, after capturing a surface of the sample, for example using a fine-beam ion source, the sample to be ablated layer by layer, and after each layer has been removed, the sample to be captured again, enabling the determination of a 3D structure of the sample. The protective aperture shields the electron detector from the ions during the ion treatment.

[0101] In this way, the electron detector can be protected without having to switch it off.

[0102] A suitable drive or manual device may be provided for repositioning the protective cover.

[0103] According to a further embodiment of the invention, the reflection optics comprise a radiation source which is configured to emit electromagnetic radiation along the optical axis, in particular along the excitation beam direction, through the reflection optics.

[0104] According to a second aspect of the invention, an X-ray microscope is disclosed, in particular a scanning X-ray microscope, wherein the X-ray microscope comprises the reflection optics according to an embodiment of the first aspect of the invention.

[0105] An X-ray microscope also includes, in particular, a sample holder designed to hold a sample, especially in the focal plane.

[0106] According to another embodiment, the X-ray microscope is configured as an epi-X-ray microscope, in particular as a scanning epi-X-ray microscope.

[0107] This means that both detection and excitation are arranged on the same side with respect to the sample or sample holder.

[0108] According to a further embodiment of the invention, the X-ray microscope has a fine ion beam source which is designed to remove a sample to be examined layer by layer by means of ion irradiation.

[0109] As is known from the technical literature, the English term "Focused Ion-Beam Source" is used as a fine ion beam source, which is designed to focus an ion beam onto a sample.

[0110] In particular, the ion fine beam source is arranged on the side of the reflection optics with respect to the focal plane.

[0111] Such a microscope makes it possible to remove and record a sample layer by layer, so that 3D structures of a sample can be determined using the microscope according to the invention.

[0112] According to a further embodiment of the invention, the reflection optics can be displaced along the optical axis between a first state and a second state, wherein in the first state a distance between a focal plane and the detection aperture is so large that the protective aperture can be moved into the first position between the focal plane and the detection aperture, and in the second state is arranged so close to the focal plane that the protective aperture no longer fits between the focal plane and the detection aperture.

[0113] The microscope is specifically designed to hold the surface of a sample to be examined in the focal plane, for example in the sample holder.

[0114] This embodiment allows as many electrons as possible originating from a sample to be detected, since the distance between the detection aperture and the sample is kept as small as possible during the measurement, while at the same time ensuring that the sample can be removed layer by layer with the detector protected.

[0115] According to a further embodiment of the invention, the microscope has a fluorescence detector on the side of the reflection optics, which is designed to detect the fluorescence produced by the interaction of the electromagnetic radiation from the reflection optics with a sample.

[0116] Such a microscope makes it possible to capture and evaluate not only the electrons from the sample but also the fluorescence in epigeometry. Examples and character description

[0117] Further features and advantages of the invention are explained below with reference to the description of exemplary embodiments in the figures. These show: Fig. 1 a state-of-the-art X-ray microscope system; Fig. 2 a schematic illustration of a reflection optic according to the invention; Fig. 3 a schematic illustration of a further embodiment of the invention comprising a Wolter optic type II; Fig. 4 a schematic illustration of a further embodiment of the invention comprising a Wolter optic type III; Fig. 5 a schematic illustration of a further embodiment of the invention comprising a Schwarzschild optic type; and Fig. 6 a schematic illustration of a further embodiment of the invention comprising a protective cover.

[0118] In Fig. Figure 1 is a schematic representation of a prior art X-ray microscope 1000. The X-ray microscope 1000 comprises an excitation optic 1' with an X-ray lens 2 and an OSA 3, which are arranged along an optical axis 200 of the microscope 1000. The beam path of the excitation radiation 300 is schematically represented by the arrows 300 pointing towards a focal plane 100 with a sample 400. The in Fig. The diffractive X-ray lens shown in Figure 1 is a zone plate 2 designed such that a first diffraction order of the incident electromagnetic radiation 300, generated by the zone plate 2, is diffracted to a focus 103 in the focal plane 100 of the microscope 1000. A zeroth diffraction order is blocked by a filter arranged centrally on the optical axis, which may be part of the zone plate 2, and does not reach the sample 400. Following the zone plate 2 along an excitation direction 201 is an OSA 3, order sorting aperture, arranged on the optical axis 200, which in the context of this specification is also referred to as the diffraction order filter aperture.

[0119] In principle, instead of the zone plate shown in the examples, another type of refractive or diffracting X-ray lens can also be used, so the examples should not be understood as being limited to the zone plate.

[0120] The OSA 3 has a central opening, the aperture 3-1, arranged on the optical axis 200, which blocks all further diffraction orders of the electromagnetic beam 300 generated by the zone plate 2, and allows only the first diffraction order to propagate through the aperture 3-1 towards the sample 400, where it forms a focus 103 in the focal plane 100, which extends perpendicular to the optical axis 200 and encompasses the focus, and wherein the microscope 1000 can be used to scan at least partially with the focus 103.

[0121] A sample holder 401 of the microscope 1000 holds a sample 400 to be examined in the focal plane 100.

[0122] The focal plane 100 essentially divides the space into two areas. A first area is referred to in the context of this specification as the excitation space 101, and lies on the side of the focal plane 100 that includes the focusing element.

[0123] A second area is referred to in the context of the specification as transmission space 102 and comprises a space extending in the transmission direction 201 to the focal plane 100, i.e. the space which extends on the side of the focal plane 100 opposite the excitation space 101.

[0124] The excitation beam 300 striking the sample can interact with the sample 400 in a variety of ways.

[0125] Firstly, the excitation beam 300 generates a sample fluorescence FL, which can be detected by means of a fluorescence detector 1001 on the side of the excitation chamber 101.

[0126] Furthermore, irradiation with X-rays may induce an electric current in the sample, which can be detected by means of a current sensor 1002 connected to the sample 400.

[0127] Provided the sample 400 is sufficiently thin, the excitation beam 300 can transmit electrons (e) on the transmission side, depending on the properties of the sample. - ) from the sample. These can be detected by means of an electron detector 1003 arranged in the transmission chamber 102. In addition, the transmitted electromagnetic radiation 302 can be measured by means of a detector 1004, for example a photodiode, arranged along the optical axis 200.

[0128] A disadvantage of this arrangement is that this microscope 1000 does not allow the electrons emitted by the sample 400 to be measured on the excitation space side, i.e., in epi-geometry, either as well as or alternatively. -to distinguish electrons that were generated by the interaction of the excitation radiation 300 with components of the X-ray optics 1', e.g., the zone plate 2 and the OSA 3. An electron detector positioned on the side of the excitation chamber 101 (not shown) would only detect all electrons, which would not provide any information about the sample properties.

[0129] This arrangement is also unsuitable for focusing electromagnetic radiation in the range of, in particular, 50 eV to 500 eV.

[0130] In Fig. Figure 2 shows a first exemplary embodiment of the reflection optics 1 according to the invention. The reflection optics 1 comprises a focusing element 11, which includes a tube 11-1 with a wall 11-2. In contrast to the optics in Fig. 1, a focusing optic based solely on reflection. Incident electromagnetic radiation 300 is reflected, in particular by total internal reflection, at the wall 11-2 of the tube 11-1. Due to the cross-sectional contour of the tube 11-1 along the optical axis 200, the electromagnetic radiation is focused in the focal plane 100.

[0131] The reflection of the electromagnetic radiation in the focusing element 11 is therefore caused in particular by total internal reflection. Specifically, the reflection of the electromagnetic radiation in the focusing element 11 is caused exclusively by total internal reflection.

[0132] The tube 11-1 extends along the optical axis 200 of the reflection optics 1. A central stop 12 is arranged in an entrance region of the tube 11-1, defining an annular aperture 18 between the wall 11-2 of the tube 11-1 and the central stop 12. The annular aperture 18 extends concentrically around the optical axis 200. Electromagnetic radiation, in particular essentially collimated electromagnetic radiation 300, can be provided by a radiation source (not shown) and directed into the tube 11-1 via the annular aperture 18.

[0133] In the tube 11-1, the electromagnetic radiation (represented by dotted lines in ray optics) propagates towards an exit region of the tube 11-1, which includes a solid window 13 at one end. The focusing element 11, together with the center stop 12, the solid window 13, and the wall 11-2 of the tube 11-1, therefore encloses a first volume V1. The tube is shaped such that at least a portion of the incident electromagnetic radiation is reflected at the wall 11-2 of the tube.

[0134] While the electromagnetic radiation propagates through the massive window 13, component-generated electrons, which can be produced by collisions of the electromagnetic radiation with components of the reflection optics—for example, the center stop 12, the wall 11-2, or the massive window 13—are shielded from the focal plane. This prevents these component-generated electrons from colliding with sample electrons. - can be detected by an electron detector on the side of the focusing element 11.

[0135] The massive window 13 can, for example, comprise or be designed as a silicon nitride foil or a silicon membrane, which advantageously implements the aforementioned properties.

[0136] The transmission level of the massive window 13 significantly affects the measurement time. Depending on the wavelength of the electromagnetic radiation, a Si3N4 (silicon nitride) film or a silicon membrane with a thickness of 10 nm to 100 nm would provide sufficiently high transmission, while component-generated electrons would be reliably shielded from the focal plane by the window. A lower limit of 5% would be particularly suitable for the transmission to ensure that the measurement times remain within a reasonable range.

[0137] The electromagnetic radiation can strike a sample 400 in the focal plane 100 after passing through the massive window 13, where it interacts with the sample to generate electrons (sample electrons) and also fluorescence. These electrons are primarily released on the side of the focusing element 11. The fluorescence can also be detected on the side of the focusing element by a fluorescence detector.

[0138] The expression "on the side of the focusing element" refers specifically to the half-space that lies on the same side of the focal plane 100 as the focusing element 11 – in the context of this specification, this half-space is also referred to as the excitation space 101. The half-space 102 on the other side of the focal plane 100 is also referred to as the transmission space 102 in the context of this specification.

[0139] The cross-sectional contour of the tube 11-1 can be shaped as in the example of Fig. 2 taper first hyperbolically and then parabolically towards the focal plane 100. In particular, the focusing element 11 can be shaped as a Wolter optic type I. The focusing element 11 is shaped such that the reflection of the electromagnetic radiation always occurs on the inside of the wall 11-2 of the tube 11-1.

[0140] In Fig. Figure 2 shows an electron detector 10 on the side of the focusing element 11. This detector has a detection tube 10-1, which extends around the focusing element 11 with a recess 10-2 in a wall 10-3 and forms a detection aperture 10-4 in the direction of the focal plane 100. The focusing element 11, including the center stop 12 and solid window 13, is positioned through the recess 10-2 in the detection tube 10-1 towards the detection aperture 10-4. Thus, the reflection optics 1 allows excitation and detection from the same side with respect to the focal plane 100. This is known in technical circles as an epi-configuration (epi-geometry).

[0141] This arrangement is only possible because component-generated electrons cannot reach the electron detector 10 through the tube 11-1, the center stop 12, and the massive window 13, and thus only electrons e- originating from the focal plane 100 can be detected by the electron detector 10.

[0142] The detection tube 10-1 opens in a funnel shape towards the detection aperture 10-4 and tapers along a funnel axis bent away from the optical axis 200 towards a detection unit (not shown) of the electron detector 10, which is designed to detect the electrons.

[0143] Other electron detectors are conceivable. In particular, electron detectors capable of determining the energy of the detected electrons can be advantageous. Furthermore, it can be beneficial to also determine the direction from which, or the angle at which, the electrons were emitted from the focal plane. For this purpose, the detector can be designed to resolve energy and / or angle.

[0144] It can be advantageous to set the tube 11-1 to a negative electrical potential relative to the focal plane 100 or the sample 400. In particular, the focal plane 100 or a sample 400 arranged thereon can be kept at a ground potential. This prevents electrons originating from the sample 400 from being absorbed by the tube 11-1 and reaching the electron detector 10. The electron detector 10, in turn, can be set to a positive potential relative to the tube 11-1 and / or the sample 400, so that electrons originating from the sample 400 are directed towards the electron detector 10.

[0145] The wall 11-2 of the tube has a material that can accept, in particular absorb, electrons and is at least opaque to electrons. This material can be an electrically conductive material, such as a metal, or a non-conductive material such as glass, or a non-conductive material such as glass coated with a conductive layer of metal.

[0146] For adjustment purposes, the reflection optics 1 can have an adjustment device (not shown) that allows the focusing element 11 to be moved laterally with respect to the optical axis 200. The adjustment device can also be configured to move the focusing element 11 along the optical axis 200.

[0147] The following illustrations depict exemplary embodiments, which are particularly distinguished from the ones described in the following figures. Fig. The reflection optics shown in Figure 11 are characterized as follows: In particular, identical components with identical or analogous properties are designated with the same reference symbols and are not described redundantly with respect to the respective figure. It is evident that features from the other figures can be used to specify the respective figure shown.

[0148] In Fig. Figure 3 shows a focusing element 11, which essentially corresponds to a Wolter optic type II. A fundamental distinction must be made between the embodiment in which the tube forms part of the Wolter optic, i.e., is arranged and designed as a reflective component for focusing the radiation, and the embodiment in which it merely forms an enclosure for the Wolter optic. Both embodiments have various advantages. An exemplary embodiment in which the tube forms part of the Wolter optic is described below.

[0149] The focusing element 11 includes another tubular optical element 14, which is arranged concentrically to the tube 11-1 in the first volume V1.

[0150] The focusing element 11 is further configured such that electromagnetic radiation 300 incident via the annular aperture 18 can be described by a beam path of the following kind: Behind the annular aperture 18 (i.e. in the first volume V1) the electromagnetic radiation is reflected at the wall 11-2 of the tube 11-1, whereby the tubular optical element 14, here in the form of a second tube with a wall, subsequently reflects the electromagnetic radiation on an outside of the wall of the tubular optical element 14.

[0151] The cross-sectional contours of the tube 11-1 and the tubular optical element 14 are designed such that reflection takes place at an acute angle and the respective reflection angles are such that the electromagnetic radiation is focused in the focal plane 100.

[0152] To achieve this, the wall 11-2 of the tube 11-1 follows a paraboloid, particularly on the inside where reflection takes place, while the outside of the wall of the tubular optical element 14 is shaped as a hyperboloid.

[0153] The reflective surfaces and reflection areas are shown in the figures as examples of reinforced black lines.

[0154] This geometry allows a larger working distance between the X-ray lens 11 and the focal plane 100.

[0155] The tubular optical element 14 is completely enclosed in the first volume V1 and limits it around the optical axis 200. Thus, the solid window 13 at the exit region of the tube 11-1 still forms an electron-impermeable seal for the focusing element 11.

[0156] This focusing element 11 - like all focusing elements according to the invention - has exclusively reflective components for the purpose of focusing electromagnetic radiation 300 and does not include any diffracting or refractive components.

[0157] If the tube is only intended to house the Wolter optics, another optical element must perform the tube's function within the Wolter optics. In this case, the tube encloses all components of the Wolter optics and does not contribute to focusing, but merely shields component-generated electrons (this variant is not shown).

[0158] In Fig. Figure 4 shows a focusing element 11 according to an embodiment of the invention, which essentially corresponds to a Wolter optic type III. Here, too, a distinction can be made between two embodiments.

[0159] In one embodiment, the tube forms part of the Wolter optics, meaning it is arranged and designed as a reflective component for focusing the radiation. In another embodiment, the tube merely serves as an enclosure for the Wolter optics. Both embodiments have various advantages. An exemplary embodiment in which the tube forms part of the Wolter optics is described below.

[0160] The massive window 13 is arranged on one end face of the tube 11-1 and closes off the first volume V1 in the direction of the firing plane.

[0161] This includes the focusing element 11 as well as the focusing element in Fig. 3 a tubular optical element 14, which is arranged concentrically to the tube 11-1 in the first volume V1.

[0162] In contrast to the focusing element in Fig. 2 and Fig. 3 the center stop 12 is smaller, whereby an aperture element 19 may be provided that scales the ring-shaped aperture 18 accordingly.

[0163] The in Fig. The focusing element 11 shown in Figure 4 has a smaller rear focal plane than the focusing element 11 shown in Figure 4. Fig. 2 and Fig. 3 and is therefore advantageously suited for processing small beam diameters.

[0164] The focusing element 11 is further configured such that electromagnetic radiation 300 incident via the annular aperture 18 can be described by the following beam path: Behind the annular aperture 18, the electromagnetic radiation is reflected off an outer surface of a wall of the tubular optical element 14 in the direction of the wall 11-2 of the tube 11-1 (i.e., away from the optical axis 200). Subsequently, the electromagnetic radiation is reflected off an inner surface of the wall 11-2 of the tube 11-1 again in the direction of the optical axis 200, so that a focus 103 is formed in a focal plane 100 of the focusing element 11.

[0165] The cross-sectional contours of the tube 11-1 and the tubular optical element 14 are designed such that reflection takes place at an acute angle and the respective reflection angles are such that the electromagnetic radiation is focused in the focal plane 1000.

[0166] To achieve this, the wall 11-2 of the tube 11-1 follows an ellipsoid, particularly on the inside where reflection takes place, while the outside of the wall of the tubular optical element 14 is shaped as a paraboloid.

[0167] The reflective surfaces and reflection areas are shown in the figures as examples of reinforced black lines.

[0168] The tubular optical element 14 is completely enclosed within the first volume V1 and limits it around the optical axis 200. Thus, the solid window 13 at the exit region of the tube 11-1 continues to form an electron-impermeable seal for the focusing element 11. The focal plane 100 and the focus (focal area) 103 lie outside the first volume V1 with respect to the solid window 13.

[0169] This focusing element 11 - like all focusing elements according to the invention - has exclusively reflective components for the purpose of focusing electromagnetic radiation and does not include any diffracting or refracting components.

[0170] In Fig. Figure 5 shows a focusing element 11 according to an embodiment of the invention, which essentially corresponds to a Schwarzschild optic, wherein the solid window 13 is additionally arranged at the end of the tube 11-1. It should be noted that this focusing element 11 is not based on total internal reflection.

[0171] The focusing element 11 includes an aperture 16 in the entrance area, which allows incident electromagnetic radiation to enter the tube 11-1 only in a region around the optical axis 200. The center stop 12 is located behind this aperture 16 along the optical axis.

[0172] The center stop 12 is designed as a central mirror 15, i.e. the center stop 12 is configured on a first side, which points towards the aperture 16, such that it reflects the incident electromagnetic radiation 300 back by means of convex reflection, so that the previously collimated electromagnetic radiation subsequently propagates divergently along the optical axis towards the aperture 16.

[0173] The aperture 16 is concave on at least one side, the side facing the solid window 13, so that the incident electromagnetic radiation is reflected towards the solid window 13 and simultaneously focused into the focal plane 100 outside the first volume. The aperture 16 thus forms a focusing mirror 16 of the Schwarzschild optics on one side.

[0174] Reflection of the electromagnetic radiation at the wall 11-2 of the tube 11-1 is not essential. In this embodiment, the tube 11-1 serves in particular as a boundary or enclosure for the first volume V1 and the Schwarzschild optics, so that component-generated electrons are retained in the first volume V1 and cannot reach the focal plane 100.

[0175] This focusing element 11 - like all focusing elements according to the invention - has exclusively reflective components for the purpose of focusing electromagnetic radiation and does not include any diffracting or refracting components.

[0176] In Fig. 6A and Fig. 6B is a further training course offered by the Fig. The embodiment shown in section 2 is illustrated. However, the further development can be applied analogously to the embodiments of the Fig. 3 to 5 can be applied.

[0177] Reflection optics 1 in Fig. 6 additionally features a protective cover 4, which is located between a first position (shown in Fig. 6A) and a second position (shown in Fig. 6B) is movable. In the first position, the protective aperture 4 is located between the focal plane 100 and the detection aperture 10-4 and completely covers it with respect to the focal plane 100.

[0178] In the second position, which is in Fig. As shown in Figure 6B, the protective aperture 4 completely exposes the detection aperture 10-4 with respect to the focal plane 100.

[0179] In the first position, it is then possible to irradiate the sample 400 using a fine ion beam source 17 and simultaneously protect the electron detector 10 from the ion radiation 500. In particular, negatively charged ions can damage the electron detector 10.

[0180] This embodiment is particularly advantageous in X-ray microscopes that have a reflection optic 1 according to the invention.

[0181] Additionally, the reflection optics 1 can be displaced along the optical axis 200 between a first state and a second state. In the first state, the distance between the focal plane 100 and the detection aperture 10-4 is such that the protective aperture 4 can be moved into the first position between the focal plane 100 and the detection aperture 10-4, and in the second state, the distance is so small that the protective aperture 4 no longer fits between the focal plane 100 and the detection aperture 10-4.

[0182] This has the advantage that the electron detector 10 in the second state can be brought very close to the focal plane 100 and thus to a sample 400 arranged there, so that an electron detection efficiency is increased compared to the first state.

[0183] The distance between the focal plane 100 and the detection aperture 10-4 can in particular be defined as the distance between a plane encompassed by the detection aperture 10-4 and the focal plane 100.

[0184] The focal plane 100 is, in particular, a plane that can be determined solely from the reflection optics. The focal plane 100 can extend at a distance from the reflection optics such that the focus 103 of electromagnetic radiation focused by the reflection optics 1 is encompassed in this focal plane 100; it can therefore correspond to the focal plane 100 of the focusing element 11. Furthermore, the focal plane can extend orthogonally to the optical axis 200 of the reflection optics 1. Reference list 1 Reflection optics 1' X-ray optics (state of the art) 2 zone plate 3 OSA (State of the Art) 3-1 Aperture (State of the Art) 4 Protective cover 10 Electron detector 10-1 detection tube 10-2 Exclusion 10-3 wall 10-4 Detector aperture 11 Focusing element 11-1 tubes 11-2 wall 12. Mid-stop 13 massive windows 14 tubular optical elements 15 central mirrors 16 aperture, focusing mirror 17 ion source 18 annular aperture 100 focal plane 101 Inspiration Room 102 Transmission space 103 Focus 200 optical axis 201 Excitation direction / Transmission direction 300 excitation radiation 302 transmitted X-rays 400 samples 401 Sample holders 500 ion radiation 1000 X-ray microscope 1001 Photon Detector / Photodiode 1002 Current sensor 1003 Electron detector 1004 X-ray detector e electrons FL Fluorescence V1 first volume

Claims

[1] A reflection optic (1) for focusing electromagnetic radiation (300) into a focal plane (100), comprising at least the following components: - a central stop (12) which is arranged on an optical axis (200) of the reflection optics (1) and is configured to prevent electromagnetic rays (300) incident into the reflection optics (1) along the optical axis (200) from propagating parallel to the optical axis (200), - a reflection-based focusing element (11) with a tube (11-1) extending at least between the center stop (12) and the focal plane (100) along the optical axis (200) of the reflection optics (1) and defining a first volume (V1) radially around the optical axis (200), such that electrons (e) generated by electromagnetic radiation in the first volume (V1) - ) be shielded, - a massive window (13) which limits the first volume (V1) towards the focal plane (100) and is enclosed all around by the tube (11-1), wherein the massive window (13) is designed such that electrons generated by electromagnetic radiation in the first volume (V1) are shielded from the focal plane (100) by the massive window (13). [2] The reflection optics (1) according to claim 1, wherein the reflection optics (1) has an electron detector (10) which is arranged on the same side with respect to the focal plane (100) as the focusing element (11). [3] The reflection optics (11) according to one of the preceding claims, wherein the tube (11-1) is shaped as a paraboloid of revolution or as an ellipsoid of revolution, which points at its vertex to the focal plane (100). [4] The reflection optics (1) according to one of the preceding claims, wherein the focusing element (11) comprises a Wolter optics type I, II or III and the tube forms a radial shield of the Wolter optics type I, II or III, or wherein the tube forms a component for focusing the electromagnetic radiation of a Wolter optics type I, II or III. [5] The reflection optics (1) according to one of the preceding claims, wherein the focusing element (11) comprises a Schwarzschild optic, with a convex central mirror (15) and a focusing mirror (16) with a central aperture, wherein the center stop (12) is formed by the convex central mirror (15), wherein the central mirror (15) is arranged in the tube (11-1). [6] The reflection optics (1) according to any one of claims 2 to 5, characterized by, that the electron detector (10) has a detector wall (10-3) having a detection aperture (10-4) on one end face, which points towards the focal plane (100), wherein the detector wall (10-3) has a recess (10-2) in which the tube (11-1) is arranged. [7] The reflection optics (1) according to any one of claims 2 to 6, wherein the electron detector (10) comprises one or more detectors selected from the group consisting of - a Channeltron, - a photon energy-resolving electron detector, - a photon angle-resolving electron detector, includes. [8] The reflection optics (1) according to any one of claims 2 to 7, characterized by, that the reflection optics (1) comprises a protective aperture (4) which can be moved from a first position to a second position, wherein the protective aperture (4) in the first position covers a detection aperture (10-4) of the electron detector (10), wherein the protective aperture (4) in the second position exposes the detection aperture (10-4). [9] A microscope comprising a reflection optic (1) according to any one of the preceding claims. [10] The microscope according to claim 9, characterized by , that the microscope has a fluorescence detector on the side of the reflection optics (1) which is designed to detect the fluorescence produced by the interaction of the electromagnetic radiation from the reflection optics (1) with a sample.

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