X-ray optics and X-ray microscope with X-ray optics

Abstract

An X-ray optic (1) for focusing X-ray radiation (300) into a focal plane (100), comprising at least the following components: - a diffractive X-ray lens (2) and - a diffraction order filter aperture (3), OSA, wherein the diffractive X-ray lens (2) and the diffraction order filter aperture (3) are arranged along an optical axis (200) of the X-ray optics (1), characterized in that the X-ray optics (1) has a holding device (12) extending along the optical axis (200) and a first shielding device (11) extending along the optical axis (200), wherein the holding device (12) is connected to the diffractive X-ray lens (2), wherein the first shielding device (11) is designed as a first shielding device (11) enclosing the optical axis (200), and is connected to the diffraction order filter aperture (3) and delimits a first volume (V1) in which both the holding device (12) and the diffractive X-ray lens (2) are fully shielded, so that electrons generated by X-rays (300) in the first volume (V1) (e -) are shielded by the first shielding device (11).

Description

[0001] The invention relates to an X-ray optic for an X-ray microscope and to an X-ray microscope with the X-ray optic according to the invention.

[0002] 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.

[0003] Typically, X-rays in the soft and tender X-ray range, i.e., in the range of 0.124 nm to 24.8 nm or in the energy range of 50 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.

[0004] 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, on the X-ray optics side, the interaction generates the excitation of X-ray fluorescence and photoelectrons, which can emanate from the sample near the surface. These latter secondary signals, like transmitted X-rays, allow for the imaging of complementary information.

[0005] 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.

[0006] 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.

[0007] Exposure of the sample to X-rays also induces an electrical sample current, which can be detected using a picoammeter.

[0008] On the transmission side, the X-rays also generate 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-rays produce a fluorescence signal, which can also be recorded using a photodetector.

[0009] 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.

[0010] Typically, the distance between the zone plate and the focal plane, and thus a sample, is only a few millimeters, so that by applying an electrical potential it is not possible to separate the component-generated electrons from the electrons from the X-ray focus in the sample.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] US Patent 6,504,901 B1 discloses a device for focusing X-rays in which a capillary waveguide or a polycapillary lens is arranged on a first axis closely coupled to a mirror for focusing X-rays. The mirror has an inner reflective surface with a symmetry axis of rotation corresponding to a second axis, the first and second axes being substantially collinear with each other.

[0016] An X-ray lens arrangement is disclosed in US 7,711,092 B2. This arrangement comprises a tubular element with an inlet and an outlet for X-rays, and a capillary X-ray lens mounted inside the tubular element. The X-ray lens is secured within the tubular element by a stabilizing means. The tubular element can have internal and external cross-sections of any shape. The cross-sections can, for example, be circular, oval, or polygonal. The X-ray lens can include one or more capillaries.

[0017] US Patent 9,646,732 B2 discloses an X-ray system and various methods using this system. The X-ray system employs near-field imaging with a high-resolution scintillator coupled to a camera. The object under investigation is positioned in close proximity to a thin scintillator, which converts X-rays into visible light. When collimated X-rays are directed at the object, a detailed, high-resolution near-field X-ray shadow image (X-ray image) is generated on the scintillator. The scintillator then converts the X-ray image into a high-resolution visible-light image, and a high-magnification optical microscope produces a magnified optical image of the X-ray image on a 2D optical sensor, such as a CCD or CMOS detector.

[0018] The object of the invention is therefore to provide a device that eliminates the aforementioned disadvantages.

[0019] The problem according to the invention is solved by an X-ray optic according to claim 1. Advantageous embodiments of the invention are specified in the dependent claims and are described below.

[0020] According to a first aspect of the invention, an X-ray optic for focusing X-ray radiation into a focal plane for an X-ray microscope, in particular for a scanning X-ray microscope, comprises at least the following components: - a diffractive X-ray lens, - an order sorting aperture (OSA), wherein the diffractive X-ray lens and the order sorting aperture (OSA) are arranged along an optical axis of the X-ray optics, the X-ray optics comprising a holding device extending along the optical axis and a first shielding device extending along the optical axis, the holding device being connected to the diffractive X-ray lens, the first shielding device being designed as a first shielding device enclosing the optical axis, and being connected to the order sorting aperture (OSA) in particular in a terminating and circumferential manner and delimiting a first volume in which both the holding device and the diffractive X-ray lens are circumferentially shielded, so that electrons generated by X-rays in the first volume are shielded by the first shielding device and in particular by the OSA,especially absorbed.

[0021] X-ray optics allow for the definition of an excitation beam direction, where the excitation beam direction runs along the optical axis and establishes a sequence along this axis. Thus, the diffractive X-ray lens is positioned closer to an X-ray source along this direction than the OSA. Consequently, the first volume also includes the diffractive X-ray lens.

[0022] The holding device can be designed in the form of a support rod that extends laterally offset to the optical axis along the optical axis, so that it does not interfere or only interferes slightly with an excitation beam.

[0023] The OSA can include an absorber material designed to absorb X-rays in the wavelength range of 0.124 nm to 24.8 nm, or in the energy range of 50 eV to 10 keV. For example, the OSA can include gold or be made of gold.

[0024] The OSA comprises in particular a disc-shaped element having an aperture, in particular wherein the aperture has a diameter in the range of 0.01 mm to 0.3 mm, in particular a diameter in the range of 0.02 mm to 0.08 mm.

[0025] The diffractive X-ray lens is, in particular, a focusing diffractive X-ray lens. According to one embodiment of the invention, the diffractive X-ray lens comprises a zone plate, such as a Fresnel zone plate. The diffractive X-ray lens can also be configured as a zone plate.

[0026] In particular, the X-ray lens can include a Fresnel zone plate with a center stop, so that an undiffracted X-ray beam is not propagated through the X-ray lens.

[0027] The diffractive X-ray lens is specifically designed to diffract incident X-ray radiation in a first and possibly also higher diffraction order.

[0028] The diffractive X-ray lens can be configured to block the zeroth diffraction order (i.e., undiffracted X-rays) of an excitation beam while allowing the first diffraction order to pass through. The diffractive X-ray lens can also be configured to selectively block or transmit higher orders.

[0029] According to the invention, the first shielding device is particularly shaped such that it shields the optical axis circumferentially and thus delimits the first volume, which is delimited in particular along the optical axis by the OSA and radially, for example, by means of a wall of the first shielding device. This achieves shielding of electrons that are generated within the first volume, for example, by interaction of excitation X-rays with the X-ray lens or by interaction with a side of the OSA facing into the first volume.

[0030] Such electrons, generated by the X-ray optics or other device components in interaction with the X-ray 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.

[0031] In a direction opposite to the excitation beam direction of the OSA, the first volume is at least partially transparent to excitation radiation, so that X-rays can be directed into the X-ray optics.

[0032] The first shielding device 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. In particular, the first shielding device extends over a length of between 5 mm and 50 mm, and especially over a length of between 15 mm and 25 mm, along the optical axis.

[0033] In particular, the first shielding device and the holding device are rigidly connected to the OSA or the X-ray lens.

[0034] In this way, an X-ray optic is provided that, for the first time, makes it possible to perform quantitative measurements on the excitation chamber side with respect to the number of electrons originating from a sample. Thus, the X-ray optic according to the invention allows the realization of an epi-geometry (i.e., in the excitation chamber above the sample surface facing the excitation beam direction) with respect to an electron detector, such as a channeltron or an X-ray microscope, and therefore enables surface measurement of samples that are so thick that no or only a marginal fraction of X-ray radiation is measurable in transmission.

[0035] According to one embodiment of the invention, the holding device is designed as a second shielding device encompassing the optical axis, which encloses a second volume along the optical axis with the X-ray lens, which lies in the first volume, so that electrons generated by X-ray radiation in the second volume are shielded, in particular absorbed, by the second shielding device.

[0036] In particular, the second shielding device is completely and circumferentially connected to the X-ray lens.

[0037] The design of the holding device as a second shielding device improves, on the one hand, the stability of the holding device, and on the other hand, improved shielding of component-generated electrons is achieved, which are generated in the area of ​​the X-ray optics and do not represent a signal of the sample.

[0038] The second shielding device is of such a shape in particular that it shields the optical axis all around and thus limits the second volume, which is limited in particular along the optical axis by the X-ray lens and radially, for example, by means of a wall of the second shielding device.

[0039] In a direction opposite to the excitation beam direction of the X-ray lens, the second volume is at least partially transparent to excitation radiation.

[0040] The second shielding device extends, in particular, over a length along the optical axis such that electrons generated by components in the X-ray optics cannot propagate in the direction of the excitation beam. In particular, the second shielding device extends over a length of between 5 mm and 50 mm, and especially over a length of between 15 mm and 25 mm, along the optical axis.

[0041] This achieves a shielding of component-generated electrons, which are produced within the second volume, for example, by the interaction of excitation X-ray radiation with the X-ray lens.

[0042] Accordingly, the second shielding device has in particular a material that is opaque to X-rays.

[0043] This embodiment provides an X-ray optic that has a plurality of absorber walls or non-transparent walls, such that the probability of electron absorption in the first and second volumes is so high that the component-generated electrons escaping despite shielding devices are negligible.

[0044] According to a further embodiment of the invention, it is provided that the first shielding device at least partially encompasses the second shielding device, so that the first volume is at least partially limited on an inner side of the first volume by the second shielding device.

[0045] This embodiment allows for improved shielding of component-generated electrons in X-ray optics.

[0046] According to a further embodiment of the invention, the first and second volumes are arranged concentrically to each other along the optical axis.

[0047] According to a further embodiment of the invention, the first shielding device terminates with a first end face with the diffraction order filter aperture (OSA) and / or the holding device terminates with a first end face with the X-ray lens.

[0048] This embodiment defines a substantially cylindrical first shielding device and a holding device that form an end face from which component-generated electrons cannot escape.

[0049] A second end face of the first shielding device and / or the holding device is particularly transparent to excitation radiation and can therefore be open.

[0050] According to a further embodiment of the invention, the first shielding device is a tube (elongated hollow body), in particular a straight tube and / or wherein the holding device is also a tube.

[0051] Each of these tubes therefore has a wall, with at least the wall of the first shielding device having an electron-absorbing material. The same can also apply to the holding device, especially if it is designed as a shielding device.

[0052] The tube of the first shielding device has a particularly cylindrical wall, in particular wherein the first end face is bounded by the OSA.

[0053] 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.

[0054] The tube of the holding device has a particularly cylindrical wall, in particular wherein the first end face is limited by the X-ray lens.

[0055] 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.

[0056] According to a further embodiment of the invention, the X-ray optics comprises a first adjustment device, wherein the first adjustment device is configured to move the diffraction order filter aperture (OSA) at least perpendicular to the optical axis, in particular along second axes, in particular wherein the first adjustment device is configured to also move the diffraction order filter aperture along the optical axis and / or wherein the X-ray optics comprises a second adjustment device, wherein the second adjustment device is configured to move the X-ray lens at least perpendicular to the optical axis, in particular along second axes, in particular wherein the second adjustment device is configured to also move the X-ray lens along the optical axis.

[0057] The first and second adjustment devices can be combined in one adjustment arrangement or be designed separately.

[0058] The first and / or second adjustment mechanism allows the X-ray lens and / or the OSA to be aligned with respect to an excitation beam. It can be advantageous if the X-ray lens and / or the OSA can also be moved along the optical axis.

[0059] The first and second adjustment devices allow the X-ray lens and the OSA to be moved relative to each other and also relative to the optical axis.

[0060] The first and / or the second adjustment device is located, in particular, outside the first and the second volume.

[0061] According to a further embodiment of the invention, the first adjustment device is connected to the diffraction order filter aperture (DPA) via the first shielding device, such that the first adjustment device is configured to move the first shielding device together with the diffraction order filter aperture. Additionally or alternatively, it can be provided that the second adjustment device is connected to the X-ray lens via the holding device, such that the second adjustment device is configured to move the holding device together with the X-ray lens.

[0062] This allows the OSA or the X-ray lens to be aligned with respect to an excitation beam by relocating the first shielding device and / or the holding device.

[0063] This embodiment also allows the first and / or adjustment device to be arranged outside the first volume, contributing to a compact X-ray optics design.

[0064] According to a further embodiment of the invention, the first shielding device is electrically conductive at least in one area, wherein the first shielding device in this area is configured to be placed at an electrical potential relative to a ground potential, so that, in particular, component-generated electrons are attracted to the first shielding device in the case of a positive electrical potential or repelled in the case of a negative electrical potential, in particular wherein the ground potential is located at a sample to be examined or in the focal plane.

[0065] The electrical potential relative to the ground potential ranges in magnitude from 1 V to several kV, particularly up to 100 kV. The magnitude of the potential depends, for example, on the energy of the incident X-ray radiation.

[0066] In particular, it may be provided that the electrical potential can be adjusted vertically by means of an adjustment device. The adjustment device may be encompassed by, connected to, or connectable to the X-ray optics.

[0067] Provided that the first shielding device is set to a positive potential, this embodiment allows component-generated electrons in the first volume to be directed towards the first shielding device, thus achieving improved shielding.

[0068] Provided that the first shielding device is set to a negative potential, it is sufficiently ensured that electrons originating from a sample are not attracted to the first shielding device and thus may not be detected.

[0069] For this purpose, the first shielding device can be supplied with a positive or negative electrical potential, e.g. by an adjustable voltage source whose ground potential is on the sample or in the focal plane and whose positive or negative electrical pole is electrically connected to the first shielding device.

[0070] In particular, the electrical potential of the first shielding device can be set equal to the ground potential. The electrical conductivity of the first shielding device then ensures that no unwanted electrical potentials build up relative to the sample.

[0071] For this purpose, the first shielding device can be coated with a suitable conductive coating or comprise an electrically conductive material.

[0072] For the purposes of this specification, electrical conductivity is defined in particular as an electrical conductivity greater than 1 S / m, especially greater than 10 4 S / m viewed.

[0073] According to a further embodiment of the invention, the holding device, in particular the second shielding device, is electrically conductive at least in one area, wherein the holding device is configured to be placed at an electrical potential relative to a ground potential, so that component-generated electrons are attracted to the holding device, in particular wherein the ground potential is located at a sample to be examined or in the focal plane.

[0074] The electrical potential of the first and second shielding devices can be the same or different from each other.

[0075] Preferably, the first shielding device can be held at a negative potential and the second shielding device at a positive potential relative to ground potential.

[0076] Alternatively, it can be provided that the first shielding device is held at a positive potential and the second shielding device at a negative potential relative to ground potential.

[0077] Alternatively, it can be provided that both the first shielding device are held at a negative or positive potential and the second shielding device is held at the same potential relative to ground potential.

[0078] Alternatively, it can be provided that the first shielding device is held at ground potential and the second shielding device is held at a positive or negative potential relative to ground potential.

[0079] Alternatively, it can be provided that the first shielding device is held at a positive or negative potential and the second shielding device is held at ground potential relative to ground potential.

[0080] Alternatively, it can be provided that the first shielding device and the second shielding device are held at ground potential.

[0081] This embodiment makes it possible to direct electrons generated in the first and second volumes towards the second shielding device, or to deflect them away from it, so that improved shielding of component-generated electrons from the sample is achieved.

[0082] For this purpose, the second shielding device can be supplied with a positive or a negative electrical potential, e.g. by a voltage source whose ground potential is on the sample or in the firing plane and whose positive or negative electrical pole is electrically connected to the second shielding device.

[0083] In particular, the electrical potential of the second shielding device can be set equal to the ground potential. The electrical conductivity then ensures that no unwanted electrical potentials build up relative to the sample.

[0084] For this purpose, the second shielding device can be coated with a suitable conductive coating or comprise an electrically conductive material.

[0085] According to a further embodiment of the invention, the diffraction order filter aperture (OSA) comprises a solid, i.e., a mass-bearing X-ray window that covers an aperture of the diffraction order filter aperture, wherein the X-ray window is designed to shield electrons so that they do not propagate from the first volume through the X-ray window.

[0086] In particular, the X-ray window should be transparent to X-rays. That is, the transparency of the X-ray window should be at least 5%.

[0087] This embodiment provides a further improved X-ray optics system, which achieves improved shielding of electrons originating from the X-ray optics.

[0088] Such an X-ray window can, for example, be designed as a film. The film can have a thickness in the range of 20 nm to 500 nm, particularly in the range of 50 nm to 300 nm, and especially in the range of 75 to 150 nm.

[0089] The X-ray window may, for example, contain silicon nitrite or consist of silicon nitrite.

[0090] Regardless, the OSA can also include silicon or even consist of silicon.

[0091] According to a further embodiment of the invention, the diffraction order filter aperture (OSA) has a first side and a second side, wherein the first side is, for example, oriented with a normal vector to the side of the X-ray lens and points into an excitation space, and the second side points in the opposite direction, wherein an excitation beam direction along the optical axis from the X-ray lens points towards the diffraction order filter aperture (OSA) in the direction of the transmission space.

[0092] This embodiment serves to clearly define the structural and geometric design of the X-ray optics.

[0093] According to a further embodiment of the invention, the X-ray optics comprise an electron detector, in particular a channel electron multiplier, wherein the electron detector is arranged on the same side with respect to the focal plane as the diffraction order filter aperture (OSA) and the X-ray lens.

[0094] A channel electron multiplier is commonly referred to as a channeltron in technical circles and also within the scope of this specification.

[0095] This embodiment discloses that the electron detector, which is configured to detect electrons emitted from a sample by interaction with the excitation radiation, is arranged on the same side of the focal plane as the X-ray lens and the OSA. The side is defined here in relation to an epi-geometry with respect to the X-ray optics and the electron detector, particularly in contrast to a transmission geometry in which the electron detector is oriented towards the excitation beam beyond a sample.

[0096] In particular, the electron detector is arranged so that it is aligned in the direction of an excitation beam (and not against this direction).

[0097] This combination of electron detector and excitation optics (i.e., OSA and X-ray lens) on the same side of the excitation space (with respect to the transmission space) is particularly useful only if the X-ray optics include the first and / or the second shielding device.

[0098] According to a further embodiment of the invention, the electron detector is provided to be set up and configured to determine a direction and / or an energy of the detected electrons.

[0099] In other words, the electron detector can be configured to determine a detection angle of the incident electrons and an electron energy.

[0100] Such detectors are known, for example, in connection with measurement methods and apparatuses known as LEED (from the English: LEED: Low-Energy Electron-Diffraction).

[0101] This embodiment allows for the determination of additional information about the sample structure and sample properties. According to a further embodiment of the invention, the electron detector comprises a detection tube having a detection aperture on one end face of the detection tube, which points towards the focal plane, wherein the detection tube has a recess in a wall of the detection tube in which the first shielding device is arranged; in particular such that the diffraction order filter aperture (OSA) is located in the region of the detection aperture.

[0102] In particular, the OSA lies in the same plane as the detection aperture.

[0103] The recess in the detection tube allows for an ultra-compact design, in which the excitation optics – comprising the OSA and the X-ray lens – can be arranged in the excitation chamber together with the detection optics – comprising the detection tube and electron detector. In particular, the recess is large enough to allow the first shielding device some leeway for lateral adjustment.

[0104] The recess takes the form of an opening in the detection tube, which may be completely enclosed. The opening may be, in particular, 10% to 50% larger in circumference than the first shielding device.

[0105] According to a further embodiment of the invention, the detection tube is funnel-shaped, wherein a funnel axis of the funnel-shaped detection tube is curved, in particular wherein the funnel axis curves away from the optical axis starting from the focal plane, wherein the detection tube widens towards the detection opening of the detection tube.

[0106] In particular, the funnel axis and the optical axis can coincide in the focal plane.

[0107] This design of the detection tube allows the electron detector to be positioned laterally offset from the optical axis of the excitation beam. This is particularly important because the X-ray lens and the OSA are already located along the optical axis, and it is difficult to also position an electron detector on the optical axis due to space constraints.

[0108] According to a further embodiment of the invention, the X-ray 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 the detection aperture, 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 ion beam source, are absorbed and / or reflected by the protective aperture when it is in the first position.

[0109] 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 recaptured (microscopically examined) so that a 3D structure of the sample can be determined. The protective aperture shields the electron detector from the ions during ion treatment.

[0110] In this way, the electron detector can be protected without having to switch it off.

[0111] A suitable drive or manual device may be provided for repositioning the protective cover.

[0112] According to a further embodiment of the invention, the X-ray optics comprise an X-ray source which is configured to emit X-rays along the optical axis, in particular along the excitation beam direction, through the X-ray optics.

[0113] 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 X-ray optics according to one of the embodiments of the first aspect of the invention.

[0114] An X-ray microscope also includes, in particular, a sample holder designed to hold a sample.

[0115] 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. This means that both detection and excitation are arranged on the same side with respect to the sample or a sample holder.

[0116] 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.

[0117] As is known from the technical literature, the term "Focused Ion-Beam Source" is used, which is designed to focus an ion beam onto a sample.

[0118] In particular, the ion fine beam source is arranged on the side of the X-ray optics with respect to the focal plane.

[0119] Such an X-ray 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 X-ray microscope according to the invention.

[0120] According to a further embodiment of the invention, the X-ray optics are displaceable 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.

[0121] The X-ray microscope is specifically designed to hold the surface of a sample to be examined in the focal plane, for example in the sample holder.

[0122] 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. Examples and character description

[0123] 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 an X-ray optic according to the invention; and Fig. 3 a schematic illustration of a further embodiment of the invention.

[0124] 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 X-ray 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 X-ray radiation 300, generated by the zone plate 2, is diffracted to a focus 301 in the focal plane 100 of the X-ray microscope 1000. A zeroth diffraction order is blocked by a filter 2-1 arranged centrally on the optical axis, e.g., by a center stop, which can be part of the zone plate 2, and does not reach the sample 400. Following the zone plate 2 along an excitation direction 201, an OSA 3 (order sorting aperture) is arranged on the optical axis 200 and is also referred to in the context of this specification as the diffraction order filter aperture.

[0125] In principle, instead of the zone plate shown in the examples, another type of diffractive X-ray lens can also be used, so the examples should not be understood as being limited to the zone plate.

[0126] 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 X-ray 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 301 in the focal plane 100, the focal plane extending perpendicular to the optical axis 200, and can be scanned at least partially with the focus 301 by means of the X-ray microscope 1000.

[0127] A sample holder 401 of the X-ray microscope 1000 holds a sample 400 to be examined in the focal plane 100.

[0128] The focal plane 100 essentially divides the space into two areas. A first area is referred to in the context of this specification as excitation space 101 and lies on the side of the focal plane 100 that includes the X-ray lens, or zone plate 2 and the OSA 3.

[0129] A second area is referred to in the context of this 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.

[0130] The excitation beam 300 striking the sample can interact with the sample 400 in a variety of ways. Firstly, the excitation beam 300 generates sample fluorescence FL, which can be detected by a fluorescence detector 1001 on the side of the excitation chamber 101. Furthermore, the irradiation with X-rays may induce an electric current in the sample, which can be detected by a current sensor 1002 connected to the sample 400.

[0131] 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 X-ray radiation 302 can be measured by means of a detector 1004, for example a photodiode, arranged along the optical axis 200.

[0132] A disadvantage of this arrangement is that this prior art X-ray 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 or alternatively. - to distinguish between electrons generated by the interaction of the excitation radiation 300 with components of the X-ray optics 1', 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.

[0133] This hypothetical situation is in Fig. 2, Panel A). In Fig. Figure 2, Panel A) shows an electron detector 10, which is arranged on the side of the excitation chamber 101. The X-ray optics 1' comprise an X-ray lens 2 and the OSA 3. The X-ray radiation 300 striking these elements generates electrons e- (also referred to as component-generated electrons in the context of this specification) through interaction with them, which are detected by the electron detector 10. Additionally, the X-ray radiation 300 striking the sample 400 also generates electrons e-, which are likewise detected by the detector 10. A detection signal thus acquired cannot be evaluated because the signal-to-noise ratio is too low due to the component-generated electron component to determine the electron component originating from the sample.

[0134] An improvement in X-ray optics 1 for this type of application is in Fig. 2 Panel B) shown schematically.

[0135] In Fig. Panel 2 (B) shows an advantageous embodiment of the invention comprising a first and a second shielding device 11, 12, which also serve as holding devices.

[0136] The X-ray optics 1 includes an OSA 3 and an X-ray lens in the form of a zone plate 2, which are arranged on an optical axis 200 of the X-ray optics 1. According to the arrangement of the OSA 3 and the zone plate 2, an excitation beam direction 201 can be defined, which points along the optical axis 200 from the zone plate 2 towards the OSA 3.

[0137] X-rays 300 from an X-ray source not shown are indicated by dashed arrows.

[0138] The X-ray radiation 300 incident on the X-ray optics 1 is diffracted into different diffraction orders by the zone plate 2 due to an imprinted Fresnel structure.

[0139] The zeroth diffraction order of zone plate 2, i.e., the undiffracted component of the X-ray radiation 300, is blocked by filter 2-1 and OSA 3, so that the zeroth diffraction order of the zone plate is filtered out behind the OSA. The first diffraction order of the zone plate propagates through the OSA to the focus on the sample. Further diffraction orders propagate towards OSA 3 and are partially filtered out by it.

[0140] The task of the OSA 3 is to propagate only a specific diffraction order, such as the first diffraction order of the excitation X-ray beam 300 towards the focal plane 100.

[0141] The OSA 3 is a circular disk with a centrally located aperture 3-1, which has a diameter in the sub-millimeter range. The OSA can, for example, be made of or consist of a metal or silicon, or be made of silicon coated with a thin silicon nitride layer that covers the open area of ​​the OSA and is transparent to X-rays.

[0142] The OSA 3 is designed to absorb soft X-rays – except in the region of aperture 3-1, where it is transparent. This allows X-rays 300 to pass only through aperture 3-1 towards focal plane 100 and form a focus 301 in focal plane 100, so that a sample 400 positioned there can be scanned with focus 301.

[0143] X-ray radiation 300, which hits the X-ray lens 2, the OSA 3 or other components of the X-ray optics 1, can lead to the release of electrons from the material of these components, which interfere with a measurement of electrons from a sample in the focal plane.

[0144] For this reason, the X-ray optics 1 according to the invention provides a first shielding device 11 which extends cylindrically (as a tube) around the optical axis 200 and terminates on a first end face 11-1 with the OSA 3, so that the cylindrical first shielding device 11 encloses a first volume V1 with a wall 11-2 of the first shielding device 11.

[0145] The wall 11-2 of the first shielding device 11 comprises a material that can receive, in particular absorb, electrons, but 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] The first shielding device 11 extends across the X-ray lens 2 in the opposite direction to the excitation beam 201, so that the X-ray lens 2 is also enclosed in the first volume V1. In particular, the first shielding device 11 extends even further than the X-ray lens 2 in the opposite direction to the excitation beam 201, in particular by several millimeters.

[0147] In this way, the first shielding device 11 encloses the first volume V1, from which no electrons can escape towards the focal plane 100, except through the aperture 3-1 of the OSA 3.

[0148] To also rule out this possibility of component-generated electron contamination, aperture 3-1 of OSA 3 can be covered by an X-ray window (not shown). The X-ray window is transparent to X-rays, has a material that does not tend to release electrons when irradiated with X-rays, and is not transparent to electrons. The X-ray window can, for example, comprise or be designed as a silicon nitride foil, which advantageously implements the aforementioned properties.

[0149] The transmission level of the X-ray window significantly affects the measurement time. Depending on the wavelength of the X-rays, a 100 nm thick Si3N4 (silicon nitrite) foil would have a transmission of more than 50% (approximately 50% at 300 eV photon energy and over 90% at photon energies above 1 keV). A lower limit of 5% for the transmission would be suitable to keep measurement times within a reasonable range.

[0150] To further improve the shielding of component-generated electrons and to ensure improved stability of the X-ray lens 2 in the X-ray optics 1, the [description of the following is missing from the original text] Fig. 2 Panel B) shows X-ray optics 1 and a second shielding device 12.

[0151] In the example shown, the second shielding device 12 also has a cylindrical wall (tube) 12-2, which terminates at a first end face 12-1 with the X-ray lens 2 and extends from there along the optical axis 200 in the opposite direction to the excitation beam 201.

[0152] The wall 12-2 of the second shielding device 12 encloses a cylindrical second volume V2, which is arranged within the first volume V1. The first and second shielding devices 11, 12 are arranged, at least partially, in particular concentrically around the optical axis 200.

[0153] The second volume V2 is designed to intercept electrons generated within the second volume V2 with the wall 12-2 of the second shielding device 12 and to prevent them from propagating into the first volume V1 extending around it.

[0154] For this reason, the wall 12-2 of the second shielding device 12 has a material suitable for this task, for example a metal, as already described in connection with the first shielding device 11.

[0155] The first and second shielding devices 11,12 thus essentially form two concentrically arranged tubes, wherein the second shielding device 12 has a smaller diameter than the first shielding device 11 and is therefore arranged inside the first shielding device 11.

[0156] This arrangement of the shielding devices 11, 12 allows component-generated electrons to be contained within the first and second volumes V1, V2. This allows, as in Fig. Figure 2 B) shows an electron detector 10 on the same side, in the excitation chamber 101, as the OSA 3 and the X-ray lens 2 are arranged with respect to the focal plane 100 (epi-geometry). This configuration was not practical in the X-ray microscopes known from the prior art for the reasons mentioned above.

[0157] Opposite the excitation chamber 101 with respect to the firing plane 100 extends the transmission chamber 102.

[0158] The electron detector 10 has a detection tube 10-1 which extends around the first shielding device 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 first shielding device 11, together with the OSA 3 and the internally located second shielding device 12 with the X-ray lens 2 attached to it, are arranged by a recess 10-2 in the wall 10-3 of the detection tube 10-1 in the direction of the detection aperture 10-4. Thus, the X-ray optics 1 allow excitation and detection from the same side with respect to the focal plane 100. This is known in technical circles as an epiconfiguration (geometry).

[0159] This arrangement is only possible because component-generated electrons cannot reach the electron detector 10 through the first and second shielding devices 11, 12, the X-ray lens 2, the OSA 3 and, if applicable, the X-ray window, and thus only electrons originating from the focal plane 100 e - are detectable by the electron detector 10.

[0160] 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.

[0161] It can be advantageous to set the first shielding device 11 to an electrical potential that is negative 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 first shielding device 11 and reaching the electron detector 10. The electron detector 10, in turn, can be set to a potential that is positive relative to the first shielding device 11 and / or relative to the sample 400, so that electrons originating from the sample 400 are directed towards the electron detector 10.

[0162] Furthermore, a negative potential of the first shielding device 11 causes component-induced electrons in the first volume V1 to be deflected towards the wall 11-2 of the second shielding device 12, thus increasing the probability of being absorbed by the wall of the second shielding device 12 and not propagating to the focal plane 100.

[0163] To enhance this effect, the second shielding device 12 can be subjected to a positive electrical potential.

[0164] Alternatively, the electrical potentials of the first and second shielding devices 11, 12 can be configured as shown in the embodiments of the invention. In particular, it can be advantageous to set the electron detector 10 to a positive potential relative to the focal plane 100 or sample 400, as well as to the first and second shielding devices 11, 12.

[0165] It should always be ensured that the electrical potentials of the first and second shielding devices are set, or are set, so low that electrons originating from the focal plane 100 can still reach the detection unit of the electron detector 10 without also being absorbed, in particular, by the first shielding device 11. This can be achieved by setting the electron detector 10, or the detection unit, to a positive electrical potential relative to the focal plane 100.

[0166] For adjustment purposes, the X-ray optics 1 can have a first and / or a second adjustment device (not shown) that allows the first or second shielding device 11, 12 to be moved laterally with respect to the optical axis in order to optimally align the X-ray lens 2 or the OSA 3 attached thereto with respect to the optical axis 200 and an excitation beam 300. The first and / or the second adjustment device can further be configured to also move the X-ray lens 2 or the OSA 3 along the optical axis 200. The movement of the X-ray lens 2 and the OSA 3 is carried out, in particular, relative to each other. The first and the second adjustment devices can be combined in an adjustment arrangement.

[0167] In Fig. 3, Panel A) and B) is a training course of the in Fig. 2 illustrated embodiment.

[0168] X-ray optics 1 in Fig. 3 additionally features a protective cover 4, which can be moved between a first and a second position. In the first position, which is in Fig. As shown in Panel A), 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.

[0169] In the second position, which is in Fig. As shown in Panel B (3), the protective aperture 4 completely exposes the detection aperture 10-4 with respect to the focal plane 100.

[0170] In the first position, it is then possible to irradiate the sample 400 using a fine ion beam source 5 and simultaneously protect the electron detector 10 from the ion radiation 500. In particular, negatively charged ions can damage the electron detector 10.

[0171] The method of alternating X-ray microscopy and ablation of the sample is particularly advantageous in X-ray microscopes which have an X-ray optic 1 according to the invention.

[0172] Additionally, the X-ray optics 1 can be displaced along the optical axis 200 between a first state and a second state. In the first state, the distance d between the focal plane 100 and the detection aperture 10-4 is such that the protective diaphragm 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 d is so small that the protective diaphragm 4 no longer fits between the focal plane 100 and the detection aperture 10-4.

[0173] 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.

[0174] The distance d 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.

[0175] The focal plane is, in particular, a plane that can be determined solely from the X-ray optics. The focal plane can extend at a distance from the X-ray optics such that the focus of X-rays focused by the X-ray optics is encompassed by this focal plane. Furthermore, the focal plane can extend orthogonally to the optical axis of the X-ray optics. The distance can be measured, in particular, with respect to one of the optical components of the X-ray optics; for example, the distance can correspond to the distance between the X-ray lens and the OSA (Optical Sight Area).

[0176] For this reason, the distance of the focal plane, e.g., to the X-ray lens, can depend on the wavelength of the X-ray radiation used, but is always clearly and unambiguously determinable within a very limited distance range (between 3 mm and 15 mm), which does not impede the implementation of the teaching according to the invention. Reference list 1 X-ray optics 1' X-ray optics (state of the art) 2-zone plate / X-ray lens 2-1 Mid-stop 3 OSA 3-1 Aperture 10 Electron detector 10-1 detection tube 10-2 Exclusion 10-3 wall 10-4 Detection aperture 11 first shielding device 11-1 Front 11-2 wall 12 second shielding device / holding device 12-1 Front 12-2 wall 100 focal plane 101 Inspiration Room 102 Transmission space 200 optical axis 201 Excitation direction / Transmission direction 300 excitation radiation 301 Focus 302 transmitted X-rays 400 samples 401 Sample holders 500 ion radiation 1000 microscope 1001 Photon Detector / Photodiode 1002 Current sensor 1003 Electron detector 1004 X-ray detector d distance to the focal plane e - electrons FL Fluorescence V1 first volume V2 second volume

Claims

An X-ray optic (1) for focusing X-ray radiation (300) into a focal plane (100), comprising at least the following components: - a diffractive X-ray lens (2) and - a diffraction order filter aperture (3), OSA, wherein the diffractive X-ray lens (2) and the diffraction order filter aperture (3) are arranged along an optical axis (200) of the X-ray optic (1), characterized in that the X-ray optic (1) has a holding device (12) extending along the optical axis (200) and a first shielding device (11) extending along the optical axis (200), wherein the holding device (12) is connected to the diffractive X-ray lens (2), wherein the first shielding device (11) is designed as a first shielding device (11) enclosing the optical axis (200), and is connected to the diffraction order filter aperture (3) and delimits a first volume (V1) with it.in which both the holding device (12) and the diffractive X-ray lens (2) are fully shielded, so that electrons (e-) generated by X-ray radiation (300) in the first volume (V1) are shielded by the first shielding device (11). The X-ray optics according to claim 1, characterized in that the holding device (12) is designed as a second shielding device (12) enclosing the optical axis (200), which encloses a second volume (V2) along the optical axis (200) with the diffractive X-ray lens (2), which lies in the first volume (V1), so that electrons generated by X-ray radiation (300) in the second volume (V2) are shielded by the second shielding device (12). The X-ray optics according to claim 2, characterized in that the first shielding device (11) at least partially comprises the second shielding device (12), such that the first volume (V1) is at least partially limited on an inner side of the first volume (V1) by the second shielding device. The X-ray optics (1) according to one of the preceding claims, characterized in that the first shielding device (11) is electrically conductive at least in one region, wherein the first shielding device (11) is configured in this region to be placed at a positive or a negative electrical potential relative to a ground potential, so that electrons (e-) are attracted or repelled by the first shielding device (11) and / or wherein the holding device (12) is electrically conductive at least in one region, wherein the holding device (12) is configured to be placed at a positive or a negative electrical potential relative to a ground potential, so that electrons are attracted or repelled by the holding device (12). The X-ray optics (1) according to one of the preceding claims, characterized in that the diffraction order filter aperture (3) comprises a solid X-ray window that covers an aperture (3-1) of the diffraction order filter aperture (3), wherein the X-ray window is configured to shield electrons so that they do not propagate through the X-ray window. The X-ray optics (1) according to one of the preceding claims, characterized in that the X-ray optics (1) comprises an electron detector (10), wherein the electron detector (10) is arranged on the same side with respect to the focal plane (100) as the diffraction order filter aperture (3) and the diffractive X-ray lens (2). The X-ray optics (1) according to claim 6, characterized in that the X-ray 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). An X-ray microscope comprising an X-ray optic (1) according to one of the preceding claims. The X-ray microscope according to claim 8 is characterized in that the X-ray microscope has an ion fine beam source (5) which is configured to remove a sample (400) to be examined layer by layer by means of ion irradiation. The X-ray microscope according to one of claims 8 or 9 as well as claim 7, characterized in that the X-ray optics (1) is displaceable along the optical axis (200) between a first state and a second state, wherein in the first state a distance (d) between the focal plane (100) and the detection aperture (10-4) is such that the protective diaphragm (4) can be displaced between the focal plane (100) and the detection aperture (10-4) into the first position, and in the second state is arranged so close to the focal plane (100) that the protective diaphragm (4) no longer fits between the focal plane (100) and the detection aperture (10-4).

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