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DE-102024002214-B4 - Reflection optics and microscope with reflection optics

DE102024002214B4DE 102024002214 B4DE102024002214 B4DE 102024002214B4DE-102024002214-B4

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 limiting a first volume (V1) radially around the optical axis (200), so that electrons ( e- ) generated by electromagnetic radiation in the first volume (V1) are 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).

Inventors

  • Gerd Schneider
  • Stefan Rehbein

Assignees

  • Helmholtz-Zentrum Berlin für Materialien und Energie Gesellschaft mit beschränkter Haftung

Dates

Publication Date
20260513
Application Date
20240625

Claims (10)

  1. A reflection optic (1) for focusing electromagnetic radiation (300) into a focal plane (100), comprising at least the following components: - a center stop (12) arranged on an optical axis (200) of the reflection optic (1), configured to prevent electromagnetic rays (300) incident into the reflection optic (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 optic (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) are shielded, - a solid window (13) which opens the first volume (V1) to the focal plane (100) is limited 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 as the focusing element (11) with respect to the focal plane (100).
  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 one of the Claims 2 until 5 , characterized in that the electron detector (10) has a detector wall (10-3) which has a detection aperture (10-4) on an end face which points in the direction of 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 one of the Claims 2 until 6 , wherein the electron detector (10) is one or more detectors selected from the group consisting of - a channeltron, - a photon energy-resolving electron detector tor, - a photon angle resolving electron detector, comprises.
  8. The reflection optics (1) according to one of the Claims 2 until 7 , characterized in 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 one of the preceding claims.
  10. The microscope after Claim 9 , characterized in 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.

Description

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. Focusing electromagnetic radiation is an essential element of microscopes that operate in the far field. 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. 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. 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. 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. 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. 1 This shows the typical setup of a scanning X-ray microscope with its 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. 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. Exposure of the sample to X-rays also induces an electrical sample current, which can be detected using a picoammeter. 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. 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. 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. 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. 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. 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. 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. 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. In the JP H08 -146 197 A A holding device for a