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EP-4118673-B1 - CERTAIN IMPROVEMENTS OF MULTI-BEAM GENERATING AND MULTI-BEAM DEFLECTING UNITS

EP4118673B1EP 4118673 B1EP4118673 B1EP 4118673B1EP-4118673-B1

Inventors

  • SAROV, YANKO
  • BIHR, ULRICH
  • FRITZ, HANS
  • ZEIDLER, DIRK
  • Kurij, Georg
  • LENKE, RALF
  • MAJOR, András, G.
  • RIEDESEL, CHRISTOF

Dates

Publication Date
20260506
Application Date
20210309

Claims (20)

  1. A multi-beam raster unit (71), such as a multi-aperture unit or a multi-beam deflector or multi-beam stigmator, configured for forming, during use, a plurality of electrostatic elements for influencing a plurality of transmitting beamlets (77) of charged particles, comprising - a first multi-aperture plate (73.1) having an inner zone forming a membrane (123) with first thickness L1 with a plurality of first apertures (85.1), a beam entrance side (74) and a beam exit side (107), - the membrane (123) of the first multi-aperture plate (73.1) comprising at least a first segment (101.1) on the beam entrance side, having a first segment thickness L1.1 where the plurality of first apertures are cylindrical apertures having a first diameter D1 at the beam entrance side (74), and a second segment (101.2) on the beam exit side where the plurality of first apertures have a second diameter D2 at the beam exit side (107), - a second multi-aperture plate (73.2) having an inner zone forming a membrane (123) with a plurality of second apertures (85.2), and a beam entrance side (173), with the plurality of second apertures (85.2) having a third diameter D3 at the beam entrance side, - a gap of a thickness L2 between the membranes (123) of the first (73.1) and second (73.2) multi-aperture plate, - at least a first electrode (108, 114) configured in proximity of at least a first aperture (85.1) of the first multi-aperture plate (73.1) at the beam exit side (107) of the first multi-aperture plate (73.1), and - at least a plurality of second electrodes (79) configured in proximity to the plurality of second apertures (85.2) of the second multi-aperture plate (73.2) at the beam entrance side (173) of the second multi-aperture plate (73.2), - wherein the second diameter D2 is larger than the first diameter D1, characterized in that - the second diameter D2 is in a range between second thickness L2 and two times the second thickness L2, thus L2 < D2 < 2*L2, - the first segment thickness L1.1 is smaller than 10µm, in particular smaller than 5µm, and - the first electrode (108, 114) and each of the plurality of second electrodes (79) are configured for forming during use the electrostatic elements for influencing a plurality of transmitting beamlets (77) of charged particles passing through the pluralities of first and second apertures.
  2. A multi-beam raster unit (71) according claim 1, wherein an inner sidewall surface of at least one aperture (85.1) of the plurality of apertures in the second segments (101.2) has a surface shape sloping away from the direction of the transmitting beamlet (77) of charged particles.
  3. A multi-beam raster unit (71) according claim 2, wherein the surface shape is a curved surface shape in direction of the transmitting beamlets (77) of charged particles.
  4. A multi-beam raster unit (71) according to any one of the preceding claims, wherein an inner sidewall surface of at least one aperture (85.1) of the plurality of apertures (85.1) in the second segment (101.2) has a surface shape such that the diameter of an aperture opening continuously increases with increasing z-coordinate, wherein the z-coordinate is defined by the direction of the transmitting beamlets (77) of charged particles during use of the multi-beam raster unit (71).
  5. A multi-beam raster unit (71) according claim 3 or 4, wherein the surface shape in direction of the transmitting beamlets (77) of charged particles is of spherical shape formed by isotropic etching.
  6. A multi-beam raster unit (71) according any of the preceding claims, further comprising etch stop rings (109) at the apertures (85.1) of the beam exit side (107) of the first multi-aperture plate (73.1) or at the beam entrance side (173) of the second multi-aperture plate (73.2).
  7. A multi-beam raster unit (71) according any of the preceding claims, wherein in direction of the plurality of transmitting beamlets (77) of charged particles, the first multi-aperture plate (73.1) is arranged in the beam-path upstream of the second multi-aperture plate (73.2).
  8. A multi-beam raster unit (71) according any of the preceding claims, wherein in direction of the plurality of transmitting beamlets (77) of charged particles, at least a third multi-aperture plate (73.3) is arranged in the beam-path downstream of the first (73.1) and the second (73.2) multi-aperture plate.
  9. A multi-beam raster unit (71) according any of the preceding claims, wherein the second diameter D2 is in a range between first segment thickness L1.1 and four times the first segment thickness L1.1, thus L1.1 ≤ D2 ≤ 4* L1.1, in particular L1.1 ≤ D2 ≤ 3* L1.1 or L1.1 ≤ D2 ≤ 2* L1.1.
  10. A multi-beam raster unit (71) according any of the preceding claims, wherein the third diameter D3 is larger than the first diameter D1.
  11. A multi-beam raster unit (71) according any of the preceding claims, wherein the third diameter D3 is in a range between the first diameter D1 and the second diameter D2.
  12. A multi-beam raster unit (71) according to any one of the preceding claims, wherein the first multi-aperture plate (73.1) comprises an absorbing layer (99) on the beam entrance side (74), wherein during use the absorbing layer (99) is connected to ground level.
  13. A multi-beam raster unit (71) according to any one of the preceding claims, wherein the first multi-aperture plate (73.1) comprises a conductive layer (108) on the beam exit side (107), the conductive layer (108) forming the first electrodes.
  14. A multi-beam raster unit (71) according to any one of the preceding claims, wherein the beam exit side (107) of the first multi-aperture plate (73.1) comprises ring-shaped conductive layers or electrodes (114) around or in proximity to the apertures of diameter D2, which during use are connected to a constant voltage potential, the ring-shaped conductive layers or electrodes (114) forming the first electrodes.
  15. A multibeam raster unit (71) according to any one of the preceding claims, wherein the beam exit side (107) of the first multi-aperture plate (73.1) does not comprise a shielding electrode.
  16. A multibeam raster unit (71) according to any one of the preceding claims, wherein the second multi-aperture plate (73.2) comprises ring-shaped electrodes (79) arranged around the second apertures (85.2), wherein during use a drive voltage is applied to the ring-shaped electrodes (79), the ring-shaped electrodes (79) forming the second electrodes.
  17. A multibeam raster unit (71) according to the preceding claim, wherein the ring-shaped electrodes (79) basically extend through the second multi-aperture plate (73.2).
  18. A multi-beam raster unit (71) according any of the preceding claims, wherein the beam entrance side (173) of the second multi-aperture plate (73.2) is covered by a shielding layer (177) with at least one plunging extension (189) into at least one of the apertures (85.21) of the second multi-aperture plate (73.2).
  19. A multi-beam raster unit (71) according any of the preceding claims, wherein the first (101.1) and the second segment (101.2) are separate segments attached to each other.
  20. A multi-beam charged particle microscope comprising a multi-beam raster unit (71) according to any one of the preceding claims.

Description

Field of the invention The disclosure relates to multi-beam raster units such as multi-beam generating units and multi-beam deflector units of a multi-beam charged particle microscopes. Background of the invention WO 2005/024881 A2 discloses an electron microscope system which operates with a multiplicity of electron beamlets for the parallel scanning of an object to be inspected with a bundle of electron beamlets. The bundle of electron beamlets is generated by directing a primary electron beam onto a first multi-aperture plate, which has a multiplicity of openings. One portion of the electrons of the electron beam is incident onto the multi-aperture plate and is absorbed there, and another portion of the beam transmits the openings of the multi-aperture plate and thereby in the beam path downstream of each opening an electron beamlet is formed whose cross section is defined by the cross section of the opening. Furthermore, suitably selected electric fields which are provided in the beam path upstream and/or downstream of the multi-aperture plate cause each opening in the multi-aperture plate to act as a lens on the electron beamlets passing the opening so that said each electron beamlet is focused in a surface which lies at a distance from the multi-aperture plate. The surface in which the foci of the electron beamlets are formed is imaged by downstream optics onto the surface of the object or sample to be inspected. The primary electron beamlets trigger secondary electrons or backscattered electrons to emanate as secondary electron beamlets from the object, which are collected and imaged onto a detector. Each of the secondary beamlets is incident onto a separate detector element so that the secondary electron intensities detected therewith provide information relating to the sample at the location where the corresponding primary beamlet is incident onto the sample. The bundle of primary beamlets is scanned systematically over the surface of the sample and an electron microscopic image of the sample is generated in the usual way for scanning electron microscopes. The resolution of a scanning electron microscope is limited by the focus diameter of the primary beamlets incident onto the object. Consequently, in multi-beam electron microscopy all the beamlets should form the same small focus on the object. It is understood that the system and method illustrated in WO 2005/024881 in great detail at the example of electrons is very well applicable in general to charged particles. The present invention correspondingly has an object of proposing a charged particle beam system which operates with a multiplicity of charged particle beams and can be used to achieve a higher imaging performance, such as a better resolution and narrower range of resolution for each beamlet of the plurality of beamlets. Multiple beamlets for a multi-beam, charged particle microscope (MCPM) are generated in a multi-beam generating unit. Multi-beam charged particle microscopes (MCPM) commonly use both micro-optical (MO) elements and macroscopic elements in a charged particle projection system. Multi-beam generating units comprise elements for splitting, partially absorbing, and influencing a beam of charged particles. As a result, a set of beamlets of charged particles in a predefined raster configuration is generated. Multi-beam generating units comprise micro-optical elements, such as the first multi-aperture plate, further multi-aperture plates and micro-optical deflection elements, and macroscopic elements, such as lenses, in a special element design and special arrangement. A multi-beam generating unit can be formed in an assembly of two or more parallel planar substrates or wafers, for example created by silicon micro structuring. During use, a plurality of electrostatic optical elements is formed by aligned apertures in at least two of such planar substrates or wafers. Some of the apertures may be equipped with one or more vertical electrodes, arranged with axial symmetry around the apertures, creating for example electrostatic lens arrays. The optical aberrations of such electrostatic lens arrays are known to be highly sensitive to the manufacturing inaccuracies of the plurality of apertures. The roughness of each aperture contour or edge cause astigmatism and higher order aberrations. The inner surface of the electrostatic lens is usually formed in Silicon by vertical anisotropic etching with an inner surface having a roughness of typically between 100nm and 500nm. For generation of predefined electrostatic optical elements, it is important to precisely control the plurality of electrodes, for example the geometry of the electrodes and the lateral alignment with respect to each beamlet of a plurality of charged particle beamlets, as well the distances between the electrodes in direction of a transmitting plurality of charged particle beamlets. Deviations in the fabrication processes of planar substrates, the electrodes and the