EUV Schwarzschild objective

Front side of Schwarzschild objective.
© Fraunhofer IOF
EUV-Schwarzschild-Objektiv für Anwendungen in der EUV-Lithographie.
Back side of Schwarzschild objective.
© Fraunhofer IOF
Schwarzschild objectives for applications in the EUV spectral range consists of a convex and a concave Mo/Si multilayer mirror. Depending on the optical path applications in microscopy or lithography can be realized. The integration of a laser plasma source allowed for the direct structuring of selected materials.

Motivation

Schwarzschild objectives are increasingly used in the EUV spectral region as imaging optics because of their large aperture, high mechanical stability, and freedom from chromatic aberrations. An EUV Schwarzschild objective is made of a primary and a secondary Mo/Si coated multilayer mirror, on which both spheres and aspheres can be used. The optical elements are stress-free and were mounted mechanically stable using solid state hinges. It is possible to correct the mirror adjustment during operation.

 

Competencies

  • Realization of diffraction-limited optical assembly for 13.5 nm wavelength with a resolution of < 20 nm
  • EUV optics design according to customized requirements
  • Fabrication of coated optics components for 13.5 nm
  • Mechanics design and construction of optical assembly
  • Low-stress mounting of optical components, ensuring minimum deformation of optical surfaces
  • Positioning accuracy of optical surfaces: < 1.5 µm lateral misalignment, < 10 µm axial offset
  • Hydrocarbon-free mounting design

 

Our work

  • Design and fabrication of Schwarzschild objectives for the EUV spectral region according to customized requirements
  • Coating of Schwarzschild objectives with laterally graded Mo/Si multilayers, Transmission: T > 45 % @ 13,5 nm
  • Dimensioning, calculation and realization of the mirror mounting system