High-Precision Multilayer Coatings and Reflectometry for EUV Lithography Optics

The topic of this paper is the fabrication and characterization of EUV reflective coatings based on molybdenum/silicon (Mo/Si) multilayers. For the fabrication of such nanometer structures, the technologies of magnetron sputter deposition (MSD) and ion beam sputter deposition (IBSD) are used in IWS Dresden. The main challenges for extreme ultraviolet (EUV) optics are high reflectance, precise thickness profiles, low internal stress and long‐term stability. Reflectances > 70 %, uniformities > 99.9 % and overall internal stresses < 20 MPa have been reached. In addition to sophisticated deposition technologies, precise metrology tools are mandatory for the characterization of the coatings. Together with a number of partners, IWS Dresden has developed a stand‐alone EUV reflectometer that makes it possible to measure EUV reflectance R and peak position λ on substrates with diameters of up to 500 mm. Current improvements of the reflectometer resulted in differences compared to calibrated measurements at PTB/BES...