Optical constants for EUV scatterometry

Development of efficient absorber masks and highly reflective mirrors in the EUV spectral range is a key challenge for upcoming lithography techniques in semiconductor technology. There is an improved need to precisely know the optical constants of the materials at hand for specialized applications such as phase shifting absorber masks. A further field of application is the interpretation and accompanied modeling of scattering data of complex nanostructures. At PTB, we measured the spectral reflectance of thin film samples in the angular range from normal incidence to grazing incidence in the range of 10nm to 20nm using PTB’s lubrication-free Ellipso-Scatterometer at the soft x-ray beamline at the electron storage ring BESSY II. This allowed us to determine the optical constants of a variety of metals, semimetals and their alloys from model fits based on Fresnel’s equations for layered material stacks.