Ion-enhanced growth in planar and structured Mo/Si multilayers

Nanoscale molybdenum/silicon (Mo/Si) multilayer structures are employed as reflective optical elements for wavelengths in the extreme ultraviolet (EUV, =13.5 nm). When using appropriate ion-beam parameters, Kr+ bombardment and sputtering of a-Si layers is known to suppress layer growth intrinsic roughness in Mo/Si multilayers. In chapter 2 the scalability of the smoothing process is investigated, aiming for optimization suppression of substrate roughness. In chapter 3 is reported on modifications of the in-layer structure of a-Si layers by implantation of H+ ions. The resulting increased layer porosity is found to enhance Kr+-induced smoothing, towards ultrasmooth surfaces. In chapter 4 the interface roughness in Mo/Si multilayers as a function of the noble gas ion polishing species (Ne, Ar, Kr, and Xe) is investigated by grazing incidence small angle x-ray scattering (GISAXS). Optimal interface smoothness is obtained by Xe+ polishing, however, Kr+ polishing yields highest EUV reflectance. This is clarified by the residual amounts of polishing gas in the Si layers, affecting the optical constants. Chapter 5 discusses the application of an EUV reflective multilayer on a non-flat, grating substrate, which is appealing as a high EUV throughput optical filtering device. The deposition of multilayers onto non-flat substrate topographies as a model system for real gratings, is described in chapter 6. With these findings, multilayer deposition on a grating is shown feasible. However, the tolerances on grating roughness and flatness of the facets are extremely tight. In chapter 7 a deposition scheme of a class of rectangular grating phaseshift reflectors on flat substrates is reported.