Highly reflective Molybdenum/Silicon multilayer mirrors for 13.5 nm are characterized at-wavelength using a new laboratory size measurement system for EUV reflectance and scattering. Roughness analysis before and after coating by Atomic Force Microscopy indicates roughness enhancement as well as smoothing effects during thin film growth. The impact of the substrate finish and the deposition process onto the scattering distribution and scatter losses with regard to the specular reflectance is analyzed.