Angle-resolved scattering and reflectance of extreme-ultraviolet multilayer coatings: Measurement and analysis

Roughness-induced light scattering critically affects the performance of optical components, in particular at short wavelengths.We present a stand-alone instrument for angle-resolved scattering and reflectance measurements at 13:5nm in the extreme-ultraviolet (EUV) spectral range. The achieved dynamic range allows even the scattering of high-quality EUV mirrors on extremely smooth substrates to be investigated. For Mo/Si multilayers, total scatter losses of several percent have been observed, depending on the substrate qualities as well as on roughening and smoothing effects during coating. Different approximate models for estimating the impact of roughness on scatter losses are discussed and compared with experimental results.