One of the most challenging requirements for the next generation EUV lithography is an extremely low amount of critically sized defects on mask blanks. Fast and reliable inspection of mask blanks is still a challenge. Here we present the current status of the development of our actinic Schwarzschild objective based microscope operating in dark field with EUV discharge produced plasma source. For characterization of the microscope performance, several programmed defect structures - artificial pits and bumps were created on top of multilayer mirror (ML) surfaces and investigated both with EUV microscope and atomic force microscope (AFM). Defect size sensitivity of actinic inspection in dark field mode without resolving the defects is under study. The dependency between defect shape, size and position in relation to the ML surface and its scattering signal will be discussed. Furthermore, first results of a defect mapping algorithm are presented.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.