Actinic inspection of EUVL mask blank defects by photoemission electron microscopy: Effect of inspection wavelength variation

Extreme ultraviolet (EUV) photoemission electron microscopy (PEEM), which employs standing wave field illumination of a sample, is a potential tool for at-wavelength inspection of phase defects on extreme ultraviolet lithography (EUVL) mask blank. In this paper, we will demonstrate that the contrast of an underneath multilayer programmed defect in EUV-PEEM image is strongly dependent on the inspection wavelength. The observed contrast variation at different inspection wavelengths is in good agreement with the simulation result of a standing wave field on surface of multilayer stack in the mask blank sample. We also observed some native defects on the programmed defect sample, and found that some of them reverse their contrast with varying inspection wavelengths while others do not.