Actinic EUV Scatterometry for Parametric Mask Quantification

摘要

There are many applications where fast, accurate light scattering from EUV photomasks must be computed, including inverse mask design, actinic die-to-database inspection, and actinic scatterometry. However, so-called mask 3D effects make this calculation much more challenging than traditional optical lithography. These 3D effects arise from the optically thicker absorber, the lack of illumination symmetry about normal incidence, the multilayer mirror reflection function, and multiple scattering off the absorber. In this paper, we explore using actinic scatterometry at the CXRO EUV reflectometer to characterize both the multilayer and absorber of an EUV photomask: we then introduce the Multilayer Multiple Scattering (MLMS) mathematical model that conveniently separates the effects of the multilayer and the absorber and explore the implications of this model on the origins of mask 3D effects.