Implications of image plane line-edge roughness requirements on extreme ultraviolet mask specifications

Abstract

Achieving line-edge/width roughness (LER/LWR) specifications remains as one of the most significant challenges facing the commercialization of extreme ultraviolet (EUV) lithography. LER is typically viewed as a resist problem; however, recent simulation results have shown that the mask can also be a significant contributor. Problems arise from both mask absorber LER as well as mask multilayer roughness leading to random phase variations in the reflected beam and consequently speckle. Here we describe these effects in detail and explore how they will impact EUV mask requirements for the 22-nm half-pitch node and beyond. Process window analysis yields mask multilayer roughness specifications on the order of 50 pm.