Exploring high-NA EUV mask specification for logic metal

We explore high Numerical Aperture (NA) Extreme Ultraviolet (EUV) mask specification for logic metal layer targeting A7 node. A requirement of minimum Critical Dimension (CD) of absorber on mask is investigated by Source Mask Optimization (SMO) and wafer printing simulation for pitch 20nm logic metal pattern in a horizontal direction. The Sub-Resolution Assist Feature (SRAF) horizontal absorber line width needs to be less than 4nm (1X) to avoid being printed on wafer. A minimum absorber line end tip-to-tip is also explored as a key metrics of high NA single patterning limit in Bright-Field (BF) mask with a benefit of low-n attenuated phase-shift mask.