In this paper we extend our work into the impact of Mask Topography induced effects in current state of the art lithography by looking at the phase in the diffracted orders. By analyzing and describing the phase in a similar and systematic way as done for projection lenses, we could identify already known effects as best focus differences and pattern asymmetry, but also a new significant effect was found: contrast loss. We used the phase range in the diffracted orders as a metric to be used during lithography set-up. We were able to link the performance of different mask absorber types and parameters with the phase range in the diffracted orders.
"Mask 3D induced phase and the mitigation by absorber optimization", Proc. SPIE 9426, Optical Microlithography XXVIII, 942605 (18 March 2015); doi: 10.1117/12.2178288; https://doi.org/10.1117/12.2178288