Anamorphic imaging at high-NA EUV: mask error factor and interaction between demagnification and lithographic metrics

This paper presents some of the main imaging properties introduced with the design of a possible new EUV High-NA (NA > 0.5) exposure system with anamorphic projection lens, a concept not new in optics but applied for the first time in semiconductor lithography. The system is projected to use a demagnification of 4 in the X-direction and of 8 in the Y-direction. We show that a new definition of the Mask Error Factor needs to be used in order to describe correctly the property introduced by the anamorphic optics. Moreover, for both 1-Dimensional (1D) and 2-Dimensional (2D) features the reticle writing error in the low demagnification direction X is more critical than the error in high demagnification direction Y. The effects of the change in demagnification on imaging are described on an elementary case, and are ultimately linked to the basic physical phenomenon of diffraction.