Optimization flow for EUV low-k1 logic with the low-n mask

The EUV low-n attenuated phase shift mask can strongly enhance contrast and reduce exposure dose. Here, we focus on the implementation of the low-n mask for advanced node metal layers, where multiple pitches need to be printed simultaneously. In contrast to the DUV situation, printing semi-isolated and isolated pitches along with the dense part of the chip is non-trivial in EUV imaging; best-focus shifts between features can arise and need to be mitigated. We study the physics of printing multiple pitches simultaneously with the low-n mask and present generic guidelines for source-mask optimization through pitch.