Interaction between aberrations and mask 3D effects for low-n and Ta-based absorbers in extreme ultraviolet lithography

Low-n masks have gained strong interest due to their potential to simultaneously improve dose and imaging contrast for dense clips. We have previously presented that for the imaging of isolated features mask bias, assist features are crucial to minimize the focus range through pitch. In this paper, we elaborate on aberration sensitivity for different mask-absorber types. We observe that even aberration sensitivities can change significantly by changing the mask-absorber type for the same use case. We show that even aberration sensitivity and best-focus shifts are coupled and that they can also be solved together by applying mask and target bias and/or assist features. Finally, we show how assist-feature position optimization can reduce the impact of odd aberrations on two-bar features.