Mask and illumination optimization for low-k1 EUV lithography

Source-mask optimization and EUV mask structure optimization are studied to maximize DOF and NILS for honeycomb hole arrays at 0.55NA. Optimization flow on mask structure conditions for good and stable NILS performance, such as peak-NILS, NILS-DOF, and NILS-MEEF, is proposed to minimize the local CD variation as a result of EUV mask properties. Using NILS metrics, the absorber thickness and the mask CD with optimized illumination conditions are determined for the maximum performance, together with the tolerance of absorber thickness and mask CD. EUV binary absorbers using high-n/mid-k and low-n/high-k materials, and EUV PSM absorbers using low-n/low-k and highreflectance materials, are compared for 28-, 26-, and 24-nm honeycomb hole arrays.