2D inner assist features for 0.55NA: mask and wafer data characterization

As EUV lithography moves to 0.55NA, reduced depth of focus and reduced pitch/CD requires new optical proximity correction (OPC) strategies. This work explored segmented inner 2D assist features (AFs) as a complementary approach to sub-resolution gratings (SRGs). Simulations indicated potential benefits in NILS and controlled best focus shifts; motivating experimental validation on an anamorphic high-NA mask. Mask characterization confirms that these segmented inner assist features (SRIFs) can be made with reasonable fidelity and variability across segmentation configurations. There is no impact of the SRIFs on main feature manufacturability on the mask. Wafer level characterization showed that MCD on wafer remains stable in the presence of AFs, and minor shifts in CD can be corrected through OPC in future designs. These first ever SRIFs results from a 0.55NA mask confirm their potential as an OPC knob. Future work will