Comparison between e-beam direct write and immersion lithography for 20-nm node

E-beam direct write (EBDW) process window (PW) simulations were performed on critical layers in Altera designs of the 20-nm node (minimum metal half-pitch 32 nm). For selected layout clips, a direct comparison is made with 193i simulation results. Local interconnect and Via0 (single patterning) and Metal1 (litho-etch-litho-etch double patterning) layers are considered. The EBDW dose latitude was found to exceed that of the 193i process by a factor of 4. As the electron beam total spot size is of the order of the critical dimension for the considered node, interplay between neighboring features is low. This results in straightforward data preparation with typically two kernels and “clean” PWs. The latter are mainly limited by edge placement errors of line ends. The curves for the various simulation sites roughly overlap, as opposed to the 193i case in which they significantly differ. In EBDW, the performance of square vias equals that of rectangular vias, enabling a denser via packing.