Enhanced Super-resolution Imaging by Bilayer Aluminum Superlens in DUV Photolithography

A photolithographic system with bilayer metal planar superlens was investigated to improve super-resolution imaging. The optical transfer function could have up to 4 amplification peaks among spatial frequency range of evanescent waves, and each amplification peak was associated with a corresponding surface plasmon polariton (SPP) mode of five-layer insulator-metal-insulator-metal-insulator (IMIMI) waveguide. Since the strong amplification at low spatial frequency of evanescent waves would deteriorate super-resolution imaging, optical transfer function of 193 nm photolithographic system with bilayer Aluminum (A1) superlens was flattened by trimming off the highest amplification peak of evanescent waves, which was achieved via cutting off associated symmetrically-coupled long range SPP (s-LRSPP) mode. Improved super-resolution imaging for a tungsten (W) mask with two slits of a 15 nm slit width and a 15 nm spacer was verified by full-vector Finite-Difference Time-Domain (FDTD) simulations.