Experimental comparison of resolution and pattern fidelity in single- and double-layer planar lens lithography

An experimental comparison of the performance of single- and double-layer planar lens lithography has been carried out. A direct comparison is made with a single 50 nm silver lens and a double silver lens with two 30 nm layers. Sub-diffraction-limited features have been imaged in both cases, with dense grating periods down to 145 and 170 nm for the single- and double-layered stacks, respectively. For the same total thickness of silver, the resolution limit is qualitatively better for a double-layer stack. However, pattern fidelity is reduced in the double-layer experiments, owing to increased surface roughness. Finite-difference time-domain simulations are also presented to back up the experimental results.