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 (PLL) has been carried out. A direct comparison is made with a single 50nm silver lens and a double silver lens with two 30nm layers. Sub-diffraction-limited features have been imaged in both cases, with dense grating periods down to 145nm and 170nm 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 due to increased surface roughness. Finite-difference time-domain simulations are also presented to back up the experimental results.