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

Abstract

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 doublelayered 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.

Super-resolution near-field lithography using planar silver lenses: A review of recent developments

“…We have explored the imaging properties of both singlelayer [1,4,5] and double-layer silver planar lenses [6]; it has been predicted that for a given mask-resist separation the resolution can be improved by using a multilayer silver lens instead of a single layer [7], but our initial studies are inconclusive in this matter. In addition, we have compared broadband and narrowband exposures through singlelayer silver lenses [8]; broadband exposures offer the advantage of shorter exposure times (and therefore higher throughput for photolithography), however the resolution is compromised due to the dispersive nature of the planar lensing phenomenon.…”

Analysis and comparison of simulation techniques for silver superlenses

“…Previous analysis [13] performed using the T-matrix technique showed that multi-layer superlenses [4] had better transmission at higher wave numbers (k x / 2S) than equivalent single-layer superlenses (Fig. 1).…”

“…These remarkable achievements resulted in further research on possible superlens designs and geometries, with papers published that detailed multi-layer [4], patterned [5] and perforated [6] multipole programming [8] and finite element modelling (FEM) [9,10,11] were used successfully in the past; however, they were all relatively computationally intense and could be slow to produce solutions. Hence, a computationally efficient transfer matrix (T-matrix) method was developed [12] to give an estimate of lens performance using only a few, relatively simple calculations.…”

Subwavelength imaging with composite metamaterials

“…The epsilon negative lenses are thin because the surface plasmon modes on the rear surface of the lens can only be excited by an input wave if the front and rear surfaces are strongly coupled [9]. However, it was found experimentally that for thin metallic films the surface roughness increases, which causes the reduction of the image quality and may lead to hotspots in the image plane [21]. The hotspots are caused by the surface roughness of the outermost metallic layer, which builds the lens.…”