Optimization of thin-film design for multi-layer dielectric grating

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Optimization of thin-film design for multi-layer dielectric grating
Abstract
Thin-film design used to fabricate multi-layer dielectric (MLD) gratings should provide high transmittance during holography exposure, high
% f# ?: T% c8 y& p, {reflectance at use wavelength and sufficient manufacturing latitude of the grating design making the MLD grating achieve both high diffraction
% l, \+ y+ m$ a' Z" d4 Vefficiency and low electric field enhancement. Based on a (HLL)9H design comprising of quarter-waves of high-index material and half-waves of
low-index material, we obtain an optimum MLD coating meeting these requirements by inserting a matching layer being half a quarter-wave of
Al2O3 between the initial design and an optimized HfO2 top layer. The optimized MLD coatings exhibits a low reflectance of 0.017% under
6 Z2 j3 W$ b! Wphotoresist at the exposure angle of 17.88 for 413 nm light and a high reflectance of 99.61% under air at the use angle of 51.28 for 1053 nm light.
Numerical calculation of intensity distribution in the photoresist coated on the MLD film during exposure shows that standing-wave patterns are
( K) }# N9 s" v5 [( {greatly minimized and thus simulation profile of photoresist gratings after development demonstrates smoother shapes with lower roughness.
Furthermore, a MLD gratings with grooves etched into the top layer of this MLD coating provides a high diffraction efficiency of 99.5% and a low
7 r8 B, L2 _1 x+ Belectric field enhancement ratio of 1.53. This thin-film design shows perfect performances and can be easily fabricated by e-beam evaporation.
# x' m$ p" l5 J3 C4 T2 p4 b# 2006 Elsevier B.V. All rights reserved.
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