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Title: Reverse-absorbance-modulation-optical lithography for optical nanopatterning at low light levels

Abstract

Absorbance-Modulation-Optical Lithography (AMOL) has been previously demonstrated to be able to confine light to deep sub-wavelength dimensions and thereby, enable patterning of features beyond the diffraction limit. In AMOL, a thin photochromic layer that converts between two states via light exposure is placed on top of the photoresist layer. The long wavelength photons render the photochromic layer opaque, while the short-wavelength photons render it transparent. By simultaneously illuminating a ring-shaped spot at the long wavelength and a round spot at the short wavelength, the photochromic layer transmits only a highly confined beam at the short wavelength, which then exposes the underlying photoresist. Many photochromic molecules suffer from a giant mismatch in quantum yields for the opposing reactions such that the reaction initiated by the absorption of the short-wavelength photon is orders of magnitude more efficient than that initiated by the absorption of the long-wavelength photon. As a result, large intensities in the ring-shaped spot are required for deep sub-wavelength nanopatterning. In this article, we overcome this problem by using the long-wavelength photons to expose the photoresist, and the short-wavelength photons to confine the “exposing” beam. Thereby, we demonstrate the patterning of features as thin as λ/4.7 (137 nm for λmore » = 647 nm) using extremely low intensities (4-30 W/m{sup 2}, which is 34 times lower than that required in conventional AMOL). We further apply a rigorous model to explain our experiments and discuss the scope of the reverse-AMOL process.« less

Authors:
; ; ;  [1]; ;  [2];  [3]
  1. Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States)
  2. Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
  3. Mulhouse Institute for Material Sciences, CNRS LRC 7228, BP2488, Mulhouse 68200 (France)
Publication Date:
OSTI Identifier:
22611568
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 6; Journal Issue: 6; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION; BEAMS; DIFFRACTION; LAYERS; MODULATION; MOLECULES; PHOTONS; VISIBLE RADIATION; WAVELENGTHS

Citation Formats

Majumder, Apratim, E-mail: apratim.majumder@utah.edu, Wan, Xiaowen, Masid, Farhana, Menon, Rajesh, Pollock, Benjamin J., Andrew, Trisha L., and Soppera, Olivier. Reverse-absorbance-modulation-optical lithography for optical nanopatterning at low light levels. United States: N. p., 2016. Web. doi:10.1063/1.4954178.
Majumder, Apratim, E-mail: apratim.majumder@utah.edu, Wan, Xiaowen, Masid, Farhana, Menon, Rajesh, Pollock, Benjamin J., Andrew, Trisha L., & Soppera, Olivier. Reverse-absorbance-modulation-optical lithography for optical nanopatterning at low light levels. United States. doi:10.1063/1.4954178.
Majumder, Apratim, E-mail: apratim.majumder@utah.edu, Wan, Xiaowen, Masid, Farhana, Menon, Rajesh, Pollock, Benjamin J., Andrew, Trisha L., and Soppera, Olivier. 2016. "Reverse-absorbance-modulation-optical lithography for optical nanopatterning at low light levels". United States. doi:10.1063/1.4954178.
@article{osti_22611568,
title = {Reverse-absorbance-modulation-optical lithography for optical nanopatterning at low light levels},
author = {Majumder, Apratim, E-mail: apratim.majumder@utah.edu and Wan, Xiaowen and Masid, Farhana and Menon, Rajesh and Pollock, Benjamin J. and Andrew, Trisha L. and Soppera, Olivier},
abstractNote = {Absorbance-Modulation-Optical Lithography (AMOL) has been previously demonstrated to be able to confine light to deep sub-wavelength dimensions and thereby, enable patterning of features beyond the diffraction limit. In AMOL, a thin photochromic layer that converts between two states via light exposure is placed on top of the photoresist layer. The long wavelength photons render the photochromic layer opaque, while the short-wavelength photons render it transparent. By simultaneously illuminating a ring-shaped spot at the long wavelength and a round spot at the short wavelength, the photochromic layer transmits only a highly confined beam at the short wavelength, which then exposes the underlying photoresist. Many photochromic molecules suffer from a giant mismatch in quantum yields for the opposing reactions such that the reaction initiated by the absorption of the short-wavelength photon is orders of magnitude more efficient than that initiated by the absorption of the long-wavelength photon. As a result, large intensities in the ring-shaped spot are required for deep sub-wavelength nanopatterning. In this article, we overcome this problem by using the long-wavelength photons to expose the photoresist, and the short-wavelength photons to confine the “exposing” beam. Thereby, we demonstrate the patterning of features as thin as λ/4.7 (137 nm for λ = 647 nm) using extremely low intensities (4-30 W/m{sup 2}, which is 34 times lower than that required in conventional AMOL). We further apply a rigorous model to explain our experiments and discuss the scope of the reverse-AMOL process.},
doi = {10.1063/1.4954178},
journal = {AIP Advances},
number = 6,
volume = 6,
place = {United States},
year = 2016,
month = 6
}
  • Optical lithography is the most prevalent method of fabricating micro-and nano-scale structures in the semiconductor industry due to the fact that patterning using photons is fast, accurate and provides high throughput. However, the resolution of this technique is inherently limited by the physical phenomenon of diffraction. Absorbance-Modulation-Optical Lithography (AMOL), a recently developed technique has been successfully demonstrated to be able to circumvent this diffraction limit. AMOL employs a dual-wavelength exposure system in conjunction with spectrally selective reversible photo-transitions in thin films of photochromic molecules to achieve patterning of features with sizes beyond the far-field diffraction limit. We have developed amore » finite-element-method based full-electromagnetic-wave solution model that simulates the photo-chemical processes that occur within the thin film of the photochromic molecules under illumination by the exposure and confining wavelengths in AMOL. This model allows us to understand how the material characteristics influence the confinement to sub-diffraction dimensions, of the transmitted point spread function (PSF) of the exposure wavelength inside the recording medium. The model reported here provides the most comprehensive analysis of the AMOL process to-date, and the results show that the most important factors that govern the process, are the polarization of the two beams, the ratio of the intensities of the two wavelengths, the relative absorption coefficients and the concentration of the photochromic species, the thickness of the photochromic layer and the quantum yields of the photoreactions at the two wavelengths. The aim of this work is to elucidate the requirements of AMOL in successfully circumventing the far-field diffraction limit.« less
  • In this study, the multiple-exposure nanosphere-lens lithography method utilizing the polystyrene nanospheres with focusing behavior is investigated and introduced to fabricate diverse photonic crystals (PCs) on indium tin oxide to enhance the optical output power of GaN-based light-emitting diode (LED). Simulated results indicate that the focused light intensity decreases with increasing tilted angle due to the shadow effect introduced by adjacent nanospheres. The fill factor of nanopattern is tunable by controlling tilted angles and exposure times. To attain quadruple PC without overlapping patterns, mathematical calculation model is used to define the optimum range of tilted angles. Angular emission patterns andmore » three-dimensional finite-difference time domain simulated results indicate that the enhanced light extraction of PC LEDs results mainly from diffused scattering effects, and the diffraction effects of PC on light extracted efficiency increase with the increase of fill factor. Furthermore, it is confirmed that the multiple PC can extract more light from GaN into air than common PC with same period and fill factor.« less
  • Recently, many methods based on amplitude or phase modulation to reduce the focal spot and enhance the longitudinal field component of a tight-focused radially polarized light beam have been suggested. But they all suffer from spot size limit 0.36λ/NA and large side lobes strength in longitudinal component. Here, we report a method of generating a tighter focused spot by focusing radially polarized and azimuthally polarized beams of different wavelengths on a thin photochromic film through a high-numerical-aperture lens simultaneously. In this method, by suppressing the radial component and compressing the longitudinal component of radially polarized beam, absorbance modulation makes themore » ultimate spot size break the size limit of 0.36λ/NA with side-lobe intensity of longitudinal component below 1% of central-peak intensity. The theoretical analysis and simulation demonstrate that the focal spot size could be smaller than 0.1λ with nearly all radial component blocked at high intensity ratio of the two illuminating beams.« less
  • The light-emitting diodes (LEDs) with single, twin, triple, and quadruple photonic crystals (PCs) on p-GaN are fabricated by multiple-exposure nanosphere-lens lithography (MENLL) process utilizing the focusing behavior of polystyrene spheres. Such a technique is easy and economical for use in fabricating compound nano-patterns. The optimized tilted angle is decided to be 26.6° through mathematic calculation to try to avoid the overlay of patterns. The results of scanning electron microscopy and simulations reveal that the pattern produced by MENLL is a combination of multiple ovals. Compared to planar-LED, the light output power of LEDs with single, twin, triple, and quadruple PCsmore » is increased by 14.78%, 36.03%, 53.68%, and 44.85% under a drive current 350 mA, respectively. Furthermore, all PC-structures result in no degradation of the electrical properties. The stimulated results indicate that the highest light extraction efficiency of LED with the clover-shape triple PC is due to the largest scattering effect on propagation of light from GaN into air.« less
  • The absorbance of a thin film of photochromic material can be reversibly modified by exposure to two different wavelengths, {lambda}{sub 1} and {lambda}{sub 2}. When such a film is illuminated by both wavelengths simultaneously, and the longer wavelength {lambda}{sub 2} possesses a node in its intensity distribution, then the absorbance of the layer can be made high except at an arbitrarily small region near the node. By exploiting the large nonlinearity introduced by this mechanism, combined with the reversibility of the absorbance of the photochromic layer, the authors demonstrate that spatial frequencies larger than those present in incident intensity distributionsmore » may be generated. They show photoresist exposures to demonstrate this technique.« less