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Title: Single pulse excimer laser nanostructuring of thin silicon films: Nanosharp cones formation and a heat transfer problem

Abstract

We present analytical and computer modeling along with an experiment on the formation of sharp conical tips on monocrystalline silicon thin films, silicon-on-insulator, subjected to irradiation by single 25 ns pulses from a KrF excimer laser focused into a spot several micrometers in diameter. These fabricated structures have heights of about 1 {mu}m and apical radii of curvature of several tens of nanometers. We offer a simplified analytical model for the formation of these structures. The computer simulation includes two-dimensional time-dependant heat transfer and phase transformations in Si films on SiO{sub 2} substrates that result from the laser irradiation (the Stefan problem). It is shown that upon irradiation and initial melting, the liquid/solid interface remains mainly parallel to the surface of the film. After the laser pulse, the molten material self-cools and resolidifies. The solid/liquid interface moves predominately laterally toward the center of the irradiated spot, forming an almost vertical front. We discuss the relation between the dynamics of the melting/freezing front movement and the displacement of material in the irradiated spot.

Authors:
; ; ; ;  [1];  [2];  [2]
  1. Department of Electrical and Computer Engineering, Wayne State University, Detroit, Michigan 48202 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20982847
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 9; Other Information: DOI: 10.1063/1.2720185; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COMPUTERIZED SIMULATION; FREEZING; HEAT TRANSFER; IRRADIATION; KRYPTON FLUORIDE LASERS; LASER MATERIALS; LASER RADIATION; MELTING; NANOSTRUCTURES; PULSES; SEMICONDUCTOR MATERIALS; SILICON; SILICON OXIDES; SUBSTRATES; THIN FILMS; TIME DEPENDENCE; TWO-DIMENSIONAL CALCULATIONS

Citation Formats

Eizenkop, Julia, Avrutsky, Ivan, Auner, Gregory, Georgiev, Daniel G., Chaudhary, Vipin, Department of Electrical Engineering and Computer Science, University of Toledo, Toledo, Ohio 43606-3390, and Department of Computer Science and Engineering, The State University of New York, Buffalo, New York 14260. Single pulse excimer laser nanostructuring of thin silicon films: Nanosharp cones formation and a heat transfer problem. United States: N. p., 2007. Web. doi:10.1063/1.2720185.
Eizenkop, Julia, Avrutsky, Ivan, Auner, Gregory, Georgiev, Daniel G., Chaudhary, Vipin, Department of Electrical Engineering and Computer Science, University of Toledo, Toledo, Ohio 43606-3390, & Department of Computer Science and Engineering, The State University of New York, Buffalo, New York 14260. Single pulse excimer laser nanostructuring of thin silicon films: Nanosharp cones formation and a heat transfer problem. United States. doi:10.1063/1.2720185.
Eizenkop, Julia, Avrutsky, Ivan, Auner, Gregory, Georgiev, Daniel G., Chaudhary, Vipin, Department of Electrical Engineering and Computer Science, University of Toledo, Toledo, Ohio 43606-3390, and Department of Computer Science and Engineering, The State University of New York, Buffalo, New York 14260. Tue . "Single pulse excimer laser nanostructuring of thin silicon films: Nanosharp cones formation and a heat transfer problem". United States. doi:10.1063/1.2720185.
@article{osti_20982847,
title = {Single pulse excimer laser nanostructuring of thin silicon films: Nanosharp cones formation and a heat transfer problem},
author = {Eizenkop, Julia and Avrutsky, Ivan and Auner, Gregory and Georgiev, Daniel G. and Chaudhary, Vipin and Department of Electrical Engineering and Computer Science, University of Toledo, Toledo, Ohio 43606-3390 and Department of Computer Science and Engineering, The State University of New York, Buffalo, New York 14260},
abstractNote = {We present analytical and computer modeling along with an experiment on the formation of sharp conical tips on monocrystalline silicon thin films, silicon-on-insulator, subjected to irradiation by single 25 ns pulses from a KrF excimer laser focused into a spot several micrometers in diameter. These fabricated structures have heights of about 1 {mu}m and apical radii of curvature of several tens of nanometers. We offer a simplified analytical model for the formation of these structures. The computer simulation includes two-dimensional time-dependant heat transfer and phase transformations in Si films on SiO{sub 2} substrates that result from the laser irradiation (the Stefan problem). It is shown that upon irradiation and initial melting, the liquid/solid interface remains mainly parallel to the surface of the film. After the laser pulse, the molten material self-cools and resolidifies. The solid/liquid interface moves predominately laterally toward the center of the irradiated spot, forming an almost vertical front. We discuss the relation between the dynamics of the melting/freezing front movement and the displacement of material in the irradiated spot.},
doi = {10.1063/1.2720185},
journal = {Journal of Applied Physics},
number = 9,
volume = 101,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • We present computer modeling along with experimental data on the formation of sharp conical tips on silicon-based three-layer structures that consist of a single-crystal Si layer on a 1 {mu}m layer of silica on a bulk Si substrate. The upper Si layers with thicknesses in the range of 0.8-4.1 {mu}m were irradiated by single pulses from a KrF excimer laser focused onto a spot several micrometers in diameter. The computer simulation includes two-dimensional time-dependent heat transfer and phase transformations in Si films that result from the laser irradiation (the Stefan problem). After the laser pulse, the molten material self-cools andmore » resolidifies, forming a sharp conical structure, the height of which can exceed 1 {mu}m depending on the irradiation conditions. We also performed computer simulations for experiments involving single-pulse irradiation of bulk silicon, reported by other groups. We discuss conditions under which different types of structures (cones versus hollows) emerge. We confirm a correlation between the presence of the lateral resolidification condition after the laser pulse and the presence of conical structures on a solidified surface.« less
  • Cross-sections of laser fabricated nanosharp tips and microbumps on silicon and metal thin films are produced and examined in this work. These structures are formed with a Q-switched neodymium doped yttrium aluminum garnet nanosecond-pulse laser, emitting at its fourth harmonic of 266 nm, using a mask projection technique to generate circular laser spots, several microns in diameter. Cross-section of selected structures were produced using a focused ion beam and were characterized via electron microscopy. The diffraction patterns of the silicon samples indicate that the laser formed tip maintains the same single crystal structure as the original silicon film. Examinations ofmore » the laser formed structures in metal films confirm that the microbumps are hollow, while revealing that the vertical protrusions are solid.« less
  • Ferroelectric thin films of Pb(Zr,Ti)O{sub 3} (PZT) were fabricated on platinum-coated silicon using the process of direct-current glow discharge assisted laser deposition, where the substrate was electrically grounded. The films deposited at 730{degree}C with +800 V discharge voltage are oriented mostly with the c-axis perpendicular to the substrate surface, and exhibit good ferroelectric hysteresis loops. A possible mechanism for the improvement of the deposition process has been proposed. {copyright} {ital 1997 Materials Research Society.}
  • Spectroscopic ellipsometry was used to monitor excimer laser annealed thin ({approximately}100nm) amorphous silicon (a-Si) films grown on quartz substrates by low pressure chemical vapor deposition (LPCVD). The peak position of the imaginary part of the complex dielectric function {epsilon}{sub 2} was used to determine the degree of crystallization of the a-Si. The amplitude of {epsilon}{sub 2} at the Si E{sub 1} transition energy is found to be a good indicator of the polycrystalline silicon (poly-Si) grain size after laser annealing with good correlation between {ital ex situ} ellipsometric data and poly-Si grain sizes being observed. Spectroscopic ellipsometry provides a contactless,more » nondestructive, and simple technique for monitoring laser annealing both {ital in situ} during the annealing process or {ital ex situ} after annealing. {copyright} {ital 1997 American Institute of Physics.}« less
  • A pulsed KrF excimer laser with nanosecond pulse duration is used for surface melting of thin polycrystalline silicon films. The velocity of the moving phase boundary during melting and solidification, the maximum melting depth, as well as the melting duration are experimentally determined by combined optical and electrical methods. A melting interface tracking model is used to calculate the melt front propagation and the transient temperature field in the semiconductor. A phase-change model, which allows the occurrence of melting and solidification at temperatures other than the equilibrium melting temperature, is employed in the numerical calculation. The effect of interfacial superheating/undercoolingmore » is discussed. 23 refs., 12 figs.« less