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Title: Dry-etch of As{sub 2}S{sub 3} thin films for optical waveguide fabrication

Abstract

Plasma etching to As{sub 2}S{sub 3} thin films for optical waveguide fabrication has been studied using a helicon plasma etcher. The etching effects using the processing gases or gas mixtures of O{sub 2}, Ar, and CF{sub 4} were compared. It was found that the O{sub 2} plasma had no chemical etching effect to the As{sub 2}S{sub 3}, but it could oxidize the surface of the As{sub 2}S{sub 3}. The Ar plasma provided a strong ion sputtering effect to the films. The CF{sub 4} plasma exhibited a too strong chemical etch to the As{sub 2}S{sub 3}, leading to serious undercutting and very rough sidewalls of the waveguides. Ar and O{sub 2} gases were compared as the additives to dilute the CF{sub 4} processing gas. The etch rate of the As{sub 2}S{sub 3} was reduced dramatically from over 2000 nm/min to a few hundred nm/min when the pure CF{sub 4} gas was heavily diluted with 70% Ar or O{sub 2} gas. The undercutting and sidewall roughness of the etched waveguides were also decreased greatly when above dilution was made, which was associated with an enormous weakening of the isotropic chemical etch induced by neutral reactants in the plasma. In addition, the O{submore » 2} showed a better dilution effect than the Ar in reducing the etch rate of the As{sub 2}S{sub 3}; and the O{sub 2}/CF{sub 4} plasma also enabled a much lower erosion rate to Al mask layers than the Ar/CF{sub 4} plasma at similar plasma conditions. The As{sub 2}S{sub 3} waveguides with near vertical and very smooth sidewalls were obtained using an optimized O{sub 2}/CF{sub 4} plasma. Moreover, the etching behaviors and mechanisms were explained base on the etching results, and on the characteristics of the applied plasma diagnosed using Langmuir probe and optical spectroscopy techniques.« less

Authors:
; ; ; ;  [1];  [2]
  1. Laser Physics Center, Australian National University, Canberra 0200 (Australia)
  2. (Australia)
Publication Date:
OSTI Identifier:
20723209
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films; Journal Volume: 23; Journal Issue: 6; Other Information: DOI: 10.1116/1.2049308; (c) 2005 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ADDITIVES; ARGON; ARSENIC SULFIDES; CARBON TETRAFLUORIDE; DILUTION; EROSION; ETCHING; FABRICATION; LANGMUIR PROBE; LAYERS; MIXTURES; OXIDATION; OXYGEN; PLASMA; PLASMA DIAGNOSTICS; ROUGHNESS; SPECTROSCOPY; SPUTTERING; THIN FILMS; WAVEGUIDES

Citation Formats

Li Weitang, Ruan Yinlan, Luther-Davies, Barry, Rode, Andrei, Boswell, Rod, and Plasma Research Lab, Australian National University, Canberra 0200. Dry-etch of As{sub 2}S{sub 3} thin films for optical waveguide fabrication. United States: N. p., 2005. Web. doi:10.1116/1.2049308.
Li Weitang, Ruan Yinlan, Luther-Davies, Barry, Rode, Andrei, Boswell, Rod, & Plasma Research Lab, Australian National University, Canberra 0200. Dry-etch of As{sub 2}S{sub 3} thin films for optical waveguide fabrication. United States. doi:10.1116/1.2049308.
Li Weitang, Ruan Yinlan, Luther-Davies, Barry, Rode, Andrei, Boswell, Rod, and Plasma Research Lab, Australian National University, Canberra 0200. Tue . "Dry-etch of As{sub 2}S{sub 3} thin films for optical waveguide fabrication". United States. doi:10.1116/1.2049308.
@article{osti_20723209,
title = {Dry-etch of As{sub 2}S{sub 3} thin films for optical waveguide fabrication},
author = {Li Weitang and Ruan Yinlan and Luther-Davies, Barry and Rode, Andrei and Boswell, Rod and Plasma Research Lab, Australian National University, Canberra 0200},
abstractNote = {Plasma etching to As{sub 2}S{sub 3} thin films for optical waveguide fabrication has been studied using a helicon plasma etcher. The etching effects using the processing gases or gas mixtures of O{sub 2}, Ar, and CF{sub 4} were compared. It was found that the O{sub 2} plasma had no chemical etching effect to the As{sub 2}S{sub 3}, but it could oxidize the surface of the As{sub 2}S{sub 3}. The Ar plasma provided a strong ion sputtering effect to the films. The CF{sub 4} plasma exhibited a too strong chemical etch to the As{sub 2}S{sub 3}, leading to serious undercutting and very rough sidewalls of the waveguides. Ar and O{sub 2} gases were compared as the additives to dilute the CF{sub 4} processing gas. The etch rate of the As{sub 2}S{sub 3} was reduced dramatically from over 2000 nm/min to a few hundred nm/min when the pure CF{sub 4} gas was heavily diluted with 70% Ar or O{sub 2} gas. The undercutting and sidewall roughness of the etched waveguides were also decreased greatly when above dilution was made, which was associated with an enormous weakening of the isotropic chemical etch induced by neutral reactants in the plasma. In addition, the O{sub 2} showed a better dilution effect than the Ar in reducing the etch rate of the As{sub 2}S{sub 3}; and the O{sub 2}/CF{sub 4} plasma also enabled a much lower erosion rate to Al mask layers than the Ar/CF{sub 4} plasma at similar plasma conditions. The As{sub 2}S{sub 3} waveguides with near vertical and very smooth sidewalls were obtained using an optimized O{sub 2}/CF{sub 4} plasma. Moreover, the etching behaviors and mechanisms were explained base on the etching results, and on the characteristics of the applied plasma diagnosed using Langmuir probe and optical spectroscopy techniques.},
doi = {10.1116/1.2049308},
journal = {Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films},
number = 6,
volume = 23,
place = {United States},
year = {Tue Nov 15 00:00:00 EST 2005},
month = {Tue Nov 15 00:00:00 EST 2005}
}
  • Dry-etch of SiO{sub 2} layers using a CF{sub 4} plasma in a helicon plasma etcher for optical waveguide fabrication has been studied. Al{sub 2}O{sub 3} thin films, instead of the conventional materials, such as Cr or photoresist, were employed as the masking materials. The Al{sub 2}O{sub 3} mask layer was obtained by periodically oxidizing the surface of an Al mask in an oxygen plasma during the breaks of the SiO{sub 2} etching process. A relatively high SiO{sub 2}/Al{sub 2}O{sub 3} etching selectivity of {approx}100:1, compared with a SiO{sub 2}/Al selectivity of {approx}15:1, was achieved under certain plasma condition. Such amore » high etching selectivity greatly reduced the required Al mask thickness from over 500 nm down to {approx}100 nm for etching over 5-{mu}m-thick silica, which make it very easy to obtain the mask patterns with near vertical and very smooth sidewalls. Accordingly, silica wavegudies with vertical sidewalls whose roughness was as low as 10 nm were achieved. In addition, the mechanism of the profile transformation from a mask to the etched waveguide was analyzed numerically; and it was found that the slope angle of the sidewalls of the mask patterns only needed to be larger than 50 deg. for achieving vertical sidewalls of the waveguides, if the etching selectivity was increased to 100.« less
  • An alcoholysis exchange between tris(hydroxymethyl)ethane (THME-H{sub 3}) or tris(hydroxymethyl)propane (THMP-H{sub 3}) and group IV metal isopropoxides yields compounds of the general formula (THMR){sub 2}M{sub 4}(OCHMe{sub 2}){sub 10}[M = Ti (R = E, 1; P, 2); Zr (R = E, 3; P, 4)]. 1 and 2 are formed in toluene, at ambient glovebox temperatures, and adopt a typical fused-M{sub 3}O{sub 12} structure where each titanium atom is surrounded by six oxygens in a slightly distorted face-shared bioctahedral arrangement. All of the oxygens of the central core are from the THMR ligand, present as {mu}-O and {mu}{sub 3}-O oxygen bridges. Generation ofmore » 3 or 4 requires heating in toluene at reflux temperatures. The zirconium atoms of 3 possess an extremely distorted edge-shared bioctahedral geometry where the central core consists of a Zr{sub 4}O{sub 8} ring (eight oxygens: six from THME ligands and two from isopropoxide ligands). Each of the zirconium atoms is six-coordinated with four bridging oxygens and two terminal isopropoxide ligands. Spincast deposited films generated from toluene solutions of 1 and 3 indicate that increased uniformity of the films and decreased hydrolysis occur in comparison to the cases of Ti(OCHMe{sub 2}){sub 4}, 5, and [Zr(OCHMe{sub 2}){sub 4}{center_dot}HOCHMe{sub 2}]{sub 2}, 6, respectively.« less
  • The investigations of etch characteristics and mechanisms for both In{sub 2}O{sub 3} and SnO{sub 2} thin films in the HBr-based inductively coupled plasmas were carried out. The etch rates were measured as functions of gas mixing ratio (0%-100% Ar), input power (400-700 W), and gas pressure (4-10 mTorr) at fixed bias power (200 W) and gas flow rate [40 SCCM (SCCM denotes cubic centimeter per minute at STP)]. Plasma parameters and composition were determined using a combination of plasma diagnostics by double Langmuir probe and global (zero-dimensional) plasma model. The correlations between the behaviors of etch rates and fluxes ofmore » plasma active species allow one to infer both In{sub 2}O{sub 3} and SnO{sub 2} etch mechanisms as the transitional regime of ion-assisted chemical reaction, which is controlled by neutral and charged fluxes together.« less
  • This article reports a study carried out on a model-based analysis of the etch mechanism for ZrO{sub 2} thin films in a BCl{sub 3}/He inductively coupled plasma. It was found that an increase in the He mixing ratio at a fixed gas pressure and input power results in an increase in the ZrO{sub 2} etch rate, which changes from 36 to 57 nm/min for 0-83% He. Langmuir probe diagnostics and zero-dimensional plasma modeling indicated that both plasma parameters and active species kinetics were noticeably influenced by the initial composition of the BCl{sub 3}/He mixture, resulting in the nonmonotonic or nonlinearmore » behaviors of species densities. Using the model-based analysis of etch kinetics, it was demonstrated that the behavior of the ZrO{sub 2} etch rate corresponds to the ion-flux-limited etch regime of the ion-assisted chemical reaction.« less
  • The pulsed laser deposition process of 300 nm thick films of Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}){sub 0.67}-(PbTiO{sub 3}){sub 0.33} on (001)-oriented SrTiO{sub 3} was studied by varying deposition pressure, substrate deposition temperature, laser fluence on the target and target-substrate distance. Perovskite phase pure, (001)-oriented, epitaxial smooth films were obtained in a narrow range of deposition parameters. The ferroelectric and dielectric properties of films fabricated within this parameter range still vary significantly. This shows the sensitivity of the system for growth conditions. The best film has a polarization value close to that expected for a (001) poled, stress free single crystal film.more » All films show deposition conditions dependent variations in the self-bias field. The self-bias is very stable during long cycling for films made at optimum deposition conditions. The piezoelectric coefficients of the films are strongly reduced with respect to bulk single crystal values due to the film clamping. The properties variations are ascribed to changes in the grain boundary properties in which film defects are expected to accumulate. Notably slight off-stoichiometry may cause localized screening charges, affecting specifically the polarization and dielectric constant.« less