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Title: Nanoparticle growth and transport mechanisms in capacitively coupled silane discharges: a numerical investigation

Abstract

A self-consistent 1D fluid model is used to investigate the formation, growth and transport mechanisms of sub-micrometer particles in a low pressure capacitively coupled radio-frequency silane (SiH4) discharge. In this contribution we analyze the competition between the different forces governing the transport of nanometer-sized particles and the specific role of the thermophoretic force arising from a thermal gradient in gas temperature induced by heating or cooling of the electrodes. Further growth of the nanoparticles due to coagulation is also described by coupling the 1D fluid model with an aerosol dynamics model.

Authors:
;  [1];  [2]
  1. PLASMANT, Dept. of Chemistry, University of Antwerp (Ukraine), Universiteitsplein 1, 2610 Wilrijk (Belgium)
  2. FOM Institute for Plasma Physics 'Rijnhuizen', Association EURATOM-FOM, Trilateral Euregio Cluster, P.O. Box 1207, 3430 BE Nieuwegein (Netherlands)
Publication Date:
OSTI Identifier:
20726747
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 799; Journal Issue: 1; Conference: 4. international conference on the physics of dusty plasmas, Orleans (France), 13-17 Jun 2005; Other Information: DOI: 10.1063/1.2134600; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AEROSOLS; ELECTRODES; FLUIDS; HIGH-FREQUENCY DISCHARGES; NANOSTRUCTURES; NUMERICAL ANALYSIS; PARTICLES; PLASMA; PLASMA SIMULATION; RADIOWAVE RADIATION; SILANES; TEMPERATURE GRADIENTS

Citation Formats

Bleecker, K. de, Bogaerts, A., and Goedheer, W.J.. Nanoparticle growth and transport mechanisms in capacitively coupled silane discharges: a numerical investigation. United States: N. p., 2005. Web. doi:10.1063/1.2134600.
Bleecker, K. de, Bogaerts, A., & Goedheer, W.J.. Nanoparticle growth and transport mechanisms in capacitively coupled silane discharges: a numerical investigation. United States. doi:10.1063/1.2134600.
Bleecker, K. de, Bogaerts, A., and Goedheer, W.J.. Mon . "Nanoparticle growth and transport mechanisms in capacitively coupled silane discharges: a numerical investigation". United States. doi:10.1063/1.2134600.
@article{osti_20726747,
title = {Nanoparticle growth and transport mechanisms in capacitively coupled silane discharges: a numerical investigation},
author = {Bleecker, K. de and Bogaerts, A. and Goedheer, W.J.},
abstractNote = {A self-consistent 1D fluid model is used to investigate the formation, growth and transport mechanisms of sub-micrometer particles in a low pressure capacitively coupled radio-frequency silane (SiH4) discharge. In this contribution we analyze the competition between the different forces governing the transport of nanometer-sized particles and the specific role of the thermophoretic force arising from a thermal gradient in gas temperature induced by heating or cooling of the electrodes. Further growth of the nanoparticles due to coagulation is also described by coupling the 1D fluid model with an aerosol dynamics model.},
doi = {10.1063/1.2134600},
journal = {AIP Conference Proceedings},
number = 1,
volume = 799,
place = {United States},
year = {Mon Oct 31 00:00:00 EST 2005},
month = {Mon Oct 31 00:00:00 EST 2005}
}
  • A two-dimensional (2D) self-consistent fluid model is developed to describe the formation, subsequent growth, transport, and charging mechanisms of nanoparticles in a capacitively coupled silane discharge applied by two very high frequency (VHF) sources with phase shift. In this discharge process, large anions are produced by a series of chemical reactions of anions with silane molecules, while the lower limit of the initial nanoparticles are taken as large anions (Si{sub 12}H{sub 25}{sup -} and Si{sub 12}H{sub 24}{sup -}) to directly link the coagulation module with the nucleation module. And then, by using the coagulation module, the particle number density quicklymore » decreases over several orders of magnitude, whereas the particle size strongly increases. We investigate in particular the growth of the nanoparticles ranging in size from {approx}1 to 50 nm in coagulation processes. The influences of controlled phase shifts between VHF (50 MHz) voltages on the electron density, electron temperature, nanoparticle uniformity, and deposition rate, are carefully studied. It is found from our simulation that the plasma density and nanoparticle density become center high and more uniform as the phase shift increases from 0 to 180 deg. Moreover, the role of phase-shift control in the silane discharge diluted with hydrogen gas is also discussed.« less
  • The behavior of nanoparticles in dual-frequency capacitively coupled silane discharges is investigated by employing a one-dimensional self-consistent fluid model. The numerical simulation tries to trace the formation, charging, growth, and transport of dust particles during the discharge, under the influences of the high- and low-frequency electric sources, as well as the gas pressure. The effects of the presence of the nanoparticles and larger anions on the plasma properties are also discussed, especially, for the bulk potential, electron temperature, and densities of various particles. The calculation results show that the nanoparticle density and charge distribution are mainly influenced by the voltagemore » and frequency of the high-frequency source, while the voltage of the low-frequency source can also exert an effect on the nanoparticle formation, compared with the frequency. As the discharge lasts, the electric potential and electron density keep decreasing, while the electron temperature gets increasing after a sudden drop.« less
  • In low-pressure capacitively coupled parallel-plate radio-frequency (RF) discharges, such as those used in plasma processing of semiconductor materials, power deposition and the rate of electron-impact excitation collisions depend upon time during the RF cycle and position in the discharge. Power is coupled into the discharge in at least two ways: by way of a high-energy ''e-beam'' component of the electron distribution resulting from electrons falling through or being accelerated by the oscillating sheaths, and by ''joule heating'' in the body of plasma. This paper discusses the method of power deposition by electrons and the spatial dependence of electron-impact excitation ratesmore » in low-pressure capacitively coupled RF discharges with results from a Monte Carlo plasma simulation code. Mixtures of argon and silane are examined as typical examples of discharges used for the plasma deposition of amorphous silicon.« less
  • The temperature of gaseous neutrals in capacitively coupled discharges of chlorine, argon, and hydrogen has been measured using optical emission spectroscopy. This has been accomplished by adding small amounts of nitrogen to the ambient. The temperature can then be obtained by fitting the unresolved second rotational positive band of nitrogen. It has been found that the gaseous temperature in argon saturates for higher pressures logarithmically, whereas in chlorine, a linear behavior is observed up to the highest pressures and power inputs. Highest temperatures in chlorine have been found to be about 1100 deg. C, whereas in hydrogen, temperatures higher thanmore » 500 deg. C are rarely observed. Likewise, the effective collision frequency in chlorine increases significantly in the medium pressure range indicating a change in excitation/dissipation from the regime of stochastic heating to Ohmic heating, whereas the discharge in the inert gas still remains in the regime of stochastic heating. The experimental data for the collision frequency of the electrons with neutrals can be perfectly modeled for chlorine with these reduced gaseous densities.« less
  • The electron density is measured in low-pressure dual-frequency (2/60 MHz) capacitively coupled oxygen discharges by utilizing a floating hairpin probe. The dependence of electron density at the discharge center on the high frequency (HF) power, low frequency (LF) power, and gas pressure are investigated in detail. A (1D) particle-in-cell/Monte Carlo method is developed to calculate the time-averaged electron density at the discharge center and the simulation results are compared with the experimental ones, and general agreements are achieved. With increasing HF power, the electron density linearly increases. The electron density exhibits different changes with the LF power at different HFmore » powers. At low HF powers (e.g., 30 W in our experiment), the electron density increases with increasing LF power while the electron density decreases with increasing LF power at relatively high HF powers (e.g., 120 W in our experiment). With increasing gas pressure the electron density first increases rapidly to reach a maximum value and then decreases slowly due to the combined effect of the production process by the ionization and the loss processes including the surface and volume losses.« less