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Title: Neutral gas temperature measurements of high-power-density fluorocarbon plasmas by fitting swan bands of C{sub 2} molecules

Abstract

The neutral gas temperature of fluorocarbon plasmas in a remote toroidal transformer-coupled source was measured to be greater than 5000 K, under the conditions of a power density greater than 15 W/cm{sup 3} and pressures above 2 torr. The rovibrational bands of C{sub 2} molecules (swan bands, d {sup 3}{pi}{sub g}{yields}a {sup 3}{pi}{sub u}) were fitted to obtain the rotational temperature that was assumed to equal the translational temperature. This rotational-translational temperature equilibrium assumption was supported by the comparison with the rotational temperature of second positive system of added N{sub 2}. For the same gas mixture, the neutral gas temperature is nearly a linear function of plasma power, since the conduction to chamber wall and convection are the major energy-loss processes, and they are both proportional to neutral gas temperature. The dependence of the neutral gas temperature on O{sub 2} flow rate and pressure can be well represented through the power dependence, under the condition of constant current operation. An Arrhenius type of dependence between the etching rate of oxide film and the neutral gas temperature is observed, maybe indicating the importance of the pyrolytic dissociation in the plasma formation process when the temperature is above 5000 K.

Authors:
; ;  [1];  [2];  [2]
  1. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20787782
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 99; Journal Issue: 1; Other Information: DOI: 10.1063/1.2159545; (c) 2006 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; CARBON; CARBON FLUORIDES; CONVECTION; ELECTRON TEMPERATURE; ETCHING; FLOW RATE; ION TEMPERATURE; MIXTURES; MOLECULES; ORGANIC COMPOUNDS; OXIDES; PLASMA; PLASMA DIAGNOSTICS; POWER DENSITY; PRESSURE DEPENDENCE; PRESSURE RANGE PA; PYROLYSIS; TEMPERATURE DEPENDENCE; TEMPERATURE MEASUREMENT; TEMPERATURE RANGE OVER 4000 K

Citation Formats

Bai Bo, Sawin, Herbert H., Cruden, Brett A., Department of Chemical Engineering and Electrical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and NASA Ames Center for Nanotechnology, Moffett Field, California 94035. Neutral gas temperature measurements of high-power-density fluorocarbon plasmas by fitting swan bands of C{sub 2} molecules. United States: N. p., 2006. Web. doi:10.1063/1.2159545.
Bai Bo, Sawin, Herbert H., Cruden, Brett A., Department of Chemical Engineering and Electrical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, & NASA Ames Center for Nanotechnology, Moffett Field, California 94035. Neutral gas temperature measurements of high-power-density fluorocarbon plasmas by fitting swan bands of C{sub 2} molecules. United States. doi:10.1063/1.2159545.
Bai Bo, Sawin, Herbert H., Cruden, Brett A., Department of Chemical Engineering and Electrical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and NASA Ames Center for Nanotechnology, Moffett Field, California 94035. Sun . "Neutral gas temperature measurements of high-power-density fluorocarbon plasmas by fitting swan bands of C{sub 2} molecules". United States. doi:10.1063/1.2159545.
@article{osti_20787782,
title = {Neutral gas temperature measurements of high-power-density fluorocarbon plasmas by fitting swan bands of C{sub 2} molecules},
author = {Bai Bo and Sawin, Herbert H. and Cruden, Brett A. and Department of Chemical Engineering and Electrical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 and NASA Ames Center for Nanotechnology, Moffett Field, California 94035},
abstractNote = {The neutral gas temperature of fluorocarbon plasmas in a remote toroidal transformer-coupled source was measured to be greater than 5000 K, under the conditions of a power density greater than 15 W/cm{sup 3} and pressures above 2 torr. The rovibrational bands of C{sub 2} molecules (swan bands, d {sup 3}{pi}{sub g}{yields}a {sup 3}{pi}{sub u}) were fitted to obtain the rotational temperature that was assumed to equal the translational temperature. This rotational-translational temperature equilibrium assumption was supported by the comparison with the rotational temperature of second positive system of added N{sub 2}. For the same gas mixture, the neutral gas temperature is nearly a linear function of plasma power, since the conduction to chamber wall and convection are the major energy-loss processes, and they are both proportional to neutral gas temperature. The dependence of the neutral gas temperature on O{sub 2} flow rate and pressure can be well represented through the power dependence, under the condition of constant current operation. An Arrhenius type of dependence between the etching rate of oxide film and the neutral gas temperature is observed, maybe indicating the importance of the pyrolytic dissociation in the plasma formation process when the temperature is above 5000 K.},
doi = {10.1063/1.2159545},
journal = {Journal of Applied Physics},
number = 1,
volume = 99,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Inductively coupled hydrogen-added fluorocarbon (CF{sub 4}/Ar/H{sub 2} and C{sub 4}F{sub 8}/Ar/H{sub 2}) plasmas were used to etch HfO{sub 2}, which is a promising high-dielectric-constant material for the gate of complementary metal-oxide-semiconductor devices. The etch rates of HfO{sub 2} and Si were drastically changed depending on the additive-H{sub 2} flow rate in C{sub 4}F{sub 8}/Ar/H{sub 2} plasmas. The highly selective etching of HfO{sub 2} over Si was done in the condition with an additive-H{sub 2} flow rate, where the Si surface was covered with the fluorocarbon polymer. The results of x-ray photoelectron spectroscopy indicated that the carbon content of the selectivelymore » etched HfO{sub 2} surface was extremely low compared with the preetched surface contaminated by adventitious hydrocarbon in atmosphere. In the gas phase of the C{sub 4}F{sub 8}/Ar/H{sub 2} plasmas, Hf hydrocarbide molecules such as metal-organic compounds and Hf hydrofluoride were detected by a quadrupole mass analyzer. These findings indicate that the fluorine species, carbon, and hydrogen can work to etch HfO{sub 2} and that the carbon species also plays an important role in selective etching of HfO{sub 2} over Si.« less
  • The (0-0) band of the C/sub 2/ Swan electronic system d/sup 3/ Pi/sub g/..-->..a/sup 3/Pi/sub u/ has been recorded by Fourier spectroscopy. The three isotopes species /sup 12/C/sub 2/, /sup 13/C/sub 2/, and /sup 12/C/sup 13/C were investigated. The observed wavenumbers were reduced to molecular parameters using a nonlinear least-square fitting procedure. Well-known perturbations at N' = 47 and N' = 51 again observed in the e /sup 12/C/sub 2/d/sup 3/Pi/sub g/ (v = 0) level. Perturbations of the same kind are present in the /sup 13/C/sub 2/ spectrum at N' = 34 and N' = 44,48,52. The /sup 12/C/supmore » 13/C spectrum exhibits in the observed spectral range a unique perturbation for N' = 41.« less
  • Observed spectra of R Coronae Borealis (RCB) and hydrogen-deficient carbon (HdC) stars are analyzed by synthesizing the C{sub 2} Swan bands (1, 0), (0, 0), and (0, 1) using our detailed line list and the Uppsala model atmospheres. The (0, 1) and (0, 0) C{sub 2} bands are used to derive the {sup 12}C abundance, and the (1, 0) {sup 12}C{sup 13}C band to determine the {sup 12}C/{sup 13}C ratios. The carbon abundance derived from the C{sub 2} Swan bands is about the same for the adopted models constructed with different carbon abundances over the range 8.5 (C/He = 0.1%)more » to 10.5 (C/He = 10%). Carbon abundances derived from C I lines are about a factor of four lower than the carbon abundance of the adopted model atmosphere over the same C/He interval, as reported by Asplund et al., who dubbed the mismatch between adopted and derived C abundance as the 'carbon problem'. In principle, the carbon abundances obtained from C{sub 2} Swan bands and that assumed for the model atmosphere can be equated for a particular choice of C/He that varies from star to star. Then, the carbon problem for C{sub 2} bands is eliminated. However, such C/He ratios are in general less than those of the extreme helium stars, the seemingly natural relatives to the RCB and HdC stars. A more likely solution to the C{sub 2} carbon problem may lie in a modification of the model atmosphere's temperature structure. The derived carbon abundances and the {sup 12}C/{sup 13}C ratios are discussed in light of the double degenerate and the final flash scenarios.« less
  • Absolute emission and absorption measurements of rotational lines and band heads of the 0-0 C/sub 2/ Swan system have been made for carbon vapor inequilibrium with graphite at 2853-3051/sup 0/K. The data were treated for deviation from the linear curve of growth and for partial reversal in experiments with an external light source. At 3000/sup 0/K fN''/sub v0K1J0/ = 1.6 x 10/sup 8/ molecules/cm/sup 3/. The sum over all rotational lines of the 0-0 transition yields fN''/sub v0/ = 6.1 x 10/sup 11/ molecules/cm/sup 3/. The average of nine independent fN determinations from the literature yield fN''/sub v0K1J0/ = 1.9more » x 10/sup 8/ molecules/cm/sup 3/. These values averaged with lifetime measurements yield f/sub 0,0/ = 0.027 corresponding to a radiative lifetime or the v' = 0 level of 110 ns. The values are consistent with ..delta..H/sub 0//sup 0//R = 101,000 K for the sublimation of C/sub 2/ (a/sup 3/II) from graphite. These values for the Swan system are compared with the corresponding values from the literature for six other band systems of C/sub 2/. 69 references, 1 figure, 5 tables.« less
  • We report the systematic comparison of the optical emission intensity of the d {sup 3}{Pi} {yields} a {sup 3}{Pi} (0, 0) vibrational band of the C{sub 2} Swan system with the absolute C{sub 2} concentration in Ar/H{sub 2}/CH{sub 4} and Ar/H{sub 2}/C{sub 60} microwave plasmas used in the deposition of nanocrystalline diamond. The absolute C{sub 2} concentration is obtained using white-light absorption spectroscopy. Emission intensity correlates linearly with C{sub 2} density for variations of several plasma parameters and across two decades of species concentration. Although optical emission intensity generally is not an accurate quantitative diagnostic for gas phase species concentrations,more » these results confirm the reliability of the (0,0) Swan band for relative determination of C{sub 2} density with high sensitivity under conditions used for hydrogen-deficient plasma-enhanced chemical vapor deposition of diamond.« less