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Chemkin 4.1.1 Chapter 4: Materials Problems surface species have reacted. All the surface reactions are irreversible. As a result, the thermodynamic properties for surface species provide the elemental composition of the surface species, but the polynomial fitting parameters are merely placeholder values. 4.4.5 Chlorine Plasma This chemistry set is for a pure chlorine plasma without surface etching reactions that 37, 38 is based on work published by Meeks and coworkers. The gas-phase chemistry in the chlorine plasma is relatively simple. The element list contains 3 elements: E (the electron), Cl and Si. Si does not actively participate in any chemical reactions, as it only appears in surf.inp in the composition of surface species on the wall material, but it still needs to be included in the element list in the GAS- PHASE KINETICS input file. The gas-phase species list contains seven species: Cl 2 , Cl, Cl * (chlorine atoms in a metastable electronically excited state), Cl + 2 , Cl + , Cl - and E. The gas-phase reactions include electron collisions with Cl 2 leading to vibrational and electronic excitation, dissociation, ionization, and dissociative attachment. Electron reactions with Cl include electronic excitation into a number of excited states, including Cl* formation, and ionization. The gas-phase reaction mechanism also includes electron collisions with Cl - leading to electron detachment, electron collisions with Cl* leading to ionization, and gas-phase neutralization of Cl - with Cl + + and Cl 2 ions. All the reactions are irreversible as is typical of non-thermal plasmas. In lowpressure plasmas, ionization and dissociation are balanced primarily by surface recombination reactions. The rates for the electron-impact reactions depend on the electron energy, rather than the neutral gas temperature. The surface mechanism for reactions occurring on the reactor wall is also fairly simple. It only involves neutralization of Cl + + and Cl 2 with electrons (subject to the Bohm criterion), de-excitation of Cl* and radical recombination reactions for Cl to Cl 2 . The neutralization and de-excitation reactions are non-site specific, but the recombination reactions are described in terms of open and Cl covered sites. Although this example problem does not include surface etching reactions, surface recombination and neutralization reactions can be quite important in determining the 37. “Modeling of Plasma-Etch Processes Using Well Stirred Reactor Approximations and Including Complex Gas-Phase and Surface-Reactions”, E. Meeks and J. W. Shon, IEEE Transactions On Plasma Science, 23(#4):539-549 (1995). 38. “Effects of Atomic Chlorine Wall Recombination: Comparison of a Plasma Chemistry Model With Experiment,” E. Meeks, J. W. Shon, Y. Ra, P. Jones, JVSTA 13(#6):2884- 2889 (1995). © 2007 Reaction Design 158 RD0411-C20-000-001
Chapter 4: Materials Problems <strong>Tutorials</strong> <strong>Manual</strong> overall composition of these kinds of low-pressure plasmas. All the surface reactions are irreversible. The thermodynamic properties for surface species, therefore, provide the elemental composition of the surface species, but the polynomial fitting parameters are considered placeholder values and are not used in the simulation. 4.4.6 Fluorocarbon Plasma with SiO 2 Etch Products This chemistry set is for a fluorocarbon plasma (C 2 F 6 ) used for etching silicon dioxide films, a process that is used in the fabrication of microelectronic and MEMS devices. The chemistry set includes detailed surface reactions, including multiple materials with different reaction sets. Although it is quite complex, this mechanism is actually a small, early version of a more complete mechanism developed by Meeks and coworkers for etching several fluorocarbon precursors. Detailed descriptions of the full mechanisms, including information on the sources of rate parameters, can be 39, 40, 41 found in their publications. The gas-phase chemistry described in the chem.inp file involves 6 elements, 36 species, of which there are 9 positive ions, 3 negative ions, the electron, and 23 neutral species. There are 149 gas-phase reactions. Of these, 75 are electron-impact reactions leading to dissociation, dissociative ionization, attachment, vibrational and electronic excitation. Such reactions are included for the starting reactant C 2 F 6 , dissociation fragments such as CF 3 and CF 2 , as well as etching products such as O 2 and SiF 4 . The electron-impact reactions are all irreversible, and the rates depend on the electron energy, rather than the neutral gas temperature. There are 22 irreversible reactions describing the neutralization between positive and negative ions in the gas phase. Such reactions have high A-factors and are not energy dependent. The remaining 46 reactions are reactions of neutral gas-phase species, mostly reversible, some with explicitly specified reverse reaction rates. Many of the reactions include the participation of new specific collision partners (M), and a number of the unimolecular decomposition/bimolecular recombination reactions have detailed descriptions of the pressure dependence of the rate parameters. 39. “Modeling the Plasma Chemistry of C 2 F 6 and CHF 3 Etching of Silicon Dioxide, with Comparisons to Etch Rate and Diagnostic Data”, P. Ho, J. E. Johannes, R. J. Buss, and E. Meeks, J. Vac. Sci. Technol. A 19:2344 (2001). 40. “Plasma Modeling”, E. Meeks and P. Ho, Chapter 3 in “Advanced Plasma Processing Technologies”, edited by R. J. Shul and S. J. Pearton, Springer-Verlag, Heidelberg, (2000). 41. “Chemical Reaction Mechanisms for Modeling the Fluorocarbon Plasma Etch of Silicon Oxide and Related Materials”, P. Ho, J. E. Johannes, R. J. Buss and E. Meeks, Sandia National Laboratories Technical Report No. SAND2001-1292. RD0411-C20-000-001 159 © 2007 Reaction Design
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Chemkin 4.1.1 Contents Table of Con
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Chemkin 4.1.1 Tables List of Tables
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Tutorials Manual 4.1.1 Figures List
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List of Figures Tutorials Manual 2-
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Chemkin 4.1.1 1 1 Introduction The
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Chemkin 4.1.1 2 2 Combustion in Gas
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Chapter 2: Combustion in Gas-phase
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Chemkin 4.1.1 3 3 Catalytic Process
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