Tutorials Manual

Chemkin 4.1.1
Chapter 4: Materials Problems
The chem.inp file includes 3 elements, 11 gas-phase species, and 9 reversible gasphase
reactions. The gas-phase reactions are reversible decomposition reactions of
various chlorosilanes and chlorinated disilanes. These reactions cause the
conversion of some of the initial chlorosilane starting material to these other gasphase
species, which can be significant because the less-chlorinated molecules have
higher surface reactivities. These reactions are written as unimolecular
decomposition reactions at their high-pressure limit, so this reaction mechanism
would tend to overstate the importance of gas-phase chemistry if it were used at lower
total pressures.
The surf.inp file has 3 surface species: open silicon surface sites, hydrogen-covered
sites, and chlorine-covered sites, plus solid silicon as a bulk phase. There are 10
surface reactions, all written as irreversible reactions with placeholders for the
thermodynamic data of the surface species. These reactions include the dissociative
adsorption of SiCl 3 H, SiCl 2 H 2 and SiCl 4 , which result in the formation of deposited
silicon and hydrogenated/chlorinated silicon surface species. These are “lumped
reactions” to the extent that the initial adsorption event, plus the successive transfer of
H and Cl atoms from the initially adsorbed Si to other surface Si atoms, are all
described as one step. The physical interpretation of this “lumping” is that adsorption
of the gas-phase species is assumed to be slow compared to subsequent transfer of
H and Cl atoms on the surface. For a chemically balanced reaction, this is written as
involving 4 open sites, which by default would make the reaction fourth order in open
sites, so the coverage dependence option has been used to set the kinetics to a more
reasonable first-order dependence. Other reactions include the dissociative
adsorption and associative desorption of H 2 , HCl and SiCl 2 , plus the dissociative
adsorption of HSiCl. In many cases, the rate parameters are based on experimental
surface-science studies, in other cases they are the result of fitting a model to
experimental silicon deposition rate data from a specific CVD reactor.
4.4.4 Alumina ALD
This chemistry set describes the atomic layer deposition (ALD) of alumina from
trimethylaluminum (TMA) and ozone. This mechanism is deliberately simplistic for
illustration purposes only. It demonstrates one way of describing the ALD of alumina,
but it should generally be considered as illustrative only and not used as a source of
35. “Chemical Kinetics for Modeling Silicon Epitaxy from Chlorosilane”, P. Ho,
A. Balakrishna, J. M. Chacin, A. Thilderkvist, B. Haas, and P. B. Comita, in “Fundamental
Gas-Phase and Surface Chemistry of Vapor-Phase Materials Synthesis”,
T. J. Mountziaris, M. D. Allendorf, K. F. Jensen, R. K. Ulrich, M. R. Zachariah, and
M. Meyyappan, Editors, PV 98-23, p. 117-122, Proceedings of the 194th Meeting of the
Electrochemical Society, 11/1-6/98, The Electrochemical Society Proceedings Series,
Pennington, NJ (1999).
© 2007 Reaction Design 156 RD0411-C20-000-001