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Calculation of Transport-Shifted CVD Phase Diagrams

Published online by Cambridge University Press:  21 February 2011

Daniel E. Rosner  and
Joshua Collins
Daniel E. Rosner
Affiliation:
Yale University, Department of Chemical Engineering, High Temperature Chemical Reaction Engineering Laboratory, New Haven CT 06520-2159, USA.
Joshua Collins
Affiliation:
Yale University, Department of Chemical Engineering, High Temperature Chemical Reaction Engineering Laboratory, New Haven CT 06520-2159, USA.
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Abstract

A non-iterative method is presented for constructing CVD phase diagrams which include the systematic effects of chemical element segregation in mass-transfer controlled flow reactors. Element segregation is shown to substantially shift predicted deposit phase boundaries when the vapor/deposit interface equilibrium is calculated using the local element fractions instead of the feed gas elemental composition, as is usually done. The mass transfer analysis developed here accounts for both Fick and Soret multicomponent diffusion acting across a non-isothermal boundary layer. The gas phase is assumed to be chemically frozen, with local thermochemical equilibrium imposed only at the vapor/deposit interface (as in a cold wall reactor with a hot substrate). As a specific example, this model is applied to the chemical vapor deposition of titanium diboride from TiCl4(g), BC13(g) and H2(g) in an Ar(g) carrier gas for ceramic composite material applications. These calculations, which account for boron and titanium transport via 17 chemical species, are illustrated for a long cylindrical reactor with a resistively heated coaxial fiber deposition substrate and coaxial annular flow. However, the method presented here is general in that both the chemical system and CVD reactor geometry can be changed to any other system of interest, provided: i) adequate themochemical and thermophysical data are available, ii) the deposition rate is vapor transport controlled, and iii) convective-diffusion heat and mass transfer coefficients are estimable.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 168 , 1989 , 43
Copyright
Copyright © Materials Research Society 1990

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Footnotes

a

Professor of Chemical Engineering and Director, Yale HTCRE Laboratory

b

Graduate Research Assistant and NASA GSRP Fellow, Yale HTCRE Laboratory

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