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Dynamic parameter estimation of atomic layer deposition kinetics applied to in situ quartz crystal microbalance diagnostics

Holmqvist, Anders LU ; Törndahl, Tobias; Magnusson, Fredrik LU ; Zimmermann, Uwe and Stenström, Stig LU (2014) In Chemical Engineering Science 111. p.15-33
Abstract
This paper presents the elaboration of an experimentally validated model of a continuous cross-flow atomic layer deposition (ALD) reactor with temporally separated precursor pulsing encoded in the Modelica language. For the experimental validation of the model, in situ quartz crystal microbalance (QCM) diagnostics was used to yield submonolayer resolution of mass deposition resulting from thin film growth of ZnO from Zn(C2H5)2 and H2O precursors. The ZnO ALD reaction intrinsic kinetic mechanism that was developed accounted for the temporal evolution of the equilibrium fractional surface concentrations of precursor adducts and their transition states for each half-reaction. This mechanism was incorporated into a rigorous model of reactor... (More)
This paper presents the elaboration of an experimentally validated model of a continuous cross-flow atomic layer deposition (ALD) reactor with temporally separated precursor pulsing encoded in the Modelica language. For the experimental validation of the model, in situ quartz crystal microbalance (QCM) diagnostics was used to yield submonolayer resolution of mass deposition resulting from thin film growth of ZnO from Zn(C2H5)2 and H2O precursors. The ZnO ALD reaction intrinsic kinetic mechanism that was developed accounted for the temporal evolution of the equilibrium fractional surface concentrations of precursor adducts and their transition states for each half-reaction. This mechanism was incorporated into a rigorous model of reactor transport, which comprises isothermal compressible equations for the conservation of mass, momentum and gas-phase species. The physically based model in this way relates the local partial pressures of precursors to the dynamic composition of the growth surface, and ultimately governs the accumulated mass trajectory at the QCM sensor. Quantitative rate information can then be extracted by means of dynamic parameter estimation. The continuous operation of the reactor is described by limit-cycle dynamic solutions and numerically computed using Radau collocation schemes and solved using CasADi's interface to IPOPT. Model predictions of the transient mass gain per unit area of exposed surface QCM sensor, resolved at a single pulse sequence, were in good agreement with experimental data under a wide range of operating conditions. An important property of the limit-cycle solution procedure is that it enables the systematic approach to analyze the dynamic nature of the growth surface composition as a function of process operating parameters. Especially, the dependency of the film growth rate per limit-cycle on the half-cycle precursor exposure dose and the process temperature was thoroughly assessed and the difference between ALD in saturating and in non-saturating film growth conditions distinguished. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Atomic layer deposition, Mathematical modeling, In situ film characterization, Experimental model validation, Parameter identification, Optimization
in
Chemical Engineering Science
volume
111
pages
15 - 33
publisher
Elsevier
external identifiers
  • wos:000334527100002
  • scopus:84897785414
ISSN
0009-2509
DOI
10.1016/j.ces.2014.02.005
project
collocation
LCCC
language
English
LU publication?
yes
id
5fbd51d2-71c1-4535-a2d0-9bd3cca63b20 (old id 4353922)
alternative location
http://dx.doi.org/10.1016/j.ces.2014.02.005
date added to LUP
2014-03-11 16:40:52
date last changed
2017-01-16 18:30:01
@article{5fbd51d2-71c1-4535-a2d0-9bd3cca63b20,
  abstract     = {This paper presents the elaboration of an experimentally validated model of a continuous cross-flow atomic layer deposition (ALD) reactor with temporally separated precursor pulsing encoded in the Modelica language. For the experimental validation of the model, in situ quartz crystal microbalance (QCM) diagnostics was used to yield submonolayer resolution of mass deposition resulting from thin film growth of ZnO from Zn(C2H5)2 and H2O precursors. The ZnO ALD reaction intrinsic kinetic mechanism that was developed accounted for the temporal evolution of the equilibrium fractional surface concentrations of precursor adducts and their transition states for each half-reaction. This mechanism was incorporated into a rigorous model of reactor transport, which comprises isothermal compressible equations for the conservation of mass, momentum and gas-phase species. The physically based model in this way relates the local partial pressures of precursors to the dynamic composition of the growth surface, and ultimately governs the accumulated mass trajectory at the QCM sensor. Quantitative rate information can then be extracted by means of dynamic parameter estimation. The continuous operation of the reactor is described by limit-cycle dynamic solutions and numerically computed using Radau collocation schemes and solved using CasADi's interface to IPOPT. Model predictions of the transient mass gain per unit area of exposed surface QCM sensor, resolved at a single pulse sequence, were in good agreement with experimental data under a wide range of operating conditions. An important property of the limit-cycle solution procedure is that it enables the systematic approach to analyze the dynamic nature of the growth surface composition as a function of process operating parameters. Especially, the dependency of the film growth rate per limit-cycle on the half-cycle precursor exposure dose and the process temperature was thoroughly assessed and the difference between ALD in saturating and in non-saturating film growth conditions distinguished.},
  author       = {Holmqvist, Anders and Törndahl, Tobias and Magnusson, Fredrik and Zimmermann, Uwe and Stenström, Stig},
  issn         = {0009-2509},
  keyword      = {Atomic layer deposition,Mathematical modeling,In situ film characterization,Experimental model validation,Parameter identification,Optimization},
  language     = {eng},
  pages        = {15--33},
  publisher    = {Elsevier},
  series       = {Chemical Engineering Science},
  title        = {Dynamic parameter estimation of atomic layer deposition kinetics applied to in situ quartz crystal microbalance diagnostics},
  url          = {http://dx.doi.org/10.1016/j.ces.2014.02.005},
  volume       = {111},
  year         = {2014},
}