Challenges of introducing quantitative elementary reactions in multiscale models of thin film deposition

Abstract

The implementation of detailed surface kinetic mechanisms describing the thin film growth dynamics into models of chemical vapor deposition (CVD) reactors has been a challenge for many years. In this article we review the literature concerning the study of the dynamics of the Si(100)2×1 surface and introduce a multiscale model that captures the main features of its reactivity. The model combines the results of ab initio calculations with an atomistic description of the Si surface, obtained using a 3D-kineticMonte Carlo (KMC)model that explicitly accounts for the 2×1 surface reconstruction and the formation and diffusion of Si dimers on a hydrogenated surface. At the atomistic scale, we determined pre-exponential factors and activation energies of hydrogen desorption reactions proceeding through the 2H, 3H, and 4H mechanisms. The calculated kinetic constants were embedded in the KMC model and used to simulate literature TPD experimental data. The simulations were used to fit the activation energies of hydrogen desorption reactions, which showed that DFT calculations performed with B3LYP functionals are likely to overestimate hydrogen desorption energies by up to 9 kcalmol^-1, which was confirmed by successive ab initio calculations. Two examples of the solution of the KMC model in conjunction with a reactor scale model are provided, in which the coupling was performed adopting both a hierarchic and a two-way coupling strategy.We found that in the plasma deposition of nanocrystalline silicon performed at low substrate temperatures the growth proceeds through a layer-by-layer mechanism on a surface almost completely covered by hydrogen. The application of the same model to the simulation of the thermal CVD of Si showed that at intermediate growth temperatures, when the hydrogen surface concentration is high, a new hydrogen desorption mechanism, in which Si adatoms play an important role, is active. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

CVD precursors for transition metal oxide nanostructures: molecular properties, surface behavior and temperature effects

“…Moreover, knowledge of precursor molecular properties is a crucial step to understand how they interact with the growth surface, as well as with other gaseous species, under the CVD operating conditions . In this context, modeling approaches are playing an increasingly important role, but further progress is needed in order to gain fundamental knowledge of the basic chemistry of CVD processes .…”

Opening the Pandora's jar of molecule-to-material conversion in chemical vapor deposition: Insights from theory

“…Modeling of actual CVD growth processes is currently accessible to large‐scale kinetic Monte Carlo simulations, which, however, need rate constants determined from first principles as input parameters. Such a scenario has stimulated the development of multiscale models for the CVD growth, that comprise a set of submodels tailored for dealing with different length scales . On the other hand, the study of the plasma‐activated SiH 3 formation and of its reactivity with other plasma‐generated species requires a very high theory level and should be performed with post‐HF methods …”

“…Up to now, examples related to the surface behavior of small, already activated precursors and of a coordinatively insaturated transition‐metal precursor have been considered. In both cases, the structure of the precursor molecule allows Si or Cu to directly interact, and finally bind, with surface atoms.…”

“…It should be stressed, however, that TBMD‐based approaches might become in the future a viable route to the simulation of CVD growth processes, an issue so far restricted to classical methodologies, which will, however, continue to play a key role in modeling the macroscale processes that occur inside a CVD reactor . To this aim, further development of multiscale modeling approaches should be pursued …”

Reactivity of Silicon Surfaces in the Presence of Adsorbed Hydrogen and Chlorine

“…It must, however, be pointed out that the schematization of the hydrogen desorption process in terms of the four reactions sketched in Figure 1 is simplistic as the overall process dynamics, in particular if a reactive gas phase is present, can in general be influenced by other surface processes, such as the diffusion of adatoms, and by the surface coverage. Some recent experimental10 and theoretical11 advances in the study of the hydrogenated surface dynamics have been published recently.…”