Modeling of Silicon Nanodots Nucleation and Growth Deposited by LPCVD on SiO2 : From Molecule/Surface Interactions to Reactor Scale Simulations
Résumé
We present first results combining models at continuum and atomistic (DFT, Density
Functional Theory) levels to improve understanding of key mechanisms involved in silicon
nanodots (NDs) synthesis on SiO2 silicon dioxide surface, by Low Pressure Chemical Vapor
Deposition (LPCVD) from silane SiH4. In particular, by simulating an industrial LPCVD reactor
using the CFD (Computational Fluid Dynamics) code Fluent, we find that deposition time could
be increased and then reproducibility and uniformity of NDs deposition could be improved by
highly diluting silane in a carrier gas. A consequence of this high dilution seems to be that the
contribution to deposition of unsaturated species such as silylene SiH2 highly increases. This
result is important since our first DFT calculations have shown that silicon chemisorption on
silanol Si-OH or siloxane Si-O-Si bonds present on SiO2 substrates could only proceed from
silylene (and probably from other unsaturated species). The silane saturated molecule could only
contribute to NDs growth, i.e. silicon chemisorption on already deposited silicon bonds.
Increasing silylene contribution to deposition in highly diluting silane could then also exalt
silicon nucleation on SiO substrates and then increase NDs density.
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