Modeling of Silicon Nanodots Nucleation and Growth Deposited by LPCVD on SiO{sub}2: From Molecule/Surface Interactions to Reactor Scale Simulations

摘要

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 SiO{sub}2 silicon dioxide surface, by Low Pressure Chemical Vapor Deposition (LPCVD) from silane SiH{sub}4. 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 SiH{sub}2 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 SiO{sub}2 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{sub}2 substrates and then increase NDs density.