Development of an original model for the synthesis of silicon nanodots by Low Pressure Chemical Vapor Deposition

Using the Computational Fluid Dynamics code Fluent, a simulation model of an industrial Low Pressure Chemical Vapor Deposition reactor has been developed for the synthesis of silicon nanodots from silane SiH4 on silicon dioxide SiO2 substrates. A comparison between experimental and simulated deposition rates has shown that classical kinetic laws largely over-estimated these deposits. So, an original heterogeneous kinetic model is proposed as a first attempt to quantify the temporal evolution of deposition rates and of surface site numbers, as a function of operating conditions and of the chemical nature of substrate sites, for the early stages of silicon deposition. Contributions of silane and of the homogeneously born silylene SiH2 to nucleation and growth have been considered on different surface sites, silanol Si-OH, siloxane Si-C-Si and fresh silicon bonds. Simulations have revealed that for the conditions tested, the classical heterogeneous kinetic laws over-estimate, by more than 60%, silicon deposition during the first stages. The assumption that silylene and more largely all the unsaturated species formed in the gas phase contribute in priority to nucleation has been validated. Nucleation appears as a mandatory step to form the first fresh Si sites to allow deposition to occur from silane via growth phenomena. (C) 2008 Elsevier B.V. All rights reserved.