Structural properties of silicon dioxide thin films densified by medium-energy particles
2001; American Physical Society; Volume: 64; Issue: 11 Linguagem: Inglês
10.1103/physrevb.64.115429
ISSN1095-3795
AutoresAlexis Lefèvre, Laurent J. Lewis, L. Martinů, M. R. Wertheimer,
Tópico(s)Thin-Film Transistor Technologies
ResumoClassical molecular-dynamics simulations have been carried out to investigate densification mechanisms in silicon dioxide thin films deposited on an amorphous silica surface, according to a simplified ion-beam assisted deposition scenario. We compare the structures resulting from the deposition of near-thermal (1 eV) ${\mathrm{SiO}}_{2}$ particles to those obtained with increasing fraction of 30 eV ${\mathrm{SiO}}_{2}$ particles. Our results show that there is an energy interval---between 12 and 15 eV per condensing ${\mathrm{SiO}}_{2}$ unit, on average---for which the growth leads to a dense, low-stress amorphous structure, in satisfactory agreement with the results of low-energy ion-beam experiments. We also find that the crossover between low- and high-density films is associated with a tensile-to-compressive stress transition, and a simultaneous healing of structural defects of the $a\ensuremath{-}{\mathrm{SiO}}_{2}$ network, namely, threefold and fourfold rings. It is observed, finally, that densification proceeds through significant changes at intermediate length scales $(4--10 \mathrm{\AA{}}\mathrm{}),$ leaving essentially unchanged the ``building blocks'' of the network, viz. the $\mathrm{Si}({\mathrm{O}}_{1/2}{)}_{4}$ tetrahedra. This latter result is in qualitative agreement with the mechanism proposed to explain the irreversible densification of amorphous silica recovered from high pressures $(\ensuremath{\sim}15--20 \mathrm{GPa}).$
Referência(s)