The structure of thermally grown noncrystalline SiO 2 films on silicon

Abstract

Oxygen transport during thermal growth of noncrystalline (nc) SiO 2 films on silicon reveals a subtle differences in their structure as compared with silica glass. The kinetics of oxide growth demonstrated that the oxygen transport parameter increases with increasing oxide thickness and may even exceed that calculated from O 2 permeation in SiO 2 glass. This effect is suggested to be due to the formation of structural channels in the oxide film during its growth. Concomitant with this change the activation energy decreases from ∼ 2.2 to ∼ 0.9 eV. These values indicate that transport in thin (< ∼ 70 nm) films is associated with interactions between O 2 molecules and network O atoms (> ∼ 1.2 eV), whereas an essentially non-interactive transport of O 2 molecules dominates in thicker (> ∼ 100 nm) films (⩽ ∼ 1.2 eV). Recent results by Rochet et al. on the intercorporation of 18O atoms into SiO 2 films corroborate this conclusion as an analysis of their data reveals that the interactive component of the oxygen flux decreases with oxide thickness as this process is partially tied to the flux of O 2 molecules. Remarkably, both components of the oxygen transport in nc-SiO 2 films are affected by the crystallographic orientation of the Si substrate.