The breakage of the silicon-oxygen bond is one of the most crucial issues in the field of reliability of SiO2 films. Several research groups claim that Si-O bond rupture is the essential contributor to Hot-Carrier-induced (HCI) damage as well as to Time-Dependent-Dielectric-Breakdown (TDDB). A recently proposed model for Si-O bond-breakage by McPherson considers binding potentials as a function of the Si ion displacement from its equilibrium position in the center of the SiO4 tetrahedron. Within this model, the transition of the Si ion from the 4-fold coordinated position to the 3-fold coordination beyond the O3 plane is interpreted as the rupture of the Si-O bond followed by a formation of a Si-Si bridge. The symmetry of a single tetrahedron determines the potential profile acting on the Si ion. However, it is obvious that the contribution of the whole lattice substantially changes the matter.
We thus extended the initial model for Si-O bond-breakage in a manner so as to capture the effect of the whole surrounding lattice on the silicon-oxygen bond-breakage energetics. It is shown that the secondary minimum corresponding to the transition of the Si atom from the 4-fold to the 3-fold coordinated position occurs in a different direction with a rather high activation energy (~6eV vs. ~2.3eV obtained in the McPherson model). Such a high activation energy suggests that bond rupture purely by means of an electric field is practically impossible. Thus a bond weakening, by, for example hole capture, bond angle variations or build-in of strain, is an essential condition for the Si-O bond rupture. Another possible condition for this bond rupture is acceleration of the Si ion transmission by the energy delivered by other particles, hot carriers and/or hydrogen.
The statistical analysis of the bond-breakage variation induced by the O-Si-O angle fluctuations (typical for amorphous SiO2) shows that the mean bond-breakage rate is substantially higher and the standard deviation is the same order of magnitude as the rate calculated for the fixed angle 109.48°. This circumstance complicates the matter: in fact while the trap cluster is being formed, new defects are most probably created in the vicinity of the pre-existed ones and thus the spot with the highest breakage rate (even though realized by a small probability) acts as a precursor for the formation of a percolation path.