Mechanism of time-dependent oxide breakdown in thin thermally grown SiO2 films

In the thermally grown silicon dioxide (SiO2) films, thermochemical-breakdown and hole-induced-breakdown models are theoretically formulated to explain the external electric-field dependence of time-dependent dielectric breakdown (TDDB) phenomenon. Long-term TDDB test results proved to support the thermochemical-breakdown model. The time-dependent oxide breakdown mechanism is further studied on the basis of quantum physical chemistry. The structural transformations of a-SiO2 up to breakdown are simulated by a semiempirical molecular orbital calculation method (PM3 method) using Si5O16H12 clusters. The structural transformations can be classified into: (a) amorphous-like SiO2 (a-SiO2), (b) hole-trapped SiO2 (hole trap), and (c) electrically broken down SiO2 (breakdown) structures. The atom configuration shows a shortened length between the nearest oxygen atoms due to hole trapping. This leads to time-dependent oxide breakdown, and the breakdown structure consists of a pair of oxygen-excess (Si–O–O–Si) and oxygen-vacancy (Si–Si) defects. The heat of formation and frontier orbital energies of structural transformations account well for the physical aspects of the TDDB phenomenon.