Oxide breakdown mechanism and quantum physical chemistry for time-dependent dielectric breakdown

Thermochemical-breakdown and hole-induced-breakdown models are theoretically formulated to explain the field-acceleration of 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-SiO/sub 2/ up to breakdown are simulated by the semiempirical molecular orbital calculation method (PM3 method) using Si/sub 5/O/sub 16/H/sub 12/ clusters. The structural transformations can be classified into (a) amorphous-like-SiO/sub 2/ (a-SiO/sub 2/), (b) hole-trapped-SiO/sub 2/ (hole-trap), and (c) electrically-brokendown-SiO/sub 2/ (breakdown) structures. The atom configuration shows a shortened length between the nearest oxygen atoms due to hole trapping. This leads to 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.