No abstract

The conduction mechanism and origin of the electrical stress-induced leakage current (SILC) in thin silicon dioxide (SiO2) films thermally grown on silicon substrate were clarified from various electrical properties. The properties examined consisted of the I-V characteristics, the oxide trap charge buildup, the generation of the Si/SiO2 interface states, and the generation of the neutral oxide traps. The electrical properties were obtained from films of different oxide thicknesses fabricated by different oxidation processes. The conduction mechanism of SILC was investigated from the viewpoint of oxide thickness dependence, using 92- and 56-Å-thick oxide films. From the oxide-thickness-dependent studies it was found that the SILC phenomenon was not correlated with the oxide trap charge buildup and interface state generation, but rather closely correlated with neutral electron trap generation. The conduction mechanism for nonequilibrium SILC was theoretically deduced from one-dimensional ballistic triangular barrier tunneling that occurred only during the filling process. The tunneling was directed from a leakage spot at the electron-injecting cathode to neutral electron trap sites uniformly generated within the oxide at a trap level (≊1.17 eV from the cathode conduction band and ≊2.0 eV from the SiO2 conduction band) lower than the SiO2 barrier height during only the filling process. The origin of the SILC was also investigated from the viewpoint of oxidation process dependence, using both wet and dry oxides of 86 and 50 Å thicknesses. The oxidation-process-dependent studies revealed that the SILC associated with a wet oxide after the stress application was less than that of a stressed dry oxide. The oxide trap charge buildup and the interface state generation associated with a wet oxide after the stress application was, however, greater than that of a stressed dry oxide. This result suggested that the SILC originated not from water-related chemical reactions, but from the distortion of the thermally grown SiO2 bond structure during electrical stressing. The SILC of both wet and dry oxides after the application of stress were well fitted by Fowler-Nordheim lines, confirming that the leakage conduction mechanism is independent of the oxidation process.

Abstruct-Thermochemical-breakdown and hole-inducedbreakdown 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-Si02 up to breakdown are simulated by the semiempirical molecular orbital calculation method (PM3 method) using Si5OI6H12 clusters. The structural transformations can be classified into (a) amorphous-like-Si02 (a-Si02), (b) holetrapped-Si02 (hole-trap), and (c) electrically-brokendown-Si02 (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-0-0-Si) and oxygenvacancy (Si-Si) defects. The heat of formation and frontier orbital energies of structural transformations account well for the physical aspects of the TDDB phenomenon.

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.