Time-dependent-dielectric-breakdown characteristics of Hf-doped Ta_2O_5/SiO_2 stack

摘要

The Time-Dependent-Dielectric Breakdown (TDDB) characteristics of MOS capacitors with Hf-doped Ta_2O_5 films (8 nm) have been analyzed. The devices were investigated by applying a constant voltage stress at gate injection, at room and elevated temperatures. Stress voltage and temperature dependences of hard breakdown of undoped and Hf-doped Ta_2O_5 were compared. The doped Ta_2O_5 exhibits improved TDDB characteristics in regard to the pure one. The maximum voltage projected for a 10 years lifetime at room temperature is -2.4 V. The presence of Hf into the matrix of Ta_2O_5 modifies the dielectric breakdown mechanism making it more adequate to the percolation model. The peculiarities of Weibull distribution of dielectric breakdown are discussed in terms of effect of three factors: nature of preexisting traps and trapping phenomena; stress-induced new traps generation; interface layer degradation.