Time-dependent-dielectric-breakdown characteristics of Hf-doped Ta2O5/SiO2 stack

• Hf-doped Ta2O5 exhibits improved TDDB characteristics with respect to the pure Ta2O5.
• The hard breakdown in Hf-doped Ta2O5 is a complex effect of three factors.
• Pre-existing traps, new traps generation and interface layer define the breakdown.
• The nature of pre-existing traps controls the breakdown mechanism in high-k stack.

The Time-Dependent-Dielectric Breakdown (TDDB) characteristics of MOS capacitors with Hf-doped Ta2O5 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 Ta2O5 were compared. The doped Ta2O5 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 Ta2O5 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 pre-existing traps and trapping phenomena; stress-induced new traps generation; interface layer degradation.

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