Constant current stress of lightly Al-doped Ta2O5

The response of lightly Al-doped Ta2O5 stacked films (6 nm) to constant current stress (CCS) under gate injection (current stress in the range of 1 to 30 mA/cm2 and stressing time of 50–400 s) has been investigated. The stress creates positive oxide charge, which is assigned to oxygen vacancies but it does not affect the dielectric constant of the films. The most sensitive parameter to the stress is the leakage current. Different degradation mechanisms control the stress-induced leakage current (SILC) in dependence on both the stress conditions and the applied measurement voltage. The origin of SILC is not the same as that in pure and Ti- or Hf-containing Ta2O5. The well known charge trapping in pre-existing traps operates only at low level stress resulting in small SILC at accumulation. The new trap generation plays a key role in the SILC degradation and is the dominant mechanism controlling the SILC in lightly Al-doped Ta2O5 layers.