Constant current stress-induced leakage current in mixed HfO_2-Ta_2O_5 stacks

摘要

The electrical characteristics of HfO_2-Ta_2O_5 mixed stacks under constant current stress (CCS) at gate injection with 20 mA/cm~2 and stressing times of 50 and 200 s have been investigated. A very weak effect of the stress on the global dielectric constant, on fast and slow states in the stack as well as on the dominant conduction mechanism is detected. The most sensitive parameter to the CCS is the leakage current. The stress-induced leakage current (SILC) is voltage and thickness dependent. The pre-existing traps govern the trapping kinetics and are a key parameter to evaluate the stress response. Two processes - positive charge build-up and new bulk traps generation - are suggested to be responsible for SILC: the domination of one of them depends on both the film thickness and the stressing time. The positive charge build-up is localized close to the gate electrode implying gate-induced defects could be precursors for it. It is established that unlike the case of single SiO_2 layer, the bulk traps closer to the gate electrode control SILC in the mixed Ta_2O_5-HfO_2-based capacitors.