Characterization of high-k/metal gate stack breakdown in the time scale of ESD events

Catastrophic gate oxide breakdown of MOSFETs with high-k gate was characterized under ESD-like pulsed stress. It was found that the excessive gate current after gate oxide failure may result in a loss of gate contact and form a resistive path between the drain and source. Using constant voltage stress (CVS) method, the gate oxide breakdown voltages (V
_BD
) of NMSOFETs and PMOSFETs were extracted. NMOSFETs under positive stress were found to have the smallest VBD, while the V
_BD
of the PMOSFETs under positive stress were significantly increased due to the well resistance. Compared to that measured using the CVS method, the V
_BD
from the transmission line pulse method (TLP) was smaller by only less than 10%. Despite the cumulative damages caused by the TLP method, the result is a conservative estimation of the breakdown voltage. The VBD corresponding to the failure time of 1-ns measured using TLP method agrees well with the extrapolation result from the CVS measurements on the time scale ranging from ~100 ns to ~20 μs, suggesting that the failure mechanism remains the same as in the longer time scale.