Failure mechanisms in HfO2 high-k gate stack MOSFETs

Abstract

The failure mechanisms in HfO2 high-k/polycrystalline-silicon (poly-Si) and

HfO2 high-k/TaN/TiN gate stack n/p-metal-oxide-semiconductor field effect

transistors (MOSFETs) under inversion and accumulation mode constant voltage stress have been studied both electrically and physically with the aid of high resolution transmission electron microscopy (HRTEM), energy dispersive spectrometry (EDS) and electron energy loss spectrometry (EELS) and EELS elemental dot mapping. Silicon oxynitride (SiOxNy)/poly-Si, silicon nitride (Si3N4) semi-high-k/poly-Si gate stack MOSFETs have also been studied for comparison. The associated dielectric degradation has been correlated with the microstructural changes during breakdown event to understand the actual failure mechanisms. It is found that the breakdown phenomenon and the fundamental failure mechanisms responsible for

breakdown in HfO2 high-k gate stacks are significantly different from that of SiOxNy and Si3N4 gate stack MOSFETs. Several new failure mechanisms/defects have been observed in HfO2 high-k/poly-Si and HfO2 high-k/TaN/TiN gate stack n/pMOSFETs.