Defect generation and activation processes in HfO₂thin films: Contributions to stress-induced leakage currents

Abstract

An important source of degradation in thin dielectric material layers is the generation and migration of oxygen vacancies. We investigated the formation of Frenkel pairs (FPs) in HfO 2 as the first structural step for the creation of new defects as well as the migration of preexisting and newly built oxygen vacancies by nudged elastic band (NEB) calculations and stress induced leakage current (SILC) experiments. The analysis indicates, that for neutral systems no stable intimate FPs are built, whereas for the charge states q ¼ AE 2 FPs are formed at threefold and at fourfold coordinated oxygen lattice sites. Their generation and annihilation rate are in equilibrium according to the Boltzmann statistics. Distant FPs (stable defects) are unlikely to build due to high formation energies and therefore cannot be accounted for the measured gate leakage current increase of nMOSFETs under constant voltage stress. The negatively charged oxygen vacancies were found to be very immobile in contrast to positively charged V 0 's with a low migration barrier that coincides well with the experimentally obtained activation energy. We show that rather the activation of preexisting defects and migration towards the interface than the defect generation are the cause for the gate oxide degradation.

A microscopic mechanism of dielectric breakdown in SiO2 films: An insight from multi-scale modeling

“…In particular, a similar electroninjection-assisted mechanism of Frenkel defect creation recently proposed in monoclinic HfO 2 (Refs. [66][67][68] can contribute to BD in HfO 2 based devices and this process will be considered in separate publication. (RRAM) and memristive behaviour in silicon rich silicon oxides.…”

First principles calculations of optical properties for oxygen vacancies in binary metal oxides

“…18,19 The existing and newly generated oxygen vacancies in HfO 2 have been implicated in degradation of these devices and play the central role in the electroforming process in Resistive Random Access Memory (RRAM) devices. [20][21][22][23] Again, spectroscopic signatures of these defects are still controversial.…”

Relevance of non-equilibrium defect generation processes to resistive switching in TiO2

“…The generation of such defects, assisted by a non-equilibrium electric field and charge injection, is often discussed in the literature and included explicitly in some device simulations. 11,[20][21][22][23][24][25][26] However, resistive switching models are also developed considering field driven diffusion of pre-existing defects only, without defect generation. [27][28][29] Experimentally, definitive evidence for one view over the other has proven extremely challenging to obtain, and the uncertainty that remains presents an obstacle to addressing pressing technological issues, such as controlling cycle-to-cycle and device-to-device variability, increasing endurance, and improving reliability.…”