Reliability of La-Doped Hf-Based Dielectrics nMOSFETs

In this paper, the reliability of hafnium oxide gate dielectrics incorporating lanthanum (La) is investigated. The HfON with La demonstrated higher breakdown voltage and lower gate leakage than the control HfON with a similar equivalent oxide thickness and physical thickness. The superior breakdown characteristics of HfON that incorporate La are explained using La-induced interface-dipole formation. The La-induced dipole field at the interface between the SiOx and high-k hinders carrier injection in the inversion sweep, which in turn decreases gate leakage. In the accumulation region, the dipole formed near the interface regime appears to enhance the local field, which may lead to a local breakdown. While the devices with La show better immunity to positive-bias-temperature instability (PBTI) under normal operating conditions, the threshold-voltage shift (DeltaV _th) at high field PBTI is significant. The results of a transconductance shift (DeltaG _m) and flicker-noise analysis show that traps are easily generated during high field stress because the La weakens atomic bonding in the interface layer. These La-induced generated traps act like a capture/emission center, resulting in Lorentzian-like noise.