Bias temperature instability in metal-oxide-semiconductor field-effect transistors with atomic-layer-deposited Si-nitride/SiO2 stack gate dielectrics

Abstract

Bias temperature instability (BTI) in p+ poly-Si gated metal-oxide-semiconductor field-effect transistors (MOSFETs) with atomic-layer-deposited (ALD) Si-nitride/SiO2 stack gate dielectrics was systematically studied using drain current-gate voltage (Id-Vg) and modified direct-current current-voltage (DCIV) measurements. They exhibited quite unique behaviors as compared to the conventional SiON counterpart: turnaround of the threshold voltage shift (ΔVth) during stressing and significant positive BTI in nMOSFETs. The observed phenomena were consistently explained within the framework of conventional reaction-diffusion model for BTI but with two additional assumptions: (1) there exist pre-existing traps in the ALD Si-nitride/SiO2 stack dielectrics and (2) it is the inversion carriers (electrons or holes) rather than the accumulation carriers which effectively dissociate the SiH bonds at the SiO2∕Si interface during BTI stressing. Owing to the absence of nitrogen near the SiO2∕Si interface and the compensation effect on ΔVth between the charge trapping in the pre-existing traps and the dissociation of the SiH bonds under small voltage stress, the ALD Si-nitride/SiO2 stack dielectrics at the operating voltage may have similar or even longer BTI lifetime than the pure SiO2.