Total Dose Effects and Bias Instabilities of (NH₄)₂S Passivated Ge MOS Capacitors With Hf_{<italic>x</italic>}Zr_{1–<italic>x</italic>}O_{<italic>y</italic>}Thin Films

Abstract

The effects of biased irradiation on Ge MOS capacitors with HfxZr1-xOy (0.43<x<1) gate dielectrics have been investigated. These devices were irradiated by a 662-KeV Cs 137 γray radiation source with 0.5 V or-0.5 V gate bias. Prior to irradiation exposure, leakage behavior and bias-instability of HfxZr1-xOy films were also examined. Gate leakage current density increases with the increasing of Zr composition in gate oxide. In addition, Zr-containing dielectrics under positive bias exhibited more oxide negative trapped charges than that of HfO2, which suggested that the oxygen-vacancy concentration in HfxZr1-xOy was increased by the addition of Zr. Larger flat-band voltage shifts (ΔVFB) were extracted under positive biased irradiation than the bias only results. The results indicate that radiation-induced interface traps (ΔNit) are the dominant factor for ΔVFB in HfO2 thin films, whereas the radiation response for Zr-containing dielectrics under positive bias was mainly due to oxide traps. Under negative biased irradiation, ΔVFB was attributed to the combined effect of the net oxide trapped charges and the passivation of Ge dangling bonds at the Ge/high-k interface. Additionally, both bias-induced and radiation-induced charge trapping have a crucial effect on radiation response of HfxZr1-xOy at each dose level. HfxZr1-xOy is identified as a promising gate dielectric for advanced CMOS technologies.