Interfacial traps and mobile ions induced flatband voltage instability in 4H-SiC MOS capacitors under bias temperature stress

Abstract

Bias temperature stresses (BTSs) are critical factors that cause severe threshold voltage (Vth) instability in silicon carbide (SiC) metal-oxide-semiconductor (MOS) devices. In this work, we studied the behavior of flatband voltage (Vfb) instability in 4H-SiC MOS capacitors under various BTSs from low temperature (LT) to high temperature (HT) considering the combined effects of interfacial traps and mobile ions. Results showed that nitrogen and nitrogen–hydrogen plasma passivation improved the Vfb instability. The initial sweeping gate voltage determined the direction of Vfb shift. BTSs from LT to HT induced different capacitance–voltage hysteresis characteristics. The Vfb shift was further separated according to the contribution of the interface trapped, oxide trapped, and mobile ionic charges. At LT, the charge trapping dominated the shift behavior. The interface trap density was also extracted by another high-frequency and quasi-static method, which was the same as the separated interface trap density at 100 K, confirming the separation correctness of Vfb shift. At room temperature, charge trapping and mobile ions with very weak mobility contributed to the Vfb shift. At HT, mobile ions that counteracted the charge-trapping effect determined the Vfb shift, although the additional traps were activated in the interface and oxide. Physical models of Vfb instability under different temperature stresses were proposed. Finally, we chose the 100 K, 273 K, and 423 K to analyze gate bias stresses and stress time induced Vfb instabilities as well as their mechanisms.