Factors Affecting Bias Temperature Instability in 4H-SiC MOS Capacitors

The threshold voltage of 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) show instability during normal operation, especially after bias temperature stress (BTS), and this phenomenon is called bias temperature instability (BTI). In this work, to study the factors affecting threshold voltage (Vth) instability of SiC MOSFETs, flat-band voltage (Vfb) instability of 4H-SiC metal-oxide-semiconductor (MOS) capacitors is discussed instead. Some factors, including the polarity of gate bias stress, stress time, and stress temperature, are analyzed by performing one-way bias stress C-V measurements in the devices. Firstly, positive bias stress leads to a positive Vfb shift, and negative bias stress leads to a negative one. Moreover, the Vfb shift appears to exhibit a linear relationship with log (stress time). Furthermore, the Vfb shift decreases over the temperature range of 225 K to 400 K, but slightly increases at 475 K. Finally, the Vfb stability of the MOS devices fabricated by 1200 °C NO post-oxidation annealing (POA) and those fabricated by 1250 °C NO POA is similar.