Bias-Temperature Instabilities in 4H-SiC Metal–Oxide–Semiconductor Capacitors

Abstract

Bias-temperature instabilities (BTIs) are investigated for n- and p-substrate 4H-SiC metal–oxide–semiconductor (MOS) capacitors. The midgap voltage $(V_{ \rm mg})$ shifts positively under positive bias stress at high temperatures for n-substrate capacitors with 67.5-nm nitrided oxides and shifts negatively under negative bias for p-substrate capacitors with 55-nm nitrided oxides. The magnitudes of the $V_{\rm mg}$ shifts are less than 0.5 V for electric fields of magnitudes of approximately $\pm$ 3.1 MV/cm for up to one day of stress at 150 $^{\circ}\hbox{C}$ or 20 min of stress at 300 $^{\circ}\hbox{C}$ . Switched-bias stressing at 150 $^{\circ}\hbox{C}$ causes partially reversible shifts for the n-substrate capacitors, while the p-substrate capacitors show monotonically increasing negative shifts. Based on the measured temperature dependence of the $V_{\rm mg}$ shifts, the effective activation energy for BTI that is measured between room temperature and 250 $^{\circ}\hbox{C}$ is 0.12 $\pm$ 0.02 eV for the n-substrate capacitors (positive shifts) and 0.23 $\pm$ 0.02 eV for the p-substrate capacitors (negative shifts). The midgap voltage shifts in these wide-bandgap devices are caused by charge capture at deep interface traps and N-related defects at or near the $\hbox{SiC}{-}\hbox{SiO}_{2}$ interface, which can be enhanced at elevated temperatures by the generation of additional carriers due to the ionization of deep dopants in the SiC during bias-temperature stress.