Bias-Temperature Instabilities in 4H-SiC Metal–Oxide–Semiconductor Capacitors (2012)

Bias-temperature instabilities (BTIs) are investigated for n- and p-substrate 4H-SiC metal–oxide–semiconductor (MOS) capacitors. The midgap voltage <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(V_{ \rm mg})$</tex></formula> 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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{\rm mg}$</tex></formula> shifts are less than 0.5 V for electric fields of magnitudes of approximately <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex> </formula> 3.1 MV/cm for up to one day of stress at 150 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex> </formula> or 20 min of stress at 300 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex></formula> . Switched-bias stressing at 150 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex></formula> 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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $V_{\rm mg}$</tex></formula> shifts, the effective activation energy for BTI that is measured between room temperature and 250 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex></formula> is 0.12 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex></formula> 0.02 eV for the n-substrate capacitors (positive shifts) and 0.23 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex></formula> 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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{SiC}{-}\hbox{SiO}_{2}$</tex> </formula> 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.