Fixed nitrogen atoms in the SiO2/SiC interface region and their direct relationship to interface trap density

Nitrogen atoms fixed in the SiO2/SiC interface region were studied by x-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) measurements. A thin oxide film (<5 Å) formed during annealing in an NO atmosphere on a (0001) 4H-SiC surface, incorporating nitrogen atoms into the interface region. Even after complete removal of the oxide layer by etching in hydrofluoric acid, XPS spectra clearly showed a strong N 1 s peak, revealing the presence of fixed nitrogen atoms with an areal density of 1014 cm−2 in the interface region. To evaluate their influence on interface traps, metal-oxide-semiconductor capacitors were formed by deposition of a gate oxide layer. The fixed nitrogen atoms decrease the interface trap density after post-annealing at high temperature.