Annealing influence on stoichiometry and band alignment of 4H-SiC/SiO2 interface evaluated by x-ray photoelectron spectroscopy

Post oxidation annealing (POA) is a crucial technique for enhancing the performance of SiC metal-oxide-semiconductor field effect transistors (MOSFETs). This study investigates the impact of nitrogen-based POA on the 4H-SiC/SiO2 interface, utilizing x-ray photoelectron spectroscopy to assess changes in stoichiometry and band alignment. We discovered that high-temperature nitrogen POA significantly refines the interface quality, shifting the SiOxCy binding energy from 101.3 eV (at 400 degrees C) to 102.1 eV (at 1150 degrees C) and reducing the C:Si ratio from 1.120 (at 400 degrees C) to 0.972 (at 1150 degrees C), indicating reoxidation and transition from C-rich interface to Si-rich interface. Despite improvements, the conduction band offset at the interface, decreases from 2.59 eV to 1.62 eV with increasing annealing temperature, suggesting a higher likelihood of electron tunneling. This finding underscores the necessity of evaluating band offsets introduced by POA to ensure the reliability of SiC MOSFETs. Additionally, excessive Ar ion etching introduces residual Ar and surface charges, causing band bending and an increased density of states in the valence band of the 4H-SiC substrate.