Influence of annealing environment on the ALD-Al₂O₃/4H-SiC interface studied through XPS

The instability of Al₂O₃/4H-SiC interface at various process temperatures and ambient is investigated by the annealing of Al₂O₃/4H-SiC in low vacuum conditions as well as in N₂ environments. Atomic layer deposited Al₂O₃ on a 4H-SiC substrate with 3, 6 and 10 nm of thicknesses is treated at 300, 500, 700 and 900 °C under the vacuum level of 10⁻¹ torr. The as-deposited and annealed structures are analyzed using x-ray photoelectron spectroscopy. It is hypothesized that the minute quantity of oxygen present in low vacuum conditions diffuses through thin layers of Al₂O₃ and helps in forming SiO₂ at the interface even at low temperatures (i.e. 300 °C), which plays a pivotal role in determining the electrical properties of the interface. It is also proved that the absence of oxygen in the ambient prevents the formation of SiO₂ at low temperatures. Additionally, it is observed that Al–OH is present in as-deposited layers, which gradually reduces after annealing. However, at around 700 °C, the concentration of oxygen in the whole structure increases to maximum and reduces at 900 °C. (paper)