Impact of the NO annealing duration on the SiO2/4H-SiC interface properties in lateral MOSFETs: The energetic profile of the near-interface-oxide traps

In this work, the effects of the duration of the post deposition annealing (PDA) in nitric oxide (NO) on the properties of SiO2/4H-SiC interfaces in n-channel lateral MOSFETs are investigated, with a special focus on the modifications of the energy profile of near-interface-oxide traps (NIOTs). For this purpose, the electrical characteristics of lateral MOSFETs were studied in strong inversion conditions, monitoring the threshold voltage variations due to charge trapping effects. To determine the energetic position of the NIOTs with respect of the SiO2 conduction band edge, the Fermi level position in the insulating layer was evaluated by TCAD simulations of the band diagrams. PDAs of the gate oxide of different duration resulted into similar shape of the energetic profile of the traps inside the insulator with respect of the SiO2 conduction band edge, but with different magnitude. Finally, the effective decrease of the insulator traps is demonstrated despite a saturation of the interface state density under prolonged PDAs and in particular the charge trapped at the NIOTs is reduced from 1 to 2 x 1011 cm-2 down to 3 x 1010 cm-2 varying the PDA duration from 10 up to 120 min in NO at 1175 degrees C.