Formation and passivation of interface traps in irradiated n-channel power VDMOSFETs during thermal annealing

The annealing of γ-ray irradiated commerical n-channel power VDMOSFETs at elevated temperature is investigated. Rebound effect, observed in the samples annealed with positive gate bias, is primarily the consequence of a very long-term postirradiation interface-trap buildup. At later annealing times, a significant decrease in the number of interface traps is observed. In order to explain obtained results, we propose a modification to the hydrogen ion transport model for the formation of interface traps. According to our model, H+ ions created during irradiation are responsible only for the initial fraction of the total interface-trap buildup. The other fraction is attributed to H+ ions produced when molecular hydrogen, released at the SiSiO2 interface in interface-trap creation reaction, diffuses back into the bulk of the oxide and is cracked at positive charge centres. Simultaneously with the generation of interface traps, their passivation also takes place. Passivation, probably caused by hydrogen atoms and water molecules, becomes predominant at later annealing times, leading to the decrease in interface-trap density.