Characterization on the current-voltage curves of ultrathin silicon dioxides incorporated with fluorine and/or nitrogen

The current-voltage (I-V) characteristics of ultrathin silicon dioxides incorporated with fluorine (F) and/or nitrogen (N) are investigated in this paper. A generalized trap-assisted tunnelling model is used to simulate the leakage current at electric fields of 4-10 MV cm^-1. This model can directly derive trap energy level (Φ_t) and trap concentration (N_t) values from simple I-V curves. From the simulation results, trap energy levels of fluorine and nitrogen are characterized to be 1.62-1.83 and 2.0-2.25 eV, respectively, while the trap concentrations range between 10¹⁵ and 10¹⁸ cm^-3 for F or N impurities depending on the experimental conditions. With the introduction of nitrogen into SiOF films, Φ_t and N_t values change significantly due to the formation of complex compounds of Si, O, F and N in silicon dioxides. Some possible explanations are given to clarify this mixing effect.