Further Investigation on Mechanism of Trap Level Modulation in Silicon Nitride Films by Fluorine Incorporation

Modulation of electron trap levels in fluorine (F) incorporated silicon nitride (SiNx) films was investigated by temperature-dependent discharging current transient spectroscopy (DCTS). The shallower trap level is observed in F incorporated SiNx films. F incorporation has more influence on the energy level of traps in the most Si rich SiNx film (x = 1.05) than the other SiNx films (x = 1.11 and 1.23). Considering with physical analyses by secondary ion mass spectrometry (SIMS), X-ray-reflectometry (XRR) and X-ray photoelectron spectroscopy (XPS), we found that depth profiles of F are different among these SiNx films because F atoms can diffuse easily as increasing of Si content. It is plausible that the F incorporation around the charge centroid causes trap level shallowing. It is inferred that F atom terminates Si dangling bond and F-terminated puckered nitrogen vacancy originates the extracted very shallow trap level, which is suggested from first-principles calculations.