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Analysis of Carrier Traps in Si3N4 in Oxide/Nitride/Oxide for Metal/Oxide/Nitride/Oxide/Silicon Nonvolatile Memory

The energy level, density and attempt to escape frequency of carrier traps in an Si3N4 film in tunnel oxide/nitride/oxide (ONO) multilayer for metal/oxide/nitride/oxide/silicon (MONOS) nonvolatile memory are investigated by discharging current transient spectroscopy (DCTS). To analyze the electrical properties of carrier traps observed through DCTS, a new model including the tunneling probability of the tunnel oxide film between the Si3N4 film and an Si substrate was proposed. As a result, the electron traps in the Si3N4 film, which are assumed to be related to the threshold voltage decay, i.e. data retention, were found for the first time. The energy level of the electron traps in the Si3N4 film in the ONO multilayer was 0.8–0.9 eV from the conduction band and the density was 1–5×1018 cm-3. The attempt to escape frequency of 2×1014 s-1 was also obtained. The energy level of the hole traps and its density were 0.8–0.9 eV from the top of the valence band and 1–4×1018 cm-3, respectively. The magnitude of the trap density obtained from DCTS shows good agreement with that obtained from memory hysteresis characteristics. These results indicate that their carrier traps are amphoteric traps.