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

Abstract

The energy level, density and attempt to escape frequency of carrier traps in an Si 3 N 4 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 Si 3 N 4 film and an Si substrate was proposed. As a result, the electron traps in the Si 3 N 4 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 Si 3 N 4 film in the ONO multilayer was 0.8–0.9 eV from the conduction band and the density was 1–5×10 18 cm -3 . The attempt to escape frequency of 2×10 14 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 1–4×10 18 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.