The Study on Charge-trapping Mechanism in Nitride Storage Flash Memory Device

Abstract

In this work, the charge-trapping distributions of polysilicon-oxide-nitride-oxide-silicon (SONOS) structure are studied. The trapping energy level of SiN_x films with different composition ratio deposited by low-pressure chemical vapor deposition (LPCVD) were first characterized by photoluminescence (PL) measurement. Moreover, using F-N/CHE program and charge pumping techniques, the vertical location and the lateral distribution of programmed charges are investigated in the nitride films with different composition ratio. The study offers strong evidence that the density of charge-trapping levels in the Si-rich nitride is higher than the standard nitride. A simple qualitative model and calculation explains that the trapping level distributions in the SiN_x films are shallower by increasing relative Si-content. Furthermore, we have observed the nitride trap vertical location was changed by adjusted Si/N composition ratio. And the lateral distribution of hot electron programmed charges in the modified nitride is broader than that in the standard nitride because it offered more charge-trapping sites and shallower charge-trapping levels. In summary, the study can help researchers to understand the nitride charge-trapping mechanism and the analysis of optical/electrical characteristics.