Engineering of the nitride charge trapping layer for non-volatile memory

Three different nitride-based trapping layers have been investigated: a standard silicon nitride, a Silicon-rich and an Oxygen-rich silicon nitride deposited by Low Pressure Chemical Vapor Deposition (LPCVD). First the physical properties of the films are studied. A gap of 5.3 eV and a refractive index of 2.07 were found for the standard Silicon Nitride using spectroscopic ellipsometry. Excess silicon reduces the gap to 4.7 eV and increases the refractive index to 2.24. Excess oxygen increases the gap to 5.8 eV and reduces the refractive index to 1.84. Hydrogen content in the three layers was also investigated by infrared Multi Internal Reflection (MIR) Spectrometry and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). Then electrical characterization was performed on the three different trapping layers in a SONOS structure. Program/Erase characteristics and data retention were tested in Fowler-Nordheim (FN) mode. Excess silicon improves erasing but degrades data retention while excess oxygen slows erasing characteristic but improves data retention.