Characterization of Charge Traps in Metal-Oxide-Nitride-Oxide-Semiconductor (MONOS) Structures for Embedded Flash Memories

A characterization of electron and hole traps in MONOS (metal-oxide-nitride-oxide-semiconductor) structures is studied to improve the reliability of embedded flash memories. Trap distributions are analyzed using a combination of avalanche charge injection and C-V (capacitance-voltage) measurement with varying thicknesses of the oxide and nitride layers in MONOS structures. We consequently find that electron traps mainly locate at both top and bottom oxide/nitride interfaces, whereas hole traps locate at the same interfaces as well as in the nitride bulk. The respective interface trap densities of the electron and hole traps are of the order of 10¹³ and 10¹² cm^-2, and the in hole trap density of the nitride bulk is of the order of 10¹⁸cm^-3. We further investigate the electron trap at the oxide/nitride interface. The mechanism of electron emission from the trap is thermal assisted tunneling, and the electron trap level is distributed between 0.9 eV and 1.7 eV