Effects of Nitridation on the Electrical Properties of MONOS Nonvolatile Memories

We investigated the mechanism that causes decreases in data erase and data retention times of metal-oxide-nitride-oxide-semiconductor (MONOS) nonvolatile memories when nitridation is applied to tunnel oxide film. Data erase and data retention times of MONOS nonvolatile memories decrease as nitrogen concentration in tunnel oxide film increases. Decreasing data erase times result from increasing hole current caused by lowering of the barrier height of the hole between the valence band of the tunnel oxide film and the silicon substrate. Lowering of barrier height is caused by nitridation of the tunnel oxide film. Decreases in data retention times of MONOS nonvolatile memories caused by nitridation of tunnel oxide film are due to increases in both electron current and hole current during data retention. Hole current increases as the temperature increases, but electron current does not change. Therefore, increases in electron current are due to increases in interface trap density between the silicon substrate and tunnel oxide film caused by nitridation. Increases in the hole current conducted through the tunnel oxide film caused by nitridation are due to the generation of hole traps in tunnel oxide film during nitridation. An activation energy of 0.12-0.14 eV was obtained for the hole current conducted through the tunnel oxide film.