Mechanisms and solutions to gate oxide degradation in flash memory by tunnel-oxide nitridation engineering

Increasing attention has been paid to the peripheral gate-oxide integrity degradation of Flash memory devices that is induced by the tunnel-oxide nitridation. In this letter, the mechanisms of tunnel-oxide nitridation-induced degradation are characterized. We report that both a local oxide thinning effect and nitrogen residue will impact the integrity of gate-oxide. Minimizing the local thinning effect with an in situ steam generation (ISSG) oxidation process and removing the nitrogen residues from the silicon wafer surface by either an additional sacrificial oxide process or over-dip are proven to be useful in recovering the gate-oxide integrity. An optimum approach with the tunnel-oxide nitridation is proposed in this work that results in comparable or even better gate-oxide property than other approaches that have no tunnel-oxide nitridation process.