Influence of ISSG tunnel oxide with decoupled plasma nitridation on erase characteristic of NOR-type floating-gate flash memories

• Influence of ISSG tunnel oxide layer with DPN on the erase reliability was investigated.
• The erase performance of flash cells was significantly degraded when DPN was applied.
• The bulk oxide traps contribution to Vth shift is increased more notably in ISSG tunnel oxide with DPN.
• The bulk trap density will be increasing with the nitrogen from DPN.
• The high bulk nitrogen concentration is deleterious to the reliability of flash cell.

This paper investigated the influence of ISSG (in situ steam generation) tunnel oxide layer with decoupled plasma nitridation (DPN) on the erase reliability of NOR-type floating-gate flash memory devices. The experimental results demonstrated that the tunnel oxide with ISSG process achieves better thickness uniformity and higher breakdown voltage than that with conventional dry oxidation process. However, the erase performance of flash cells was significantly degraded when DPN was applied to the ISSG oxide. The higher bulk nitrogen content from DPN process could lead to more bulk traps generation by substituting the strong Si–O bonds for the weak Si–N bonds in the tunnel oxide. During program/erase cycling, the more electrons trapped in the bulk tunnel oxide the less the FN erase electric field will be, which is responsible for the degradation of erase performance.