New degradation mode of program disturb immunity of sub 90-nm node split-gate SONOS memory

We found a new-mode degradation of program-disturb immunity in split-gate SONOS memory with 90-nm technology node. The degradation proved to be caused by hot holes created during erase operation: they can reach word gate (WG) oxide over memory gate (MG). The captured holes within the WG oxide reduce effective inhibit-field that is applied to the WG of non-selected cells during program operation, thereby degrading program-disturb immunity. Hole-trapping defects in the WG oxide seem to be induced in cell fabrication processes, especially in processes using plasma excitation, not by program/erase (P/E) cycling. The degradation was suppressed by implementing a proper gate protection diode.