Mobile ion-induced data retention failure in NOR flash memory cell

Data retention failures due to nonoptimized processes in NOR-type flash memory cells are presented. Contrary to the charge leakage through defective oxide dielectric surrounding the floating gate, the data loss observed depends on whether the bit line contact is close to the cell or not. It is found that the data loss exhibits a charge-state dependence during baking stresses as well as temperature dependence. Based on experimental results, sodium movement in sidewall spacers is established as an origin for the data retention failure in NOR-type flash memory cells. Employing a thin nitride overlayer results in a good data retention, supporting the hypothesis of sodium movement.