DIELECTRIC-BREAKDOWN AND CURRENT CONDUCTION OF OXIDE NITRIDE OXIDE MULTILAYER STRUCTURES

We present a detailed study on the effect of bottom- and top-oxide thicknesses on the current conduction and the dielectric breakdown of oxide/nitride/oxide (ONO) multi-layer dielectrics. An abrupt reduction in current is observed when the oxide that is contiguous to the anode is thicker than 3 nm. This leads us to conclude that the thick oxide (>3 nm) impedes hole injection from anode into nitride. The injected charge-to-breakdown (Q(BD)) and the time-to-breakdown (T(BD)) are measured to study the breakdown mechanism. We observe that a substantial increase in T(BD) occurs in spite of the reduction in Q(BD) when the thick oxide is contiguous to anode. This phenomenon is explained by a hole-induced breakdown model for the ONO structure with thin bottom- and top-oxides (<3 nm). Hole injection is suppressed by the thick oxide that is contiguous to anode. The increase in T(BD) is attributed to the reduction in injected holes. We conclude that the dielectric breakdown of the ONO.structure with the thin oxides is induced by injected holes. We also observe that the thermal activation energy of the T(BD) changes at 3 nm in bottom-oxide thickness under negative gate bias. Therefore, this value of 3 nm is determined as a threshold thickness for the change of the breakdown mechanism.