Charge trapping in interpoly ONO film

The stacked capacitor structure used in DRAM cells usually takes the form of an interpoly capacitor where the dielectric layer is sandwiched between two polycrystalline silicon plates. The charge trapping characteristics of the oxide-nitride-oxide (ONO) film in an interpoly capacitor structure has been investigated. The hole trapping characteristics are observed under constant current stress. The trapped charge centroid is found to be localised at the top oxide/nitride interface under both stress polarities. The larger hole trapping observed under negative stress correlates to a shorter electrical lifetime.