Bottom-oxide scaling for thin nitride/oxide interpoly dielectric in stacked-gate nonvolatile memory cells

The authors present results concerning the nitride-oxide (NO) interpoly dielectric in nonvolatile memories. Optimized NO films with a thick top oxide and a thin nitride structure offer sufficient charge retention capability in the 12-nm effective oxide thickness region. However, this structure shows an anomalous threshold voltage increase due to the back tunneling of electrons from the NO film to a floating gate. Such electrons can be injected into the NO film during programming and baking. The magnitude of this voltage depends on the NO film structure and the electric field during the program and bake procedure. Therefore, these phenomena must be taken into consideration in designing the cell structure and its operating conditions. The results obtained are also useful when considering ONO (oxide-nitride-oxide) scaling in the thin bottom-oxide region for nonvolatile memory applications