THICKNESS SCALING LIMITATION FACTORS OF ONO INTERPOLY DIELECTRIC FOR NONVOLATILE MEMORY DEVICES

This paper describes the scaling limitation factors of ONO interpoly d ielectric thickness, mainly considering the charge retention capabilit y and threshold voltage stability for nonvolatile memory cell transist ors with a stacked-gate structure, based on experimental results. For good intrinsic charge retention capability, either the top- or bottom- oxide thickness should be greater than around 6 nm. On the other hand, a thicker top-oxide structure is preferable to minimize degradation d ue to defects, It has been confirmed that a 3.2 nm bottom-oxide shows detectable threshold voltage instability, but 4 mm does not. Effective oxide thickness scaling down to around 13 nm should be possible for f lash memory devices with a quarter-micron design rule.