Band engineered tunnel oxides for improved TANOS-type flash program/erase with good retention and 100K cycle endurance

Abstract

We demonstrate for the first time improved program, erase, and endurance for charge trap flash TaN-Al2O3-Si3N4-“Tunnel-oxide (TO)”-Si MOSFETs through band engineered tunnel oxides (BETO). Several high-K dielectrics (HfO2, HfSiO, Al2O3, Si3N4) and tunnel stack sequences (SiO2-high-k, SiO2-high-k-SiO2) are compared. New results are as follows: SiO2/Al2O3 (OA) BE-TO and SiO2/Si3N4/SiO2 (ONO) BE-TO ΔVth windows improve ≫300% vs. standard SiO2-TO. Both OA and ONO stacks endure P/E cycles to at least 100K cycles maintaining a window ≫4V. Results are consistent with a model based on high-k conduction/valence band offsets. Increased erase efficiency for BE-TO enables improved endurance without sacrificing P/E window due to lower P/E voltage stressing. These large, enduring windows are favorable for multi-level cell application and may extend TANOS flash beyond the 20nm node.