First Theoretical Modeling of the Bandgap-Engineered Oxynitride Tunneling Dielectric for 3D Flash Memory Devices Starting from the Ab Initio Calculation of the Band Diagram to Understand the Programming, Erasing and Reliability

Bandgap engineered (BE) tunneling barrier using oxynitride (SiON) is a key enablement of charge-trapping devices adopted in commercial 3D Flash memories. For the first time we use the ab initio quantum simulation to model the bandgap for oxynitride, and explain the measured data of programming, erasing, and reliability aspects. Various nitrogen concentration effects are studied extensively and it is demonstrated that a modest nitrogen-doped SiON provides adequate valence band offset (VBO) of ∼3.2eV from silicon, which is ∼1.4eV smaller than the conventional silicon oxide so that efficient –FN (Fowler-Nordheim) hole erasing performance is enabled for 3D Flash memory products. Meanwhile, sufficient hydrogen concentration is important to passivate the dangling bonds of oxynitride and stabilize the bandgap to suppress interfacial states. An interesting finding is that nitrogen mostly affects VBO while the conduction band offset (CBO) is rarely reduced from oxide, thus providing good electron retention. After a strong P/E cycling (>10K), it is suggested that oxynitride not only generates interfacial state (Dit) but also bulk traps that degrades the endurance.