Charge Loss Improvement in 3D Flash Memory by Molecular Oxidation of Tunneling Oxide

Bandgap Engineered (BE) tunnel barriers utilizing oxynitride (SiON) play a crucial role in the development of charge trapping devices used in commercial 3D flash memories. Theoretical analysis indicates that SiON provides an adequate valence band offset (VBO) to offer efficient hole tunneling for the erasing, while the conduction band offset keep sufficient to maintain electron retention. SiON is quite flexible in adjusting its nitrogen content, contributing to various endurance and retention properties. In this work, we explore two oxidation methods to optimize the BE SiON. Molecular-mode oxidation operates in a diffusion-based manner, leading to deeper oxidation throughout the entire SiON. In contrast, radical-mode oxidation, classified as an exchange-mode process, primarily targets the SiON surface due to its exceptionally low activation energy, resulting in rapid oxidation. Using our 3D AND-type NOR Flash memory, both molecular and radical oxidation techniques were applied to the BE-MANOS device for chip-level reliability study. Both molecular and radical oxidation to change hydrogen distribution and content in SiON, which results in reduced interface state trap generations in SiON, shows obvious improvements (15-25%) in post-cycled retention performances.