Ion Irradiation through SiO2/Si-interfaces: Non-conventional Fabrication of Si Nanocrystals for memory applications

Si nanocrystals for multi-dot floating-gate memories have been produced by non-conventional ion beam synthesis (IBS). Due to ion beam mixing irradiation with 1015-1016 Si+ cm-2 at 50-100 keV through 50 nm poly-Si and 15 nm SiO2 on (001)Si results in a considerable Si excess within the oxide. At the upper and lower interfaces of the gate oxide, this ion irradiation forms a metastable SiOx (x < 2) composition. Post-irradiation RTA thermal treatment leads to phase separation into Si and SiO2. Adjacent to the recovering interfaces, narrow SiO2 zones become denuded of excess Si. More distant excess Si precipitates as Si NCs in the gate oxide. MOSFET characteristics in terms of write/erase voltage, duration of the programming time, endurance and retention have been evaluated.