Ion beam sythesized Au nanocrystals in ultra-thin SiO2

Studies of semiconductor nanocrystals (NC's) in the MOS gate oxide received much interest due to their potential application in non-volatile memory devices. However, the detailed charge storage mechanism is still under discussion. Defect-based charge trapping at NC surfaces is hard to distinguish from storage in the conduction band of NC's. For metal NC's in SiO2 the situation is different. Charge traps at the Au/SiO2 interface are assumed to be negligible at first sight. In this contribution, Au NC's serve as a model system for the charge storage phenomena in NC containing gate oxides with dox<40 nm. For the present study, Au NC's were synthesized by low-energy ion implantation followed by annealing. The Au depth distribution was measured by RBS with high depth-resolution. The process of phase separation during annealing is traced by a series of X-TEM images. A fraction of Au diffuses to the Si/SiO2 interface, forms silicon supersaturated by Au and nucleates liquid Au:Si lenses at the interface. The Au NC's in the SiO2 layer above these lenses are stabilized due to the modified detailed balance of Au-atoms detachment/attachment. Additionally, a zone denuded by NC's forms at the interface. Preliminary electrical results will be presented.