Effect of Annealing Time on Structure, Composition and Electrical Characteristics of Self-Assembled Pt Nanocrystals in Metal-Oxide-Semiconductor Memory Structures

Effect of annealing time on structure, composition and memory characteristics of self-assembled Pt nanocrystals from reduction of an embedded PtOx ultrathin film in metal-oxide-semiconductor (MOS) memory structures were investigated in this work. The morphology and dimension of Pt nanocrystals are obviously dependent on the time of annealing in vacuum. It can be seen that the Pt nanocrystals have a narrow size distribution in the range of 2-3 nm and are well separated in SiO2 matrix annealed for 25 and 50 mins. Meanwhile, it clearly exhibits that the nanocrystals contain mainly pure Pt metal along with a slight amount of Pt silicide by X-ray photoelectron spectroscopy. The increase of Pt silicide amount with increasing the annealing time was observed and the almost saturation amount of Pt silicide was found in the device annealed for 50 mins. A significant charge storage effect, a threefold increase of stored charge density and the superior retention characteristic of the device annealed for 50 mins are achieved most likely due to the small lateral charge loss between Pt nanocrystals, and the decrease of the defect injection effect. The magnitude of the hysteresis (Vfb, hysteresis) almost remained unchanged at different frequencies, indicating that the C-V hysteresis loop results mainly from the change that is trapped inside the potential well of Pt nanocrystals in SiO2 matrix.