Large Storage Window in a-SiN_x/nc-Si/a-SiN_x Sandwiched Structure for Nanocrystalline Silicon Floating Gate Memory Application

An a-SiN_x/nanocrystalline silicon (nc-Si)/a-SiN_x sandwiched structure is fabricated in a plasma enhanced chemical vapour deposition (PECVD) system at low temperature (250°C). The nc-Si layer is fabricated from a hydrogen-diluted silane mixture gas by using a layer-by-layer deposition technique. Atom force microscopy measurement shows that the density of nc-Si is about 2×10¹¹cm^-2. By the pretreatment of plasma nitridation, low density of interface states and high-quality interface between the Si substrate and a-SiN_x insulator layer are obtained. The density of interface state at the midgap is calculated to be 1×10¹⁰cm^-2eV^-1 from the quasistatic and high frequency C-V data. The charging and discharging property of nc-Si quantum dots is studied by capacitance-voltage (C-V) measurement at room temperature. An
ultra-large hysteresis is observed in the C-V characteristics, which is attributed to storage of the electrons and holes into the nc-Si dots. The long-term charge-loss process is studied and ascribed to low density of interface states at SiN_x/Si substrate.