High-k MNOS-Like Stacked Dielectrics for Non-Volatile Memory Application

Charge-trapping memories such as SONOS and MONOS have attracted considerable attention as promising alternatives for next-generation flash memories due to dielectric layer’s scalability, process simplicity, power economy, operation versatility. Nevertheless, the continued miniaturization of the devices forces an application of high-k dielectrics. In this work high-k stacked dielectric structures based on the combination of Hf-based and SiN_x materials were fabricated. Their structural and electrical properties versus deposition conditions are studied by means of FTIR-ATR and high-resolution TEM techniques. All samples demonstrated smooth surface (roughness below 1 nm) and abrupt interfaces between the different stacked layers. No crystallization of Hf-based layers was observed after annealing at 800°C for 30 min, demonstrating their amorphous nature and phase stability upon annealing. Electrical characterization was carried out for all samples through capacitance-voltage (C-V) measurements of MIS capacitors. Uniform C-V characteristics were measured along the samples for all stacks. Besides, significant flat-band hysteresis due to charging of the stacks caused by carrier injection from the substrate was observed for the structures with pure HfO₂ layers.