Temperature-induced interfacial intermixing and trap modulation in ONO-based flash memory capacitors

We investigated the effects of hydrogen annealing on the electrical properties and reliability of NAND flash memory capacitors featuring an oxide-nitride-oxide charge-trap dielectric stack. A thin interfacial SiO<i>_x</i>N<i>_y</i>transition layer, inherently formed between SiO₂and Si₃N₄during processing, was analyzed for compositional and structural changes across annealing temperatures ranging from 300 °C to 500 °C. Key electrical characteristics, including capacitance-voltage behavior, programming speed, data retention, and endurance, were evaluated as a function of annealing temperature. The results demonstrate that annealing in forming gas at temperatures between 400 °C-450 °C optimally enhances device performance by increasing charge injection, reducing interface trap density, and stabilizing the memory window. Structural analysis by transmission electron microscopy and electron energy-loss spectroscopy revealed improved passivation of interface traps and the formation of deep trap states in the nitride, which together contribute to improved charge retention and reduced charge loss through trap-assisted tunneling.