Performance and reliability optimizations of BE-SONOS NAND Flash using SiON bandgap-tuning tunneling barrier

Bandgap-tunable SiON (oxynitride) tunnel barrier is developed to optimize the performance and reliability of BE-SONOS NAND Flash devices. The HTO O2 layer of the ONO tunnel barrier is replaced by SiON thin films with various refractive index (n) and thickness. We found that with n ≤ 1.72, SiON can provide excellent data retention comparable to conventional BE-SONOS. On the other hand, the erase speed can be greatly improved by using SiON O₂ when n > 1.50. We suggest that hole barrier lowering by SiON is the root cause of such erase speed improvement. Our results suggest an optimal 35 Å SiON O2 layer with n = 1.63 for the best program/erase speed and data retention performance. Finally, a 75 nm BE-SONOS NAND device is fabricated to validate the performances of this concept.