IMPROVING RADIATION HARDNESS OF EEPROM FLASH CELL BY N2O ANNEALING/

The effects of an N2O anneal on the radiation effects of a split-gate electrical erasable programmable read only memory (EEPROM)/flash cell with a recently-proposed horn-shaped floating gate were studied. We ha ve found that although the cells appear to survive 1 Mrad(Si) Co-60 ir radiation without data retention failure, the write/erase cycling endu rance was severely impeded after irradiation. Specifically, the write/ erase cycling endurance was degraded to 20 K from the pre-irradiation value of 50 K, However, by adding an N2O annealing step after the inte rpoly oxidation, the after-irradiation write/erase cycling endurance o f the resultant cell can be significantly improved to over 45 K, N2O a nnealing also improves the after-irradiation program and erase efficie ncies. The N2O annealing step therefore presents a potential method fo r enhancing the robustness of the horn-shaped floating-gate EEPROM/fla sh cells for radiation-hard applications.