Impact of tunnel film oxynitridation on band-to-band tunneling current and electron injection in flash memory

The impact of the use of oxynitride tunnel film on write, erase and read operations of flash memories was investigated. We found that during electron ejection from a floating gate into a drain, band-to-band tunneling currents of flash memory cells with tunnel films having a high degree of nitridation are two orders of magnitude smaller than that of flash memory cells with oxide tunnel films. Consequently, higher-nitridation tunnel films improve the endurance characteristics of flash memory. However, during electron injection from a channel into the floating gate, Fowler-Nordheim tunneling gate currents of flash memory cells with higher-nitridation tunnel films are two orders of magnitude smaller than that of flash memory cells with oxide tunnel films. Moreover, the threshold voltage of flash memory cells with oxynitride tunnel films is 0.24-0.48 V smaller than that of flash memory cells with oxide tunnel films in read operations. These results can be explained by the modification of the electric field under oxynitride tunnel films due to the formation of donor layers, which is induced by nitridation of tunnel oxide films.