Study of Charge Loss Mechanism of SONOS-Type Devices using Hot-Hole Erase and Methods to Improve the Charge Retention

The retention degradation mechanism of NBit/NROM (Eitan et al., 2000) is examined by several unique techniques that promise unequivocal results. The in-situ 150degC electrical testing is used to examine the electron/hole stability. We find no discernable electron/hole lateral migration in the nitride. Next, we apply the refill and soft erase methods (Lue et al., 2005) with various electrical conditions to study the charge loss mechanism. We demonstrate that the refill method can electrically modify the trap energy spectrum, and soft erase method can recover the damages induced by hot-hole stressing. The experimental results show that the vertical charge loss measured by Vg-accelerated retention test at 25degC is highly correlated to the charge loss measured at 150degC baking. Since refill and soft erase techniques alter the trapped electron energy spectrum and the excess-hole distribution differently, these correlations strongly support the vertical charge loss model. Finally, the retention is greatly improved by the refill and soft erase methods and further improvement may be expected by engineering the nitride traps