Effects of Hydrogen on Endurance Characteristics in NAND Flash Memories

Abstract

This study comprehensively investigates the effect of hydrogen content in forming gas annealing (FGA) on the endurance of NAND flash memories by statistically analyzing the transconductance (Gm,max) characteristics. The Gm,max degradation (ΔGm,max) worsened with higher cycling temperature, delayed time period from erasing to programming (tEP) operation, and higher word-line bias (VA) during tEP. Moreover, these effects become more pronounced as the hydrogen content in FGA increases. Using the measured Gm,max distributions and Monte -Carlo TCAD technology, the activation energy (EA) of oxide damage creation can be extracted. The extracted EA values were 50 meV and 160 meV for the diluted (4%) and pure (100%) hydrogen samples, respectively. This suggests that a higher hydrogen concentration results in more ionized hydrogen atoms remaining in the oxide layer. During tEP, these hydrogen ions can drift near the Si/SiO2 surface, where they may react to form trap states. EA is revealed to have a linear relationship with respect to VA, where the slope is independent of the hydrogen content in FGA.