Probing defects in 3D NAND flash memory with temperature-dependent leakage current

초록

This study investigated the defect profiles of highly stacked 3D NAND flash memory using trap-assisted leakage current analysis. By extracting the activation energy (E-a), we examined leakage mechanisms under hydrogen (H) and fluorine (F) gas annealing conditions for device passivation. This temperature-dependent leakage analysis provides a stress minimized probing technique for evaluating trap distributions in 3D NAND devices. This suggests the presence of abundant trap states in the polycrystalline silicon (poly-Si) channel, where trapped carriers are readily activated by the electric field from control gates. In contrast, the E-a under F passivation remained field-independent, and the leakage current increased with temperature. This indicates that while F passivation suppresses bulk poly-Si traps, temperature-sensitive defects at the poly-Si/SiO2 interface persist. Devices with F passivation showed larger subthreshold swing due to higher interface trap densities but higher transconductance (g(m)) compared to H-passivated devices. This is attributed to reduced trap density inside the poly-Si channel in the F-passivated condition. Series resistance (R-s) and its corresponding E-a further confirmed this behavior; F-passivated devices exhibited lower R-s and reduced E-a of R-s, implying that energy barriers at grain boundaries (GBs) were effectively suppressed. Finally, retention characteristics were also improved under F passivation, supporting the conclusion that carrier transport in the poly-Si channel is more strongly hindered by GB traps in H-passivated devices.

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