Observation of Soft-Breakdown in Ultra-Thin SiO2 Films under Repetitive Ramped Voltage Stress by Using Conductive Atomic Force Microscopy
Y-L Wu, S-T Lin and J-C Liao
National Chi-Nan University, TW
conductive atomic force microscopy, oxide breakdown, soft breakdown
The degradation and breakdown characteristics of ultra-thin SiO2 (Tox = 5 nm) were investigated by using conductive AFM (C-AFM). Repetitive ramped voltage stress (RVS) was applied through the C-AFM tip to the oxide with polarity that electrons were injected from the substrate. The I-V characteristics, topographies and current images after repetitive RVS were all monitored by C-AFM. Contrary to what has been reported in the literature, we observed that the threshold voltage Vth in the I-V characteristics shifted back and forth rather than along one direction of the voltage axis during repetitive RVS. We also found that the breakdown spots propagate along some fixed direction as the number of repetitive RVS increases. No sign of hard breakdown was observed even after 45 times of RVS applied.
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Nanotech 2005 Conference Program Abstract