Breakdown spots propagation in ultra-thin SiO2 films under repetitive ramped voltage stress using conductive atomic force microscopy

In this work, the post-breakdown behavior of ultra-thin (3.4 and 5 nm) SiO2 films under repetitive ramped voltage stress (RVS) was studied by using conductive atomic force microscopy (AFM). Our experimental results showed that both the 3.4- and 5-nm-thick SiO2 films have similar pre-stressed and post-stressed current-voltage (I-V) characteristics. From the topography and current images, however, we found that the breakdown spots (BDS) on 3.4-nm-thick SiO2 surface propagated as the number of RVS increases. For 5-nm-thick samples, no such BDS propagation was observed. We suspected that structural damage of weak spots near the stressed point induced by the higher defect density and higher electric field across the oxide films in the 3.4-nm-thick samples is the main reason to cause this BDS propagation.