Evolution of leakage paths in Hf O2 Si O2 stacked gate dielectrics: A stable direct observation by ultrahigh vacuum conducting atomic force microscopy

A conducting atomic force microscopy (C-AFM) in ultrahigh vacuum (UHV) is used to directly observe the evolution of leakage path in Hf O2 Si O2 stacked gate dielectrics. Thanks to the UHV environment, reproducible results for both positive and negative tip biases are obtained without material formation on the surface, which has been a problem for atmospheric C-AFM. It is found that the density of leakage spots increases exponentially as a function of tip bias and that it is a large factor for leakage current increase.