Quantitative characterization of roughness at SiO2/Si interfaces by using cross-sectional high-resolution transmission electron microscopy

We have developed a new method that can quantitatively characterize the correlation length and the asperity height of the roughness at a SiO2/Si interface. This method involves, first, [110] cross-sectional high-resolution transmission electron microscopy (HREM) of the interfaces in very thin specimens (less than or equal to 5 nm thick). Pairs of closely spaced Si atomic columns appear in the HREM image as black dots. The next step involves measuring the HREM image intensity distribution along each black-dot layer parallel to the interface. Then these intensity distributions, which are affected by interfacial roughness, are examined layer-by-layer by Fourier analysis. Moreover, to enable detailed observation of the interfacial roughness, we developed a specimen-preparation technique in which CF4-O-2 plasma etching is used to remove ion-milling artifacts. We demonstrate that this examination can provide quantitative indices of the interfacial roughness. Our method can also detect interfacial roughness that has a correlation length of only a few nanometers.