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 cor relation length and the asperity height of the roughness at a SiO2/Si inter face. This method involves, first, [110] cross-sectional high-resolution tr ansmission electron microscopy (HREM) of the interfaces in very thin specim ens (less than or equal to 5 nm thick). Pairs of closely spaced Si atomic c olumns appear in the HREM image as black dots. The next step involves measu ring the HREM image intensity distribution along each black-dot layer paral lel to the interface. Then these intensity distributions, which are affecte d 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 examinat ion can provide quantitative indices of the interfacial roughness. Our meth od can also detect interfacial roughness that has a correlation length of o nly a few nanometers.