Tomographic measurement of buried interface roughness

The authors demonstrate that electron tomography allows accurate measurement of roughness of buried interfaces in multilayer samples. The method does not require the interface to be exposed at the surface of the sample, or does it require a laterally extended sample. Therefore, it enables quantitative site specific analysis of individual elements within semiconductor devices. The standard deviation of the interface distance from a plane fitted to an interface is used as a measure of the interface roughness. The roughness is evaluated in three dimensions, eliminating the uncertainties inherent to roughness measurements on cross-sectional images from a single projection. The apparent interface roughness depends on the signal-to-noise ratio (S/N) arising from electron counting statistics in the data. To eliminate the effect of the S/N, multiple images were collected at each tilt. The roughness was extrapolated to an asymptotic value with a high S/N. This value was taken as the true interface roughness. The method was validated on computer generated data by demonstrating a good agreement between known roughness values and asymptotic values obtained using the above method.