Quantitative measurement of surface roughness of TEM specimens

Abstract

The thickness and the local thickness variation of thin film specimens are critical parameters for many types of AEM analysis. The local thickness variation of the thin film specimen can be estimated from the surface roughness of the specimen. TEM specimens of most materials, especially multi-phase materials, have rough surfaces as observed by secondary electron imaging. However, there is little quantitative assessment of the surface roughness because of the difficulty of specimen thickness measurement. In this study, surface roughness of TEM specimens prepared using chemical etching, electropolishing, and ion beam thinning was measured using a direct phase detecting optical interferometer. This interferometer gives a quantitative three dimensional map of the surface topography with a depth resolution of ∼0.7 nm by converting digitized light intensity at each point of a 1024×1024 array into the optical path difference using the three-measurement algorithm. The horizontal resolution of the interferometer (∼340 nm) is limited by optical diffraction and is poor by the TEM standard. The quantitative information obtained by the interferometer is complimentary to the secondary electron imaging in STEM or PEG SEM for characterizing TEM specimen surfaces.