Measurement of object height in emission electron microscopy

Abstract

The possibility of measuring the height of an object in emission electron microscopy (EEM) is investigated. If the specimen is characterized by an equipotential surface with the relief h(x,y), the image is equivalent to a specimen with an ideal flat surface and a corresponding distribution of the electric potential φ(x,y)=−E _ext h(x,y). As a consequence of the interaction with the microfields grad φ(x,y), the trajectories of electrons forming the image become deformed, which leads to characteristic image distortion. From EEM, images obtained at different voltages of the extractor V _ext,φ(x,y) can be derived and thereby h(x,y) is reconstructed. If the surface of the specimen is characterized both by a distribution of the potential and in addition by a relief h(x,y), then for the reconstruction one needs an additional EEM image taken at a different voltage of the extractor. The maximal sensitivity to microfields/relief is exploited when using the electron microscope in the mirror operation mode. We illustrate the performance of the method by means of a test pattern of Au on Si. For quantitative comparison, the same structure was investigated by atomic force microscope.