Film thickness measurement by a cross-sectional SEM

It is well known that metal films evaporated or sputtered in vacuum are not continuous at a thickness of less than several ten nanometers, but show fine particle distributions or have island granularities as thickness increases. Morphorogy of deposited thin films have been one of the major investigation areas in nucleation, crystal growth, crystal surface studies and so on. There is a room for discussions concerning physical properties such as non-ohmic conductivities of the thin metal films in relation to morphorogy.However, almost all micrographs obtained by electron microscopes, both TEMs and SEMs, showing such thin metal films are two dimensional, that is, there is not much information how deposited films are growing on the substrate. Owing to the recent development of a high resolution SEM having a probe size of smaller than 1nm by a combination of highly excited condenser-objective lens and a field emission electron source, three dimensional information for the thin film can be provided as shown in Fig. 1. These specimens are Pt sputter-coated on Si wafers at room temperature with a so-called “magnetron” sputter coater, and then fractured for crosssection study by the HRSEM.