Errors in nanometrology by SEM

Scanning electron microscopy (SEM) is widely used for the inspection of nanostructures such as nanocrystallites and nanotubes as well as quantum wells and many other sub-micrometre devices. Some published papers show that the apparent size of small details in SEM images appear larger than their real dimension as obtained from transmission electron microscopy, for instance. A possible explanation is deduced here from the use of two simple models for the radial distribution of the emitted secondary electrons to simulate SEM intensity profiles across stripes of increasing widths, D, with respect to the incident probe diameter, d. Supported by a comparison to published data obtained on quantum wells of increasing widths, the results show that the apparent size of small details appears to be larger than their real dimension and the apparent distance between small details may appear less than their real dimension. The same approach permits us to define strategies to minimize the errors when the dimension of details is of the order of or less than the effective resolution of the operated SEM.