Comparison of experimental and Monte Carlo simulated BSE spectra of multilayered structures and `in-depth' measurements in a SEM*

Experimental measurements of the energy distribution of the backscattered electrons (BSE) in a SEM were made with an improved electrostatic toroidal spectrometer and Monte Carlo simulations were used to calculate these BSE spectra. Pure materials, thin films on a substrate and multilayered `sandwich'-structures were used to record and calculate the energy spectra. The experimental BSE spectra were compared with the results of Monte Carlo simulations. It is shown that from the BSE spectral curves, the depth and thickness of buried films in multilayered structures or of different subsurface inhomogenities can be estimated. The relation between the penetration depth inside the specimen from which the BSE were reflected and the energy of the BSE is given by the Thomson-Whiddington law. The accuracy for the determination of the depth of subsurface layers is generally about 10-20% using appropriate acceleration voltages.