Theoretical Simulation of Backscattering Electron Coefficient for Si xGe1-x/Si Heterostructure as a Function of Primary Electron Beam Energy and Ge Concentration

Abstract

This study aims to investigate the backscattering electron coefficient for
Si
xGe1-x/Si heterostructure sample as a function of primary electron beam energy (0.25-20
keV) and Ge concentration in the alloy. The results obtained have several characteristics
that are as follows: the first one is that the intensity of the backscattered signal above the
alloy is mainly related to the average atomic number of the SixGe1-x alloy. The second
feature is that the backscattering electron coefficient line scan shows a constant value
above each layer at low primary electron energies below 5 keV. However, at 5 keV and
above, a peak and a dip appeared on the line scan above Si-Ge alloy and Si, respectively,
close to the interfacing line. Furthermore, the shape and height of peak and dip broadening
depend on the primary electron energy and incidence position with respect to the
interfacing line. The last feature is that the spatial resolution of the backscattered signal at
the interfacing line is improving by decreasing the primary electron energy (below 5 keV)
and the shared element (Si) concentration. On the other hand, a poor compositional contrast
has been shown at low primary electron energy below 5 keV. For energies above 5 keV,
the spatial resolution becomes weak. These results can be explained by the behavior of the
incident electrons inside the solid (interaction volume), especially at a distance close to the
interfacing line and their chance to backscatter out of the sample. In general, a good
compositional contrast with a high spatial resolution can be achieved at primary electron
energy equal to 1 keV.

Keywords: Monte Carlo model, Backscattering electron coefficient, Si-Ge/Si, Elastic
scattering, Spatial resolution, Compositional contrast.