Analysis of light elements in superposed layers by Monte Carlo simulation of EELS spectra

A Monte Carlo code, previously set up to simulate electron energy loss spectra of carbon films on silicon at 100 kV, has been extended to the analysis, at 300 kV, of a Si/SiO₂/Si structure; the final goal is the determination of the oxygen concentration in SiO_x precipitates embedded in a Si matrix. The upgrading of the programme has required the introduction of relativistic kinematics and relativistic corrections to elastic and inelastic cross sections.The Si/SiO₂/Si samples have been prepared by CVD deposition of a 16 nm thick silicon film onto a silicon wafer covered with a 11 nm thick thermal oxide. The thickness of both films has been checked by transmission electron microscopy on cross sections. The EELS experiments have been performed on planar sections, in regions of different thickness; the EELS spectra have been acquired with a parallel 666 Gatan spectrometer, fitted to a Philips CM 30 TEM/STEM, operating at 300 kV. The stoichiometry of the SiO_x can be obtained by the ratioing of the areas under the OK and SiK edges, taking advantage of the possibility given by the Monte Carlo simulation to separate the background electrons from the one suffering the characteristic energy loss. The agreement between experiments and calculations in the case examined is satisfactory, so that the application of this procedure to SiO_x precipitates is promising.