ANALYSIS OF LIGHT-ELEMENT SIN SUPERPOSED LAYERS BY MONTE-CARLO SIMULATION OF EELS SPECTRA

A Monte Carlo code, previously set up to simulate electron energy spec tra of carbon films on silicon at 100 kV, has been extended to the ana lysis, at 300 kV, of a Si/SiO2/Si structure; the final goal is the det ermination of the oxygen concentration in SiO(x) precipitates embedded in a Si matrix. The upgrading of the programme has required the intro duction of relativistic kinematics and relativistic corrections to ela stic and inelastic cross sections. The Si/SiO2/Si samples have been pr epared 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 se ctions. The EELS experiments have been performed on planar sections, i n 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 obta ined by the ratioing of the areas under the 0 K and Si K edges, taking advantage of the possibility given by the Monte Carlo simulation to s eparate the background electrons from the one suffering the characteri stic energy loss. The agreement between experiments and calculations i n the case examined is satisfactory, so that the application of this p rocedure to SiO(x) precipitates is promising.