Thickness Determination of Ultra-Thin Films on Si Substrates by EPMA

Abstract.

Results from thickness determination of single-element ultra-thin (<10 nm) films by electron probe microanalysis (EPMA) are presented. The studied samples were Ge, Sn, Ag and Au thin films deposited by resistive evaporation on Si substrates. The thickness of the films was controlled during evaporation by means of a quartz crystal, previously calibrated using samples with overlayers of different thicknesses (>20 nm) measured by Rutherford backscatter spectrometry and optical interferometry. EPMA measurements were performed on an electron microprobe CAMECA SX-50, with incident electron energies ranging from 4 keV to 20 keV. Film thicknesses were derived from the measured k-ratios using the analytical programs X-Film and Layerf and the Monte Carlo simulation code Penelope. The ionization cross sections used in the simulations were calculated with the distorted-wave Born approximation. Film thicknesses obtained from the EPMA measurements using the various computational methods are compared with those measured with the quartz crystal. The maximum relative difference between results from the different techniques does not exceed 5%.