Microchim. Acta 145, 13–17 (2004) DOI 10.1007/s00604-003-0120-3 Original Paper Thickness Determination of Ultra-Thin Films on Si Substrates by EPMA Christiani S. Campos 1;3 , Marcos A. Z. Vasconcellos 1 , Xavier Llovet 2; , and Francesc Salvat 3 1 Instituto de Fı ´sica, Universidade Federal do Rio Grande do Sul (UFRGS), 91501-970 Porto Alegre, RS, Brazil 2 Serveis Cientı ´fico-T ecnics, Universitat de Barcelona, Lluı ´s Sol e i Sabarı ´s 1-3, E-08028 Barcelona, Spain 3 Facultat de Fı ´sica (ECM), Universitat de Barcelona, Societat Catalana de Fı ´sica, Diagonal 647, E-08028 Barcelona, Spain Received May 22, 2003; accepted October 20, 2003; published online March 8, 2004 # Springer-Verlag 2004 Abstract. Results from thickness determination of single-element ultra-thin ( < 10 nm) films by electron probe microanalysis (EPMA) are presented. The stud- ied samples were Ge, Sn, Ag and Au thin films depos- ited by resistive evaporation on Si substrates. The thickness of the films was controlled during evapora- tion by means of a quartz crystal, previously calibrated using samples with overlayers of different thicknesses ( > 20 nm) measured by Rutherford backscatter spec- trometry and optical interferometry. EPMA measure- ments were performed on an electron microprobe CAMECA SX-50, with incident electron energies rang- ing 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 sec- tions used in the simulations were calculated with the distorted-wave Born approximation. Film thicknesses obtained from the EPMA measurements using the var- ious computational methods are compared with those measured with the quartz crystal. The maximum rela- tive difference between results from the different tech- niques does not exceed 5%. Key words: EPMA; Monte Carlo simulation; thickness determination The determination of thicknesses of very thin films (fre- quently less than several tens of nanometres) deposited on substrates is important for practical applications in semiconductor research and thin-film technology. Mea- surements of inner-shell ionization cross sections are also usually performed using very thin films, to mini- mize multiple scattering effects; the accurate determi- nation of the active film thickness is crucial to infer absolute cross section values from these experiments. Measurements of thin-film thicknesses can be per- formed by a number of different techniques such as electron probe microanalysis (EPMA), Rutherford backscattering spectrometry (RBS), optical interfero- metry (OI), etc. EPMA is a non-destructive technique, originally developed for determining the composition of bulk samples. In recent years, it has been applied to the determination of both thickness and composition of thin films and multilayered structures. The method is based on the measurement, for varying incident elec- tron energies, of the ratios of x-ray intensities emitted by the elements in the film and substrate to those emitted from bulk standards of the same elements. The observed variation of the k-ratio with incident elec- tron energy is the input of the EPMA quantification code, which determines the thickness of the overlayer by least-squares fitting of the experimental k-ratios with an analytical x-ray emission model (see e.g. [1–3]).  Author for correspondence. E-mail: xavier@giga.sct.ub.es