Contact atomic force microscopy (C-AFM) as an indispensable auxiliary tool for the measurement of nano-film thickness by the XRF absorption spectroscopy technique

Abstract

This study discloses the indispensability of the use of the contact atomic force microscopy (C-AFM) technique besides the use of the x-ray fluorescence (XRF) absorption spectroscopy technique for obtaining accurate and reliable data for thin film thickness evaluation. Several copper films with different thicknesses (a few nanometres to more than 600 nm) were deposited on smooth Corning Glass substrates in a sputter coater system by electron beam evaporation. The calculated thicknesses of the films according to the XRF emission spectroscopy method (using two analyser crystals, LiF (2 2 0) and LiF (2 0 0)) were compared with the experimental data obtained by the thickness monitor (rotating quartz crystal). The discrepancies observed using different crystals are discussed. It is demonstrated that ignoring the thin film surface topology may induce severe errors in the calculated thickness values based on the XRF technique especially for thicknesses in the range of 20–150 nm. This is while the measurement error assumes substantially lower values for thicknesses lower than 20 nm. The latter is also discussed considering the AFM results.