THICKNESS DETERMINATION OF THIN POLYCRYSTALLINE FILM BY LOW ANGLE INCIDENCE X-RAY DIFFRACTION

R. Kužel¹, J. Lhotka¹, G. Cappuccio² and V. Valvoda¹

¹Faculty of Mathematics and Physics, Charles University, 12116 Prague 2,
Czech Republic,
²Istituto di Strutturistica Chimica, CNR, C.P. 10, I-00016 Montelibretti Sc., Italy

Thickness measurement based on absorption of X-rays in thin films has been tested on polycrystalline TiN film deposited on WC substrate and on diamond coatings on TiC substrate. Parallel beam low-angle incidence technique was used. Intensities of three reflections from each material were measured for incidence angles of the primary beam ranging from 0.5° to 35°. After experimental correction for texture effects, data from the film, from the substrate and ratio of both were fitted by known functions using least squares routines. The substrate reflection intensities were found to be more suitable for determining the thickness of the overlaying thin film. The ratio of substrate and film reflections can be used too. The average thicknesses of the films determined from the substrate reflections were in fair agreement with the average value obtained from optical microscopy.

Considering the results of our studies, we recommend using the substrate reflection for thin-film thickness measurement when the substrate reflections are sufficiently strong and only slightly influenced by grain size statistics and reasonably simple texture effects (small and systematic changes in reflection intensities during c-scans). Thickness determination based on the thin-film reflections is very unreliable because of high sensitivity of this approach to unavoidable instrumental and sample effects at low angles. The tested methods are not routine techniques, but they can be used when microscopy is excluded, e.g., when the sample must not be destroyed, or when the information on the average thickness of the film is required instead of just the local information obtained by a microscope.