Question

How to estimate thickness from two minima points of x-ray reflectivity profile?

Answer 1

XRD may give you the film thickness as well as the roughness, if the crystallites that form the film are elongated from the substrate to the air/vacuum surface. In that particular case, the average film thickness is identical to the crystallite size, and you may get the value from the peak broadening as mentioned above. If the films are smooth, then you will also observe side-lobes at both sides of the bragg-peak (see enclosure) and by a modelling, you may get the films roughness. In the attached example, the XRD evaluation results in a thickness of about 65.3 nm (+/- 1.5 nm) while an independent thickness measurement using profilometry and X-ray reflectivity gave 66.5 nm. Thus in that case, we can assume that the crystallites forming the films are of the same size as the film thickness. It should be noted, that prior to annealing, the crystallites were smaller, and thus the XRD evaluation did not reproduced the film thickness!

This implies that this kind of thickness estimation by XRD is dangerous!

Good luck,