Determination of the thickness of polycrystalline thin films by using X-ray methods

Abstract

The knowledge of the thickness of thin layer on substrate is quite important, sometimes even critical, for analysis of the layer properties and behavior. Among a large number of methods the X–ray methods are non-destructive and can simultaneously provide information about the structure and microstructure of the layer. These methods are capable to resolve the thickness of the layer within the range 5–300 nm for in-house diffractometers. The method of the first choice is usually the X-ray reflectivity. In the case of reflection of X-rays the most limiting factor is the roughness of the interfaces, i.e. the layer and substrate and the thickness inhomogeneity. If the roughness increases certain value the intensity of the specularly reflected intensity drops down very suddenly and the thickness of the layer couldn't be decided. In that case one can use X-ray powder diffraction in very asymmetric geometry, for example in the coplanar grazing-exit parallel beam setup. In this setup the thickness of the layer can be determined from attenuation of the integrated intensity by decreasing the angle of exit of the diffracted rays. Another X-ray based method is the X-ray fluorescence spectrometry where the layer thickness is determined by analyzing the X-ray spectral lines from the layer/substrate. In our contribution we will demonstrate how to use the mentioned methods in order to determine the thickness of the thin layer on the example of TiO2 thin polycrystalline films.