Feasibility study to probe thin inorganic and organic coatings on aluminium substrates by means of visible and infrared spectroscopic ellipsometry

The major optical technique applied in this paper is spectroscopic ellipsometry. Ellipsometry measures the polarization change of the light due to interaction with the sample surface. It is called ‘spectroscopic’ if the measurement is performed at various wavelengths within a spectral interval. Spectroscopic ellipsometry performed in the visual spectrum allows the characterization of very thin films on metals, e.g. anodic oxide films or conversion layers on Al. In this contribution the optical modelling that leads to accurate thickness measurements of such films is shown. Visual spectroscopic ellipsometry (VISSE) fails to give chemical information due to the absence of absorption peaks in the spectrum. Therefore, an original approach has been followed by the use of the new infrared spectroscopic ellipsometry (IRSE) technique. This method combines the advantages of VISSE to the characteristic information revealed by Fourier transform infrared spectroscopy. In this paper we used IRSE on the anodic oxide and chromium phosphate films. The infrared optical modelling is discussed and calculated thickness values are compared to thickness measurements obtained by VISSE. Copyright © 2000 John Wiley & Sons, Ltd.