The Use of Infrared Spectroscopic Ellipsometry for the Thickness Determination and Molecular Characterization of Thin Films on Aluminum

Like reflection-absorption Fourier transform infrared spectroscopy, infrared spectroscopic ellipsometry (IRSE) is a nondestructive infrared reflection technique, which allows a chemical characterization of thin films on metals. However, the stronger absorptions of inorganic compounds in the spectra obtained with both techniques feature optically induced peak shifts that can lead to erroneous interpretations of the spectra. Since IRSE measurements contain information concerning the film thickness, which also determines the magnitude of the peak shifts, they can be corrected more easily using IRSE. This is illustrated in the present paper, which discusses the joint chemical characterization and thickness determination of thin anodic oxide films and chromium phosphate conversion films on aluminum by means of IRSE. Though the spectra of the anodic oxide films and those from the chromium phosphate conversion films feature vibrations of different types (longitudinal and transversal optical modes), the procedure for the interpretation of the spectra is applicable in both cases.