COPPER-OXIDE FILM STUDIES FROM ANALYSIS OF SPECTROSCOPIC METHODS

In this paper, three spectroscopic methods used for measuring the film thickness of an oxide layer, obtained by dry oxidation of a polished copper foil, are described. The spectral range investigated is 50000-400 cm-1. The first part of this range (50000-12500 cm-1), the second one (12500-4000 cm-1) and the third one (4000-400 cm-1) are respectively typical of photoluminescence spectrometry, diffuse reflectance spectroscopy and FTIR spectroscopy. The photoluminescence method can be used if an interference effect is observed. With a model based on the diffuse and specular reflectance spectra, we first prove that the roughness of the oxide/metal interface is in agreement with the existence of fringes. Then, the film thickness is calculated from interference fringes in the wavelength range of interest. A change in 15% between the different experimental results is observed. The lower value is always given by the FTIR spectroscopy and the higher one by the photoluminescence method. The structure of the oxide layer may be inhomogenous, with different chemical composition. The Wagner theory of metal oxidation neglect the effect of scale thickness growth on the diffusional flux of metal. So, the refractive index, n, is not constant on all the layer. Microprobe analysis studies of the oxide composition explain these experimental data.