MEASUREMENT OF THE ABSORPTION-EDGE OF THICK TRANSPARENT SUBSTRATES USING THE INCOHERENT REFLECTION MODEL AND SPECTROSCOPIC UV VISIBLE NEAR IR ELLIPSOMETRY

A model taking into account the incoherent reflection in a thick trans parent substrate (approx. 1 mm) is described and tested. The incoheren t model makes it possible to calculate the averaged elements of the Mu eller matrix describing the sample, for comparison with data obtained by Spectroscopic Phase Modulated Ellipsometry (SPME). By performing PM E in two different configurations, the degree of polarisation is calcu lated from the measured intensities and compared to the theory. The st rong transition from incoherent to coherent reflection at the onset of the extinction or absorption edge, makes it possible to measure extre mely weak extinction coefficients (k similar to 10(-5)) using ellipsom etry. In particular, the electronic absorption edge in the UV-visit?le region, giving the transition from incoherent to coherent reflection, is found to be adequately modelled by the Forouhi-Bloomer (F and B) o r the Tauc-Lorentz (TL) dispersion formulas. Industrial applications o f ellipsometry often involve transparent substrates and examples of ch aracterisation of thin films on glass are given. (C) 1998 Elsevier Sci ence S.A.