ERROR MINIMIZATION METHOD FOR SPECTROSCOPIC AND PHASE-MODULATED ELLIPSOMETRIC MEASUREMENTS ON HIGHLY TRANSPARENT THIN-FILMS

We point out that there is an intrinsic magnification of error in the measurement of transparent or semitransparent thin films by the usual method of phase-modulated ellipsometry. This procedure is suitable for absorbing materials, but for nonabsorbing materials it gives a great amount of error in the measurement of ellipsometric angles at some critical values. We propose a new methodology for the phase-modulated ellipsometric measurements that avoids this magnification. We illustrate the advantages of this new method by measuring the index of refraction of a low-pressure chemical-vapor-deposited a-SiO2 thin film with greater accuracy than that achieved by the usual method.