AN IR PHASE-MODULATED ELLIPSOMETER USING A FOURIER-TRANSFORM SPECTROMETER FOR IN-SITU APPLICATIONS

A new Fourier transform IR phase-modulated ellipsometer is presented. It combines the fast modulation (omega = 37 kHz) provided by a photoel astic modulator and the low frequency (below 1 kHz) corresponding to a Michelson interferometer. As a consequence, highly sensitive measurem ents can be obtained even when using a conventional IR source. The num erical signal processing is based on a modern microprocessor (digital signal processor) dedicated to the fast Fourier transform computations . The ellipsometric angles PSI and DELTA are obtained from the combina tion of the interferograms corresponding to the d.c., omega and 2omega contributions to the detected signal through a self-consistent spectr al procedure. A full spectrum recording (from 900 to 4000 cm-1) can be achieved in 2 s. Thus, it appears well adapted for kinetic in situ st udies. The resolution on PSI and DELTA can reach 0.03-degrees when the integration time is increased to 380 s. The sensitivity of this Fouri er transform IR phase-modulated ellipsometer is illustrated by the mea surements of vibrational properties of thin films.