Infrared phase-modulated ellipsometer for in-situ characterization of surfaces and thin films

A new infrared phase modulated ellipsometer (IRPME) is presented here. The polarization phase modulation technique takes advantage of the high frequency modulation (37 kHz) provided by a ZnSe photoelastic modulator. In order to increase the signal to noise ratio, the conventional globar source was superseded by a cascade arc, which emitted intensity corresponds to that of a blackbody at a temperature > 10,000 K. Ellipsometric measurements can be recorded from 700 up to 4000 cm^-1 combining photovoltaic InSb and MCT detectors. A monochromator is used to record spectra, with a 2 - 5 cm^-1 spectral resolution, depending on the wavelength domain. The signal acquisition and data processing is based on the use of a numerical electronic system. The improvements of both optical and electronic parts of the ellipsometer result in increased performances by more than one order of magnitude. The precision on Ψ and Δ is now ≈ 0.01 deg., achieving a submonolayer sensitivity.