Improvement of the accuracy of the In-situ ellipsometric measurements of temperature and alloy composition for MBE grown HgCdTe LWIR/MWIR structures

Spectroscopic ellipsometry (SE) has proven to be a very reliable technique for the in-situ monitoring of the substrate temperature and alloy composition during the HgCdTe epitaxy. In this work, the influence of the variations in the angle of incidence and the spectral wavelength shift on the measured accuracy of the growth temperature and alloy composition are studied, and a method for precisely determining these variations independent of the modeling of the SE data has been developed. It is shown that the stability of the fittings of the optical models for in-situ applications increases and that the couplings between model parameter decreases upon either eliminating the angle of incidence as an independent model parameter or correcting for the shifts of the wavelength offset. The variations in the angle of incidence and wavelength shift, which arise in the M88 ellipsometer from reflected beam deflections, were precisely calibrated in two dimensions as a function of alignment parameters, using a thick thermally grown SiO₂/Si sample and were parameterized for our experimental geometry. A new extension of theWVASE software was developed to correct the raw SE data in real time for wavelength shift and the angle of incidence drift. A comparison of the corrected and uncorrected results of in-situ temperature measurements for HgCdTe and CdZnTe(211) B/Si(211) clearly demonstrates that the proposed method significantly enhances the accuracy of temperature and composition readings over a broad range of values in these parameters.