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 compositi on during the HgCdTe epitaxy. In this work, the influence of the variations in the angle of incidence and the spectral wavelength shift on the measure d accuracy of the growth temperature and alloy composition are studied, and a method for precisely determining these variations independent of the mod eling 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 t hat the couplings between model parameter decreases upon either eliminating the angle! of incidence as an independent model parameter or correcting fo r the shifts of the wavelength offset. The variations in the angle of incid ence and wavelength shift, which arise in the M88 ellipsometer from reflect ed beam deflections, were precisely calibrated in two dimensions as a funct ion of alignment parameters using a thick thermally grown SiO2/Si sample an d were parameterized for our experimental geometry. A new extension of the WVASE software was developed to correct the raw SE data in real time for wa velength shift and the angle of incidence drift. A comparison of the correc ted and uncorrected results of in-situ temperature measurements for HgCdTe and CdZnTe(211)B/Si(211) clearly demonstrates that the proposed method sign ificantly enhances the accuracy of temperature and composition readings ove r a broad range of values in these parameters.