Generalized ellipsometry for the characterization of anisotropic materials:: influence of the sample adjustment on the extracted optical indices

A new method to extract accurately the optical properties of anisotropic materials and multilayer structures is presented. The main difference compared to the literature is that we measure the Fourier coefficients of the ellipsometric signal alpha and beta vs. the sample azimuth at one analyzer position and adjust the optical properties of the sample directly on alpha and beta by a regression algorithm. Measurements are made in rotating polarizer configuration at various wavelengths. In these conditions, the measurement behavior for the different optical and instrumental parameters can be clearly identified almost for uniaxial crystals. The tilt of the optical axis from the normal of the sample surface breaks the symmetry of the oscillations of alpha and beta vs. the azimuth. The oscillation amplitude is directly related to the ordinary and extraordinary indices. Measurement is also extremely sensitive to the sample surface horizontality, which can induce large errors on the optical axis orientation and on all the extracted optical parameters. Our method includes directly the alignment imperfection that is calibrated on isotropic sample. In these conditions the accuracy of the method is around +/-0.002 on the optical indices for transparent samples. (C) 2004 Elsevier B.V. All rights reserved.