Generalized ellipsometry for the characterization of anisotropic materials: influence of the sample adjustment on the extracted optical indices P. Boher, J.P. Piel, B. Sacépé, SOPRA, 26 rue Pierre Joigneaux, F-92270 Bois-Colombes, France Abstract: A new method to extract accurately the optical properties of anisotropic materials and multilayer structures is presented. The main differences compared to the literature is that we measure the Fourier coefficients of the ellipsometric signal α and β versus the sample azimuth at one analyzer position and adjust the optical properties of the sample directly on α and β 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 α and β versus 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. Keywords: Generalized ellipsometry, Fourier coefficients, anisotropic optical constant 1) Introduction: Among polarization-dependent optical techniques, spectroscopic ellipsometry is now a standard method to characterize thin films and multilayer structures. Most of the results obtained with ellipsometry concern isotropic materials. Nevertheless, anisotropic layered systems are more and more common in industry for various applications and the need to characterize this type of structure in an easy way is desirable. Generalized ellipsometry has been introduced for many years to measure the so-called optical Jones matrix components [1- 2]. 4x4 matrix algebra has been developed for electromagnetic plane waves reflected and transmitted by an arbitrary anisotropic and homogeneous layered system. A procedure has been defined to use rotating polarizer or analyzer instruments to extract the diagonal and non diagonal reflection coefficients of the samples. The basis of generalized ellipsometry is to define and determine three linear independent normalized reflection matrix elements R pp , R ps and R ss for one set of sample azimuth angle, incidence angle and analyzer or polarizer positions. The physical parameters (ordinary and extraordinary optical indices and thickness) are then fitted on these reflection coefficients [3]. Even if in theory this approach can be applied in all cases, in practice the extraction of the elements of the reflection matrix is generally difficult especially for the non diagonal terms which are generally small compared to the diagonal components. The number of polarizer or analyzer positions needed to extract accurately the R ps coefficient is generally very important and leads to very long measurements when one is interested in spectroscopic information. Also the need to realize two successive regressions, one for the determination of the reflection coefficients and the other to extract the physical parameters produces a result