In situ measurement of principal refractive indices of thin films by two-angle ellipsometry

We show that the principal refractive indices of a tilted-columnar biaxial film can be determined from ellipsometric measurements made simultaneously at two angles in the deposition plane during the growth of the film. The index n(3), perpendicular to the deposition plane, is determined by a standard method using interference modulations in the s-polarized transmittance T-s versus thickness d profile recorded by one ellipsometer. For the computation of n(1) and n(2), we simultaneously log the data for mio profiles of phase retardation Delta versus d. These profiles are subject to substantial interference modulations, but the smoothed gradients correspond to material values in the absence of interference. An algebraic solution is developed for n(1) and n(2). This requires the columnar angle psi, which we determine from a scanning electron microscope photograph of a section of the film fractured in the deposition plane. (C) 1998 Elsevier Science S.A.