TRANSMISSION-MODE PERPENDICULAR INCIDENCE ELLIPSOMETRY OF ANISOTROPIC THIN-FILMS

We show that transmission-mode perpendicular incidence ellipsometry, which yields the trivial values PSI = 45-degrees, DELTA = 0 for an isotropic thin film, can be used to provide useful data during the vacuum deposition of anisotropic coatings. Thus the number of quarter-wave film thicknesses necessary for a quarter-wave retardation plate can be determined simply by counting interference modulations on a DELTA versus PSI graph, and the material property DELTAn, the difference between the slow and fast axis refractive indices, is available from the gradient of a smoothed DELTA versus thickness graph. The influences of differential absorption, differential refractive index inhomogeneity, and instrumental errors on the ellipsometric parameters are discussed.