Optical and interferometric investigations of some metallic thin films

Abstract

A sensitivity study is conducted on the polarimetric measurable [delta] = ([delta]p-[delta]s), the differential change of phase on reflection air/metallic p s-film. A computer aided study shows the quantity A to he sensitive to the extinction coefficient k and to film thickness. It is only sensi-tive to the refractive index n in certain ranges of n , k and for certain d values. For films of d 2001, A becomes insensitive to n but maintains high sensitivity to k , while ford £200 A it shows some sensitivity to n as well as k in certain ranges of lower values of k 2.5. An interferometric technique due to Tolansky (1944), is used to determine A as a function of 6 , the angle of incidence for films of Ag , Au and At at different wavelengths in the visible region of the spectrum. It is shown that this interferometric technique, when critically applied, is capable of an accuracy of +/-0.003. The extinction coefficients of films investigated are found from curves of A vs n for constant values of k . They are shown to be accurate to +/-0.03 when A is accurate to +/-0.003 tt thus rendering a simple and inexpensive technique an accurate and effective method for the determination of the extinction coefficient of highly reflecting metallic films.A new optical system to produce multiple beam interference fringes of variable chromaticity in the first order is described. The system enables the surveying of features within the order. It also removes the ambiguity met in conventional monochromatic interferometry concerning the order of interference to which a fringe may belong. White light multiple fringes are obtained first and the orders are recognized. Some outlines are projected for investigating the sensitivity of the optical phase properties of metallic films, namely the phase changes on reflection air/metallic film [beta], dielectric substrate/metallic film [beta] and in transmission [gamma], at normal incidence, to n, k and d . It is proposed to try to explain and link the behaviour of these phase quantities with thickness for d 200. in terms of n and k. Also a compact new monochromator to produce fringes of variable chromaticity for surface microtopography studies is projected.