ELLIPSOMETRIC STUDY OF A THIN TRANSPARENT FILM OVERLAID ON A TRANSPARENT SUBSTRATE HAVING A SURFACE LAYER

The presence of a very thin surface layer in the substrate surface may have a serious influence on the ellipsometric determination of the refractive index nf and thickness df of a film overlaid on a substrate of known index nb. The surface layer is regarded as a homogeneous film of index ns and thickness ds, and Δ and tan ψ are calculated for the system [{(nf, df) + (ns, ds)} on substrate nb]. The film index n and thickness d obtained by using the ordinary Δ-tanψ chart, i.e. the index and thickness of a homogeneous film ellipsometrically equivalent to {(nf, df) + (ns, ds)}, can be used as approximations to nf and df in certain cases; but in other cases they are quite different from nf and df. The conditions for (n, d) to be, or not to be, useful as approximations to (nf, df) are discussed on the basis of the characteristics of the equi-index curves on the Δ-tan ψ chart. © 1969.