Determination of optical constants of absorbing materials using transmission and reflection of thin films on partially metallized substrates: analysis of the new (T,R(m)) technique.

A new accurate technique for determining the optical constants of thin absorbing films is presented. The configuration used includes a conventional spectrophotometer and a transparent substrate, half of which is covered with an opaque highly reflecting metal layer prior to the deposition of the film to be studied. The normal incidence transmission T of the thin film on the transparent substrate is then combined with a measurement of the near normal reflection R(m) of the same film on the metal covered part of the substrate. The combination (T,R(m)) yields an accurate and experimentally simple technique for determining the optical constants of thin films. A detailed evaluation of the accuracy of the extracted optical constants n and k of the thin film is obtained from numerical computations using realistic assumptions of various experimental uncertainties. Comparison with conventional techniques shows a greatly improved accuracy of the new technique.