Optical properties of thin films on transparent surfaces by ellipsometry; internal reflection for film covered surfaces near the critical angle

Abstract

The application of ellipsometry to the determination of the optical properties of thin films on transparent substrates by the use of internal reflection and angles of incidence near the critical angle for total reflection is described and illustrated. Four cases are considered: 1. the angle of incidence, ?i, is less than either the critical angle for total reflection between the substrate and the film, ?c1,2, and the critical angle between the substrate and the surrounding medium, ?c1,3; 2. ?c1,3>?i>?c1,2; 3. ?c1,3 ?c1,2. For case 1, at certain critical values of film thickness d and refractive index n2, the reflected light may be polarized with its electric vector either entirely in or normal to the plane of incidence. Near these conditions the sensitivity of ellipsometric measurements is extremely high, but the intensity of the reflected light is very low. Except under these conditions the intensity is adequate for experimental measurements, as it is also in case 2. For case 1 it is always possible to determine n2 and d by a single measurement; for case 2 this is possible only for thin films. For cases 3 and 4, and case 2 for thick films, only one of these may be determined. Under these conditions, however, the reflectivity is 100 percent.