Ellipsometry of rough surfaces.

Ellipsometry measurements on several different kinds of rough surfaces were compared with stylus measurements of the surface texture. For steeply sloped periodic surfaces, the ellipsometric angles Delta and psi varied rapidly as the angle of incidence was varied near a diffraction minimum. This effect is interpreted in terms of the Kirchhoff theory and is ascribed to interference between singly and doubly reflected light waves. For a set of Ni replicas of machined surfaces with random surface profiles, Delta and psi varied systematically with surface texture. These variations persisted even after the surface composition was changed by evaporating first Al then Au on the surfaces. The systematic effects due to surface roughness are in disagreement with those of a previous experiment and are not readily explainable in terms of the Kirchhoff theory. The possible reasons for this are discussed along with the prospects for using ellipsometry as a tool for measuring surface roughness.