ELLIPSOMETRY STUDY OF THIN METALLIC-FILMS UNDER CONSTRAINT BY THE SIZE EFFECT

The ellipsometry of thin metallic films with thicknesses varying from 12.5 nm to 200.0 nm are studied theoretically and experimentally. The ellipsometry angles psi, and delta deviated from their bulk values by about 41.7% and -21.5%, respectively, as the film thickness is reduced below 12.5 nm. This deviation can be expressed more fully by the opti cal size effect, which implies a thickness dependence on the optical c onstant. Atomic force microscopy reveals that the surface roughness on the ultra-thin metallic films is about 60 Angstrom. The depolarizatio n due to the surface roughness seems not to play an essential role in the determination of the optical constant of thin metallic films by el lipsometry.