It has been reported earlier that the attenuation lengths of photoelectrons from very thin amorphous silicon nitride films (3 to 11 nm) increase with film thickness. These changes were attributed to systematic variations in the film density. Spectroscopic ellipsometry has been used here as an independent technique to evaluate the refractive indexes of several of the same films. The ellipsometric results are consistent with the earlier finding that the relative densities of these films vary with thickness. The density variations may be attributed to either structural changes in the films or differences in the oxygen content of the films with film thickness.