Ellipsometric study of optical properties and small inhomogeneities of Nb2O5 films

摘要

Abstract: Spectroscopic ellipsometry has become one of the most powerful tools of the investigation of the optical properties of thin films. In this paper we show that it enables one to successfully detect even fine properties of high-quality thin films, such as small bulk and surface inhomogeneities. In our experiments, niobium pentoxide films were deposited by ac magnetron sputtering on to quartz substrates with a thickness approximately equal to 500 nm. A J.A. Woolam variable angel spectroscopic ellipsometer was used to measure the ellipsometric parameters of the films over a spectral range from 400 nm to 850 nm. The measured ellipsometric data obtained at the different incidence angles were then analyzed using the OptiChar characterization software. All measurements indicated the presence of a surface micro-roughness in the film, estimated to be around 1 nm. This surface micro-roughness was modeled by a surface overlayer with a 50 percent packing density. The films also possess a small positive bulk inhomogeneity on the order of about 1.5 percent. In the specific case of Nb$-2$/O$-5$/ films on a quartz substrate, the ellipsometric angle $Psi at a 65 degree angle of incidence is the most sensitive to surface and bulk inhomogeneities. The presence of inhomogeneities of both types is clearly seen at certain wavelength points. !8