Ellipsometric measurement of the optical properties and electrical conductivity of indium tin oxide thin films

Abstract

Films of indium tin oxide (ITO) are ubiquitous in display applications as they combine optical transparency and good electrical conductivity. Thin ITO films are often difficult to characterize optically as they are often inhomogeneous and have complicated optical absorption spectra. In this work, we have used variable angle of incidence spectroscopic ellipsometry (VASE) to gauge the thickness, grading, and surface roughness of ITO films ranging from a few tens of nm to hundreds of nm thick on glass substrates. A two Lorentz oscillator model is used, with one oscillator representing the interband absorption in the UV end of the spectrum, and the second oscillator modeling the Drude-like free carrier absorption in the infrared. The Drude parameters obtained from the analysis of the films can be used to estimate the electrical (D.C.) conductivity of the film from the simple Drude model for free carriers. We present results for several films from 7 to 40 nm thick, and compare the nominal electrical resistivity of these films to the resistivity derived from the VASE measurements.