Accurate and rapid determination of thickness, n and k spectra, and resistivity of indium–tin–oxide films

The transparent conductor, indium–tin–oxide (ITO), is an important thin film component of flat panel displays. An optimum ITO film should be both highly transparent to visible wavelengths and at the same time, conductive. In practice, however, a tradeoff exists between these two attributes, making it difficult to produce a film that simultaneously meets both demands. In order to achieve the optimum balance between these properties, an effective method of characterizing ITO films is necessary. In this article we will present results of a new measurement technique that simultaneously determines, thickness, the spectra of the refractive index n and extinction coefficient k from 190 to 1100 nm, and the energy band gap of ITO films deposited on either transparent or opaque substrates. In addition, we will demonstrate how the film’s resistivity can be correlated to the film’s extinction coefficient. This technique is based on wide-band spectrophotometry, combined with spectral analysis that incorporates the Forouhi–Bloomer dispersion equations for n and k [Forouhi and Bloomer, Phys. Rev. B 34, 7018 (1996); 38, 1865 (1998)]. The measurement technique is nondestructive and takes 1–2 s.