Unambiguous determination of optical constants of absorbing films by reflectance and transmittance measurements

We describe a three-stage process for the determination of the optical constants n and k of thin absorbing films on the basis of reflectance, transmittance, and thickness measurements. The first stage uses a bivariate optimization based on the functions (1 ± R)/T, R denoting a reflectance and T the transmittance. The second stage uses a phase-variate approach based on an algorithm for locating the complex zeros of analytic functions. The third stage uses an evolution curve, giving the single-wavelength reflectance as a function of film thickness. We illustrate the process using practical examples drawn from recent studies of films of amorphous silicon, hydrogenated carbon, and hydrogenated silicon.