Abstract

We have been sputtering TiO₂ and SiO₂ for use in wide-band anti-reflection coatings on glass. We have made a study of the the optical properties of single material depositions of each of the constituent films on Corning 7059 and Silicon Wafer substrates. We have also taken some of the TiO₂ depositions and deposited a SiO₂ film on top of them during the same run in which the individual SiO₂ sample was deposited. We are interested in knowing if the optical properties of the TiO₂ or the SiO₂ are affected by the deposition of SiO₂ on top of the TiO₂. Optical studies have been made of the six types of samples: SiO₂, TiO₂, and SiO₂/TiO₂ on the 7059 glass and Silicon wafers. Data has been taken with a Variable Angle Spectroscopic Ellipsometer (VASE ref. 1) from 300nm to 1000nm in wavelength and at a variety of angles of incidence from 50 to 80 degrees. In addition transmission and reflection data near normal incidence has been taken using a VW reflection accessory on a CARY 17DI dual-beam spectrophotometer from 350 nm to 750 nm. First the TiO₂ ellipsometric data was analysed. The TiO₂ was sufficiently transparent in the visible and near infrared that it was possible to set the extinction coefficient to zero and solve for the index of refraction and physical thickness of the sample. Having established a value for the physical thickness, the ellipsometric data, Psi and Delta, was used to find the value of n and k at each wavelength by a recursive process. After making many studies of several different samples of TiO₂, it was found that the simplest way to characterize a particular sample of TiO₂ was as a mixture of two extreme material types labeled TiO₂ (Low Index) and TiO₂ (High Index). We have used the effective medium approximation (EMA) to combine them and use the volume fraction of the TiO₂ (Low Index) that is mixed into the TiO₂ (High Index) as the adjustable parameter, vf₁₀.

© 1992 Optical Society of America