DETERMINATION OF REFRACTIVE-INDEX PROFILES BY A COMBINATION OF VISIBLE AND INFRARED ELLIPSOMETRY MEASUREMENTS

Model inhomogeneous silicon oxynitride films were produced by ion-beam sputtering and characterized by ellipsometry in the visible and infra red ranges. These films exhibit strong intentional gradients of the re fractive index that cannot be considered linear. A discrete descriptio n of the index profile with a few layers or a continuous description w ith a polynomial are examined; regressions by the use of measurements in the visible only or in the total spectral range (visible and infrar ed) are performed. Acquisition of data in an extended range is found t o be a guarantee of the reliability of the calculated index profiles. (C) 1996 Optical Society of America