Spectral Characteristics of an Inhomogeneous Film 2. Determination of Refractive Index Profile from Reflectance/Transmittance Spectrum

Abstract

The refractive index profile with depth in silica films that are severa/microns thick and may be inhomogeneolls to a greater or lesser extent. deposited 011 silicon substrates. has been detennindfrom the measured reflectance V.I' wavelellgth specrral clln'es. As compared to some sophisticated and complex cllrve-filtin,~ optimi:.atioll techniques IIsed by other researchersfor this purpose. a simplified approach has beell adopted here. all the basis of studies by the authors of the variatiolls with lVav£'lellgth of tile ellve/opes of the reflectance/transmittance extrema for different inhomogelleous film models (Ihe subject of the previous paper), the most likely model of the illil. 'lIIogeneolls silica film has been idelltified as a starling point. The calculated reflec/lillce vs wavelength curve of this model film-coated substrate has then been filled with tile experimelltal data using a constrained optimization techllique to detemlille the refraclive index profile and thickness of the film. The procedure has been illustrated for afew silica films. and the ranges ofuncertainty in the detenllinedfilm parameters have been itulicated.