Determination of the Refractive Index and Thickness of a Transparent Film on Opaque Substrate Via Cryogenic Spectrometric Ellipsometry

Abstract

Cryogenic spectrometric ellipsometer (CSE) for studying bulk material and film optical properties was developed. CSE permits determination of optical reflectivity (ellipsometric) data in the range between 0.3 and 2 μm, in temperature interval from 5 to 300K. The special small continuos flow cryostat has been designed for the studies. Angles of incidence can be changed from 45° to 70° discretely. A method for determining refractive index and thickness of a transparent film on any substrate (opaque or transparent) system without thickness limitations was developed. The method is based on the usage of numerical computations to process ellipsometric data. This enables both a quick and precise determination of the film parameters and a semianalytical discussion of the relative errors involved in the measurements, leading to optimal values for the experimental parameters. Using the method, one can find analytic inversion of ellipsometric data at any angle of incidence and for any substrate, provided the film is transparent. It has the advantage to find physical solution without initial guess and with a precision as good as the other methods. The method was tested on a real system (air-native film-Si substrate) and proved to be accurate.