<title>Thickness And Refractive Index Measurements By Light Coupling: Design Guidelines Of A Prism Coupler</title>

Abstract

Simultaneous measurement of the refractive index and thickness of a thin film to a sufficient degree of accuracy is usually cumbersome and often requires an elaborate data reduction procedure. In comparison with the conventional techniques that use either a spectrophotometer or an ellipsometer, the prism coupling method, which relies on the coupling of light waves into thin films by a guided wave mechanism, could be more accurate and is easily adaptable for rapid measurements. Prism couplers, though developed mainly to characterize thin-film guided-wave optical devices, are also useful in diverse applications, particularly for the semiconductor industry. The design guidelines of a prism coupler, which involve considerations of parameters such as prism features, light beam, and air gap at the coupling point, have been identified, and the accuracy requirements determined. The results obtained by a prism coupler for the very small absorption due to gap states in hydrogenated amorphous semiconducting thin films are also presented.