Determining the thickness and composition of SiGe heterostructures using an optical microscope

Abstract

We demonstrate a novel method of determining the thickness and Ge concentration in multilayer SiGe heterojunctions using an optical microscope. The sample preparation is a two-step process: first the layer structure is bevelled under a shallow angle to enlarge the width of the layers, followed by a wet thermal oxidation step at low temperatures. Differences in the oxide thickness, due to the dependence of oxidation rate on Ge composition, result in colour differences in the layers that are visible under an optical microscope. The Ge concentration is calibrated using XRD results, and the measured layer thickness is compared to TEM results.