Robust Optical Modeling of SiGe Layers

摘要

Epitaxial Silicon Germanium layers are commonly used in the semiconductor industry to compress the P-FET transistor channel and thus increase its drive current. Accurate metrology of SiGe thickness and Ge content is required, preferably by a fast and nondestructive method, such as spectroscopic ellipsometry. In principle, an optical measurement of Ge concentration is possible, since the composition of a single-crystalline SiGe alloy determines its optical properties. However, the complex nature of this relationship makes the analysis difficult in general. In addition, more than a single SiGe layer is often present due to manufacturing constraints, which complicates the analysis of ellipsometric spectra even further. An analytical description for the dielectric function of SiGe is developed that enables robust and accurate analysis of ellipsometric data for Ge concentrations up to 50%.