Composition Measurement of Tri-layer SiGe Stack using Broadband Spectroscopic Ellipsometry

This paper discusses the development and implementation of a Broadband Spectroscopic Ellipsometry (BBSE) composition measurement to characterize a tri-layer stack consisting of 2 SiGe layers of different Germanium concentrations topped by an epitaxial Si layer. The designed experiment wafer set and the composition model development based on AES and XRD reference data are discussed. The spectral sensitivity of the composition model and the correlation to reference metrology are shown. Wafer to wafer and within wafer variation, stability and tool to tool matching performance are quantified based on the implementation of the composition model as an inline measurement for a 20nm development vehicle. The paper arrives at the conclusion that BBSE is a feasible high throughput metrology option for this application, while leaving room for improvement in future revisions of the model.