Advanced Spectroscopic Ellipsometry Application for Multi-Layers SiGe at 28nm Node and Beyond

Spectroscopic Ellipsometry (SE) is a commonly used non-destructive method to perform in-line monitoring of film thicknesses and optical indexes for the semiconductor industry. SE metrology can also monitor film composition by correlating optical indexes to species concentration. Germanium concentration (Ge%) measurement after SiGe epitaxial layer is a critical application at 40/28nm nodes to evaluate strain induced in the PMOS channel;. however, for 28nm and beyond, metrology needs to monitor Ge% on more complex SiGe film processes. This paper describes accurate and stable Ge% measurement on multi-SiGe layers by using optimized optical models and multiple correlation methodologies using SE metrology and how SiGe and Si-cap thicknesses can be reported simultaneously and independently. This paper demonstrates how to create enhanced SiGe models using KLA-Tencor Off-Line Spectral Analysis software based on DoE wafers with wide range split. Five different Ge% conditions are considered and multiple correlations created to report Ge% with less than 1% absolute offset to XRD reference tool. The final measured result also shows excellent Ge% stability (STDEV ~ 0.13%) even when multi-SiGe thicknesses are changed.