Spectrometric ellipsometry application to optical metrology of Silicon-Germanium layer

Now an accurate metrology of Silicon-Germanium (SiGe) thickness and Ge concentration is becoming more and more important for beyond 40nm technology. Traditional solution is normally Transmission Electron Microscope (TEM) for thickness and Second Ion Mass Spectrometry (SIMS) for Ge concentration, which is suffering from sample destruction and makes inline monitoring impossible. On the contrary, optical spectrometric ellipsometry (SE), a non-destructive method with high throughput, can be used to measure SiGe layer thickness and Ge concentration at the same time. In this work, design of experiment (DoE) wafers of multi-layer SiGe stack was used for metrology model setting. The thickness and Ge concentration of each layer were measured. TEM and SIMS work as reference to qualify the model. The metrology stability was also tested if can meet production criteria.