Off-axis Raman spectroscopy for nanoscale stress metrology

Abstract

Raman spectroscopy is an effective tool for stress and compositional metrology in the semiconductor industry. However, its application toward decoupling a complex stress state in semiconductor materials requires the use of liquid immersion lenses that are process line incompatible. In this work, a practical design concept for off-axis Raman spectroscopy is presented. By tilting the incident light away from the normal incident axis, forbidden Raman modes can be accessed allowing determination of the in-plane stress tensor in semiconductor materials. Furthermore, we benchmark off-axis Raman spectroscopy against oil-immersion Raman spectroscopy for stress characterization in 20 nm-wide strained Ge fin field-effect transistor channels. We demonstrate that off-axis Raman allows anisotropic stress metrology without reliance on liquid immersion lenses, highlighting its viability in the process line. The stress state is validated through nanobeam diffraction measurements. Published under an exclusive license by AIP Publishing.