Off-axis Raman spectroscopy for nanoscale stress metrology

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.