Linearized radially polarized light for improved precision in strain measurements using micro-Raman spectroscopy

Abstract

Strain engineering in semiconductor transistor devices has become vital in the semiconductor industry due to the ever increasing need for performance enhancement at the nanoscale. Raman spectroscopy is a non-invasive measurement technique with high sensitivity to mechanical stress that does not require any special sample preparation procedures in comparison to characterization involving transmission electron microscopy (TEM), making it suitable for inline strain measurement in the semiconductor industry. Indeed at present, strain measurements using Raman spectroscopy are already routinely carried out in semiconductor devices as it is cost effective, fast and non-destructive. In this paper we explore the usage of linearised-radially polarised light as an excitation source, which does provide significantly enhanced accuracy and precision as compared to linearly polarised light for this application. Numerical simulations are done to quantitatively evaluate the electric field intensities that contribute to this enhanced sensitivity. We benchmark the experimental results against TEM diffraction-based techniques like nano-beam diffraction and Bessel diffraction. Differences between both approaches are assigned to strain relaxation due to sample thinning required in TEM setups, demonstrating the benefit of Raman for nondestructive inline testing.

Off-axis Raman spectroscopy for nanoscale stress metrology

“…The technique has been successfully applied for excitation of forbidden Raman modes towards decoupling the in-plane stress tensor in nanostructures. [13][14][15][16] However, such high-NA objective lenses require liquid immersion (oil/water) environments, 17 contaminating the sample and are a clear roadblock to its in-line adoption. To this end, a "dry" alternative is required.…”