Critical dimension metrology using Raman spectroscopy

Abstract

In this paper, we demonstrate the capabilities of Raman spectroscopy for the measurement of the critical dimensions of metallic nanostructures. Using tungsten-based nanogratings, we show that the Raman signal originating from the Si substrate underlying a metallic nanograting is primarily sensitive to the distance between the nanolines, as could be expected for such metallic waveguides. However, surprisingly, when using incident light polarized perpendicular (transverse-magnetic) to the nanolines, the technique becomes strongly sensitive to the width of the lines. Using a simple analytical model, we explain the experimental data quantitatively and show that the very high sensitivity to the width under transverse-magnetic illumination is due to the strong impact of their nanometer variations on the absorption properties of the fundamental transverse-magnetic mode excitable within the nanogratings. This work constitutes an important milestone for the Raman technique to become a routine dimensional metrology tool for nanophotonic and nanoelectronic applications.