Probing the mechanical properties of high-k dielectric nano-films by Brillouin light scattering study

As microelectronic transistors scale to smaller dimensions, device functionality suffers from current leakage. This problem can be overcome by using thicker gate materials with a high dielectric constant. SiO$_{\mathrm{2}}$ has been the material of choice, but becomes unsuitable due to its relatively low dielectric constant (k $=$ 3.9). Alternate materials, such as BN:H (k $=$ 5.7) and HfO$_{\mathrm{2}}$ (k $=$ 25) are promising choices to replace SiO$_{\mathrm{2}}$ to achieve the desired performance while preserving ultra-thin thickness (\textless 10 nm). Despite these promising features, one concern of including these materials, are their mechanical and thermal properties that could degrade device functionality. There is thus a growing need for non-destructive techniques to evaluate the mechanical properties of such laminar structures since traditional methods like nano-indentation are not effective at these dimensions. We report on Brillioun light scattering studies to determine the individual elastic constants and, thus the mechanical properties of BN:H and HfO$_{\mathrm{2}}$ high-k films with thicknesses as low as 24 nm. Young's modulus (E) and Poisson's ratio ($\nu )$ were determined by measuring the frequency dispersion of confined and traveling transverse and longitudinal acoustic waves as well as their associated light scattering intensities.