Solid state dewetting of thin plasmonic films under focused cw-laser irradiation

Elevated temperatures and large thermal gradients are a significant source of component failure in microelectronics, and are the limiting factor in heat-assisted magnetic recording (HAMR). We have investigated the effect of solid-state dewetting in Au thin films, as a function of local temperature, film thickness, and substrate adhesion. In this work, a localized temperature rise is induced in thin (≤50 nm) polycrystalline Au films on SiO₂ substrates via focused continuous-wave laser irradiation at 488 nm. The magnitude and distribution of the total temperature rise is measured using CCD-based thermoreflectance. This also allows a sensitive measurement of the temperature at which dewetting occurs, showing that for thin Au films without adhesion layers, rapid dewetting can occur at temperatures as low as 50 °C, which corresponds with an absorbed laser power of 4 mW. The time decay of the reflected light from the illuminating laser is used to monitor locally the dynamics of solid state dewetting. TEM diffraction analysis shows significant changes in the microstructure and crystallographic texture of the films as far as 10 μm away from the illuminated area. The use of a thin metallic adhesion layer (such as Ti or Cr) is shown to significantly improve the adhesion of the Au to the substrate, inhibit grain growth, reduce the tendency towards dewetting, and to allow the film to develop a pseudo-biaxial texture.