Improving the crystal quality of AlN films by nanosecond laser annealing

Aluminum nitride (AlN) thin film of thickness 300 nm grown on sapphire substrate was annealed by a nanosecond laser at a wavelength of 532 nm. The laser energy values were 2 J, 3 J, 4 J, and 4.5 J, respectively. In order to increase the absorption of laser energy by the sample, 50 nm thick tungsten films were deposited on the left half of the sample. Surface morphology and Raman spectrum of AlN films were characterized before and after annealing using scanning electron microscope (SEM) and Raman spectrometer, respectively. The SEM micrographs have shown that the surface of AlN film had a large number of voids before annealing. After annealing, the size of the voids becomes smaller and their number decreases with the increase of laser energy density. The full width at half maximum (FWHM) of AlN film was roughly 6-10 cm−1 before annealing and 4-8 cm−1 after annealing. The results showed that the surface morphology and FWHM of the AlN films were improved after laser annealing compared with those before annealing. Finally, COMSOL Multiphysics simulated the temperature field change of AlN film after laser irradiation and the evolution of its surface.