Excimer laser modification of thin AlN films

The potential of excimer laser micro-processing for surface modification of aluminum nitride (AlN) thin films was studied. Thin films of AlN were deposited by plasma-source molecular beam epitaxy (PSMBE) on silicon and sapphire substrates. These films were then exposed to different fluence levels of KrF (λ = 248 nm) excimer laser radiation in an ambient air environment, and the changes in the film surface were studied by X-ray photoelectron spectroscopy, atomic force microscopy and optical spectrophotometry. The results show that there is a narrow range of laser fluences, just above 1.0 J/cm2, within which mostly photochemical transformations of the film surface take place. These transformations consist of both oxidation and decomposition to metallic Al of the original film within a very thin sub-surface layer with thickness of several tens of nanometers. No changes were observed at fluences below 1.0 J/cm2. Above a fluence of 1.0 J/cm2, severe photomechanical damage consisting of film cracking and detachment was found to accompany the photochemical and photothermal changes in the film.