Surface Morphology Studies of Sub-Ps Pulsed-Laser-Deposited AlN Thin Films

Abstract

Aluminum nitride thin films were deposited by multipulse KrF* (λ = 248 nm, τ∼450 fs) excimer laser ablation of AlN targets in low-pressure nitrogen. We investigated the morphology of the deposited films by scanning as well as transmission electron microscopy, as a function of laser fluence and ambient nitrogen pressure. The AlN films entirely consist of grains (clusters) with average diameters of a few tens of nanometers. In addition, particulates several hundreds of nanometers in diameter (spherical droplets) were observed on the surfaces of the deposited films. Besides these particulates, we noticed the presence of micrometer-size whiskers, or dendritic- and wave-like structures, consisting of agglomerates of nanoparticles. The particulates density decreases with the decrease of the laser fluence, or with the increase of the ambient nitrogen pressure, while their average size increases. This indicates that clustering is the dominant particulates formation mechanism, as a result of the enhanced number of collisions in the fs laser generated ablation plasma.