Thin film of aluminum oxide through pulsed laser deposition: a micro-Raman study

Successful use of micro-Raman spectroscopy to characterize the surface of the thin Al2O3 films deposited on Si(010) substrate through pulsed laser ablation is presented. The micro-Raman spectra have been recorded on several spots (sized ≈1 μm) over the length and the breadth of the films in a systematic fashion. The as-deposited films are inhomogeneous from spot-to-spot over the surface. The variation in characteristic properties of 521 cm−1 line of crystalline Si (c-Si) have been used to estimate the thickness of the Al2O3 films. The thickness of the films has been found to depend on the position of the substrate with respect to the plume boundaries produced by the laser pulse after hitting the Al target. The thickness also depends on the position of the spot on a film placed at a fixed distance from the target surface. The thickness profiling of the deposited films on the basis of micro-Raman spectroscopic investigations corroborates the theoretical prediction of the model of the plume formation and the formation of the shock-front region in the pulsed laser deposition technique. All the seven Raman active modes (2A1g+5Eg) observable in single crystals of sapphire (c-Al2O3) powder have been identified in the complex spectra obtained from deposited film surfaces under varying experimental conditions. The intensity variation of an isolated line (750 cm−1) of Al2O3 corroborates the deposition profiling obtained from c-Si line parameters. The most intense Raman lines in the micro-Raman spectra of the deposited films are two infrared active modes around 450 and 600 cm−1. The strong presence of these infrared active modes in the micro-Raman spectra suggests a highly distorted micro-crystalline structure of the films. The local micro-stress created by the micro-crystals on the Si-substrate is maximum near the stopping distance of the plume. Largest micro-crystal of Al2O3 are also seen over the spot near the stopping distance of the plume.