Correlation of compositional and structural changes during pulsed laser deposition of tantalum oxide films

Abstract

Tantalum oxide films have been grown by KrF excimer laser ablation of a tantalum target in oxygen atmosphere. The ambient pressure was varied from 1.5 to 50 Pa to investigate the structural and compositional changes during the transition from non-stoichiometric to Ta2O5 films. The growth rate was determined not only as the rate of thickness increase, but also as elemental deposition rates, i.e. the quantity of Ta and O atoms sticking to the substrate surface. On the basis of compositional, structural and roughness information, derived from the analysis of Rutherford backscattering spectra, three domains have been identified. Below 10–12 Pa sub-oxides are obtained in form of dense, compact films. Nearly stoichiometric films can be deposited in the pressure window between approximately 12 and 25 Pa with slightly increasing porosity. Exceeding 25 Pa the films become very porous, ready to trap oxygen-containing molecules from the surrounding atmosphere. Both ellipsometric and Rutherford backscattering spectrometry data confirm that the films grown at 400 °C substrate temperature are denser than those deposited at RT.