In situ stress evolution during and after sputter deposition of Al thin films

Abstract

The stress, growth, and morphology evolution of Al thin filmsup to 300 nm thick, sputter deposited at a constant rate of0.04 nm s−1 onto thermally oxidized Si(100) substrates have been investigated for varioussputter pressures in the range from 0.05 to 6 Pa. The stress evolution has beenstudied during and after the film deposition by means of in situ substrate curvaturemeasurements using an optical two-beam deflection method. In order to obtain insightinto the mechanisms of stress generation and relaxation, the microstructure ofthe films was investigated by scanning electron microscopy, focused-ion-beammicroscopy, and atomic force microscopy. The stress evolution during the early stage ofdeposition of films is consistent with the Volmer–Weber growth mode knownfor metals with high adatom mobility. For thicker films, the compressive stressincreases in the sputter pressure range of 0.05–0.5 Pa, whereas at even higher sputterpressures a transition from compressive to tensile stress takes place. This transition iscorrelated with a change from a relatively dense to a more porous microstructurecharacterized by decreasing mass density and increasing electrical resistivity withincreasing sputter pressure. The dependence of the stress and microstructure on thesputter pressure can be consistently understood through a combination of the stressmechanisms for vapor and sputter deposited films proposed in the literature.