Stress evolution during and after sputter deposition of thin Cu–Al alloy films

Abstract

The stress evolution during and after sputter deposition of thin Cu–Al alloy filmscontaining 1 and 2 at.% Al onto oxidized Si(100) substrates has been studied up tothicknesses of 300 nm by means of in situ substrate curvature measurements. In order tocorrelate stress and morphology, the microstructure was investigated by focused ion beammicroscopy, scanning electron microscopy, and atomic force microscopy. The evolution ofthe stress and microstructure of the Cu–Al alloy films is similar to that for sputtered pureCu films. Film growth proceeds in the Volmer–Weber mode, typical for high mobilitymetals. It is characterized by nucleation, island, percolation, and channel stages before thefilms become continuous, as well as lateral grain growth in the compact films. Withincreasing Al content the overall atom mobility and, thus, the average grain size of thealloy films are reduced. Increase of the sputter pressure from 0.5 to 2 Pa leads tofilms with larger grain size, rougher surface morphology and higher electricalresistivity.