In situ stress evolution during sputter deposition of Cu∕Co bilayers and multilayers

Abstract

The stress evolution of Cu ∕ Co bilayers and multilayerssputtered onto oxidized Si ( 100 ) ( SiO x ) substrates has been studied by in situ substrate curvature measurements with the thickness of the individual layers ranging from 3 to 10 nm. In order to understand the stress developing during deposition, we investigated the microstructure of single layers and bilayers by scanning electron microscopy as well as of the multilayers by cross-section transmission electron microscopy. The growth of Cu and Co on SiO x substrates proceeds by the Volmer-Weber mechanism. Due to the lower mobility, Co layers exhibit a finer grain morphology compared to Cu. The stress evolution and morphology of the first Cu ∕ Co or Co ∕ Cu bilayer are still influenced by the SiO x substrates and differ from that of subsequent bilayers. The metal on metalgrowth of subsequent bilayers is discussed in terms of the surface energies of Cu and Co, respectively. Accordingly, Cu wets Co and Co forms three-dimensional (3D) islands on Cu. After a transition region of 5−10 bilayers, a steady state with respect to the evolution of stress and morphology is reached. In both, the Cu and Co layers, the lattice mismatch gives rise to stress during deposition of the first monolayers.