Deformation Mechanisms in Pure and Alloyed Copper Films

In this work, the evolution of microstructure and the thermo-mechanical behavior of co pper and dilute copper alloy thin films was investigated. 0.3 to 2.0 μm thick film s were deposited by magnetron sputtering under ultra high vacuum conditions onto diffusion-barrier coated silicon substrates and subjected to wafer curvature measurements. Pure copper films annealed in ultra high vacuum exhibited a large grain size, a sharp (111) texture, and very few twin grains. Grain growth in the single-phase copper-aluminum system was similar to that in pure copper films; abnormal grain growth and inhibition of normal grain growth was observed in the two-phase copper-yttrium system. The thermal stress evolution in pure copper films was described for the first time with a constitutive law for diffusional creep in a thin film under the constraint of a substrate. Diffusional creep was suppressed by aluminum alloying. This was accounted for by the i nhibition of surface diffusion due to a segregation layer of aluminum oxide. Creep voiding occurred in oxidized copper-aluminum alloy films. Creep voiding, which was observed for the first time in a two-dimensional grain structure, was ascribed to the high thermal stresses, which cannot be avoided in the heat treatment of metal films on silicon substrates. Max-Planck-Institut für Metallforschung und Institut für Metallkunde der Universität Stuttgart, 2000 Alle Rechte, auch das des auszugsweisen Nachdrucks, der auszugsweisen oder vollständ igen Wiedergabe (Fotokopie, Mikroskopie), der Speicherung in Datenverarbeitungsanlagen und das der Übersetzung, vorbehalten. Als Manuskript gedruckt. Printed in Germany.