Molecular Dynamics Study of Cu Thin Film Deposition on β-Ta Peter Klaver* and Barend J. Thijsse Delft University of Technology, Department of Materials Science, Rotterdamseweg 137, 2628AL Delft, The Netherlands. *t.p.c.klaver@tnw.tudelft.nl ABSTRACT Molecular Dynamics simulations were performed to study Cu film deposition on β-Ta. Three different β-Ta surfaces were used, two being atomically flat, and one resulting from Ta on Ta growth. We find that the Cu films develop a (111) texture with vertical grain boundaries between grains having different epitaxial relations with the β-Ta substrate. The epitaxial rotation angles were determined, as 5.2° and 10-13°, and the resulting strain reductions in the Cu films were identified. The effects of the substrate differences on the interfacial Ta/Cu intermixing and the epitaxy and grain boundary structure of the films are discussed. INTRODUCTION Copper is the metal of choice for modern IC interconnects. However, copper diffuses into silicon and silicon oxide quite rapidly, degrading the device properties. Therefore diffusion barriers must be used to keep copper from interacting with silicon and silicon oxide. Tantalum is one of a number of metals and compounds under consideration for their good barrier properties. Understanding the growth of Cu thin films on Ta substrates is therefore not only fundamentally interesting, but also technologically relevant, since the microstructure of the Cu film affects its adhesion to Ta and its electromigration resistance. The purpose of this molecular dynamics simulations work is to obtain atomic-level information on the growth of Cu films on different β-Ta substrates. β-Ta is a metastable crystal structure frequently found in thin films. Phenomena studied include epitaxial relations, film texture, nonequilibrium interface mixing, and defect production and evolution. This work, the successor to our recent work on Ta on Ta deposition [1], is part of a more comprehensive deposition study of the Cu/Ta system. COMPUTATIONAL DETAILS The simulations were performed using the CAMELION Molecular Dynamics code developed in Delft [2], employing Embedded Atom Method (EAM) potentials in the Johnson-Oh form [3,4]. We used the unlike-atom pair potential form by Johnson [5], which has only one free parameter. This parameter was fitted to the slightly positive heat of solution (0.03 eV/atom) of a 50-50 atom% Ta-Cu random alloy. This value was determined from the Miedema model [6]. Several conditions in the simulations are copied from experiments carried out in our group, like the slightly off-normal incidence of the Cu vapour flux (15°). The in-plane direction of each incoming Cu atom is chosen randomly, which is intended as an “arbitrary” angle without a specific relation to the crystal structure. The Cu atoms arrive with a thermal energy Mat. Res. Soc. Symp. Proc. Vol. 721 © 2002 Materials Research Society J2.3.1