Kinetics of voiding and agglomeration of copper nanolayers on silica

We report the kinetics of annealing-induced dewetting of sub-60-nm-thick Cu films on silicon dioxide based upon in situ electrical resistance, ex situ scanning electron microscopy and atomic force microscopy measurements. Cu films become discontinuous upon annealing between ∼300 and 600°C through void nucleation and island formation. Films dewet via two kinetically limiting sequential processes: void nucleation by grain boundary grooving (activation energy Ea=1.2eV) followed by void growth and islanding through surface diffusion of Cu at the Cu-SiO2 interface, i.e., surface spreading, (activation energy Ea=0.7eV). The kinetic pathway for dewetting is film-thickness dependent. For film thinner than 20nm, complete dewetting occurs between 300 and 450°C and is limited by surface diffusion of Cu at the Cu-SiO2 interface, while for thicker films (>20nm) dewetting is governed solely by grain boundary grooving. This thickness-dependent dewetting is described by a phenomenological model validated by the evolution of mean roughness and lateral correlation length of the Cu surface. This work provides a framework for evaluating the morphological stability on ultrathin metal films on dielectric materials, in particular those being considered for use in micro- and nanodevice structures. © 2005 The American Physical Society.