Correlations between island nucleation and grain growth for polycrystalline films

Abstract

ABSTRACTFor Physical Vapor Deposition (PVD) processes the nucleation and growth of stable islands on monocrystalline and even polycrystalline substrates can be described by the rate equation theory in a mean field approximation. The observable quantity which can be derived from the rate equations is the global density of stable islands. Interisland correlations and island size distributions, on the other hand, cannot be obtained from this formalism. The array of stable islands, in turn, forms the template for the subsequent growth of a polycrystalline thin film. For the initial grain shape and grain size therefore both, the global island density as well as possible interisland correlations play a key role.This paper presents the results of simulations which take into account the effects of both, the global island density as well as island/island correlations on the growth of a thick polycrystalline film. The simulations consist of two steps: first a polycrystalline template is generated from an initial distribution of stable islands by employing an algorithm for the construction of Voronoi-zones. The Voronoi zone network mimics the state of the film just after island coalescence and just before the onset of grain growth. Then the well known q-state Potts model of grain growth is employed to study the further steps of microstructural evolution.A higher initial island density leads to a faster onset of grain growth while a very homogenous distribution of islands significantly retards grain growth. The reasons for these effects are briefly discussed.