Reversible stress changes at all stages of Volmer–Weber film growth

Abstract

Stresses caused by Volmer–Weber growth of polycrystalline Cu films have been measured in situ during: Island nucleation and growth, island coalescence, and post-coalescence film thickening. Growth interruptions followed by resumption of growth resulted in the observation of reversible stress changes in all regimes. Reversible stress changes in the pre-coalescence and post-coalescence regimes are similar in that: The stress evolves in the tensile direction during growth interruptions, the initial rate of stress evolution is significantly faster when growth is resumed than when growth is first interrupted, and the magnitude of the reversible stress change increases with increasing pre-interruption deposition rate. It is argued that reversible stress changes are associated with changes in adatom and other surface defect concentrations, corresponding with changes in the growth flux. It is shown that the change in stress-thickness product with changing film thickness (the instantaneous stress) can be related to the adatom–surface interaction energy. High sensitivity stress measurements were made at a rate of 1000 measurements per second, and the instantaneous stress at the initiation of growth was measured at all stages of growth. The initial instantaneous stress and the adatom–surface interaction energy increased in the pre-coalescence regime and reached a fixed, maximum value once coalescence had occurred. The measured interaction energy in the post-coalescence regime is 0.67±0.1 eV, which corresponds well with values calculated using molecular dynamics.