The effect of strain on abnormal grain growth in Cu thin films

To understand a grain growth mechanism in Cu thin films that were deposited on rigid substrates by sputter deposition and subsequently annealed at various temperatures, microstructures of the Cu films with or without the rigid substrates were analyzed by x-ray diffraction (XRD), transmission electron microscopy (TEM), and electrical resistivity measurements. Significant grain growth (with bimodal grain size distribution) was observed during room-temperature storage in the Cu films deposited on the Si3N4 and rock salt substrates. However, in the free-standing Cu films, no grain growth was observed during room temperature storage. The present result suggested that the grain growth rates in the Cu thin films were strongly influenced by the existence of the rigid substrates, indicating stress (or strain) introduced in the films was a primary factor to induce the grain growth in the Cu films.