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

The effect of intrinsic strain on grain growth in Cu thin films was studied by both plan-view and cross-sectional scanning ion microscope in a focused ion beam system. Significant grain growth with bimodal grain size distribution was observed during room temperature storage in the Cu films which were deposited on the Si3N4 substrates by a sputter-deposition technique. In the thick Cu films, a non-uniform grain size distribution was observed along a direction normal to the film surface: the large grains were observed at the location close to the substrate surface. This grain size distribution coincided with inhomogeneous strain distribution normal to the film surface. We concluded that the grain growth in the Cu thin films was facilitated by the strain intrinsic in the Cu films deposited on the rigid substrates, and that strain (or stress) introduced in the films was a primary factor to induce the grain growth in the Cu films at room temperature.