CONSTRAINED DIFFUSIONAL CREEP IN UHV-PRODUCED COPPER THIN FILMS

摘要

The thermomechanical behavior of metallic thin films on stiff substrates is relevant for thin-mm devices, but its mechanisms are not fully understood. In this investigation, the mechanical properties of pure Cu and Cu-1 at. percent Al films on diffusion-barrier coated Si substrates were studied with the wafer-curvature technique. In ultra-pure films, which were sputtered and annealed under ultra-high vacuum conditions, characteristic stress relaxation at high temperatures was measured, which could be clearly attributed to diffusional creep. Good quantitative agreement with a recent model of diffusional creep constrained by a substrate was obtained. These features were absent in the Cu-Al alloy films, in which Al surface segregation and oxidation bad produced a "self-passivating" effect, and in films produced in less clean environments. Based on these results, we propose a model of thin-film deformation based on dislocation glide and constrained diffusional creep.