Effect of the underlayer on the microstructure and surface evolution in Al-0.5wt.%Cu polycrystalline thin films
The effects of the Ti underlayer on the evolution of grain morphology, crystallographic texture, and surface roughness of Al-0.5wt.%Cu thin films during sputter deposition have been characterized. In comparison to SiO2 substrates, Ti underlayers reduce the AlCu thickness at which film continuity is reached, reduce the AlCu columnar grain size, and allow exact Al (111) fiber texture development. The AlCu films on both Ti and SiO2 are primarily randomly oriented at early stages of deposition. A near-(111) Al fiber texture in AlCu/SiO2 films initiates during the preferential growth of ≈5° offset islands prior to film continuity, seeding the near Al (111) texture as film continuity is reached. The exact Al (111) fiber orientation in AlCu/Ti films develops after film continuity. The near-(111) and exact (111) fiber textures strengthen with further deposition due to combined normal and abnormal grain growth. Film coalescence and grain growth lead to a significant smoothing effect during the early stages of deposition.