摘要
Metallic thin films with nanotwins have garnered significant interest due to their superior mechanical properties and enhanced electrical conductivity; however, their thermal stability and microstructural evolution under post-deposition annealing conditions remain insufficiently understood, particularly for nanotwinned Ag (nt-Ag) thin films used in advanced electronic packaging and interconnect applications. In this study, the thermal stability and microstructural evolution of nt-Ag thin films deposited on Si substrates with a Ti interlayer were systematically investigated by vacuum annealing (4.6 mTorr) at temperatures ranging from 150 °C to 600 °C for 1 h. Cross-sectional FIB–SEM and X-ray diffraction analyses reveal that the 〈111〉 − oriented nanotwinned columnar structure exhibits excellent thermal stability up to 400 °C. Ex-situ and semi in-situ FIB observations reveal that annealing activates columnar grain growth along inclined grain boundaries (GBs), with a dominant downward component that progressively consumes through GB migration. The pronounced curvature difference between the columnar growth front and nanocrystalline grains provides a strong driving force for this migration. The annealed films retain a columnar structure with a high density of twin-related planar defects, which is mechanistically consistent with annealing-twin formation models in low stacking-fault-energy FCC metals, although direct crystallographic identification of newly formed twins is beyond the scope of this study. Below 400 °C, electrical resistivity and residual tensile stress decrease concurrently, while hardness remains nearly unchanged due to the preservation of the near-surface columnar structure containing coherent twin boundaries. At elevated temperatures of 500–600 °C, abnormal grain growth, texture transition from to 〈100〉, and interdiffusion at the Ag/Ti/Si interfaces lead to degradation in electrical and mechanical properties. These results identify annealing below 400 °C as an effective thermal window for maintaining the functional stability of nt-Ag thin films.
•Sputtered T-zone nanotwinned Ag films stable up to 400 °C under vacuum annealing.•Nanocrystalline bottom layer elimination is dominated by downward grain growth•Electrical, stress, and hardness evolution controlled by nanotwin retention.•At 500–600 °C, abnormal grain growth and interfacial diffusion degrade properties.•Findings guide design of thermally stable Ag films for advanced electronics.