Influence of Substrate on the Mechanical Machining Characteristics of Copper Thin Films for Nano/Micro Pattern Fabrication

As semiconductor devices continue to be scaled down, the demand for high-resolution and highprecision patterning technologies has increased significantly. Nanomachining offers a promising alternative to planar photolithography by enabling chemical-free processing, simplified fabrication steps, and compatibility with curved or three-dimensional structures. While previous research has primarily focused on bulk materials, studies on thin film-based nanomachining remain limited. In thin film machining, the films are significantly thinner than the substrates and are thus strongly influenced by the mechanical properties of the underlying substrate. To enable reliable and controllable patterning, it is essential to understand how these substrate characteristics affect thin film machinability. In this study, copper thin films were deposited on silicon and glass substrates and patterned using nanomechanical machining under normal loads ranging from 2 to 16 mN. Despite the use of identical film material, machining profiles varied significantly depending on the substrate. Notably, films on glass substrates exhibited 8~9% greater machining depth than those on silicon, indicating that the underlying substrate significantly affects machinability. Given the critical role of hardness in machinability, nanoindentation analysis was conducted to evaluate the mechanical response of each film-substrate system. The analyses revealed distinct hardness transitions from the intrinsic film hardness region (F) to two composite hardness regions (C1 and C2), which closely corresponded to the changes in machining behavior observed in the load-depth curves. These results demonstrate that the substrate influence plays a critical role in determining the machinability of thin films, and affects both cutting behavior and patterning outcomes. These findings provide fundamental insight into substrate-film mechanical interactions and support the optimization of process conditions for reliable nanoscale patterning in advanced electronics and device fabrication.