The crystallization character of W-Cu thin films at the early stage of deposition

A series of W-25 at.% Cu ultrathin films were prepared by direct current magnetron co-sputtering. The crystallization process of these films was discussed systematically under different deposition times (10 s, 20 s, 30 s) and substrate temperatures (Room Temperature, 80 °C, 150 °C, 400 °C). After depositing for 10 s, the W-Cu films (less than 10 nm) were amorphous at every substrate temperature. Because of the short deposition time and the diffusion barrier effect of W, the diffusion of Cu atoms was too limited to form ordered lattice resulting in the amorphous phase remained at the very beginning of the film. As the substrate temperature and deposition time were further increased, these films gradually crystallized due to the increased diffusion ability of Cu atoms. We found that the effect was more sensitive to substrate temperature than deposition time because it can contribute more obviously to the atoms' diffusion. The schematic diagram of structural transformation can provide a basis for preparing a film with a specific microstructure in W-Cu systems, even in different immiscible systems.