Effect of sputtering power and thickness ratios on the materials properties of Cu–W and Cu–Cr bilayer thin films using high power impulse magnetron and DC magnetron sputtering

Abstract

This study investigates the influence of Cu thickness ratios on the structural, morphological, and mechanical properties of sputtered Cu–W and Cu–Cr bilayer thin films. Employing high power impulse magnetron sputtering (HiPIMS), five distinct thickness ratios of 1:3, 3:5, 1:1, 5:3, and 3:1 were analyzed and compared to bilayer films developed using direct current magnetron sputtering (DCMS). The microstructural and surface characteristics of these films were evaluated using x-ray diffraction (XRD), atomic force microscopy, and scanning electron microscopy. Electrical properties were measured using a four-point probe, while mechanical properties were assessed through nanoindentation. Results reveal that increasing Cu thickness in Cu–W and Cu–Cr bilayers inversely affects hardness, grain size, and roughness, highlighting the influence of thickness ratios on film properties. Films with a higher Cu thickness ratio in both Cu–W and Cu–Cr bilayer systems deposited by HiPIMS exhibited lower hardness, smaller grain size, and reduced average roughness. Cross-sectional analysis and XRD confirmed the impact of thickness ratio on crystal phase and microstructure, indicating smoother columnar structures. Specifically, the HiPIMS-deposited Cu–Cr 3-1 film exhibited the lowest resistivity, at 4.77 μΩ cm, and hardness, measuring 8.26 GPa. Moreover, the 1:1 ratio films of Cu–W and Cu–Cr demonstrated hardness values of 13.81 and 11.37 GPa, respectively, which were 1.39 times higher than the films grown by DCMS. Additionally, variations in the bilayer thickness ratio significantly affected the electrical properties of the films. The enhanced properties of HiPIMS films are attributed to the higher peak power density of the target, leading to increased ion energy and deposition of dense grain structures.