FIB-DIC ring-core measurement of the residual stress on HiPIMS W/Cu and Cr/Cu multilayer thin films

Residual stress in multilayer coatings is a complex phenomenon influenced by layer number and thickness, layer and substrate materials, deposition technique, process parameters, and working pressure. It is crucial to realize these stresses because they have a significant impact on the performance and reliability of multilayer structures in their applications. The measurement of the residual stress on multilayer thin films locally and globally is crucial. This study employed ring-core milling residual stress measurement on the High-Power Impulse Magnetron Sputtering (HiPIMS) fabricated Tungsten/Copper (W/Cu) Chromium/Copper (Cr/Cu) multilayer thin films. The displacement transformation strain was analyzed using Focused Ion Beam (FIB) ring-core milling combined with Digital Image Correlation (DIC), and the strain stress transformation calibration coefficients were analyzed through Finite Element Method (FEM) to investigate the residual stress of the thin films layer by layer. The study results indicated that the hard thin films (W, Cr) were the main source of residual stress in the multilayer thin film structure, while the soft thin film (Cu) had a lower residual stress. Having Cu as the intermediate layer was found to be effective for controlling the residual stress of thin films. The hard thin films encapsulated by the soft thin films had smaller stress values than those with hard films on the surface. In addition, the study observes the stress gradient and distribution at different depths and locations on the sample to reveal process parameters to balance between the soft and hard thin films and could help to predict the location of the damage on the multilayer thin films caused by higher stress.