Effects of film thickness and microstructures on residual stress

The accurate measurement of stress is an essential requirement of residual stress studying. In this paper, Cu thin films with different thickness were prepared by magnetron sputtering. The micromorphologies of the films were observed using atomic force microscopy, and the microstructures were analysed by transmission electron microscopy and X-ray diffraction. The residual stress distributions of the films were measured by the curvature and nanoindentation methods. The results show that Cu films present polycrystalline state, and the grains size grew up with increasing film thickness. The residual stress calculation results from nanoindentation tests using the Suresh model were consistent with the curvature method, the residual compressive stress changed into residual tensile stress and the D values (the difference between the maximum and minimum stress value) decreased with increasing film thickness, and the stress distribution became uniform. The interface stress of the films weakened with the film thickness increasing because the crystalline grains grew larger.