Deformation mechanics of sputtered copper layers during nanoindentation tests
Keywords:Hardening curve, hardness, nanoindentation test, sputtered copper coating, Young’s modulus
The mechanical properties of the thin sputtered copper layer on the SiO2-coated silicon substrate is needed as part of the requirements in quantifying the reliability of the Through-Silicon Via (TSV) interconnects. In this respect, two different Cu coating layers, each from the different sputtering process, are examined. A series of nanoindentation tests are performed on the Cu coating layer samples with indenter speeds ranging from 80 to 400 nm/s, and the indentation depths of 320 nm. The properties of elastic modulus, hardness and the hardening behavior of the Cu coating layers have been quantified. Results show that the coating with higher contamination of C at 8.41 wt. % displays a significant hardening and a peak load level, as reflected in the measured nanoindentation load-displacement curves. However, insignificant effect of the applied probe displacement speeds up to 400 nm/s on the resulting properties of the coating is registered. The Johnson-Cook constitutive equation adequately describes the strain rate-dependent hardening behavior of the Cu coating layer.