Influence of thermal treatment on mechanical characteristics of Al-Si-Cu thin films evaluated by biaxial tensile testing

In this article, the influence of annealing on the mechanical characteristics of sputtered aluminum-silicon copper (Al-Si-Cu) thin films is described. The in-plane biaxial tensile tester developed by the authors was used for uniaxial and biaxial tensile tests in ambient air. In uniaxial test results, the Young´s modulus did not depend on annealing, whereas the yield stress was influenced by annealing. However, both the characteristics were not dependent on strain rate. After biaxial tests with various strain rate ratios, yield stresses were determined by using finite element analysis result. The yield locus in non-annealed films was different from that in annealed films. The yield locus for non-annealed and annealed films could be respectively fitted by using Hill equation with different R values, which indicates that annealed films can deform easily to transversal direction. From Auger spectroscopic analyses, Al₂Cu precipitation was made at grain boundary by annealing. The precipitation played a role as a bond between grains; consequently, transversal strain in annealed films would have become larger.