Stress relaxation in Al-Cu and Al-Si-Cu thin films

Abstract

Substrate curvature measurements were used to study stress changes during thermal cycling and isothermal tensile stress relaxation in 800 nm Al-0,5 wt% Cu and Al-l wt% Si-0.5 wt% Cu films. For both compositions dislocation glide can describe the relaxation data well for temperatures up to 120 degrees C for Al-Si-Cu and up to 100 degrees C for Al-Cu. The average activation energy for Al-Si-Cu and Al-Cu is 1.7 +/- 0.2 eV and 3.0 +/- 0.3 eV, respectively. The athermal flow stress is the same for both and equal to 600 +/- 200 MPa. This result is consistent with the obstacles for glide being Al2Cu precipitates, which, in the case of Al-Si-Cu, are fine and can be cut by the dislocations, and, in the case of Al-Cu, are strong and provide Orowan strengthening. Also, the stress changes during thermal cycling in the Al-Cu films are different from these in the Al-Si-Cu films. For Al-Cu films, the room temperature stress decreases after each thermal cycle, while for Al-Si-Cu stress changes during thermal cycling are stable from the second cycle on. These observations are supported by thorough transmission electron microscopy (TEM) studies.