Creep behavior of submicron copper films under irradiation

The creep behavior under heavy ion irradiation of 200 nm and 500 nm thick annealed Cu films is characterized using on chip uniaxial microtensile test structures. The tests are performed at room temperature with an applied stress between 100 and 250 MPa and a damage rate of 5 × 10−4 and 6.3 × 10−4 dpa s−1. The deformation rates produced under irradiation are several orders of magnitude larger than when measured out of flux. The main advantage of this method is that it allows the simultaneous measurement of several tens of specimens fully irradiated over their entire thickness. The plasticity mechanisms appear remarkably more homogeneous during irradiation creep than under static loading. The creep power law involves a stress exponent equal to 5 depending only weakly on the microstructure of the films. The SEM and TEM microstructural observations suggest that the creep mechanism results from climb-assisted glide of dislocations as rationalized by a simple closed-form model.