Electric-Current Induced Crack Growth in Thin Films: Experimental Observations and Continuum Description

Electric-current (EC) induced failure of pre-cracked, wide unpassivated interconnections is studied on a 0.2 mmthick, pure aluminum film. The film is deposited by high vacuum evaporation coating (HVEC) and patterned into test structures of varying widths. The specimens were electrically loaded to failure under EC via step, and slow or fast ramp loading. The EC induced failure was observed as localized crack growth or spread of a damage zone, depending on the rate of EC loading and the uncracked ligament width. Both crack and damage zone grew or spread towards the positive electrode. The experimental measurements of EC to failure showed a square root dependence on the uncracked ligament width, irrespective of the details of the failure mechanics. Based on this observation, the macroscopic critical current intensity factor is proposed to be used as the material property of the failure criterion, similar to the fracture toughness KIC for brittle fracture.