Stress relaxation behavior of Cu thin films in electro-thermo-mechanical multiple fields

The stress relaxation behavior of copper thin films in electro-thermo-mechanical multiple fields has been studied by a developed wafer-curvature method. Experimental results reveal that the electromigration plays an important role in the relaxation process. At tensile stress state, coupled surface diffusion and grain boundary diffusion are the dominant mechanisms even at low temperature. In addition, at compressive stress state, the stress relaxation is split into two stages: a fast stress relaxation dominated by coble-creep and a slow stress relaxation dominated by hillock formation. In multiple fields, the stress relaxation both at tensile stress and compressive stress state shows obvious difference from that in thermo-mechanical field.