Tuning sample length effect on mass transport in current carrying Cu-Si thin-film systems via interfacial engineering

Often, electric current-induced mass depletion at the cathode decreases with a decrease in the sample length; this is known as the Blech length effect. However, we recently demonstrated that coupling between thermomigration and electromigration, which is spontaneously established upon passage of an electric current through thin-film conductors with bends, results in an increase in the mass depletion at the cathode with a decrease in the sample length; we term this behavior inverse Blech length phenomenon. Here, we study the possibility of switching the mass transport in Cu thin films between the above two extreme phenomena by tuning the interlayer placed in between the Cu film and SiO₂/Si substrate. Tests were performed by passing electric currents of high density through Cu thin film deposited on SiO₂/Si substrate, with Ta or Ti interlayer. While inverse Blech length phenomenon was observed in the Cu-Ta sample, the classic Blech length effect was observed in the Cu-Ti sample. Moreover, partial oxidation of the Ti interlayer resulted in the observation of inverse Blech length phenomenon in the Cu-Ti sample also. The observations have been rationalized through characterization of the structure of the interfacial layer using a transmission electron microscope and estimation of the temperature field using finite element analysis. We also discuss the implications of our findings on the design of robust microelectronic interconnects.