In situscanning-tunneling-microscopy studies of early-stage electromigration in Ag

The mass-transport mechanisms that are responsible for the early stages (resistance change <1%) of electromigration damage in metals are poorly understood. A deeper understanding of these processes is important both for the direct application to metal lines in electronic devices and for expanding our basic knowledge of these complex phenomena. A major reason for our lack of understanding is that the structural changes that must take place during early-stage electromigration occur at extremely small length scales that are beyond the resolution capabilities of conventional electromigration experiments. We report in situ studies of early-stage electromigration using scanning tunneling microscopy. A single 2-μm square region of a 2100-Å Ag film was studied under UHV conditions for over 200 h with current densities up to 4.5×${10}^4$ A/${\mathrm{cm}}^2$. Although the temperature and resistivity of the sample remained nearly constant throughout this period, significant small-scale morphology changes occurred that were a result of the applied current.