Scanning Thermal Microscope Study of a Metal Film Under Current Stressing: Role of Temperature Inhomogeneity in Damage Process

We report direct observation of the evolution of local temperature inhomogeneity and the resulting atomic migration in a metal film (Ag on Si) stressed by a current by using a Scanning Thermal Microscope that allows simultaneous temperature mapping and topography imaging. The experimental observation is analyzed using a model based simulation. The experimental observation and the simulation show that due to current stressing the temperature of the film becomes significantly inhomogeneous over time (with local temperature deviating strongly from the mean). This creates local stress as well as local temperature gradient that lead to mass migration in addition to the electromigration. We show that the local temperature inhomogeneity serves as one of the main agents for local atomic migration which leads to change in film microstructure. The migration leads to damage and eventual failure as simultaneously monitored by in-situ resistance measurement.