Scanning thermal microscope study of a metal film under current stressing: role of temperature inhomogeneity in the damage process

Abstract

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 high electrical current is reported. Experiments were carried out by simultaneous temperature mapping and topography imaging using a scanning thermal microscope in combination with resistance measurements. The experimental observation is analysed 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 the local temperature deviating strongly from the mean). This creates local stress as well as local temperature gradients (as high as ≈3 μm⁻¹) that lead to mass migration in addition to electromigration. The local temperature inhomogeneity serves as one of the main agents for local atomic migration which leads to a change in the film microstructure. The migration leads to damage and eventual failure as simultaneously monitored by in situ resistance measurements.