Analysis of failure mechanisms in electrically stressed gold nanowires

An analysis of polycrystalline Au thin-film interconnects of widths ranging from 850 to 25 nm, and lengths ranging from 1 μm to 20 nm which have been electrically stressed to the point of failure is presented. A new method for testing failure of interconnects is proposed, based on a quantity we call the failure current density. The mean time to failure for fixed current density and also the failure current density are seen to decrease with decreasing wire width contrary to expectations. The failure current density for a given wire width increases as the length decreases. An analysis of the temperature and stress profiles based on calculations of a simple model is presented which shows that the length dependence is due to thermal stresses rather than electromigration, and the width dependence is due to enhanced electromigration due to surface diffusion.