Effect of temperature on preventing electromigration damage based on increasing threshold current density in a thin metal passivated line

Abstract

The influencing factors associated with the temperature dependence of electromigration (EM) damage are discussed. EM is the atomic diffusion in a metal line when the line is stressed with high current density and causes EM damage called voids and hillocks. Voids are the depletion of the metal atoms and lead to breaking of the lines. Hillocks are the accumulation of the metal atoms and cause short circuits. Passivation covering the metal lines has been used as one of the ways to prevent EM damage because it constrains the formation of hillocks and voids at the same time owing to the conservation of mass. The passivation characteristics such as hardness affect the ability to inhibit EM damage. EM damage is significantly affected by temperature, and to reveal the relation of the passivation hardness with temperature contributes to improving EM reliability. In addition, other factors are thought to affect the temperature dependence of EM damage. In the present paper, we investigate the temperature dependence of EM damage measured by means of threshold length product and clarify several factors affecting the temperature dependence of EM damage. A tetraethyl orthosilicate layer is used as passivation on a conventional Al line-type structure sample. Through the experiments, we demonstrate that EM damage can be prevented much more by decreasing temperature and the increase of the passivation hardness with decreasing temperature is assumed to have an influence on the ability of passivation to prevent EM damage. We also discuss the effective bulk modulus and the electrical resistivity of Al as the factors affecting the temperature dependence of EM damage.