Evidence of The Electromigration Short-Length Effect in Aluminum-Based Metallurgy With Tungsten Diffusion Barriers

Abstract

AbstractSeveral phenomena related to the short-length effect were observed during lifetime measurements of a two-level structure consisting of Ti-AICu-Ti stripes connected by interlevel tungsten (W) stud-vias. A linear increase in resistance was followed by a resistance change with time that approached zero. The threshold product is not a constant at 250 °C for stripe lengths of 30, 50 and 100 μm. The sigma of the lognormal distribution increased as the current density decreased and/or as the fail criterion increased. The lifetime, or t50, at relatively small current densities did not obey Black's empirical equation. Rather, the lifetime data obeyed a modified version of this equation that includes a critical current density, jc, as a new parameter. This critical current density is strongly dependent on the fail criterion, but is independent of temperature in the range 210-250 °C.