14nm BEOL TDDB reliability testing and defect analysis

Abstract

14nm BEOL (back end of line) TDDB (time to dielectric defect breakdown) test site structures successfully detect reliability defects but pose significant challenges in defect analysis At these advanced technology nodes, the reduction in copper land cross sectional area is accompanied by increased current density and electromigration failure rates. TDDB reliability test structures must be sensitive to capturing reliability defects. These same TDDB test site structures combined with porous ultra low-k (ULK) dielectric films represent real challenges in localizing and then determining BEOL reliability defects. Defect localization is difficult due to the complexity of these multiple metal layers along with the presence of the porous, low k dielectric films which exhibit shrinkage or void formation when exposed to an e-beam/FIB ion beam > 1 keV. Due to the porosity of these ULK dielectric films, they are especially susceptible to gallium ion implantation. It has been reported elsewhere that suppressing copper diffusion at the copper land/cap interface can be achieved by depositing a thin layer of CoWP and doping the copper seed layer with manganese [15, 16, 17]. However, a method for analytically confirming that these approaches for suppressing the copper diffusion do not affect TDDB performance/electromigration behavior must be demonstrated.