Metallization and dielectric reliability in Cu interconnects: Effect of cap layers and surface treatments

Abstract

In advanced copper interconnects, most of the reliability failures originate at and propagate through the interface. Interface engineering by the use of suitable surface treatments or the use of compositionally similar top cap layer and buried cap layer resulted in enormous improvements in dielectric and metallization reliability. In this study, NH3, H2 plasma, and silane surface treatments were employed after CMP to study electromigration lifetimes. These surface treatments can alter the Cu/dielectric interface and consequently influence the dominant Cu/dielectric cap interfacial electromigration. Electromigration performance was assessed by package level electromigration tests and silane and H2 plasma surface treatments were found to significantly increase electromigration lifetimes. Electrical leakage and breakdown characteristics of low dielectric constant (low-k) materials are a major challenge as the interconnects scale towards the 0.1 μm technology node. These issues are greatly alleviated by the implementation of a buried capping layer (BCL) in Cu damascene structures. It is found that a BCL of 100 A thickness in Cu/SiOC interdigitated comb structures reduces the leakage current by 1 order of magnitude and improves breakdown strength by a factor of 1.5 to 2. In addition, the BCL is able to suppress the formation of process-induced traps in the low-k dielectric. Use of SiC capping layer also improved the dielectric breakdown performance significantly. Finite element analysis, XPS surface analysis, and FIB studies were used to reveal the underlying mechanisms which were in almost all cases related to modifications of the Cu / dielectric cap interface, These findings can have important reliability considerations for Cu/low-k integration schemes. © 2005 Materials Research Society.