The encaging of cobalt interconnect lines with an ordered amino-based self-assembled monolayer for electromigration mitigation using an all-wet electroless process

Abstract

A self-assembled monolayer (SAM) encaging Cu interconnects as a barrier layer has been well developed to enhance thermal stability and electromigration (EM) reliability for interconnect metallization. However, the SAM-encapsulated and associated electromigration behaviors of interconnects of Co, an interconnecting material for sub-10-nm technology nodes, have yet to be evaluated. In this study, an all-wet electroless trench-filling process is presented to fabricate interconnect lines of SAM-encapsulated Co for the evaluation of their EM characteristics, using unsealed Co lines as a control. Empirical data obtained from accelerated bias-stressing tests, including EM failure lifetimes, current-density scaling factors, and activation energies, consistently show that electromigration reliability of the Co lines is markedly enhanced by the SAM encapsulation. The mechanical properties measured by nanoscratch testing reveal that the enhancement of adhesion between Co and SiO₂ through the SAM encapsulation strongly contributes to the superior EM mitigation by preventing interfacial diffusion. The adhesion strength and Joule-heating data of the Co and Co(SAM) lines are provided for the discussion of the difference in their electromigration performance and failure mechanism. Correlations between mechanical properties and EM characteristics of the electrolessly-plated Co as an interconnect material are also given.