Investigation of the Homovalent Impurity in Aluminum to Form Alloys With Enhanced Interconnect Reliability

Abstract

ABSTRACTDiffusion-induced failures such as stress-induced voiding and electromigration (EM) are a major concern for interconnect metallization in silicon integrated circuits. The addition of solute elements to aluminum interconnects often leads to “blocking” of high diffusivity paths such as grain boundaries and thus to an improvement in the resistance to electromigration failure. This research investigates Al-In, Al-La, and Al-In-La alloys to improve interconnect EM resistance. The choice of these alloying elements is based on the fact that they have negligible solid solubility in aluminum and are homovalent. Lower solubilities may lead to grain boundary stuffing and hence to improved EM resistance. In addition, the homovalency minimizes the adverse effect on the metal resistivity from addition of impurities to aluminum. Multicomponent diffusion principles are used to tailor aluminum-based ternary alloy compositions which would exhibit the multicomponent effect of zero flux planes (ZFPs), or regions in the reaction zone of a diffusion couple where the flux of a component goes to zero. This study involves modeling the occurrence of ZFPs for aluminum in several diffusion couples of Al-In-La, thus limiting the bulk diffusive spreading of aluminum so that the electromigration behavior can be inhibited or eliminated. This paper presents our experimental findings and discusses the modeling approach to determine ternary alloys exhibiting ZFPs.