Molecular dynamics study of diffusion and atomic configuration in layered structures for Al circuit interconnects

Abstract

Diffusion at Al(1 1 1)/underlay-metal interfaces, which is a dominant factor of electromigration-induced open-circuit failures in Al interconnects, was investigated by molecular dynamics simulation. The author focused on interfaces between the (1 1 1) plane in Al and the plane of greatest atomic density in ®ve kinds of metals that have high melting temperatures: Ti, Cr, Mo, W, and Ta. The calculated self-diffusion coef®cients of Al atoms near the Al/Ti and Al/Cr interfaces were smaller than those near the other three interfaces. This result is consistent with experimental results by other works that showed that Ti and Cr are effective underlay metals for suppressing the diffusion in Al interconnects. This result on the self-diffusion coef®cient was linked to the result on the atomic con®g-urations. The con®gurations of Al atoms at Al/Ti and Al/ Cr interfaces were close to that for bulk Al, while the con®gurations at the other three interfaces were signi®-cantly different from that for bulk Al. It was found that diffusion as well as atomic con®guration at the Al/underlay-metal interface is determined by the lattice mismatch between the (1 1 1) plane in Al and the plane of greatest atomic density in the underlay metal.

Adhesion analysis of silane coupling agent/copper interface with density functional theory

“…The DFT simulation is a quantum mechanical modeling method for investigating the electronic structure of many-body systems. On the other hand, a technique of a molecular dynamic simulation for determining the adhesion strength of metal/metal (Iwasaki, 1999(Iwasaki, , 2000(Iwasaki, , 2001(Iwasaki, and 2004, resin/metal (Iwasaki, 2009), resin/ceramics (Iwasaki, 2010), and resin/resin (Miyazaki, et al, 2012) interfaces has been carried out in the previous papers. Molecular dynamic simulation provides a step-by-step numerical solution for the classical equation of motion.…”

Molecular dynamics study of adhesion strength and diffusion at interfaces between interconnect materials and underlay materials

“…The method of diffusion analysis is explained in the previous paper (Iwasaki 1999). The self-diffusion coef®cient D of Cu atoms near the Cu/underlay-material interface is calculated by using the following Einstein relation (Kwok et al 1984):…”

“…6 (T = 700 K). Differences in the bulk lattice constants a and b of different materials are called lattice mismatches (Gu Ènther et al 1995;Iwasaki 1999), expressed as a percentage. The Cu/underlay-material lattice mismatches obtained from Fig.…”

“…In the previous work, this technique was used to analyze the diffusion and atomic con®guration at the interfaces between Al ®lms and underlay materials (Iwasaki 1999). And the analysis showed that Ti is one of the most effective underlay materials for suppressing the diffusion of Al atoms and thus for improving the electromigration resistance.…”

“…The aim of this analysis is to ®nd appropriate underlay materials that have good adhesion to Cu ®lms and that are effective for making the surface of Cu ®lms smooth by suppressing the diffusion of Cu atoms. The adhesion and diffusion are discussed in terms of the lattice mismatch, which is de®ned as the difference between the lattice constants of Cu and the underlay material in their bulk phases (Gu Ènther et al 1995;Iwasaki 1999). the total potential energy of the material-connected state ( Fig.…”