In an interconnect structure of advanced large scale integrated (LSI) circuits, Cu diffusion leads to migration failure, known as stress migration and electro migration. In order to prevent these failures and to improve interconnect reliability, interface properties should be improved between Cu and a barrier layer. Among various interface properties, adhesion strength can be measured easily and be used as a representative interface property related to reliability. This paper show the relationship of interface adhesion strength with wettability, energy, and diffusivity. Then the effects of the adhesion strength on SM and EM reliability are discussed. Finally, key factors to improve the adhesion strength are proposed, together with our recent experimental evidences.