A New Approach To Cu-cu Direct Bump Bonding

Abstract

A new approach to direct bonding at room temperature between Cu bump to Cu substrate was proposed. The proposed method combines following two techniques: the surface activated bonding (SAB) which has been developed by the authors for room temperature bonding, and a special electroless-plating technique which enablcs gaps between Cu bump and the substrate due to the height difference of Cu bumps to be filled. In the present paper the method is referred as SAB-GIP method. Amodel chip was bonded at first by SAB method. In the bonding procedure, the surfaces of Cu bump and Cu substrate are sputter-cleaned by Ar fast atom beam irradiation and brought into contact under a pressure in rage of several grains per bump. Subsequently a solution for Cu electroless plating is injected between chip and substrate and. The effect of filling of Cu in the gap between bump and substrate by cyclic injection electroless-plating could be confirmed by SEM observation. Characterization of the bonding was made by measuring the contact resistance as well as the shear strength. An additional ideas related to the method was also proposed to provide self-alignment effect to the bonding by using solder bumps which are formed either on the tip or on the substrate.