Interdiffusion of Cu-Sn system with Ni ultra-thin buffer layer and material analysis of IMC growth mechanism

In this paper, Ni ultra-thin diffusion buffer layer between Cu/Sn is inserted to suppress the IMC (η-phase) inter-diffusion reaction. We analogy the bonding condition by using single side Cu/Ni buffer layer/Sn structure. The inter-diffusion behaviors and IMC growth are investigated under the same thermal budget of bonding temperature during the heating step. Cu/Sn IMC formation behavior with Ni buffer layer is summarized by the SEM inspection. In the results of different Ni buffer layers (t_Ni = 0, 50, 100, 150 Å) and thermal durations (0 to 60 sec), Ni buffer layer insertion can effectively reduce Cu/Sn IMC thickness. In addition, rapid growth of ~1.5 μm Cu/Sn IMC thickness at 250°C for only 10 sec is discovered. As results, 100 Å Ni buffer layer is necessary to apply as the Cu/Sn system enters the submicron pad bonding interconnects.