Interdiffusion of Cu-Sn System with Ni Ultra-thin Buffer Layer and Material Analysis of IMC Growth Mechanism

Abstract

In this paper, Ni ultra-thin diffusion buffer layer between Cu/Sn is inserted to suppress the IMC (n-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 angstrom) and thermal durations (0 to 60 sec), Ni buffer layer insertion can effectively reduce Cu/Sn IMC thickness. In addition, rapid growth of similar to 1.5 mu m Cu/Sn IMC thickness at 250 degrees C for only 10 sec is discovered. As results, 100 angstrom Ni buffer layer is necessary to apply as the Cu/Sn system enters the submicron pad bonding interconnects.