Intermixing Reactions in Nanometric Cu/Sn and Cu/Ni/Sn/Ni Multilayer Interconnects

摘要

Current push for miniaturization and 3D packaging makes it important to understand reactions in interconnects with ultra small volume. In order to reduce processing time and to have more homogeneous interconnects, solder can be designed in a multilayer form with components layer thickness in the sub-micron or even nanometer range. In this work, reaction kinetics in multilayer interconnects consisting of stacks of [2 x (1300 nm Cu/1100 nm Sn)] and [2 x (1300 nm Cu/70 nm Ni/1100 nm Sn/70 nm Ni)] deposited by electrodeposition were investigated at room temperature and 150 °C. The progress of the reaction in the multilayers was monitored by using XRD, SEM and EDX. Results show that by inserting a 70 nanometer thick nickel layer between copper and tin, premature reaction between Cu and Sn at room temperature can be avoided. The addition of the nickel layers also allows the selective formation of Cu_6Sn_5 which is considered to have better properties compared to Cu_3Sn. Details of the reaction sequence and mechanisms are discussed.