Novel Growth of Whole Preferred Orientation Intermetallic Compound Interconnects for 3D IC Packaging

In the present article, we report a breakthrough approach for the rapid growth of whole void-free and highly preferred orientation Cu6Sn5 IMC interconnects of 50 µm thick by the current driven bonding (CDB) interconnect method and the use of a single crystal seeding substrate. There was no grain boundaries within the Cu6Sn5 IMC interconnect and no voids at both interfaces, which is beneficial for the electrical and mechanical properties of IMC interconnect. The single crystal (001) Cu enables the unidirectional growth of [0001] Cu6Sn5 grains at the very early stage of wetting reaction. The current stressing supplies energy and promotes the novel and rapid growth of the Cu6Sn5 texture. The growth rate of the [0001] Cu6Sn5 under the current stressing can reach 4~6 µm/min. The initial perpendicular prism-type Cu6Sn5 grains transform into large paralleled prism-type ones and then merge into a single crystal due to the ripening effect. The experimental results show that the single crystal, void-free, high-melting-point Cu6Sn5 interconnect have a superior mechanical strength and electromigration reliability, which is expected to offer a promising application in 3D IC packaging. This concept of fabricating highly preferred orientation IMC interconnects by the CDB interconnect method can also be applied to other IMC systems, including Cu-Sn, Ni-Sn, Ag-Sn, and In-Sn.