Development and investigation of ultra-thin buffer layers used in symmetric Cu/Sn bonding and asymmetric Cu/Sn-Cu bonding for advanced 3D integration applications

In this work, a particular ultra-thin buffer layer (UBL) with various thickness ranging from 10 nm to 100 nm and different materials including Co, Ni, Pd and Ti is inserted between Cu/Sn to delay the interdiffusion prior to eutectic bonding. The efficacy of the buffer layer and the bonding quality are systematically conferred using microstructure imaging, material analysis, and electrical performance. In addition to symmetric Cu/Sn bonding with UBL, an asymmetric Cu/Sn-Cu bonding which is proposed to relieve the heat-enhanced interdiffusion issues thereby enhancing the reliability performance is demonstrated with the assistance of UBL technology.