Interfacial void ripening in Cu Cu joints

Abstract

Cu-to-Cu direct bonding technology has been adopted to achieve ultra-high- density interconnects for 3D IC integration. Although the voids in the bonding interface was observed, there was no report on the size distribution and evolution of voids due to ripening. In this paper, we used focused ion beam to prepare specimens for transmission electron microscopy (TEM) study under a specific direction to obtain the plan view images of interface. The voids size distributions under 200 °C for 30, 60 and 120 min were obtained. The interfacial ripening effect was observed. The average void diameter is 49 nm, 70 nm, and 96 nm for the joint annealed for 30, 60, and 120 min, respectively. In addition, the void count within 10 μm2 is 183, 65 and 34 for the three conditions. A simple kinetic model of ripening is developed, and the relationship between radius and annealing time is in good agreement with experimental data.